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[EN] The structurally simple complex {Fe-II[tren(6F-py)(3)]}(BF4)(2) [tren(6F-py)(3) = tris(3-aza-4-(6-fluoro-2-pyridyl)-3-butenyl)amine] undergoes an abrupt spin transition (ST) with the critical temperature T down arrow(1/2) = 243 K on cooling and T up arrow(1/2) = 281 K on heating, with a 38 K wide hysteresis, while the ClO4- congener shows ST spanning the room temperature region at T down arrow(1/2) = 267 K and T up arrow(1/2) = 295 K with a 28 K wide hysteresis. Calorimetric data confirm the occurrence of a highly energetic ST process, while multi-temperature single crystal X-ray structural studies identify a concerted symmetry-breaking P2(1)/n P2(1)/c as the origin of the rare strong cooperativity and the large hysteresis loop. The analysis of the experimental data discloses two distinct interdependent events, namely, the combination of a gradual ST and an induced crystallographic phase transition, which endows the material with strong bistability and makes it an excellent platform for investigating new generations of ST based electronic and spintronic devices., This work was supported by grant PID2019-106147GB-I00 funded by MCIN/AEI/10.13039/501100011033, Unidad de Excelencia Maria de Maeztu (CEX2019-000919-M); the Generalitat Valenciana through PROMETEO/2016/147 and EU Framework FET-OPEN project COSMICS (grant agreement 766726), by the grant of the Ministry of Education and Science of Ukraine for perspective development of a scientific direction "Mathematical sciences and natural sciences" at Taras Shevchenko National University of Kyiv. We thank Prof. Dr Eric Collet for invaluable comments and suggestions.

Controlled modulation of the spin-crossover (SCO) behavior through the sorption-desorption of invited molecules is an extensively exploited topic because of its potential applications in molecular sensing. For this purpose, understanding the mechanisms by which the spin-switching properties are altered by guest molecules is of paramount importance. Here, we show an experimental approach revealing a direct probe of how the interplay between SCO and host-guest chemistry is noticeably activated by chemically tuning the host structure. Thus, the axial ligand 4-phenylpyridine (4-PhPy) in the 2D Hofmann clathrates {Fe(4-PhPy)2[M(CN)4]} (PhPyM; M = Pt, Pd) is replaced by 2,4-bipyridine (2,4-Bipy), resulting in the isomorphous compounds {Fe(2,4-Bipy)2[M(CN)4]} (BipyM; M = Pt, Pd), which basically differ from the former in that they have a noncoordinated N heteroatom in the ancillary aromatic substituent, i.e., 2-pyridyl instead of phenyl. Our chemical, magnetic, calorimetric, and structural characterizations demonstrate that this subtle chemical composition change provokes outstanding modifications not only in the capability to adsorb small guests as water or methanol but also in the extent to which these guests affect the SCO characteristics.

Self-assembly of [Hg(SeCN)4]2- tetrahedral building blocks, iron(II) ions, and a series of bis-monodentate pyridyl-type bridging ligands has afforded the new heterobimetallic HgII-FeII coordination polymers {Fe[Hg(SeCN)3]2(4,4'-bipy)2}n (1), {Fe[Hg(SeCN)4](tvp)}n (2), {Fe[Hg(SeCN)3]2(4,4'-azpy)2}n (3), {Fe[Hg(SeCN)4](4,4'-azpy)(MeOH)}n (4), {Fe[Hg(SeCN)4](3,3'-bipy)}n (5) and {Fe[Hg(SeCN)4](3,3'-azpy)}n (6) (4,4-bipy = 4,4'-bipyridine, tvp = trans-1,2-bis(4-pyridyl)ethylene, 4,4'-azpy = 4,4'-azobispyridine, 3,3-bipy = 3,3'-bipyridine, 3,3'-azpy = 3,3'-azobispyridine). Single-crystal X-ray analyses show that compounds 1 and 3 display a two-dimensional robust sheet structure made up of infinite linear [(FeL)n]2n+ (L = 4,4'-bipy or 4,4'-azpy) chains linked by in situ formed {[Hg(L)(SeCN)3]2}2- anionic dimeric bridges. Complexes 2 and 4-6 define three-dimensional networks with different topological structures, indicating, in combination with complexes 1 and 3, that the polarity, length, rigidity, and conformation of the bridging organic ligand play important roles in the structural nature of the products reported here. The magnetic properties of complexes 1 and 2 show the occurrence of temperature- and light-induced spin crossover (SCO) properties, while complexes 4-6 are in the high-spin state at all temperatures. The current results provide a new route for the design and synthesis of new SCO functional materials with non-Hofmann-type traditional structures.

Aiming at investigating the suitability of Hofmann-type two-dimensional (2D) coordination polymers {FeII(Lax)2[MII(CN)4]} to be processed as single monolayers and probed as spin crossover (SCO) junctions in spintronic devices, the synthesis and characterization of the MII derivatives (MII = Pd and Pt) with sulfur-rich axial ligands (Lax = 4-methyl- and 4-ethyl-disulfanylpyridine) have been conducted. The thermal dependence of the magnetic and calorimetric properties confirmed the occurrence of strong cooperative SCO behavior in the temperature interval of 100-225 K, featuring hysteresis loops 44 and 32.5 K/21 K wide for PtII-methyl and PtII/PdII-ethyl derivatives, while the PdII-methyl derivative undergoes a much less cooperative multistep SCO. Excluding PtII-methyl, the remaining compounds display light-induced excited spin-state trapping at 10 K with TLIESST temperatures in the range of 50-70 K. Single-crystal studies performed in the temperature interval 100-250 K confirmed the layered structure and the occurrence of complete transformation between the high- and low-spin states of the FeII center for the four compounds. Strong positional disorder seems to be the source of elastic frustration driving the multistep SCO observed for the PdII-methyl derivative. It is expected that the peripheral disulfanyl groups will favor anchoring and growing of the monolayer on gold substrates and optimal electron transport in the device.

The research of new multifunctional materials, as those undergoing spin crossover (SCO) and luminescent properties, is extremely important in the development of further optical and electronic switching devices. As a new step towards this ambitious aim, the coupling of SCO and fluorescence is presented here following two main strategies: whether the fluorescent agent is integrated as a part of the main structure of a 3D SCO coordination polymer {FeII(bpan)[MI(CN)2]2} (bpan = bis(4-pyridyl)anthracene, MI = Ag (FebpanAg), Au (FebpanAu)) or is a guest molecule inserted within the cavities of the 3D switchable framework {FeII(bpb)[MI(CN)2]2}·pyrene (bpb = bis(4-pyridyl)butadiyne, MI = Ag (FebpbAg·Pyr), Au (FebpbAu·Pyr)). The magnetic, calorimetric, structural, UV-Vis absorption and fluorescent characterizations were performed confirming the occurrence of a SCO-fluorescence interplay in the studied compounds. Moreover, the relevance of the intrinsic or extrinsic nature of the luminescence on the efficiency of the interplay is discussed on the basis of the available information.

Rare loop-like isostructural one-dimensional coordination polymer (1D-CP) systems formulated as {Fe(DPIP)2(NCSe)2}n·4DMF (1) and {Fe(DPIP)2(NCSe)2}n·4DMF (2) were obtained by self-assembling FeII and pseudohalide NCX−(X = S, Se) ions in presence of the V-shaped bidentate bridging ligand, namely, N,N′-dipyridin-4-ylisophthalamide (DPIP), and were characterized by elemental analysis, IR spectroscopy, TGA, single crystal X-ray diffraction and powder X-ray diffraction. The magnetic studies show that complex 2 undergoes a complete thermally induced spin crossover (SCO) behavior centered at T1/2 = 120 K with ca. 5 K thermal hysteresis loop and light-induced excited spin state trapping effect (LIESST) with TLIESST = 65 K. However, either the homologous X = S (1) or the desolvated form of complex 2 is high spin at all temperatures, proving further the concerted synergy for the SCO of 2 between the intrinsic ligand field and that indirectly induced via hydrogen bond interaction. The current results provide valuable information for the design of new 1D SCO systems via the rational control of the cooperated effects derived from the intramolecular coordination bond and the intermolecular supramolecular interactions.

[EN] Self-assembly of octahedral FeII ions, trans-1,2-bis(4-pyridyl) ethane (bpe) bridging ligands and [Hg(XCN)(4)](2-) (X = S (1), Se (2)) tetrahedral building blocks has afforded a new type of hetero-bimetallic Hg-II-Fe-II spin-crossover (SCO) 3D 6,4-connected coordination polymer (CP) formulated {Fe(bpe)[Hg(XCN)(4)]}(n). For X = S (1), the ligand field is close to the crossing point but 1 remains paramagnetic over all temperatures. In contrast, for X = Se (2) the complex undergoes complete thermal induced SCO behaviour centred at T-1/2 = 107.8 K and complete photoconversion of the low spin state into a metastable high-spin state (LIESST effect) with T-LIESST = 66.7 K. The current results provide a new route for the design and synthesis of new SCO functional materials with non-Hoffmann-type structures., We are very thankful for the support from the National Natural Science Foundation of China (21671121 and 21773006) the Spanish Ministerio de Economiay Competitividad (MINECO) and FEDER funds (CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). F. J. V. M. thanks MINECO for a predoctoral FPI grant.

The MOF $[{\text{Fe(tvp)}}_{2}{(\text{NCS})}_{2}]\ifmmode\cdot\else\textperiodcentered\fi{}2\text{BzCHO}$ is demonstrated to undergo a complex sequence of phase transitions and spin-crossover behavior of its constitutive ${\text{Fe}}^{\text{II}}$ ions upon adsorption of benzaldehyde guest molecules. Our study, combining Raman and synchrotron x-ray diffraction measurements on a single crystal, reveals that the conversion from the pure high-spin to the pure low-spin phases implies a rich sequence of intermediate phases, with symmetry breaking forming at least three different space groups. These different symmetries involve spin-state ordering, ligand ordering, and guest ordering, interpreted by combining magnetic susceptibility, Raman measurements, density functional theory, and force field molecular dynamics calculations.

[EN] Competition between spin-crossover and structural ligand ordering is identified as responsible for multistability and generation of six different phases in a rigid two-dimensional coordination polymer formulated {Fe-II[Hg-II(SCN)(3)](2) mu-(4,4'-bipy)(2)}(n) (1) (4,4'-bipy = 4,4'-bipyridine). The structure of 1 consists of infinite linear [Fe(mu-4,4'-bipy)](n)(2n+) chains linked by in situ formed {[Hg-II(SCN)(3)](2)(mu-4,4'-bipy)}(2n-) anionic dimers. The thermal dependence of the high-spin fraction, his, features four magnetic phases defined by steps following the sequence gamma(HS) = 1 (phase 1) gamma(HS) = 1/2 (phase 2) gamma(HS) approximate to 1/3 (phase 3) gamma(HS) = 0 (phase 4) These four magnetic states are consistent with structural ordering stemming from the different commensurate or incommensurate high and low-spin populations [HS] [HS:LS], approximate to [HS:2LS] [LS1] inferred from single crystal-analysis. Furthermore, two additional phases are generated at low temperature. One, LS2 (gamma(HS) = 0, phase 5); is due to spontaneous symmetry breaking of the : LS-1 state below 85 K The other results from irradiating the low-temperature-LS2 Phase at 15 K with red light to photogenerate a HS phase of low symmetry (HS*) (gamma(HS) = 1, phase 6). Detailed structural studies of the six phases-unravd the pivotal role-played by the internal dihedral angle of the 4,4'-bipy ligands in the microscopic. mechanism responsible for multistability and multistep behavior in 1., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (CTQ2013-46275-P and CTQ2016-78341-P), Unidad de Excelencia Maria de Maeztu (MDM-201S-0538), the Generalitat Valenciana through PROMETEO/2016/147, and the Institut Universitaire de France, the National Research Agency (ANR-13-BS04-0002), Rennes Metropole and CNRS (Post-Doc funding of E.T.). L.P.L. and F.J.V.M. thank to the Universidad de Valencia and a MINECO for a predoctoral (FPI) grant. Prof. D. Zhang thanks for the support from the Natural Science Foundation of China (21671121).

[EN] A multistable spin crossover (SCO) molecular alloy system [Fe1-xMx(nBu-im)(3)(tren)](P1-yAsyF6)(2) (M = Zn-II, Ni-II; (nBu-im)(3)(tren) = tris(n-butyl-imidazol(2-ethylamino))amine) has been synthesized and characterized. By controlling the composition of this isomorphous series, two cooperative thermally induced SCO events featuring distinct critical temperatures (T-c) and hysteresis widths (Delta T-c, memory) can be selected at will. The pristine derivative 100As (x = 0, y = 1) displays a strong cooperative two-step SCO and two reversible structural phase transitions (PTs). The low temperature PTLT and the SCO occur synchronously involving conformational changes of the ligand's n-butyl arms and two different arrangements of the AsF6- anions [T-c(1) = 174 K (Delta T-c(1) = 17 K), T-c(2) = 191 K (Delta T-c(2) = 23 K) (scan rate 2 K min(-1))]. The high-temperature PTHT takes place in the high-spin state domain and essentially involves rearrangement of the AsF6- anions [T-c(PT) = 275 K (Delta T-c(PT) = 16 K)]. This behavior strongly contrasts with that of the homologous 100P [x = 0, y = 0] derivative where two separate cooperative one-step SCO can be selected by controlling the kinetics of the coupled PTLT at ambient pressure: (i) one at low temperatures, T-c = 122 K (Delta T-c = 9 K), for temperature scan rates (>1 K min(-1)) (memory channel A) where the structural modifications associated with PTLS are inhibited; (ii) the other centered at T-c = 155 K (Delta T-c = 41 K) for slower temperature scan rates PF6- substitution, and hence of the PTLT kinetics, selectively selects the memory channel B of 100P when x = 0 and y approximate to 0.7. Meanwhile, substitution of Fe-II with Zn-II or Ni-II [x approximate to 0.2, y = 0] favors the low temperature memory channel A at any scan rate. This intriguing interplay between PT, SCO and isomorphous substitution was monitored by single crystal and powder X-ray diffractometries, and magnetic and calorimetric measurements., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (CTQ2016-78341-P), Unidad de Excelencia Maria de Maeztu (MDM-2015-0538), and the Generalitat Valenciana through PROMETEO/2016/147 and an EU Framework Program for Research and Innovation (RISE project number 734322). F. J. V. M. and M. M. S. thank MINECO for a predoctoral (FPI) grant.

[EN] The synthesis, structural characterization and magnetic properties of two new isostructural porous 3D compounds with the general formula {FeII(pina)[MI(CN)2]2}·xMeOH (x = 0¿5; pina = N-(pyridin-4-yl)isonicotinamide; MI = AgI and x ~ 5 (1·xMeOH); MI = AuI and x ~ 5 (2·xMeOH)) are presented. The single-crystal X-ray diffraction analyses have revealed that the structure of 1·xMeOH (or 2·xMeOH) presents two equivalent doubly interpenetrated 3D frameworks stabilized by both argentophilic (or aurophilic) interactions and interligand C¿O···HC H-bonds. Despite the interpenetration of the networks, these compounds display accessible void volume capable of hosting up to five molecules of methanol which interact with the host pina ligand and establish an infinite lattice of hydrogen bonds along the structural channels. Interestingly, the magnetic studies have shown that solvated complexes 1·xMeOH and 2·xMeOH display two- and four-step hysteretic thermally driven spin transitions, respectively. However, when these compounds lose the methanol molecules, the magnetic behavior changes drastically giving place to gradual spin conversions evidencing the relevant influence of the guest molecules on the spin-crossover properties. Importantly, since the solvent desorption takes place following a single-crystal-to-single-crystal transformation, empty structures 1 and 2 (x = 0) could be also determined allowing us to evaluate the correlation between the structural changes and the modification of the magnetic properties triggered by the loss of methanol molecules., We thank the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER funds (CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). F.J.V.-M. thanks MINECO for a predoctoral FPI grant.

The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)(2) (bztpen=N-benzyl-N,N',N'-tris(2-pyridylmethyl)ethylenediamine) displays an S=1/2 S=3/2 spin crossover (SCO) behavior (T-1/2=370 K, Delta H= 12.48 kJmol(-1), Delta S=33 JK(-1) mol(-1)) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0 S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120-420 K affording a detailed picture of how the electronic distribution of the t(2g)-e(g) orbitals modulates the structure of the {FeNO}(7) bond, providing valuable magneto-structural and spectroscopic correlations and DFT analysis., The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P, CTQ2015-64579-C3-1-P, and Unidad de Excelencia Maria de Maeztu MDM-2015-0538) and the Generalitat Valenciana (PROMETEO/2012/049). L.P.L. thanks the Generalitat Valenciana and the Universidad de Valencia for a predoctoral fellowship. J.C. and E.R. thank the Generalitat de Catalunya for a Beatriu de Pinos grant and an ICREA Academia award, respectively.

[EN] The unprecedented bimetallic 2D coordination polymer {Fe[(Hg(SCN)3)2](4,4’-bipy)2}n exhibits a thermal high-spin (HS)$low-spin (LS) staircase-like conversion characterized by a multi-step dependence of the HS molar fraction gHS. Between the fully HS (gHS = 1) and LS (gHS = 0) phases, two steps associated with different ordering appear in terms of spin-state concentration waves (SSCW). On the gHS 0.5 step, a periodic SSCW forms with a HS-LS-HS-LS sequence. On the gHS 0.34 step, the 4D superspace crystallography structural refinement reveals an aperiodic SSCW, with a HS-LS sequence incommensurate with the molecular lattice. The formation of these different long-range spatially ordered structures of LS and HS states during the multi-step spin-crossover is discussed within the framework of “DevilÏs staircase”-type transitions. Spatially modulated phases are known in various types of materials but are uniquely related to molecular HS/LS bistability in this case., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER (CTQ2013-46275-P), Unidad de Excelencia Maria de Maeztu MDM-2015-0538, the Generalitat Valenciana through PROMETEO/2012/049. L.P.L. and F.J.V.M. thank the Universidad de Valencia and a MINECO for a predoctoral (FPI) grant. D.Z. thanks the Natural Science Foundation of China and China Scholarship Council. This work was supported by the Institut Universitaire de France, the National Research Agency (ANR-13-BS04-0002), Rennes Metropole and CNRS (Post-Doc funding of E.T.). E.C. and J.A.R. would like to thank G. Chastanet for meditations on the Devil's staircase.

A series of spin transition neutral compounds [FeL(NCS)2] has been synthesized and characterized by means of magnetic susceptibility studies, X-ray diffraction, IR and Mossbauer spectroscopic, and calorimetric measurements (L = N,N-bis((3-alkoxypyridin-2-yl)methylene)-propane-1,3-diamine, number of carbon atoms in chains (n) = 4, 12, 14, 16, 18, 20). The shortest chain compound is crystalline and displays a gradual spin transition above ambient temperature. Growing the aliphatic substituent up to n = 12 and 14 leads to loss of crystalline order and deterioration of magnetic properties. At the critical chain length n = 16 and above, the compounds undergo a phase transition reflected by a spin transition and resulting in the appearance of susceptibility hysteresis initially not observed for the short chain congener. For the compound with n = 20, hysteresis becomes the most pronounced. The study shows the importance of chain length optimization for effective feedback between phase and spin transitions.

[EN] Fe-II spin-crossover (SCO) coordination polymers of the Hofmann type have become an archetypal class of responsive materials. Almost invariably, the construction of their architectures has been based on the use of monotopic and linear ditopic pyridine like ligands. In the search for new Hofmann-type architectures with SCO properties, here we analyze the possibilities of bridging ligands with higher connectivity degree. More precisely, the synthesis and structure of {Fe-II(L-N3)[M-I(CN)(2)](2)}center dot(Guest) (Guest = nitro-benzene, benzonitrile, o-dichlorobenzene; M-I = Ag, Au) and {Fe-II(L-N4)[Ag-2(CN)(3)][Ag(CN)(2)]}center dot H2O are described, where L-N3 and L-N4 are the tritopic and tetratopic ligands 1,3,5-tris(pyridin-4-ylethynyl)benzene and 1,2,4,5-tetrakis(pyridin-4-ylethynyl)benzene. This new series of Hofmann clathrates displays thermo- and photoinduced SCO behaviors., We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). FJ.V.-M. thanks MINECO for a predoctoral FPI grant. We also thank Dr. Carlos Marti for helping us with ToposPro software.

[EN] We report an unprecedented series of two-dimensional (2D) spin-crossover (SCO) heterobimetallic coordination polymers generically formulated as {Fe-II[(He(SCN)(3))(2)](L)(x))}center dot Solv, where x = 2 for L = tvp (trans-(4,4'-vinylenedipyridine)) (1tvp), bpmh ((1E,2E)-1,2-bis(pyridin-4-ylmethylene)hydrazine) (1bpmh center dot nCH(3)OH; n = 0, 1), by eh ( (1E,2E)-1,2-bis (1-(pyridin-4-yl) ethyliden e) hydrazine) (Ibpeh center dot nH(2)O; n = 0, 1) and x = 2.33 for L = 0 0 bpbz (1,4-bis(pyridin-4-yl)benzene) (1bpbz center dot nH(2)O; n = 0, 2/ 3). The results confirm that self-assembly of Fell, [Hg-II(SCN)(4)](2-), and ditopic rodlike bridging ligands L containing 4-pyridyl moieties favors the formation of linear [Fe(mu-L)](n)(2n+) chains and in situ generated binuclear units {[Hg-II(SCN)(3)](2)(mu-L)}(2)-. The latter act as bridges between adjacent chains generating robust 2D layers. The [(FeN6)-N-II] centers are equatorially surrounded by four NCS- groups and two axial N atoms of the organic ligand L. The compound 1tvp and the unsolvated form of 1bpmh undergo complete SCO centered at T-1/2 = 177 and 226 K, characterized by the enthalpy and entropy variations Delta H = 12.3 and 10.5 kJ mol(-1) and Delta S = 69.4 and 48 J KT-1 mol(-1), respectively. The almost complete SCO of the unsolvated form of 1bpeh occurs at ca. T-1/2 = 119 K and exhibits a complete LIESST effect. Regardless of the degree of solvation, a half-spin conversion at T-1/2 < 100 K occurs for 1bpbz center dot nH(2)O, which becomes almost complete at p = 0.65 GPa. The labile solvent molecules present in 1bpmh center dot CH3OH and 1bpely center dot H2O have a dramatic influence on the corresponding SCO behavior., We thank the Spanish Ministerio de Economia y Competitividad (MINECO), FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), and Generalitat Valenciana (PROMETEO/2016/147). FJ.V.-M. thanks MINECO for a predoctoral FPI grant. D.Z. acknowledges support from the Natural Science Foundation of China (21671121).

[EN] Two new 3D spin-crossover (SCO) Hofmann-type coordination polymers {Fe(2,6-naphthy)[Ag(CN)2][Ag2(CN)3]} (1; 2,6-naphthy = 2,6-naphthyridine) and {Fe(2,6-naphthy)- [Au(CN)2]2}·0.5PhNO2 (2) were synthesized and characterized. Both derivatives are made up of infinite stacks of {Fe[Ag(CN)2]2- [Ag2(CN)3]}n and {Fe[Au(CN)2]2}n layered grids connected by pillars of 2,6-naphthy ligands coordinated to the axial positions of the FeII centers of alternate layers., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO), Fondos Europeos para el Desarrollo Regional (FEDER) (CTQ2013-46275-P and CTQ2016-78341-P), Unidad de Excelencia Maria de Maeztu (MDM-2015-0538), and the Generalitat Valenciana through PROMETEO/2016/147. L. P. L. and F. J. V. M. thank the Universidad de Valencia and MINECO, respectively for predoctoral (FPI) grants.

[Fe(tvp)(2)(NCS)(2)] (1) (tvp=trans-(4,4-vinylenedipyridine)) consists of two independent perpendicular stacks of mutually interpenetrated two-dimensional grids. This uncommon supramolecular conformation defines square-sectional nanochannels (diagonal approximate to 2.2nm) in which inclusion molecules are located. The guest-loaded framework 1@guest displays complete thermal spin-crossover (SCO) behavior with the characteristic temperature T-1/2 dependent on the guest molecule, whereas the guest-free species 1 is paramagnetic whatever the temperature. For the benzene-guest derivatives, the characteristic SCO temperature T-1/2 decreases as the Hammet sigma(p) parameter increases. In general, the 1@guest series shows large entropy variations associated with the SCO and conformational changes of the interpenetrated grids that leads to a crystallographic-phase transition when the guest is benzonitrile or acetonitrile/H2O., The research reported herein was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P; MAT2012-34740), the Basque Government (project IT-779-13), and Generalitat Valenciana (PROMETEO/2012/049). T.R.M. thanks the Spanish Ministerio de Economia y Competitividad (MINECO) for a predoctoral grant (FPI.). L.P.-L. thanks the Generalitat Valenciana for a predoctoral fellowship in the frame of the project PROMETEO/2012/049.

Solvated and unsolvated forms of the complex [Fe(HAT)(NCS)2]∞·(nMeOH) (1) (n = 1.5, 0; HAT = 1,4,5,8,9,12-hexaazatriphenylene) were prepared. The structure of 1·(1.5MeOH), measured at 120 K, showed that this system crystallizes in the homochiral P43 tetragonal space group. The solid is constituted of stacks of one-dimensional coordination polymers running along c-axis. All the FeII centres have the same Λ or Δ conformation and are in the LS state at 120 K. In the range of temperatures 10–300 K the magnetic properties of 1·(1.5MeOH) shows the occurrence of reversible spin crossover behaviour. However, above ca. 310 K complete desolvation of 1·(1.5MeOH) to give 1 was observed from crystal structure analysis, magnetic behaviour and thermal analysis. Compound 1 displays a two-step spin crossover behaviour characterised by a plateau 60 K wide. Simulation of the two-step behaviour in the frame of the regular solutions theory afforded, respectively, the critical temperatures (Tci), the interaction parameters (Γi), and the enthalpy (ΔHi) and entropy (ΔSi) variations for steps i = 1 and 2: Tc1(Tc2) = 172 (358) K, Γ1(Γ2) = 1.6 (3.0) kJ mol−1, ΔH1(ΔH2) = 5.7 (18.3) kJ mol−1 and ΔS1(ΔS2) = 33.4 (51.0) J K mol−1.

[EN] The synthesis, crystal structure, magnetic, calorimetric, and Mo¿ ssbauer studies of a series of new Hofmann-type spin crossover (SCO) metal¿organic frameworks (MOFs) is reported. The new SCO-MOFs arise from self-assembly of FeII, bis(4-pyridyl)butadiyne (bpb), and [Ag(CN)2] ¿ or [MII(CN)4] 2¿ (MII = Ni, Pd). Interpenetration of four identical 3D networks with ¿-Po topology are obtained for {Fe(bpb)[AgI (CN)2]2} due to the length of the rod-like bismonodentate bpb and [Ag(CN)2] ¿ ligands. The four networks are tightly packed and organized in two subsets orthogonally interpenetrated, while the networks in each subset display parallel interpenetration. This nonporous material undergoes a very incomplete SCO, which is rationalized from its intricate structure. In contrast, the single network Hofmann-type MOFs {Fe(bpb)[MII(CN)4]}·nGuest (MII = Ni, Pd) feature enhanced porosity and display complete one-step or two-step cooperative SCO behaviors when the pores are filled with two molecules of nitrobenzene or naphthalene that interact strongly with the pyridyl and cyano moieties of the bpb ligands via ¿¿¿ stacking. The lack of these guest molecules favors stabilization of the high-spin state in the whole range of temperatures. However, application of hydrostatic pressure induces one- and two-step SCO., We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538) and Generalitat Valenciana (PROMETEO/2016/147). L.P.-L. and F.J.V.-M. thank, respectively, the Universidad de Valencia and MINECO for a predoctoral FPI grant.

[EN] Understanding the origin of cooperativity and the equilibrium temperature of transition (T1/2) displayed by the spin-crossover (SCO) compounds as well as controlling these parameters are of paramount importance for future applications. For this task, the occurrence of polymorphism, presented by a number of SCO complexes, may provide deep insight into the influence of the supramolecular organization on the SCO behavior. In this context, herein we present a novel family of mononuclear octahedral FeII complexes with formula cis- [Fe(bqen)(NCX)2], where bqen is the chelating tetradentate ligand N,N¿-bis(8-quinolyl)ethane-1,2-diamine and X = S, Se. Depending on the preparation method, these compounds crystallize in either the orthorhombic or the trigonal symmetry systems. While the orthorhombic phase is composed of a racemic mixture of mononuclear complexes (polymorph I), the trigonal phase contains only one of the two possible enantiomers (¿ or ¿), thereby generating a chiral crystal (polymorph II). The four derivatives undergo SCO behavior with well-differentiated T1/2 values occurring in the interval 90¿233 K. On one hand, T1/2 is about 110 K (polymorph I) and 87 K (polymorph II) higher for the selenocyanate derivatives in comparison to those for their thiocyanate counterparts. These differences in T1/2 are ascribed not only to the higher ligand field induced by the selenocyanate anion but also to a remarkable difference in the structural reorganization of the [FeN6] coordination core upon SCO. Likewise, the higher cooperativity observed for the thiocyanate derivatives seems to be related to their stronger intermolecular interactions within the crystal. On the other hand, T1/2 is about 53 K (thiocyanate) and 29 K (selenocyanate) higher for the trigonal polymorph II in comparison to those for the orthorhombic polymorph I. These differences, and the small changes observed in cooperativity, stem from the slightly different hetero- and homochiral crystal packing generated by the cis-[Fe(bqen)(NCX)2] molecules, which determines subtle adaptations in the intermolecular contacts and the FeII coordination core., We thank the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and CTQ2016-78341-P and Unidad de Excelencia Maria de Maeztu MDM-2015-0538), Generalitat Valenciana (PROM-ETEO/2016/147), and EU Framework Program for Research and Innovation (RISE project number 734322). FJ.V.-M. thanks MINECO for a predoctoral FPI grant

Six clathrate compounds of the three-dimensional spin crossover metal−organic framework formulated [Fe(TPT)2/3{MI (CN)2}2]· nG, where TPT is 2,4,6-tris(4-pyridyl)-1,3,5-triazine, MI = Ag or Au and G represent the guest molecules furan, pyrrole and thiophene, were synthesized using slow diffusion techniques. The clathrate compounds were characterized by single-crystal X-ray diffraction at 120 and 300 K, thermogravimetric analysis and thermal dependence of the magnetic susceptibility. All compounds crystallize in the R3̅ m trigonal space group. The FeII defines a unique [FeN6] crystallographic site with the equatorial positions occupied by four dicyanometallate ligands while the axial positions are occupied by the TPT ligands. Each TPT ligand links three FeII sites, while the dicyanometallate ligands bridge two FeII sites thereby generating two interlocked three-dimensional frameworks with the NbO topology. The choice of the TPT ligand favors the generation of pores where the guest molecules are located. The thermal dependence of the magnetic susceptibility of samples constituted of single crystals was investigated for the six compounds to assess the influence of the guest molecules on the spin crossover behavior. In general, the magnetic properties of the six clathrates suggest a gradual stabilization of the high-spin state as the molecular volume of the guest increases., The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P) and Generalitat Valenciana (PROMETEO/2012/049). Z.A.C. thanks the Spanish M.E.C.D. for a predoctoral FPU fellowship. L.P.L. thanks the Generalitat Valenciana for a predoctoral fellowship in the frame of the project PROMETEO/2012/049.

The chemisorption of sulfur dioxide (SO2) on the Hofmann-like spin crossover porous coordination polymer (SCO-PCP) {Fe(pz)[Pt(CN)4]} has been investigated at room temperature. Thermal analysis and adsorption-desorption isotherms showed that ca. 1 mol of SO2 per mol of {Fe(pz)[Pt(CN)4]} was retained in the pores. Nevertheless, the SO2 was loosely attached to the walls of the host network and completely released in 24 h at 298 K. Single crystals of {Fe(pz)[Pt(CN)4]}·nSO2 (n ≈ 0.25) were grown in water solutions saturated with SO2, and its crystal structure was analyzed at 120 K. The SO2 molecule is coordinated to the Pt(II) ion through the sulfur atom ion, Pt-S = 2.585(4) Å. This coordination slightly stabilizes the low-spin state of the Fe(II) ions shifting the critical temperatures of the spin transition by 8-12 K. DFT calculations have been performed to rationalize these observations.

Self-assembling iron(II), 2-fluoropyrazine (Fpz), and [MII(CN)4] 2− (MII = Ni, Pd, Pt) or [AuI (CN)2] − building blocks have afforded a new series of two- (2D) and threedimensional (3D) Hofmann-like spin crossover (SCO) coordination polymers with strong cooperative magnetic, calorimetric, and optical properties. The iron(II) ions, lying on inversion centers, define elongated octahedrons equatorially surrounded by four equivalent centrosymmetric μ4-[MII(CN)4]2− groups. The axial positions are occupied by two terminal Fpz ligands affording significantly corrugated 2D layers {Fe(Fpz)2([MII(CN)4]}. The Pt and Pd derivatives undergo thermal- and light-induced SCO characterized by T1/2 temperatures centered at 155.5 and 116 K and hysteresis loops 22 K wide, while the Ni derivative is high spin at all temperatures, even at pressures of 0.7 GPa. The great stability of the high-spin state in the Ni derivative has tentatively been ascribed to the tight packing of the layers, which contrasts with that of Pt and Pd derivatives in the high- and low-spin states. The synthesis and structure of the 3D frameworks formulated {Fe(Fpz)[Pt(CN)4]}·1/2H2O and {Fe(Fpz)[Au(CN)2]2}, where Fpz acts as bridging ligand, which is also discussed. The former is high spin at all temperatures, while the latter displays very strong cooperative SCO centered at 243 K accompanied by a hysteresis loop 42.5 K wide. The crystal structures and SCO properties are compared with those of related complexes derived from pyrazine, 3-fluoropyridine, and pyridine., The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P and Unidad de Excelencia Maria de Maeztu MDM- 2015-0538) and Generalitat Valenciana (PROMETEO/2016/147). F.J.V.M. thanks the MINECO for a predoctoral FPI fellowship.

Two new isostructural two-dimensional (2D) coordination polymers exhibiting spin crossover (SCO) behavior of formulation [Fe(4,4'-bipy)(2)(NCX)(2)]·4CHCl(3) (4,4'-bipy = 4,4'-bipyridine; X = S [1·4CHCl(3)], Se [2·4CHCl(3)]) have been synthesized and characterized, and both undergo cooperative spin transitions (ST). For 1·4CHCl(3) the ST takes place in two steps with critical temperatures of T(c1)(down) = 143.1 K, T(c2)(down) = 91.2 K, T(c1)(up) = 150.7 K, and T(c2)(up) = 112.2 K. 2·4CHCl(3) displays half ST characterized by T(c)(down) = 161.7 K and T(c)(up) = 168.3 K. The average enthalpy and entropy variations and cooperativity parameters associated with the ST have been estimated to be ΔH(1)(av) = 5.18 kJ mol(-1), ΔS(1)(av) = 35 J K(-1) mol(-1), and Γ(1) = 2.8 kJ mol(-1) and ΔH(2)(av) = 3.55 kJ mol(-1), ΔS(2)(av) = 35 J K(-1) mol(-1), and Γ(2) = 2.6 kJ mol(-1) for 1·4CHCl(3), and ΔH(av) = 6.25 kJ mol(-1), ΔS(av) = 38.1 J K(-1) mol(-1), and Γ = 3.2 kJ mol(-1) for 2·4CHCl(3). At T > [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))], both compounds are in the space group P2/c while at T < [T(c1) (1·4CHCl(3)); T(c) (2·4CHCl(3))] they change to the C2/c space group and display an ordered checkerboard-like arrangement of iron(II) sites where the high- and low-spin states coexist at 50%.

Precise control of spin transition temperature (T(c)) is one of the most important challenges in molecular magnetism. A Hofmann-type porous coordination polymer {Fe(pz)[Pt(II)(CN)(4)]} (1; pz = pyrazine) exhibited cooperative spin transition near room temperature (T(c)(up) = 304 K and T(c)(down) = 284 K) and its iodine adduct {Fe(pz)[Pt(II/IV)(CN)(4)(I)]} (1-I), prepared by oxidative addition of iodine to the open metal sites of Pt(II), raised the T(c) by 100 K. DSC and microscopic Raman spectra of a solid mixture of 1-I and 1 revealed that iodine migrated from 1-I to 1 through the grain boundary after heating above 398 K. We have succeeded in precisely controlling the iodine content of {Fe(pz)[Pt(CN)(4)(I)(n)]} (1-In; n = 0.0-1.0), which resulted in consecutive modulation of T(c) in the range 300-400 K while maintaining the hysteresis width. Furthermore, it was demonstrated that iodine migration in the solid mixture was triggered by the spin transition of 1-I. The magnetically bistable porous framework decorating guest interactive open-metal-site in the pore surface makes it possible to modulate T(c) ad arbitrium through unique postsynthetic method using iodine migration.

Structural, magnetic, calorimetric and Mo¨ssbauer studies of the cooperative spin crossover naphthalene and nitrobenzene clathrates of the novel FeII Hofmann-like porous metal–organic framework {Fe(bpb)[Pt(CN)4]}2Guest are described (bpb = bis(4-pyridyl)butadiyne)., The Spanish MINECO, FEDER (CTQ2010-18414) and the GV (PROMETEO/2012/049) are acknowledged for funding. MS thanks the EU for a Marie Curie fellowship (IIF-253254). LPL thanks the GV for a pre-doctoral fellowship. We acknowledge Prof. P. Gutlich and Dr V. Ksenofontov from the University of Mainz (Germany) for providing access to Mossbauer spectrometers.

Complex [Fe III (bztpen)(OCH 3 )](PF 6 ) 2 (1) crystallizes as the major yellow-brown product from spontaneous oxidation of its corresponding iron(II) counterpart in methanol solution. Magnetic measurements and EPR spectra demonstrate that 1 undergoes a poorly cooperative 6 A 1 ↔ 2 T 2 spin conversion in the temperature range 300-50 K, with characteristic thermodynamic parameters ΔH = 6.15 kJ mol -1 , ΔS = 39.88 J K -1 mol -1 , and T 1/2 = 154 K. The crystal structure of 1 has been investigated at 100 and 293 K.

Twelve coordination polymers with formula {Fe(3-Xpy)(2)[M(II)(CN)(4)]} (M(II): Ni, Pd, Pt; X: F, Cl, Br, I; py: pyridine) have been synthesised, and their crystal structures have been determined by single-crystal or powder X-ray analysis. All of the fluoro and iodo compounds, as well as the chloro derivative in which M(II) is Pt, crystallise in the monoclinic C2/m space group, whereas the rest of the chloro and all of the bromo derivatives crystallise in the orthorhombic Pnc2 space group. In all cases, the iron(II) atom resides in a pseudo-octahedral [FeN(6)] coordination core, with similar bond lengths and angles in the various derivatives. The major difference between the two kinds of structure arises from the stacking of consecutive two-dimensional {Fe(3-Xpy)(2)[M(II)(CN)(4)]}(infinity) layers, which allows different dispositions of the X atoms. The fluoro and chloro derivatives undergo cooperative spin crossover (SCO) with significant hysteretic behaviour, whereas the rest are paramagnetic. The thermal hysteresis, if X is F, shifts toward room temperature without changing the cooperativity as the pressure increases in the interval 10(5) Pa-0.5 GPa. At ambient pressure, the SCO phenomenon has been structurally characterised at different significant temperatures, and the corresponding thermodynamic parameters were obtained from DSC calorimetric measurements. Compound {Fe(3-Clpy)(2)[Pd(CN)(4)]} represents a new example of a "re-entrant" two-step spin transition by showing the Pnma space group in the intermediate phase (IP) and the Pnc2 space group in the low-spin (LS) and high-spin (HS) phases.

The synthesis and characterization of a series of 1-3D cyanide-bridged iron(II)-copper(I) bimetallic coordination polymers formulated as {Fe(3-Xpy)(2)[Cu(3-Xpy)(z)(CN)(2)](2)}, where 3-Xpy is a 3-halogenpyridine ligand with X = F (z = 1.5, 1), Cl (z = 1, 2 and 3), Br (z = 1, 4), and I (z = 1, 5), are reported. In all derivatives, the Fe(II) ion lies in pseudoctahedral [FeN(6)] sites defined by four in situ formed [Cu(3-Xpy)(z)(CN)(2)](-) bridging ligands and two 3-Xpy terminal ligands occupying the equatorial and axial positions, respectively. 1 consists of stacks of corrugated grids whose square windows are defined by pseudotrigonal and pseudotetrahedral [Cu(3-Fpy)(CN)(2)](-) and [Cu(3-Fpy)(2)(CN)(2)](-) units, respectively. 2 is a 3D coordination polymer with the topology of the open-framework CdSO(4). The [Cu(3-Clpy)(CN)(2)](-) rods connecting the pseudooctahedral Fe(II) sites are arranged in such a way that interpenetration is avoided. 3, an architectural isomer of 2, is defined by arrays of linear chains. 4 and 5 are isostructural to 3. Polymer 1 is essentially a low-spin (LS) compound with ca. 19% of residual Fe(II) ions in the high-spin (HS) state at 293 K. It undergoes an irreversible spin transition at T(c) = 356 K. Subsequent cooling-warming cycles give a new spin-crossover behavior characterized by T(c) = 187 K. The structural analysis at 130 and 293 K and at 293 K after irreversible transformation (293 K*) reveals a large unit cell volume variation of 67 A(3) per Fe atom. In addition to the volume change associated with the spin-state conversion, remarkable bond and angle modifications around the Cu(I) sites account for the high flexible nature of the crystal. 2 displays a complete not well-resolved two-step spin conversion, T(c1) = 169 K and T(c2) = 210 K, reflecting the occurrence of two distinct crystallographically Fe(II) sites. The large unit cell volume variation per Fe atom in 2, 59 A(3), has been rationalized in terms similar to those for 1. 1D polymers 3-5 are HS compounds.

Three new tetranuclear compounds of formula [Fe(4)(mu-CN)(4)(phen)(4)(L)(2))](PF(6))(4) x G where L = tris(pyridin-2-ylmethyl)amine (TPMA) [G = 0] (1), (6-methylpyrid-2-ylmethyl)-bis(pyrid-2-ylmethyl)amine (MeTPMA) [G = 0] (2), or bis(6-methylpyrid-2-ylmethyl)-(pyrid-2-ylmethyl)amine (Me(2)TPMA) [G = NH(4)PF(6)] (3) and phen = 1,10-phenanthroline) have been synthesized and characterized. The three compounds crystallize in the C2/c space group and consist of [Fe(4)(mu-CN)(4)(phen)(4)(L)(2))](4+) square shaped cations with two distinct iron(II) sites. The sites, associated with [Fe(phen)(2)(CN)(2)] and [Fe(L)(NC)(2)] moieties, are connected by cyanide bridging ligands and reside in different [FeN(4)C(2)] and [FeN(6)] ligand field strength environments. For 1, the structural features of both sites at 100 and 293 K are those of an iron(II) atom in the low-spin state, according to the magnetic properties. At 370 K the structure of the [FeN(6)] site is consistent with a quite complete change of spin state from the low-spin state to the high-spin state, a behavior confirmed by the magnetic study. Introduction of a methyl substituent in the sixth position of one or two pyridine groups to get MeTPMA or Me(2)TPMA derivatives, respectively, induce in 2 and 3 notable steric constraint in the [FeN(6)] site making longer the average Fe-N bond distances thereby weakening the ligand field strength and stabilizing the high-spin state. The [FeN(4)C(2)] site remains in the low-spin state in the three compounds.

This study reports the syntheses and the characterization of 12 ferric complexes of pyridoxal thiosemicarbazone. The richness of the coordination chemistry of this ligand is highlighted by the modulation of its charge from neutral H 2 L to anionic L 2− , thus leading to a wide family of ferric compounds with charge varying from +3 to −1. The structures of complexes [Fe(HL) 2 ]ClO 4 · 2H 2 O and [Fe(HL)L] · 4.5H 2 O were solved and discussed with a particular attention brought to the intermolecular interactions occurring between the complexes. The investigation of magnetic properties of these compounds revealed that two of them are in the HS state at any temperature, whereas the others are in the LS state. These results are discussed in relation to the modulation of the electronic properties of the ligand.

A new ttf (tetrathiofulvalene) ligand containing an amidopyridine moiety was synthesized and characterized. The electrochemical study of the 4-tetrathiofulvalenylcarboxamidopyridine (ttf–adpy) ligand showed two reversible oxidation processes at EI′1/2 = 0.08 V/Fc+–Fc and EII′1/2 = 0.26 V/Fc+–Fc. The crystal structure of [(ttf–adpyH)2Pt(CN)4] (1) was solved at 293 K, where 1 displays the triclinic space group P. The ttf–adpyH+ molecule is planar, and the bond lengths within the ttf core are in the usual range for neutral ttf moieties. The ttf–adpyH+ molecules and the [Pt(CN)4]2– anions organize in a three-dimensional network by means of hydrogen bonds and short S···S contacts. In the network, the ttf–adpy molecules order following the pattern -D-A-D-A- (D = donor, pyridine; A = acceptor, ttf moieties). Reaction of the Fe(BF4)2·6H2O salt, ttf–adpy ligand and the [M(CN)4]2– coordinating counterions led to the 2D Hofmann-like polymers {Fe(ttf–adpy)2[M(CN)4]}·nH2O [M = NiII; n = 1.5 (2), 0 (5); PdII; n = 2 (3), 0 (6); PtIIn = 2 (4), 0 (7)]. A 2D structure for 2–7 was proposed on the basis of analytical data. Compounds 2–4 present a complete thermally induced two-step spin transition. It is observed in the temperature interval from 100 to 200 K for 2; whereas for 3 and 4 it occurred in the interval of 200–250 K. The spin-transition properties of 2–4 were found to be strongly dependent on the water content, as nonhydrated materials 5–7 are paramagnetic in the studied temperature range (5–350 K). The thermodynamic parameters associated with the spin transition estimated from DSCmeasurements are: ΔH1 = 5.7 kJ mol–1 (3), 6.2 kJ mol–1 (4),ΔH2 = 6.5 kJ mol–1 (3), 7.2 kJ mol–1 (4) and ΔS1 = 24 J K–1 mol–1 (3), 26.6 J K–1 mol–1 (4), ΔS2 = 30.4 J K–1 mol–1 (3) and32.8 J K–1 mol–1(4).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Three new compounds formulated (ClO4)2[Fe(pq)3] (1), (BF4)2[Fe(pq)3] · EtOH (2) and {(ClO4)[MnCr(C2O4)3][Fe(pq)2(H2O)2]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)3]2+ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 A on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol−1, ΔS = 50 J K−1 mol−1and Γ = 1.35 kJ mol−1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mossbauer spectra of 3 show the occurrence of a magnetic order at T ⩽ 4.2 K.

Two new series of oxamato-bridged heterobimetallic coordination networks of general formula Li5[Li3M2(mpba)3(H2O)6] · 31H2O [M = NiII (1a) and CoII (1b)] and Li2[Mn3M2(mpba)3(H2O)6] · 22H2O [M = NiII (2a) and CoII (2b)] have been prepared from the metal-mediated self-assembly of the hexakis(bidentate), triple-stranded dinickel(II) and dicobalt(II) complexes [M2(mpba)3]8− [mpba = meta-phenylenebis(oxamato)] with either monovalent lithium(I) or divalent manganese(II) ions respectively, in water. X-ray structural analyses of 1a and 1b show an anionic three-dimensional network formed by an infinite parallel array of oxamato-bridged Li 3 I M 2 II (M = Ni and Co) hexagonal layers, which are interconnected through three m-phenylenediamidate bridges between the MII ions of opposite propeller chirality (Δ and Λ) to give dinuclear metallacryptand cores of the meso-helicate-type. The intralayer Li–M distance through the oxamate bridge is 5.380(3) (1a) and 5.396(5) (1b) A, while the interlayer M–M distance through the triple m-phenylenediamidate bridge is 6.856(3) (1a) and 6.851(3) (1b) A. Overall, this leads to an open-framework honeycomb structure with large hexagonal pores of ca. 21.8 (1a) and 21.5 A (1b) in diameter which are occupied by linear arrays of water-bridged LiI countercations. Variable-temperature (2.0–300 K) dc magnetic susceptibility and variable-field (0–5.0 T) magnetization measurements on these two series of compounds reveal a distinct magnetic behavior mainly depending on the diamagnetic or paramagnetic nature of the LiI and MnII ions, respectively. Compounds 1a and 1b behave as rather well-isolated M 2 II (M = Ni and Co) dimers with a moderate to weak ferromagnetic coupling (JNi–Ni = +3.17 cm−1 and JCo–Co = +1.03 cm−1) between the two MII ions across the triple m-phenylenediamidate bridge, together with either an appreciable to remarkable local ion axial magnetic anisotropy (DNi = −3.35 cm−1) or spin–orbit coupling (λCo = −167.3 cm−1); the next nearest-neighbor magnetic interactions between the MII ions through the diamagnetic LiI ions are negligible. Compounds 2a and 2b behave instead as strongly coupled oxamato-bridged Mn 3 II M 2 II (M = Ni and Co) ferrimagnetic planes which are weakly interacting through the m-phenylenediamidate bridges, leading thus to a long-range 3D ferromagnetic order at TC = 6.5 K. In addition, the variable-temperature (2.0–12 K) ac magnetic susceptibility measurements on 2a and 2b show an intriguing frequency-dependent magnetic behavior characteristic of a spin-glass dynamics. This glassy behavior is likely attributed to their amorphous character and/or the moderate to strong magnetic anisotropy of the dinickel(II) and dicobalt(II) precursors.

A new family of cyanide-based spin-crossover polymers with the general formula {Fe(5-Br-pmd)z[M(CN)x]y} [M=AgI (1), AuI (2), NiII (3), PdII (4), PtII (5); 5-Br-pmd=5-bromopyrimidine; z=1 or 2, x=2 or 4, and y=2 or 1] have been synthesized and characterized using single-crystal X-ray diffraction (XRD), X-ray powder diffraction (XRPD), magnetic susceptibility measurements, and differential scanning calorimetry (DSC). At 293 K, compound 1 presents the monoclinic space group C2/c, whereas at 120 K, it changes to the monoclinic space group P21/c. At 293 K, the crystal structure of 1 displays an uninodal three-dimensional network whose nodes, constituted of FeII, lie at the inversion center of an elongated octahedron. The equatorial bond lengths are defined by the N atoms of four [AgI(CN)2]- groups belonging to two crystallographically nonequivalent AgI atoms, Ag(1) and Ag(2). They are shorter than those of the axial positions occupied by the N atoms of the 5-Br-pmd ligands. The Fe-N average bond length of 2.1657(7) A is consistent with a high-spin (HS) state for the FeII ions. At 120 K, the crystal structure changes refer mainly to the FeII environment. There are two crystallographically independent FeII ions at this temperature, Fe(1) and Fe(2), which adopt the HS and low-spin (LS) states, respectively. The average Fe-N bond length for Fe(1) [2.174(5) A] and Fe(2) [1.955(5) A] agrees well with the reported magnetic data at this temperature. The spin transition of the FeII ions labeled as Fe(1) is found to be centered at Tc downward arrow=149 K and Tc upward arrow=167 K and accompanied by a drastic change of color from orange (HS) to red (LS). Magnetic susceptibility measurements under applied hydrostatic pressure performed on 1 have shown a linear displacement of the transition to higher temperatures while the hysteresis width remains unaltered in the interval of pressures of 105 Pa to 0.34 GPa. A further increase of the pressure induces the spin transition in the Fe(2) ions, which is completely accomplished at 1.12 GPa (T1/2=162 K). Compounds 1 and 2 are isostructural, but 2 does not exhibit spin-transition properties; the FeII centers remain in the HS state in the temperature range investigated, 5-300 K. Compounds 3-5 are not similar or isostructural with 1. A two-dimensional structure for 3-5 has been proposed on the basis of analytical data and the XRPD patterns. Compounds 3-5 undergo first-order spin transition where the critical temperatures for the cooling (Tc downward arrow) and warming (Tc upward arrow) modes are 170 and 180 K (3), 204 and 214 K (4), and 197 and 223 K (5), respectively. It is worth mentioning the color change from yellow to orange observed in 3-5 upon spin transition. The thermodynamic parameters associated with the spin transition estimated from DSC measurements are DeltaH=6 kJ mol(-1) (1), 11 kJ mol(-1) (3), 16 kJ mol(-1) (4), and 16 kJ mol(-1) (5) and DeltaS=38 J K(-1) mol(-1) (1), 62 J K(-1) mol(-1) (3), 76 J K-1 mol(-1) (4), and 81 J K(-1) mol(-1) (5).

[EN] Two novel bis(oxo)-bridged dinuclear manganese(IV) complexes with the binucleating ligand o-phenylenebis(oxamate) (opba), formulated as (Me4N)(4)[Mn2O2(opba)(2)] (1a) and (Me4N)(2)(Ph4P)(2)[Mn2O2(opba)(2)] (.) 8H(2)O (1b), have been synthesized and characterized structurally and magnetically. Like the parent complex (Ph4P)(4)[Mn2O2(opba)(2)] (.) 4H(2)O (1c), they possess unique Mn-2(mu-O)(2) bridging cores with two additional o-phenylenediamidate bridges which lead to exceptionally short Mn-Mn distances (2.63-2.67 angstrom) and fairly bent Mn-O-Mn angles (93.8-95.5 degrees). Complexes 1a-c show a moderate to strong antiferromagnetic coupling between the two high-spin Mn-IV ions through the bis(oxo)bis(o-phenylenediamidate) quadruple bridge (-J = 70-164 cm(-1); H = -JS(1) (.) S-2) Along this series, the -J values increase with the shortening of the Mn-Mn distance and/or the lessening of the Mn-O-Mn angle. Electronic structure calculations on model complexes reproduce the observed dependence of -J with the Mn-O-Mn angle at short intermetallic distances, and reveal that the magnetic coupling is dominated by the in-plane 3d(x2-y2) type superexchange pathway via the oxo bridges with a small but nonnegligible contribution from direct 3d(x2-y2) type Mn-Mn sigma-bond., This work was supported by the Oficina de Ciencia i Tecnología de la Generalitat Valenciana (Spain) through the Plan Valenciano de Investigación Científica, Desarrollo Tecnológico e Innovación (PVIDI) (CTIDIA2002-131) and the Ministerio de Ciencia y Tecnología (MCYT) (Spain) through the Ramón y Cajal program. R.R.-G. thanks all his colleagues in the research group of Prof. José R. Pedro at the Universitat de València where he has developed the work on the biomimetic chemistry of high-valent transition metal complexes in the last years. He is specially thankful to Dr. X. Ottenwaelder (Stanford University) for very stimulating talks and unselfish help during this period.

In the search for new multifunctional spin crossover molecular materials, here we describe the synthesis, crystal structures and magnetic and photomagnetic properties of the complexes trans-[Fe(Fctzpy)2(NCX)2]·CHCl3 where Fc-tzpy is the ferrocene-appended ligand 4-(2-pyridyl)-1H-1,2,3-triazol- 1-ylferrocene, X = S (1) and X = Se (2). Both complexes display thermal- and light-induced (LIESST) spin crossover properties characterised by T1/2 = 85 and 168 K, ΔS = 55 and 66 J K−1 mol−1 , ΔH = 4.7 and 11.1 kJ mol−1 and TLIESST = 47 K and 39 K for 1 and 2 respectively. The crystal structure of 1 and 2 measured at 275 K is consistent with the iron(II) ion in the high-spin state while the crystal structure of 2 at 120 K denotes the occurrence of complete transformation to the low-spin state., The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P) and Generalitat Valenciana (PROMETEO/2012/049). T.R.M. and F.J.V.M. thank MINECO for a FPI grant. L.P.L. thanks the Generalitat Valenciana and the Universidad de Valencia for a predoctoral fellowship.

The synthesis, crystal structures, magnetic behavior, and electron paramagnetic resonance studies of five new FeIII spin crossover (SCO) complexes are reported. The [FeIIIN5O] coordination core is constituted of the pentadentate ligand bztpen (N5) and a series of alkoxide anions (ethoxide, propoxide, n-butoxide, isobutoxide, and ethylene glycoxide). The methoxide derivative previously reported by us is also reinvestigated. The six complexes crystallize in the orthorhombic Pbca space group and show similar molecular structures and crystal packing. The coordination octahedron is strongly distorted in both the high- and low-temperature structures. The structural changes upon spin conversion are consistent with those previously observed for [FeIIIN4O2] SCO complexes of the Schiff base type, except for the Fe−O(alkoxide) bond distance, which shortens significantly in the highspin state. Application of the Slichter−Drickamer thermodynamic model to the experimental SCO curves afforded reasonably good simulations with typical enthalpy and entropy variations ranging in the intervals ΔH = 6−13 kJ mol−1 and ΔS = 40−50 J mol−1 K−1 , respectively. The estimated values of the cooperativity parameter Γ, found in the interval 0−2.2 kJ mol−1 , were consistent with the nature of the SCO. Electron paramagnetic resonance spectroscopy confirmed the transformation between the high-spin and low-spin states, characterized by signals at g ≈ 4.47 and 2.10, respectively. Electrochemical analysis demonstrated the instability of the Fe(II) alkoxide derivatives in solution., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P) and Generalitat Valenciana (PROME-TEO/2012/049). L.P.-L. thanks the Generalitat Valenciana and Universitat de Valencia for a predoctoral fellowship.

Deprotonation of the ionogenic tetradentate ligand 6,6′-bis(1H-tetrazol-5-yl)-2,2′-bipyridine [H2bipy(ttr)2] in the presence of FeII in solution has afforded an anionic mononuclear complex and a neutral two-dimensional coordination polymer formulated as, respectively, NEt3H{Fe[bipy(ttr)2][Hbipy(ttr)2]}·3MeOH (1) and {Fe[bipy(ttr)2]}n (2). The anions [Hbipy(ttr)2]− and [bipy(ttr)2]2– embrace the FeII centers defining discrete molecular units 1 with the FeII ion lying in a distorted bisdisphenoid dodecahedron, a rare example of octacoordination in the coordination environment of this cation. The magnetic behavior of 1 shows that the FeII is high-spin, and its Mössbauer spectrum is characterized by a relatively large average quadrupole splitting, ΔEQ = 3.42 mm s–1. Compound 2 defines a strongly distorted octahedral environment for FeII in which one [bipy(ttr)2]− anion coordinates the equatorial positions of the FeII center, while the axial positions are occupied by peripheral N-tetrazole atoms of two adjacent {Fe[bipy(ttr)2]}0 moieties thereby generating an infinite double-layer sheet. Compound 2 undergoes an almost complete spin crossover transition between the high-spin and low-spin states centered at about 221 K characterized by an average variation of enthalpy and entropy ΔHav = 8.27 kJ mol–1, ΔSav = 37.5 J K–1 mol–1, obtained from calorimetric DSC measurements. Photomagnetic measurements of 2 at 10 K show an almost complete light-induced spin state trapping (LIESST) effect which denotes occurrence of antiferromagnetic coupling between the excited high-spin species and TLIESST = 52 K. The crystal structure of 2 has been investigated in detail at various temperatures and discussed., The research reported here was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P) and Generalitat Valenciana (PROMETEO/2012/049). L.P.-L. thanks the Generalitat Valenciana and the Universidad de Valencia for a predoctoral fellowship. M.S. thanks the EU for a Marie Curie fellowship (IIF-253254).

The synthesis, structure and magnetic properties of [Fe(bpe)4(H2O)2](TCNQ)2 (1) are reported. 1 crystallizes in the triclinic P space group, a = 13.481(5), b = 14.887(3), c = 16.663(4) A, α = 101.048(18), β = 112.84(2), γ = 90.92(2)°, V = 3009.6(14) A3, Z = 2. The iron atom defines a compressed octahedron with the equatorial positions occupied by the bpe molecules which act as monodentate ligands and the two axial positions occupied by water molecules. The TCNQ− radical counterions are uncoordinated and interact by pairs defining (TCNQ)22− units strongly coupled antiferromagnetically. The iron(II) atoms are in the high spin state and its magnetic behaviour indicates the occurrence of zero-field splitting of the S = 2 ground state.

The dinuclear iron(II) complex {[Fe(CH3bipy)(NCS)2]2bpym} has been synthesised and its crystal structure determined at 293 K. The magnetic properties display intramolecular antiferromagnetic coupling at 1 bar (J = −4.2 cm−1), and the onset of a pressure-induced spin conversion is observed at 11 kbar. Magnetic field Mossbauer measurements have been carried out at 4.2 K, and indicate that the HS species correspond to [HS-HS] pairs. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

[EN] The suitability of the system [Fe(4,4`-bipy)(H2O)2(NCX)2]·(4,4`-bipy), where 4,4`-bipy stands for 4,4`-bipyridine and X = S (1) and Se (2), as a precursor for the synthesis of new polymeric spin-crossover compounds has been studied. The reaction of 1 or 2 with bt (2,2`-bithiazoline) afforded the polymeric compounds of formula [Fe(4,4`-bipy)(bt)(NCX)2] (X = S (3), Se (4)). Compounds 3 and 4 are isostructural, but only the crystal structure of 3 has been fully determined. It crystallizes in the orthorhombic system, Fdd2 space group, Z = 24, with a = 38.962(8) Å, b = 11.545(2) Å, c = 30.889(6) Å, V = 13895(5) Å3. The structure consists of linear chains constituted by trans-4,4`-bipy linked iron(II) ions; two cis equatorial positions are occupied by two pseudohalide ligands, and the remaining positions are filled by the bidentate bt ligand. Investigation of their magnetic properties and Mössbauer spectra has revealed the occurrence of a low-spin (LS) ¿ high-spin (HS) conversion involving 12% (3, S) and 20% (4, Se) of the Fe(II) ions. The thermal variation of the HS fraction is gradual with onset temperatures as low as 60 K. A theoretical approach based on the Ising-like model, completed with molecular vibrations, through harmonic oscillators, fits the data successfully, leading to an energy gap of 65 cm-1 (3) and 86 cm-1 (4) between the lowest LS and HS levels, and an average vibration frequency ¿¿LS of 382 cm-1 (3) and 365 cm-1 (4) in the LS state. The ca. 1.05 ¿LS(3)/¿LS(4) ratio is close to the ca. 1.09 Se/S molar mass ratio. The simple electrovibrational Ising-like model permits us to explain, for the first time, a mass effect through the molecular vibrations in a spin-crossover complex that is in the unusual situation of equienergy among the HS and LS states., We thank the financial assistance from the Ministerio Español de Ciencia y Tecnología (Project BQU 2001-2928). We acknowledge the European Commission for granting the TMR-Network Thermal and Optical Switching of Molecular Spin States (TOSS) , Contract noERB-FMRX-CT98-0199EEC/TMR.

The influence of the charge and steric hindrance on the spin state of a series of four monomeric Fe-II complexes derived from the tridentate tigands 2-(1H-benzoimidazol-2-yl)-1,10-phenanthroline (Hphenbi) and 2-(1H-benzoimidazol-2-yl-9-methyl-1,10-phenanthroline (Hmphenbi) and their deprotonated forms (phenbi(-), mphenbi(-)) are investigated. The crystal structure and magnetic properties show that [Fe(Hphenbi)(2)](BF4)(2)center dot 1.5C(6)H(5)NO(2)center dot H2O (1) and its neutral form [Fe(phenbi)(2)]center dot 2CHCl(3)center dot H2O (2) are low-spin complexes at 400 K due to the strong ligand field imparted by the terpyridine-like tigand. In contrast, the steric hindrance induced by the methyl group in [Fe(Hmphenbi)21(BF4)2 (3) stabilizes the high-spin state of the Fe-II ion at all temperatures. Application of a hydrostatic pressure of 0.43 GPa shows that 3 displays incomplete thermal-induced spin crossover behaviour. However, upon deprotonation of the ligand the resulting neutral complex [Fe(mphenbi)(2)]center dot 2CHCl(3) (4) shows a complete two-step spin crossover behaviour at ambient pressure., This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO) and FEDER funds (CTQ2013-46275-P), and the Generalitat Valenciana through PROMETEO/2012/049. MS thanks the EU for a Marie Curie fellowship (IIF-253254).

The synthesis, structure, and magnetic properties of three clathrate derivatives of the spin-crossover porous coordination polymer {Fe(pyrazine)[Pt(CN)(4)]} (1) with five-membered aromatic molecules furan, pyrrole, and thiophene is reported. The three derivatives have a cooperative spin-crossover transition with hysteresis loops 14-29 K wide and average critical temperatures T-c=201 K (1.fur), 167 K (1.pyr), and 114.6 K (1.thio) well below that of the parent compound 1 (T-c=295 K), confirming stabilization of the HS state. The transition is complete and takes place in two steps for 1.fur, while 1.pyr and 1.thio show 50% spin transition. For 1.fur the transformation between the HS and IS (middle of the plateau) phases occurs concomitantly with a crystallographic phase transition between the tetragonal space groups P4/mmm and I4/mmm, respectively. The latter space group is retained in the subsequent transformation involving the IS and the LS phases. 1.pyr and 1.thio display the tetragonal P4/mmm and orthorhombic Fmmm space groups, respectively, in both HS and IM phases. Periodic calculations using density functional methods for 1.fur, 1.pyr, 1.thio, and previously reported derivatives 1.CS2, 1.I, 1.bz(benzene), and 1.pz(pyrazine) have been carried out to investigate the electronic structure and nature of the host-guest interactions as well as their relationship with the changes in the LS-HS transition temperatures of 1.Guest. Geometry-optimized lattice parameters and bond distances in the empty host 1 and 1.Guest clathrates are in general agreement with the X-ray diffraction data. The concordance between the theoretical results and the experimental data also comprises the guest molecule orientation inside the host and intermolecular distances. Furthermore, a general correlation between experimental T-c and calculated LS-HS electronic energy gap was observed. Finally, specific host-guest interactions were studied through interaction energy calculations and crystal orbital displacement (COD) curve analysis., The research reported herein was supported by the Spanish Ministerio de Ciencia e Innovacion (MICINN) and FEDER funds (CTQ2013-46275-P and CTQ2011-23862-C02-01), Generalitat de Catalunya (2009SGR-1459) and Generalitat Valenciana through PROMETEO/2012/049. D. A. thanks Conicyt-Chile for a predoctoral fellowship. Z.A.C. thanks the Spanish M.E.C.D. for a predoctoral FPU fellowship. M.O. thanks a Grant-In-Aid for Science Research for Innovative Areas "Coordination Programming (Area 2107, No. 22108512)" and for Scientific Research Program (A) (No. 23245014) from MEXT, Japan. The authors thankfully acknowledge the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputer Center.

[EN] The new complexes of formulae PPh4[Cr(dpa)(ox)(2)] (1), AsPh4[Cr(dpa)(OX)(2)] (2), Hdpa[Cr(dpa)(ox)(2)]-4H(2)O (3), Rad[Cr(dpa)(ox)(2)] . H2O (4) and Sr[Cr(dpa)(ox)(2)](2) . 8H(2)O (5) [PPh4 = tetraphenylphosphonium cation; AsPh4 = tetraphenylarsoniurn cation; dpa = 2,T-dipyridylamine; ox = oxalate dianion; Rad = 2-(4-N-methylpyridinium)4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-a-oxyl-3-N-oxide] have been prepared and characterised by single-crystal X-ray diffraction. The structures of 1-4 consist of discrete [Cr(dpa)(ox)(2)](-) anions, tetraphenylphosphonium. (1), tetraphenylarsonium (2), monoprotonated Hdpa (3) and univalent radical (4) cations and uncoordinated water molecules (2-4). The chromium environment in 1-4 is distorted octahedral with Cr-O bond distances between 1.982(2)-1.946(2) Angstrom and Cr-N bonds of 2.0716(17)-2.048(3) Angstrom. The angles subtended at the chromium atom by the two oxalates are 83.6(2)-81.71(8)degrees, whereas the N-Cr-N angles are 87.76(7)-86.24(9)degrees. The [Cr(dpa)(ox)(2)](-) unit of 1-4 is also present in 5 but it acts as a chelating ligand through its two oxalato groups towards divalent strontium cations, yielding heterobimetallic zig-zag chains that run parallel to the a axis. Each chain is formed of diamond-shaped units sharing the strontium atoms, while the two other corners are occupied by two crystallographically independent chromium atoms. The [Cr(dpa)(ox)(2)](-) unit in 5 retains the environment observed in 1-4 and the strontium atom is coordinated to eight oxalate oxygens from four oxalate ligands. The two crystallographycally independent chromium centres within each double chain have opposite chirality. However, the adjacent double chains are related by an inversion centre resulting in achiral layers parallel to the ac plane. The magnetic properties of 1-5 have been investigated in the temperature range 1.9-290 K. A quasi Curie law behaviour is observed for 1-3 and 5 in agreement with their crystal structures, whereas a significant antiferromagnetic interaction between the chromium(m) and the radical centre occurs in the case of 4. The synthetic possibilities offered by the use of the heteroleptic species [CrL(ox)(2)](-) (L = alpha -diimine-type ligand) as a ligand towards metal ions is analysed and discussed in the fight of the available structural results., Financial support from the Spanish Dirección General de Investigación Científica y Técnica (DGICYT) through Projects PB97-1397 and PB98-1044, the Romanian Ministry of Education (Grants 30C/CNCSIS and 1D/CNCSIS) and the TMR Program from the European Union (Contract ERBFMRXCT98-0181) is acknowledged. Thanks are also extended to the Centre d'Informàtica de la Universitat de València for computer resource support.

[EN] The new bimetallic nickel(II) compound (PPh4)4[Ni2(2)]·6H2O (3), where H8[2] stands for N,N',N'',N'''-1,2,4,5-benzene-tetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni2(n4:n4-2)]4- anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni2(n4:n4-2)]4- generates the metallo-radical species [Ni2(n4:n4-2·+)]3- with characteristic intra-ligand ¿cation radical transitions in the visible region (475-550 nm) as well as a typical quasi-isotropic EPR signal at g ¿ 2.0., This work was supported by the CNRS (France) and the DGICYT (Spain) through project PB9421002. B. Cervera thanks the Conselleria de Educació i Ciència de la Generalitat Valenciana (Spain) for a grant.

[EN] Two new heterobimetallic complexes [Cu(pdmg)Ni(Me-3[12]N-3)(CH3CH2OH)](ClO4)(2)(2) and [Cu(pdmg) Mn(bipy)(2)]-ClO4)(2) . H2O (3) (H(2)pdmg = 3,9-dimethyl-4,8-diazaundeca-3,8-diene-2 10-dione dioxime; Me-3[12]N-3 = 2,4,4-trimethyl-1,5,9-triazacyclododeca-1-ene; bipy = 2,2'-bipyridyl) have been prepared and characterized. The structure of 2 has been determined by single-crystal X-ray diffraction methods. It consists of [Cu(pdmg)Ni(Me-3[12]N-3)(CH3CH2OH)](2+) cations and non-coordinated perchlorate anions. The [Cu(pdmg)(CH3CH2OH)] complex coordinates to the [Ni(Me-3[12]N-3)](2+) fragment to afford the binuclear unit doubly-bridged by oximato groups in cis arrangement. The coordination geometry around the copper atom is square-pyramidal, whereas the nickel atom exhibits a trigonal-bipyramidal surrounding The intramolecular Cu-Ni distance is 3.810(6) Angstrom. In the crystal, two [(CuNII)-N-II] dimeric units are related through an inversion center, giving rise to a bis-binuclear entity with a relatively short intermolecular Cu-Cu separation of 4.175(6) Angstrom. Variable-temperature magnetic susceptibility measurements (2.0-300 K) for 2 correspond to an almost isolated Cu(II)Ni(Ir) pair with an intrapair interaction parameter J= -143.6(2) cm(-1). However, the EPR spectrum at 4.2 K is that of a triplet spin state arising from the interaction between the two doublet spin states within the [(CuNiII)-Ni-II](2) bis-binuclear entity. The magnetic properties of 3 unambiguously reveal the bis-binuclear nature of this compound, as is the case for the related homometallic complex [Cu(pdmg)Cu(bipy)(H2O)(2)](ClO4)(2). H2O (1). The intra- (J) and interpair (j) interaction parameters for 3, as deduced from the analysis of its magnetic susceptibility data in the temperature range 2.0-300 K, are - 50.9(2) and 1.50(2) cm(-1), respectively. The field dependence of the magnetization of 3 at 2.0 K corresponds to that of a nonet state arising from the interaction between two quintuplet spin states within the [(CuMnII)-Mn-II](2) bis-binuclear entity. The interaction between the heterobinuclear Cu(II)Mn(II) molecules and its influence on the nature of the ground spin state for 3 are analyzed and discussed in the framework of a spin polarization scheme., This work was supported by the Dirección General de Investigación Cientı́fica y Técnica (DGICYT) (Spain) through Project PB97-1397 the Spanish French Integrated Actions and the TMR program of the European Union through project ERBFMRXCT-980181. B. Cervera and R. Ruiz acknowledge the Conselleria de Cultura, Educació i Ciència de la Generalitat Valenciana and the Ministerio de Educación y Ciencia (Spain) for doctoral and post-doctoral grants, respectively. We are very indebted to Dr Ally Aukauloo for fruitful discussions during the preparation of the manuscript and continuous interest in this work.