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The metal ion, countercation and crystallization solvent control the packing of bis(dithiooxalato-k2S,S′)metallate(ii) complex anions in the solid state.

The coexistence of field-induced blockage of the magnetization and significant magnetocaloric effects in the low-temperature region occurs in a mononuclear holmium(III) diethylenetriamine-N,N,N′,N″,N″-pentaacetate complex, whose gadolinium(III) analogue is a commercial MRI contrast agent. Both properties make it a suitable candidate for cryogenic magnetic refrigeration, thus enlarging the variety of applications of this simple class of multifunctional molecular nanomagnets., A mononuclear holmium(III) complex is proposed as a new prototype of a multifunctional molecular nanomagnet for the physical implementation of cryomagnetic refrigeration near the strategically relevant hydrogen liquefaction temperature. Significant magnetocaloric effects occur in a wide temperature range just above the field-induced magnetization blockage.

The coexistence of field-induced slow magnetic relaxation and moderately large magnetocaloric efficiency in the supra-Kelvin temperature region occurs in the 2D compound [GdIII2(ox)3(H2O)6]n·4nH2O (1), a feature that can be exploited in the proof-of-concept design of a new class of slow-relaxing magnetic materials for cryogenic magnetic refrigeration.

Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(II) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin CoII ion (SCo = 1/2) to the diamagnetic low-spin CoIII ion (SCo = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.

A leitmotiv in the field of molecular magnetism is the study of the electron exchange (EE) magnetic interactions among distant metal centers through the corresponding bridging ligands in polynuclear coordination compounds. The present review provides a historical perspective on the use of dinuclear copper(II) complexes with either simple inorganic or extended organic bridging ligands as experimental and theoretical models for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the EE interaction across σ- and π-type orbital pathways. Particular focus is placed on the work by Professor Miguel Julve, outstanding researcher and an excellent teacher, best friend and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th anniversary.

A new two-dimensional (2D) coordination polymer of the formula {Cu(ox)(4-Hmpz)·1/3H2O}n (1) (ox = oxalate and 4-Hmpz = 4-methyl-1H-pyrazole) has been prepared, and its structure has been determined by single-crystal X-ray diffraction. It consists of corrugated oxalato-bridged copper(II) neutral layers featuring two alternating bridging modes of the oxalate group within each layer, the symmetric bis-bidentate (μ-κ2O1,O2:κ2O2′,O1′) and the asymmetric bis(bidentate/monodentate) (μ4-κO1:κ2O1,O2:κO2′:κ2O2′,O1′) coordination modes. The three crystallographically independent six-coordinate copper(II) ions that occur in 1 have tetragonally elongated surroundings with three oxygen atoms from two oxalate ligands, a methylpyrazole-nitrogen defining the equatorial plane, and two other oxalate-oxygen atoms occupying the axial positions. The monodentate 4-Hmpz ligands alternatively extrude above and below each oxalate-bridged copper(II) layer, and the water molecules of crystallization are located between the layers. Compound 1 exhibits a fast and selective adsorption of methylamine vapors to afford the adsorbate of formula {Cu(ox)(4-Hmpz)·3MeNH2·1/3H2O}n (2), which is accompanied by a concomitant color change from cyan to deep blue. Compound 2 transforms into {Cu(ox)(4-Hmpz)·MeNH2·1/3H2O}n (3) under vacuum for three hours. The cryomagnetic study of 1–3 revealed a unique switching from strong (1) to weak (2 and 3) antiferromagnetic interactions. The external control of the optical and magnetic properties along this series of compounds might make them suitable candidates for switching optical and magnetic devices for chemical sensing.

Two novel copper(II) complexes of formulas {[Cu(4-Hmpz)4][Cu(4-Hmpz)2(µ3-ox-κ2O1,O2:κO2′:κO1′)(ClO4)2]}n (1) and {[Cu(3,4,5-Htmpz)4]2[Cu(3,4,5-Htmpz)2(µ3-ox-κ2O1,O2:κO2′:κO1′)(H2O)(ClO4)]2[Cu2(3,4,5-Htmpz)4(µ-ox-κ2O1,O2:κ2O2′,O1′)]}(ClO4)4·6H2O (2) have been obtained by using 4-methyl-1H-pyrazole (4-Hmpz) and 3,4,5-trimethyl-1H-pyrazole (3,4,5-Htmpz) as terminal ligands and oxalate (ox) as the polyatomic inverse coordination center. The crystal structure of 1 consists of perchlorate counteranions and cationic copper(II) chains with alternating bis(pyrazole)(µ3-κ2O1,O2:κO2′:κO1′-oxalato)copper(II) and tetrakis(pyrazole)copper(II) fragments. The crystal structure of 2 is made up of perchlorate counteranions and cationic centrosymmetric hexanuclear complexes where an inner tetrakis(pyrazole)(µ-κ2O1,O2:κ2O2′,O1′-oxalato)dicopper(II) entity and two outer mononuclear tetrakis(pyrazole)copper(II) units are linked through two mononuclear aquabis(pyrazole)(µ3-κ2O1,O2:κO2′:κO1′-oxalato)copper(II) units. The magnetic properties of 1 and 2 were investigated in the temperature range 2.0–300 K. Very weak intrachain antiferromagnetic interactions between the copper(II) ions through the µ3-ox-κ2O1,O2:κO2′:κO1′ center occur in 1 [J = −0.42(1) cm−1, the spin Hamiltonian being defined as H = −J∑S1,i · S2,i+1], whereas very weak intramolecular ferromagnetic [J = +0.28(2) cm−1] and strong antiferromagnetic [J’ = −348(2) cm−1] couplings coexist in 2 which are mediated by the µ3-ox-κ2O1,O2:κO2′:κO1′ and µ-ox-κ2O1,O2:κ2O2′,O1′ centers, respectively. The variation in the nature and magnitude of the magnetic coupling for this pair of oxalato-centered inverse copper(II) complexes is discussed in the light of their different structural features, and a comparison with related oxalato-centered inverse copper(II)-pyrazole systems from the literature is carried out.

International audience; Molecular magnetism has made a long journey, from the fundamental studies on through-ligand electron exchange magnetic interactions in dinuclear metal complexes with extended organic bridges to the more recent exploration of their electron spin transport and quantum coherence properties. Such a field has witnessed a renaissance of dinuclear metallacyclic systems as new experimental and theoretical models for single-molecule spintronics and quantum computing, due to the intercrossing between molecular magnetism and metallosupramolecular chemistry. The present review reports a state-of-the-art overview as well as future perspectives on the use of oxamato-based dicopper(II) metallacyclophanes as promising candidates to make multifunctional and multiresponsive, single-molecule magnetic (nano)devices for the physical implementation of quantum information processing (QIP). They incorporate molecular magnetic couplers, transformers, and wires, controlling and facilitating the spin communication, as well as molecular magnetic rectifiers, transistors, and switches, exhibiting a bistable (ON/OFF) spin behavior under external stimuli (chemical, electronic, or photonic). Special focus is placed on the extensive research work done by Professor Francesc Lloret, an outstanding chemist, excellent teacher, best friend, and colleague, in recognition of his invaluable contributions to molecular magnetism on the occasion of his 65th birthday.

A primary goal of molecular spintronics is detecting the response of the spins from a single magnetic molecule to an external stimulus and, eventually, being able to implement logic quantum memory capabilities for information data storage and processing applications in quantum computation. Having this in mind, a novel hexanuclear oxamatocopper(II) complex of formula {[Cu2(naba)2][Cu(pmdien)]4}(ClO4)4·8H2O (2) [naba = N,N'-1,5-naphthalenebis(oxamate) and pmdien = N,N,N’,N”,N”-pentamethyldiethylenetriamine] has been prepared by the reaction of stoichiometric amounts of (nBu4N)4[Cu2(naba)2] · 4H2O (1) (nBu4N+ = tetra-n-butylammonium cation) and [Cu(pmdien)](ClO4)2 (1:4 molar ratio) in water. 2 exhibits a ladder-like “dimer-of-trinuclears” structure featuring a photoactive dicopper(II) naphthalenophane core acting as inverse coordination centre (centroligand) towards four peripheral [Cu(pmdien)]2+ groups through the outer amidate/carboxylate oxygen atoms of the oxamato fragments. 2 undergoes a unique magnetic photoswitching ON/OFF behaviour upon UV light irradiation because of an intramolecular (“pseudo-bimolecular”) photocycloaddition of the two facing naphthalene spacers through the more reactive carbon atoms at the 1,4 and 1’,4’ positions of the benzene rings to afford the putative [4 + 4] cycloaddition product c-2. Hence, the two oxamato-bridged S = 1/2 CuII3 linear units antiferromagnetically coupled within the CuII6 precursor (2, ON state) become magnetically uncoupled in the corresponding [4 + 4] photocycloaddition product (c-2, OFF state) [jeff = –2.13 (2) and 0 cm−1 (c-2); H = – jeffSA.SB with SA = SB = 1/2]. This new example of inverse coordination complex constitutes thus a potential candidate to molecular magnetic photoswitch in the “bottom-up” approach to nanometer-scale spintronic and quantum computing devices.

Molecular magnetism has travelled a long way from the pioneering studies on electron exchange and double exchange or spin crossover and valence tautomerism in small oligonuclear complexes, from mono- to di- and tetranuclear species, to the current investigations about magnetic anisotropy and spin dynamics or quantum coherence of simple mono- or large polynuclear complexes, behaving as switchable bistable molecular nanomagnets for potential applications in information data storage and processing. In this review, we focus on the origin and development of the research in the field of molecular magnetism from a coordination chemistry viewpoint, which dates back to the establishment of magnetochemistry as a novel discipline among the molecular sciences. This overview is conceived as an attempt to orientate coordination chemists regarding their role in the future direction that molecular magnetism will undergo in its further evolution toward molecular spintronics and quantum computation. A particular emphasis will be given to some selected recent advances in single-molecule spintronic circuitry and quantum computing devices based on the large class of multiresponsive and multifunctional magnetic metal complexes to stimulate the progress in the field of molecular magnetism.

The use of simple pyrazolate anions and related polychelating acyclic or macrocyclic pyrazolate derivatives as bridging ligands, and occasionally additional blocking ligands, has led to the stereospecific Cu II -mediated self-assembly of both homo- and heteroleptic di-μ-pyrazolatodicopper(II) complexes of the metallacyclophane type, so-called dicopper(II) pyrazolenophanes. Besides their unique molecular conformation features and binding abilities toward both neutral molecules and charged anionic species, which have illustrated the putative role of weak intramolecular π–π stacking, hydrogen bonding, and coordinative interactions in the self-assembling process, dicopper(II) pyrazolenophanes have been also studied by their magnetic properties. In the present review, a comprehensive investigation has been carried out to determine the influence of subtle structural factors ( e.g. , trigonal or tetrahedral distortions at the metal center and deviations from planarity of the metallacyclic core) on the strength of the magnetic coupling in these series of homo- and heteroleptic di-μ-pyrazolatodicopper(II) complexes. New magneto-structural correlations have emerged from this study which point out to a dual σ- and π-type orbital pathway for the propagation of the electron exchange interaction between the two Cu II ions across the two pyrazolate bridges in this unique family of dicopper(II) pyrazolenophanes.

A novel series of dinuclear copper(II) pyrazolenophanes of the formula [Cu2(μ-4-Mepz)2(μ-ClO4)(ClO4)(bpm)2] (1), [Cu2(μ-pz)2(μ-H2O)(ClO4)(4,7-Me2phen)2]ClO4·H2O·CH3CN (2), [Cu2(μ-pz)2(μ-H2O)(ClO4)3/2(H2O)1/2(phen)2]2[Cu2(μ-pz)2(μ-ClO4)(ClO4)2(phen)2]·8H2O (3), and [Cu2(μ-pz)2(CH3CN)2(3,4,7,8-Me4phen)2](ClO4)2 (4) (Hpz = pyrazole, H-4-Mepz = 4-methylpyrazole, bpm = 2,2'-bipyrimidine, phen = 1,10-phenanthroline, 4,7-Me2phen = 4,7-dimethyl-1,10-phenanthroline, and 3,4,7,8-Me4phen = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been synthesized and magneto-structurally investigated. The crystal structures of 1–4 contain bis(pyrazolate)(perchlorate)- (1 and 3), bis(pyrazolate)(aqua)- (2 and 3), or bis(pyrazolate)-bridged (4) dicopper(II) entities of the metallacyclophane-type with bpm (1), 4,7-Me2phen (2), phen (3), and 3,4,7,8-Me4phen (4) as blocking bidentate ligands. All of them exhibit a saddle conformation with an overall not planar but bent, six-membered Cu–(N–N′)2–Cu metallacyclic core with relatively short intermetallic distances across the bis(pyrazolate)(perchlorate) [r = 3.3076(5) (1) and 3.382(1) A (3)], bis(pyrazolate)(aqua) [r = 3.383(1) (2) and 3.357(1) A (3)], and bis(pyrazolate) bridges [r = 3.098(1) A (4)]. The analyses of the variable-temperature magnetic susceptibility of 1–4 reveal the occurrence of a moderately strong antiferromagnetic coupling across the bis(pyrazolate)(perchlorate) [−J = 228 (1) and 193 cm−1 (3)], bis(pyrazolate)(aqua) [−J = 189 (2) and 221 cm−1 (3)], and bis(pyrazolate) bridges [−J = 197 cm−1 (4)] (the spin Hamiltonian being defined as H = −JS1·S2 with S1 = S2 = SCu = ½).

International audience; The aim of this review is to pay tribute to the legacy of O. Kahn. Kahn's credo was to synthesize magnetic compounds with predictable structure and magnetic properties. This is illustrated herein with results obtained by Kahn's group during his Orsay period thirty years ago, but also on the basis of our recent results on the synthesis of coordination polymers with oxamate ligands. The first part of this review is devoted to a short description of the necessary knowledge in physics and theoretical chemistry that Kahn and his group have used to select oxamate ligands, the complex‐as‐ligand strategy and the synthesis of heterobimetallic systems. Then, we describe the strategies we have later used to obtain the desired target compounds. The use of complexes as building‐blocks, associated to a control of the metal ions chirality and stoichiometry, allowed us to obtain coordination polymers with predictable dimensionality. For the synthesis of single‐chain magnets (SCMs) we show that the ligand chemical flexibility makes the isolation of the chains in the solid and the occurence of slow magnetic relaxation possible. For 1D and 2D molecule‐based magnets (MBMs), the magnetic ordering strongly depends on the interchain or interplane interactions, which are difficult to control. Again the flexibility of the oxamate ligands allowed their strengthening in the solid sate, yielding MBMs with critical temperatures up to 30 K. We will also present our results on 3D coordination polymers, particularly on the porous magnets displaying large octagonal channels. This family of porous MBMs possess outstanding chemical properties, such as post‐synthetic transformation in the solid state. Finally, we will also show that oxamate ligands allows the design of multifunctional materials, as in the case of the first chiral SCM. Overall, the results presented in this review show the impressive potential the oxamate ligands have for the design of coordination polymers.

Dinuclear copper(II) complexes of the metallacyclophane-type, (nBu4N)4[Cu2(2,6-anba)2] (1) and (nBu4N)4[Cu2(1,5-naba)2]·4H2O (2) with photoactive 2,6-anthracene-(2,6-anba) and 1,5-naphthalenebis(oxamate) (1,5-naba) bridging ligands, are reported. They undergo a thermally reversible, solid-state photomagnetic (ON/OFF) switching between the moderately strong antiferromagnetically coupled dicopper(II) species and the corresponding magnetically uncoupled [4+4] photocycloaddition product. Density functional calculations give further insights on the intramolecular (“pseudo-bimolecular”) photocycloaddition reaction of the two facing 2,6-anthracene or 1,5-naphthalene spacers in this novel family of dicopper(II) oligoacenophanes. The unique ability of oligoacenes as photoswitchable antiferromagnetic wires between two CuII ions separated by relatively long intermetallic distances could be the basis for the development of new kinds of molecular spintronic devices, referred to as molecular magnetic switches., This work was supported by the Spanish MINECO (projects CTQ2016-75068P and CTQ2016-75671P), the Unidad de Excelencia María de Maeztu (Project MDM-2015-0538), the Generalitat Valenciana (GV2012/051 and PROMETEOII/2014/070), and the ACIISI-Gobierno Autónomo de Canarias (Spain) (Project PIL-2070901).

Metallosupramolecular complexes constitute an important advance in the emerging fields of molecular spintronics and quantum computation and a useful platform in the development of active components of spintronic circuits and quantum computers for applications in information processing and storage. The external control of chemical reactivity (electro- and photochemical) and physical properties (electronic and magnetic) in metallosupramolecular complexes is a current challenge in supramolecular coordination chemistry, which lies at the interface of several other supramolecular disciplines, including electro-, photo-, and magnetochemistry. The specific control of current flow or spin delocalization through a molecular assembly in response to one or many input signals leads to the concept of developing a molecule-based spintronics that can be viewed as a potential alternative to the classical molecule-based electronics. A great variety of factors can influence over these electronically or magnetically coupled, metallosupramolecular complexes in a reversible manner, electronic or photonic external stimuli being the most promising ones. The response ability of the metal centers and/or the organic bridging ligands to the application of an electric field or light irradiation, together with the geometrical features that allow the precise positioning in space of substituent groups, make these metal-organic systems particularly suitable to build highly integrated molecular spintronic circuits. In this Account, we describe the chemistry and physics of dinuclear copper(II) metallacyclophanes with oxamato-containing dinucleating ligands featuring redox- and photoactive aromatic spacers. Our recent works on dicopper(II) metallacyclophanes and earlier ones on related organic cyclophanes are now compared in a critical manner. Special focus is placed on the ligand design as well as in the combination of experimental and computational methods to demonstrate the multifunctionality nature of these metallosupramolecular complexes. This new class of oxamato-based dicopper(II) metallacyclophanes affords an excellent synthetic and theoretical set of models for both chemical and physical fundamental studies on redox- and photo-triggered, long-distance electron exchange phenomena, which are two major topics in molecular magnetism and molecular electronics. Apart from their use as ground tests for the fundamental research on the relative importance of the spin delocalization and spin polarization mechanisms of the electron exchange interaction through extended π-conjugated aromatic ligands in polymetallic complexes, oxamato-based dicopper(II) metallacyclophanes possessing spin-containing electro- and chromophores at the metal and/or the ligand counterparts emerge as potentially active (magnetic and electronic) molecular components to build a metal-based spintronic circuit. They are thus unique examples of multifunctional magnetic complexes to get single-molecule spintronic devices by controlling and allowing the spin communication, when serving as molecular magnetic couplers and wires, or by exhibiting bistable spin behavior, when acting as molecular magnetic rectifiers and switches. Oxamato-based dicopper(II) metallacyclophanes also emerge as potential candidates for the study of coherent electron transport through single molecules, both experimentally and theoretically. The results presented herein, which are a first step in the metallosupramolecular approach to molecular spintronics, intend to attract the attention of physicists and materials scientists with a large expertice in the manipulation and measurement of single-molecule electron transport properties, as well as in the processing and addressing of molecules on different supports.

Two oxalato-bridged dinuclear copper(II) complexes, [{Cu(Hdmpz)3}2(μ-ox)](ClO4)2·2H2O (1) and [{Cu(Htmpz)3}2(μ-ox)](ClO4)2·2H2O (2) (Hdmpz = 3,5-dimethyl-1H-pyrazole and Htmpz = 3,4,5-trimethyl-1H-pyrazole), have been synthesized and structurally and magnetically characterized. The crystal structures of 1 and 2 consist of asymmetric bis-bidentate μ-oxalatodicopper(II) complex cations with two short [Cu–O = 1.976(2) (1) and 1.973(2) Å (2)] and two long copper–oxygen bonds [Cu–O = 2.122(2) (1) and 2.110(2) Å (2)]. The environment at each CuII ion in 1 and 2 is closer to the trigonal bipyramidal geometry than to the square pyramidal [τ = 0.633 (1) and 0.711 (2)]. The magnetic properties of 1 and 2 show moderate antiferromagnetic coupling between the CuII ions through the oxalato bridge [J = −129 (1) and 161 cm−1 (2); H = −JS1 · S2 with S1 = S2 = SCu = ½]. A thorough magneto-structural analysis has been carried out for the family of asymmetric μ-oxalatodicopper(II) complexes with different terminal ligands to determine the influence on the sign and strength of the magnetic coupling of subtle structural factors, such as the trigonal distortion of the metal geometry and the lengthening or the asymmetry of the metal-oxalato bond distances.

Double-stranded anionic dinuclear copper(II) metallacyclic complexes of the paracyclophane type [Cu2L2]4- have been prepared by the CuII-mediated self-assembly of different para-phenylenebis(oxamato) bridging ligands with either zero-, one-, or four-electron-donating methyl substituents (L=N,N′-para- phenylenebis(oxamate) (ppba; 1), 2-methyl- N,N′-para-phenylenebis(oxamate) (Meppba; 2), and 2,3,5,6-tetramethyl- N,N′-para-phenylenebis(oxamate) (Me4ppba; 3)). These complexes have been isolated as their tetra-n-butylammonium (1 a-3 a), lithium(I) (1 b-3 b), and tetraphenylphosphonium salts (1 c-3 c). The X-ray crystal structures of 1 a and 3 c show a parallel-displaced π-stacked conformation with a smaller deviation from perpendicularity between the two benzene rings and the basal planes of the square planar CuII ions when increasing the number of methyl substituents (average dihedral angles (φ) of 58.72(7) and 73.67(5)° for 1 a and 3 c, respectively). Variable-temperature (2.0-300 K) magnetic-susceptibility measurements show an overall increase of the intramolecular antiferromagnetic coupling with the number of methyl substituents onto the para-phenylene spacers (-J=75-95, 100-124, and 128-144 cm-1 for 1 a-c, 2 a-c, and 3 a-c, respectively; H=-JS1×S 2). Cyclic voltammetry (CV) measurements show a reversible one-electron oxidation of the double polymethyl-substituted para- phenylenediamidate bridging skeleton at a relatively low formal potential that decreases with the number of methyl substituents (E1=+0.33, +0.24, and +0.15 V vs. SCE for 1-3, respectively). The monooxidized dicopper(II) π-radical cation species 3′ prepared by the chemical oxidation of 3 with bromine exhibits intense metal-to-ligand charge-transfer (MLCT) transitions in the visible and near-IR (λmax=595 and 875 nm, respectively) regions together with a rhombic EPR signal with a seven-line splitting pattern due to hyperfine coupling with the nuclear spin of the two CuII ions. Density functional (DF) calculations for 3′ evidence a characteristic iminoquinonoid-type short-long-short alternating sequence of C-N and C-C bonds for both tetramethyl-para-phenylenediamidate bridges and a large amount of spin density of negative sign mainly delocalized along each of the four benzene C atoms directly attached to the amidate N atoms, which is in agreement with a fully delocalized π-stacked monoradical ligand description. Hence, the spins of the two CuII ions (SCu=1/2) that are antiparallel aligned in 3 (OFF state) become parallel in 3′ (ON state). Further developments may be then envisaged for this new permethylated dicopper(II) paracyclophane with a redox noninnocent ligand as a prototype for molecular magnetic electroswitch. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim., This work was supported by the MICINN (Spain) (Projects CTQ2010–15364, MAT2010–16981, CSD2007–00010, CSD2006–00015, and DPI2010–21103-C04–03), the University of Valencia (Project UV-INVAE11–38904), the Generalitat Valenciana (Spain) (Project PROMETEO/2009/108, GV/2012/051, and ISIC/2012/002), the ACIISI-Gobierno Autónomo de Canarias (Spain) (Project PIL-2070901), the ESRF (France) (Project HS3902), and the Ministero dell'Istruzione, dell'Università e della Ricerca Scientifica (Italy) through the Centro di Eccellenza CEMIF.CAL (Grant CLAB01TYEF). M.C. and J.F.-S. thank the MICINN and the Generalitat Valenciana, respectively, for doctoral grants. E.P. thanks the MICINN (Project “Juan de la Cierva”) for a postdoctoral contract.

Two novel double-stranded dicopper(II) metallacyclophanes of formula (nBu4N)4[Cu2(dpeba)2]·4MeOH·2Et2O (1) and (nBu4N)4[Cu2(tpeba)2]·12H2O (2) have been prepared by the Cu(II)-mediated self-assembly of the rigid ('rod-like') bridging ligands N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and N,N'-1,4-di(4-phenylethynyl)phenylenebis(oxamate) (tpeba), respectively. Single crystal X-ray diffraction analysis of 1 confirms the presence of a dicopper(II)tetraaza[3.3]4,4'-diphenylethynophane metallacyclic structure featuring a very long intermetallic distance between the two square planar Cu(II) ions [r = 14.95(1) Å]. The overall parallel-displaced π-stacked conformation of the two nearly planar para substituted diphenylethyne spacers [dihedral angle (ψ) of 7.8(1)°] leads to important deviations from the perpendicular orientation of the copper mean basal planes with respect to the facing benzene planes [dihedral angles (φ) of 56.4(1) and 58.4(1)°]. X-band EPR spectra together with variable-temperature magnetic susceptibility and variable-field magnetization measurements of 1 and 2, both in solution and in the solid state, show the occurrence of a non-negligible, moderate to weak intramolecular antiferromagnetic coupling [-J = 3.9-4.1 (1) and 0.5-0.9 cm(-1) (2); H = -JS1·S2 with S1 = S2 = SCu = 1/2]. Density functional calculations on the BS singlet (S = 0) and triplet (S = 1) spin states of the model complexes 1 and 2 with an ideal orthogonal molecular geometry (ψ = 0° and φ = 90°) support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the dxy orbital of each square planar Cu(II) ion through the predominantly π-type orbital pathway of the double p-diphenylethyne (1) and di(phenylethynyl)phenylene spacers (2). Time-dependent density functional calculations reproduce the observed bathochromic shift of the main intraligand (IL) π-π* transition in the electronic absorption spectra of 1 and 2 [λ1 = 308 (1) and 316 nm (2)]. In the series of orthogonal model complexes 1-5 with linear oligo(p-phenylene-ethynylene) (OPE) spacers, -C6H4(C≡CC6H4)n- (n = 1-5), a linear increase of the IL π-π* transition energy with the reciprocal of the intermetallic distance is theoretically predicted [νmax = 1.99 × 10(4) + 2.15 × 10(5) (1/r) (S = 0) or ν = 2.01 × 10(4) + 2.18 × 10(5) (1/r) (S = 1)], which clearly indicates that the effective π-conjugation length increases with the number of phenylethyne repeating units. This is accompanied by an exponential decay of the antiferromagnetic coupling with the intermetallic distance [-J = 1.08 × 10(3) exp(-0.31r)], which supports the ability of the extended π-conjugated OPEs to mediate the exchange interaction between the unpaired electrons of the two Cu(II) centers with intermetallic distances in the range of 1.5-4.3 nm. Further developments may be then envisaged for this new family of oxamato-based dicopper(II) oligo-p-phenylethynophanes on the basis of the unique ligand capacity to act as a molecular antiferromagnetic wire.

A novel heterotetranuclear chromium(III)–copper(II) complex of formula {[CrIII(bpy)(ox)2]2CuII2(bpy)2(ox)}·6H2O (1) has been synthesized by the ligand exchange reaction between Ph4P[CrIII(bpy)(ox)2]·H2O and [CuII(bpy)2(NO3)]NO3·MeOH in methanol (bpy = 2,2′-bipyridine; ox2− = oxalate dianion). The X-ray crystal structure of 1 consists of neutral oxalato-bridged CrIII2Cu2II zigzag entities which are formed by the monodentate coordination of two [CrIII(bpy)(ox)2]− mononuclear anionic units through one of its two oxalato groups toward a [CuII2(bpy)2(ox)]2+ dinuclear cationic moiety featuring relatively long axial bonds at the square pyramidal CuII ions. Variable temperature (2.0–300 K) magnetic susceptibility and variable-field (0–5.0 T) magnetization measurements for 1 have been interpreted on the basis of the linear tetranuclear topology of the CrIII2CuII2 entities [H = –J(S1 · S2 + S3 · S4) – J′ S2 · S3 with S1 = S4 = SCr = 3/2 and S2 = S3 = SCu = 1/2]. A weak antiferromagnetic coupling occurs between the outer CrIII and inner CuII ions through the peripheral bidentate/monodentate(outer) oxalates (J = –8.7 cm−1), while a strong antiferromagnetic coupling is operative between the inner CuII ions across the central bis-bidentate oxalate (J′ = –472.2 cm−1), leading thus to a S = (SCr – SCu) – (SCr – SCu) = 0 ground spin state for the CrIII2CuII2 entity of 1. A simple orbital analysis of the electron exchange interaction in the oxalato-bridged CuII2 and CrIIICuII fragments identify the σ-type pathways involving the d x 2 - y 2 (Cu)/ d x 2 - y 2 (Cu) and dxy(Cr)/ d x 2 - y 2 (Cu) pairs of magnetic orbitals as the two main contributions responsible for the different strength of the intramolecular magnetic coupling parameters for 1. A magneto-structural correlation between the nature and magnitude of the magnetic coupling and the bending angle at the axial carbonyl-oxygen to copper bond has been established for 1 and related oxalato-bridged chromium(III)–copper(II) dinuclear complexes.

Two novel heterobimetallic complexes of formula [Cr(bpy)(ox)(2)Co(Me(2)phen)(H(2)O)(2)][Cr(bpy)(ox)(2)]·4H(2)O (1) and [Cr(phen)(ox)(2)Mn(phen)(H(2)O)(2)][Cr(phen)(ox)(2)]·H(2)O (2) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and Me(2)phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the "complex-as-ligand/complex-as-metal" strategy by using Ph(4)P[CrL(ox)(2)]·H(2)O (L = bpy and phen) and [ML'(H(2)O)(4)](NO(3))(2) (M = Co and Mn; L' = phen and Me(2)phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis(oxalato)chromate(III) mononuclear anions, [Cr(III)L(ox)(2)](-), and oxalato-bridged chromium(III)-cobalt(II) and chromium(III)-manganese(II) dinuclear cations, [Cr(III)L(ox)(μ-ox)M(II)L'(H(2)O)(2)](+)[M = Co, L = bpy, and L' = Me(2)phen (1); M = Mn and L = L' = phen (2)]. These oxalato-bridged Cr(III)M(II) dinuclear cationic entities of 1 and 2 result from the coordination of a [Cr(III)L(ox)(2)](-) unit through one of its two oxalato groups toward a [M(II)L'(H(2)O)(2)](2+) moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct Cr(III) ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin M(II) ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the Cr(III) (S(Cr) = 3/2) ion and the high-spin Co(II) (S(Co) = 3/2) or Mn(II) (S(Mn) = 5/2) ions across the oxalato bridge within the Cr(III)M(II) dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm(-1) (2); H = -JS(Cr)·S(M)]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 Cr(III)Co(II) and S = 4 Cr(III)Mn(II) ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d(yz)(Cr)/d(xy)(M), d(xz)(Cr)/d(xy)(M), d(x(2)-y(2))(Cr)/d(xy)(M), d(yz)(Cr)/d(xz)(M), and d(xz)(Cr)/d(yz)(M) pairs of orthogonal magnetic orbitals and the d(x(2)-y(2))(Cr)/d(x(2)-y(2))(M), d(xz)(Cr)/d(xz)(M), and d(yz)(Cr)/d(yz)(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2.

The concept of "molecular magnetic sponges" was introduced for the first time in 1999 by the creative imagination of the late Olivier Kahn. It refers to the exotic spongelike behavior of certain molecule-based materials that undergo a dramatic change of their magnetic properties upon reversible dehydration/rehydration processes. Here we report a unique example of a manganese(II)-copper(II) mixed-metal-organic framework of formula [Na(H(2)O)(4)](4)[Mn(4){Cu(2)(mpba)(2)(H(2)O)(4)}(3)]·56.5H(2)O (1) (mpba=N,N'-1,3-phenylenebis(oxamate)). Compound 1 possesses a 3D Mn(II)(4)Cu(II)(6) pillared layer structure with mixed square and octagonal pores of approximate dimensions 1.2×1.2 nm and 2.1×3.0 nm, respectively, hosting a large amount of crystallization H(2)O molecules and hydrated Na(I) countercations as guests. It reversibly switches from a crystalline hydrated phase with long-range ferromagnetic ordering at a rather high critical temperature (T(c)) of 22.5 K to an amorphous dehydrated phase with T(c) as low as 2.3 K, which is accompanied by a breathing-type dynamic effect involving a large crystal volume (ca. 45%) and color changes after water desorption/adsorption. The combination of both the open-framework structure and the spongelike optical, mechanical, and magnetic switching behavior in this new class of oxamato-based porous magnets offers fascinating possibilities in designing multifunctional materials for host-guest molecular sensing.

A novel series of copper(II) complexes of formula [Cu(tren)(mpda)](ClO4)2 · 1/2H2O (1), [Cu2(tren)2(mpda)](ClO4)4 · 2H2O (2), and [Cu2(tren)2(ppda)](ClO4)4 · 2H2O (3) containing the tetradentate tris(2-aminoethyl)amine (tren) terminal ligand and the potentially bridging 1,n-phenylenediamine [n = 3 (mpda) and 4 (ppda)] ligand have been prepared and spectroscopically characterized. X-ray diffraction on single crystals of 1 and 3 show the presence of mono- (1) and dinuclear (3) copper(II) units where the mpda (1) and ppda (3) ligands adopt terminal monodentate (1) and bridging bis(monodentate) (3) coordination modes toward [Cu(tren)]2+ cations with an overall non-planar, orthogonal disposition of the phenylene group and the N–Cu–N threefold axis of the trigonal bipyramid of each copper(II) ion [values of the Cu–N–C–C torsion angle ( ϕ ) in the range of 50.8(3)–79.2(2) (1) and 80.9(2)–86.5(2)° (3)]. Variable-temperature magnetic susceptibility measurements on the dinuclear complexes 2 and 3 show the occurrence of moderate ferromagnetic (J = +8.3 cm−1, 2) and strong antiferromagnetic (J = −51.4 cm−1, 3) couplings between the two copper(II) ions across the meta- and para-phenylenediamine bridges, leading to S = 1 (2) and S = 0 (3) ground spin states [H = −JS1 · S2 with S1 = S2 = SCu = 1/2]. Density functional theory (DFT) calculations on the triplet (2) and broken-symmetry (BS) singlet (3) ground spin states, support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction through the predominantly π-type orbital pathway of the 1,n-phenylenediamine bridge. Finally, a new magneto-structural correlation between the magnitude of the magnetic coupling (J) and the Cu–N–C–C torsion angle ( ϕ ) has been found which reveals the role of σ- versus π-type orbital pathways in the modulation of the magnetic coupling for m- and p-phenylenediamine-bridged dicopper(II) complexes.

Two novel dinuclear copper(II) complexes of formulae [Cu2(tren)2(bpda)](ClO4)4 (2) and [Cu2(tren)2(tpda)](ClO4)4 (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two [Cu(tren)]2+ units with an overall non-planar, orthogonal anti configuration of the N–Cu–N threefold axis of the trigonal bipyramidal CuII ions and the biphenylene group. The electronic absorption spectra of 2 and 3 in acetonitrile reveal the presence of four moderately weak d–d transitions characteristic of a slightly distorted trigonal bipyramid stereochemistry of the CuII ions. TDDFT calculations on 2 identify these transitions as those taking place between the four lower-lying, doubly occupied a2 (dyz)2, b2 (dxz)2, b1 (dxy)2, and a1 ( d x 2 - y 2 )2 orbitals and the upper, singly occupied a1 ( d z 2 )1 orbital of each trigonal bipyramidal CuII ion. Variable-temperature magnetic susceptibility measurements of 2 and 3 show the occurrence of moderate (J = −8.5 cm−1) to weak intramolecular antiferromagnetic couplings (J = −2.0 cm–1) [H = −JS1·S2 with S1 = S2 = SCu = ½] inspite of the relatively large copper–copper separation across the para-substituted biphenylene- (r = 12.3 A) and terphenylenediamine (r = 16.4 A) bridges, respectively. DFT calculations on 2 and 3 support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the d z 2 orbital of each trigonal bipyramidal CuII ion through the predominantly π-type orbital pathway of the oligo-p-phenylenediamine bridges, as reported earlier for the parent compound [Cu2(tren)2(ppda)](ClO4)4·2H2O (1) with the 1,4-phenylenediamine (ppda) bridging ligand. Finally, a rather slow exponential decay of the antiferromagnetic coupling (–J) with the number of phenylene repeat units, –(C6H4)n– (n = 1–3), has been found both experimentally and theoretically along this series of oligo-p-phenylenediamine-bridged dicopper(II) complexes. These results further support the ability of linear π-conjugated oligo-p-phenylene spacers to transmit the exchange interaction between the unpaired electrons of the two CuII centers with intermetallic distances in the range of 7.5–16.4 A.

Two novel heterotrinuclear chromium(III)-cobalt(II) complexes of formula {[Cr(III)(bpy)(ox)(2)](2)Co(II)(Me(2)bpy)}.2H(2)O (1) and {[Cr(III)(phen)(ox)(2)](2)Co(II)(Me(2)bpy)}.1.5H(2)O (2) [ox = oxalato, bpy = 2,2'-bipyridine, Me(2)bpy = 6,6'-dimethyl-2,2'-bipyridine, and phen = 1,10-phenanthroline] have been synthesized using the "complex-as-ligand/complex-as-metal" strategy. The X-ray crystal structure of 2 consists of neutral oxalato-bridged Cr(III)(2)Co(II) bent entities formed by the coordination of two anionic [Cr(III)(phen)(ox)(2)](-) complexes through one of their oxalato groups toward a cationic cis-[Co(II)(Me(2)bpy)](2+) complex. The three tris(chelated), six-coordinated metal atoms possess alternating propeller chiralities leading thus to a racemic mixture of heterochiral (Lambda,Delta,Lambda)- and (Delta,Lambda,Delta)-Cr(III)Co(II)Cr(III) triads, whereby the two peripheral chromium(III) ions adopt a trigonal distorted trapezoidal bipyramidal geometry and the central high-spin cobalt(II) ion exhibits a compressed rectangular bipyramidal one. The intermolecular pi-pi stacking interactions between the enantiomeric pairs of heterochiral Cr(III)(2)Co(II) entities through the aromatic diimine terminal ligands lead to a unique two-dimensional supramolecular network. Variable temperature (2.0-300 K) magnetic susceptibility and variable-field (0-5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak but non-negligible intermolecular antiferromagnetic interactions [zj = -0.012 (2a) and -0.08 cm(-1) (2b)] between the Cr(III)(2)Co(II) molecules possessing a moderately anisotropic S = 9/2 ground state. This results from the moderately weak intramolecular ferromagnetic coupling [J = +2.43 (1) and +2.34 cm(-1) (2)] between the two peripheral Cr(III) (S(Cr) = 3/2) and the central high-spin Co(II) (S(Co) = 3/2) ions across the oxalato bridge as well as the appreciable single-ion axial magnetic anisotropy of the central high-spin Co(II) (S(Co) = 3/2) ion [D(Co) = -2.29 (1) and -2.15 cm(-1) (2)]. A simple molecular orbital analysis of the exchange interaction in 1 and 2 identifies the sigma- and pi-type pathways involving the d(x(2)-y(2))(Cr)/d(xy)(Co) and d(xz)(Cr)/d(yz)(Co) pairs of orthogonal magnetic orbitals, respectively, as the two main individual contributions responsible for the overall ferromagnetic coupling observed.

New homo- and heterobimetallic tetranuclear complexes of formula [Cu4(mpba)(Me4en)4(H2O)4](ClO4)4·3H2O (1), [Cu4(mpba)(Me4en)4(H2O)4](PF6)4·2H2O (2), [Cu4(ppba)(Me4en)4(H2O)4](ClO4)4·2H2O (3), [Cu4(mpba)(dipn)4](ClO4)4·3H2O (4), [Cu4(ppba)(dipn)4](ClO4)4·2H2O (5), and [Cu2Ni2(ppba)(dipn)4(H2O)2](PF6)4 (6) [mpba = N,N′-1,3-phenylenebis(oxamate), ppba = N,N′-1,4-phenylenebis(oxamate), Me4en = N,N,N′,N′-tetramethylethylenediamine, and dipn = dipropylenetriamine] have been synthesized and structurally and magnetically characterized. Complexes 1−6 have been prepared following a molecular-programmed self-assembly method, where a heteropolytopic tetranucleating phenylenedioxamato bridging ligand (L = mpba or ppba) is bound to four metal ions of identical or different natures (M = CuII and/or NiII) with partially blocked coordination sites by bi- or tridentate polyamine terminal ligands (L′ = Me4en or dipn). The structures of 1−6 consist of cationic tetranuclear CuII2MII2 entities with an overall 4R rack-type arc...

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.

New homo- and heterometallic, hexa- and pentanuclear complexes of formula {[Cu2(mpba)2(H2O)F][Cu(Me5dien)]4}(PF6)3·5H2O (1), {[Cu2(Me3mpba)2(H2O)2][Cu(Me5dien)]4}(ClO4)4·12H2O (2), {[Cu2(ppba)2][Cu(Me5dien)]4}(ClO4)4 (3), and [Ni(cyclam)]{[Cu2(mpba)2][Ni(cyclam)]3}(ClO4)4·6H2O (4) [mpba = 1,3-phenylenebis(oxamate), Me3mpba = 2,4,6-trimethyl-1,3-phenylenebis(oxamate), ppba = 1,4-phenylenebis(oxamate), Me5dien = N,N,N‘N‘ ‘,N‘ ‘-pentamethyldiethylenetriamine, and cyclam = 1,4,8,11-tetraazacyclotetradecane] have been synthesized through the use of the “complex-as-ligand/complex-as-metal” strategy. The structures of 1−3 consist of cationic CuII6 entities with an overall [2 × 2] ladder-type architecture which is made up of two oxamato-bridged CuII3 linear units connected through two m- or p-phenylenediamidate bridges between the two central copper atoms to give a binuclear metallacyclic core of the cyclophane-type. Complex 4 consists of cationic CuII2NiII3 entities with an incomplete [2 × 2] ladder-type archite...

Two new series of neutral ox-amato-bridged heterobimetallic chains of general formula [MCu(L x ) 2 ]- m DMSO (m=0-4) (L 1 =N-2-methyl-phenyloxamate, M=Mn (1a) and Co (1 b); L2 = N-2,6-dimethylphenyloxamate, M=Mn (2a) and Co (2b); L 3 = N-2,4,6-trimethylphenyloxamate, M= Mn (3a) and Co (3b)) have been prepared by reaction between the corresponding anionic oxamatocopper(II) complexes [Cu(L x ) 2 ] 2- with Mn 2+ or Co 2+ cations in DMSO. The crystal structures of [CoCu(L 2 ) 2 (H 2 O) 2 ] (2b') and [CoCu(L 3 ) 2 (H 2 O) 2 ]·4H 2 O (3b') have been solved by single-crystal X-ray diffraction methods. Compounds 2b' and 3b' adopt zigzag and linear chain structures, respectively. The intrachain Cu···Co distance through the oxamate bridge is 5.296(1) A in 2b' and 5.301(2) A in 3b', while the shortest interchain Co···Co distance is 5.995(5) A in 2b' and 8.702(3) A in 3b', that is, the chains are well isolated in the crystal lattice due to the presence of the bulky methyl-substituted phenyl groups. Although both Mn II Cu II and Co II Cu II chains exhibit ferrimagnetic behaviour with moderately strong intrachain antiferromagnetic coupling (-J Mn,Cu =24.7-27.9 cm -1 and -J Co,Cu = 35.0-45.8cm -1 ; H= E -J M,Cu S M,i S Cu,i ), only the Co II Cu II chains show slow magnetic relaxation at low temperatures (T B

[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.

Silica-based mesoporous materials have been employed as the support host for a suitably designed small octanuclear nickel(II) guest complex with a moderately anisotropic S = 4 ground spin state (D = −0.23 cm−1), which behaves as a single-molecule magnet at low temperature (TB = 3.0 K). Both unimodal MCM-41 and bimodal UVM-7 porous silica provide appropriate template conditions for the incorporation and aggregation of the Ni8 complex precursor into larger complex aggregates, showing slow relaxation of the magnetization at higher blocking temperatures than the crystalline material. By playing with the initial complex vs. silica concentration, two series of samples with varying complex loading amounts have been obtained. The degree of aggregation varies, largely depending on the silica used, being higher for the bimodal UVM-7 silica series. The mesophasic and porous nature of the Ni8 adsorbed silica samples has been verified from XRD and TEM images. N2 adsorption–desorption isotherms show that incorporation initiates inside the small intra-particle mesopores while subsequent aggregation occurs at the external particle surface (close to the mesopore entrances). Both DC and AC magnetic susceptibility measurements have demonstrated the occurrence of such a unique silica-mediated surface aggregation process of cationic Ni8 molecules into oligomeric [Ni8]x aggregates of large spin values (S = 4x) and high blocking temperatures (TB = 4.5–10.5 K). The existence of a wide distribution of aggregates with different conformation and association degree (size distribution) and the presence of weak interactions between the aggregates leads to an exotic spin glass magnetic behavior for this family of host–guest hybrid nanocomposite materials.

[EN] A new dinuclear iron(III) complex with the tetradentate ligand N,N'-o-phenylenebis(oxamate) (opba) has been synthesised, and structurally, magnetically and electrochemically characterised. It possesses an unprecedented triply bridged Fe-2(mu-O)(mu-RCO2...H2O...O2CR)(2) core, whereby two N-amides from the opba ligand complete the square-pyramidal coordination sphere of the O-carboxylate rich iron site (Fe-N = 2.053 Angstrom and Fe-O = 2.015 Angstrom), The antiferromagnetic exchange interaction between the two high-spin Fe-III ions through the oxo bridge (J = -190 cm(-1); H = -JS(1)(.)S(2)) is weaker than that found in related mu-oxo singly bridged diiron(III) complexes. The lessened antiferromagnetic coupling correlates to the remarkably long Fe-O distance (R = 1.808 Angstrom), which is associated to the relatively bent Fe-O-Fe angle (alpha = 131.8degrees) in the Fe2O unit. It experiences an irreversible one-electron oxidation process in acetonitrile at 25degreesC (E = 0.63 V versus SCE) to give the putative mixed-valent diiron(III, IV) species which is unstable under the experimental conditions. The reactivity of this unique oxo-bridged diiron(III) oxamate complex toward hydrogen peroxide activation and hydrocarbon oxidation in the presence of dioxygen has been examined. It catalyses the oxidation of alkanes like cyclohexane and adamantane to the corresponding alcohols and ketones by H2O2 and O-2 in acetonitrile at room temperature with limited catalytic activities (total yields of ca. 5% after 24 h) and modest selectivities (A/K = 0.9, KIE = 2.4, tert/sec = 3.0). Overall, these results are more in line with a mechanism involving alkyl radicals as transient intermediates, although they do not exclude the possibility that a metal-based active oxidant is also involved in this C-H bond oxidation chemistry., This work was supported by the Ministerio de Ciencia y Tecnologı́a (MCYT) (Spain) through the Plan Nacional de Investigación Cientı́fica, Desarrollo e Innovación Tecnológica (I + D + I) (BQU2001 2928) and the Ramón y Cajal programme. Further support from the Oficina de Ciencia i Tecnologı́a de la Generalitat Valenciana (Spain) through the Plan Valenciano de Investigación Cientı́fica, Desarrollo Tecnológico e Innovación (PVIDI) (CTIDIA2002 131) is also acknowledged. E.P. thanks the Ministerio de Educación, Cultura y Deporte (Spain) for a FPU grant. We are specially thankful to Dr. E. Anxolabèhere-Mallart for the assistance with the electrochemical measurements and Dr. J. Cano for very stimulating talks and unselfish help during the realisation of this work.

Self-assembly of the rigid rodlike ligand N,N'-4,4'-diphenylethynebis(oxamate) (dpeba) and Cu(2+) ions affords a novel dinuclear copper(II) metallacyclophane (nBu(4)N)(4)[Cu(2)(dpeba)(2)]·4MeOH·2Et(2)O (1) featuring a very long intermetallic distance (r = 15.0 Å). Magnetic susceptibility measurements for 1 reveal a moderately weak but nonnegligible intramolecular antiferromagnetic coupling between the two metal centers across the double para-substituted diphenylethynediamidate bridge (J = -3.9 cm(-1); H = -JS(1)S(2), where S(1) = S(2) = S(Cu) = (1)/(2)). Density functional electronic structure calculations on 1 support the occurrence of a spin polarization mechanism.

Two new dinuclear copper(II) metallacyclophanes with 1,4-disubstituted 9,10-anthraquinonebis(oxamate) bridging ligands are reported that can reversibly take and release electrons at the redox-active ligand and metal sites, respectively, to give the corresponding mono- and bis(semiquinonate and/or catecholate) Cu(II)2 species and mixed-valent Cu(II)/Cu(III) and high-valent Cu(III)2 ones. Density functional calculations allow us to give further insights on the dual ligand- and metal-based character of the redox processes in this novel family of antiferromagnetically coupled di- copper(II) anthraquinophanes. This unique ability for charge storage could be the basis for the development of new kinds of molecular spintronic devices, referred to as molecular magnetic capacitors (MMCs).

International audience

The new dinuclear copper(II) metallacyclophane with the non-innocent N,N'-1,4-bis(oxamate)-9,10-anthraquinone bridging ligand possesses a dual multielectron redox behavior featuring stepwise one-electron oxidation of the antiferromagnetically coupled Cu(II) ions and two-electron reduction of the anthraquinone spacers in a π-stacked anti conformation.

Two new hexanuclear oxamatocopper(II) complexes 3 and 4 have been synthesized from the binuclear copper(II) complexes of the meta- and para-phenylenebis(oxamate) ligands, respectively. Complexes 3 and 4 possess an overall ladderlike structure made up of two oxamate-bridged linear trinuclear units ("rails") connected through two phenylenediamidate bridges ("rungs") between the central copper atoms to give metallacyclic cores of the meta- and para-cyclophane type, respectively. They show different ground spin states, S = 1 (3) or S = 0 (4), depending on the substitution pattern in the aromatic spacers. The triplet state molecule 3 containing two spin doublet Cu(II)3 units connected by two m-phenylenediamidate bridges represents a successful extension of the concept of "ferromagnetic coupling units" to metal complexes, which is a well-known approach toward high spin organic radicals.

International audience; The novel mononuclear Co(II) complex cis-[Co-II(dmphen)(2)(NCS)(2)]center dot 0.25EtOH (1) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co-II ion (D = +98 cm(-1) and E = +8.4 cm(-1)). Slow magnetic relaxation effects were observed for 1 in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co(II) complex with a transverse anisotropy energy barrier.

Two metallacyclic complexes of general formula Na-8[(M2L3)-L-II]center dot xH(2)O [M = Ni (4) and Co (5) with x = 15 (4) and 17 (5)] have been self-assembled in aqueous solution from N,N'-1,3-phenylenebis(oxamic acid) (H4L) and M2+ ions in a ligand/metal molar ratio of 3 : 2 in the presence of NaOH acting as base. X-Ray structural analyses of 4 and 5 show triple-stranded, dinuclear anions of the meso-helicate-type (so-called mesocates) with C-3h molecular symmetry. The two octahedral metal-tris(oxamate) moieties of opposite chiralities (Delta, Lambda form) are connected by three m-phenylene spacers at intermetallic distances of 6.822(2) (4) and 6.868(2) angstrom (5) to give a metallacryptand core. In the crystal lattice, the binding of these heterochiral dinickel(II) and dicobalt(II) triple mesocates to sodium(I) ions leads to oxamato-bridged heterobimetallic three-dimensional open-frameworks with a hexagonal diamond architecture having small pores of 17.566(4) (4) and 17.640(2) angstrom (5) in diameter where the crystallization water molecules and the sodium(I) countercations are hosted. Variable temperature (2.0-300 K) magnetic susceptibility measurements reveal relatively anisotropic S = 2 Ni-2(II) (4) and S = 3 Co-2(II) (5) ground states resulting from the moderate to weak intramolecular ferromagnetic coupling between the two high-spin Ni-II (S-Ni = 1) or Co-II (S-Co = 3/2) ions across the m-phenylenediamidate bridges [J = +3.6 (4) and +1.1 cm(-1) (5); H = -JS(1)center dot S-2]. A simple molecular orbital analysis of the electron exchange interaction identifies the p-type pathways of the meta-substituted phenylene spacers involving the d(z2) and d(x2-y2) pairs of magnetic orbitals of the two trigonally distorted octahedral high-spin M-II ions (M = Ni and Co) as responsible for the overall ferromagnetic coupling observed in 4 and 5 in agreement with a spin polarization mechanism. The decrease of the overall ferromagnetic coupling from 4 to 5 is in turn explained by the additional antiferromagnetic exchange contribution involving the d(xy) pair of magnetic orbitals of the two trigonally distorted octahedral high-spin Co-II ions across the sigma-type pathway of the meta-substituted phenylene spacers., This work was supported by the MICINN (Spain) (Projects CTQ2010-15364, MAT2010-16981, CSD2007-00010, and CSD2006-00015), the University of Valencia (Project UV-INVAE11-38904), the Generalitat Valenciana (Spain) (Projects PROMETEO/2009/108, GVACOMP2011-108, GV/2012/051 and ISIC/2012/002), the ACIISI-Gobierno Autónomo de Canarias (Spain) (Project PIL-2070901), the MFR and the CNRS (France). E. P. acknowledges the MICINN for a postdoctoral (‘‘Juan de la Cierva’’) contract. M.-C. Dul and M. C. thank the MFR and the MICINN respectively, for doctoral grants.

Homo- and heterometallic octanuclear complexes of formula Na₂{[Cu₂(mpba)₃][Cu(Me₅dien)]₆}-(ClO₄)₆·12H₂O (1), Na₂{[Cu₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (2), Na₂{[Ni₂(mpba)₃]-[Cu(Me₅dien)]₆}(ClO₄)₆·12H₂O (3), Na₂{[Ni₂(Mempba)₃][Cu(Me₅dien)]₆}(ClO₄)₆·9H₂O (4), {[Ni₂(mpba)₃][Ni(dipn)(H₂O)]₆}(ClO₄)₄·12.5H₂O (5), and {[Ni₂(Mempba)₃][Ni(dipn)-(H₂O)]₆}(ClO₄)₄·12H₂O (6) [mpba = 1,3-phenylenebis(oxamate), Mempba = 4-methyl-1,3-phenylenebis(oxamate), Me₅dien = N,N,N',N'',N''-pentamethyldiethylenetriamine, and dipn = dipropylenetriamine] have been synthesized through the "complex-as-ligand/complex-as-metal" strategy. Single-crystal X-ray diffraction analyses of 1, 3, and 5 show cationic M(II)₂M'(II)₆ entities (M, M' = Cu and Ni) with an overall double-star architecture, which is made up of two oxamato-bridged M(II)M'(II)₃ star units connected through three meta-phenylenediamidate bridges between the two central metal atoms leading to a binuclear metallacryptand core of the meso-helicate-type. Dc magnetic susceptibility data for 1-6 in the temperature range 2-300 K have been analyzed through a "dimer-of-tetramers" model [H = - J(S(1A)·S(3A) + S(1A)·S(4A) + S(1A)·S(5A) + S(2B)·S(6B) + S(2B)·S(7B) + S(2B)·S(8B)) - J'S(1A)·S(2B), with S(1A) = S(2B) = S(M) and S(3A) = S(4A) = S(5A) = S(6B) = S(7B) = S(8B) = S(M')]. The moderate to strong antiferromagnetic coupling between the M(II) and M'(II) ions through the oxamate bridge in 1-6 (-J(Cu-Cu) = 52.0-57.0 cm⁻¹, -J(Ni-Cu) = 39.1-44.7 cm⁻¹, and -J(Ni-Ni) = 26.3-26.6 cm⁻¹) leads to a non-compensation of the ground spin state for the tetranuclear M(II)M'(II)₃ star units [S(A) = S(B) = 3S(M') - S(M) = 1 (1 and 2), 1/2 (3 and 4), and 2 (5 and 6)]. Within the binuclear M(II)₂ meso-helicate cores of 1-4, a moderate to weak antiferromagnetic coupling between the M(II) ions (-J'(Cu-Cu) = 28.0-48.0 cm⁻¹ and -J'(Ni-Ni) = 0.16-0.97 cm⁻¹) is mediated by the triple m-phenylenediamidate bridge to give a ground spin singlet (S = S(A) - S(B) = 0) state for the octanuclear M(II)₂Cu(II)₆ molecule. Instead, a weak ferromagnetic coupling between the Ni(II) ions (J'(Ni-Ni) = 2.07-3.06 cm⁻¹) operates in the binuclear Ni(II)₂ meso-helicate core of 5 and 6 leading thus to a ground spin nonet (S = S(A) + S(B) = 4) state for the octanuclear Ni(II)₈ molecule. Dc magnetization data for 5 reveal a small but non-negligible axial magnetic anisotropy (D = -0.23 cm⁻¹) of the S = 4 Ni(II)₈ ground state with an estimated value of the energy barrier for magnetization reversal of 3.7 cm⁻¹ (U = -DS²). Ac magnetic susceptibility data for 5 show an unusual slow magnetic relaxation behaviour at low temperatures which is typical of "cluster glasses". The temperature dependence of the relaxation time for 5 has been interpreted on the basis of the Vogel-Fulcher law for weakly interacting clusters, with values of 2.5 K, 1.4 × 10⁻⁶ s, and 4.0 cm⁻¹ for the intermolecular interaction parameter (T₀), the pre-exponential factor (τ₀), and the effective energy barrier (U(eff)), respectively.

A novel bis(oxalato)chromium(III) salt of a ferromagnetically coupled, oxalato-bridged dinuclear chromium(III)-cobalt(II) complex of formula [CrL(ox)(2)CoL'(H(2)O)(2)][CrL(ox)(2)]·4H(2)O (1) has been self-assembled in solution using different aromatic α,α'-diimines as blocking ligands, such as 2,2'-bipyridine (L = bpy) and 2,9-dimethyl-1,10-phenanthroline (L' = Me(2)phen). Thermal dehydration of 1 leads to an intriguing solid-state reaction between the S = 3/2 Cr(III) anions and the S = 3 Cr(III)Co(II) cations to give a ferromagnetically coupled, oxalato-bridged trinuclear chromium(III)-cobalt(II) complex of formula {[CrL(ox)(2)](2)CoL'} (2). Complex 2 possesses a moderately anisotropic S = 9/2 Cr(III)(2)Co(II) ground state, and it exhibits slow magnetic relaxation behavior at very low temperatures (T(B) < 2.0 K).