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Ein Prototyp eines SQUID ‐ artigen magnetometrischen Messgeräts, das Schaltvorgänge in Spin ‐ Crossover ‐ Nanopartikeln bei Raumtemperatur indirekt detektiert, wurde entwickelt und an Nanopartikeln aus [Fe(hptrz)3](OTs)2 getestet (hptrz=4 ‐ Heptyl ‐ 1,2,4 ‐ triazol, OTs=p ‐ Toluolsulfonyl). Der mikromagnetometrische Ansatz hat klare Vorteile gegenüber herkömmlichen SQUID ‐ und Nano ‐ SQUID ‐ Techniken. [ABSTRACT FROM AUTHOR]

A series of framework coordination polymers reveals the use of 1,2,4,5-tetrazines as efficient bridging ligands towards silver(I) and copper(I) ions. All four nitrogen atoms were functional as lone pair donors leading to an unprecedented m4-coordination of the ligands (1,2,4,5-tetrazine, ttz; 3,6-dimethyl-1,2,4,5-tetrazine, Me2ttz) in [Ag(ttz)(X)] (X = NO3, 1; ClO4, 2), [Ag2(Me2ttz)(NO3)2] (3), [Ag2(Me2ttz)(H2O)2(ClO4)2] (4), [Ag3(Me2ttz)(H2O)2(CF3SO3)3] (5) and [Cu4Cl4(Me2ttz)] (6). In 1 and 2, μ4-tetrazines and silver ions (AgN4, Ag-N 2.42-2.53Å ) compose a 3D framework of {42;84} topology. Structures 3 and 4 were based on disilver-tetrazine ribbons, while in 5 μ4-tetrazines interconnect silver-triflate chains. In 6, μ4-ligands connect inorganic layers sustained by copper-chloride squares, hexa- and octagons (1.974(2) and 1.981(2)Å ). Multiple N-coordination to metal ions enhances the ability of the electron deficient tetrazine system for anion … π binding. Compounds 1 and 2 exhibit very short interactions of this type with corresponding O… C(N) separations down to a record value of 2.78Å and O… π 2.61Å . For 6, π-acidity of tetrazine was reflected by contacts Cl … π of 3.30Å . Results of high level ab initio calculations (RI-MP2/aug-cc-pVTZ) were in good agreement with experimental results, and were suggestive of the progressive enhancement of the π-acidity by increasing the number of Ag(I) ions N-coordinated to tetrazine. [ABSTRACT FROM AUTHOR]

Spin crossover compounds are considered to be a viable alternative for creating display, memory and switching devices due to the bistability of their magnetic, optical, mechanical and electrical properties. This Letter presents the study of the dielectric and transport properties of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4-triazole) complex in a wide temperature and frequency range. Our results reveal a singular behavior of the dielectric modulus upon the spin transition in conjunction with the switching of the conductivity between the high spin and low spin states. [ABSTRACT FROM AUTHOR]

Spin crossover compounds are considered to be a viable alternative for creating display, memory and switching devices due to the bistability of their magnetic, optical, mechanical and electrical properties. This Letter presents the study of the dielectric and transport properties of the [Fe(Htrz)2(trz)](BF4) (Htrz = 1H-1,2,4-triazole) complex in a wide temperature and frequency range. Our results reveal a singular behavior of the dielectric modulus upon the spin transition in conjunction with the switching of the conductivity between the high spin and low spin states. [ABSTRACT FROM AUTHOR]

Poly[[μ4-4,4′-bipyridazine-μ5-sulfato-disilver(I)] monohydrate], {[Ag2(SO4)(C8H6N4)]·H2O} n, (I), and poly[[aqua-μ4-pyridazino[4,5- d]pyridazine-μ3-sulfato-disilver(I)] monohydrate], {[Ag2(SO4)(C6H4N4)(H2O)]·H2O} n, (II), possess three- and two-dimensional polymeric structures, respectively, supported by N-tetradentate coordination of the organic ligands [Ag—N = 2.208 (3)–2.384 (3) Å] and O-pentadentate coordination of the sulfate anions [Ag—O = 2.284 (3)–2.700 (2) Å]. Compound (I) is the first structurally examined complex of the new ligand 4,4′-bipyridazine; it is based upon unprecedented centrosymmetric silver–pyridazine tetramers with tetrahedral AgN2O2 and trigonal–bipyramidal AgN2O3 coordination of two independent AgI ions. Compound (II) adopts a typical dimeric silver–pyridazine motif incorporating two kinds of square-pyramidal AgN2O3 AgI ions. The structure exhibits short anion–π interactions involving noncoordinated sulfate O atoms [O...π = 3.041 (3) Å]. [ABSTRACT FROM AUTHOR]

Here we describe the elaboration and investigation of composites prepared from the spin-crossover (SCO) complex [Fe(pyrazine){Au(CN) 2 } 2 ] and poly(vinylidene fluoride) matrix, with different contents of the active phase (10–35 wt%). Optical measurements demonstrated that all composites preserve temperature induced hysteretic spin transitions. Tensile mechanical analysis showed a non-linear change of the Young's modulus upon increase of the complex content. Thermomechanical analysis upon a constant strain demonstrated pronouncable alterations of the applied stress in the SCO region. Composites with smaller loads require less stress to attain a given strain in the high-spin state, however for those with high loads the behaviour is more sophisticated. The modelling of stress vs. temperature behaviour revealed that this may be interpreted through a miscellaneous interplay of expansion of both the polymer and the complex, the contribution of both components to the elastic properties of composites, and the effects of SCO on these properties. [Display omitted] • Insertion of a spin-crossover complex into PVDF leads to switchable composites. • Reinforcement of the films with low loads of the complex is observed. • Thermomechanical behaviour of composites reveals mechanical effects of SCO. • Basic tensile properties of SCO composites are emerged. [ABSTRACT FROM AUTHOR]

Hybrid halide perovskites form a promising class of light-absorbing materials. Among the numerous 3D semiconducting perovskites, there is a group of emerging aziridinium-based hybrids that are considered to be prospective materials for optoelectronic applications. In this work, we report the mixed halide aziridinium perovskites of (AzrH)PbBrxI3-x series (AzrH = aziridinium). Small changes in the composition of perovskites are shown to have a defining impact on the optoelectronic properties of the reported materials. Halogen substitution allowed a variation in band gap values of these compounds, ranging from 1.57 to 2.23 eV, as established using electronic spectroscopy. Crystal structures of (AzrH)PbBrxI3-x perovskites were studied using single crystal and powder X-ray diffraction analysis. The lattice constant had a linear dependence on the Br content in the structure, thus strictly following Vegards's law. Importantly, the reported compounds displayed a preferential inclusion of iodine upon synthesis, revealing that the mixed halide perovskite composition cannot be estimated based on the precursors' ratio only, and it should be post-synthetically checked. The reported results expand the range of hybrid perovskites with tuneable band gaps beyond the conventional methylammonium and formamidinium-based perovskites and offer a new series of metal-halide hybrids suitable for photovoltaic and other optoelectronic applications.

This study presents the synthesis, characterization and Hirshfeld surface analysis of a small organic ammonium salt, C 2 H 7 BrN + ·Br - . Small cations like the one in the title compound are considered promising components of hybrid perovskites, crucial for optoelectronic and photovoltaic applications. While the incorporation of this organic cation into various hybrid perovskite structures has been explored, its halide salt counterpart remains largely uninvestigated. The obtained structural results are valuable for the synthesis and phase analysis of hybrid perovskites. The title compound crystallizes in the solvent-free form in the centrosymmetric monoclinic space group P 2 1 / c , featuring one organic cation and one bromide anion in its asymmetric unit, with a torsion angle of -64.8 (2)° between the ammonium group and the bromine substituent, positioned in a gauche conformation. The crystal packing is predominantly governed by Br⋯H inter-actions, which constitute 62.6% of the overall close atom contacts., (© Semenikhin et al. 2024.)

Chemical composition is leading among the numerous factors that determine the spin transition properties of coordination compounds. Classic dicyanometallic bridges {M(CN) 2 } - are commonly used to build Hofmann-like spin-crossover frameworks, but some extended bridges are also synthetically available. In this paper, we describe a successful synthesis of two very similar spin-crossover frameworks that differ in the cyanometallic bridges involved, namely [Fe(etpz) 2 {Ag(CN) 2 } 2 ] (1) and {Fe(etpz) 2 [Ag 2 (CN) 3 ][Ag(CN) 2 ]} (2) (where etpz = 2-ethylpyrazine). Magnetic and Mössbauer studies demonstrated the occurrence of abrupt one-step high-spin (HS) ↔ low-spin (LS) transitions for both complexes. The spin transition temperatures are T 1/2 ↓ = 233 K and T 1/2 ↑ = 243 K for 1 and T 1/2 ↓ = 188 K and T 1/2 ↑ = 191 K for 2 with thermal hysteresis loops of 10 K for 1 and 3 K for 2. The bridging mononuclear [Ag(CN) 2 ] - units and Fe II cations assemble to form infinite 2D layers in the structure of 1. Interestingly, compound 2 forms 2D layers of Fe II cations bridged by both binuclear [Ag 2 (CN) 3 ] - and mononuclear [Ag(CN) 2 ] - units. The structures of 1 and 2 comprise different types of intermolecular interactions including Ag⋯Ag and Ag⋯N etpz , which induce the creation of supramolecular 3D frameworks. The synergy between metallophilic interactions and the spin transition is also confirmed by the variation of Ag⋯Ag distances during spin crossover. The characterization of such analogues allowed us to analyze in detail the effect of the cyanometallic bridge on the structure of new frameworks and on the bistability in Hofmann-like complexes.

In the crystal structure of the title compound, [Cu(NO 3 ) 2 (C 3 H 5 N 3 ) 4 ], the Cu II atom is situated on an inversion center (Wyckoff position 2 c of space group P 2 1 / n ) and shows an octa-hedral [N 4 O 2 ] coordination environment. The axial positions are occupied by O atoms of nitrate anions, while the equatorial positions are taken up by the N atoms of four 3-amino-pyrazole ligands. As a result of the tautomerism of the latter, two coordinate with the N 1 -atom of 3-amino-pyrazole while the other two with the N 2 -atom. The presence of pyrrole-like N-H groups and amine substituents as donor groups leads to numerous intra- and inter-molecular hydrogen-bonding inter-actions, which were qu-anti-fied by Hirshfeld surface analysis., (© Kucheriv et al. 2023.)

The crystal structure of the title salt, bis-(3-carb-oxy-1-methyl-pyridinium) octa-bromide, 2C 7 H 8 NO 2 + ·Br 8 2- , consists of 3-carb-oxy-1-methyl-pyridinium ( N -methyl-nicotinic acid) cations, which are stacked between relatively rare [Br 8 ] 2- anions. The polybromide [Br 8 ] 2- anions connected with a Br 3 mol-ecule in a - anions connected with a Br 2 mol-ecule in a Z anions through π⋯Br inter-actions that induce the creation of a supra-molecular tri-periodic network. In addition, the presence of weak C-H⋯Br contacts leads to the creation of layers, which align parallel to (11).8 ] 2- anions through π⋯Br inter-actions that induce the creation of a supra-molecular tri-periodic network. In addition, the presence of weak C-H⋯Br contacts leads to the creation of layers, which align parallel to (11)., (© Sirenko et al. 2023.)

Lead halide hybrid perovskites incorporating chiral organic cations attract considerable attention due to their promising application in multifarious optoelectronic devices. However, the examples of chiral hybrid perovskites are still limited, which greatly impedes their further studies in various optoelectronic fields. Herein, we report on new low-dimensional lead-halide hybrid perovskites incorporating the enantiopure chiral α-amino acid L-proline. Two hybrid perovskites (L-proH)PbBr 3 ·H 2 O ( Pro-PbBr 3 ) and (L-proH) 4 Pb 3 Br 10 ·4H 2 O ( Pro-Pb 3 Br 10 is built upon a rare two-dimensional (2D) [Pb Pro-PbBr 3 is built of one-dimensional (1D) [PbX 3 ] ∞ n - lead halide chains, whereas the inorganic sublattice of compound Pro-Pb 3 Br 10 is built upon a rare two-dimensional (2D) [Pb 3 Br 10 ] ∞ 4 n - honeycomb-type inorganic framework. Hirshfeld surface analysis revealed an important role of various hydrogen bonding interactions in providing the binding between organic and inorganic parts of these hybrid perovskites. The optical band gap values of new hybrid perovskites as estimated using the Tauc plot approach are 4.19 eV ( Pro-PbBr 3 ) and 4.13 eV ( Pro-Pb 3 Br 10 ). Also, new compounds display low-temperature broadband photoluminescence which can be attributed to the self-trapped excitons. These results show the potential of α-proline for constructing novel and highly demanded chiral hybrid perovskites, which will hold great promise for further optoelectronic applications.

Spin-crossover complexes with multistep transitions attract much attention due to their potential applications as multi-switches and for data storage. A four-step spin crossover is observed in the new iron(II)-based cyanometallic guest-free framework compound Fe(2-ethoxypyrazine) 2 {Ag(CN) 2 } 2 during the transition from the low-spin to the high-spin state. A reverse process occurs in three steps. Crystallographic studies reveal an associated stepwise evolution of the crystal structures. Multiple transitions in the reported complex originate from distinct Fe II sites which exist due to the packing of the ligand with a bulky substituent., (© 2022 Wiley-VCH GmbH.)

In the title compound [Fe 2 (C 2 O 4 )(C 8 H 8 N 4 ) 4 ](CH 3 C 6 H 4 SO 3 ) 2 ·2.75H 2 O, the two Fe II ions have a highly distorted octa-hedral FeN 4 O 2 environment formed by two bidentate triazole-based chelating ligands and a bis-bidentate oxalate bridging anion that connects the metal ions. Stabilization within the crystal structure is provided via a system of O-H⋯O and N-H⋯O hydrogen bonding, which determines the formation of a two-dimensional architecture along the a- axis direction., (© Petrenko et al. 2022.)

In the title polymeric coordination compound, {[FePt(CN) 4 (H 2 O) 2 ]·1.33CH 3 OH} n , the Fe II cation (site symmetry 4/ mm.m ) is coordinated by the N atoms of four cyanide anions (CN - ) and the O atoms of two water mol-ecules, forming a nearly regular [FeN 4 O 2 ] octa-hedron. According the Fe-N and Fe-O bond lengths, the Fe II atom is in the high-spin state. The cyanide anions act in a bridging manner to connect the Fe II and Pt II atoms. The [Pt(CN) 4 ] 2- moieties (Pt with site symmetry 4/ mm.m ) have a perfect square-planar shape. The latter anion is located perpendicular to the FeN 4 plane, thus ensuring the creation of a three-dimensional framework. The crystal structure features methanol solvent mol-ecules of which 4/3 were located per Fe II cation. These solvent mol-ecules are located in hexa-gonal pores; they inter-act with coordinating water mol-ecules through weak hydrogen bonds. Other guest mol-ecules could not be modelled in a satisfactory way and their contribution to the scattering was removed by a mask procedure., (© Hiiuk et al. 2022.)

9-Amino-acridinium chloride N , N -di-methyl-formamide monosolvate, C 13 H 11 N 2 + Cl - ·C 3 H 7 NO, crystallizes in the monoclinic space group P 2 1 / c. The salt was crystallized from N , N -di-methyl-formamide. The asymmetric unit consists of two C 13 H 11 N 2 + Cl - -di-methyl-formamide mol-ecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an anti-parallel manner. The mol-ecules are linked N a network of multidirectional π-π inter-actions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic inter-actions between ions.N -di-methyl-formamide mol-ecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an anti-parallel manner. The mol-ecules are linked via a network of multidirectional π-π inter-actions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic inter-actions between ions., (© Fritsky et al. 2021.)

In the title compound [Fe(bpe)(Hbpe)Au(CN) 2 ][Au(CN) 2 ] 2 ·bpe·2H 2 O} n [where bpe = 1,2-bis-(pyridin-4-yl)ethene, C 12 H 10 N 2 ], the Fe II ion is coordinated in a distorted octa-hedral [FeN 4 O 2 ] environment by two di-cyano-aurate anions, two water mol-ecules and two partially protonated 1,2-di(4-pyrid-yl)ethyl-ene mol-ecules. Di-cyano-aurate anions bridge the Fe II cations, forming infinite chains, which propagate along the a- axis direction. The chains are connected via aurophilic inter-actions with two non-coordinated di-cyano-aurate anions for each Fe II ion. The polymeric chains inter-act with each other via π-π stacking between the guest bpe mol-ecules and multiple hydrogen bonds., (© Partsevska et al. 2020.)

Hofmann-like cyanometalates constitute a large class of spin-crossover iron(II) complexes with variable switching properties. However, it is not yet clearly understood how the temperature and cooperativity of a spin transition are influenced by their structure. In this paper, we report the synthesis and crystal structures of the metal-organic coordination polymers {Fe II (Mepz)[Au I (CN) 2 ] 2 } ( [Au] ) and {Fe II (Mepz) 2 [Ag I (CN) 2 ] 2 } ( [Ag] ), where Mepz = 2-methylpyrazine, along with characterization of their spin-state behavior by variable-temperature SQUID magnetometry and Mössbauer spectroscopy. The compounds are built of cyanoheterometallic layers, which are pillared by the bridging Mepz ligands in [Au] but separated in [Ag] . The complex [Au] exhibits an incomplete stepped spin transition as a function of the temperature with T SCO1 = 170 K and T SCO2 = 308 K for the two subsequent steps. In contrast, the complex [Ag] attains the high-spin state over the whole temperature range. In the crystal structure of [Ag] , weak interlayer contacts (Ag-π, Me-π, and Ag-N) are found that may be responsible for an unusual axial elongation of the FeN 6 polyhedra. We propose that this structural distortion contributes to the trapping of iron in its high-spin state.

In the asymmetric unit of the title coordination compound, {[Cu(CN)(C 4 H 3 OC 2 H 5 N 2 )][Cu(CN)]} n , there are two Cu atoms with different coordination environments. One Cu I ion is coordinated in a triangular coordination geometry by the N atom of the 2-eth-oxy-pyrazine mol-ecule and by two bridging cyanide ligands, equally disordered over two sites exchanging C and N atoms, thus forming polymeric chains parallel to the c axis. The other Cu atom is connected to two bridging cyanide groups disordered over two sites with an occupancy of 0.5 for each C and N atom, and forming an almost linear polymeric chain parallel to the b axis. In the crystal, the two types of chain, which are orthogonal to each other, are connected by cuprophilic Cu⋯Cu inter-actions [2.7958 (13) Å], forming two-dimensional metal-organic coordination layers parallel to the bc plane. The coordination framework is further stabilized by weak long-range (electrostatic type) C-H⋯π inter-actions between cyano groups and 2-eth-oxy-pyrazine rings., (© Partsevska et al. 2019.)

In the title polymeric complex, {[FePt(CN) 4 (H 2 O) 2 ]·2C 3 H 6 O} n , the Fe II cation has an octa-hedral [FeN 4 O 2 ] geometry being coordinated by two water mol-ecules and four cyanide anions. The Pt cation is located on an inversion centre and has a square-planar coordination environment formed by four cyanide groups. The tetra-cyano-platinate anions bridge the Fe II cations to form infinite two-dimensional layers that propagate in the bc plane. Two guest mol-ecules of acetone per Fe II are located between the layers. These guest acetone mol-ecules inter-act with the coordinated water mol-ecules by O-H⋯O hydrogen bonds., (© Kuzevanova et al. 2019.)

In the title metal-organic framework, [Fe(C 6 H 8 N 2 ) 2 {Cu(CN) 2 } 2 ] n , the low-spin Fe II ion lies at an inversion centre and displays an elongated octa-hedral [FeN 6 ] coordination environment. The axial positions are occupied by two symmetry-related bridging 2-ethyl-pyrazine ligands, while the equatorial positions are occupied by four N atoms of two pairs of symmetry-related cyanide groups. The Cu I centre is coordinated by three cyanide carbon atoms and one N atom of a bridging 2-ethyl-pyrazine mol-ecule, which form a tetra-hedral coordination environment. Two neighbouring Cu atoms have a short Cu⋯Cu contact [2.4662 (7) Å] and their coordination tetra-hedra are connected through a common edge between two C atoms of cyanide groups. Each Cu 2 (CN) 2 unit, formed by two neighbouring Cu atoms bridged by two carbons from a pair of μ-CN groups, is connected to six Fe II centres via two bridging 2-ethyl-pyrazine mol-ecules and four cyanide groups, resulting in the formation of a polymeric three-dimensional metal-organic coordination framework.

In the title polymeric complex, {[Fe(CN) 2 (C 10 H 8 N 2 ) 2 (H 2 O) 2 ][Au(CN) 2 ]} n , the Fe II ion, which is located on a twofold rotation axis, has a slightly distorted FeN 4 O 2 octa-hedral geometry. It is coordinated by two phenyl-pyrazine mol-ecules, two water mol-ecules and two di-cyano-aurate anions, the Au atom also being located on a second twofold rotation axis. In the crystal, the coordinated di-cyano-aurate anions bridge the Fe II ions to form polymeric chains propagating along the b -axis direction. In the crystal, the chains are linked by O water -H⋯N di-cyano-aurate anions hydrogen bonds and aurophillic inter-actions [Au⋯Au = 3.5661 (3) Å], forming layers parallel to the bc plane. The layers are linked by offset π-π stacking inter-actions [inter-centroid distance = 3.643 (3) Å], forming a supra-molecular metal-organic framework.

In the title metal-organic framework, [Fe(C 4 H 3 BrN 2 ) 2 {Cu(CN) 2 } 2 ] n , the Fe II cation is located on an inversion center and has a slightly elongated octa-hedral coordination environment [FeN 6 ], ligated by two pyrazine N atoms of symmetry-related bridging 2-bromo-pyrazine mol-ecules in the axial positions and by four N atoms of pairs of symmetry-related cyanido groups in the equatorial positions. The Cu I center has a fourfold coordination environment [CuC 3 N], with an almost perfect trigonal-pyramidal geometry, formed by three cyanido C atoms and an N atom of a bridging 2-bromo-pyrazine mol-ecule. Copper(I) centers related by a twofold rotation axis are bridged by two carbon atoms from a pair of μ-CN groups, resulting in Cu 2 (CN) 2 units. Each Cu 2 (CN) 2 unit is linked to six Fe II cations via a pair of linear CN units, the pair of μ-CN groups and two bridging 2-bromo-pyrazine ligands, resulting in the formation of a metal-organic framework, which is additionally stabilized by the short Cu⋯Cu contacts of 2.4450 (7) Å.

In the title polymeric complex, {[Fe(C 12 H 10 N 2 ) 2 (H 2 O) 4 ](CH 3 C 6 H 4 SO 3 ) 2 ·2CH 3 OH} n , the Fe II cation, located on an inversion centre, is coordinated by four water mol-ecules in the equatorial positions and two 1,2-bis-(pyridin-4-yl)ethene mol-ecules in the axial positions. This results in a distorted octa-hedral geometry for the [N 2 O 4 ] coordination polyhedron. The 1,2-bis-(pyridin-4-yl)ethene mol-ecules bridge the Fe II cations, forming polymeric chains running along the a- axis direction. Stabilization of the crystal structure is provided by O-H⋯O hydrogen bonds; these are formed by coordinated water mol-ecules as donors towards the O atoms of the methanol mol-ecules and tosyl-ate anions as acceptors of protons, leading to the formation of a three-dimensional supra-molecular network. Weak C-H⋯O hydrogen bonds are also observed in the crystal.

In the title polymeric complex, [Au 2 Fe(CN) 4 (C 4 H 3 IN 2 ) 2 (C 2 H 6 O)] n , the Fe II cation is coordinated by two iodo-pyrazine mol-ecules, one ethanol mol-ecule and three di-cyano-aurate anions in a distorted N 5 O octa-hedral geometry. In the crystal, the di-cyano-aurate anions bridge the Fe II cations to form polymeric chains propagating along the b- axis direction. Stabilization of the crystal structure is provided by O-H⋯N hydrogen bonds and π-π stacking between parallel iodo-pyrazine rings of neighbouring chains, the centroid-centroid distances being 3.654 (10) and 3.658 (9) Å.

CeO 2- x nanorods show a reduction in biofouling comparable to Cu 2- x nanorods show a reduction in biofouling comparable to Cu 2 O, the most typical biocidal pigment., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The diversity of spin crossover (SCO) complexes that, on the one hand, display variable temperature, abruptness and hysteresis of the spin transition, and on the other hand, are spin-sensitive to the various guest molecules, makes these materials unique for the detection of different organic and inorganic compounds. We have developed a homochiral SCO coordination polymer with a spin transition sensitive to the inclusion of the guest 2-butanol, and these solvates with (R)- and (S)-alcohols demonstrate different SCO behaviours depending on the chirality of the organic analyte. A stereoselective response to the guest inclusion is detected as a shift in the temperature of the transition both from dia- to para- and from para- to diamagnetic states in heating and cooling modes respectively. Furthermore, the Mössbauer spectroscopy directly visualizes how the metallic centres in a chiral coordination framework differently sense the interaction with guests of different chiralities., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The title salt, [Fe(II)(C4H3ClN2)2(H2O)4](C7H7O3S)2, contains a complex cation with point group symmetry 2/m. The high-spin Fe(II) cation is hexa-coordinated by four symmetry-related water and two N-bound 2-chloro-pyrazine mol-ecules in a trans arrangement, forming a distorted FeN2O4 octa-hedron. The three-dimensional supra-molecular structure is supported by inter-molecular O-H⋯O hydrogen bonds between the complex cations and tosyl-ate anions, and additional π-π inter-actions between benzene and pyrazine rings. The methyl H atoms of the tosyl-ate anion are equally disordered over two positions.

In the crystal of the title compound, [Fe(NCS)3(H2O)3]·3C6H8N2, the Fe(III) cation is located on a threefold rotation axis and is coordinated by three N atoms of the thiocyanate anions and three water mol-ecules in a fac arrangement, forming a slightly distorted N3O3 octa-hedron. Stabilization within the crystal structure is provided by O-H⋯N hydrogen bonds; the H atoms from coordinating water mol-ecules act as donors to the N atoms of guest 2,3-di-methyl-pyrazine mol-ecules, leading to a three-dimensional supra-molecular framework.

In the title compound, (C5H6N)[Fe(NCS)4(C5H5N)2], the Fe(III) ion is coordinated by four thio-cyanate N atoms and two pyridine N atoms in a trans arrangement, forming an FeN6 polyhedron with a slightly distorted octa-hedral geometry. Charge balance is achieved by one pyridinium cation bound to the complex anion via N-H⋯S hydrogen bonding. The asymmetric unit consists of one Fe(III) cation, four thio-cyanate anions, two coordinated pyridine mol-ecules and one pyridinium cation. The structure exhibits π-π inter-actions between pyridine rings [centroid-centroid distances = 3.7267 (2), 3.7811 (2) and 3.8924 (2) Å]. The N atom and a neighboring C atom of the pyridinium cation are statistically disordered with an occupancy ratio of 0.58 (2):0.42 (2).

New methods are proposed for the synthesis of spin-crossover nano- and micro-objects. Several nano-objects that are based upon the spin-crossover complex [Fe(hptrz)(3)](OTs)(2) (hptrz=4-heptyl-1,2,4-triazole, Ts=para-toluenesulfonyl) were prepared in homogeneous media. The use of various reagents (Triton X-100, PVP, TOPO, and PEGs of different molecular weights) as stabilizing agents yielded materials of different size (6 nm-2 μm) and morphology (nanorods, nanoplates, small spherical particles, and nano- and micro-crystals). In particular, when Triton X-100 was used, a variation in the morphology from nanorods to nanoplates was observed by changing the nature of the solvent. Interestingly, the preparation of the nanorods and nanoplates was always accompanied by the formation of small spherical particles. Alternatively, when PEG was used, 200-400 nm crystals of the complex were obtained. In addition, a very promising polymer-free synthetic method is discussed that was based on the preparation of relatively stable Fe(II)-triazole oligomers in CHCl(3). Their specific treatment led to micro-crystals, small nanoparticles, or gels. The size and morphology of all of these objects were characterized by TEM and by dynamic light scattering (DLS) where possible. Their spin-crossover behavior was studied by optical and magnetic measurements. The spin-transition features for large particles (>100 nm) were very similar to that of the bulk material, that is, close to room temperature with a hysteresis width of up to 8 K. The effects of the matrix and/or size-reduction led to modification of the transition temperature and an abruptness of the spin transition for oligomeric solutions and small nanoparticles of 6 nm in size., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of framework coordination polymers reveals the use of 1,2,4,5-tetrazines as efficient bridging ligands towards silver(i) and copper(i) ions. All four nitrogen atoms were functional as lone pair donors leading to an unprecedented mu(4)-coordination of the ligands (1,2,4,5-tetrazine, ttz; 3,6-dimethyl-1,2,4,5-tetrazine, Me(2)ttz) in [Ag(ttz)(X)] (X = NO(3), ; ClO(4), ), [Ag(2)(Me(2)ttz)(NO(3))(2)] (), [Ag(2)(Me(2)ttz)(H(2)O)(2)(ClO(4))(2)] (), [Ag(3)(Me(2)ttz)(H(2)O)(2)(CF(3)SO(3))(3)] () and [Cu(4)Cl(4)(Me(2)ttz)] (). In and , micro(4)-tetrazines and silver ions (AgN(4), Ag-N 2.42-2.53 A) compose a 3D framework of {4(2);8(4)} topology. Structures and were based on disilver-tetrazine ribbons, while in mu(4)-tetrazines interconnect silver-triflate chains. In , micro(4)-ligands connect inorganic layers sustained by copper-chloride squares, hexa- and octagons (1.974(2) and 1.981(2) A). Multiple N-coordination to metal ions enhances the ability of the electron deficient tetrazine system for anionpi binding. Compounds and exhibit very short interactions of this type with corresponding OC(N) separations down to a record value of 2.78 A and Opi 2.61 A. For , pi-acidity of tetrazine was reflected by contacts Clpi of 3.30 A. Results of high level ab initio calculations (RI-MP2/aug-cc-pVTZ) were in good agreement with experimental results, and were suggestive of the progressive enhancement of the pi-acidity by increasing the number of Ag(i) ions N-coordinated to tetrazine.