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In the solid state, the thermal properties of SCO materials give rise to a rich variety of behaviors, ranging from (i) simple continuous gradual spin transitions, corresponding to a Boltzmann population of two degenerate states to (ii) sharp first-order hysteretic[11] transitions, including (iii) incomplete transitions and (iv) two-step or multi-step spin transitions,[12] characterized by the presence of a macroscopic intermediate state in the course of the transition between the LS and the HS states. Ndiaye I et al i .[33] establish the existence of an isomorphism between the electro-elastic models developed for the spin transition and Ising-like models including competing interactions, which confirms the relevance of the spin models in describing the multi-step spin transitions. Indeed, due to the volume change accompanying the spin transition between the LS and the HS states, crystallography appears as a direct probe of the spin transition at several scales, giving information about the deformation of the molecular structure and its consequence on the expansion/contraction of the lattice along the spin transformation. Later on, new interesting initiatives emerge through the introduction of spin-phonon models and elastic models in which the spin states were coupled to the atomic displacements of the SCO lattice, renormalizing the ligand field to which an elastic contribution arising from the lattice is added. [Extracted from the article]

A new series of three spin crossover (SCO) Fe(II) complexes based on a cyanocarbanion and on the neutral quinolin-8-amine (aqin) ligands, [Fe(aqin)2(tcnsme)2] (1), [Fe(aqin)2(tcnset)2] (2), and [Fe(aqin)2(tcnspr)2] (3), has been studied. The three complexes display similar molecular structures consisting of discrete [Fe(aqin)2(tcnsR)2] complexes [R = Me (1), Et (2), and Pr (3)]. Infrared spectroscopy and magnetic studies, performed on the three complexes, revealed the presence of similar SCO behaviors which strongly differ by their transition temperatures [234 K (1) < 266 K (2) < 360 K (3)]. The increase of the transition temperatures when passing from 1 to 3 may be explained by electronic and packing effects. Thus, when passing from Me (1) to Et (2) and Pr (3), the electron donor effect increases, resulting in an increase of the ligand field and, accordingly, in an increase of the transition temperature. On the other side, examination of the different coordination modes of the cyanocarbanions in the three complexes clearly reveals the crucial role of these coordination modes on the crystal packing and, therefore, on the transition temperature. We can, therefore, attribute the important increase of the transition temperature from complexes 1 to 3 to both effects: the electron donor character of the alkyl groups and the packing effects of the versatile cycnocarbanion ligands. [ABSTRACT FROM AUTHOR]

An original copper(II) dimeric compound formulated as [Cu2(μ1,1‐N3)2L2(N3)2].2CHCl3 (1), with L = 2,6‐pyridinedicarboxaldehydebis(p‐iodophenyl‐imine), has been synthesized and characterized. Single crystal X‐ray structural characterization revealed that this complex displays a centrosymmetric dinuclear structure in which the two Cu(II) centers are connected by double symmetric μ1,1 (end‐on, EO) azido bridges, generating distorted octahedral CuN6 coordination geometry. Magnetic susceptibility measurements indicate a ferromagnetic Cu···Cu coupling with J = 26.7 cm−1 (J being the parameter of the exchange Hamiltonian H = −2JS1S2). The catalytic properties of complex 1 have been evaluated in the one‐pot azide‐alkyne cycloaddition reaction in water without any additional reducing agents or bases. As expected, the absence of any catalyst did not lead to product formation, whereas when complex 1 was introduced as catalyst, the reaction led to the desired product with different chemical yields (10–98%), for which the highest one (98%) corresponds to the reaction performed in the presence of 125 ppm of 1 in water at 90 C. These optimized parameters have been then taken into account to extend the initial reaction based on benzyl chloride and simple alkyne to different substituted benzyl chloride and alkyne molecules. [ABSTRACT FROM AUTHOR]

The study reports three new examples of the copper(II)-tcpd system in which two different neutral ligands are introduced as co-ligands. Compound [Cu2-(bpym)(tcpd)2(H2O)4].2H2O which involves a bridging polynitrile and a bis-chelating bpym is described as mono-dimensional chain and the use of a chelating ligand instead of the bridging bpym led to compound [Cu(tn)(tcpd)] with a 3D architecture and to compound [Cu(tn)2(tcpd).H2O with a 1D structure.

Research has been conducted on the magnetic dinuclear anion. The results of the electrochemical combination of this anion with the bis(ethylenedithio)tetrathiafulvalene organic pi-donor which produces isostructural molecular hybrid salts are discussed.

Syntheses, structures, and properties of radical salts made with bis(ethylenedithio)tetrathiafulvalene (ET) and monosubstituted alpha-Keggin polyoxoanions are described. Crystallization of salts occur in two series. Alternating layers of the organic donor and Keggin polyoxometalates appear in the general structure. An eclipsed chain with almost totally ionized ET molecules and a dimerized one with partially charged ET molecules form the organic layers. Magnetic behaviors exhibited by salts with discrete magnetic anions relate to the sum of the magnetic contributions of the two lattices.

The new alpha-1 and alpha-2 series of radical salts, alpha-1-ET8(XW12O40) (X = Co{II}, Cu{II}, 2{H+} and Fe{III}) and alpha-2-ET8(XW12O40) (X = Co{II}, Cu{II}, 2{H+}, Fe{III} and B{III}) where ET = bis(ethylelenedithio)- tetrathiafulvalene, are prepared from ET and Keggin polyoxoanions. The Keggin polyanions form closed packed pseudohaxagonal layers in the alpha phases. The monoclinic alpha-1 has alternating layers of the organic donor and the Keggin polyoxometalates. In alpha-2 phase the organic donor layers have only two crystallographically independent molecules.