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In this paper, we discuss the effects of metal dilution on the spin-crossover behavior of iron(II) solid solutions [Fe x Ni 1− x (bpp) 2 ](NCSe) 2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine), including chemical synthesis, physical properties and light induced bistability aspects. For all the materials investigated, the thermal spin-crossover properties, T 1/2 , were measured and the stability of the photoinduced high-spin states was probed through determination of the T(LIESST) values associated with the light-induced excited spin-state trapping (LIESST) effect. It was found that T 1/2 decreases with the metal dilution while T(LIESST) remains globally unchanged. These results were discussed and compared with previous results obtained in the same series with Zn(II) and Mn(II) used to substitute Fe(II). This comparison gives insights on the effect of the diluting ion size on the [T(LIESST), T 1/2 ] temperatures. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Light-Induced Excited Spin-State Trapping (LIESST) is a well-known phenomenon in spin-crossover (SCO) materials, studied since 1982 in solution and 1984 in the solid state, as it offers some interesting prospects in data storage. In this paper we discuss the influence of metal dilution on the lifetime of the photo-induced state in two 1D chain solid solution series: [Fe x Zn 1− x (btzp) 3 ](BF 4) 2 and [Fe x Zn 1− x (endi) 3 ](BF 4) 2 { btzp = 1,2-bis(tetrazol-1-yl)propane and endi = 1,2-bis(tetrazol-1-yl)ethane}. For each composition, we have determined the thermal spin transition temperature, T 1/2 , and the relaxation temperature of the photoinduced high-spin state, T (LIESST). A detailed analysis of the relaxation kinetics allowed a discussion of the evolution of this lifetime as a function of metal dilution. [ABSTRACT FROM AUTHOR]

Abstract: We report on a detailed analysis of the thermal transition hysteresis loop and the relaxation curves of the recently investigated compound [FeII(L)2][ClO4]2 ·C7H8 [V. Mishra et al., Inorg. Chem. (2008)]. We developed a variant of a previous kinetic cooperative model, modified for including short-range and long-range Gaussian distributions of energy parameters. The resulting set of coupled master equations was solved numerically for the dynamic and the quasi-static case. We have elucidated the various correlations between the distribution widths and the long-range interaction parameter, which basically have opposite effects. It is shown that presence of a steep hysteresis loop may hide a sizable short-range distribution, while the stretched character of the relaxation curves may also hide the presence of strong interactions. We also show that the coherent analysis of the set of relaxation curves at different temperatures does not allow to disentangle properly all the relevant parameters. We discuss these data with respect to the other photomagnetic experiments, T(LIESST) curve and light-induced thermal hysteresis (LITH) loop, and finally we try to address the question of the real nature of the cooperative relaxation process. [Copyright &y& Elsevier]

Abstract: Metal complexes of Schiff bases derived from an aromatic hydrazide are well characterised and have been reported several times. Single crystal structures of metal hydrazone complexes derived from an aliphatic hydrazide are very rare and still remain unexplored. In this paper we report two new end-on azido bridged dinuclear copper(II) and cobalt(III) hydrazone complexes derived from an aliphatic hydrazide. The Schiff base [LH =CH3C(O)NHNf5H4N] has resulted from the condensation of acetic hydrazide and pyridine-2-carboxaldehyde. The ligand and the complexes [Cu2(L)2(μ1,1-N3)2] (1) and [Co2(L)2(μ1,1-N3)2(N3)2] (2) are characterised by elemental analysis, IR and UV–Vis spectral studies and in addition mass spectroscopy has been also carried out for LH. The structures of 1 and 2 have been established by X-ray crystallography. Variable temperature magnetic susceptibility measurement studies of 1 indicate the χ M T values remain constant in the whole range of temperature 10 to 300K at a value close of 0.75cm3 Kmol−1, which is in good agreement with the one expected for two uncoupled copper(II) centers. [Copyright &y& Elsevier]

Two new pseudohalide bridged di- and poly-nuclear copper(II) complexes [Cu2(L)2(μ1,1-N3)2] (1), [Cu(L)(μ1,3-NCS)]n (2), [LH = C6H5C(O)NHN=C(CH3)C5H4N] have been synthesised and characterised by elemental analysis, IR and UV–Vis spectral studies. Structures of both the complexes have been established by X-ray crystallography. A tridentate hydrazone ligand (LH) obtained by the condensation of benzhydrazide and 2-acetylpyridine is used for the preparation of complexes 1 and 2. Variable temperature magnetic susceptibility measurement studies indicate there is a weak ferromagnetic interaction between the two copper(II) ions in 1 (J = +0.75 cm−1), while weak antiferromagnetic interaction is observed with J values −0.23 cm−1 for 2. [Copyright &y& Elsevier]

Abstract: The difference in coordination behavior of one new flexible polytopic ligand H 2 L (L =C16H14N6O2) has been examined with Cu(II) and Ni(II) acetate. It leads to the formation of a polynuclear pentacoordinated Cu(II) assemblage and a mononuclear four coordinated Ni(II) complex. Both the compounds are characterized spectroscopically and electrochemically. In the complexes 1 and 2 the ligand binds the metal centers in trans- and cis-orientation (exo and endo-fashion), respectively. The polynuclear copper complex exhibits strong antiferromagnetic behavior at low temperature with J =−327cm−1 and DFT calculation is also carried out for this complex. [Copyright &y& Elsevier]