Spin Crossover and Thermochromism in Iron(II) Complexes with 2,6-Bis(1H-imidazol-2-yl)-4-methoxypyridine

New iron(II) complexes with 2,6-bis(1H-imidazol-2-yl)-4-methoxypyridine (L) of the composition [FeL(2)]A(n)∙mH(2)O (A = SO(4)(2−), n = 1, m = 2 (I); A = ReO(4)(−), n = 2, m = 1 (II); A = Br(−), n = 2, m = 2 (III)) have been synthesized and investigated. To determine the coordination ability of the ligand, a single crystal of a copper(II) complex of the composition [CuLCl(2)] (IV) was obtained and studied by X-ray technique. Compounds I–III were studied using methods of X-ray phase analysis, electron (diffuse reflection spectra), infrared and Mössbauer spectroscopy, static magnetic susceptibility. The study of the µ(eff)(T) dependence showed that the (1)A(1) ↔ (5)T(2) spin crossover manifests itself in the compounds. The spin crossover is accompanied by thermochromism: there is a distinct color change orange ↔ red-violet.