Spin Crossover in Iron(II) Complexes with 2,6-bis(1H-imidazol-2-yl)Pyridines. Review

This review presents the results of a cycle of works on the synthesis and analysis of iron(II) coordination compounds with polynitrogeneous heterocyclic ligands - 2,6-bis(1H-imidazol-2-yl)pyridine derivatives. Ligands of this class are coordinated to the Fe(II) ion in the tridentate cyclic mode via two nitrogen atoms of imidazole rings and the pyridine nitrogen atom with the formation of [ML2]2+ cation complexes (FeN6 coordination core). The study of the temperature dependence of magnetic susceptibility shows that the majority of complexes obtained exhibit spin crossover 1A1 ↔ 5T2. In a number of compounds, a change in spin multiplicity is accompanied by thermochromism. The factors affecting the spin crossover temperature and character are discussed.