Investigations on the spin-crossover complex [Fe(bzimpy)2](ClO4)2 and its Mn2+, Co2+, Ni2+ and Zn2+ analogues

Summary A series of transition metal complexes [M(bzimpy)₂](ClO₄)₂ (M=Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺;bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) was synthesized and characterized by elemental analysis, UV-Vis and far-IR spectroscopy. The electronic spectra of [Ni(bzimpy)₂](ClO₄)₂ in solution and solid state reveal a ligand field splitting parameter ₀ in the range of 11470 cm^–1 to 11840 cm^–1. The simultaneous existence of two species with distinct spin state is found for [Fe(bzimpy)₂](ClO₄)₂ by means of variable temperature far-IR measurements. Assignments of the observed far-IR bands are given on the basis of the investigations of the variation of the metal ion in [M(bzimpy)₂](ClO₄)₂.This paper is dedicated to Professor Ulrich Wannagat on the occasion of his 70^th birthday with warmest personal wishes.