COMPLEXES OF STRUCTURAL ANALOGS OF TERPYRIDYL WITH IRON AND ZINC - THE X-RAY CRYSTAL-STRUCTURE OF BIS[2,6-BIS(BENZIMIDAZOL-2-YL)PYRIDINE]IRON(II) TRIFLUOROMETHYLSULFONATE BIS-ETHANOL SOLVATE

Complexes of iron(II) and zinc(II) with a series of tridentate ligands of the type [2,6-bis(benz-X-azol-2-yl)pyridine] (X = imid, thi, ox) have been prepared. The crystal structure of [Fe(2,6-bis(benzimidazol-2-yl)pyridine)2](CF3SO3)2.2C2H5OH shows the iron(II) to be low spin with a meridional octahedral coordination by two tridentate ligands. Fe-57 Mossbauer spectra of the complexes [FeL2]2+ show strong dependence of ligand strength on the non-coordinated heteroatom, X, of the ligand : benzimidazole ligands give low spin complexes, benzoxazoles give high spin complexes and benzthiazoles show spin-crossover properties. Derivatization of the imidazole nitrogen has only a small effect on the ligand strength. The complexes [FeLX2] (X = anion) are all high spin. Partial dissociation is observed in solvents with a strong affinity for iron(II); the iron(II) complexes show metal-to-ligand charge transfer transitions whose intensity depends strongly on the spin state of the iron.