Iron complexes of pyridylimidazole derivatives

Complexes of iron(II) with 2-(2-pyridyl)benzimidazole (pbi) and 2-(6- methyl-2-pyridyl)benzimidazole (mpbi) have been characterized. [Fe(pbi)3] [BF4]2 undergoes a temperature-induced spin transition the course of which is determined by the extent of hydration. [Fe(mpbi)3] [ClO4]2 is high-spin and the differences in the properties of the two complexes are correlated with electronic spectral data. [Fe(pbi)2(CN)2] is low-spin. Iron(III) complexes of deprotonated pbi and 2-(2- pyridyl)imidazole (pyim), [Fe(pbi-H)3] and [Fe(pyim-H)3], result when the cationic iron(II) complexes are treated with base. Magnetic and Mossbauer effect data show that these complexes, which display strong π → t2 charge-transfer absorption, are low-spin.