The Nature of the 'Mono' Ligand Complexes of Iron(II) with 1,10-Phenanthroline-2-carbothioamide and 2,2´-Bipyridine-6-carbothioamide. Low-Spin Iron(II) and High-Spin Iron(III) Systems

Abstract

Interaction of 2,2′-bipyridine-6-carbothioamide (bta) with iron(II) chloride leads to three different products: [Fe(bta)<sub>2</sub>]Cl<sub>2</sub>·H<sub>2</sub>O, [Fe(bta)<sub>2</sub>][FeCl<sub>4</sub>] and an apparently ‘mono’-ligand complex analogous to the previously described Fe(pta)Cl<sub>2</sub>·H<sub>2</sub>O (pta = 1,10-phenanthroline-2-carbothioamide). Electronic and Mössbauer spectroscopic data show that all three complexes of bta contain the [Fe(bta)<sub>2</sub>]<sup>2+</sup> cation. The Mössbauer spectra, together with the magnetic properties, indicate that the [Cl<sub>3</sub>Fe–O–FeCl<sub>3</sub>]<sup>2–</sup> ion is associated with the cation in the ‘mono’ complex which is formulated as [Fe(bta)<sub>2</sub>]<sub>2</sub>[Cl<sub>3</sub>Fe–O–FeCl<sub>3</sub>]Cl<sub>2</sub>·3H<sub>2</sub>O. The unusual temperature dependence of the Mössbauer spectrum, and the magnetism of this complex, arises from the presence of different iron sites, one being low-spin iron(II) and the other high-spin iron(III). Two of the latter are antiferromagnetically coupled in the oxobridged anion. 2,2′-Bipyridine-6-carboxamide (bca) yields an iron(II) mono-ligand derivative, Fe(bca)Cl<sub>2</sub>·H<sub>2</sub>O, which is a simple high-spin paramagnet.