Structural and Mossbauer Spectral Studies of Iron(II) Complexes of Thiazole-Containing Bidentates

Abstract

Comparison of the Mössbauer spectral data for low-spin tris(ligand) iron(II) complexes of the series of bidentate N–N ligands 2,2′-bipyridine (bpy), 4-(pyridin-2-yl)thiazole (4pyt), 2-(pyridin-2-yl)thiazole (2pyt), 4,4′-bithiazole (4bt) and 2,2′-bithiazole (2bt) shows a progressive reduction in the p-acceptor character of the ligand with increase in the number of thiazole rings, the effect being greater for the 4-thiazolyl derivatives. The structure of [Fe(4pyt)₃]²⁺ is remarkably similar to that of [Fe(bpy)₃]²⁺ with an average Fe–N distance of 1.96 Å. Attempts to characterize structurally [Fe(2bt)₃]²⁺ were not successful and led to crystallization of [Fe(2bt)₂(H₂O)₂] [ClO₄]_2·(2bt)₄. In the complex cation, which has the trans structure, the average Fe–N distance is 2.21 Å and the Fe–O distance is 2.08 Å. Mössbauer spectral data indicate a quintet ground state for this species. [Fe(4pyt)₃] [BF₄]_2·H₂O: monoclinic, space group P2₁/c, a 10.213(7), b 13.436(6), c 23.12(1) Å, b 109.65(3)˚, Z 4. [Fe(2bt)₂(H₂O)₂] [ClO₄]_2·(2bt)_4: triclinic, space group P–1, a 10.822(7), b 11.451(8), c 12.945(8) Å, a 70.31(5), b 69.92(5), g 63.32(6)˚, Z 1.