Structural and Mossbauer spectral studies of iron(II) complexes of thiazole-containing bidentates

Comparison of the Mossbauer 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'-bithi azole (4bt) and 2,2'-bithiazole (2bt) shows a progressive reduction in the pi-acceptor character of the ligand with increase in the number of thiazole rings, the effect being greater for the 4-thiazolyl derivatives. The struc ture of [Fe(4pyt)(3)](2+) is remarkably similar to that of [Fe(bpy)(3)](2+) with an average Fe-N distance of 1.96 Angstrom. Attempts to characterize s tructurally [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 ha s the trans structure, the average Fe-N distance is 2.21 Angstrom and the F e-O distance is 2.08 Angstrom. Mossbauer spectral data indicate a quintet g round state for this species. [Fe(4pyt)(3)] [BF4](2). H2O: monoclinic, spac e group P2(1)/c, a 10.213(7), b 13.436(6), c 23.12(1) Angstrom, beta 109.65 (3)degrees, Z 4. [Fe(2bt)(2)(H2O)(2)] [ClO4](2).(2bt)(4): triclinic, space group P (1) over bar, a 10.822(7), b 11.451(8), c 12.945(8) Angstrom, 70.31 (5), beta 69.92(5), gamma 63.32(6)degrees, Z 1.