The Formation Constants and Configurations of the Complexes of Cr(II), Mn(II), Fe(II), Co(II), Cu(II), and Zn(II) with 2,2′-Bipyridine and of Co(II) with 2,2′:6′,2″-Terpyridine in Hexamethylphosphoric Triamide

The absorption spectra and the first formation constants, K19 of complexes [M(bpy)]2+ (M(II)=Cr(II), Mn(II), Fe(II), Co(II), Cu(II), and Zn(II), bpy=2,2′-bipyridine) were determined spectrophotometrically in hexamethylphosphoric triamide(HMPA). The values of log K1 obtained were 4.61±0.02, 3.10±0.12, 4.82±0.04, 5.84±0.07, 7.33±0.02, and 1.77±0.07 for respective metal ions. The configurations of complexes [M(bpy)]2+ were discussed on the basis of these data. The K1 values of [Cr(bpy)]2+, [Mn(bpy)]2+, [Fe(bpy)]2+, and [Co(bpy)]2+ in HMPA are slightly larger than those in H2O, indicating that their configurations are tetrahedral, whereas the value of [Cu(bpy)]2+ in HMPA is slightly smaller than that in H2O, indicating that its configuration in HMPA is either square planar or tetragonal. It seems that [Zn(bpy)]2+ is octahedral in HMPA, because its K1 value is smaller about three orders of magnitude than that in H2O. In addition, the second formation constant, K2, of complex [Co(bpy)2]2+, and the first and sec...