Spectroscopic Study of Cobalt(III) β-Aminoethylate Complexes

Abstract

Aqueous solutions of fac- and mer-isomers of [Co(NH2C2H4O)3] · 3H2O were investigated by the 13C NMR spectroscopy method. The spectrum of the fac-isomer exhibited only two signals with δ 47.08 (CN) and 63.87 (CO) ppm, which points to a high symmetry of the compound and to the presence of a complex in the solution (unlike the crystal) with one type of polyhedron (probably, of a trigonal-prismatic type). The spectrum of the mer-isomer solution is more complicated: the CNand COsignals are split into three components with δ 48.81, 47.18, and 46.11 ppm and 64.70, 64.45, and 64.23 ppm, respectively. This fact confirms deterioration of the symmetry of the coordination polyhedron due to nonequivalence of β-aminoethylate ions bound to the central atom. The successive protonation of the complexes does not affect either the symmetry of the coordination sphere of the fac-isomer or the asymmetry of the coordination sphere of the mer-isomer. The 1H, 13C, 59Co NMR and IR spectroscopy data made it possible to suggest that both fac-[Co(NH2C2H4O)3] fragments in the binuclear fac-[H3(Co(NH2C2H4O)3)2](NO3)3complex are linked together by three symmetrical hydrogen bridges.