Investigation of the structure and reactivity of cobalt(III) carbonato complexes by using EHMO calculation

Abstract

Extended Hückel molecular orbital (EHMO) calculations on modified structures of [CoCO 3(NH 3) 4] + have been performed to investigate the influence of the strain caused by a chelated carbonato ligand on the complex structure and on the decarboxylation of carbonato cobalt(III) complexes with tetraamine ligands ([CoCO 3(N) 4] + type). It was suggested that the CO 3 2− chelation enlarges the NCoN angle (θ) trans to the OCoO angle to some extent and in the most stable structure the angle θ of [CoCO 3(NH 3) 4] + is about 94°, which is slightly larger than the octahedral angle (90°). The existence of d electrons in the d xy orbital seems to be a key point for controlling the NCoN angle in this type of complex. Furthermore, the difference in decarboxylation rate between trans-[CoCO 3(NH 3) 2en] + and trans-[CoCO 3(NH 3) 2tn] +, in which en and tn refer to ethylenediamine and trimethylenediamine, respectively, was examined on the basis of the calculated potential energies of the structure-modified [CoCO 3(NH 3) 4] + as a model compound.