The mechanisms of substitution reactions in octahedral complexes from the point of view of ligand field theory

Abstract

Two possible mechanisms for substitution reactions in octahedral complexes, ML6, are discussed in terms of molecular orbital theory. Jorgensen's model with angular parameters is used to calculate the change in activation energy on forming complexes of the type ML5 (D3h symmetry), ML5 (C4v symmetry), and ML7 D5h symmetry). Analysis of the quantities obtained (Table 4) shows that high spin ML6 octahedral complexes of metals with d3 or d8 electronic configurations, and low spin complexes with d6 electronic configurations are particularly stable. An SN1 mechanism is, apparently, characteristic for complexes of metals with d1 or d2 electronic configurations. The formation of π bonds facilitates the course of substitution reactions in octahedral complexes. The results we have obtained explain the available experimental material and permit us to make some predictions.