The electronic and geometric structures of the early transition metal cations MCH +, MCH 2+ and MCH 3+

Abstract

The electronic and geometric structures of several transition metal cations MCH 3 +, MCH 2 + and MCH +, where M is Sc, Ti, V and Cr, have been studied by ab initio methods (MCSCF and MCSCF+1+2). The calculated lengths of the metal-carbon single, double and triple bonds are somewhat insensitive to the metal, having average values of 2.19±0.06 Å, 1.96±0.04 Å and 1.76±0.01 Å respectively. This is to be contrasted with the calculated bond strengths which vary from 46-18 kcal mol −in the MCH 3 + series; from 68-39 kcal mol −1 in the MCH 2 + series; and from 96-71 kcal mol −1 in the MCH + series. In all cases the bond energy decreases as one goes from Sc + to Cr +. The trend in the calculated bond strengths/calculated bond lengths for this series of molecules is interesting in that the Sc compounds always have the larger bond length as well as the larger bond energy, a situation not normally found in molecules composed entirely of main group elements.