Cis,trans,cis or All-cis Geometry in d⁰ Octahedral Dioxo Complexes. An IMOMM Study of the Role of Steric Effects

The relative stabilities of two different isomers of d0 MoO2Cl2L2 species are examined for two different complexes with the help of the integrated molecular orbital molecular mechanics method IMOMM. The experimentally reported preference of the MoO2Cl2(N,N,N,'N'-tetramethylethylenediamine) complex for the all-cis arrangement and that of the MoO2Cl2(N,N'-di-terf-butyl-l,4-diaza-l,3-butadiene) complex for the cis,trans,cis arrangement are properly reproduced. The inversion of relative stabilities is shown to be associated to the balance between electronic and steric contributions, the former favoring the cis,trans,cis arrangement and the latter stabilizing the all-cis form.