Specific features of the chemical structure of the oxo-complexes of d⁰ and d² metals with monodentate and polydentate ligands

The structure of the oxo-complexes of transition d⁰ and d² Group V–VII metals is discussed. Two types of distortion isomerism are considered: the trans-influence isomerism (the lengthening of the M=O multiple bond on passing from one isomer to another is accompanied by a shortening of the M–L_trans bond) and the multiple bond isomerism (the lengthening of the M=O bond is not accompanied by a shortening of the M–L_trans bond). The choice of the trans-partner out of the set of competing functional groups for the d⁰ metal is determined by the self-consistency principle, while for the d² metal the rule becomes more complex and the choice of the trans-partner of the oxo-ligand depends on the individual features of the trans-ligand (on the combination of its σ- and π-donor properties). It is shown in relation to the d⁰-MoO₂ and d²-ReO complexes with isotypical chelate O, N-donor ligands that the latter are coordinated to the metal in different ways.
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