Group VIA Donor Ligands

Group VIA Donor Ligands. The structure of the diamagnetic compound, [FeCo2(CO)gS] has been determined and, when compared with [C03-(CO)gS], it provides direct evidence that the unpaired electron in the latter occupies an MO that is strongly antibonding with respect to the cobalt atomic 

measurements and X-ray studies show that the extra electron in the tricobalt compound occupies an antibonding orbital made up primarily of a combination of two cobalt 3d orbitals localized in the plane of the three cobalt atoms. Replacement of one Co by Fe again leads to a decrease in the metal-metal bond lengths [0.039 A (av)]. The effect is therefore not so marked as with the sulphur analogues and the effect of replacing sulphur by selenium in [C03-(CO)gS] is to decrease the metal-metal distances by 0.021 The relevant data for the three compounds are given below  

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