Carbon chain bridged metals: a theoretical approach. Odd chains

A theoretical investigation (DFT) allowed us to single out the most appropriate valence structure for the [MCxM′] unit in a variety of homonuclear [{Cp(CO)2M}2(μ-Cx)] (M=Cr, Fe+, x=3; M=Mn, x=3, 5, 7) and heteronuclear [{Cp(CO)2M}(μ-Cx){Cp(CO)2M′}] (M=Fe+, M′=Mn, x=3; M=Fe, M′=Cr, x=3, 5, 7) model compounds and to foresee it on the basis of the molecular parameters, such as (i) the nature of the metals and their oxidation states; (ii) the dn configurations and the metal co-ordination numbers; (iii) the chain length. The valence structure of the [MCxM′] unit is diagnostic of the metal-to-metal communication. A simple electron-counting scheme has been developed to predict the valence structure, based on the dn configuration of the MLm (M′L′m′) fragments and the number of pπ electrons of the ‘linear’ Cx unit.