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-C-x-M] unit in a variety of homonuclear [{CP(CO)(2)M}(2)(mu-C-x)] (M = Cr, Fe+, x = 3; M = Mn, x = 3, 5, 7) and heteronuclear [{CP(CO)(2)M}(mu-C-x){Cp(CO)(2)M'}] (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 d" configurations and the metal coordination numbers; (iii) the chain length. The valence structure of the [M-C-x-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 d" configuration of the MLm(M'L-m') fragments and the number of p(pi) electrons of the 'linear' C-x unit. (C) 2002 Elsevier Science B.V. All rights reserved.