Electronic Structure of and of Related Early-Transition-Metal Arene Clusters

The electronic structure of the recently synthesized trimetal cluster ion has been studied (by using its Cp model) theoretically with both the extended Huckel and the SCF method. Both independent computational schemes agree in their bonding description of the highly symmetric cluster ion symmetry), yielding four lowest lying metal-derived levels belonging to the symmetries le’, and 2e’. These MOs are Filled with four valence electrons in the case of the Re₃ cluster ion, resulting in a triplet ground state, at variance with the reported interpretation of NMR data, which indicate diamagnetism. The same MO sequence is found by EH calculations and is used to rationalize the electronic structure of the related early-transition-metal clusters of the general type (M = Nb, Ta, Ti, Zr; X = Cl, Br; n = 1, 2; C₆Me₆ = hexamethylbenzene). The occupation pattern of the four relevant levels in all these clusters varies between five and eight electrons and correlates well with the available information on structure, bonding, and electrochemical behavior of these compounds.