MOLECULAR-STRUCTURE AND CRYSTAL-STRUCTURE GENERATION FOR [FE-3(CO)(12)]

The electronic structure of [Fe-3(CO)(12)] has been investigated by :m eans of extended-Huckel calculations and compared to that of [RU(3)(CO )(12)], showing that the bridged structure, observed in the solid stat e, arises because of electronic reasons, namely a weaker metal-metal r epulsion in the case of the lighter cluster. This is associated with t he bridge-formation process and becomes determining for the energetic balance in compounds of heavier metals. The possible existence of crys tal structures which are alternative to the observed disordered one kn own for [Fe-3(CO)(12)] has been explored by means of the atom-atom pai rwise potential-energy method. Alternative ordered molecular arrangeme nts have been generated and compared with the experimental crystal str ucture in terms of packing efficiency and cohesive energy.