INTRAMOLECULAR AND INTERMOLECULAR BONDING IN RU-3(CO)(12), RU-3(CO)(9)(MU(3)ETA(2)ETA(2)-C6H6), AND RU-3(CO)(6)(MU-CO)(3)(MU(3)-S3C3H6)

The relationship between molecular and crystal structures of Ru-3(CO)(12) (1), of the benzene derivative Ru-3(CO)(9)(mu(3)-eta(2):eta(2):eta(2)-C6H6) (2), and of the 1,3,5-trithiacyclohexane derivative Ru-3-(CO)(6)(mu-CO)(3)(mu(3)-S3C3H6) (3) has been investigated by a combined use of extended Huckel molecular orbital calculations, empirical atom-atom pairwise packing potential energy calculations and computer graphics. The presence of CO bridges has been related to the capabilities of the ''facial'' ligand (C6H6 and S3C3H6) as a pi-acceptor or a pi-donor. Bridging carbonyl groups in the equatorial plane are more effective in competing with the facial ligand for back-donation, and thus they stabilize pi-donors. In Ru-3(CO)(12), three carbonyls replace C6H6 as pi-acceptors. Hydrogen-bonding networks of the C-H---O type involving the carbonyl oxygen atoms have been detected in crystalline 2 and 3. Bridging CO's are observed to form preferential interactions with respect to terminal ligands.