INTRAMOLECULAR AND INTERMOLECULAR BONDING IN BENZENE CLUSTER ISOMERS

The bonding in the prototypical high-nuclearity arene cluster complexe s Ru5C(CO)12(C6H6) and Ru6C(CO)11-(C6H6)2 has been investigated using extended Huckel calculations. The relative stability of the known isom eric pairs Ru5C(CO)12(eta6-C6H6) and RusC(CO)12(mu3-eta2:eta2:eta2-C6H 6), Ru6C(CO)11(eta6-C6H6)2 and Ru6C(CO)11(eta6-C6H6)-(mu3-eta2:eta2:et a2-C6H6) has been related to the chemically characterized interconvers ion process occurring in solution. Attention has been focused on the r elationship between the apical (eta6) and facial (mu3-eta2:eta2:eta2) bonding modes of benzene with the central cluster unit. The calculatio ns lead to the conclusion that the apical isomers are the more stable, although the local benzene-ruthenium interaction is stronger in the f acial isomers. The molecular organization in the respective crystal st ructures as well as the relative cohesion of the solid materials has b een investigated by empirical packing potential energy calculations. T he relationship between stability of the individual arene cluster mole cules and that of the same molecules in the solid state has been addre ssed in terms of the relative crystal cohesion. Hydrogen bonds of the C-H..O-C type have been detected in crystals of the apical isomers. In crystalline trans-Ru6C(CO)11(eta6-C6H6)2 molecular piles are formed b y molecules joined by direct benzene-benzene interactions; a similar p acking motif is also present in crystalline Ru6C(CO)11(eta6-C6H6)(mu3- eta2:eta2:eta2-C6H6).