STATIC AND DYNAMIC STRUCTURE OF RU3(CO)9(MU-3-ETA-2-ETA-2-ETA-2-C6H6) AT ROOM-TEMPERATURE AND 193-K

The solid-state structure of the cluster benzene complex Ru3(CO)9(mu-3-eta-2:eta-2:eta-2-C6H6) (1) has been determined at room temperature (RT) and 193 K (LT) by single-crystal X-ray diffractometry. 1 is monoclinic, space group P2(1), Z = 2, a = 9.027 (1) angstrom, b = 12.665 (2) angstrom, c = 9.049 (3) angstrom, beta = 118.15 (2)-degrees for RT and a = 8.985 (1) angstrom, b = 12.527 (2) angstrom, c = 9.011 (1) angstrom, beta = 118.217 (9)-degrees for LT. The benzene ligand shows a clear Kekule-type distortion: ''long'' and ''short'' C-C bonds [1.45 (1), 1.40 (2) and 1.45 (1), 1.41 (1) angstrom for RT and LT, respectively] alternate within the C6H6 fragment, the short bonds being involved in the coordination to the metal atoms. The H atoms bend away from the metal frame [average bending 21.1-degrees and 21.5-degrees for RT and LT, respectively]. Insights into the structure and bonding in 1 are obtained by semiempirical Fenske-Hall calculations. The differences in solid-state structures between 1 and the osmium analogue Os3(CO)9(mu-3-eta-2:eta-2:eta-2-C6H6) (2) are discussed in terms of intermolecular packing interactions. The molecular motion about the equilibrium position of 1 is studied by means of thermal motion analysis, while potential energy barrier calculations within the atom-atom approach are used to show that neither intramolecular nor intermolecular potential energy interactions oppose the reorientational motion of the benzene fragment in the solid state.