DYNAMICS AND MOLECULAR AGGREGATION IN CRYSTALLINE [(M(C5H5))(3)(MU(3)-ETA(2)ETA(2)ETA(2)-C(6)H(5)R)] [M=CO, R=CH(PH)ME, CH(2)CH(2)PH OR CHCHME, M=RH, R=H] CLUSTERS

The intermolecular aggregation in crystalline arene clusters of the ty pe [{M(C5H5)}(3)(mu(3)-eta 2:eta(2):eta(2)-C(6)H(5)R)] [M = Co, R = CH (Ph)Me, CH(2)CH(2)Ph or CHCHMe; M = Rh, R = H] has been investigated b y atom-atom packing potential-energy calculations and computer graphic s. The ease of reorientation of the arene fragments and of the cyclope ntadienyl ligands in the solid state has been investigated by calculat ing intramolecular and intermolecular potential-energy barriers. It ha s been shown that, except for the benzene ligand in [{Rh(C5H5)}(3)(mu( 3) eta-(2):eta(2):eta(2)-C6H6)], the facial arenes cannot undergo reor ientation in the solid state, whereas the reorientational motion of th e cyclopentadienyl ligands is under intramolecular control.