THE HETERONUCLEAR CLUSTER CHEMISTRY OF THE GROUP IB METALS .19. X-RAYCRYSTAL-STRUCTURE AND DYNAMIC BEHAVIOR IN SOLUTION OF THE MIXED-METALCLUSTER (MU(3)-H)(3)(CO)(12))(2)(MU-PH(2)P(CH2)(2)PPH(2))] - AN INVESTIGATION OF THE EFFECT OF A BIDENTATE DIPHOSPHINE LIGAND LINKING 2 CLUSTER SUBUNITS

The structure of the mixed-metal cluster [{CuRu4(mu(3)-H)(3)(CO)(12)}( 2){mu-Ph(2)P (CH2)(2)PPh(2)}] 1 has been determined by a single-crysta l x-ray diffraction study, which shows that 1 is composed of two trigo nal bipyramidal CuRu4 subunits linked together by the bidentate diphos phine ligand Ph(2)P(CH2)(2)PPh(2). The copper atom in each CuRu4 subun it occupies an axial site and each copper atom is bonded to a phosphor us atom at opposite ends of the Ph(2)P(CH2)(2)PPh(2) ligand. A compari son of the equivalent metal-metal separations in the two subunits of 1 reveals that crystal packing farces cause differences of up to ca 0.1 18 Angstrom for the Cu-Ru distances and up to ca 0.132 Angstrom for th e Ru-Ru separations. The structure of 1 is also compared with that of the closely related analogous cluster [CuRu4(mu(3)-H)(3)(CO)(12)(PMePh (2))]. The C-13{H-1} NMR spectrum of 1 at -90 degrees C demonstrates t hat the whole of each {CuRu4(mu(3)-H)(3)(CO)(12)} subunit undergoes ra pid rotation around its Cu-P bond. The free energy of activation of th is fluxional process seems surprisingly low in view of the fact that t he CuRu4 subunits are fairly sterically demanding.