High nuclearity carbonyl clusters of rhodium. Synthesis and crystal structure of (NMe4)3[Rh14H(CO)25] \ub7 Me2CO

The compound (NMe4)3[Rh14H(CO)25] \ub7 Me2CO has been obtained by treatment of (NMe4)4[Rh14(CO)25] with acids. The (NMe4)+ salt of the trianion, containing solvated acetone molecules, crystallizes in the orthorhombic Pmcn space group (non-standard setting of Pnma, No. 62), with a 16.436(2), b 17.655(4), c 21.490(4) \uc5 and Z = 4. The structure was refined by full-matrix least-squares, on the basis of 3472 significant unique reflections, to a final R value of 0.056. The anion shows a structure related to that of the parent [Rh14(CO)25]4-, which is a distorted fragment of body-centered cubic packing with C4\u3c5 symmetry. However, the insertion of the hydride ligand in an interstitial position, confirmed also by NMR studies, causes significant changes both in the metallic skeleton and in the CO stereochemistry, reducing the overall symmetry to Cs. The RhRh distances are scattered. The central metal exhibits 8 short (mean 2.657 \uc5), two normal (2.878(1) \uc5 and three very long (mean 3.258 \uc5) contacts with the surface metals. The RhRh surface interactions range from 2.692(1) to 3.356(2) \uc5. The metal atom polyhedron can be described as intermediate between a body-centered cubic and a closest-packed entity. The carbonyl ligands are bound 10 terminally (mean RhC and CO 1.86 and 1.15 \uc5), 13 almost symmetric double-bridging (mean RhC and CO 2.01 and 1.17 \uc5), and two markedly asymmetric double-bridging (short RhC 1.89(2), long RhC 2.41(2) and CO 1.16(2) \uc5). The structure is compared with those of related high-nuclearity rhodium clusters. \ua9 1989