High nuclearity carbonyl clusters of rhodium. Part 3. Crystal and molecular structure of hexadeca-µ-carbonyl-enneacarbonyl-polyhedro-tetradecarhodate(4–) in its tetraethylammonium salt

Abstract

The title compound, [NEt4]4[Rh14(CO)25], crystallises in the tetragonal space group P4/ncc, with unit-cell dimensions a= l7.060(3), c= 27.220(6)A, and Z= 4. The structure has been solved by Patterson and Fourier methods from X-ray single-crystal counter data and refined by least-squares methods to R= 0.046 for 1 224 significant reflections. The [Rh14(CO)25]4– anion contains a metal-atom cluster which can be described as a distorted fragment of a body-centred cubic lattice, of C4v idealized symmetry, with one interstitial metal atom which exhibits eight short metal–metal bonds (mean 2.638 A), four longer contacts (3.076 A), and one very long interaction [3.372(4)A] with the capping atom on the four-fold axis. The Rh–Rh surface interactions are very scattered, ranging from 2.724(2) to 3.325(2)A. There are nine terminally bound carbonyls (mean Rh–C and C–O, 1.80 and 1.17 A respectively) and 16 edge-bridging groups. Of these, 12 are symmetric (mean Rh–C and C–O, 1.99 and 1.19 A) and four, on the Rh(3)–Rh(5) edges, are markedly asymmetric [Rh(3)–C(6) 1.91(2) and Rh(5)–C(6) 2.33(2)A].