Crystal and molecular structure of the anion [Rh7(CO)16]3– in its tetramethylammonium salt

Abstract

The structure of [NMe₄]₃[Rh₇(CO)₁₆] has been reinvestigated by diffractometric X-ray analysis. The crystals are orthorhombic, space group Pnma, with a= 24.537(5), b= 13.933(3), c= 12.218(4)Å, and Z= 4. The refinements were carried out by full-matrix least squares, on the basis of 2 411 independent significant reflections, to a final R value of 0.026. The Rh₇ cluster is a monocapped octahedron and the ligand geometry exhibits some distortions with respect to the ideal C_3v symmetry. The Rh–Rh bond lengths are in the range 2.711(1)–2.880(1)Å. The capping metal is bound to the octahedron with one longer and two shorter metal–metal bonds (difference of 0.14 Å). The three µ₃-CO ligands show asymmetric bonding, in agreement with the results of ¹³C n.m.r. investigations.