A novel metal cluster in the tetramethylammonium salt of the dioctahedral triacontacarbonyl dodecarhodate dianion, [Rh 12(CO) 30] 2−

Abstract

The crystal and molecular structure of the tetramethylammonium salt of the triacontacarbonyldodecarhodate dianion [N(CH 3) 4] 2[Rh 12(CO) 30] has been determined from three-dimensional X-Ray data collected by counter methods. The structure has been refined by least squares on 1800 F o's down to an R factor of 0.05. This salt crystallizes in the monoclinic space group P2 1/ c ( C 5 2h) with the following cell parameters: a = 9.491(5) Å, b = 17.185(7) Å, c = 17.756(7) Å, β = 96°57'(15'), Z = 2. The structure is composed of anionic and cationic layers. The anion is a centrosymmetric dimer of the [Rh 6(CO) 15] − unit. The catenation between the symmetry related sub-units takes place by a metalmetal bond and two CO groups bridged over it. The coordination pattern around the rhodium atoms is very similar to that found in the neutral molecule Rh 6(CO) 16 with the exception of the catenating Rh atoms which display nine-fold coordination. The overall symmetry of the anion is D 2h. The metal cluster exhibits a range of RhRh distances from 2.68 Å to 2.85 Å. The independent CO groups fall into 3 classes: 10 are linearly bonded, 4 are triply asymmetrically bridged on alternating octahedral faces and 1 is connecting the two octahedral sub-units through a symmetric double bridge.