Structural and infrared spectroscopic characterization of Co6C(CO)12S2: a high-nuclearity carbido carbonyl cluster spontaneously formed from dicobalt octacarbonyl and carbon disulphide

Abstract

Co6C(CO)12S2 (I) has been isolated in crystalline form from the mixture of more than a dozen of carbonyl products formed when Co2(CO)8 reacts at room temperature with CS2. Crystals of I are monoclinic with space group Cc, and lattice constants a  16.250(5), b  9.413(4), c  16.036(5) Å, β  116.77(4)°. Structure refinement gave R  0.034 for 1974 reflections. The CCo6S2 core of the molecule possesses idealized D3h geometry. It is composed of a Co6 trigonal prism, enclosing a C atom in the centre, and the triangular faces are capped symmetrically by the two S atoms. The core contains two sorts od CoCo distances: short one (2.432 Å) along the triangular edges, and long ones (2.669 Å) along the lateral edges. The average CoC distance is 1.94 Å, and the average CoS distance 2.192 Å. 13CO-enriched samples were prepared photochemically and their IR spectra used in the assignment of the CO stretching frequencies. The CO stretching force constant was calculated to be 1670(2) Nm-1. By the use of 13CS2, I has also been obtained in a selectively carbido-13C-labelled form. The vibrational frequencies of the carbide atom were observed, and that at 819 cm-1 (13C: 790 cm-1) assigned to the species , and that at 548 cm-1 (13C: 535.5 cm-1) to species E′. For the Co-C(carbide) force constant a value of 155 Nm-1 was calculated. The cobalt—sulphur stretching frequencies were found at 309 cm-1 () and 239 cm-1 (E′). The CoS stretching force constant, 78 Nm-1, is considerably lower than that obtained for SCo3-(CO)9, viz. 112 Nm-1.