THE CRYSTAL-STRUCTURE OF CO6C(CO)12E2 (E=SE) AND ITS RELEVANCE TO THEVIBRATIONAL-SPECTRA OF THE SPECIES E=S, SE

Co6C(CO)12Se2 crystallizes in the monoclinic system, space group Cc wi th a = 16.365(4) angstrom, b = 9.429(2) angstrom, c = 17.479(5) angstr om, beta = 122.75(2)-degrees, Z = 4 and (Mo - K(alpha)) = 0.71070 angs trom. The final reliability indices are R = 0.051 and R(w) = 0.048 for 2081 observed reflections having F> 4.0sigma(F). The molecule consist s of a Co6 trigonal prism with the triangular faces capped by selenium atoms. Each cobalt is bonded to two terminal CO groups. A carbon atom is embedded at the centre of the Co6 prism. The Raman spectra of poly crystalline samples of this compound and of the sulphur analogue have been recorded. These, together with the corresponding infrared data, c an only be understood in terms of a dominant intermolecular coupling o n the nu(Co-E) modes (E = S, Se). The origin of this coupling is the c lose contact between neighbouring clusters in one distinct direction w hich gives rise to a chain of molecules in the crystal. The significan t effect of these oriented close contacts on the vibrational modes is demonstrated.