Crystal structure of Co4(CO)10S2 and Co4(CO)10Se2; v(CO) vibrations of a model cluster molecule: Co4(CO)10S2

Abstract

The crystal structure of Co4(CO)10S2 has been redetermined and that of Co4(CO)10Se2 obtained by X-ray analysis. The compounds are monoclinic and isomorphous, space groupP21/n,Z=2, with (S compound)a=10.42(2)A,b=6.794(1)A,c=12.421(2)A,β=97.27(1) and (Se compound)a=10.110(2)A,b=6.747(2)A,c=12.592(4)A,β=96.37(2); finalR(S)=0.029,R w =0.032 for 1414 reflections and finalR (Se)=0.052,R w =0.054 for 1264 reflections. The molecules, which lie on a crystallographic center of symmetry, consist of a rectangle with Co atoms at the corners, each face of the rectangle being capped by a chalcogen atom. Each Co atom is bonded to two terminal CO groups; there are two bridging CO groups, one on each member of a pair of opposite sides of the rectangle. The vibrational spectra of the sulfur compound are considered in detail. A study of the crystal structure, and recognition of an approximate spectroscopic space group, are shown to be essential for an understanding of thev(CO) infrared spectrum of polycrystalline Co4(CO)10S2. In this molecule, intramolecular vibrational coupling in the crystal leads to extensive modifications of the infrared-activev(CO) molecular coordinates.