Abstract Co 6C(CO) 12Se 2 crystallizes in the monoclinic system, space group Cc with a = 16.365(4) Å, b = 9.429(2) Å, c = 17.479(5) Å, β = 122.75(2)°, Z = 4 and (Mo — K a ) = 0.71070 Å. The final reliability indices are R = 0.051 and R W = 0.048 for 2081 observed reflections having F > 4.0σ( F). The molecule consists of a Co 6 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 Co 6 prism. The Raman spectra of polycrystalline samples of this compound and of the sulphur analogue have been recorded. These, together with the corresponding infrared data, can only be understood in terms of a dominant intermolecular coupling on the ν(Co—E) modes (E = S, Se). The origin of this coupling is the close contact between neighbouring clusters in one distinct direction which gives rise to a chain of molecules in the crystal. The significant effect of these oriented close contacts on the vibrational modes is demonstrated.