[Vibrational spectroscopic investigation of a series of heterometallic cubane-like M'-Mo (W) cluster compounds].

By combining the results of IR spectroscopic experiments with the molecular structures, the main stretching vibrations of a series of the heterometallic tetranuclear cluster compounds with [M3YS3M'] cluster core (M = Mo, W; Y = O, S; M' = Cu, Sn, Pb, Sb, Bi) have been assigned. The characteristic features and the bonding situations of the five configuration types are discussed. It is shown from the IR and Raman spectra that when M' is a transition metal such as Cu, the nu M's frequency of the [M3YS3M'] core has a value comparable to that of corresponding M'-S covalent bond thus indicating a close combination of M' with [M3YS3]. Whereas when M' is a main group metal, the nu M'-s vibration is always observed in a lower region than of the M'-S covalent bond because of a loose combination of M' with[M3YS3]. However, remarkable enhancement of M-M band strength due to the addition of M' is demonstrated by Raman spectra. Some comments for the M-M vibration of various structures of these compounds are also described.