Identification of Se Substitution Location in Ge4S9Se4− Clusters Using Ab Initio Vibrational Calculations and FT-Raman Spectroscopy

Optimization of the synthesis of mixed chalcogenide Ge4S10-xSex4- adamantanoid clusters is complicated by the nonstoichiometric one-step hydrothermal method used. The products are often amorphous and before purifn., contain significant amts. of unreacted Ge, S/Se and potentially various side products. Rapid and easy identification of the clusters in the product is required to aid the synthetic efforts. However, functional group anal. using FT-IR and FT-Raman spectroscopy was not successful because of the high degree of chem. similarity for various types of clusters and side products. A successful method was found by using ab initio vibrational calcns. to fingerprint the FT-Raman spectra. Using these calcns., a product composed of Ge4S9Se14- with the Se in one of the terminal positions was identified. The structure was subsequently confirmed using single crystal x-ray diffraction on a crystal from an optimized prepn