Theoretical studies of xanthates, dixanthogen, metal xanthates, and related compounds

Ab initio molecular orbital techniques have been used to calculate a number of properties of the xanthate anion, (OH)CS^-1₂, and related molecules, to assist in the characterization of xanthate collector species formed on sulfide mineral surfaces during froth flotation. Calculated geometries for xanthate and dithiocarbamate ions and for dixanthogen are in good agreement with experiment. For metal xanthate complexes, calculated bond lengths and angles within the xanthate moiety agree well with experiment and help us to understand observed changes in C-S and C-O stretching frequencies upon complexation. Calculated energies of frontier molecular orbitals are consistent with available experimental photoemission, electron transmission, and X-ray absorption spectral data. The highest energy occupied molecular orbitals are of S 3p nonbonding and II-bonding types, whereas the lowest energy empty orbitals are of C-S II* and C-S σ* types (or S-S σ* type in dixanthogen). X-ray absorption spectral energies are calculated at both C and S edges for many of the compounds studied. ¹³C NMR may also prove valuable for species characterization in these systems, and our calculations show that at least the nearest-neighbor geometry about C can be determined from the ¹³C NMR shielding tensor. Preliminary studies also indicate that trends in UV spectral energies for different xanthate complexes can be calculated semiquantitatively. The molecular orbital calculations facilitate the interpretation of spectral data in terms of the geometric and electronic structures of the species involved.