NATURE AND STRENGTH OF METAL-CHALCOGEN MULTIPLE BONDS IN HIGH OXIDATION-STATE COMPLEXES

Density functional theory calculations have been carried out on the tr igonal complexes OsO3E and MCl3E (M = V, Ta) and the square pyramidal systems MCl4E (M = Cr, Mo, W, Re) for E = O, S, Se, and Te as well as (C5H5)ReO3. All complexes were fully optimized, and the calculated geo metrical parameters are in reasonable agreement with gas-phase electro n diffraction data where available. The calculated M-E bond energies d ecrease from oxygen to tellurium, from bottom to top in a metal triad, and from left to right in a transition series. The trend setting fact or is the donation from the d(sigma) metal orbital to the p(sigma) acc eptor orbital on the chalcogen atom. The contribution from the chalcog en to metal pi back-donation has a maximum for sulfur and selenium. Ho wever in relative terms, the contribution from the pi back-donation to the total M-E bond energy increases from oxygen to tellurium. Compari sons are made to previous calculations and experimental data on M-E bo nd strengths.