Spontaneous sulfur dioxide activation by Group V metal (V, Nb, Ta) atoms in excess argon at cryogenic temperatures

Abstract

Reactions of laser-ablated V, Nb and Ta atoms with SO₂ in excess argon during condensation gave new absorptions in the MO stretching region, which were assigned to metal sulfide oxides SMO₂ and anions SMO₂⁻ (M = V, Nb, Ta). The metal oxide complex OV(η²-SO) was also identified through the VO and the characteristic side-on coordinated S–O stretching modes. The assignments of major vibrational modes were confirmed by appropriate S¹⁸O₂ and ³⁴SO₂ isotopic shifts, and density functional frequency calculations. DFT calculations were employed to study the behavior of reactions of Group V bare metal atoms with SO₂, and a representative profile was derived which not only showed the preferred coordinating fashion of metal atoms but also tracked the path of S–O bond activation. The η²-O,O′ bridge coordinated complexes are preferred with energy decreases of ca. 50 kcal mol⁻¹ for all three metals, which facilitate the activation of two S–O bonds in succession and finally direct the reaction to the most stable molecules SMO₂ (M = V, Nb, Ta) along the potential energy surface (PES). Finally the SMO₂ molecules capture electrons to give anions SMO₂⁻ with about 3.6 eV electron affinities based on DFT calculations.