Photo-oxidation of [V(CO)6] in low-temperature matrices containing O2: formation of a novel superoxovanadium species

Abstract

Irradiation of [V(CO)₆] in low-temperature matrices containing O₂ led to the formation of a novel superoxovanadium species A alongside free CO₂. Isotopic substitution experiments involving ¹⁸O and comparison of the IR spectrum of A with that of the known oxovanadium species [VO₂Cl₂]^– and [VO₂F₂]^– indicate that A is the superoxide [VO₂(σ-O₂)]. The ¹⁶O–¹⁸O isotopic shift for ν_asym(VO₂) of A gives an upper limit of ca. 115° for the OVO bond angle of the dioxo moiety of A; the intensity ratio of the bands arising from ν_sym and ν_asym(VO₂) suggests a value of 108 ± 5° for this angle. The reaction is initiated by loss of CO from [V(CO)₆] to form [V(CO)₅]; a step which is shown to be photochromic, and proceeds via at least one oxocarbonyl intermediate.