Structural variability in transition metal oxide clusters: gas phase vibrational spectroscopy of V3O6–8+

Abstract

We present gas phase vibrational spectra of the trinuclear vanadium oxide cations V₃O₆⁺·He_1–4, V₃O₇⁺·Ar_0,1, and V₃O₈⁺·Ar_0,2 between 350 and 1200 cm⁻¹. Cluster structures are assigned based on a comparison of the experimental and simulated IR spectra. The latter are derived from B3LYP/TZVP calculations on energetically low-lying isomers identified in a rigorous search of the respective configurational space, using higher level calculations when necessary. V₃O₇⁺ has a cage-like structure of C_3v symmetry. Removal or addition of an O-atom results in a substantial increase in the number of energetically low-lying structural isomers. V₃O₈⁺ also exhibits the cage motif, but with an O₂ unit replacing one of the vanadyl oxygen atoms. A chain isomer is found to be most stable for V₃O₆⁺. The binding of the rare gas atoms to V₃O_6–8⁺ clusters is found to be strong, up to 55 kJ/mol for Ar, and markedly isomer-dependent, resulting in two interesting effects. First, for V₃O₇⁺·Ar and V₃O₈⁺·Ar an energetic reordering of the isomers compared to the bare ion is observed, making the ring motif the most stable one. Second, different isomers bind different number of rare gas atoms. We demonstrate how both effects can be exploited to isolate and assign the contributions from multiple isomers to the vibrational spectrum. The present results exemplify the structural variability of vanadium oxide clusters, in particular, the sensitivity of their structure on small perturbations in their environment.