Multiple Metal–Metal Bond or No Bond? The Electronic Structure of V₂O₂

Abstract

Detailed knowledge of the electronic structure of vanadium oxide clusters provides the basis for understanding and tuning their significant catalytic properties. However, already for the simple four-atom V O molecule, there are contradictory reports in the literature regarding the electronic ground state and a possible vanadium-vanadium bond. We herein show through a combination of experimental (matrix isolation) studies and theoretical results that there is a multiple vanadium-vanadium bond in this benchmark vanadium oxide molecule.

Metal Cluster Models for Heterogeneous Catalysis: A Matrix‐Isolation Perspective

“…V in the oxidation state II has a 3d shell occupied by 3 (unpaired) electrons. For V 2 O 2 , in contrast to Ni 2 O 2 , the MRCI calculations show that there is bonding between the V atoms in V 2 O 2 , the overall 6 3d electrons (3 electrons per atom) are distributed among three pairs of bonding and antibonding 3d orbitals, such that the occupation of the bonding orbitals is appreciably larger than that of the antibonding orbitals, yielding a bond order of 1.7 . Accordingly, for V 2 O 2 , there are no spin ladders in the lower‐lying energy regime.…”

“…For all transition metals (except Tc), metal oxide particles have been generated and spectroscopically characterized in inert gas matrices and reviewed by Gong et al in 2009 . The oxides were generally produced by laser ablation of metals, thermal evaporation of metals, or by laser ablation of metal oxides . The monoxides MO have been generated for all transition metals except for M=Re, Os, and Pd.…”

“…There are only a few examples for M 2 O clusters, Mn 2 O, Fe 2 O, Ir 2 O, Ag 2 O . Cyclic M 2 O 2 clusters have been observed for M=Sc, Y, Ti, Zr, Hf, V, Mn, Fe, Co, Ni, and Rh and tentatively for Cr, Ta, and W . Most of the clusters are likely to be formed by reaction of the metal dimers with O 2 .…”

“…Due to lack of information from experiments, both by matrix isolation as well as by gas‐phase studies, often information about the electronic structure of transition metal oxide clusters has to be drawn from quantum chemical calculations. For Ni 2 O 2 and V 2 O 2 , quantum chemical calculations by the method of multi‐reference configuration interaction (MRCI), based on orbitals from complete active space self‐consistent field calculations, yield information about the structure and the lower‐lying electronic terms . Ni in the oxidation state II has a 3d shell that is occupied by 8 electrons, thereof two unpaired electrons.…”

“…Reactions of metal clusters have been studied with O 2 , N 2 , CO, N 2 O and H 2 O . There are only a few examples for reactions of clusters with organic molecules …”