A Theoretical Study of 51V Electric Field Gradient Tensors in Pyrovanadates and Metavanadates

Abstract

A computational study of the 51V electric field gradient (EFG) tensors in pyrovanadates, α-Zn2V2O7, Cd2V2O7, β-Mg2V2O7 and BaCaV2O7, and the metavanadates, LiVO3, α-NaVO3, KVO3, ZnV2O6 and MgV2O6, is presented. Restricted Hartree–Fock and hybrid density functional theory calculations have been used to investigate the effects of the size of vanadium-oxygen clusters, basis set size, proton-termination and embedded cluster techniques on the accuracy of the calculated EFG tensors. Good agreement between theory and experiment is obtained for most of the vanadates. A sound methodology is suggested for calculating the EFG tensor in pyrovanadates which contain isolated V2O7 4− clusters. For metavanadates, the charges of the bridging oxygen atoms can be differentiated from those of terminal oxygen atoms by terminating the former with hydrogen atoms, and embedded cluster molecular orbital calculations are useful in accounting for the long-range electrostatic interactions which influence the EFG tensor components. EFG tensor orientations vary for different pyrovanadate structural types, and individual components are confined by symmetry elements in the metavanadates. A preliminary comparison is made between 51V EFG tensors calculated with ab initio and plane wave methods. Theoretical EFG tensor components and orientations, in combination with experimental 51V solid-state nuclear magnetic resonance data, are demonstrated to be useful tools for prediction of molecular structure.