Theoretical analysis of P-31 NMR chemical shifts in vanadium phosphorus oxides

Our goal is to develop a theoretical methodology for the analysis of P-31 N MR spectra in vanadium phosphorus oxide (VPO) systems important in heteroge neous catalysis. Within the framework of density functional theory, we inve stigate the shielding of the phosphorus nucleus in a series of related comp ounds. The importance of the basis set is pointed out by looking at the inf luence of polarization functions on the chemical shift of phosphorus in H3P O4. Using the B3LYP functional, very good agreement with the experimental i sotropic shielding is reached for the binuclear species [(VO2)(2)(HPO4)(2,2 '-bipy)(2)] constructed from two edge-sharing dioxovanadium(V) octahedra. A s a prime motivation, a parent vanadium(V) model of pyrophosphate catalyst is finally studied to compare P-31 numerical calculations with experiment. Satisfactory shielding constants are obtained, making phosphorus a probe to investigate the transition metal environment.