Fine Hierarchy of the V–O Bonds by Advanced Solid State NMR: Novel Pb4(VO2)(PO4)3 Structure as a Textbook Case

We report here a complete structural characterization of a new lead Pb4(VO2)­(PO4)3 vanadophosphate compound by single crystal X-ray diffraction and 51V and 31P solid-state NMR spectroscopy. Although structural data are commonly used for the estimation of bond lengths and further delimitation of the true coordination number (e.g., octahedral: 6 versus 5 + 1 versus 4 + 2), we show here for the first time by solid-state NMR a more accurate appreciation of the V–O bonding scheme in this complex oxide which appears well adapted to the full series of vanado-phosphate materials. The direct characterization of V–O–P bridges through the J-mediated correlation 51V­{31P} heteronuclear multiple quantum coherence (J-HMQC) technique allows a contrasted hierarchy of the V–O electronic delocalization and indirectly supports the presence or not of the V–O bond. In the reported lead vanado-phosphate structure, the two vanadium polyhedra that have been assigned to octahedra from a bond length point of view have been finally reclassified as tetra- and penta-coordinated units on the basis of the solid-state NMR results. More generally, we believe that the improved characterization of interatomic bonds in various vanado-phosphate structures by solid-state NMR will contribute to a better understanding of the structure/property relationships in this important class of materials.