EMPIRICAL CORRELATIONS BETWEEN PB-207 NMR CHEMICAL-SHIFTS AND STRUCTURE IN SOLIDS

Using Pb-207 magic angle spinning and static NMR, we have resolved and assigned different lead sites in crystalline lead oxides and lead sil icates to their isotropic chemical shifts. Chemical shift anisotropies were also obtained for lead sites from the intensities of spinning si debands. Empirical correlations between Pb-207 isotropic chemical shif ts and structural parameters are proposed, For ionic compounds, we sho w good correlations between chemical shift and coordination number or mean bond length. For more covalent compounds, the best empirical corr elation has been obtained by using the degree of oxygen s-p hybridizat ion and second neighbor electronegativity similar to that previously u sed to characterize Si-29 shifts in aluminosilicates. The Pb2+ chemica l shift anisotropies increase with more positive chemical shifts. Thes e correlations, established for simple crystalline compounds, should a llow better characterization of lead environments in disordered materi als of complex composition.