Abstract
Cluster models are used in calculation of (207)Pb NMR magnetic-shielding parameters of α-PbO, β-PbO, Pb3O4, Pb2SnO4, PbF2, PbCl2, PbBr2, PbClOH, PbBrOH, PbIOH, PbSiO3, and Pb3(PO4)2. We examine the effects of cluster size, method of termination of the cluster, charge on the cluster, introduction of exact exchange, and relativistic effects on calculation of magnetic-shielding tensors with density functional theory. Proper termination of the cluster for a network solid, including approximations such as compensation of charge by the bond-valence (BV) method, is essential to provide results that agree with experiment. The inclusion of relativistic effects at the spin-orbit level for such heavy nuclei is an essential factor in achieving agreement with experiment.
Highlights
Lead has a rich and diverse co-ordination chemistry, ranging from organometallic compounds[1] to inorganic salts.[2]
The large NMR chemical-shift range (B10 000 ppm) of 207Pb,[3,4] and the strong dependence of the NMR chemical shift on co-ordination geometry and electronic structure, makes the study of the 207Pb nucleus in solid materials an attractive means to analyze them, and reports have appeared in which the experimental shifts are empirically correlated with structure.[5,6,7,8,9,10,11,12,13,14,15]
Details of the frozen core approximation (FCA) for each individual nucleus, cluster structural information, and results of calculations are given in the Electronic supplementary information (ESI).† To include relativistic effects, the zeroth order regular approximation (ZORA)[58,59,60,61] was employed at the spin–orbit level, unless otherwise indicated
Summary
Lead has a rich and diverse co-ordination chemistry, ranging from organometallic compounds[1] to inorganic salts.[2]. One solution to this practical problem is to add hydrogens to outer atoms of the cluster (maintaining proper symmetry) to stabilize the cluster This method has been employed to obtain converged solutions with meaningful NMR parameters in solids for a variety of systems.[24,25,43] Another method to account for this effect is to terminate the cluster with pseudo-atoms generated by changing the nuclear charges (Znuc) of the cluster’s outer atoms that have missing co-ordination. The aim of this procedure is to stabilize the system by reducing the non-compensated charge on the edges of the cluster. We briefly discuss effects of various methodological differences on the accuracy of calculated 207Pb magnetic-shielding tensors
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