Pb-207 NMR study of novel Pb-Pb chemical bonding in lead monoxides, alpha-PbO and beta-PbO

alpha-PbO and beta-PbO have been studied with Pb-207 NMR-MAS spectroscopy i n the solid state. The Pb-207 NMR chemical-shift tensor in alpha-PbO is axi al, with principal values delta(perpendicular to) = 3030 +/- 5, delta(paral lel to) = -270 +/- 5, and delta(iso) = 1930 +/- 10 ppm. In beta-PbO, the Pb -207 NMR powder spectrum is approximately represented by a single non-axial tensor with principal values delta(11) = 2820, delta(22) = 2760, delta(33) = -1000, delta(iso) = 1525 +/- 10 ppm and eta = 0.024, although there appe ars to be an overlap of two very similar patterns. Using normal-coordinate analysis, the Pb-207 magnetic shielding tensor is represented as a sum of c ontributions from separate Pb-O and Pb-Pb interactions. It is shown that Pb -O and Pb-Pb contributions are of the same order of magnitude. A potential underlying relativistic reason for the abnormal Pb-Pb interaction is reveal ed. (C) 1999 Elsevier Science B.V. All rights reserved.