207Pb NMR of minium, Pb3O4:: evidence for the [Pb2]4+ ion and possible relativistic effects in the Pb-Pb bond

Solid Pb3O4 has been studied with Pb-207 nuclear magnetic resonance (NMR) spectroscopy. The Pb-207 NMR chemical-shift tensor of the Pb2+ site has principal values of delta(11) = 1980 +/- 5 ppm, delta(22) = 1540 +/- 5 ppm, and delta(33) = -1108 +/- 10 ppm; delta(iso) = 804 +/- 10 ppm. The chemical-shift tensor of the Pb4+ site is axial, with principal values delta(11) = -1009 +/- 3 ppm and delta(perpendicular to) = 1132 +/- 3 ppm; delta(iso) = -1091 +/- 3 ppm. The Pb4+-Pb2+ scalar coupling constant J(Pb-Pb) = 2.3 +/- 0.1 kHz. The main contribution to the Pb2+ chemical-shift anisotropy is proposed to arise from an exchange interaction in the Pb2+-Pb2+ pairs, conventionally regarded as molecular [Pb-2](4+) ions. (C) 1999 Elsevier Science B.V. All rights reserved.