Single-crystal Pb-NMR of wulfenite, PbMoO, aided by simultaneous measurement of phosgenite, PbClCO.

The effort for determining NMR interaction tensors from orientation-dependent spectra of single crystals may be greatly reduced by exploiting symmetry relations between atoms of the observed nuclide in the unit cell, as is well documented in the literature. In this work, we determined both the full chemical shift (CS) tensor of Pb and the unknown orientation of the rotation axis for the natural mineral phosgenite, PbClCO, from a single rotation pattern, i.e. spectra of crystal orientations from 0 to 180°. In the tetragonal crystal structure of phosgenite, four symmetry-related, but magnetically inequivalent Pb are generated by the Wyckoff multiplicity. The mineral wulfenite, PbMoO, also crystallises in a tetragonal space group, but the site multiplicity for Pb generates only one magnetically inequivalent atom, thus not supplying sufficient experimental data to determine CS tensor and axis orientation from an arbitrary number of rotation patterns. One solution to this problem is to simultaneously acquire data of a known compound with high symmetry and Wyckoff multiplicity (here: phosgenite), which supplies additional constraints making the solution of the target compound (here: wulfenite) possible. The Pb CS tensors thus determined are characterised by the following eigenvalues in ppm: δ=(-2553±1), δ=(-1929±1), δ=(-1301±1) for phosgenite, and δ=(-2074±1), δ=(-2074±1), δ=(-1898±1) for wulfenite.