A DEFINITIVE EXAMPLE OF AL-27 CHEMICAL SHIELDING ANISOTROPY

Solid-state Al-27 NMR spectra have been obtained for a crystalline 1:1 complex of AlCl3 and OPCl3. Aluminum chloride phosphoryl chloride, Al Cl3. OPCl3 (1), is unusual in that the Al-O-P bond angle is close to 1 80 degrees. From analysis of the Al-27 MAS NMR spectra, it was determi ned that the Al-27 nuclear quadrupole coupling constant is 6.0(1) MHz, the asymmetry in the electric field gradient (efg) tensor is 0.15(2), and the isotropic chemical shift, delta(iso)(Al-27), is 88(1) ppm. So lid-state Al-27 NMR of a stationary sample reveals a line shape affect ed by a combination of anisotropic chemical shielding and second-order quadrupolar interactions. Analysis of this spectrum yields a chemical shift anisotropy of 60(1) ppm and orientations of the chemical shift and electric field gradient tensors in the molecular frame. Experiment al results are compared with those calculated using ab initio Hartree- Fock and density functional theory. (C) 1998 Academic Press.