Periodic ab initio calculation of nuclear quadrupole parameters as an assignment tool in solid-state NMR spectroscopy: applications to 23Na NMR spectra of crystalline materials

Periodic ab initio HF calculations using the CRYSTAL code have been used to calculate 23Na NMR quadrupole parameters for a wide range of crystalline sodium compounds including Na3OCl. An approach is developed that can be used routinely as an alternative to point-charge modelling schemes for the assignment of distinct lines in 23Na NMR spectra to specific crystallographic sodium sites. The calculations are based on standard 3-21G and 6-21G molecular basis sets and in each case the same modified basis set for sodium is used for all compounds. The general approach is extendable to other quadrupolar nuclei. For the 3-21G calculations a 1:1 linear correlation between experimental and calculated values of CQ(23Na) is obtained. The 6-21G calculations, including the addition of d-polarisation functions, give better accuracy in the calculation of η(23Na). The sensitivity of η(23Na) to hydrogen atom location is shown to be useful in testing the reported hydrogen-bonded structure of Na2HPO4.