Ab initio calculation of the 31P NMR shielding tensor for the series PO_a F_b^{-(2a+b-5)}, a+b=4 and for HPO_4^{2-}

Ab initio coupled Hartree-Fock perturbation theory (CHFPT) calculations on PO43−, PO3F2−, PO2F2−, PF3O, PF4+ and HPO42− using large polarized Gaussian bases satisfactorily reproduce experimental trends in 31P magnetic shielding anisotropies.Accurate evaluation of the shielding tensor for HPO42− requires the inclusion of the H atom. Along the series POa Fb−(2a+b−5) the calculated isotropic shielding shows a “sagging” pattern, i.e. the shielding is smallest for the intermediate member of the series PO3F2−. The shielding for this species is, however, a strong function of the P-F and P-O distances. PO3F2− and HPO42− are calculated to be similar in both average shielding and shielding anisotropy.