Ab initio study of isotropic and anisotropic hyperfine interactions in phosphoranyl and phosphorane anion radicals

A detailed ab initio study of isotropic and anisotropic hyperfine couplings (hfc) is presented for the ·PH4 (C2V, C3V), ·PF4 (C2V, C3V) and ·PF5- (C4V) radicals. Unrestricted Hartree—Fock (UHF), optionally with annihilation of the largest spin contaminant (UHF + AN), and restricted open-shell Hartree—Fock (ROHF) calculations are used to obtain electronic wave functions which describe doublet states. Throughout a 4-31G basis set is used and the influence of the implementation of d-type Gaussians on phosphorus is evaluated. All studied quantum chemical methods give good results for the isotropic hfc. Anisotropic hfcs are in good agreement with the experimental data only if the wave function describes a pure doublet state. The inclusion of d-functions leads to a serious decrease of the hyperfine interactions of the apical ligands in the C2V radicals and the equatorial ligands in the C3V radicals. The calculations clearly show that the fluorine dipolar hfc for the two ·PF4 isomers and the ·PF5- radical is not directed along the corresponding P—F linkage, but makes a pronounced angle (˜25°) with this bond.