Nuclear Quadrupole Resonances of Phosphorus Iodides and Some Phosphorus Trihalide–Boron Trihalide Complexes

Abstract

Abstract Nuclear quadrupole resonance (NQR) frequencies due to 79Br and 127I are examined in phosphorus iodides, PI3 and P2I4, and the complexes PBr3·BBr3, PBr3·BI3, and PI3·BBr3. The quadrupole coupling constants and asymmetry parameters are also derived for 127I in PI3, P2I4, and PBr3·BI3. The resonance lines of PI3 fade out above 257 K, at which temperature a structural phase transition is suggested. The number of resonance lines in P2I4 shows that the molecular symmetry of P2I4 is \bar1 instead of 2/m in its crystal. The similarity of the resonance patterns of the three complexes indicates that they are isomorphous with one another. The electronic structures of the halogens in the compounds mentioned above have been discussed by using the Townes-Dailey theory. On complexing, the electric charge of the halogen atoms in the donor PX3 decreases due to the polarization of pσ bonds, whereas that of the halogen atoms in the acceptor BY3 increases owing to the backdonation through pπ bonds.