Structure and Bonding in the Trichalcogenometaphosphate–Pyridine Anions [PX3 − Py]− (X = O, S, Se, Te)

Abstract

The structures, bonding, NMR chemical shifts, and Lewis acid/base behavior of the trichalcogenometaphosphate–pyridine anions [PX3 − Py]− (X = O, S, Se, Te) have been evaluated theoretically on the basis of B3LYP/ECP(Se,Te) + cc-pVTZ//PM3 calculations using quasirelativistic pseudopotentials for Se and Te. The molecular and electronic structures of the trichalcogenometaphosphate–pyridine adducts [PX3 − Py]− (X = O, S, Se, Te) were calculated, and the bonding was analyzed and discussed on the basis of natural bond orbital (NBO) analyses and qualitative valence bond (VB) considerations. The (σ(px)-LP(N)) → (σ(px)-LP*(P)) donor–acceptor interaction increases, and, consequently, the P‒N bond length decreases from PO3 − Py− (weak interaction, long P‒N bond) to PTe3 − Py− (strong interaction, short P‒N bond). This theoretical finding is in good accord with the measured P‒N bond lengths in [PSe3 − Py]− and [PTe3 − Py]−. In the gas phase, all four [PX3 − Py]− (X = O, S, Se, Te) adducts are unstable with respect to dissociation into free PX3 − and pyridine.