X-ray absorption near-edge spectroscopy (XANES) at the phosphorus K-edge of triorganophosphinechalcogenides

Abstract

In this paper, we present X-ray absorption near-edge structure (XANES) measurements of triorganophosphinechalcogenides at the phosphorus K-edge. Using the XANES spectra as fingerprints, we can analyse the influence of the local environment of the absorbing atom on the shape of the absorption spectra and the energy positions of the resonances. Effects caused by the first and by higher coordination shells can be distinguished by systematic variations of the type of atoms surrounding the phosphorus atom. The effect of the first coordination shell is to reflect the electronegativity of the nearest neighbours and the valency of the excited atom: the white line shifts to higher energies with increasing electronegativity of the neighbouring atoms and valency of the absorbing atom. Furthermore, we show that an aromatic substituent in the higher coordination shells causes a splitting of the first strong resonance. This can be traced back to the formation of a delocalised π-electron system which shortens the P–C aryl bond length because of its positive mesomeric effect. MS Xα calculations verify this assumption and indicate that the double-resonance structure can be interpreted by transitions of a 1s electron into the various unoccupied p-orbitals. These orbitals are mainly formed by phosphorus and carbon in the case of the low-energy resonance and by phosphorus and the chalcogene in the case of the high-energy resonance of the splitted white line. If an aliphatic ligand is bound to the excited atom there is no observable splitting in the spectra.