Jürgen Clade

Experimental and theoretical investigations of the X-ray absorption near edge spectra (XANES) of P4O6 and P4O6X (X O, S, Se)

Abstract The phosphorus oxide cage compounds P 4 O 6 and P 4 O 6 X (X  O, S, Se) were investigated by X-ray absorption near edge spectroscopy (XANES) and by calculations of inner-shell excited states using a recently developed method which combines density functional and single-excitation configuration interaction methods (DFT/SCI). For an interpretation of the shape and energy positions of the observed resonances, XANES spectra were compared with those of the reference compounds P(OPh) 3 and X  P(OPh) 3 which have a similar first coordination shell at the phosphorus atoms. On the basis of the theoretical results a complete assignment of the three resonances observed below the ionization potential could be made. Valence orbital relaxation effects and transitions to Rydberg states not considered thus seem not to play an important role for the interpretation of the spectra. The influence of the characteristics of the unoccupied orbitals on the locations and intensities of the 1s transitions of the phosphorus atoms in oxidation states +III and +V are discussed.

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.

Recent Synthetic, Structural, Spectroscopic, and Theoretical Studies on Molecular Phosphorus Oxides and Oxide Sulfides

Publisher Summary This chapter discusses the syntheses, crystal and molecular structures, spectroscopy, and theoretical studies of molecular phosphorus oxides and molecular phosphorus oxide sulfides. The phosphorus oxides and oxide sulfides considered in the chapter have one topological feature in common—they all consist of four tetrahedral (PX 4 ). Phosphorus thus is surrounded by three bridging and one terminal chalcogen atoms, the latter position being occupied by a lone pair in the case of trivalent phosphorus. If all tetrahedral groups are identical, molecules of high symmetry are generated, and the bridging chalcogen atoms are arranged as an ideal octahedron that is interpenetrated by a regular tetrahedron of phosphorus atoms. On adding, removing, or substituting one or more of the terminally bound chalcogen atoms, the symmetry is lowered and the geometry of the P 4 X 6 cage is distorted considerably. Because of the wide variety of possible modifications, this family of molecules is particularly well suited for comparative structural, spectroscopic, and theoretical studies aiming at a better understanding of the propagation of perturbations within molecules.

Tetracarbonyl(tetraphosphorus hexaoxide)-iron

The title [Fe(CO)4(P4O6) molecule consists of a trigonal-bipyramidally coordinated Fe atom, with the adamantane-like P4O6 cage in an axial position. As a consequence of the electronic effects of the iron–carbonyl group on the P4O6 cage, the P—O bond lengths show distortions similar to those observed within the series P4O7→P4O6S→P4O6Se, but the effects are slightly less pronounced.