K-edge absorption spectra of selected vanadium compounds

Abstract

High-resolution vanadium $K$-edge absorption spectra have been recorded for a number of selected vanadium compounds of known chemical structure with use of the synchrotron radiation available at the Stanford Synchrotron Radiation Laboratory (SSRL). The compounds studied include the oxides VO, ${\mathrm{V}}_2$ ${\mathrm{O}}_3$, ${\mathrm{V}}_4$ ${\mathrm{O}}_7$, ${\mathrm{V}}_2$ ${\mathrm{O}}_4$, and ${\mathrm{V}}_2$ ${\mathrm{O}}_5$; the vanadates ${\mathrm{NH}}_4$ ${\mathrm{VO}}_3$, ${\mathrm{CrVO}}_4$, and ${\mathrm{Pb}}_5$ ${\left({\mathrm{VO}}_4\right)}_3$ Cl; the vanadyl compounds ${\mathrm{VOSO}}_4$.${3\mathrm{H}}_2$O, vanadyl bis(1-phenyl-1,3-butane) dionate, vanadyl phthalocyanine, and vanadyl tetraphenylporphyrin; the intermetallics VH, ${\mathrm{VB}}_2$, VC, VN, VP, and ${\mathrm{VSi}}_2$; and ${\mathrm{V}}_2$ ${\mathrm{S}}_3$ and a vanadium-bearing mineral, roscoelite. Vanadium in these compounds exhibits a wide range of formal oxidation states (0 to +5) and coordination geometries (octahedral, tetrahedral, square pyramid, etc.) with various ligands. The object of this systematic investigation is to gain further understanding of the details of various absorption features in the vicinity of the $K$ absorption edge of a constituent element in terms of its valence, site symmetry, coordination geometry, ligand type, and bond distances. In particular, the intensity and position of a well-defined pre-edged absorption in some of these compounds have been analyzed semiquantitatively within a molecular-orbital framework and a simple coordination-charge concept.