title: Spectroscopic properties of five-coordinated Co2+ in phosphates.
abstract: Co3(PO4)2, SrCo2(PO4)2, Co2P2O7, BaCoP2O7 and SrCoP2O7 present different geometries of five-coordinated Co(2+) (([5])Co(2+)) sites, coexisting with ([6])Co(2+) in Co3(PO4)2 and Co2P2O7, and ([4])Co(2+) in SrCo2(PO4)2. ([5])Co K-edge XANES spectra show that the intensity of the pre-edge and main-edge is intermediate between those of ([6])- and ([4])Co. Diffuse reflectance spectra show the contributions of Co(2+) in (D3h) symmetry for SrCo2(PO4)2, and (C4v) symmetry for BaCoP2O7 and SrCoP2O7. In Co3(PO4)2 and Co2P2O7 the multiple transitions observed arise from energy level splitting and may be labeled in (C2v) symmetry. Spectroscopic data confirm that (D3h) and (C4v) symmetries may be distinguished upon the intensity of the optical absorption bands and crystal field splitting values. We discuss the influence of the geometrical distortion and of the nature of the next nearest neighbors.
authors.affiliation: IMPMC (UMR 7590, CNRS-Université Pierre et Marie Curie), Case Courrier 115, 4 place Jussieu, 75252 Paris Cedex 05, France. Electronic address: myrtille.hunault@impmc.upmc.fr.
authors.forename: M
authors.initials: M
authors.lastname: Hunault
authors.forename: J-L
authors.initials: JL
authors.lastname: Robert
authors.forename: M
authors.initials: M
authors.lastname: Newville
authors.forename: L
authors.initials: L
authors.lastname: Galoisy
authors.forename: G
authors.initials: G
authors.lastname: Calas
mesh_terms: D001464:Barium / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D005336:Fiber Optic Technology; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry*; D013324:Strontium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D056831:Coordination Complexes; D010710:Phosphates; D001464:Barium; D003035:Cobalt; D013324:Strontium
keywords: Cobalt(II); Five-coordination; Phosphates; UV–vis–NIR spectroscopy; XANES