Crystal structure and properties of strontium phosphate apatite with oxocuprate ions in hexagonal channels

Strontium phosphate apatites containing different amounts of copper were prepared by a solid state reaction at 1100 C or by arc melting above 1600 C in air. The samples were characterized by X-ray diffraction, ICP analysis, scanning electron microscopy. IR spectroscopy. MAS-H-1-NMR, diffuse reflectance spectroscopy, and SQUID magnetometry. X-ray crystal structure determination was carried out for a single crystal obtained from the melt. The compound is formulated as Sr-5(PO4)(3)(CuO2)(1/3) and has an apatite structure (space group P6(3)/m. a = 9.7815(4) Angstrom. c = 7.3018(4) Angstrom, Z = 2) with linear CuO23- ions occupying hexagonal channels. For solid state synthesized samples. Rietveld refinement of powder XRD patterns was performed. The samples obtained at 1100 degreesC acquire the composition Sr-5(PO4)(3)CuxOHy with x changing from 0.01 to 0.62 and y < 1-x. The copper content can be increased to x = 0.85 by annealing in argon at 950 C. The compounds represent a hydroxyapatite in which part of the protons is substituted by Cu+ and Cu2- ions. The ions form linear O-Cu-O units which acre progressively condensed creating the Cu-O-Cu bridges on increasing copper content. IR and NMR data testify existence of OH groups. non-disturbed and disturbed by neighboring Cu atoms. In the electron spectra, the samples exhibit absorption bands at 7800-7900, 14200-14500 and 17500-17550 cm(-1), which were assigned to Cu2+ d-electron transitions. By annealing the sample with x = 0.1 in oxygen at 800 degreesC copper is fully oxidized while retaining in channels in unusual for Cu-2 . linear coordination.