New monodiphosphate Li9Cr3(P2O7)(3)(PO4)(2): X-ray crystal structure and vibrational spectroscopy

摘要

The new monodiphosphate Li9Cr3(P2O7)(3)(PO4)(2) was synthesized and analyzed by single-crystal X-ray diffraction, infrared and Raman spectroscopy. It crystallizes in the trigonal space group P (3) over bar cl with the following unit cell constants: a = b = 9.684(1) angstrom, c = 13.605(1) angstrom, V = 1104.9(2) angstrom(3). The three-dimensional framework is made up of [(CrP2O7)(3)(PO4)(2)](9-) layers, with CrO6 octahedra sharing vertices and edges with mono- and diphosphate groups. Li cations, spread over three different sites, fill up the remaining cavities, stabilizing the framework via Li-O bonds, making up tetrahedral arrangements at Li(2) and Li(3), and a complex hexacoordination at Li(1). IR and Raman spectra of Li9Cr3(P2O7)(3)(PO4)(3) confirm the centrosymmetric structure and the bent configuration of the POP bridge of the diphosphate group.