ELECTRON-DENSITY DISTRIBUTION IN LITHIOPHOSPHATITE LI3PO4 - CRYSTALLOCHEMICAL FEATURES OF ORTHOPHOSPHATES WITH HEXAGONAL CLOSE PACKING

Specific features of the deformation electron-density distribution in phosphorus and Lithium tetrahedra forming the crystal structure of syn thetic lithiophosphatite Li3PO4 with the parameters a = 10.490(3), b = 6.120(2), c = 4.9266(7) Angstrom; sp. gr. Pnma; mu r = 0.1 have been analyzed on the basis of the precision experimental data (671 crystall ographically nonequivalent reflections with I greater than or equal to 1.96 sigma I, R = 0.0199, R-w = 0.0340, s = 2.0810). The 0.30-0.50-eA (-3)-height electron-density maxima at a distance of 0.8-0.9 Angstrom from the P atom on the P-O bond lines in the orthophosphate tetrahedra indicate that the phosphorus atom is in a state close to the sp(3) hy bridized state, which is confirmed by the equal (to within an accuracy of 0.001 Angstrom) distances in the tetrahedron. The character of the electron density distribution in the Li-tetrahedra confirms the exist ence of the covalent component in the Li-O bonds for tetrahedrally coo rdinated Lithium atoms. The comparison of the results obtained with th e known data on the related phases-triphylite LiFePO4, maricite NaFePO 4, and sarcopside Fe1.5PO4-showed that the character of the electron-d ensity distribution in the stable fragments of these structures (ortho phosphate tetrahedra) is determined by the distribution of LI+, Na+, a nd Fe2+ cations over the voids of the hexagonal close packing.