MULTIPOLE ANALYSIS OF THE ELECTRON-DENSITY IN TRIPHYLITE, LIFEPO4, USING X-RAY-DIFFRACTION DATA

The electron density distribution and 3d-orbital electron occupancies for the Fe atom in synthetic triphylite, LiFePO4, have been analysed using single-crystal X-ray diffraction data measured at T = 298 K with Mo Kalpha (lambda = 0.71069 angstrom) radiation to a resolution corresponding to (sintheta(max)/lambda) = 1.078 angstrom-1. Measurements of 3265 reflections gave 944 unique data [R(int)(I) = 0.036] with I > 2sigma(I). For an atomic multipole density model fitted by least-squares methods R(F) = 0.0174 for all unique reflections. The Fe atom 3d-orbital occupancies have been derived from the multipole population coefficients using point-group-specific relations. The asphericity of the electron deformation density around the Fe atom is discussed using crystal-field theory and magnetic properties of triphylite. Crystal data: lithium iron(II) phosphate, LiFePO4, M(r) = 157.76, orthorhombic, Pnma, a = 10.332 (4), b = 6.010 (5), c = 4.692 (2) angstrom, V = 291.4 (3) angstrom3, Z = 4, D(x) = 3.596 Mg m-3, mu = 5.65 mm-1, F(000) = 304.