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 Kα (λ=0.71069 A) radiation to a resolution corresponding to (sinθmax/λ)=1.078 A-1. Measurements of 3265 reflections gave 944 unique data [Rint(I)=0.036] with I>2σ(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, Mr=157.76, orthorhombic, Pnma, a=10.332(4), b=6.010(5), c=4.692(2) A, V=291.4(3) A3, Z=4, Dx=3.596 Mg m-3, μ=5.65 mm-1, F(000)=304. (orig.)