Li3[ScN2]:: The first nitridoscandate(III) -: Tetrahedral Sc coordination and unusual MX2 framework

Li-3[ScN2] was prepared from Li3N with Sc or ScN in a nitrogen atmosphere at 1020 K as a light yellow powder with an optical band gap of about 2.9 eV. The crystal structure was refined based on X-ray and neutron powder diffraction data (Ia (3) over bar, Z = 16, X-ray diffraction: R-profile = 0.078 R-Bragg = 0.070; Neutron diffraction :. R-profile = 0.077, R-Bragg = 0.074; Rietfeld: a = 1003.940(8) pm, Guinier: a = 1004.50(3) pm). Li-3[ScN2] is an isotype of Li-3[AlN2] and Li-3[GaN2] and crystallizes in an ordered superstructure of the Li2O structure type, leading to a three-dimensional framework of all-vertex-sharing tetrahedra (3)(infinity)[ScN4/23-]. Li is displaced from the center of a tetrahedron of N atoms in the direction of one trigonal face. Li-3[ScN2] decomposes above 1050 K to form ScN and Li3N. Calculations of the periodic nodal surface (PNS) and of the electron localization function (ELF) support the picture of a covalent ScN network separated from isolated Li cations, whereby scandium d orbitals are involved in the chemical bonding.