Synthesis and Characterization of the Lithium-Rich Phosphidosilicates Li₁₀Si₂P₆ and Li₃Si₃P₇

The lithium phosphidosilicates Li₁₀Si₂P₆ and Li₃Si₃P₇are obtained by high-temperature reactions of the elements or including binary Li-P precursors. Li₁₀Si₂P₆ (P2₁/n, Z = 2, a = 7.2051(4) Å, b = 6.5808(4) Å, c = 11.6405(7) Å, β = 90.580(4)°) features edge-sharing SiP₄ double tetrahedra forming [Si₂P₆]^10- units with a crystal structure isotypic to Na₁₀Si₂P₆ and Na₁₀Ge₂P₆. Li₃Si₃P₇ (P2₁/m, Z = 2, a = 6.3356(4) Å, b = 7.2198(4) Å, c = 10.6176(6) Å, β = 102.941(6)°) crystallizes in a new structure type, wherein SiP₄ tetrahedra are linked via common vertices and which are further connected by polyphosphide chains to form unique_∞ ²[Si₃P₇]^3- double layers. The two-dimensional Si-P slabs that are separated by Li atoms can be regarded as three covalently linked atoms layers: a defect α-arsenic type layer of P atoms sandwiched between two defect wurzite-type Si₃P₄ layers. The single crystal and powder X-ray structure solutions are supported by solid-state⁷Li,²⁹Si, and³¹P magic-angle spinning NMR measurements.