Supertetrahedral Networks and Lithium‐Ion Mobility in Li2SiP2 and LiSi2P3

The new phosphidosilicates Li₂SiP₂ and LiSi₂P₃ were synthesized by heating the elements at 1123 K and characterized by single‐crystal X‐ray diffraction. Li₂SiP₂ (I4₁/acd, Z=32, a=12.111(1) Å, c=18.658(2) Å) contains two interpenetrating diamond‐like tetrahedral networks consisting of corner‐sharing T2 supertetrahedra [(SiP_4/2)₄]. Sphalerite‐like interpenetrating networks of uniquely bridged T4 and T5 supertetrahedra make up the complex structure of LiSi₂P₃ (I4₁/a, Z=100, a=18.4757(3) Å, c=35.0982(6) Å). The lithium ions are located in the open spaces between the supertetrahedra and coordinated by four to six phosphorus atoms. Temperature‐dependent ⁷Li solid‐state MAS NMR spectroscopic data indicate high mobility of the Li⁺ ions with low activation energies of 0.10 eV in Li₂SiP₂ and 0.07 eV in LiSi₂P₃.