Supertetrahedral Networks and Lithium‐Ion Mobility in Li 2 SiP 2 and LiSi 2 P 3

The new phosphidosilicates Li 2 SiP 2 and LiSi 2 P 3 were synthesized by heating the elements at 1123 K and characterized by single‐crystal X‐ray diffraction. Li 2 SiP 2 ( I 4 1 / 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 LiSi 2 P 3 ( I 4 1 / 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 7 Li solid‐state MAS NMR spectroscopic data indicate high mobility of the Li + ions with low activation energies of 0.10 eV in Li 2 SiP 2 and 0.07 eV in LiSi 2 P 3 .