Please Mind the Gap: Highly Condensed P-N Networks in LiP4 N7 and Li3-x P6 N11-x (NH)x

Abstract

Alkali nitridophosphates AP₄ N₇ and A₃ P₆ N₁₁ (A=Na, K, Rb, Cs) have been known for decades. However, their Li homologues have remained elusive. In this work, the highly condensed lithium (imido)nitridophosphates LiP₄ N₇ and Li_3-x P₆ N_11-x (NH)_x (x=1.66(3)) were synthesized from LiPN₂ and P₃ N₅ in the multianvil press at 10 GPa. They constitute the first lithium nitridophosphates with 3D networks exhibiting a degree of condensation larger than 0.5 and high thermal stability. LiP₄ N₇ crystallizes in the orthorhombic space group P2₁ 2₁ 2₁ with a=4.5846(6) Å, b=8.0094(11) Å, and c=13.252(2) Å (Z=4). Li_3-x P₆ N_11-x (NH)_x crystallizes in the triclinic space group P $\stackrel{-}{1}$ with Z=2, a=4.6911(11) Å, b=7.024(2) Å, c=12.736(3) Å, α=87.726(11), β=80.279(11), and γ=70.551(12)°. Both compounds are stable against hydrolysis in air.

Keywords: high-pressure chemistry; lithium; nitridophosphates; solid-state structures.