SYNTHESIS AND CRYSTAL-STRUCTURE OF LITHIUM PHOSPHORUS NITRIDE LI7PN4 - THE 1ST-COMPOUND CONTAINING ISOLATED PN4-TETRAHEDRA

Single phase Li7PN4 was synthesized under nitrogen atmosphere at 620°C by solid state reaction of Li3N and P3N5 with molar ratio 7:1. Li7PN4 has cubic symmetry, P43n, a = 936.48(3) pm, Z = 8. (Rietveld profile refinement method; X-ray powder diffraction data; R(wp) = 0.099 and R(I, hkl) = 0.0744; 77 nonzero reflections observed, 9 positional parameters refined.) Li7PN4 is an ionic solid containing both lithium cations and isolated PN4 anions. Atomic arrangement in the solid derives from an anti-fluorite type of structure. The PN bond lengths (average: 171 pm) correspond to a bond order of approximately 1 1 4 in the PN4-tetrahedra. In the cubic unit cell the phosphorus atoms resemble β-tungsten analogous arrangement. © 1990.