Pm2O3 crystallizes in the trigonal P-3m1 space group. Pm(1) is bonded in a 7-coordinate geometry to three equivalent O(2) and four equivalent O(1) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Pm(1) atoms to form OPm4 tetrahedra that share corners with six equivalent O(2)Pm6 octahedra, corners with six equivalent O(1)Pm4 tetrahedra, edges with three equivalent O(2)Pm6 octahedra, and edges with three equivalent O(1)Pm4 tetrahedra. The corner-sharing octahedral tilt angles range from 18-56°. In the second O site, O(2) is bonded to six equivalent Pm(1) atoms to form OPm6 octahedra that share corners with twelve equivalent O(1)Pm4 tetrahedra, edges with six equivalent O(2)Pm6 octahedra, and edges with six equivalent O(1)Pm4 tetrahedra.
Pm2O3 crystallizes in the trigonal P-3m1 space group. Pm(1) is bonded in a 7-coordinate geometry to three equivalent O(2) and four equivalent O(1) atoms. All Pm(1)-O(2) bond lengths are 2.65 Å. There are three shorter (2.29 Å) and one longer (2.37 Å) Pm(1)-O(1) bond length. There are two inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Pm(1) atoms to form OPm4 tetrahedra that share corners with six equivalent O(2)Pm6 octahedra, corners with six equivalent O(1)Pm4 tetrahedra, edges with three equivalent O(2)Pm6 octahedra, and edges with three equivalent O(1)Pm4 tetrahedra. The corner-sharing octahedral tilt angles range from 18-56°. In the second O site, O(2) is bonded to six equivalent Pm(1) atoms to form OPm6 octahedra that share corners with twelve equivalent O(1)Pm4 tetrahedra, edges with six equivalent O(2)Pm6 octahedra, and edges with six equivalent O(1)Pm4 tetrahedra.