Pr2NiO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. Pr(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(1) atoms. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NiO6 octahedra. The corner-sharing octahedra are not tilted. There are two inequivalent O sites. In the first O site, O(2) is bonded to four equivalent Pr(1) and two equivalent Ni(1) atoms to form OPr4Ni2 octahedra that share corners with two equivalent O(2)Pr4Ni2 octahedra, corners with twelve equivalent O(1)Pr5Ni octahedra, edges with two equivalent O(2)Pr4Ni2 octahedra, faces with four equivalent O(2)Pr4Ni2 octahedra, and faces with four equivalent O(1)Pr5Ni octahedra. The corner-sharing octahedral tilt angles range from 0-50°. In the second O site, O(1) is bonded to five equivalent Pr(1) and one Ni(1) atom to form distorted OPr5Ni octahedra that share corners with five equivalent O(1)Pr5Ni octahedra, corners with twelve equivalent O(2)Pr4Ni2 octahedra, edges with eight equivalent O(1)Pr5Ni octahedra, and faces with four equivalent O(2)Pr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 0-50°.
Pr2NiO4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. Pr(1) is bonded in a 9-coordinate geometry to four equivalent O(2) and five equivalent O(1) atoms. All Pr(1)-O(2) bond lengths are 2.57 Å. There is one shorter (2.32 Å) and four longer (2.79 Å) Pr(1)-O(1) bond lengths. Ni(1) is bonded to two equivalent O(1) and four equivalent O(2) atoms to form corner-sharing NiO6 octahedra. The corner-sharing octahedra are not tilted. Both Ni(1)-O(1) bond lengths are 2.21 Å. All Ni(1)-O(2) bond lengths are 1.94 Å. There are two inequivalent O sites. In the first O site, O(2) is bonded to four equivalent Pr(1) and two equivalent Ni(1) atoms to form OPr4Ni2 octahedra that share corners with two equivalent O(2)Pr4Ni2 octahedra, corners with twelve equivalent O(1)Pr5Ni octahedra, edges with two equivalent O(2)Pr4Ni2 octahedra, faces with four equivalent O(2)Pr4Ni2 octahedra, and faces with four equivalent O(1)Pr5Ni octahedra. The corner-sharing octahedral tilt angles range from 0-50°. In the second O site, O(1) is bonded to five equivalent Pr(1) and one Ni(1) atom to form distorted OPr5Ni octahedra that share corners with five equivalent O(1)Pr5Ni octahedra, corners with twelve equivalent O(2)Pr4Ni2 octahedra, edges with eight equivalent O(1)Pr5Ni octahedra, and faces with four equivalent O(2)Pr4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 0-50°.