NiO2 crystallizes in the trigonal R3m space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form corner-sharing NiO4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. In the second Ni site, Ni(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Ni(1)O4 tetrahedra and edges with four equivalent Ni(2)O6 octahedra. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(1) and two equivalent Ni(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal pyramidal geometry to one Ni(1) and three equivalent Ni(2) atoms. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent Ni(2) atoms.
NiO2 crystallizes in the trigonal R3m space group. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2) and three equivalent O(1) atoms to form corner-sharing NiO4 tetrahedra. The corner-sharing octahedral tilt angles range from 57-58°. The Ni(1)-O(2) bond length is 1.90 Å. All Ni(1)-O(1) bond lengths are 1.85 Å. In the second Ni site, Ni(2) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Ni(1)O4 tetrahedra and edges with four equivalent Ni(2)O6 octahedra. The Ni(2)-O(2) bond length is 1.99 Å. The Ni(2)-O(3) bond length is 1.91 Å. Both Ni(2)-O(1) bond lengths are 1.92 Å. Both Ni(2)-O(4) bond lengths are 1.85 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(1) and two equivalent Ni(2) atoms. In the second O site, O(2) is bonded in a distorted trigonal pyramidal geometry to one Ni(1) and three equivalent Ni(2) atoms. In the third O site, O(3) is bonded in a distorted T-shaped geometry to three equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded in a water-like geometry to two equivalent Ni(2) atoms.