Ba(NiO2)4 crystallizes in the trigonal R-3m space group. Ba(1) is bonded in a hexagonal planar geometry to three equivalent O(3) and three equivalent O(4) atoms. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form edge-sharing NiO6 octahedra. In the second Ni site, Ni(2) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form edge-sharing NiO6 octahedra. In the third Ni site, Ni(3) is bonded to six equivalent O(4) atoms to form edge-sharing NiO6 octahedra. In the fourth Ni site, Ni(4) is bonded to six equivalent O(3) atoms to form edge-sharing NiO6 octahedra. There are four inequivalent O sites. In the first O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), one Ni(4), and two equivalent Ni(2) atoms. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Ni(3), and two equivalent Ni(1) atoms. In the third O site, O(1) is bonded in a distorted T-shaped geometry to three equivalent Ni(1) atoms. In the fourth O site, O(2) is bonded in a distorted T-shaped geometry to three equivalent Ni(2) atoms.
Ba(NiO2)4 crystallizes in the trigonal R-3m space group. Ba(1) is bonded in a hexagonal planar geometry to three equivalent O(3) and three equivalent O(4) atoms. All Ba(1)-O(3) bond lengths are 2.70 Å. All Ba(1)-O(4) bond lengths are 2.69 Å. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent O(1) and four equivalent O(4) atoms to form edge-sharing NiO6 octahedra. Both Ni(1)-O(1) bond lengths are 1.92 Å. All Ni(1)-O(4) bond lengths are 1.89 Å. In the second Ni site, Ni(2) is bonded to two equivalent O(2) and four equivalent O(3) atoms to form edge-sharing NiO6 octahedra. Both Ni(2)-O(2) bond lengths are 1.92 Å. All Ni(2)-O(3) bond lengths are 1.89 Å. In the third Ni site, Ni(3) is bonded to six equivalent O(4) atoms to form edge-sharing NiO6 octahedra. All Ni(3)-O(4) bond lengths are 2.02 Å. In the fourth Ni site, Ni(4) is bonded to six equivalent O(3) atoms to form edge-sharing NiO6 octahedra. All Ni(4)-O(3) bond lengths are 2.02 Å. There are four inequivalent O sites. In the first O site, O(3) is bonded in a 4-coordinate geometry to one Ba(1), one Ni(4), and two equivalent Ni(2) atoms. In the second O site, O(4) is bonded in a 4-coordinate geometry to one Ba(1), one Ni(3), and two equivalent Ni(1) atoms. In the third O site, O(1) is bonded in a distorted T-shaped geometry to three equivalent Ni(1) atoms. In the fourth O site, O(2) is bonded in a distorted T-shaped geometry to three equivalent Ni(2) atoms.