Ca(NiO2)4 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 10-coordinate geometry to one O(2), one O(3), two equivalent O(5), two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 52-55°. In the second Ni site, Ni(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 52-57°. In the third Ni site, Ni(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 54-55°. In the fourth Ni site, Ni(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 54-57°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(3) and two equivalent Ni(4) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ni(1), and two equivalent Ni(3) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Ni(4), and two equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Ni(2) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Ni(4), and two equivalent Ni(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Ni(3), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing OCa2Ni3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Ni(1), and two equivalent Ni(4) atoms to form a mixture of distorted corner and edge-sharing OCa2Ni3 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Ni(2), and two equivalent Ni(3) atoms.
Ca(NiO2)4 crystallizes in the monoclinic Cm space group. Ca(1) is bonded in a 10-coordinate geometry to one O(2), one O(3), two equivalent O(5), two equivalent O(6), two equivalent O(7), and two equivalent O(8) atoms. The Ca(1)-O(2) bond length is 2.70 Å. The Ca(1)-O(3) bond length is 2.72 Å. Both Ca(1)-O(5) bond lengths are 2.91 Å. Both Ca(1)-O(6) bond lengths are 2.43 Å. Both Ca(1)-O(7) bond lengths are 2.51 Å. Both Ca(1)-O(8) bond lengths are 2.93 Å. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2), one O(7), two equivalent O(4), and two equivalent O(5) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 52-55°. The Ni(1)-O(2) bond length is 1.84 Å. The Ni(1)-O(7) bond length is 1.93 Å. Both Ni(1)-O(4) bond lengths are 1.90 Å. Both Ni(1)-O(5) bond lengths are 1.99 Å. In the second Ni site, Ni(2) is bonded to one O(4), one O(8), two equivalent O(3), and two equivalent O(6) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 52-57°. The Ni(2)-O(4) bond length is 1.86 Å. The Ni(2)-O(8) bond length is 1.91 Å. Both Ni(2)-O(3) bond lengths are 1.92 Å. Both Ni(2)-O(6) bond lengths are 2.03 Å. In the third Ni site, Ni(3) is bonded to one O(1), one O(6), two equivalent O(2), and two equivalent O(8) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 54-55°. The Ni(3)-O(1) bond length is 1.83 Å. The Ni(3)-O(6) bond length is 1.91 Å. Both Ni(3)-O(2) bond lengths are 1.93 Å. Both Ni(3)-O(8) bond lengths are 1.99 Å. In the fourth Ni site, Ni(4) is bonded to one O(3), one O(5), two equivalent O(1), and two equivalent O(7) atoms to form a mixture of corner and edge-sharing NiO6 octahedra. The corner-sharing octahedral tilt angles range from 54-57°. The Ni(4)-O(3) bond length is 1.85 Å. The Ni(4)-O(5) bond length is 1.93 Å. Both Ni(4)-O(1) bond lengths are 1.90 Å. Both Ni(4)-O(7) bond lengths are 2.01 Å. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a trigonal planar geometry to one Ni(3) and two equivalent Ni(4) atoms. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Ca(1), one Ni(1), and two equivalent Ni(3) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ca(1), one Ni(4), and two equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Ni(2) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Ni(4), and two equivalent Ni(1) atoms. In the sixth O site, O(6) is bonded to two equivalent Ca(1), one Ni(3), and two equivalent Ni(2) atoms to form a mixture of distorted corner and edge-sharing OCa2Ni3 trigonal bipyramids. In the seventh O site, O(7) is bonded to two equivalent Ca(1), one Ni(1), and two equivalent Ni(4) atoms to form a mixture of distorted corner and edge-sharing OCa2Ni3 trigonal bipyramids. In the eighth O site, O(8) is bonded in a 3-coordinate geometry to two equivalent Ca(1), one Ni(2), and two equivalent Ni(3) atoms.