Ca(NiO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(6), and two equivalent O(7) atoms. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(5), 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), two equivalent O(4), and two equivalent O(5) atoms to form NiO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 51-56°. 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 NiO6 octahedra that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent Ni(4)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. 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 NiO6 octahedra that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent Ni(4)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. In the fourth Ni site, Ni(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form NiO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 52-56°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ni(3) and two equivalent Ni(4) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ni(1), and two equivalent Ni(3) atoms to form distorted OCaNi3 tetrahedra that share corners with two equivalent O(8)Ca2Ni3 square pyramids, corners with two equivalent O(2)CaNi3 tetrahedra,  an edgeedge with one O(8)Ca2Ni3 square pyramid, and edges with two equivalent O(6)Ca2Ni3 square pyramids. In the third O site, O(3) is bonded to one Ca(2), one Ni(4), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(6)Ca2Ni3 square pyramids, corners with two equivalent O(3)CaNi3 trigonal pyramids,  an edgeedge with one O(6)Ca2Ni3 square pyramid, and edges with two equivalent O(8)Ca2Ni3 square pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ni(2) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2) 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 OCa2Ni3 square pyramids that share corners with two equivalent O(3)CaNi3 trigonal pyramids, edges with two equivalent O(6)Ca2Ni3 square pyramids, edges with two equivalent O(8)Ca2Ni3 square pyramids, edges with two equivalent O(2)CaNi3 tetrahedra, and  an edgeedge with one O(3)CaNi3 trigonal pyramid. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ni(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Ca(2), one Ni(2), and two equivalent Ni(3) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(2)CaNi3 tetrahedra, edges with two equivalent O(6)Ca2Ni3 square pyramids, edges with two equivalent O(8)Ca2Ni3 square pyramids,  an edgeedge with one O(2)CaNi3 tetrahedra, and edges with two equivalent O(3)CaNi3 trigonal pyramids.
Ca(NiO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded in a 5-coordinate geometry to one O(2), two equivalent O(6), and two equivalent O(7) atoms. The Ca(1)-O(2) bond length is 2.41 Å. There is one shorter (2.28 Å) and one longer (2.29 Å) Ca(1)-O(6) bond length. Both Ca(1)-O(7) bond lengths are 2.29 Å. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to one O(3), two equivalent O(5), and two equivalent O(8) atoms. The Ca(2)-O(3) bond length is 2.40 Å. Both Ca(2)-O(5) bond lengths are 2.29 Å. There is one shorter (2.28 Å) and one longer (2.29 Å) Ca(2)-O(8) bond length. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(2), two equivalent O(4), and two equivalent O(5) atoms to form NiO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 51-56°. The Ni(1)-O(2) bond length is 1.97 Å. Both Ni(1)-O(4) bond lengths are 1.94 Å. Both Ni(1)-O(5) bond lengths are 2.02 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 NiO6 octahedra that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent Ni(4)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The Ni(2)-O(4) bond length is 1.90 Å. The Ni(2)-O(8) bond length is 1.96 Å. Both Ni(2)-O(3) bond lengths are 1.96 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 NiO6 octahedra that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent Ni(4)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The Ni(3)-O(1) bond length is 1.91 Å. The Ni(3)-O(6) bond length is 1.96 Å. There is one shorter (1.97 Å) and one longer (1.98 Å) Ni(3)-O(2) bond length. There is one shorter (2.04 Å) and one longer (2.05 Å) Ni(3)-O(8) bond length. In the fourth Ni site, Ni(4) is bonded to one O(3), two equivalent O(1), and two equivalent O(7) atoms to form NiO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, and edges with two equivalent Ni(4)O5 square pyramids. The corner-sharing octahedral tilt angles range from 52-56°. The Ni(4)-O(3) bond length is 1.96 Å. There is one shorter (1.93 Å) and one longer (1.94 Å) Ni(4)-O(1) bond length. There is one shorter (2.03 Å) and one longer (2.04 Å) Ni(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Ni(3) and two equivalent Ni(4) atoms. In the second O site, O(2) is bonded to one Ca(1), one Ni(1), and two equivalent Ni(3) atoms to form distorted OCaNi3 tetrahedra that share corners with two equivalent O(8)Ca2Ni3 square pyramids, corners with two equivalent O(2)CaNi3 tetrahedra,  an edgeedge with one O(8)Ca2Ni3 square pyramid, and edges with two equivalent O(6)Ca2Ni3 square pyramids. In the third O site, O(3) is bonded to one Ca(2), one Ni(4), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(6)Ca2Ni3 square pyramids, corners with two equivalent O(3)CaNi3 trigonal pyramids,  an edgeedge with one O(6)Ca2Ni3 square pyramid, and edges with two equivalent O(8)Ca2Ni3 square pyramids. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Ni(2) and two equivalent Ni(1) atoms. In the fifth O site, O(5) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(2) 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 OCa2Ni3 square pyramids that share corners with two equivalent O(3)CaNi3 trigonal pyramids, edges with two equivalent O(6)Ca2Ni3 square pyramids, edges with two equivalent O(8)Ca2Ni3 square pyramids, edges with two equivalent O(2)CaNi3 tetrahedra, and  an edgeedge with one O(3)CaNi3 trigonal pyramid. In the seventh O site, O(7) is bonded in a rectangular see-saw-like geometry to two equivalent Ca(1) and two equivalent Ni(4) atoms. In the eighth O site, O(8) is bonded to two equivalent Ca(2), one Ni(2), and two equivalent Ni(3) atoms to form OCa2Ni3 square pyramids that share corners with two equivalent O(2)CaNi3 tetrahedra, edges with two equivalent O(6)Ca2Ni3 square pyramids, edges with two equivalent O(8)Ca2Ni3 square pyramids,  an edgeedge with one O(2)CaNi3 tetrahedra, and edges with two equivalent O(3)CaNi3 trigonal pyramids.