Ca(NiO2)2 crystallizes in the monoclinic P2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 pentagonal pyramids that share corners with six equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-22°. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share edges with two equivalent Ni(3)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. In the third Ni site, Ni(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share edges with two equivalent Ni(2)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ca(1), one Ni(1), one Ni(2), and one Ni(3) atom. In the second O site, O(2) is bonded to one Ca(2), one Ni(1), one Ni(2), and one Ni(3) atom to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(2)CaNi3 trigonal pyramids, edges with two equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(4)Ca2Ni3 trigonal bipyramids. In the third O site, O(3) is bonded to one Ca(1), one Ca(2), one Ni(2), and two equivalent Ni(1) atoms to form OCa2Ni3 trigonal bipyramids that share corners with two equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(3)Ca2Ni3 trigonal bipyramid, edges with three equivalent O(4)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), one Ni(3), and two equivalent Ni(1) atoms to form OCa2Ni3 trigonal bipyramids that share corners with two equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(4)Ca2Ni3 trigonal bipyramid, edges with three equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids.
Ca(NiO2)2 crystallizes in the monoclinic P2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1), two equivalent O(3), and two equivalent O(4) atoms to form distorted CaO6 pentagonal pyramids that share corners with six equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, and edges with two equivalent Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-22°. Both Ca(1)-O(1) bond lengths are 2.31 Å. Both Ca(1)-O(3) bond lengths are 2.39 Å. Both Ca(1)-O(4) bond lengths are 2.37 Å. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Ca(2)-O(2) bond lengths are 2.31 Å. Both Ca(2)-O(3) bond lengths are 2.33 Å. Both Ca(2)-O(4) bond lengths are 2.44 Å. There are three inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form NiO6 octahedra that share corners with three equivalent Ca(1)O6 pentagonal pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. The Ni(1)-O(1) bond length is 1.86 Å. The Ni(1)-O(2) bond length is 1.89 Å. There is one shorter (1.87 Å) and one longer (2.17 Å) Ni(1)-O(3) bond length. There is one shorter (1.91 Å) and one longer (2.10 Å) Ni(1)-O(4) bond length. In the second Ni site, Ni(2) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form NiO6 octahedra that share edges with two equivalent Ni(3)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Ni(2)-O(1) bond lengths are 1.86 Å. Both Ni(2)-O(2) bond lengths are 2.02 Å. Both Ni(2)-O(3) bond lengths are 1.99 Å. In the third Ni site, Ni(3) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(4) atoms to form NiO6 octahedra that share edges with two equivalent Ni(2)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. Both Ni(3)-O(1) bond lengths are 2.10 Å. Both Ni(3)-O(2) bond lengths are 1.86 Å. Both Ni(3)-O(4) bond lengths are 1.93 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a rectangular see-saw-like geometry to one Ca(1), one Ni(1), one Ni(2), and one Ni(3) atom. In the second O site, O(2) is bonded to one Ca(2), one Ni(1), one Ni(2), and one Ni(3) atom to form distorted OCaNi3 trigonal pyramids that share corners with two equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(2)CaNi3 trigonal pyramids, edges with two equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(4)Ca2Ni3 trigonal bipyramids. In the third O site, O(3) is bonded to one Ca(1), one Ca(2), one Ni(2), and two equivalent Ni(1) atoms to form OCa2Ni3 trigonal bipyramids that share corners with two equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(3)Ca2Ni3 trigonal bipyramid, edges with three equivalent O(4)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids. In the fourth O site, O(4) is bonded to one Ca(1), one Ca(2), one Ni(3), and two equivalent Ni(1) atoms to form OCa2Ni3 trigonal bipyramids that share corners with two equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(4)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids,  an edgeedge with one O(4)Ca2Ni3 trigonal bipyramid, edges with three equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids.