Ca(NiO2)2 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1) and four equivalent O(3) 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, and edges with four equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-19°. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), and four equivalent O(3) 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 four equivalent Ni(2)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(2)O6 octahedra, edges with four equivalent Ni(1)O6 octahedra, and edges with two equivalent Ca(1)O6 pentagonal pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ni(1), and two equivalent Ni(2) atoms. In the second O site, O(2) is bonded to one Ca(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with four equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(2)CaNi3 trigonal pyramids, and edges with four equivalent O(3)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 five equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids, edges with four equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids.
Ca(NiO2)2 crystallizes in the orthorhombic Pmmn space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent O(1) and four equivalent O(3) 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, and edges with four equivalent Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-19°. Both Ca(1)-O(1) bond lengths are 2.39 Å. All Ca(1)-O(3) bond lengths are 2.36 Å. In the second Ca site, Ca(2) is bonded in a 6-coordinate geometry to two equivalent O(2) and four equivalent O(3) atoms. Both Ca(2)-O(2) bond lengths are 2.32 Å. All Ca(2)-O(3) bond lengths are 2.34 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to one O(1), one O(2), and four equivalent O(3) 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 four equivalent Ni(2)O6 octahedra, and  an edgeedge with one Ca(1)O6 pentagonal pyramid. The Ni(1)-O(1) bond length is 1.87 Å. The Ni(1)-O(2) bond length is 1.88 Å. There are two shorter (1.96 Å) and two longer (2.01 Å) Ni(1)-O(3) bond lengths. 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(2)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 1.92 Å. Both Ni(2)-O(2) bond lengths are 1.91 Å. Both Ni(2)-O(3) bond lengths are 2.08 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted rectangular see-saw-like geometry to one Ca(1), one Ni(1), and two equivalent Ni(2) atoms. In the second O site, O(2) is bonded to one Ca(2), one Ni(1), and two equivalent Ni(2) atoms to form distorted OCaNi3 trigonal pyramids that share corners with four equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with three equivalent O(2)CaNi3 trigonal pyramids, and edges with four equivalent O(3)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 five equivalent O(3)Ca2Ni3 trigonal bipyramids, corners with two equivalent O(2)CaNi3 trigonal pyramids, edges with four equivalent O(3)Ca2Ni3 trigonal bipyramids, and edges with two equivalent O(2)CaNi3 trigonal pyramids.