Mg(NiO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-58°. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form MgO5 square pyramids that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra, edges with two equivalent Mg(2)O5 square pyramids, and  a faceface with one Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-57°. 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 NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Mg(2)O5 square pyramid, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 47-57°. 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 distorted NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 47-56°. 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 distorted NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  a faceface with one Mg(2)O5 square pyramid. The corner-sharing octahedral tilt angles range from 47-57°. 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 NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Mg(1)O5 square pyramid, and edges with two equivalent Mg(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 47-56°. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Ni(3), and two equivalent Ni(4) atoms to form OMgNi3 trigonal pyramids that share corners with two equivalent O(7)Mg2Ni3 square pyramids, corners with two equivalent O(1)MgNi3 trigonal pyramids,  an edgeedge with one O(7)Mg2Ni3 square pyramid, and edges with two equivalent O(5)Mg2Ni3 square pyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Ni(1) and two equivalent Ni(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Ni(4) and two equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Ni(2), and two equivalent Ni(1) atoms to form OMgNi3 trigonal pyramids that share corners with two equivalent O(5)Mg2Ni3 square pyramids, corners with two equivalent O(4)MgNi3 trigonal pyramids,  an edgeedge with one O(5)Mg2Ni3 square pyramid, and edges with two equivalent O(7)Mg2Ni3 square pyramids. In the fifth O site, O(5) is bonded to two equivalent Mg(2), one Ni(4), and two equivalent Ni(1) atoms to form OMg2Ni3 square pyramids that share corners with two equivalent O(4)MgNi3 trigonal pyramids, edges with two equivalent O(5)Mg2Ni3 square pyramids, edges with two equivalent O(7)Mg2Ni3 square pyramids,  an edgeedge with one O(4)MgNi3 trigonal pyramid, and edges with two equivalent O(1)MgNi3 trigonal pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Ni(3), and two equivalent Ni(2) atoms. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one Ni(1), and two equivalent Ni(4) atoms to form OMg2Ni3 square pyramids that share corners with two equivalent O(1)MgNi3 trigonal pyramids, edges with two equivalent O(5)Mg2Ni3 square pyramids, edges with two equivalent O(7)Mg2Ni3 square pyramids,  an edgeedge with one O(1)MgNi3 trigonal pyramid, and edges with two equivalent O(4)MgNi3 trigonal pyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to two equivalent Mg(2), one Ni(2), and two equivalent Ni(3) atoms.
Mg(NiO2)2 crystallizes in the triclinic P1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to one O(4), two equivalent O(6), and two equivalent O(7) atoms to form MgO5 square pyramids that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Ni(4)O6 octahedra, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Mg(1)O5 square pyramids, and  a faceface with one Ni(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 6-58°. The Mg(1)-O(4) bond length is 2.07 Å. There is one shorter (2.05 Å) and one longer (2.06 Å) Mg(1)-O(6) bond length. Both Mg(1)-O(7) bond lengths are 2.03 Å. In the second Mg site, Mg(2) is bonded to one O(1), two equivalent O(5), and two equivalent O(8) atoms to form MgO5 square pyramids that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra,  an edgeedge with one Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra, edges with two equivalent Mg(2)O5 square pyramids, and  a faceface with one Ni(3)O6 octahedra. The corner-sharing octahedral tilt angles range from 7-57°. The Mg(2)-O(1) bond length is 2.07 Å. There is one shorter (2.02 Å) and one longer (2.03 Å) Mg(2)-O(5) bond length. There is one shorter (2.04 Å) and one longer (2.05 Å) Mg(2)-O(8) bond length. 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 NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Mg(2)O5 square pyramid, and edges with two equivalent Mg(1)O5 square pyramids. The corner-sharing octahedral tilt angles range from 47-57°. The Ni(1)-O(2) bond length is 1.94 Å. The Ni(1)-O(7) bond length is 2.19 Å. There is one shorter (1.94 Å) and one longer (1.96 Å) Ni(1)-O(4) bond length. There is one shorter (2.05 Å) and one longer (2.08 Å) Ni(1)-O(5) bond length. 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 distorted NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  a faceface with one Mg(1)O5 square pyramid. The corner-sharing octahedral tilt angles range from 47-56°. The Ni(2)-O(4) bond length is 1.94 Å. The Ni(2)-O(8) bond length is 1.93 Å. There is one shorter (1.89 Å) and one longer (1.95 Å) Ni(2)-O(3) bond length. There is one shorter (2.07 Å) and one longer (2.22 Å) Ni(2)-O(6) bond length. 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 distorted NiO6 octahedra that share corners with two equivalent Ni(1)O6 octahedra, corners with two equivalent Ni(4)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, corners with two equivalent Mg(2)O5 square pyramids, edges with two equivalent Ni(2)O6 octahedra, edges with two equivalent Ni(3)O6 octahedra, and  a faceface with one Mg(2)O5 square pyramid. The corner-sharing octahedral tilt angles range from 47-57°. The Ni(3)-O(1) bond length is 1.94 Å. The Ni(3)-O(6) bond length is 1.93 Å. There is one shorter (1.89 Å) and one longer (1.96 Å) Ni(3)-O(2) bond length. There is one shorter (2.07 Å) and one longer (2.24 Å) Ni(3)-O(8) bond length. 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 NiO6 octahedra that share corners with two equivalent Ni(2)O6 octahedra, corners with two equivalent Ni(3)O6 octahedra, corners with two equivalent Mg(1)O5 square pyramids, edges with two equivalent Ni(1)O6 octahedra, edges with two equivalent Ni(4)O6 octahedra,  an edgeedge with one Mg(1)O5 square pyramid, and edges with two equivalent Mg(2)O5 square pyramids. The corner-sharing octahedral tilt angles range from 47-56°. The Ni(4)-O(3) bond length is 1.93 Å. The Ni(4)-O(5) bond length is 2.16 Å. There is one shorter (1.94 Å) and one longer (1.97 Å) Ni(4)-O(1) bond length. There is one shorter (2.05 Å) and one longer (2.08 Å) Ni(4)-O(7) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded to one Mg(2), one Ni(3), and two equivalent Ni(4) atoms to form OMgNi3 trigonal pyramids that share corners with two equivalent O(7)Mg2Ni3 square pyramids, corners with two equivalent O(1)MgNi3 trigonal pyramids,  an edgeedge with one O(7)Mg2Ni3 square pyramid, and edges with two equivalent O(5)Mg2Ni3 square pyramids. In the second O site, O(2) is bonded in a trigonal planar geometry to one Ni(1) and two equivalent Ni(3) atoms. In the third O site, O(3) is bonded in a trigonal planar geometry to one Ni(4) and two equivalent Ni(2) atoms. In the fourth O site, O(4) is bonded to one Mg(1), one Ni(2), and two equivalent Ni(1) atoms to form OMgNi3 trigonal pyramids that share corners with two equivalent O(5)Mg2Ni3 square pyramids, corners with two equivalent O(4)MgNi3 trigonal pyramids,  an edgeedge with one O(5)Mg2Ni3 square pyramid, and edges with two equivalent O(7)Mg2Ni3 square pyramids. In the fifth O site, O(5) is bonded to two equivalent Mg(2), one Ni(4), and two equivalent Ni(1) atoms to form OMg2Ni3 square pyramids that share corners with two equivalent O(4)MgNi3 trigonal pyramids, edges with two equivalent O(5)Mg2Ni3 square pyramids, edges with two equivalent O(7)Mg2Ni3 square pyramids,  an edgeedge with one O(4)MgNi3 trigonal pyramid, and edges with two equivalent O(1)MgNi3 trigonal pyramids. In the sixth O site, O(6) is bonded in a 5-coordinate geometry to two equivalent Mg(1), one Ni(3), and two equivalent Ni(2) atoms. In the seventh O site, O(7) is bonded to two equivalent Mg(1), one Ni(1), and two equivalent Ni(4) atoms to form OMg2Ni3 square pyramids that share corners with two equivalent O(1)MgNi3 trigonal pyramids, edges with two equivalent O(5)Mg2Ni3 square pyramids, edges with two equivalent O(7)Mg2Ni3 square pyramids,  an edgeedge with one O(1)MgNi3 trigonal pyramid, and edges with two equivalent O(4)MgNi3 trigonal pyramids. In the eighth O site, O(8) is bonded in a 5-coordinate geometry to two equivalent Mg(2), one Ni(2), and two equivalent Ni(3) atoms.