Mg2Ni2O5 crystallizes in the orthorhombic Pbam space group. Mg(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(2), and three equivalent O(3) atoms. Ni(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing NiO5 square pyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Mg(1) and two equivalent Ni(1) atoms to form OMg4Ni2 octahedra that share corners with eight equivalent O(2)Mg2Ni2 tetrahedra, edges with two equivalent O(1)Mg4Ni2 octahedra, and edges with two equivalent O(2)Mg2Ni2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Ni(1) atoms to form OMg2Ni2 tetrahedra that share corners with four equivalent O(1)Mg4Ni2 octahedra, corners with four equivalent O(2)Mg2Ni2 tetrahedra, and  an edgeedge with one O(1)Mg4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 19-61°. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Mg(1) and two equivalent Ni(1) atoms.
Mg2Ni2O5 crystallizes in the orthorhombic Pbam space group. Mg(1) is bonded in a 7-coordinate geometry to two equivalent O(1), two equivalent O(2), and three equivalent O(3) atoms. Both Mg(1)-O(1) bond lengths are 2.44 Å. Both Mg(1)-O(2) bond lengths are 2.09 Å. There are a spread of Mg(1)-O(3) bond distances ranging from 2.09-2.72 Å. Ni(1) is bonded to one O(1), two equivalent O(2), and two equivalent O(3) atoms to form corner-sharing NiO5 square pyramids. The Ni(1)-O(1) bond length is 1.99 Å. There is one shorter (1.95 Å) and one longer (1.97 Å) Ni(1)-O(2) bond length. Both Ni(1)-O(3) bond lengths are 1.90 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded to four equivalent Mg(1) and two equivalent Ni(1) atoms to form OMg4Ni2 octahedra that share corners with eight equivalent O(2)Mg2Ni2 tetrahedra, edges with two equivalent O(1)Mg4Ni2 octahedra, and edges with two equivalent O(2)Mg2Ni2 tetrahedra. In the second O site, O(2) is bonded to two equivalent Mg(1) and two equivalent Ni(1) atoms to form OMg2Ni2 tetrahedra that share corners with four equivalent O(1)Mg4Ni2 octahedra, corners with four equivalent O(2)Mg2Ni2 tetrahedra, and  an edgeedge with one O(1)Mg4Ni2 octahedra. The corner-sharing octahedral tilt angles range from 19-61°. In the third O site, O(3) is bonded in a 4-coordinate geometry to three equivalent Mg(1) and two equivalent Ni(1) atoms.