Ba2Mg(NiO3)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Mg(1) is bonded to one O(2), two equivalent O(1), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share corners with four equivalent Ni(2)O5 square pyramids. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(1), and two equivalent O(3) atoms. In the second Ni site, Ni(2) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted NiO5 square pyramids that share corners with four equivalent Mg(1)O5 trigonal bipyramids. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and one Mg(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), one Ni(1), and one Ni(2) atom.
Ba2Mg(NiO3)2 crystallizes in the monoclinic Cm space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 7-coordinate geometry to one O(4), two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms. The Ba(1)-O(4) bond length is 2.53 Å. Both Ba(1)-O(1) bond lengths are 2.74 Å. Both Ba(1)-O(2) bond lengths are 2.87 Å. Both Ba(1)-O(3) bond lengths are 2.90 Å. In the second Ba site, Ba(2) is bonded in a 8-coordinate geometry to two equivalent O(1), two equivalent O(2), two equivalent O(3), and two equivalent O(4) atoms. Both Ba(2)-O(1) bond lengths are 2.85 Å. There is one shorter (2.68 Å) and one longer (2.82 Å) Ba(2)-O(2) bond length. Both Ba(2)-O(3) bond lengths are 2.78 Å. Both Ba(2)-O(4) bond lengths are 3.02 Å. Mg(1) is bonded to one O(2), two equivalent O(1), and two equivalent O(3) atoms to form distorted MgO5 trigonal bipyramids that share corners with four equivalent Ni(2)O5 square pyramids. The Mg(1)-O(2) bond length is 2.05 Å. Both Mg(1)-O(1) bond lengths are 2.10 Å. Both Mg(1)-O(3) bond lengths are 2.03 Å. There are two inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 5-coordinate geometry to one O(4), two equivalent O(1), and two equivalent O(3) atoms. The Ni(1)-O(4) bond length is 2.22 Å. Both Ni(1)-O(1) bond lengths are 1.89 Å. Both Ni(1)-O(3) bond lengths are 1.87 Å. In the second Ni site, Ni(2) is bonded to one O(4), two equivalent O(1), and two equivalent O(3) atoms to form distorted NiO5 square pyramids that share corners with four equivalent Mg(1)O5 trigonal bipyramids. The Ni(2)-O(4) bond length is 1.97 Å. Both Ni(2)-O(1) bond lengths are 2.04 Å. Both Ni(2)-O(3) bond lengths are 2.01 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 5-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the second O site, O(2) is bonded in a 5-coordinate geometry to two equivalent Ba(1), two equivalent Ba(2), and one Mg(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Ba(1), one Ba(2), one Mg(1), one Ni(1), and one Ni(2) atom. In the fourth O site, O(4) is bonded in a 5-coordinate geometry to one Ba(1), two equivalent Ba(2), one Ni(1), and one Ni(2) atom.