MgNi4(OF2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one F(3), one F(4), one F(8), and two equivalent F(1) atoms to form distorted MgOF5 square pyramids that share  a cornercorner with one Ni(3)OF5 octahedra, corners with two equivalent Mg(1)OF5 square pyramids,  an edgeedge with one Ni(3)OF5 octahedra,  an edgeedge with one Ni(4)OF5 octahedra, and edges with two equivalent Ni(2)OF5 octahedra. The corner-sharing octahedral tilt angles are 32°. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to one O(3), one F(1), one F(2), one F(5), and two equivalent F(3) atoms. In the second Ni site, Ni(2) is bonded to one O(4), one F(1), one F(2), one F(6), and two equivalent F(4) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(2)OF5 octahedra, edges with two equivalent Ni(4)OF5 octahedra, and edges with two equivalent Mg(1)OF5 square pyramids. The corner-sharing octahedral tilt angles are 23°. In the third Ni site, Ni(3) is bonded to one O(1), one F(3), one F(7), one F(8), and two equivalent F(5) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(3)OF5 octahedra, corners with two equivalent Ni(4)OF5 octahedra,  a cornercorner with one Mg(1)OF5 square pyramid, and  an edgeedge with one Mg(1)OF5 square pyramid. The corner-sharing octahedral tilt angles range from 8-30°. In the fourth Ni site, Ni(4) is bonded to one O(2), one F(4), one F(7), one F(8), and two equivalent F(6) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(3)OF5 octahedra, corners with two equivalent Ni(4)OF5 octahedra, edges with two equivalent Ni(2)OF5 octahedra, and  an edgeedge with one Mg(1)OF5 square pyramid. The corner-sharing octahedral tilt angles range from 8-29°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(3), and one O(4) atom. In the second O site, O(2) is bonded in a water-like geometry to one Ni(4) and one O(3) atom. In the third O site, O(3) is bonded in a water-like geometry to one Ni(1) and one O(2) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one Ni(2) and one O(1) atom. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Ni(1), and one Ni(2) atom. In the second F site, F(2) is bonded in a bent 150 degrees geometry to one Ni(1) and one Ni(2) atom. In the third F site, F(3) is bonded to one Mg(1), one Ni(3), and two equivalent Ni(1) atoms to form distorted corner-sharing FMgNi3 trigonal pyramids. In the fourth F site, F(4) is bonded to one Mg(1), one Ni(4), and two equivalent Ni(2) atoms to form distorted corner-sharing FMgNi3 trigonal pyramids. In the fifth F site, F(5) is bonded in a distorted trigonal non-coplanar geometry to one Ni(1) and two equivalent Ni(3) atoms. In the sixth F site, F(6) is bonded in a distorted T-shaped geometry to one Ni(2) and two equivalent Ni(4) atoms. In the seventh F site, F(7) is bonded in a linear geometry to one Ni(3) and one Ni(4) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped geometry to one Mg(1), one Ni(3), and one Ni(4) atom.
MgNi4(OF2)4 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one F(3), one F(4), one F(8), and two equivalent F(1) atoms to form distorted MgOF5 square pyramids that share  a cornercorner with one Ni(3)OF5 octahedra, corners with two equivalent Mg(1)OF5 square pyramids,  an edgeedge with one Ni(3)OF5 octahedra,  an edgeedge with one Ni(4)OF5 octahedra, and edges with two equivalent Ni(2)OF5 octahedra. The corner-sharing octahedral tilt angles are 32°. The Mg(1)-O(1) bond length is 2.54 Å. The Mg(1)-F(3) bond length is 1.94 Å. The Mg(1)-F(4) bond length is 1.97 Å. The Mg(1)-F(8) bond length is 1.95 Å. There is one shorter (2.02 Å) and one longer (2.03 Å) Mg(1)-F(1) bond length. There are four inequivalent Ni sites. In the first Ni site, Ni(1) is bonded in a 6-coordinate geometry to one O(3), one F(1), one F(2), one F(5), and two equivalent F(3) atoms. The Ni(1)-O(3) bond length is 1.98 Å. The Ni(1)-F(1) bond length is 2.35 Å. The Ni(1)-F(2) bond length is 1.89 Å. The Ni(1)-F(5) bond length is 2.04 Å. There is one shorter (2.05 Å) and one longer (2.09 Å) Ni(1)-F(3) bond length. In the second Ni site, Ni(2) is bonded to one O(4), one F(1), one F(2), one F(6), and two equivalent F(4) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(2)OF5 octahedra, edges with two equivalent Ni(4)OF5 octahedra, and edges with two equivalent Mg(1)OF5 square pyramids. The corner-sharing octahedral tilt angles are 23°. The Ni(2)-O(4) bond length is 2.02 Å. The Ni(2)-F(1) bond length is 2.21 Å. The Ni(2)-F(2) bond length is 1.87 Å. The Ni(2)-F(6) bond length is 2.03 Å. There is one shorter (2.04 Å) and one longer (2.05 Å) Ni(2)-F(4) bond length. In the third Ni site, Ni(3) is bonded to one O(1), one F(3), one F(7), one F(8), and two equivalent F(5) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(3)OF5 octahedra, corners with two equivalent Ni(4)OF5 octahedra,  a cornercorner with one Mg(1)OF5 square pyramid, and  an edgeedge with one Mg(1)OF5 square pyramid. The corner-sharing octahedral tilt angles range from 8-30°. The Ni(3)-O(1) bond length is 2.03 Å. The Ni(3)-F(3) bond length is 2.33 Å. The Ni(3)-F(7) bond length is 1.95 Å. The Ni(3)-F(8) bond length is 2.15 Å. There is one shorter (2.06 Å) and one longer (2.11 Å) Ni(3)-F(5) bond length. In the fourth Ni site, Ni(4) is bonded to one O(2), one F(4), one F(7), one F(8), and two equivalent F(6) atoms to form distorted NiOF5 octahedra that share corners with two equivalent Ni(3)OF5 octahedra, corners with two equivalent Ni(4)OF5 octahedra, edges with two equivalent Ni(2)OF5 octahedra, and  an edgeedge with one Mg(1)OF5 square pyramid. The corner-sharing octahedral tilt angles range from 8-29°. The Ni(4)-O(2) bond length is 1.95 Å. The Ni(4)-F(4) bond length is 2.22 Å. The Ni(4)-F(7) bond length is 1.97 Å. The Ni(4)-F(8) bond length is 2.27 Å. There is one shorter (2.06 Å) and one longer (2.09 Å) Ni(4)-F(6) bond length. There are four inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Mg(1), one Ni(3), and one O(4) atom. The O(1)-O(4) bond length is 1.35 Å. In the second O site, O(2) is bonded in a water-like geometry to one Ni(4) and one O(3) atom. The O(2)-O(3) bond length is 1.34 Å. In the third O site, O(3) is bonded in a water-like geometry to one Ni(1) and one O(2) atom. In the fourth O site, O(4) is bonded in a distorted water-like geometry to one Ni(2) and one O(1) atom. There are eight inequivalent F sites. In the first F site, F(1) is bonded in a rectangular see-saw-like geometry to two equivalent Mg(1), one Ni(1), and one Ni(2) atom. In the second F site, F(2) is bonded in a bent 150 degrees geometry to one Ni(1) and one Ni(2) atom. In the third F site, F(3) is bonded to one Mg(1), one Ni(3), and two equivalent Ni(1) atoms to form distorted corner-sharing FMgNi3 trigonal pyramids. In the fourth F site, F(4) is bonded to one Mg(1), one Ni(4), and two equivalent Ni(2) atoms to form distorted corner-sharing FMgNi3 trigonal pyramids. In the fifth F site, F(5) is bonded in a distorted trigonal non-coplanar geometry to one Ni(1) and two equivalent Ni(3) atoms. In the sixth F site, F(6) is bonded in a distorted T-shaped geometry to one Ni(2) and two equivalent Ni(4) atoms. In the seventh F site, F(7) is bonded in a linear geometry to one Ni(3) and one Ni(4) atom. In the eighth F site, F(8) is bonded in a distorted T-shaped geometry to one Mg(1), one Ni(3), and one Ni(4) atom.