MgNiP2O7 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. Ni(1) is bonded to one O(2), one O(4), one O(7), and two equivalent O(6) atoms to form NiO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Ni(1)O5 square pyramid. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O5 square pyramids,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Mg(1)O5 trigonal bipyramids. In the second P site, P(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Ni(1)O5 square pyramids,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Mg(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Ni(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom.
MgNiP2O7 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to one O(2), one O(3), one O(4), and two equivalent O(5) atoms to form MgO5 trigonal bipyramids that share corners with two equivalent Ni(1)O5 square pyramids, corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The Mg(1)-O(2) bond length is 2.14 Å. The Mg(1)-O(3) bond length is 2.01 Å. The Mg(1)-O(4) bond length is 2.17 Å. There is one shorter (2.06 Å) and one longer (2.09 Å) Mg(1)-O(5) bond length. Ni(1) is bonded to one O(2), one O(4), one O(7), and two equivalent O(6) atoms to form NiO5 square pyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Ni(1)O5 square pyramid. The Ni(1)-O(2) bond length is 2.14 Å. The Ni(1)-O(4) bond length is 2.04 Å. The Ni(1)-O(7) bond length is 1.96 Å. There is one shorter (2.05 Å) and one longer (2.10 Å) Ni(1)-O(6) bond length. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Ni(1)O5 square pyramids,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Mg(1)O5 trigonal bipyramids. The P(1)-O(1) bond length is 1.59 Å. The P(1)-O(2) bond length is 1.55 Å. The P(1)-O(5) bond length is 1.53 Å. The P(1)-O(6) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with two equivalent Ni(1)O5 square pyramids,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. The P(2)-O(1) bond length is 1.64 Å. The P(2)-O(3) bond length is 1.52 Å. The P(2)-O(4) bond length is 1.55 Å. The P(2)-O(7) bond length is 1.52 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mg(1), one Ni(1), and one P(1) atom. In the third O site, O(3) is bonded in a bent 120 degrees geometry to one Mg(1) and one P(2) atom. In the fourth O site, O(4) is bonded in a trigonal planar geometry to one Mg(1), one Ni(1), and one P(2) atom. In the fifth O site, O(5) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one P(1) atom. In the sixth O site, O(6) is bonded in a 3-coordinate geometry to two equivalent Ni(1) and one P(1) atom. In the seventh O site, O(7) is bonded in a distorted bent 150 degrees geometry to one Ni(1) and one P(2) atom.