MgCuP2O7 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(4) atoms to form distorted MgO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. Cu(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(7) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 50°. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 26-56°. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Cu(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(2) atom.
MgCuP2O7 crystallizes in the triclinic P-1 space group. Mg(1) is bonded to one O(1), one O(3), one O(5), one O(7), and two equivalent O(4) atoms to form distorted MgO6 octahedra that share corners with two equivalent P(1)O4 tetrahedra, corners with four equivalent P(2)O4 tetrahedra,  an edgeedge with one Mg(1)O6 octahedra, and edges with two equivalent Cu(1)O5 trigonal bipyramids. The Mg(1)-O(1) bond length is 2.28 Å. The Mg(1)-O(3) bond length is 2.10 Å. The Mg(1)-O(5) bond length is 2.03 Å. The Mg(1)-O(7) bond length is 2.08 Å. There is one shorter (2.08 Å) and one longer (2.14 Å) Mg(1)-O(4) bond length. Cu(1) is bonded to one O(1), one O(2), one O(3), one O(5), and one O(7) atom to form distorted CuO5 trigonal bipyramids that share corners with two equivalent P(2)O4 tetrahedra, corners with three equivalent P(1)O4 tetrahedra, and edges with two equivalent Mg(1)O6 octahedra. The Cu(1)-O(1) bond length is 1.96 Å. The Cu(1)-O(2) bond length is 1.95 Å. The Cu(1)-O(3) bond length is 2.04 Å. The Cu(1)-O(5) bond length is 2.55 Å. The Cu(1)-O(7) bond length is 1.99 Å. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form PO4 tetrahedra that share corners with two equivalent Mg(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with three equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles are 50°. The P(1)-O(1) bond length is 1.55 Å. The P(1)-O(2) bond length is 1.51 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(6) bond length is 1.61 Å. In the second P site, P(2) is bonded to one O(4), one O(5), one O(6), and one O(7) atom to form PO4 tetrahedra that share corners with four equivalent Mg(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with two equivalent Cu(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 26-56°. The P(2)-O(4) bond length is 1.52 Å. The P(2)-O(5) bond length is 1.51 Å. The P(2)-O(6) bond length is 1.61 Å. The P(2)-O(7) bond length is 1.55 Å. There are seven inequivalent O sites. In the first O site, O(1) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(1) atom. In the second O site, O(2) is bonded in a bent 150 degrees geometry to one Cu(1) and one P(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(1) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1) and one P(2) atom. In the fifth O site, O(5) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one P(2) atom. In the sixth O site, O(6) is bonded in a bent 150 degrees geometry to one P(1) and one P(2) atom. In the seventh O site, O(7) is bonded in a distorted trigonal planar geometry to one Mg(1), one Cu(1), and one P(2) atom.