MgCuP2O7 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form MgO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and edges with two equivalent Cu(1)O6 octahedra. Cu(1) is bonded to one O(3), one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted CuO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Cu(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. There are two inequivalent P sites. In the first P site, P(1) is bonded to one O(1), one O(2), one O(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Cu(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 48-56°. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Cu(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with three equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 39-52°. 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 bent 150 degrees geometry to one Mg(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one P(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Cu(1) and one P(1) 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 distorted trigonal planar geometry to one Mg(1), one Cu(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(1) atom.
MgCuP2O7 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(2), one O(3), one O(5), one O(6), and one O(7) atom to form MgO5 trigonal bipyramids that share corners with two equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra, and edges with two equivalent Cu(1)O6 octahedra. The Mg(1)-O(2) bond length is 1.96 Å. The Mg(1)-O(3) bond length is 2.11 Å. The Mg(1)-O(5) bond length is 2.00 Å. The Mg(1)-O(6) bond length is 2.07 Å. The Mg(1)-O(7) bond length is 2.04 Å. Cu(1) is bonded to one O(3), one O(5), one O(6), one O(7), and two equivalent O(4) atoms to form distorted CuO6 octahedra that share corners with three equivalent P(1)O4 tetrahedra, corners with three equivalent P(2)O4 tetrahedra,  an edgeedge with one Cu(1)O6 octahedra, and edges with two equivalent Mg(1)O5 trigonal bipyramids. The Cu(1)-O(3) bond length is 2.12 Å. The Cu(1)-O(5) bond length is 2.39 Å. The Cu(1)-O(6) bond length is 2.01 Å. The Cu(1)-O(7) bond length is 2.10 Å. There is one shorter (1.94 Å) and one longer (2.38 Å) Cu(1)-O(4) 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(4), and one O(7) atom to form PO4 tetrahedra that share corners with three equivalent Cu(1)O6 octahedra,  a cornercorner with one P(2)O4 tetrahedra, and corners with two equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 48-56°. The P(1)-O(1) bond length is 1.62 Å. The P(1)-O(2) bond length is 1.50 Å. The P(1)-O(4) bond length is 1.55 Å. The P(1)-O(7) bond length is 1.54 Å. In the second P site, P(2) is bonded to one O(1), one O(3), one O(5), and one O(6) atom to form PO4 tetrahedra that share corners with three equivalent Cu(1)O6 octahedra,  a cornercorner with one P(1)O4 tetrahedra, and corners with three equivalent Mg(1)O5 trigonal bipyramids. The corner-sharing octahedral tilt angles range from 39-52°. The P(2)-O(1) bond length is 1.60 Å. The P(2)-O(3) bond length is 1.54 Å. The P(2)-O(5) bond length is 1.52 Å. The P(2)-O(6) bond length is 1.55 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 bent 150 degrees geometry to one Mg(1) and one P(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Cu(1), and one P(2) atom. In the fourth O site, O(4) is bonded in a 3-coordinate geometry to two equivalent Cu(1) and one P(1) 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 distorted trigonal planar geometry to one Mg(1), one Cu(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(1) atom.