Mg2Mn(PO4)2 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), and two equivalent O(4) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mn(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one Mn(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 54°. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MnO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Mg(1)O5 trigonal bipyramids. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Mn(1)O6 octahedra, corners with three equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 37-57°. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Mn(1), and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(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 Mn(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(1) atom.
Mg2Mn(PO4)2 crystallizes in the monoclinic P2_1/c space group. Mg(1) is bonded to one O(1), one O(2), one O(3), and two equivalent O(4) atoms to form distorted MgO5 trigonal bipyramids that share  a cornercorner with one Mn(1)O6 octahedra, corners with three equivalent P(1)O4 tetrahedra,  an edgeedge with one Mn(1)O6 octahedra,  an edgeedge with one P(1)O4 tetrahedra, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 54°. The Mg(1)-O(1) bond length is 2.15 Å. The Mg(1)-O(2) bond length is 1.96 Å. The Mg(1)-O(3) bond length is 2.03 Å. There is one shorter (1.98 Å) and one longer (2.01 Å) Mg(1)-O(4) bond length. Mn(1) is bonded to two equivalent O(1), two equivalent O(2), and two equivalent O(3) atoms to form MnO6 octahedra that share corners with six equivalent P(1)O4 tetrahedra, corners with two equivalent Mg(1)O5 trigonal bipyramids, and edges with two equivalent Mg(1)O5 trigonal bipyramids. Both Mn(1)-O(1) bond lengths are 2.12 Å. Both Mn(1)-O(2) bond lengths are 2.27 Å. Both Mn(1)-O(3) bond lengths are 2.17 Å. P(1) is bonded to one O(1), one O(2), one O(3), and one O(4) atom to form PO4 tetrahedra that share corners with three equivalent Mn(1)O6 octahedra, corners with three equivalent Mg(1)O5 trigonal bipyramids, and  an edgeedge with one Mg(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 37-57°. The P(1)-O(1) bond length is 1.54 Å. The P(1)-O(2) bond length is 1.52 Å. The P(1)-O(3) bond length is 1.55 Å. The P(1)-O(4) bond length is 1.54 Å. There are four inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Mn(1), and one P(1) atom. In the second O site, O(2) is bonded in a 3-coordinate geometry to one Mg(1), one Mn(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 Mn(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(1) atom.