MgMn2(BO3)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  an edgeedge with one Mn(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-75°. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with four equivalent Mg(1)O4 tetrahedra and corners with four equivalent Mn(2)O4 tetrahedra. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form distorted MnO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 60-80°. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(4), and one O(5) atom. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(6) atom. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to one Mg(1), one Mn(1), one Mn(2), and one B(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one B(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mn(1), one Mn(2), and one B(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mn(1), and one B(1) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Mn(1), and one B(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(1), one Mn(2), and one B(2) atom.
MgMn2(BO3)2 crystallizes in the triclinic P1 space group. Mg(1) is bonded to one O(1), one O(4), one O(5), and one O(6) atom to form MgO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  an edgeedge with one Mn(2)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 55-75°. The Mg(1)-O(1) bond length is 2.02 Å. The Mg(1)-O(4) bond length is 1.99 Å. The Mg(1)-O(5) bond length is 1.96 Å. The Mg(1)-O(6) bond length is 2.06 Å. There are two inequivalent Mn sites. In the first Mn site, Mn(1) is bonded to one O(1), one O(2), one O(3), one O(4), one O(5), and one O(6) atom to form MnO6 octahedra that share corners with four equivalent Mg(1)O4 tetrahedra and corners with four equivalent Mn(2)O4 tetrahedra. The Mn(1)-O(1) bond length is 2.36 Å. The Mn(1)-O(2) bond length is 2.18 Å. The Mn(1)-O(3) bond length is 2.18 Å. The Mn(1)-O(4) bond length is 2.19 Å. The Mn(1)-O(5) bond length is 2.19 Å. The Mn(1)-O(6) bond length is 2.43 Å. In the second Mn site, Mn(2) is bonded to one O(1), one O(2), one O(3), and one O(6) atom to form distorted MnO4 tetrahedra that share corners with four equivalent Mn(1)O6 octahedra and  an edgeedge with one Mg(1)O4 tetrahedra. The corner-sharing octahedral tilt angles range from 60-80°. The Mn(2)-O(1) bond length is 2.21 Å. The Mn(2)-O(2) bond length is 2.03 Å. The Mn(2)-O(3) bond length is 2.07 Å. The Mn(2)-O(6) bond length is 2.13 Å. There are two inequivalent B sites. In the first B site, B(1) is bonded in a trigonal planar geometry to one O(1), one O(4), and one O(5) atom. The B(1)-O(1) bond length is 1.42 Å. The B(1)-O(4) bond length is 1.38 Å. The B(1)-O(5) bond length is 1.38 Å. In the second B site, B(2) is bonded in a trigonal planar geometry to one O(2), one O(3), and one O(6) atom. The B(2)-O(2) bond length is 1.38 Å. The B(2)-O(3) bond length is 1.37 Å. The B(2)-O(6) bond length is 1.42 Å. There are six inequivalent O sites. In the first O site, O(1) is bonded in a distorted tetrahedral geometry to one Mg(1), one Mn(1), one Mn(2), and one B(1) atom. In the second O site, O(2) is bonded in a distorted trigonal planar geometry to one Mn(1), one Mn(2), and one B(2) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mn(1), one Mn(2), and one B(2) atom. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Mg(1), one Mn(1), and one B(1) atom. In the fifth O site, O(5) is bonded in a trigonal planar geometry to one Mg(1), one Mn(1), and one B(1) atom. In the sixth O site, O(6) is bonded in a 4-coordinate geometry to one Mg(1), one Mn(1), one Mn(2), and one B(2) atom.