MgNb2(BO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(2) atoms. Nb(1) is bonded to one O(1), two equivalent O(3), and four equivalent O(2) atoms to form distorted NbO7 pentagonal bipyramids that share corners with three equivalent B(1)O4 tetrahedra, edges with three equivalent Nb(1)O7 pentagonal bipyramids, and edges with two equivalent B(1)O4 tetrahedra. B(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form BO4 tetrahedra that share corners with three equivalent Nb(1)O7 pentagonal bipyramids and edges with two equivalent Nb(1)O7 pentagonal bipyramids. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(1), and one B(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Nb(1), and one B(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Nb(1) and one B(1) atom.
MgNb2(BO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded in a 6-coordinate geometry to two equivalent O(1) and four equivalent O(2) atoms. Both Mg(1)-O(1) bond lengths are 1.94 Å. All Mg(1)-O(2) bond lengths are 2.17 Å. Nb(1) is bonded to one O(1), two equivalent O(3), and four equivalent O(2) atoms to form distorted NbO7 pentagonal bipyramids that share corners with three equivalent B(1)O4 tetrahedra, edges with three equivalent Nb(1)O7 pentagonal bipyramids, and edges with two equivalent B(1)O4 tetrahedra. The Nb(1)-O(1) bond length is 2.01 Å. There is one shorter (2.16 Å) and one longer (2.19 Å) Nb(1)-O(3) bond length. There are two shorter (2.17 Å) and two longer (2.19 Å) Nb(1)-O(2) bond lengths. B(1) is bonded to one O(1), one O(3), and two equivalent O(2) atoms to form BO4 tetrahedra that share corners with three equivalent Nb(1)O7 pentagonal bipyramids and edges with two equivalent Nb(1)O7 pentagonal bipyramids. The B(1)-O(1) bond length is 1.50 Å. The B(1)-O(3) bond length is 1.43 Å. Both B(1)-O(2) bond lengths are 1.53 Å. There are three inequivalent O sites. In the first O site, O(1) is bonded in a distorted T-shaped geometry to one Mg(1), one Nb(1), and one B(1) atom. In the second O site, O(2) is bonded in a 4-coordinate geometry to one Mg(1), two equivalent Nb(1), and one B(1) atom. In the third O site, O(3) is bonded in a 3-coordinate geometry to two equivalent Nb(1) and one B(1) atom.