Mg2Nb2WO8 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form distorted NbO6 octahedra that share corners with four equivalent W(1)O6 octahedra and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form NbO6 octahedra that share corners with four equivalent W(1)O6 octahedra and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. W(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form WO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and edges with two equivalent W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one W(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one W(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent W(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent W(1) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded to one Mg(1), two equivalent Mg(2), one Nb(1), and one Nb(2) atom to form distorted OMg3Nb2 trigonal bipyramids that share  a cornercorner with one O(8)Mg3Nb trigonal pyramid, corners with two equivalent O(7)Mg3Nb trigonal pyramids,  an edgeedge with one O(6)Mg3Nb2 trigonal bipyramid, edges with two equivalent O(7)Mg3Nb trigonal pyramids, and edges with two equivalent O(8)Mg3Nb trigonal pyramids. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(2) atom to form OMg3Nb trigonal pyramids that share corners with two equivalent O(6)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(8)Mg3Nb trigonal pyramids, edges with two equivalent O(6)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Nb trigonal pyramid. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(1) atom to form OMg3Nb trigonal pyramids that share  a cornercorner with one O(6)Mg3Nb2 trigonal bipyramid, corners with four equivalent O(7)Mg3Nb trigonal pyramids, edges with two equivalent O(6)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(8)Mg3Nb trigonal pyramid.
Mg2Nb2WO8 crystallizes in the triclinic P-1 space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 6-coordinate geometry to one O(6), one O(7), two equivalent O(5), and two equivalent O(8) atoms. The Mg(1)-O(6) bond length is 2.26 Å. The Mg(1)-O(7) bond length is 2.00 Å. There is one shorter (2.05 Å) and one longer (2.43 Å) Mg(1)-O(5) bond length. There is one shorter (2.06 Å) and one longer (2.13 Å) Mg(1)-O(8) bond length. In the second Mg site, Mg(2) is bonded in a 6-coordinate geometry to one O(5), one O(8), two equivalent O(6), and two equivalent O(7) atoms. The Mg(2)-O(5) bond length is 2.61 Å. The Mg(2)-O(8) bond length is 1.99 Å. There is one shorter (2.00 Å) and one longer (2.43 Å) Mg(2)-O(6) bond length. There is one shorter (1.98 Å) and one longer (2.10 Å) Mg(2)-O(7) bond length. There are two inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to one O(1), one O(2), one O(3), one O(5), one O(6), and one O(8) atom to form distorted NbO6 octahedra that share corners with four equivalent W(1)O6 octahedra and edges with two equivalent Nb(2)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. The Nb(1)-O(1) bond length is 2.06 Å. The Nb(1)-O(2) bond length is 2.02 Å. The Nb(1)-O(3) bond length is 2.14 Å. The Nb(1)-O(5) bond length is 2.34 Å. The Nb(1)-O(6) bond length is 2.21 Å. The Nb(1)-O(8) bond length is 1.98 Å. In the second Nb site, Nb(2) is bonded to one O(1), one O(2), one O(4), one O(5), one O(6), and one O(7) atom to form NbO6 octahedra that share corners with four equivalent W(1)O6 octahedra and edges with two equivalent Nb(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. The Nb(2)-O(1) bond length is 2.16 Å. The Nb(2)-O(2) bond length is 2.27 Å. The Nb(2)-O(4) bond length is 2.02 Å. The Nb(2)-O(5) bond length is 2.04 Å. The Nb(2)-O(6) bond length is 2.05 Å. The Nb(2)-O(7) bond length is 2.05 Å. W(1) is bonded to one O(1), one O(2), two equivalent O(3), and two equivalent O(4) atoms to form WO6 octahedra that share corners with four equivalent Nb(1)O6 octahedra, corners with four equivalent Nb(2)O6 octahedra, and edges with two equivalent W(1)O6 octahedra. The corner-sharing octahedral tilt angles range from 42-56°. The W(1)-O(1) bond length is 2.02 Å. The W(1)-O(2) bond length is 2.06 Å. There is one shorter (2.05 Å) and one longer (2.12 Å) W(1)-O(3) bond length. There is one shorter (2.12 Å) and one longer (2.16 Å) W(1)-O(4) bond length. There are eight inequivalent O sites. In the first O site, O(1) is bonded in a 3-coordinate geometry to one Nb(1), one Nb(2), and one W(1) atom. In the second O site, O(2) is bonded in a trigonal planar geometry to one Nb(1), one Nb(2), and one W(1) atom. In the third O site, O(3) is bonded in a distorted trigonal planar geometry to one Nb(1) and two equivalent W(1) atoms. In the fourth O site, O(4) is bonded in a distorted trigonal planar geometry to one Nb(2) and two equivalent W(1) atoms. In the fifth O site, O(5) is bonded in a 5-coordinate geometry to one Mg(2), two equivalent Mg(1), one Nb(1), and one Nb(2) atom. In the sixth O site, O(6) is bonded to one Mg(1), two equivalent Mg(2), one Nb(1), and one Nb(2) atom to form distorted OMg3Nb2 trigonal bipyramids that share  a cornercorner with one O(8)Mg3Nb trigonal pyramid, corners with two equivalent O(7)Mg3Nb trigonal pyramids,  an edgeedge with one O(6)Mg3Nb2 trigonal bipyramid, edges with two equivalent O(7)Mg3Nb trigonal pyramids, and edges with two equivalent O(8)Mg3Nb trigonal pyramids. In the seventh O site, O(7) is bonded to one Mg(1), two equivalent Mg(2), and one Nb(2) atom to form OMg3Nb trigonal pyramids that share corners with two equivalent O(6)Mg3Nb2 trigonal bipyramids, corners with four equivalent O(8)Mg3Nb trigonal pyramids, edges with two equivalent O(6)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(7)Mg3Nb trigonal pyramid. In the eighth O site, O(8) is bonded to one Mg(2), two equivalent Mg(1), and one Nb(1) atom to form OMg3Nb trigonal pyramids that share  a cornercorner with one O(6)Mg3Nb2 trigonal bipyramid, corners with four equivalent O(7)Mg3Nb trigonal pyramids, edges with two equivalent O(6)Mg3Nb2 trigonal bipyramids, and  an edgeedge with one O(8)Mg3Nb trigonal pyramid.