Ba3MgV2O8 crystallizes in the trigonal R-3m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(1) and nine equivalent O(2) atoms. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form distorted BaO12 cuboctahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with six equivalent Ba(2)O12 cuboctahedra, and edges with six equivalent V(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles are 9°. Mg(1) is bonded to six equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with six equivalent Ba(2)O12 cuboctahedra and faces with two equivalent V(1)O4 trigonal pyramids. V(1) is bonded to one O(1) and three equivalent O(2) atoms to form distorted VO4 trigonal pyramids that share edges with three equivalent Ba(2)O12 cuboctahedra and  a faceface with one Mg(1)O6 octahedra. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), three equivalent Ba(2), and one V(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Ba(2), three equivalent Ba(1), one Mg(1), and one V(1) atom.
Ba3MgV2O8 crystallizes in the trigonal R-3m space group. There are two inequivalent Ba sites. In the first Ba site, Ba(1) is bonded in a 10-coordinate geometry to one O(1) and nine equivalent O(2) atoms. The Ba(1)-O(1) bond length is 2.55 Å. There are three shorter (2.94 Å) and six longer (3.02 Å) Ba(1)-O(2) bond lengths. In the second Ba site, Ba(2) is bonded to six equivalent O(1) and six equivalent O(2) atoms to form distorted BaO12 cuboctahedra that share corners with six equivalent Mg(1)O6 octahedra, edges with six equivalent Ba(2)O12 cuboctahedra, and edges with six equivalent V(1)O4 trigonal pyramids. The corner-sharing octahedral tilt angles are 9°. All Ba(2)-O(1) bond lengths are 3.44 Å. All Ba(2)-O(2) bond lengths are 2.98 Å. Mg(1) is bonded to six equivalent O(2) atoms to form distorted MgO6 octahedra that share corners with six equivalent Ba(2)O12 cuboctahedra and faces with two equivalent V(1)O4 trigonal pyramids. All Mg(1)-O(2) bond lengths are 2.14 Å. V(1) is bonded to one O(1) and three equivalent O(2) atoms to form distorted VO4 trigonal pyramids that share edges with three equivalent Ba(2)O12 cuboctahedra and  a faceface with one Mg(1)O6 octahedra. The V(1)-O(1) bond length is 1.75 Å. All V(1)-O(2) bond lengths are 1.86 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a distorted linear geometry to one Ba(1), three equivalent Ba(2), and one V(1) atom. In the second O site, O(2) is bonded in a 6-coordinate geometry to one Ba(2), three equivalent Ba(1), one Mg(1), and one V(1) atom.