Ba3MgNb2O8 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 6-coordinate geometry to six equivalent O(1) atoms. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to one O(2) and nine equivalent O(1) atoms. Mg(1) is bonded in an octahedral geometry to six equivalent O(1) atoms. Nb(1) is bonded in a rectangular see-saw-like geometry to one O(2) and three equivalent O(1) atoms. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Ba(1), three equivalent Ba(2), one Mg(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a linear geometry to one Ba(2) and one Nb(1) atom.
Ba3MgNb2O8 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 6-coordinate geometry to six equivalent O(1) atoms. All Ba(1)-O(1) bond lengths are 3.07 Å. In the second Ba site, Ba(2) is bonded in a 10-coordinate geometry to one O(2) and nine equivalent O(1) atoms. The Ba(2)-O(2) bond length is 2.53 Å. There are three shorter (2.86 Å) and six longer (3.11 Å) Ba(2)-O(1) bond lengths. Mg(1) is bonded in an octahedral geometry to six equivalent O(1) atoms. All Mg(1)-O(1) bond lengths are 2.15 Å. Nb(1) is bonded in a rectangular see-saw-like geometry to one O(2) and three equivalent O(1) atoms. The Nb(1)-O(2) bond length is 1.87 Å. All Nb(1)-O(1) bond lengths are 1.98 Å. There are two inequivalent O sites. In the first O site, O(1) is bonded in a 6-coordinate geometry to one Ba(1), three equivalent Ba(2), one Mg(1), and one Nb(1) atom. In the second O site, O(2) is bonded in a linear geometry to one Ba(2) and one Nb(1) atom.