MgPr(ReO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Re(1)O5 trigonal bipyramids. Pr(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Re(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form ReO5 trigonal bipyramids that share corners with three equivalent Mg(1)O6 octahedra and  an edgeedge with one Re(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-66°. 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 Pr(1), and one Re(1) atom. In the second O site, O(2) is bonded in a distorted L-shaped geometry to two equivalent Re(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Pr(1), and one Re(1) atom.
MgPr(ReO4)2 crystallizes in the monoclinic C2/m space group. Mg(1) is bonded to two equivalent O(3) and four equivalent O(1) atoms to form MgO6 octahedra that share corners with six equivalent Re(1)O5 trigonal bipyramids. Both Mg(1)-O(3) bond lengths are 2.07 Å. All Mg(1)-O(1) bond lengths are 2.22 Å. Pr(1) is bonded in a 6-coordinate geometry to two equivalent O(3) and four equivalent O(1) atoms. Both Pr(1)-O(3) bond lengths are 2.40 Å. All Pr(1)-O(1) bond lengths are 2.41 Å. Re(1) is bonded to one O(3), two equivalent O(1), and two equivalent O(2) atoms to form ReO5 trigonal bipyramids that share corners with three equivalent Mg(1)O6 octahedra and  an edgeedge with one Re(1)O5 trigonal bipyramid. The corner-sharing octahedral tilt angles range from 44-66°. The Re(1)-O(3) bond length is 1.91 Å. Both Re(1)-O(1) bond lengths are 1.86 Å. There is one shorter (1.84 Å) and one longer (2.13 Å) Re(1)-O(2) bond length. 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 Pr(1), and one Re(1) atom. In the second O site, O(2) is bonded in a distorted L-shaped geometry to two equivalent Re(1) atoms. In the third O site, O(3) is bonded in a 3-coordinate geometry to one Mg(1), one Pr(1), and one Re(1) atom.