MgSc4(Si2O7)2 crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 7-coordinate geometry to one O(5), three equivalent O(3), and three equivalent O(4) atoms. There are two inequivalent Sc sites. In the first Sc site, Sc(1) is bonded in a 7-coordinate geometry to one O(1), one O(5), one O(6), two equivalent O(2), and two equivalent O(3) atoms. In the second Sc site, Sc(2) is bonded to one O(5), one O(6), three equivalent O(1), and three equivalent O(4) atoms to form distorted ScO8 hexagonal bipyramids that share edges with six equivalent Si(1)O6 octahedra. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form SiO6 octahedra that share corners with two equivalent Si(2)O6 octahedra, corners with four equivalent Si(1)O6 octahedra, and edges with two equivalent Sc(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 40-49°. In the second Si site, Si(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form corner-sharing SiO6 octahedra. The corner-sharing octahedral tilt angles range from 42-49°. There are six inequivalent O sites. In the first O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Sc(2), and two equivalent Si(1) atoms. In the second O site, O(5) is bonded to one Mg(1), one Sc(2), and three equivalent Sc(1) atoms to form a mixture of distorted edge and corner-sharing OMgSc4 trigonal bipyramids. In the third O site, O(6) is bonded in a rectangular see-saw-like geometry to one Sc(2) and three equivalent Sc(1) atoms. In the fourth O site, O(1) is bonded to one Sc(1), one Sc(2), and two equivalent Si(1) atoms to form distorted OSc2Si2 trigonal pyramids that share corners with four equivalent O(1)Sc2Si2 trigonal pyramids, edges with two equivalent O(2)Sc2Si2 tetrahedra, and  an edgeedge with one O(5)MgSc4 trigonal bipyramid. In the fifth O site, O(2) is bonded to two equivalent Sc(1), one Si(1), and one Si(2) atom to form distorted OSc2Si2 tetrahedra that share corners with four equivalent O(2)Sc2Si2 tetrahedra, corners with two equivalent O(5)MgSc4 trigonal bipyramids, and edges with two equivalent O(1)Sc2Si2 trigonal pyramids. In the sixth O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Sc(1), one Si(1), and one Si(2) atom.
MgSc4(Si2O7)2 crystallizes in the trigonal R3m space group. Mg(1) is bonded in a 7-coordinate geometry to one O(5), three equivalent O(3), and three equivalent O(4) atoms. The Mg(1)-O(5) bond length is 1.96 Å. All Mg(1)-O(3) bond lengths are 2.27 Å. All Mg(1)-O(4) bond lengths are 2.01 Å. There are two inequivalent Sc sites. In the first Sc site, Sc(1) is bonded in a 7-coordinate geometry to one O(1), one O(5), one O(6), two equivalent O(2), and two equivalent O(3) atoms. The Sc(1)-O(1) bond length is 2.22 Å. The Sc(1)-O(5) bond length is 2.21 Å. The Sc(1)-O(6) bond length is 2.07 Å. Both Sc(1)-O(2) bond lengths are 2.17 Å. Both Sc(1)-O(3) bond lengths are 2.59 Å. In the second Sc site, Sc(2) is bonded to one O(5), one O(6), three equivalent O(1), and three equivalent O(4) atoms to form distorted ScO8 hexagonal bipyramids that share edges with six equivalent Si(1)O6 octahedra. The Sc(2)-O(5) bond length is 2.10 Å. The Sc(2)-O(6) bond length is 1.99 Å. All Sc(2)-O(1) bond lengths are 2.33 Å. All Sc(2)-O(4) bond lengths are 2.37 Å. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded to one O(2), one O(3), two equivalent O(1), and two equivalent O(4) atoms to form SiO6 octahedra that share corners with two equivalent Si(2)O6 octahedra, corners with four equivalent Si(1)O6 octahedra, and edges with two equivalent Sc(2)O8 hexagonal bipyramids. The corner-sharing octahedral tilt angles range from 40-49°. The Si(1)-O(2) bond length is 1.87 Å. The Si(1)-O(3) bond length is 1.90 Å. Both Si(1)-O(1) bond lengths are 1.76 Å. Both Si(1)-O(4) bond lengths are 1.79 Å. In the second Si site, Si(2) is bonded to three equivalent O(2) and three equivalent O(3) atoms to form corner-sharing SiO6 octahedra. The corner-sharing octahedral tilt angles range from 42-49°. All Si(2)-O(2) bond lengths are 1.88 Å. All Si(2)-O(3) bond lengths are 1.84 Å. There are six inequivalent O sites. In the first O site, O(4) is bonded in a 4-coordinate geometry to one Mg(1), one Sc(2), and two equivalent Si(1) atoms. In the second O site, O(5) is bonded to one Mg(1), one Sc(2), and three equivalent Sc(1) atoms to form a mixture of distorted edge and corner-sharing OMgSc4 trigonal bipyramids. In the third O site, O(6) is bonded in a rectangular see-saw-like geometry to one Sc(2) and three equivalent Sc(1) atoms. In the fourth O site, O(1) is bonded to one Sc(1), one Sc(2), and two equivalent Si(1) atoms to form distorted OSc2Si2 trigonal pyramids that share corners with four equivalent O(1)Sc2Si2 trigonal pyramids, edges with two equivalent O(2)Sc2Si2 tetrahedra, and  an edgeedge with one O(5)MgSc4 trigonal bipyramid. In the fifth O site, O(2) is bonded to two equivalent Sc(1), one Si(1), and one Si(2) atom to form distorted OSc2Si2 tetrahedra that share corners with four equivalent O(2)Sc2Si2 tetrahedra, corners with two equivalent O(5)MgSc4 trigonal bipyramids, and edges with two equivalent O(1)Sc2Si2 trigonal pyramids. In the sixth O site, O(3) is bonded in a 5-coordinate geometry to one Mg(1), two equivalent Sc(1), one Si(1), and one Si(2) atom.