Mg(ScSe2)2 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. There are two inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to one Se(2), two equivalent Se(1), and two equivalent Se(3) atoms to form ScSe5 trigonal bipyramids that share corners with four equivalent Sc(2)Se6 pentagonal pyramids, corners with two equivalent Sc(1)Se5 trigonal bipyramids, and  a faceface with one Sc(2)Se6 pentagonal pyramid. In the second Sc site, Sc(2) is bonded to one Se(2), one Se(3), and four equivalent Se(1) atoms to form distorted ScSe6 pentagonal pyramids that share corners with four equivalent Sc(1)Se5 trigonal bipyramids, edges with two equivalent Sc(2)Se6 pentagonal pyramids, and  a faceface with one Sc(1)Se5 trigonal bipyramid. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(1), one Sc(1), and two equivalent Sc(2) atoms to form a mixture of distorted corner and edge-sharing SeMgSc3 trigonal pyramids. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Sc(1), and one Sc(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Sc(2), and two equivalent Sc(1) atoms.
Mg(ScSe2)2 crystallizes in the orthorhombic Pnma space group. Mg(1) is bonded in a rectangular see-saw-like geometry to one Se(2), one Se(3), and two equivalent Se(1) atoms. The Mg(1)-Se(2) bond length is 2.56 Å. The Mg(1)-Se(3) bond length is 2.66 Å. Both Mg(1)-Se(1) bond lengths are 2.65 Å. There are two inequivalent Sc sites. In the first Sc site, Sc(1) is bonded to one Se(2), two equivalent Se(1), and two equivalent Se(3) atoms to form ScSe5 trigonal bipyramids that share corners with four equivalent Sc(2)Se6 pentagonal pyramids, corners with two equivalent Sc(1)Se5 trigonal bipyramids, and  a faceface with one Sc(2)Se6 pentagonal pyramid. The Sc(1)-Se(2) bond length is 2.63 Å. Both Sc(1)-Se(1) bond lengths are 2.73 Å. There is one shorter (2.55 Å) and one longer (2.65 Å) Sc(1)-Se(3) bond length. In the second Sc site, Sc(2) is bonded to one Se(2), one Se(3), and four equivalent Se(1) atoms to form distorted ScSe6 pentagonal pyramids that share corners with four equivalent Sc(1)Se5 trigonal bipyramids, edges with two equivalent Sc(2)Se6 pentagonal pyramids, and  a faceface with one Sc(1)Se5 trigonal bipyramid. The Sc(2)-Se(2) bond length is 2.64 Å. The Sc(2)-Se(3) bond length is 2.69 Å. There are two shorter (2.75 Å) and two longer (2.86 Å) Sc(2)-Se(1) bond lengths. There are three inequivalent Se sites. In the first Se site, Se(1) is bonded to one Mg(1), one Sc(1), and two equivalent Sc(2) atoms to form a mixture of distorted corner and edge-sharing SeMgSc3 trigonal pyramids. In the second Se site, Se(2) is bonded in a distorted T-shaped geometry to one Mg(1), one Sc(1), and one Sc(2) atom. In the third Se site, Se(3) is bonded in a rectangular see-saw-like geometry to one Mg(1), one Sc(2), and two equivalent Sc(1) atoms.