Cs3Mg2Cl7 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to four equivalent Cl(1) and five equivalent Cl(2) atoms. In the second Cs site, Cs(2) is bonded to four equivalent Cl(3) and eight equivalent Cl(1) atoms to form CsCl12 cuboctahedra that share corners with four equivalent Cs(2)Cl12 cuboctahedra, faces with four equivalent Cs(2)Cl12 cuboctahedra, and faces with eight equivalent Mg(1)Cl6 octahedra. Mg(1) is bonded to one Cl(2), one Cl(3), and four equivalent Cl(1) atoms to form MgCl6 octahedra that share corners with five equivalent Mg(1)Cl6 octahedra and faces with four equivalent Cs(2)Cl12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. There are three inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Mg(1) atoms to form distorted ClCs4Mg2 octahedra that share corners with six equivalent Cl(2)Cs5Mg octahedra, corners with eight equivalent Cl(1)Cs4Mg2 octahedra, edges with three equivalent Cl(1)Cs4Mg2 octahedra, faces with two equivalent Cl(2)Cs5Mg octahedra, and faces with four equivalent Cl(1)Cs4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second Cl site, Cl(2) is bonded to five equivalent Cs(1) and one Mg(1) atom to form distorted ClCs5Mg octahedra that share corners with four equivalent Cl(2)Cs5Mg octahedra, corners with twelve equivalent Cl(1)Cs4Mg2 octahedra, edges with eight equivalent Cl(2)Cs5Mg octahedra, and faces with four equivalent Cl(1)Cs4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 3-58°. In the third Cl site, Cl(3) is bonded in a distorted linear geometry to four equivalent Cs(2) and two equivalent Mg(1) atoms.
Cs3Mg2Cl7 crystallizes in the tetragonal I4/mmm space group. There are two inequivalent Cs sites. In the first Cs site, Cs(1) is bonded in a 9-coordinate geometry to four equivalent Cl(1) and five equivalent Cl(2) atoms. All Cs(1)-Cl(1) bond lengths are 3.55 Å. There is one shorter (3.48 Å) and four longer (3.64 Å) Cs(1)-Cl(2) bond lengths. In the second Cs site, Cs(2) is bonded to four equivalent Cl(3) and eight equivalent Cl(1) atoms to form CsCl12 cuboctahedra that share corners with four equivalent Cs(2)Cl12 cuboctahedra, faces with four equivalent Cs(2)Cl12 cuboctahedra, and faces with eight equivalent Mg(1)Cl6 octahedra. All Cs(2)-Cl(3) bond lengths are 3.64 Å. All Cs(2)-Cl(1) bond lengths are 3.64 Å. Mg(1) is bonded to one Cl(2), one Cl(3), and four equivalent Cl(1) atoms to form MgCl6 octahedra that share corners with five equivalent Mg(1)Cl6 octahedra and faces with four equivalent Cs(2)Cl12 cuboctahedra. The corner-sharing octahedral tilt angles range from 0-2°. The Mg(1)-Cl(2) bond length is 2.50 Å. The Mg(1)-Cl(3) bond length is 2.61 Å. All Mg(1)-Cl(1) bond lengths are 2.57 Å. There are three inequivalent Cl sites. In the first Cl site, Cl(1) is bonded to two equivalent Cs(1), two equivalent Cs(2), and two equivalent Mg(1) atoms to form distorted ClCs4Mg2 octahedra that share corners with six equivalent Cl(2)Cs5Mg octahedra, corners with eight equivalent Cl(1)Cs4Mg2 octahedra, edges with three equivalent Cl(1)Cs4Mg2 octahedra, faces with two equivalent Cl(2)Cs5Mg octahedra, and faces with four equivalent Cl(1)Cs4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 0-60°. In the second Cl site, Cl(2) is bonded to five equivalent Cs(1) and one Mg(1) atom to form distorted ClCs5Mg octahedra that share corners with four equivalent Cl(2)Cs5Mg octahedra, corners with twelve equivalent Cl(1)Cs4Mg2 octahedra, edges with eight equivalent Cl(2)Cs5Mg octahedra, and faces with four equivalent Cl(1)Cs4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 3-58°. In the third Cl site, Cl(3) is bonded in a distorted linear geometry to four equivalent Cs(2) and two equivalent Mg(1) atoms.