RbMgCl3 is (Cubic) Perovskite-like structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to three equivalent Cl(2) and nine equivalent Cl(1) atoms to form RbCl12 cuboctahedra that share corners with three equivalent Rb(2)Cl12 cuboctahedra, corners with six equivalent Rb(1)Cl12 cuboctahedra, corners with three equivalent Mg(1)Cl6 octahedra, faces with three equivalent Rb(2)Cl12 cuboctahedra, faces with four equivalent Rb(1)Cl12 cuboctahedra, faces with three equivalent Mg(2)Cl6 octahedra, and faces with four equivalent Mg(1)Cl6 octahedra. The corner-sharing octahedral tilt angles are 14°. In the second Rb site, Rb(2) is bonded to six equivalent Cl(1) and six equivalent Cl(2) atoms to form RbCl12 cuboctahedra that share corners with six equivalent Rb(1)Cl12 cuboctahedra, corners with six equivalent Rb(2)Cl12 cuboctahedra, faces with six equivalent Rb(1)Cl12 cuboctahedra, faces with two equivalent Mg(2)Cl6 octahedra, and faces with six equivalent Mg(1)Cl6 octahedra. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Cl(1) and three equivalent Cl(2) atoms to form MgCl6 octahedra that share corners with three equivalent Rb(1)Cl12 cuboctahedra, corners with three equivalent Mg(2)Cl6 octahedra, faces with three equivalent Rb(2)Cl12 cuboctahedra, faces with four equivalent Rb(1)Cl12 cuboctahedra, and  a faceface with one Mg(1)Cl6 octahedra. The corner-sharing octahedral tilt angles are 1°. In the second Mg site, Mg(2) is bonded to six equivalent Cl(1) atoms to form MgCl6 octahedra that share corners with six equivalent Mg(1)Cl6 octahedra, faces with two equivalent Rb(2)Cl12 cuboctahedra, and faces with six equivalent Rb(1)Cl12 cuboctahedra. The corner-sharing octahedral tilt angles are 1°. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded in a distorted linear geometry to one Rb(2), three equivalent Rb(1), one Mg(1), and one Mg(2) atom. In the second Cl site, Cl(2) is bonded to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Mg(1) atoms to form a mixture of distorted face and corner-sharing ClRb4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 3-60°.
RbMgCl3 is (Cubic) Perovskite-like structured and crystallizes in the hexagonal P6_3/mmc space group. There are two inequivalent Rb sites. In the first Rb site, Rb(1) is bonded to three equivalent Cl(2) and nine equivalent Cl(1) atoms to form RbCl12 cuboctahedra that share corners with three equivalent Rb(2)Cl12 cuboctahedra, corners with six equivalent Rb(1)Cl12 cuboctahedra, corners with three equivalent Mg(1)Cl6 octahedra, faces with three equivalent Rb(2)Cl12 cuboctahedra, faces with four equivalent Rb(1)Cl12 cuboctahedra, faces with three equivalent Mg(2)Cl6 octahedra, and faces with four equivalent Mg(1)Cl6 octahedra. The corner-sharing octahedral tilt angles are 14°. All Rb(1)-Cl(2) bond lengths are 3.56 Å. There are six shorter (3.55 Å) and three longer (3.64 Å) Rb(1)-Cl(1) bond lengths. In the second Rb site, Rb(2) is bonded to six equivalent Cl(1) and six equivalent Cl(2) atoms to form RbCl12 cuboctahedra that share corners with six equivalent Rb(1)Cl12 cuboctahedra, corners with six equivalent Rb(2)Cl12 cuboctahedra, faces with six equivalent Rb(1)Cl12 cuboctahedra, faces with two equivalent Mg(2)Cl6 octahedra, and faces with six equivalent Mg(1)Cl6 octahedra. All Rb(2)-Cl(1) bond lengths are 3.60 Å. All Rb(2)-Cl(2) bond lengths are 3.55 Å. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded to three equivalent Cl(1) and three equivalent Cl(2) atoms to form MgCl6 octahedra that share corners with three equivalent Rb(1)Cl12 cuboctahedra, corners with three equivalent Mg(2)Cl6 octahedra, faces with three equivalent Rb(2)Cl12 cuboctahedra, faces with four equivalent Rb(1)Cl12 cuboctahedra, and  a faceface with one Mg(1)Cl6 octahedra. The corner-sharing octahedral tilt angles are 1°. All Mg(1)-Cl(1) bond lengths are 2.48 Å. All Mg(1)-Cl(2) bond lengths are 2.51 Å. In the second Mg site, Mg(2) is bonded to six equivalent Cl(1) atoms to form MgCl6 octahedra that share corners with six equivalent Mg(1)Cl6 octahedra, faces with two equivalent Rb(2)Cl12 cuboctahedra, and faces with six equivalent Rb(1)Cl12 cuboctahedra. The corner-sharing octahedral tilt angles are 1°. All Mg(2)-Cl(1) bond lengths are 2.50 Å. There are two inequivalent Cl sites. In the first Cl site, Cl(1) is bonded in a distorted linear geometry to one Rb(2), three equivalent Rb(1), one Mg(1), and one Mg(2) atom. In the second Cl site, Cl(2) is bonded to two equivalent Rb(1), two equivalent Rb(2), and two equivalent Mg(1) atoms to form a mixture of distorted face and corner-sharing ClRb4Mg2 octahedra. The corner-sharing octahedral tilt angles range from 3-60°.