Ca(AlSe2)2 crystallizes in the orthorhombic Cccm space group. Ca(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(2) atoms. Al(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form edge-sharing AlSe4 tetrahedra. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to two equivalent Ca(1) and two equivalent Al(1) atoms to form a mixture of corner and edge-sharing SeCa2Al2 trigonal pyramids. In the second Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Ca(1) and two equivalent Al(1) atoms.
Ca(AlSe2)2 crystallizes in the orthorhombic Cccm space group. Ca(1) is bonded in a 8-coordinate geometry to four equivalent Se(1) and four equivalent Se(2) atoms. All Ca(1)-Se(1) bond lengths are 3.21 Å. All Ca(1)-Se(2) bond lengths are 3.16 Å. Al(1) is bonded to two equivalent Se(1) and two equivalent Se(2) atoms to form edge-sharing AlSe4 tetrahedra. Both Al(1)-Se(1) bond lengths are 2.40 Å. There is one shorter (2.38 Å) and one longer (2.42 Å) Al(1)-Se(2) bond length. There are two inequivalent Se sites. In the first Se site, Se(2) is bonded to two equivalent Ca(1) and two equivalent Al(1) atoms to form a mixture of corner and edge-sharing SeCa2Al2 trigonal pyramids. In the second Se site, Se(1) is bonded in a 4-coordinate geometry to two equivalent Ca(1) and two equivalent Al(1) atoms.