Ca3Al2As4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form distorted CaAs6 octahedra that share corners with eight equivalent Al(1)As4 tetrahedra, edges with two equivalent Ca(1)As6 octahedra, and edges with two equivalent Al(1)As4 tetrahedra. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to three equivalent As(1) and three equivalent As(2) atoms. Al(1) is bonded to two equivalent As(1) and two equivalent As(2) atoms to form distorted AlAs4 tetrahedra that share corners with four equivalent Ca(1)As6 octahedra, corners with two equivalent Al(1)As4 tetrahedra,  an edgeedge with one Ca(1)As6 octahedra, and  an edgeedge with one Al(1)As4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-64°. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 6-coordinate geometry to one Ca(1), three equivalent Ca(2), and two equivalent Al(1) atoms. In the second As site, As(2) is bonded in a 7-coordinate geometry to two equivalent Ca(1), three equivalent Ca(2), and two equivalent Al(1) atoms.
Ca3Al2As4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Ca sites. In the first Ca site, Ca(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form distorted CaAs6 octahedra that share corners with eight equivalent Al(1)As4 tetrahedra, edges with two equivalent Ca(1)As6 octahedra, and edges with two equivalent Al(1)As4 tetrahedra. Both Ca(1)-As(1) bond lengths are 2.94 Å. There are two shorter (2.93 Å) and two longer (3.15 Å) Ca(1)-As(2) bond lengths. In the second Ca site, Ca(2) is bonded in a 5-coordinate geometry to three equivalent As(1) and three equivalent As(2) atoms. There are a spread of Ca(2)-As(1) bond distances ranging from 2.98-3.35 Å. There are a spread of Ca(2)-As(2) bond distances ranging from 2.88-3.61 Å. Al(1) is bonded to two equivalent As(1) and two equivalent As(2) atoms to form distorted AlAs4 tetrahedra that share corners with four equivalent Ca(1)As6 octahedra, corners with two equivalent Al(1)As4 tetrahedra,  an edgeedge with one Ca(1)As6 octahedra, and  an edgeedge with one Al(1)As4 tetrahedra. The corner-sharing octahedral tilt angles range from 21-64°. There is one shorter (2.48 Å) and one longer (2.51 Å) Al(1)-As(1) bond length. There is one shorter (2.54 Å) and one longer (2.57 Å) Al(1)-As(2) bond length. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 6-coordinate geometry to one Ca(1), three equivalent Ca(2), and two equivalent Al(1) atoms. In the second As site, As(2) is bonded in a 7-coordinate geometry to two equivalent Ca(1), three equivalent Ca(2), and two equivalent Al(1) atoms.