Eu3Al2As4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 6-coordinate geometry to two equivalent As(2) and four equivalent As(1) atoms. In the second Eu site, Eu(2) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form distorted EuAs6 octahedra that share corners with four equivalent Al(1)As4 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, and edges with four equivalent Al(1)As4 tetrahedra. Al(1) is bonded to two equivalent As(1) and two equivalent As(2) atoms to form AlAs4 tetrahedra that share corners with two equivalent Eu(2)As6 octahedra, corners with two equivalent Al(1)As4 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, and  an edgeedge with one Al(1)As4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-57°. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 7-coordinate geometry to one Eu(2), four equivalent Eu(1), and two equivalent Al(1) atoms. In the second As site, As(2) is bonded in a 6-coordinate geometry to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Al(1) atoms.
Eu3Al2As4 crystallizes in the monoclinic C2/c space group. There are two inequivalent Eu sites. In the first Eu site, Eu(1) is bonded in a 6-coordinate geometry to two equivalent As(2) and four equivalent As(1) atoms. There is one shorter (3.02 Å) and one longer (3.06 Å) Eu(1)-As(2) bond length. There are a spread of Eu(1)-As(1) bond distances ranging from 3.13-3.45 Å. In the second Eu site, Eu(2) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form distorted EuAs6 octahedra that share corners with four equivalent Al(1)As4 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, and edges with four equivalent Al(1)As4 tetrahedra. Both Eu(2)-As(1) bond lengths are 3.18 Å. There are two shorter (3.01 Å) and two longer (3.08 Å) Eu(2)-As(2) bond lengths. Al(1) is bonded to two equivalent As(1) and two equivalent As(2) atoms to form AlAs4 tetrahedra that share corners with two equivalent Eu(2)As6 octahedra, corners with two equivalent Al(1)As4 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, and  an edgeedge with one Al(1)As4 tetrahedra. The corner-sharing octahedral tilt angles range from 32-57°. There is one shorter (2.50 Å) and one longer (2.52 Å) Al(1)-As(1) bond length. There is one shorter (2.46 Å) and one longer (2.47 Å) Al(1)-As(2) bond length. There are two inequivalent As sites. In the first As site, As(1) is bonded in a 7-coordinate geometry to one Eu(2), four equivalent Eu(1), and two equivalent Al(1) atoms. In the second As site, As(2) is bonded in a 6-coordinate geometry to two equivalent Eu(1), two equivalent Eu(2), and two equivalent Al(1) atoms.