Ba3(SiAs2)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(2)As6 octahedra, corners with two equivalent Ba(3)As6 octahedra, corners with four equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(1)As6 octahedra, edges with three equivalent Ba(3)As6 octahedra, edges with four equivalent Ba(2)As6 octahedra, and edges with two equivalent Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 9-16°. In the second Ba site, Ba(2) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent Ba(3)As6 octahedra, corners with eight equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(2)As6 octahedra, edges with three equivalent Ba(3)As6 octahedra, and edges with four equivalent Ba(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 8-9°. In the third Ba site, Ba(3) is bonded to two equivalent As(2) and four equivalent As(1) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent Ba(2)As6 octahedra, corners with six equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(3)As6 octahedra, edges with three equivalent Ba(1)As6 octahedra, edges with three equivalent Ba(2)As6 octahedra, and edges with two equivalent Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 8-16°. Si(1) is bonded to one Si(1), one As(2), and two equivalent As(1) atoms to form distorted SiSiAs3 tetrahedra that share  a cornercorner with one As(2)Ba5Si octahedra, corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent As(1)Ba4Si2 octahedra, corners with three equivalent Ba(3)As6 octahedra, corners with four equivalent Ba(2)As6 octahedra,  an edgeedge with one Ba(1)As6 octahedra,  an edgeedge with one Ba(3)As6 octahedra, and  an edgeedge with one Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 16-81°. There are two inequivalent As sites. In the first As site, As(1) is bonded to one Ba(1), one Ba(2), two equivalent Ba(3), and two equivalent Si(1) atoms to form distorted AsBa4Si2 octahedra that share corners with four equivalent As(1)Ba4Si2 octahedra, corners with four equivalent As(2)Ba5Si octahedra, corners with two equivalent Si(1)SiAs3 tetrahedra, edges with three equivalent As(1)Ba4Si2 octahedra, and edges with five equivalent As(2)Ba5Si octahedra. The corner-sharing octahedral tilt angles range from 5-97°. In the second As site, As(2) is bonded to one Ba(3), two equivalent Ba(1), two equivalent Ba(2), and one Si(1) atom to form AsBa5Si octahedra that share corners with three equivalent As(2)Ba5Si octahedra, corners with four equivalent As(1)Ba4Si2 octahedra,  a cornercorner with one Si(1)SiAs3 tetrahedra, edges with five equivalent As(1)Ba4Si2 octahedra, and edges with five equivalent As(2)Ba5Si octahedra. The corner-sharing octahedral tilt angles range from 5-94°.
Ba3(SiAs2)2 crystallizes in the monoclinic C2/c space group. There are three inequivalent Ba sites. In the first Ba site, Ba(1) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(2)As6 octahedra, corners with two equivalent Ba(3)As6 octahedra, corners with four equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(1)As6 octahedra, edges with three equivalent Ba(3)As6 octahedra, edges with four equivalent Ba(2)As6 octahedra, and edges with two equivalent Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 9-16°. Both Ba(1)-As(1) bond lengths are 3.33 Å. There are two shorter (3.29 Å) and two longer (3.43 Å) Ba(1)-As(2) bond lengths. In the second Ba site, Ba(2) is bonded to two equivalent As(1) and four equivalent As(2) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent Ba(3)As6 octahedra, corners with eight equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(2)As6 octahedra, edges with three equivalent Ba(3)As6 octahedra, and edges with four equivalent Ba(1)As6 octahedra. The corner-sharing octahedral tilt angles range from 8-9°. Both Ba(2)-As(1) bond lengths are 3.55 Å. There are two shorter (3.32 Å) and two longer (3.34 Å) Ba(2)-As(2) bond lengths. In the third Ba site, Ba(3) is bonded to two equivalent As(2) and four equivalent As(1) atoms to form BaAs6 octahedra that share corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent Ba(2)As6 octahedra, corners with six equivalent Si(1)SiAs3 tetrahedra, edges with two equivalent Ba(3)As6 octahedra, edges with three equivalent Ba(1)As6 octahedra, edges with three equivalent Ba(2)As6 octahedra, and edges with two equivalent Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 8-16°. Both Ba(3)-As(2) bond lengths are 3.28 Å. There are two shorter (3.31 Å) and two longer (3.60 Å) Ba(3)-As(1) bond lengths. Si(1) is bonded to one Si(1), one As(2), and two equivalent As(1) atoms to form distorted SiSiAs3 tetrahedra that share  a cornercorner with one As(2)Ba5Si octahedra, corners with two equivalent Ba(1)As6 octahedra, corners with two equivalent As(1)Ba4Si2 octahedra, corners with three equivalent Ba(3)As6 octahedra, corners with four equivalent Ba(2)As6 octahedra,  an edgeedge with one Ba(1)As6 octahedra,  an edgeedge with one Ba(3)As6 octahedra, and  an edgeedge with one Si(1)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 16-81°. The Si(1)-Si(1) bond length is 2.40 Å. The Si(1)-As(2) bond length is 2.35 Å. Both Si(1)-As(1) bond lengths are 2.42 Å. There are two inequivalent As sites. In the first As site, As(1) is bonded to one Ba(1), one Ba(2), two equivalent Ba(3), and two equivalent Si(1) atoms to form distorted AsBa4Si2 octahedra that share corners with four equivalent As(1)Ba4Si2 octahedra, corners with four equivalent As(2)Ba5Si octahedra, corners with two equivalent Si(1)SiAs3 tetrahedra, edges with three equivalent As(1)Ba4Si2 octahedra, and edges with five equivalent As(2)Ba5Si octahedra. The corner-sharing octahedral tilt angles range from 5-97°. In the second As site, As(2) is bonded to one Ba(3), two equivalent Ba(1), two equivalent Ba(2), and one Si(1) atom to form AsBa5Si octahedra that share corners with three equivalent As(2)Ba5Si octahedra, corners with four equivalent As(1)Ba4Si2 octahedra,  a cornercorner with one Si(1)SiAs3 tetrahedra, edges with five equivalent As(1)Ba4Si2 octahedra, and edges with five equivalent As(2)Ba5Si octahedra. The corner-sharing octahedral tilt angles range from 5-94°.