Eu3(SiAs2)2 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one As(1), one As(3), two equivalent As(2), and two equivalent As(4) atoms to form distorted EuAs6 octahedra that share corners with two equivalent Eu(2)As6 octahedra, corners with two equivalent Eu(3)As6 octahedra, corners with four equivalent Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(1)As6 octahedra, edges with three equivalent Eu(2)As6 octahedra, edges with three equivalent Eu(3)As6 octahedra, and  an edgeedge with one Si(2)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 3-10°. In the second Eu site, Eu(2) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form EuAs6 octahedra that share corners with two equivalent Eu(1)As6 octahedra, corners with two equivalent Eu(3)As6 octahedra, corners with three equivalent Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, edges with three equivalent Eu(1)As6 octahedra, and edges with four equivalent Eu(3)As6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. In the third Eu site, Eu(3) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form EuAs6 octahedra that share corners with two equivalent Eu(1)As6 octahedra, corners with two equivalent Eu(2)As6 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(3)As6 octahedra, edges with three equivalent Eu(1)As6 octahedra, edges with four equivalent Eu(2)As6 octahedra, and  an edgeedge with one Si(2)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 3-10°. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Si(2), one As(1), one As(2), and one As(3) atom. In the second Si site, Si(2) is bonded to one Si(1), one As(2), and two equivalent As(4) atoms to form distorted SiSiAs3 tetrahedra that share  a cornercorner with one Eu(3)As6 octahedra,  a cornercorner with one As(2)Eu4Si2 octahedra,  a cornercorner with one As(1)Eu5Si octahedra,  a cornercorner with one As(3)Eu5Si octahedra, corners with three equivalent Eu(2)As6 octahedra, corners with four equivalent Eu(1)As6 octahedra, corners with two equivalent Si(2)SiAs3 tetrahedra,  an edgeedge with one Eu(1)As6 octahedra, and  an edgeedge with one Eu(3)As6 octahedra. The corner-sharing octahedral tilt angles range from 13-82°. There are four inequivalent As sites. In the first As site, As(4) is bonded to one Eu(2), one Eu(3), two equivalent Eu(1), and two equivalent Si(2) atoms to form distorted AsEu4Si2 octahedra that share corners with two equivalent As(2)Eu4Si2 octahedra, corners with two equivalent As(3)Eu5Si octahedra, corners with four equivalent As(1)Eu5Si octahedra,  an edgeedge with one As(1)Eu5Si octahedra, edges with two equivalent As(4)Eu4Si2 octahedra, edges with two equivalent As(3)Eu5Si octahedra, and edges with three equivalent As(2)Eu4Si2 octahedra. The corner-sharing octahedral tilt angles range from 0-93°. In the second As site, As(1) is bonded to one Eu(1), two equivalent Eu(2), two equivalent Eu(3), and one Si(1) atom to form AsEu5Si octahedra that share  a cornercorner with one As(2)Eu4Si2 octahedra, corners with two equivalent As(3)Eu5Si octahedra, corners with four equivalent As(4)Eu4Si2 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra,  an edgeedge with one As(4)Eu4Si2 octahedra, edges with two equivalent As(1)Eu5Si octahedra, edges with three equivalent As(2)Eu4Si2 octahedra, and edges with four equivalent As(3)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 0-90°. In the third As site, As(2) is bonded to one Eu(2), one Eu(3), two equivalent Eu(1), one Si(1), and one Si(2) atom to form distorted AsEu4Si2 octahedra that share  a cornercorner with one As(1)Eu5Si octahedra, corners with two equivalent As(2)Eu4Si2 octahedra, corners with two equivalent As(4)Eu4Si2 octahedra, corners with three equivalent As(3)Eu5Si octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent As(3)Eu5Si octahedra, edges with three equivalent As(4)Eu4Si2 octahedra, and edges with three equivalent As(1)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 4-95°. In the fourth As site, As(3) is bonded to one Eu(1), two equivalent Eu(2), two equivalent Eu(3), and one Si(1) atom to form AsEu5Si octahedra that share corners with two equivalent As(4)Eu4Si2 octahedra, corners with two equivalent As(1)Eu5Si octahedra, corners with three equivalent As(2)Eu4Si2 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent As(2)Eu4Si2 octahedra, edges with two equivalent As(4)Eu4Si2 octahedra, edges with two equivalent As(3)Eu5Si octahedra, and edges with four equivalent As(1)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 2-93°.
Eu3(SiAs2)2 crystallizes in the monoclinic P2_1/c space group. There are three inequivalent Eu sites. In the first Eu site, Eu(1) is bonded to one As(1), one As(3), two equivalent As(2), and two equivalent As(4) atoms to form distorted EuAs6 octahedra that share corners with two equivalent Eu(2)As6 octahedra, corners with two equivalent Eu(3)As6 octahedra, corners with four equivalent Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(1)As6 octahedra, edges with three equivalent Eu(2)As6 octahedra, edges with three equivalent Eu(3)As6 octahedra, and  an edgeedge with one Si(2)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 3-10°. The Eu(1)-As(1) bond length is 3.04 Å. The Eu(1)-As(3) bond length is 3.06 Å. There is one shorter (3.10 Å) and one longer (3.23 Å) Eu(1)-As(2) bond length. There is one shorter (3.09 Å) and one longer (3.17 Å) Eu(1)-As(4) bond length. In the second Eu site, Eu(2) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form EuAs6 octahedra that share corners with two equivalent Eu(1)As6 octahedra, corners with two equivalent Eu(3)As6 octahedra, corners with three equivalent Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(2)As6 octahedra, edges with three equivalent Eu(1)As6 octahedra, and edges with four equivalent Eu(3)As6 octahedra. The corner-sharing octahedral tilt angles range from 3-7°. The Eu(2)-As(2) bond length is 3.14 Å. The Eu(2)-As(4) bond length is 3.21 Å. There is one shorter (3.04 Å) and one longer (3.05 Å) Eu(2)-As(1) bond length. There is one shorter (3.06 Å) and one longer (3.07 Å) Eu(2)-As(3) bond length. In the third Eu site, Eu(3) is bonded to one As(2), one As(4), two equivalent As(1), and two equivalent As(3) atoms to form EuAs6 octahedra that share corners with two equivalent Eu(1)As6 octahedra, corners with two equivalent Eu(2)As6 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent Eu(3)As6 octahedra, edges with three equivalent Eu(1)As6 octahedra, edges with four equivalent Eu(2)As6 octahedra, and  an edgeedge with one Si(2)SiAs3 tetrahedra. The corner-sharing octahedral tilt angles range from 3-10°. The Eu(3)-As(2) bond length is 3.11 Å. The Eu(3)-As(4) bond length is 3.15 Å. There is one shorter (3.07 Å) and one longer (3.08 Å) Eu(3)-As(1) bond length. There is one shorter (3.03 Å) and one longer (3.09 Å) Eu(3)-As(3) bond length. There are two inequivalent Si sites. In the first Si site, Si(1) is bonded in a 4-coordinate geometry to one Si(2), one As(1), one As(2), and one As(3) atom. The Si(1)-Si(2) bond length is 2.36 Å. The Si(1)-As(1) bond length is 2.35 Å. The Si(1)-As(2) bond length is 2.45 Å. The Si(1)-As(3) bond length is 2.36 Å. In the second Si site, Si(2) is bonded to one Si(1), one As(2), and two equivalent As(4) atoms to form distorted SiSiAs3 tetrahedra that share  a cornercorner with one Eu(3)As6 octahedra,  a cornercorner with one As(2)Eu4Si2 octahedra,  a cornercorner with one As(1)Eu5Si octahedra,  a cornercorner with one As(3)Eu5Si octahedra, corners with three equivalent Eu(2)As6 octahedra, corners with four equivalent Eu(1)As6 octahedra, corners with two equivalent Si(2)SiAs3 tetrahedra,  an edgeedge with one Eu(1)As6 octahedra, and  an edgeedge with one Eu(3)As6 octahedra. The corner-sharing octahedral tilt angles range from 13-82°. The Si(2)-As(2) bond length is 2.39 Å. There is one shorter (2.42 Å) and one longer (2.43 Å) Si(2)-As(4) bond length. There are four inequivalent As sites. In the first As site, As(4) is bonded to one Eu(2), one Eu(3), two equivalent Eu(1), and two equivalent Si(2) atoms to form distorted AsEu4Si2 octahedra that share corners with two equivalent As(2)Eu4Si2 octahedra, corners with two equivalent As(3)Eu5Si octahedra, corners with four equivalent As(1)Eu5Si octahedra,  an edgeedge with one As(1)Eu5Si octahedra, edges with two equivalent As(4)Eu4Si2 octahedra, edges with two equivalent As(3)Eu5Si octahedra, and edges with three equivalent As(2)Eu4Si2 octahedra. The corner-sharing octahedral tilt angles range from 0-93°. In the second As site, As(1) is bonded to one Eu(1), two equivalent Eu(2), two equivalent Eu(3), and one Si(1) atom to form AsEu5Si octahedra that share  a cornercorner with one As(2)Eu4Si2 octahedra, corners with two equivalent As(3)Eu5Si octahedra, corners with four equivalent As(4)Eu4Si2 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra,  an edgeedge with one As(4)Eu4Si2 octahedra, edges with two equivalent As(1)Eu5Si octahedra, edges with three equivalent As(2)Eu4Si2 octahedra, and edges with four equivalent As(3)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 0-90°. In the third As site, As(2) is bonded to one Eu(2), one Eu(3), two equivalent Eu(1), one Si(1), and one Si(2) atom to form distorted AsEu4Si2 octahedra that share  a cornercorner with one As(1)Eu5Si octahedra, corners with two equivalent As(2)Eu4Si2 octahedra, corners with two equivalent As(4)Eu4Si2 octahedra, corners with three equivalent As(3)Eu5Si octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent As(3)Eu5Si octahedra, edges with three equivalent As(4)Eu4Si2 octahedra, and edges with three equivalent As(1)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 4-95°. In the fourth As site, As(3) is bonded to one Eu(1), two equivalent Eu(2), two equivalent Eu(3), and one Si(1) atom to form AsEu5Si octahedra that share corners with two equivalent As(4)Eu4Si2 octahedra, corners with two equivalent As(1)Eu5Si octahedra, corners with three equivalent As(2)Eu4Si2 octahedra,  a cornercorner with one Si(2)SiAs3 tetrahedra, edges with two equivalent As(2)Eu4Si2 octahedra, edges with two equivalent As(4)Eu4Si2 octahedra, edges with two equivalent As(3)Eu5Si octahedra, and edges with four equivalent As(1)Eu5Si octahedra. The corner-sharing octahedral tilt angles range from 2-93°.