Gd2Si4CN6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 5-coordinate geometry to one N(3), one N(4), one N(5), and two equivalent N(2) atoms. In the second Gd site, Gd(2) is bonded in a 6-coordinate geometry to one N(1), one N(3), one N(4), one N(5), and two equivalent N(6) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one C(1), one N(2), one N(3), and one N(6) atom to form corner-sharing SiCN3 tetrahedra. In the second Si site, Si(2) is bonded to one C(1), one N(1), one N(2), and one N(4) atom to form corner-sharing SiCN3 tetrahedra. In the third Si site, Si(3) is bonded to one C(1), one N(1), one N(3), and one N(5) atom to form corner-sharing SiCN3 tetrahedra. In the fourth Si site, Si(4) is bonded to one C(1), one N(4), one N(5), and one N(6) atom to form corner-sharing SiCN3 tetrahedra. C(1) is bonded to one Si(1), one Si(2), one Si(3), and one Si(4) atom to form CSi4 tetrahedra that share corners with two equivalent N(2)Gd2Si2 tetrahedra, corners with two equivalent N(3)Gd2Si2 tetrahedra, corners with two equivalent N(6)Gd2Si2 tetrahedra, and corners with two equivalent N(5)Gd2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to two equivalent Gd(1), one Si(1), and one Si(2) atom to form NGd2Si2 tetrahedra that share  a cornercorner with one N(6)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Gd2Si2 tetrahedra, corners with two equivalent N(5)Gd2Si2 trigonal pyramids, and  an edgeedge with one N(2)Gd2Si2 tetrahedra. In the second N site, N(3) is bonded to one Gd(1), one Gd(2), one Si(1), and one Si(3) atom to form distorted NGd2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(2)Gd2Si2 tetrahedra, corners with three equivalent N(6)Gd2Si2 tetrahedra,  a cornercorner with one N(5)Gd2Si2 trigonal pyramid, and  an edgeedge with one N(5)Gd2Si2 trigonal pyramid. In the third N site, N(4) is bonded in a 4-coordinate geometry to one Gd(1), one Gd(2), one Si(2), and one Si(4) atom. In the fourth N site, N(5) is bonded to one Gd(1), one Gd(2), one Si(3), and one Si(4) atom to form distorted NGd2Si2 trigonal pyramids that share  a cornercorner with one N(3)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(2)Gd2Si2 tetrahedra, corners with three equivalent N(6)Gd2Si2 tetrahedra, and  an edgeedge with one N(3)Gd2Si2 tetrahedra. In the fifth N site, N(6) is bonded to two equivalent Gd(2), one Si(1), and one Si(4) atom to form distorted NGd2Si2 tetrahedra that share  a cornercorner with one N(2)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Gd2Si2 tetrahedra, corners with three equivalent N(5)Gd2Si2 trigonal pyramids, and  an edgeedge with one N(6)Gd2Si2 tetrahedra. In the sixth N site, N(1) is bonded in a distorted trigonal planar geometry to one Gd(2), one Si(2), and one Si(3) atom.
Gd2Si4CN6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Gd sites. In the first Gd site, Gd(1) is bonded in a 5-coordinate geometry to one N(3), one N(4), one N(5), and two equivalent N(2) atoms. The Gd(1)-N(3) bond length is 2.45 Å. The Gd(1)-N(4) bond length is 2.36 Å. The Gd(1)-N(5) bond length is 2.60 Å. There is one shorter (2.38 Å) and one longer (2.40 Å) Gd(1)-N(2) bond length. In the second Gd site, Gd(2) is bonded in a 6-coordinate geometry to one N(1), one N(3), one N(4), one N(5), and two equivalent N(6) atoms. The Gd(2)-N(1) bond length is 2.38 Å. The Gd(2)-N(3) bond length is 2.41 Å. The Gd(2)-N(4) bond length is 2.65 Å. The Gd(2)-N(5) bond length is 2.38 Å. There is one shorter (2.38 Å) and one longer (2.55 Å) Gd(2)-N(6) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one C(1), one N(2), one N(3), and one N(6) atom to form corner-sharing SiCN3 tetrahedra. The Si(1)-C(1) bond length is 1.89 Å. The Si(1)-N(2) bond length is 1.75 Å. The Si(1)-N(3) bond length is 1.74 Å. The Si(1)-N(6) bond length is 1.76 Å. In the second Si site, Si(2) is bonded to one C(1), one N(1), one N(2), and one N(4) atom to form corner-sharing SiCN3 tetrahedra. The Si(2)-C(1) bond length is 1.93 Å. The Si(2)-N(1) bond length is 1.73 Å. The Si(2)-N(2) bond length is 1.76 Å. The Si(2)-N(4) bond length is 1.77 Å. In the third Si site, Si(3) is bonded to one C(1), one N(1), one N(3), and one N(5) atom to form corner-sharing SiCN3 tetrahedra. The Si(3)-C(1) bond length is 1.92 Å. The Si(3)-N(1) bond length is 1.74 Å. The Si(3)-N(3) bond length is 1.76 Å. The Si(3)-N(5) bond length is 1.75 Å. In the fourth Si site, Si(4) is bonded to one C(1), one N(4), one N(5), and one N(6) atom to form corner-sharing SiCN3 tetrahedra. The Si(4)-C(1) bond length is 1.92 Å. The Si(4)-N(4) bond length is 1.76 Å. The Si(4)-N(5) bond length is 1.75 Å. The Si(4)-N(6) bond length is 1.77 Å. C(1) is bonded to one Si(1), one Si(2), one Si(3), and one Si(4) atom to form CSi4 tetrahedra that share corners with two equivalent N(2)Gd2Si2 tetrahedra, corners with two equivalent N(3)Gd2Si2 tetrahedra, corners with two equivalent N(6)Gd2Si2 tetrahedra, and corners with two equivalent N(5)Gd2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to two equivalent Gd(1), one Si(1), and one Si(2) atom to form NGd2Si2 tetrahedra that share  a cornercorner with one N(6)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Gd2Si2 tetrahedra, corners with two equivalent N(5)Gd2Si2 trigonal pyramids, and  an edgeedge with one N(2)Gd2Si2 tetrahedra. In the second N site, N(3) is bonded to one Gd(1), one Gd(2), one Si(1), and one Si(3) atom to form distorted NGd2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(2)Gd2Si2 tetrahedra, corners with three equivalent N(6)Gd2Si2 tetrahedra,  a cornercorner with one N(5)Gd2Si2 trigonal pyramid, and  an edgeedge with one N(5)Gd2Si2 trigonal pyramid. In the third N site, N(4) is bonded in a 4-coordinate geometry to one Gd(1), one Gd(2), one Si(2), and one Si(4) atom. In the fourth N site, N(5) is bonded to one Gd(1), one Gd(2), one Si(3), and one Si(4) atom to form distorted NGd2Si2 trigonal pyramids that share  a cornercorner with one N(3)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(2)Gd2Si2 tetrahedra, corners with three equivalent N(6)Gd2Si2 tetrahedra, and  an edgeedge with one N(3)Gd2Si2 tetrahedra. In the fifth N site, N(6) is bonded to two equivalent Gd(2), one Si(1), and one Si(4) atom to form distorted NGd2Si2 tetrahedra that share  a cornercorner with one N(2)Gd2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Gd2Si2 tetrahedra, corners with three equivalent N(5)Gd2Si2 trigonal pyramids, and  an edgeedge with one N(6)Gd2Si2 tetrahedra. In the sixth N site, N(1) is bonded in a distorted trigonal planar geometry to one Gd(2), one Si(2), and one Si(3) atom.