Y2Si4N6C crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one N(2), one N(3), one N(4), one N(6), and two equivalent N(1) atoms to form distorted YN6 pentagonal pyramids that share corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with three equivalent Si(2)CN3 tetrahedra, corners with three equivalent Si(4)CN3 tetrahedra,  an edgeedge with one Y(1)N6 pentagonal pyramid, and  an edgeedge with one Si(1)CN3 tetrahedra. In the second Y site, Y(2) is bonded in a 6-coordinate geometry to one N(2), one N(3), one N(4), one N(6), and two equivalent N(5) atoms. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one C(1), one N(1), one N(2), and one N(3) atom to form SiCN3 tetrahedra that share corners with two equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(2)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with two equivalent Si(4)CN3 tetrahedra, and  an edgeedge with one Y(1)N6 pentagonal pyramid. In the second Si site, Si(2) is bonded to one C(1), one N(2), one N(4), and one N(6) atom to form SiCN3 tetrahedra that share corners with three equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. In the third Si site, Si(3) is bonded to one C(1), one N(3), one N(5), and one N(6) atom to form SiCN3 tetrahedra that share corners with two equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. In the fourth Si site, Si(4) is bonded to one C(1), one N(1), one N(4), and one N(5) atom to form SiCN3 tetrahedra that share corners with three equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, and corners with two equivalent Si(3)CN3 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(1)Y2Si2 tetrahedra, corners with two equivalent N(4)Y2Si2 tetrahedra, corners with two equivalent N(5)Y2Si2 tetrahedra, and corners with two equivalent N(2)Y2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to one Y(1), one Y(2), one Si(1), and one Si(2) atom to form distorted NY2Si2 trigonal pyramids that share  a cornercorner with one N(4)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(5)Y2Si2 tetrahedra, corners with three equivalent N(1)Y2Si2 tetrahedra, and  an edgeedge with one N(4)Y2Si2 tetrahedra. In the second N site, N(3) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Si(1), and one Si(3) atom. In the third N site, N(4) is bonded to one Y(1), one Y(2), one Si(2), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(1)Y2Si2 tetrahedra, corners with three equivalent N(5)Y2Si2 tetrahedra,  a cornercorner with one N(2)Y2Si2 trigonal pyramid, and  an edgeedge with one N(2)Y2Si2 trigonal pyramid. In the fourth N site, N(5) is bonded to two equivalent Y(2), one Si(3), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share  a cornercorner with one N(1)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(4)Y2Si2 tetrahedra, corners with two equivalent N(2)Y2Si2 trigonal pyramids, and  an edgeedge with one N(5)Y2Si2 tetrahedra. In the fifth N site, N(6) is bonded in a 3-coordinate geometry to one Y(1), one Y(2), one Si(2), and one Si(3) atom. In the sixth N site, N(1) is bonded to two equivalent Y(1), one Si(1), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share  a cornercorner with one N(5)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(4)Y2Si2 tetrahedra, corners with three equivalent N(2)Y2Si2 trigonal pyramids, and  an edgeedge with one N(1)Y2Si2 tetrahedra.
Y2Si4N6C crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Y sites. In the first Y site, Y(1) is bonded to one N(2), one N(3), one N(4), one N(6), and two equivalent N(1) atoms to form distorted YN6 pentagonal pyramids that share corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with three equivalent Si(2)CN3 tetrahedra, corners with three equivalent Si(4)CN3 tetrahedra,  an edgeedge with one Y(1)N6 pentagonal pyramid, and  an edgeedge with one Si(1)CN3 tetrahedra. The Y(1)-N(2) bond length is 2.34 Å. The Y(1)-N(3) bond length is 2.59 Å. The Y(1)-N(4) bond length is 2.38 Å. The Y(1)-N(6) bond length is 2.34 Å. There is one shorter (2.35 Å) and one longer (2.50 Å) Y(1)-N(1) bond length. In the second Y site, Y(2) is bonded in a 6-coordinate geometry to one N(2), one N(3), one N(4), one N(6), and two equivalent N(5) atoms. The Y(2)-N(2) bond length is 2.55 Å. The Y(2)-N(3) bond length is 2.33 Å. The Y(2)-N(4) bond length is 2.42 Å. The Y(2)-N(6) bond length is 2.89 Å. There is one shorter (2.34 Å) and one longer (2.36 Å) Y(2)-N(5) bond length. There are four inequivalent Si sites. In the first Si site, Si(1) is bonded to one C(1), one N(1), one N(2), and one N(3) atom to form SiCN3 tetrahedra that share corners with two equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(2)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with two equivalent Si(4)CN3 tetrahedra, and  an edgeedge with one Y(1)N6 pentagonal pyramid. The Si(1)-C(1) bond length is 1.90 Å. The Si(1)-N(1) bond length is 1.76 Å. The Si(1)-N(2) bond length is 1.74 Å. The Si(1)-N(3) bond length is 1.74 Å. In the second Si site, Si(2) is bonded to one C(1), one N(2), one N(4), and one N(6) atom to form SiCN3 tetrahedra that share corners with three equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. The Si(2)-C(1) bond length is 1.90 Å. The Si(2)-N(2) bond length is 1.73 Å. The Si(2)-N(4) bond length is 1.75 Å. The Si(2)-N(6) bond length is 1.72 Å. In the third Si site, Si(3) is bonded to one C(1), one N(3), one N(5), and one N(6) atom to form SiCN3 tetrahedra that share corners with two equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. The Si(3)-C(1) bond length is 1.91 Å. The Si(3)-N(3) bond length is 1.75 Å. The Si(3)-N(5) bond length is 1.75 Å. The Si(3)-N(6) bond length is 1.72 Å. In the fourth Si site, Si(4) is bonded to one C(1), one N(1), one N(4), and one N(5) atom to form SiCN3 tetrahedra that share corners with three equivalent Y(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, and corners with two equivalent Si(3)CN3 tetrahedra. The Si(4)-C(1) bond length is 1.87 Å. The Si(4)-N(1) bond length is 1.75 Å. The Si(4)-N(4) bond length is 1.74 Å. The Si(4)-N(5) bond length is 1.74 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(1)Y2Si2 tetrahedra, corners with two equivalent N(4)Y2Si2 tetrahedra, corners with two equivalent N(5)Y2Si2 tetrahedra, and corners with two equivalent N(2)Y2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to one Y(1), one Y(2), one Si(1), and one Si(2) atom to form distorted NY2Si2 trigonal pyramids that share  a cornercorner with one N(4)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(5)Y2Si2 tetrahedra, corners with three equivalent N(1)Y2Si2 tetrahedra, and  an edgeedge with one N(4)Y2Si2 tetrahedra. In the second N site, N(3) is bonded in a 4-coordinate geometry to one Y(1), one Y(2), one Si(1), and one Si(3) atom. In the third N site, N(4) is bonded to one Y(1), one Y(2), one Si(2), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(1)Y2Si2 tetrahedra, corners with three equivalent N(5)Y2Si2 tetrahedra,  a cornercorner with one N(2)Y2Si2 trigonal pyramid, and  an edgeedge with one N(2)Y2Si2 trigonal pyramid. In the fourth N site, N(5) is bonded to two equivalent Y(2), one Si(3), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share  a cornercorner with one N(1)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(4)Y2Si2 tetrahedra, corners with two equivalent N(2)Y2Si2 trigonal pyramids, and  an edgeedge with one N(5)Y2Si2 tetrahedra. In the fifth N site, N(6) is bonded in a 3-coordinate geometry to one Y(1), one Y(2), one Si(2), and one Si(3) atom. In the sixth N site, N(1) is bonded to two equivalent Y(1), one Si(1), and one Si(4) atom to form distorted NY2Si2 tetrahedra that share  a cornercorner with one N(5)Y2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(4)Y2Si2 tetrahedra, corners with three equivalent N(2)Y2Si2 trigonal pyramids, and  an edgeedge with one N(1)Y2Si2 tetrahedra.