Tb2Si4CN6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one N(3), one N(4), one N(5), one N(6), and two equivalent N(2) atoms to form distorted TbN6 pentagonal pyramids that share corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, corners with three equivalent Si(3)CN3 tetrahedra, corners with three equivalent Si(4)CN3 tetrahedra,  an edgeedge with one Tb(1)N6 pentagonal pyramid, and  an edgeedge with one Si(2)CN3 tetrahedra. In the second Tb site, Tb(2) is bonded in a 5-coordinate geometry to one N(3), one N(4), one N(5), and two equivalent N(1) 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(4), and one N(6) atom to form SiCN3 tetrahedra that share corners with two equivalent Tb(1)N6 pentagonal pyramids, corners with two equivalent Si(2)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. In the second Si site, Si(2) is bonded to one C(1), one N(2), one N(4), and one N(5) atom to form SiCN3 tetrahedra that share corners with two equivalent Tb(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with two equivalent Si(4)CN3 tetrahedra, and  an edgeedge with one Tb(1)N6 pentagonal pyramid. In the third Si site, Si(3) 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 three equivalent Tb(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(3), one N(5), and one N(6) atom to form SiCN3 tetrahedra that share corners with three equivalent Tb(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)Tb2Si2 tetrahedra, corners with two equivalent N(2)Tb2Si2 tetrahedra, corners with two equivalent N(3)Tb2Si2 tetrahedra, and corners with two equivalent N(5)Tb2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to two equivalent Tb(1), one Si(2), and one Si(3) atom to form distorted NTb2Si2 tetrahedra that share  a cornercorner with one N(1)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Tb2Si2 tetrahedra, corners with three equivalent N(5)Tb2Si2 trigonal pyramids, and  an edgeedge with one N(2)Tb2Si2 tetrahedra. In the second N site, N(3) is bonded to one Tb(1), one Tb(2), one Si(3), and one Si(4) atom to form distorted NTb2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(1)Tb2Si2 tetrahedra, corners with three equivalent N(2)Tb2Si2 tetrahedra,  a cornercorner with one N(5)Tb2Si2 trigonal pyramid, and  an edgeedge with one N(5)Tb2Si2 trigonal pyramid. In the third N site, N(4) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Si(1), and one Si(2) atom. In the fourth N site, N(5) is bonded to one Tb(1), one Tb(2), one Si(2), and one Si(4) atom to form distorted NTb2Si2 trigonal pyramids that share  a cornercorner with one N(3)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(1)Tb2Si2 tetrahedra, corners with three equivalent N(2)Tb2Si2 tetrahedra, and  an edgeedge with one N(3)Tb2Si2 tetrahedra. In the fifth N site, N(6) is bonded in a distorted trigonal planar geometry to one Tb(1), one Si(1), and one Si(4) atom. In the sixth N site, N(1) is bonded to two equivalent Tb(2), one Si(1), and one Si(3) atom to form NTb2Si2 tetrahedra that share  a cornercorner with one N(2)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Tb2Si2 tetrahedra, corners with two equivalent N(5)Tb2Si2 trigonal pyramids, and  an edgeedge with one N(1)Tb2Si2 tetrahedra.
Tb2Si4CN6 crystallizes in the monoclinic P2_1/c space group. There are two inequivalent Tb sites. In the first Tb site, Tb(1) is bonded to one N(3), one N(4), one N(5), one N(6), and two equivalent N(2) atoms to form distorted TbN6 pentagonal pyramids that share corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(2)CN3 tetrahedra, corners with three equivalent Si(3)CN3 tetrahedra, corners with three equivalent Si(4)CN3 tetrahedra,  an edgeedge with one Tb(1)N6 pentagonal pyramid, and  an edgeedge with one Si(2)CN3 tetrahedra. The Tb(1)-N(3) bond length is 2.39 Å. The Tb(1)-N(4) bond length is 2.63 Å. The Tb(1)-N(5) bond length is 2.36 Å. The Tb(1)-N(6) bond length is 2.36 Å. There is one shorter (2.37 Å) and one longer (2.53 Å) Tb(1)-N(2) bond length. In the second Tb site, Tb(2) is bonded in a 5-coordinate geometry to one N(3), one N(4), one N(5), and two equivalent N(1) atoms. The Tb(2)-N(3) bond length is 2.42 Å. The Tb(2)-N(4) bond length is 2.34 Å. The Tb(2)-N(5) bond length is 2.59 Å. There is one shorter (2.37 Å) and one longer (2.38 Å) Tb(2)-N(1) 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(4), and one N(6) atom to form SiCN3 tetrahedra that share corners with two equivalent Tb(1)N6 pentagonal pyramids, corners with two equivalent Si(2)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, and corners with two equivalent Si(4)CN3 tetrahedra. The Si(1)-C(1) bond length is 1.92 Å. The Si(1)-N(1) bond length is 1.76 Å. The Si(1)-N(4) bond length is 1.77 Å. The Si(1)-N(6) bond length is 1.73 Å. In the second Si site, Si(2) is bonded to one C(1), one N(2), one N(4), and one N(5) atom to form SiCN3 tetrahedra that share corners with two equivalent Tb(1)N6 pentagonal pyramids, corners with two equivalent Si(1)CN3 tetrahedra, corners with two equivalent Si(3)CN3 tetrahedra, corners with two equivalent Si(4)CN3 tetrahedra, and  an edgeedge with one Tb(1)N6 pentagonal pyramid. The Si(2)-C(1) bond length is 1.91 Å. The Si(2)-N(2) bond length is 1.77 Å. The Si(2)-N(4) bond length is 1.76 Å. The Si(2)-N(5) bond length is 1.75 Å. In the third Si site, Si(3) 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 three equivalent Tb(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 1.88 Å. The Si(3)-N(1) bond length is 1.75 Å. The Si(3)-N(2) bond length is 1.76 Å. The Si(3)-N(3) bond length is 1.75 Å. In the fourth Si site, Si(4) 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 three equivalent Tb(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 1.91 Å. The Si(4)-N(3) bond length is 1.76 Å. The Si(4)-N(5) bond length is 1.74 Å. The Si(4)-N(6) bond length is 1.73 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)Tb2Si2 tetrahedra, corners with two equivalent N(2)Tb2Si2 tetrahedra, corners with two equivalent N(3)Tb2Si2 tetrahedra, and corners with two equivalent N(5)Tb2Si2 trigonal pyramids. There are six inequivalent N sites. In the first N site, N(2) is bonded to two equivalent Tb(1), one Si(2), and one Si(3) atom to form distorted NTb2Si2 tetrahedra that share  a cornercorner with one N(1)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Tb2Si2 tetrahedra, corners with three equivalent N(5)Tb2Si2 trigonal pyramids, and  an edgeedge with one N(2)Tb2Si2 tetrahedra. In the second N site, N(3) is bonded to one Tb(1), one Tb(2), one Si(3), and one Si(4) atom to form distorted NTb2Si2 tetrahedra that share corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(1)Tb2Si2 tetrahedra, corners with three equivalent N(2)Tb2Si2 tetrahedra,  a cornercorner with one N(5)Tb2Si2 trigonal pyramid, and  an edgeedge with one N(5)Tb2Si2 trigonal pyramid. In the third N site, N(4) is bonded in a 4-coordinate geometry to one Tb(1), one Tb(2), one Si(1), and one Si(2) atom. In the fourth N site, N(5) is bonded to one Tb(1), one Tb(2), one Si(2), and one Si(4) atom to form distorted NTb2Si2 trigonal pyramids that share  a cornercorner with one N(3)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with two equivalent N(1)Tb2Si2 tetrahedra, corners with three equivalent N(2)Tb2Si2 tetrahedra, and  an edgeedge with one N(3)Tb2Si2 tetrahedra. In the fifth N site, N(6) is bonded in a distorted trigonal planar geometry to one Tb(1), one Si(1), and one Si(4) atom. In the sixth N site, N(1) is bonded to two equivalent Tb(2), one Si(1), and one Si(3) atom to form NTb2Si2 tetrahedra that share  a cornercorner with one N(2)Tb2Si2 tetrahedra, corners with two equivalent C(1)Si4 tetrahedra, corners with three equivalent N(3)Tb2Si2 tetrahedra, corners with two equivalent N(5)Tb2Si2 trigonal pyramids, and  an edgeedge with one N(1)Tb2Si2 tetrahedra.