Ce2Ni17Si9 crystallizes in the orthorhombic Fmmm space group. Ce(1) is bonded in a 24-coordinate geometry to four equivalent Ni(1), four equivalent Ni(2), four equivalent Ni(3), four equivalent Ni(4), four equivalent Si(1), and four equivalent Si(2) atoms. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Ce(1), one Ni(1), two equivalent Ni(2), two equivalent Ni(4), one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms to form distorted NiCe2Si5Ni5 cuboctahedra that share  a cornercorner with one Ni(5)Si4Ni8 cuboctahedra, corners with five equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, corners with six equivalent Ni(2)Ce2Si4Ni6 cuboctahedra,  a faceface with one Ni(5)Si4Ni8 cuboctahedra,  a faceface with one Si(3)Si4Ni8 cuboctahedra, faces with three equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, and faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra. In the second Ni site, Ni(2) is bonded to two equivalent Ce(1), one Ni(2), one Ni(5), two equivalent Ni(1), two equivalent Ni(3), two equivalent Si(1), and two equivalent Si(2) atoms to form NiCe2Si4Ni6 cuboctahedra that share  a cornercorner with one Si(3)Si4Ni8 cuboctahedra, corners with five equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, corners with six equivalent Ni(1)Ce2Si5Ni5 cuboctahedra,  a faceface with one Ni(5)Si4Ni8 cuboctahedra,  a faceface with one Si(3)Si4Ni8 cuboctahedra, faces with three equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra. In the third Ni site, Ni(3) is bonded in a 11-coordinate geometry to two equivalent Ce(1), one Ni(5), two equivalent Ni(2), two equivalent Ni(4), two equivalent Si(1), and two equivalent Si(2) atoms. In the fourth Ni site, Ni(4) is bonded in a 2-coordinate geometry to two equivalent Ce(1), two equivalent Ni(1), two equivalent Ni(3), one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. In the fifth Ni site, Ni(5) is bonded to four equivalent Ni(2), four equivalent Ni(3), and four equivalent Si(2) atoms to form NiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 11-coordinate geometry to two equivalent Ce(1), two equivalent Ni(1), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and one Si(3) atom. In the second Si site, Si(2) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Ni(5), two equivalent Ni(1), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and one Si(2) atom. In the third Si site, Si(3) is bonded to four equivalent Ni(1), four equivalent Ni(4), and four equivalent Si(1) atoms to form SiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra.
Ce2Ni17Si9 crystallizes in the orthorhombic Fmmm space group. Ce(1) is bonded in a 24-coordinate geometry to four equivalent Ni(1), four equivalent Ni(2), four equivalent Ni(3), four equivalent Ni(4), four equivalent Si(1), and four equivalent Si(2) atoms. All Ce(1)-Ni(1) bond lengths are 3.35 Å. All Ce(1)-Ni(2) bond lengths are 3.30 Å. All Ce(1)-Ni(3) bond lengths are 3.13 Å. All Ce(1)-Ni(4) bond lengths are 3.20 Å. All Ce(1)-Si(1) bond lengths are 3.18 Å. All Ce(1)-Si(2) bond lengths are 3.31 Å. There are five inequivalent Ni sites. In the first Ni site, Ni(1) is bonded to two equivalent Ce(1), one Ni(1), two equivalent Ni(2), two equivalent Ni(4), one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms to form distorted NiCe2Si5Ni5 cuboctahedra that share  a cornercorner with one Ni(5)Si4Ni8 cuboctahedra, corners with five equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, corners with six equivalent Ni(2)Ce2Si4Ni6 cuboctahedra,  a faceface with one Ni(5)Si4Ni8 cuboctahedra,  a faceface with one Si(3)Si4Ni8 cuboctahedra, faces with three equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, and faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra. The Ni(1)-Ni(1) bond length is 2.55 Å. There is one shorter (2.40 Å) and one longer (2.42 Å) Ni(1)-Ni(2) bond length. Both Ni(1)-Ni(4) bond lengths are 2.52 Å. The Ni(1)-Si(3) bond length is 2.27 Å. Both Ni(1)-Si(1) bond lengths are 2.45 Å. Both Ni(1)-Si(2) bond lengths are 2.49 Å. In the second Ni site, Ni(2) is bonded to two equivalent Ce(1), one Ni(2), one Ni(5), two equivalent Ni(1), two equivalent Ni(3), two equivalent Si(1), and two equivalent Si(2) atoms to form NiCe2Si4Ni6 cuboctahedra that share  a cornercorner with one Si(3)Si4Ni8 cuboctahedra, corners with five equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, corners with six equivalent Ni(1)Ce2Si5Ni5 cuboctahedra,  a faceface with one Ni(5)Si4Ni8 cuboctahedra,  a faceface with one Si(3)Si4Ni8 cuboctahedra, faces with three equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra. The Ni(2)-Ni(2) bond length is 2.51 Å. The Ni(2)-Ni(5) bond length is 2.39 Å. Both Ni(2)-Ni(3) bond lengths are 2.53 Å. Both Ni(2)-Si(1) bond lengths are 2.44 Å. Both Ni(2)-Si(2) bond lengths are 2.51 Å. In the third Ni site, Ni(3) is bonded in a 11-coordinate geometry to two equivalent Ce(1), one Ni(5), two equivalent Ni(2), two equivalent Ni(4), two equivalent Si(1), and two equivalent Si(2) atoms. The Ni(3)-Ni(5) bond length is 2.55 Å. Both Ni(3)-Ni(4) bond lengths are 2.48 Å. Both Ni(3)-Si(1) bond lengths are 2.29 Å. Both Ni(3)-Si(2) bond lengths are 2.49 Å. In the fourth Ni site, Ni(4) is bonded in a 2-coordinate geometry to two equivalent Ce(1), two equivalent Ni(1), two equivalent Ni(3), one Si(3), two equivalent Si(1), and two equivalent Si(2) atoms. The Ni(4)-Si(3) bond length is 2.52 Å. Both Ni(4)-Si(1) bond lengths are 2.56 Å. There is one shorter (2.30 Å) and one longer (2.32 Å) Ni(4)-Si(2) bond length. In the fifth Ni site, Ni(5) is bonded to four equivalent Ni(2), four equivalent Ni(3), and four equivalent Si(2) atoms to form NiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra, faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra. All Ni(5)-Si(2) bond lengths are 2.30 Å. There are three inequivalent Si sites. In the first Si site, Si(1) is bonded in a 11-coordinate geometry to two equivalent Ce(1), two equivalent Ni(1), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and one Si(3) atom. The Si(1)-Si(3) bond length is 2.46 Å. In the second Si site, Si(2) is bonded in a 12-coordinate geometry to two equivalent Ce(1), one Ni(5), two equivalent Ni(1), two equivalent Ni(2), two equivalent Ni(3), two equivalent Ni(4), and one Si(2) atom. The Si(2)-Si(2) bond length is 2.67 Å. In the third Si site, Si(3) is bonded to four equivalent Ni(1), four equivalent Ni(4), and four equivalent Si(1) atoms to form SiSi4Ni8 cuboctahedra that share corners with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, faces with four equivalent Ni(2)Ce2Si4Ni6 cuboctahedra, and faces with four equivalent Ni(1)Ce2Si5Ni5 cuboctahedra.