Ce2Pt9Al16 crystallizes in the monoclinic C2/m space group. Ce(1) is bonded in a 16-coordinate geometry to two equivalent Pt(3), four equivalent Pt(2), two equivalent Al(1), two equivalent Al(2), two equivalent Al(4), and four equivalent Al(3) atoms. There are four inequivalent Pt sites. In the first Pt site, Pt(1) is bonded in a 8-coordinate geometry to two equivalent Al(1), two equivalent Al(5), and four equivalent Al(2) atoms. In the second Pt site, Pt(2) is bonded in a 9-coordinate geometry to two equivalent Ce(1), one Al(1), one Al(4), two equivalent Al(2), and three equivalent Al(3) atoms. In the third Pt site, Pt(3) is bonded in a 8-coordinate geometry to two equivalent Ce(1), two equivalent Al(3), two equivalent Al(5), and four equivalent Al(1) atoms. In the fourth Pt site, Pt(4) is bonded in a body-centered cubic geometry to four equivalent Al(2) and four equivalent Al(4) atoms. There are five inequivalent Al sites. In the first Al site, Al(1) is bonded to one Ce(1), one Pt(1), one Pt(2), and two equivalent Pt(3) atoms to form distorted AlCePt4 tetrahedra that share corners with two equivalent Al(5)Pt4 tetrahedra, corners with three equivalent Al(4)Ce2Pt4 tetrahedra, corners with five equivalent Al(1)CePt4 tetrahedra, edges with two equivalent Al(5)Pt4 tetrahedra, and  a faceface with one Al(1)CePt4 tetrahedra. In the second Al site, Al(2) is bonded in a 5-coordinate geometry to one Ce(1), one Pt(4), two equivalent Pt(1), and two equivalent Pt(2) atoms. In the third Al site, Al(3) is bonded in a 4-coordinate geometry to two equivalent Ce(1), one Pt(3), and three equivalent Pt(2) atoms. In the fourth Al site, Al(4) is bonded to two equivalent Ce(1), two equivalent Pt(2), and two equivalent Pt(4) atoms to form distorted AlCe2Pt4 tetrahedra that share corners with two equivalent Al(4)Ce2Pt4 tetrahedra, corners with six equivalent Al(1)CePt4 tetrahedra, and edges with three equivalent Al(4)Ce2Pt4 tetrahedra. In the fifth Al site, Al(5) is bonded to two equivalent Pt(1) and two equivalent Pt(3) atoms to form distorted AlPt4 tetrahedra that share corners with two equivalent Al(5)Pt4 tetrahedra, corners with four equivalent Al(1)CePt4 tetrahedra,  an edgeedge with one Al(5)Pt4 tetrahedra, and edges with four equivalent Al(1)CePt4 tetrahedra.
Ce2Pt9Al16 crystallizes in the monoclinic C2/m space group. Ce(1) is bonded in a 16-coordinate geometry to two equivalent Pt(3), four equivalent Pt(2), two equivalent Al(1), two equivalent Al(2), two equivalent Al(4), and four equivalent Al(3) atoms. There is one shorter (3.41 Å) and one longer (3.42 Å) Ce(1)-Pt(3) bond length. There are two shorter (3.28 Å) and two longer (3.29 Å) Ce(1)-Pt(2) bond lengths. Both Ce(1)-Al(1) bond lengths are 3.32 Å. Both Ce(1)-Al(2) bond lengths are 3.40 Å. There is one shorter (3.31 Å) and one longer (3.32 Å) Ce(1)-Al(4) bond length. There are two shorter (3.33 Å) and two longer (3.34 Å) Ce(1)-Al(3) bond lengths. There are four inequivalent Pt sites. In the first Pt site, Pt(1) is bonded in a 8-coordinate geometry to two equivalent Al(1), two equivalent Al(5), and four equivalent Al(2) atoms. Both Pt(1)-Al(1) bond lengths are 2.51 Å. Both Pt(1)-Al(5) bond lengths are 2.63 Å. All Pt(1)-Al(2) bond lengths are 2.70 Å. In the second Pt site, Pt(2) is bonded in a 9-coordinate geometry to two equivalent Ce(1), one Al(1), one Al(4), two equivalent Al(2), and three equivalent Al(3) atoms. The Pt(2)-Al(1) bond length is 2.52 Å. The Pt(2)-Al(4) bond length is 2.60 Å. Both Pt(2)-Al(2) bond lengths are 2.55 Å. There is one shorter (2.49 Å) and two longer (2.66 Å) Pt(2)-Al(3) bond lengths. In the third Pt site, Pt(3) is bonded in a 8-coordinate geometry to two equivalent Ce(1), two equivalent Al(3), two equivalent Al(5), and four equivalent Al(1) atoms. Both Pt(3)-Al(3) bond lengths are 2.72 Å. Both Pt(3)-Al(5) bond lengths are 2.64 Å. All Pt(3)-Al(1) bond lengths are 2.53 Å. In the fourth Pt site, Pt(4) is bonded in a body-centered cubic geometry to four equivalent Al(2) and four equivalent Al(4) atoms. All Pt(4)-Al(2) bond lengths are 2.51 Å. All Pt(4)-Al(4) bond lengths are 2.61 Å. There are five inequivalent Al sites. In the first Al site, Al(1) is bonded to one Ce(1), one Pt(1), one Pt(2), and two equivalent Pt(3) atoms to form distorted AlCePt4 tetrahedra that share corners with two equivalent Al(5)Pt4 tetrahedra, corners with three equivalent Al(4)Ce2Pt4 tetrahedra, corners with five equivalent Al(1)CePt4 tetrahedra, edges with two equivalent Al(5)Pt4 tetrahedra, and  a faceface with one Al(1)CePt4 tetrahedra. In the second Al site, Al(2) is bonded in a 5-coordinate geometry to one Ce(1), one Pt(4), two equivalent Pt(1), and two equivalent Pt(2) atoms. In the third Al site, Al(3) is bonded in a 4-coordinate geometry to two equivalent Ce(1), one Pt(3), and three equivalent Pt(2) atoms. In the fourth Al site, Al(4) is bonded to two equivalent Ce(1), two equivalent Pt(2), and two equivalent Pt(4) atoms to form distorted AlCe2Pt4 tetrahedra that share corners with two equivalent Al(4)Ce2Pt4 tetrahedra, corners with six equivalent Al(1)CePt4 tetrahedra, and edges with three equivalent Al(4)Ce2Pt4 tetrahedra. In the fifth Al site, Al(5) is bonded to two equivalent Pt(1) and two equivalent Pt(3) atoms to form distorted AlPt4 tetrahedra that share corners with two equivalent Al(5)Pt4 tetrahedra, corners with four equivalent Al(1)CePt4 tetrahedra,  an edgeedge with one Al(5)Pt4 tetrahedra, and edges with four equivalent Al(1)CePt4 tetrahedra.