Cesium cholate: Determination of X-ray crystal structure indicates participation of the ring hydroxyl groups in metal binding

The crystal structure of cesium cholate, C₂₄H₃₆(OH)₃ COOCs has been determined with three-dimensional X-ray diffractometer data. It crystallized in the monoclinic space group P2₁ with unit-cell dimensions a = 11.543(5) Å, b = 8.614(3) Å, and c = 12.662(5) Å, β(deg) = 107.95(2), V = 1197.7 ų and Z = 2. The atomic parameters were refined to a final r = 0.0269 and Rω = 0.0280 for 2342 observed reflections. Each Cs⁺ is coordinated to 7 oxygen atoms from 5 different cholate anions with Cs-O distances ranging from 2.957(4) Å to 3.678(5) Å. In this crystal, 5 cholates are coordinated with 1 Cs⁺, and 5 Cs⁺ are coordinated with 1 cholate anion. Carboxyl and all the 3 ring hydroxyl groups of cholate anion participate in binding to Cs⁺ simultaneously, and there is no water molecule coordinated with the Cs⁺. The pattern of successive rows arranged with polar (p) and non-polar (n) faces in apposition leads to the formation of a sandwich sheet structure with polar and non-polar channels. The Cs ions lie within the polar interior of the sandwich. The H-bond network is reorganized in forming cesium cholate from cholic acid. All the oxygen atoms in cholate anion are involved in H-bonding reciprocally or with water molecules to form an extensive 3-dimensional network of H-bonds. Compared with cholic acid and other similar type of steroids, the coordination structure and H-bonding of Cs cholate crystal are distinct.