Unit cells of choline halides and structure of choline chloride

Three choline halides have been studied by single-crystal X-ray diffraction methods at room temperature.Choline chloride is orthorhombic, space group P212121, a=11.2I+0"02,b=11.59_+0"02,c=5.87+0"02A, Z=4.Atomic coordinates have been determined by least-squares refinement of three-dimensional data.Bond distances in A are: N-C (methyl), 1.53, 1.52, 1.50; N-C (side chain), 1.60;C--C, 1.56;C-O, 1-39 (each + 0-03 A).Choline bromide is orthorhombic, probable space group Pna21 or Pnam, a=19-55+_0.04,b=7.35+0.03,c=5.69+0.02A, Z=4, Choline iodide is monoclinic, probable space group P21, a=5.88+0.02,b=8.20+0.02,c=9.10+0.02A,fl=91+l °, Z=2.CGH.~CI.~,C6H.~Br.~ are isomorphous, P212121 with Z = 4.The structure is of a layer type, the molecules being planar and inclined at about _+ 27 ° to ( 001).The mean thermal expansion coefficients for C~H.~C1, from -183 °C. to 20 °C.are 58, 46, 109 x 10 -6 along a, b, c respectively.The lack of exact triangular symmetry of the molecule is shown both in the lengths of intermolecular bonds and in the anisotropy of the atomic Debye factors.The structure is compared with those of other symmetricallysubstituted ring compounds.