Crystal structure of the 1,10-diaza-18-crown-6 complex with calcium thiocyanate

The disordered crystal structure of the 1,10-diaza-18-crown-6 complex with calcium thiocyanate, DA18C6 . Ca(NCS)(2) (I), is studied by X-ray diffracti on analysis: space group <P(1)over bar>, a = 7.487, b = 8.256, c = 9.522 An gstrom, alpha = 74.64 degrees, beta = 68.52 degrees, gamma = 75.11 degrees, Z = 1. Structure I is solved by the direct method and refined anisotropica lly by the full-matrix least squares method to R = 0.067 for all 2196 uniqu e reflections (CAD-4 automated diffractometer, lambda CuKalpha). Complex I exists in the crystal as individual molecules of the host-guest type. The C a2+ cation is positioned in the center of the cavity of DA18C6 azacrown eth er (inversion center). The coordination polyhedron of Ca2+ is a distorted h exagonal bipyramid with the base formed by six heteroatoms (N and O) of the DA18C6 macrocycle and two N atoms of the SCN- anions in the axial vertices . The DA18C6 macrocycle in structure I is disordered over two overlapping p ositions (with occupancies 0.73 and 0.27) and has two different conformatio ns: crown conformation with the approximate D-3d symmetry and an unusual co nformation with two spiral fragments of the macrocycle.