Crystal structure of bis(dibenzo-18-crown-6)rubidium triiodide

Crystalline bis(dibenzo-18-crown-6)rubidium triiodide complex [Rb(DB18C6)(2)I](+) . I-3(-) (I) is synthesized and its structure is studied by X-ray diffraction analysis. The structure of I (space group Pnma, a = 23.854 Angstrom, b = 23.612 Angstrom, c = 7.863 Angstrom, Z = 4) is solved by the direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.079 against 3990 independent reflections (CAD4 automated diffractometer, lambdaMoK(alpha)). Structural units of crystal I are the I-3(-) anions and [Rb(DB18C6)(2)](+) cations. The crystal has the structure intermediate between that of a standard host-guest complex and a sandwich complex. In the structure of complex 1, the crystallographic plane with symmetry m passes through the I-3(-) anion (perpendicularly to its axis) and complex cation. The coordination polyhedron of the Rb+ cation is a strongly distorted hexagonal pyramid with the O atom of one crown ligand at the axial vertex and a base of six O atoms of another DB18C6 crown ligand.