Synthesis and crystal structure of 2: 7 (2.2.2-cryptand)potassium bromide hydrate

Crystals of (2.2.2-cryptand)potassium bromide hydrate of composition 2 : 7, [K(Crypt-222)]Br-+(- .) 3.5H(2)O (I), are synthesized and studied by X-ray diffraction analysis. The crystals are trigonal, space group P (3) over bar, a = 11.858(2) A, c = 11.370(2) A, Z = 2. The structure is solved by a direct method and refined by the fullmatrix least-squares method in the anisotropic approximation to R = 0.098 against 2668 independent reflections (CAD4 automated diffractometer, lambda MoKalpha radiation). Structure I contains complex cation [K(Crypt-222)](+) of the host-guest type arranged in crystallographic axis 3 with approximate symmetry D-3. The coordination polyhedron of the K+ cation is a two-base-centered trigonal prism somewhat distorted to form antiprism. In crystal I, bromide anions and water molecules are linked by hydrogen bonds to form an infinite chain of alternating Br- anions multiplied by integer translations along axis z and disordered cubes of water molecules and other Br- anions.