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

Abstract

Crystals of (2.2.2-cryptand)potassium bromide hydrate of composition 2 : 7, [K(Crypt-222)]⁺Br⁻ ⋅ 3.5H₂O (I), are synthesized and studied by X-ray diffraction analysis. The crystals are trigonal, space group P $\bar 3$, a = 11.858(2) Å, c = 11.370(2) Å, Z = 2. The structure is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.098 against 2668 independent reflections (CAD4 automated diffractometer, λMoK _α 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.