(18-Crown-6)sodium tribromide and (18-crown-6)potassium triiodide (with an admixture of bromodiiodide): Synthesis and crystal structure

Abstract

Two crystalline host-guest complexes are synthesized and studied using X-ray diffraction analysis: (18-crown-6)sodium tribromide [Na(18-crown-6)]+ · Br 3 − (I) and (18-crown-6)potassium tribromide (with an admixture of bromodiiodide) [K(18-crown-6)]+ · (Br0.25I2.75)− (II). The structures of compound I (space group P21/n, a = 8.957 A, b = 8.288 A, c = 14.054 A, β = 104.80°, Z = 2) and compound II (space group Cc, a = 8.417 A, b = 15.147 A, c = 17.445 A, β = 99.01°, Z = 4) are solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.098 (I) and 0.036 (II) for all 2311 (I) and 2678 (II) independent measured reflections on a CAD-4 automated diffractometer (λMoK α). Similar crystalline complexes I and II exist as infinite chains of alternating complex cations and trihalide anions linked to each other through weak Na-Br or K-I coordination bonds. In [Na(18-crown-6)]+ and [K(18-crown-6)]+ complex cations, the Na+ or K+ cation (coordination number is eight) is located in the center of the cavity of the 18-crown-6 ligand and coordinated by the six O atoms and two terminal Br or I atoms of two trihalide anions lying on opposite sides of the rms plane of the crown ligand.