Diaquabromo(18-crown-6)rubidium and triaqua(18-crown-6)barium dibromide monohydrate: Synthesis and crystal structures |
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Authors: | A N Chekhlov |
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Institution: | (1) Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432, Russia |
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Abstract: | Two complexes are synthesized: diaquabromo(18-crown-6)rubidium RbBr(18-crown-6)(H2O)2] (I) and triaqua(18-crown-6)barium dibromide monohydrate Ba(18-crown-6)(H2O)3]2+ 2Br? · H2O (II). The orthorhombic structure of compound I (space group Pnma, a = 10.124 Å, b = 15.205 Å, c = 12.544 Å, Z = 4) and the monoclinic structure of compound II (space group C 2/c, a = 17.910 Å, b = 10.315 Å, c = 14.879 Å, β = 123.23°, Z = 4) are determined by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.063 (I) and 0.042 (II) for all 2293 (I) and 3363 (II) independent measured reflections (CAD-4 automated diffractometer, λMoK α). The complex molecule RbBr(18-crown-6)(H2O)2] in compound I and the randomly disordered cation Ba(18-crown-6)(H2O)3]2+ in compound II are of the host-guest type: their Rb+ or Ba2+ cation (its coordination number is nine) is located in the cavity of the 18-crown-6 ligand and coordinated by all six O atoms. In structure I, the coordination polyhedron of Rb+ is a distorted hexagonal pyramid with a triple apex at the Br? ligand and two O atoms of the water molecules. In structure II, the Ba2+ polyhedron is a distorted hexagonal bipyramid with one apex at the O atom of the water molecule and the other split apex at two O atoms of water molecules. |
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