Crystal structures of complexes between alkali-metal salts and cyclic polyethers. Part VIII. Complexes formed by caesium thiocyanate with (7R,9R,18S,20S)-6,7,9,10,17,18,20,21-octahydro-7,9,18,20-tetramethyldibenzo[b,k][1,4,7,10,13,16]hexaoxacyclo-octadecin (tetramethyldibenzo-18-crown-6, isomer F) and its (18R,20R)-isomer (isomer G)

Abstract

The crystal structures of the two title compounds have been determined by X-ray diffraction and refined by least squares. Crystals of the isomer F compound (II) are triclinic with a= 11·12(1), b= 11·87(1), c= 13·46(1)Å, α= 107·75(2), β= 95·25(6), γ= 121·90(4)°, Z= 2, space group P, final R 0·062 on 2086 diffractometer data. Crystals of the isomer G complex (III) are tetragonal, with a= 15·22(1), c= 11·14(1)Å, Z= 2, space group P42/n, final R 0·11 on 1394 diffractometer data. Molecules of (II), a 1 : 1 complex, are dimeric and centrosymmetric with Cs–N–Cs bridges, the other co-ordinating atoms being the six oxygens of isomer F at 3·07–3·34 Å and the aryl carbons at 3·80 Å. The configuration of the methyl groups is cis,anit,cis. Compound (III) is a 1 : 2 complex consisting of [Cs(isomer G)2]+ cations having symmetry with twelve Cs–O contacts (3·12–3·36 Å), and disordered thiocyanate ions. The methyl group configuration is trans,anti,trans. There are differences in conformation between (II) and (III).