Synthesis and crystal structure of a caesium α-cyanobenzothiazole-α-carbaldehyde oximate complex with a crown ether (L): new evidence for the stability of [Cs2L3]2+ club sandwiches

The reaction of Cs 2 CO 3 , 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) and α-cyanobenzothiazole-α-carbaldehyde oxime (Hcbto) resulted in the formation of [Cs 2 (18-crown-6) 3 ][H(cbto) 2 ] 2 ·2Hcbto·2H 2 O. X-Ray diffraction analysis revealed a genuine club sandwich centrosymmetric structure for the complex cation [Cs 2 (18-crown-6) 3 ] 2+ with one of the crown ligands placed between the two caesium atoms, and is important evidence for the stability of such macrocyclic complexes. The metal atoms adopt twelve-fold co-ordination in a distorted hexagonal-antiprismatic geometry. The ‘central’ 18-crown-6 molecule displays longer co-ordination interactions Cs–O [3.393(5)–3.636(5), average ca. 3.511(5) Å] than the ‘border’ crown ligand [3.152(7)–3.431(8), average ca. 3.265(8) Å]. The caesium atom deviates from the mean plane of the six oxygen atoms by 2.167(1) Å in the first case and 1.640(3) Å in the second. Hydrogen bonding is considered to be important in the crystal packing.