The s-conformations of trans-1b–e were studied by 1H NMR spectroscopy in CD3CN solution. It was shown that in trans-1b–e intramolecular ion pairs between the SO3– group and the positively charged nitrogen atom of the benzothiazolium residue are formed. In the case of trans-1a no ionic association was observed. The complex formation of the trans- and cis-isomers of crown-containing styryl dyes with Mg2+ in CH3CN was studied spectrophotometrically. The anion-“capped” complexes formed by the cis-isomers were found to be more stable than the complexes formed by the corresponding trans-isomers. The stability constants of the complexes formed by the cis-isomers depend markedly on length and type of the N-substituent. Data from PM3 quantum-chemical calculations were used for the interpretation of some experimental data.
