CROWN-ETHER STYRYL DYES .17. INFLUENCE OF THE LENGTH OF THE N-SUBSTITUENT IN BETAINES OF CHROMOGENIC 15-CROWN-5-ETHERS ON COMPLEXATION WITHCATIONS OF ALKALINE-EARTH METALS

The stoichiometry of complexation of crown ether styryl dyes with Mg2, Ca2+, and Ba2+ ions and the dependence of the stability constants of these complexes on the length of the N-sulfoalkyl substituent were in vestigated. Introduction of a terminal sulfo group into the N-ethyl su bstituent had but a small effect on the stability constant for the com plexes with 1:1 stoichiometry. Increase in the length of the N-substit uent by one or two methylene groups resulted in a jumpwise rise of thi s constant. The effect observed was attributed to the formation of the intramolecular ion pair, The dimerization constant for Mg2+ complexes increased dramatically when passing from the sulfopropyl N-substituen t to the sulfobutyl. one. The increase in the constant results from th e decrease in steric strains in the dimeric complex.