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New bis(crown ether) ligands (1 - 3) of Schiff base type containing recognition sites for sodium and nickel guest cations have been synthesized by the condensation of two equivalents of 4′-formyl-5′-hydroxy(benzo-15-crown-5)with 1,5-diamino-3-azapentane, 1,8-diamino-3,6- diazaoctane or 1,8-diamino-3,6-dioxaoctane. Homonuclear ditopic crystalline 2:1 (Na + :ligand) complexes (1a - 3a) of the ligands with NaClO 4  have been prepared. Heteronuclear tritopic crystalline 2:1:1 (Na ⊕  : Ni 2⊕  : ligand) complexes (2b and 3b) have also been synthesized from the reactions of the ditopic complexes (2a and 3a) with Ni(CH 3 COO) 2  · 6H 2 O. The UV-VIS spectra of 1 - 3, their sodium complexes 1a - 3a and sodium-nickel complexes 2b and 3b have been recorded in polar and non-polar solvents as well as in acidic and basic media. In polar solvents and basic solutions, tautomeric equilibria (phenol-imine and keto-amine forms, O-H···N⇌O···H-N ) are present, depending on the hydrogen bonding. The results indicate that the concentrations of the keto forms of the compounds generally increase as the polarity of the solvent increases

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Synthesis, Complex Formation and Spectral Investigation of New Tritopic Bis(Crown Ether) Compounds Containing Recognition Sites for Sodium and Nickel Guest Cations*