Schiff bases and their complexes with metal ions, IV - Synthesis, complex formation and spectral investigation of new tritopic bis(crown ether) compounds containing recognition sites for sodium and nickel guest cations

New bis(crown ether) ligands (1 - 3) of Schiff base type containing recogni tion 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 NaClO4 have been prepared. Heteronuclear trit opic crystalline 2:1:1 (Na+ : Ni2+ : ligand) complexes (2b and 3b) have als o been synthesized from the reactions of the ditopic complexes (2a and 3a) with Ni(CH3COO)(2) . 6H(2)O. The W-VIS spectra of 1 - 3, their sodium compl exes 1a - 3a and sodium-nickel complexes 2b and 3b have been recorded in po lar and non-polar solvents as well as in acidic and basic media. In polar s olvents and basic solutions, tautomeric equilibria (phenol-imine and keto-a mine forms, O-H . . .N reversible arrow O . . .H-N) are present, depending on the hydrogen bonding. The results indicate that the concentrations of th e keto forms of the compounds generally increase as the polarity of the sol vent increases.