Synthesis and characterization of new bis(crown ether)s of Schiff base type containing recognition sites for sodium and nickel guest cations

New bis(crown ether) ligands of Schiff base type (2-4) containing recogniti on sites for sodium and nickel guest cations have been synthesized by the c ondensations of two equivalents of 4'-formyl-5'-hydroxy(benzo-15-crown-5) ( 1) with diamines, H2N-(CH2)(n)-NH2 (n = 2-4). Homonuclear ditopic crystalli ne 2 : I (Na+ : ligand) complexes (2a-4a, 2b-4b! of the ligands with NaSCN and NaClO4 have been prepared. The NaClO4, complexes of 3 and 4 (3b and 4b) form heteronuclear tritopic crystalline complexes with Ni-2 circle plus ca tions of stoichiometry 2 : 1 : 1 (Na-circle plus : Ni-2 circle plus : Ligan d). A homonuclear monotopic Ni-2 circle plus complex has also been prepared by the reaction with Ni(CH3COO), 6H(2)O. The UV-VIS spectra of 2-4 and the ir NaClO4, complexes (2b-4b) are studied in different solvents including ac idic and basic media. In polar solvents, tautomeric equilibria (phenol-imin e, O-H ... N and ketoamine, O ... H-N forms) are present, as supported by t he UV-VIS data.