Synthesis and co-ordination chemistry of new Schiff-base bis(crown ether) ligands containing recognition sites for alkali- and transition-metal guest cations. Crystal structure of a copper(<scp>I</scp>)–potassium complex

Abstract

New Schiff-base bis(crown ether) ligands L1–L5 containing recognition sites for alkali- and transition-metal guest cations have been prepared by the condensation of two equivalents of 15-formyl-2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecine with diamines H2NXNH2(X =[CH2]2S[CH2]2, [CH2]2S[CH2]2S[CH2]2, [CH2]2S[CH2]3S[CH2]2, [CH2]3S[CH2]2S[CH2]3 or [CH2]2NH[CH2]2). The sodium cation forms 2 : 1 Na+ : L complexes, whereas the larger potassium cation produces 1 : 1 intramolecular sandwich complexes with these ligands. Homometallic copper(I) complexes and heteropolymetallic copper(I)–sodium and –potassium complexes have also been isolated. A single-crystal X-ray structure of one copper–potassium complex has been determined. Heteropolymetallic silver(I)–sodium and –potassium ligand complexes have also been prepared. Carbon-13 NMR titration studies suggest that the stoichiometry of the Schiff-base bis(crown ether) ligand to potassium guest cations is dependent upon the stereochemical requirements of the co-bound silver(I) guest cation.