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(I)–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.