Synthesis, Structure and Binding Properties of Nickel and Copper [14]Cyclidene Complexes with Appended Aza Crown Ethers

Copper( II ) and nickel( II ) cyclidenes linked with one or two 15‐azacrown‐5 ethers ( 3Ni , 4Ni and 4Cu ) as well as similar model morpholine‐substituted derivatives ( 2Cu , 2Ni ) have been synthesized and characterized using ESI mass‐spectrometry, X‐ray diffraction, spectroscopic methods and elemental analysis. Cyclic voltammetry of the copper complexes exhibits two reversible redox couples Cu II/III and Cu II/I , whereas the nickel complexes show reversible Ni II/III and irreversible Ni II/I redox processes. Cyclic and differential pulse voltammetry have been used to study interactions of metal cations and amino acids with the above complexes. Na + and Li + interact weakly with the 3Ni complex. In the presence of Mg 2+ , the ligand isomerizes from aldehyde to enolate ion, which interacts strongly with Mg 2+ . The presence of lysine caused a more pronounced shift of the Cu II/III potential in 4Cu than did leucyne. This suggests that there are interactions between the NH 3 + group and the crown ether moiety and between the carboxylic group and the Cu III center of the former guest. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)