Stability constants of copper(I) and silver(I) complexes with open-chain, macrocyclic and -bicyclic aza-ligands in acetonitrile and comparison with results in dimethylsulfoxide

Abstract

Stability constants of copper(I) and silver(I) with butylamines, monoaza- and diaza-crown ethers and cryptands have been determined in acetonitrile (AN). The stability constants of the silver(I) complexes are markedly larger than those with copper(I), and the complexation behaviour of silver(I) is determined to a much larger extent by the tendency to form inclusion complexes involving interactions with both, oxygen and nitrogen donor atoms. Silver(I) forms only 1:1 inclusion complexes with macrobicylic cryptand ligands, for example, whereas copper(I) additionally forms 2:1 (Cu +:ligand) complexes in which the cryptands act as monodentate ligands. A comparison of the results in AN with those reported in dimethylsulfoxide (N. Heidari, A. Thaler, H. Schneider, B.G. Cox, Inorg. Chim. Acta 279 (1998) 186) shows that in cryptand complexes the cation is normally well shielded from interactions with the solvent, such that the free energies of transfer of the ligands and cryptates are very similar. All other complexes show evidence of residual interactions of the complexed cations with the solvent. The observed difference between the complexation reactions of silver(I) and copper(I) in AN and in the responses of their complex stabilities to solvent transfer, can be attributed to different preferences of the two cations for binding with nitrogen and oxygen atoms; copper(I) in particular shows a very strong preference for nitrogen donor atoms.