Stability constants of silver(I) complexes with diaza-18-crown ethers in polar solvents

The stability constants of Ag+ complexes with macrocyclic diaza-crown ethers of constant ring size [18], but with different donor atom distributions in the ligand bridges, are strongly dependent upon solvent. The effect of solvent, however, is essentially independent of the ligand involved, and this extends even to bicyclic cryptand ligands. Thus, the stability constants of any one ligand are linearly related to those of the other ligands across a wide range of polar solvents. A more detailed analysis of the results in terms of the free energies of solvation and transfer of the species involved in the complexation reaction shows that, although the dominant influence is normally the solvation of Ag+, specific solvation of either the complexed cation or the free ligand can influence complex stabilities in some cases. Effects due to the former, although relatively weak, are evident in complexes of monocyclic diaza-ligands in strongly coordinating solvents, such as dimethylformamide and dimethyl sulfoxide, and the latter is quite marked in solvents possessing acidic hydrogen atoms, such as water, methanol, and nitromethane.