Varying the metal/metal ratio in related Cu–Ca complexes

We demonstrate with the help of structural determinations and spectroscopic data that the nuclearity of Cu–Ca complexes derived from compartmental Schiff base ligands does not depend on the ionic radius of calcium. The main factors governing these reactions are the different affinities of the calcium ions for the anionic species present in solution: the tetradentate O2O2 coordination site of the ligand and the nitrato ions. Because these affinities do vary upon going from calcium to lanthanide ions, it is not possible to use the template effect of the trinuclear Cu–Ca–Cu complexes in order to prepare the corresponding Cu–Ln–Cu complexes.

Graphical abstractCopper complexes derived from compartmental Schiff base ligands react with calcium ions to yield trinuclear Cu–Ca–Cu entities while dinuclear Cu–Ca complexes can also be isolated with use of auxiliary ligands such as diketones; the trinuclear Cu–Ca–Cu entities do not allow to synthesize the corresponding trinuclear Cu–Ln–Cu complexes.Figure optionsDownload full-size imageDownload as PowerPoint slide