A tale of crystal engineering of metal complexes derived from a special ligand family having a cosmopolitan compartment†
The journey of the syntheses and studies of the structures and properties of metal complexes derived from double-compartment 3-ethoxysalicylaldehyde-diamine (H2LOEt) ligands was started in 1995, as per the CSD version 1.15 (2012) record. After dealing with mainly mononuclear complexes in the early years, the “metallo-ligand as reactant” approach was started in 2002 with the reporting of a CuIIGdIII compound, with the aim to explore the magnetic properties of 3d–4f systems. It was realized within a few years that the O(phenoxo)2O(ethoxy)2 compartment has strong potential to interact with water molecule(s) due to the formation of bifurcated hydrogen bonds, resulting in the stabilization of the mononuclear inclusion products and two-component and even three-component cocrystals. “Metallo-ligand as reactant” was reacted with several metal ions from various parts of the periodic table (s, p, 3d, d10, 4f, 5f) as well as with possible hydrogen bond donors, such as an ammonium ion, diprotonated diamines, dicarboxylic acids and aquated proton (perchloric acid). A number of cocrystals, supramolecular dimers, a new type of hydrate isomerism, systems with interesting topologies and systems showing resemblances of entirely different types of metal ions have been obtained. Eventually, we can call the H2LOEt a special ligand family and the O(phenoxo)2O(ethoxy)2 compartment a cosmopolitan compartment. This highlight deals with the metal complexes derived from 3-ethoxysalicylaldehyde-diamine ligands from a crystal engineering perspective.