The assembly of supramolecular boxes and coordination polymers based on bis-zinc-salphen building blocks

We report the assembly of supramolecular boxes and coordination polymers based on a rigid bis-zinc(II)-salphen complex and various ditopic nitrogen ligands. The use of the bis-zinc(II)-salphen building block in combination with small ditopic nitrogen ligands gave organic coordination polymers both in solution as well as in the solid state. Molecular modeling shows that supramolecular boxes with small internal cavities can be formed. However, the inability to accommodate solvent molecules (such as toluene) in these cavities explains why coordination polymers are prevailing over well-defined boxes, as it would lead to an energetically unfavorable vacuum. In contrast, for relatively longer ditopic nitrogen ligands, we observed the selective formation of supramolecular box assemblies in all cases studied. The approach can be easily extended to chiral analogues by using chiral ditopic nitrogen ligands.