Supramolecular chemistry has become one of the most interesting fields in modern day chemistry. Self-recognition and self-assembly are the most outstanding characteristics and represent the fundamental concept of supramolecular chemistry. Principally, the interactions involved in the field are mainly non-covalent forces, including but not limited to van der Waals, hydrogen bonding, ionic or coordinative interactions. Metal-ligand coordination interactions are of great importance among these forces. Of numerous examples, terpyridine ligands exhibit excellent capability to coordinate with various transition metal ions (Zn, Cd, Fe, Ru, etc.) to form stable complexes with unique magnetic, optical and electrochemical properties. Over the past decades, numerous approaches have been employed to study terpyridine-metal coordination as well as self-assembly behavior.
In this work, a three-dimensional, highly symmetric sphere-like nanoball was synthesized using a terpyridine-based flexible tridentate ligand and characterized by single crystal X-ray analysis. To employ more rigidity, the corresponding Ru2+-dimer was synthesized by pre-blocking one of the terpyridine units of the tridentate ligand utilizing a reliable "tpy-Ru2+-tpy" linkage. The self-assembly of this Ru2+-dimer and Fe2+ showed an unexpected temperature-dependent phenomenon between two irreversible isomeric three-dimensional nanocages. The effects of rigidity and in the presence of external factor (temperature) on the coordination progress and structural formations of metal-ligand framework are reported.