Unveiling the multifaceted roles of protonated 1,2-bis(4-pyridyl)ethylene (HBpe+) ligand in metal-driven supramolecular assembly: a comprehensive structural review

A protonated form of 1,2-bis(4-pyridyl)ethylene (HBpe+), produced through proton transfer or pH adjustments, plays a significant role in forming unique supramolecular structures. In contrast, non-protonated forms of the molecule (Bpe) are extensively studied in metal-organic complexes. In this review, we examine the fascinating world of HBpe+ as a monodentate ligand in the realm of coordination chemistry. It discusses how protonated ligands influence the assembly of supramolecular structures, as well as their properties and functions. Structures such as 1:1 adduct, coordination polymers, and metal clusters are often formed as a result. In these assemblies, HBpe+ engages in a variety of interactions that influence its supramolecular behavior. The interactions include coordination complexes with metal ions, hydrogen bonds, aromatic ring stacking, and double bond stacking (π⋯π stacking). The flexibility and conformation of the ligand have a significant impact on the overall structure and stability of complexes. It opens the door to developing functional materials by unraveling the unique attributes and role of HBpe+ in supramolecular assembly. With these insights, it is possible to explore the functional properties of HBpe+ through controlled assembly processes in order to create innovative and functional materials.