A highly symmetric cage-like crystal packing architecture, resulting from the interaction among metallocavitands of in-situ generated supramolecular modules

Coordination-driven metallosupramolecular platforms comprising various organic ligands and multinuclear metal clusters have attracted lately significant attention. Several methods are available for producing such supramolecular or polymeric platforms. For instance, simple coordination modes that constitute assemblies of metal ions coordinated by ligands or multinuclear metal clusters have been used to achieve symmetry, complexity and structural diversity of the supramolecular and polymeric platforms. On the other hand, advanced assembly modes have been used to produce discrete molecular platforms with structural hierarchy. However, researchers have been looking for methods for preparing solid state materials and have identified rational design of molecular interaction and supramolecular modules as promising solutions.

Organic cavitand such as calixarenes and cucurbiturils have been used to synthesis organic compounds through host-guest interactions. Therefore, the cavities are capable of enclosing other ions and molecules. However, the formation of cavities and material properties are highly influenced by the transition metals of the metallocavitands. Consequently, the host-guest interaction can result in the generation of higher-level solid state metallosupramolecular assemblies due to the presence of cavities and functional groups that acts as the host and guests respectively. This permits observation of the induced chemical and physical properties of the higher-ordered structure, thus an alternative synthetic method for synthesizing solid-state materials.

Hallym University Researchers Dr. Philjae Kang, Dr. Hien Duy Mai and led by Professor Hyojong Yoo at the Department of Chemistry synthesized new cobalt supramolecular triple-stranded helicate. They obtained metallosupramolecular crystal packing platform with structural hierarchy. Their work is currently published in the research journal, Dalton Transactions.

Briefly, the research team commenced the experimental work by interlinking ditopic ligands and two clustered cobalt assembly units thus forming a cobalt supramolecular triple-stranded helicate. Furthermore, a cage-like assembled crystal structure was generated by surrounding the bromo group by tetranuclear cobalt cluster metallocavitand. Eventually, they separately isolated two molecular cages with the same crystal-packing geometry thus paving way for the investigation of the synthetic strategies and solid-state structures of the resultant assemblies.

The authors observed that the solid structure of the cobalt supramolecular triple-stranded helicate showed coordination of four cobalt atoms by three PDA ligands thus forming tetranuclear cobalt cluster. The clusters comprised of three extension points and ditopic ligand interlinking two assembly units. Furthermore, they also observed two different molecular cages that exhibited the same crystal package geometry after successful isolation from separate reactions.

According to the authors, the crystal packing of cobalt supramolecular triple-stranded helicate in the solid state was attributed to the interactions between the cavity-like cobalt clusters as well as the bromo group that was surrounded by the tetranuclear cobalt cluster that generated cage-like crystal packing geometry by acting as metallocavitands. Professor Hyojong Yoo and his research team successfully demonstrated an unusual method for obtaining highly symmetrical cage-like structures through the interaction amongst the metallocavitands and the supramolecular modules generated.