[May 14, 2015]

Alkaline-Earth Metals Used to Build 3D Supramolecular Boxes: NCKU Study

For a long time, it has been known that construction of 2D and 3D supramolecular boxes can only be achieved through the use of directional covalent bonds formed between organic ligands and transition-metal atoms under crystal-field stabilization influence. Hence, alkaline-earth metal cations are totally neglected as the structure-building blocks for the boxes due to the lack of directional bonding.

Many years of hard work on the part of Professor Kom-Bei Shiu from the Department of Chemistry at National Cheng Kung University (NCKU), Tainan, Taiwan, and his research team has since proven the first exception to this traditional belief.

Shiu's research team revealed that non-directional alkaline-earth metal cations can also participate in the self-assembly of 3D supramolecular boxes.

This major breakthrough is expected to relax the previous false restriction and to initiate new research investigations so that supramolecular boxes can be built via both transition- and alkaline-earth metal atoms, facilitating new chemical reactions uncovered and new molecular devices fabricated in the nano-sized supramolecular boxes.

The research for this phenomenal discovery was published in Chemistry-A European Journal on May 4^th, and has been chosen as a "hot paper."

According to Shiu, in a molecular world, molecules can recognize each other by respective shapes and can feel the attractive force between them in solution. When suitable molecules are put together by man in solution, regular structures including boxes can be formed in a process called as self-assembly. Using the concept of Lego, molecules can select suitable candidates themselves to form a regular-shaped structure. Nonetheless, the difficult part of the research is to gather suitable molecules under an appropriate reaction condition.

Shiu's study showed that a common Arrhenius acid-base neutralization allows the alkaline-earth metal cations to act as charged binders, easily connecting two or more metalloligands into coordination polymers. With addition of a salt during the neutralization, the salt forms an ionic aggregate first and then the aggregate acts like a template, cyclizing the polymer into 3D boxes.

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