Mystery of clathrate material's crystal structure unraveled, 80 years after its initial discovery
In a significant breakthrough, researchers at Yokohama National University in Japan have determined the crystal structure of tetrabutylammonium bromide (TBAB) hydrate, a widely used semiclathrate hydrate, 80 years after its discovery.
The stable form of TBAB hydrate, with the composition TBAB·26H2O, has a tetragonal crystal system and the space group P4̅21c. This structure is a Jeffrey's type III semiclathrate hydrate, where the tetrabutylammonium cations are incorporated within dodecahedral water clusters.
The team, led by Sanehiro Muromachi, used synchrotron radiation single-crystal X-ray diffraction to solve this long-standing mystery. This technique enabled them to resolve the molecular arrangement in TBAB·26H2O, revealing unique features of its water cage framework and precise lattice parameters.
This breakthrough provides crucial insights into the molecular structure of TBAB hydrate, supporting its application in thermal energy storage and other industrial processes. The principles elucidated in this study, particularly the ability of the TBA cation to adapt to primitive water clusters, extend beyond clathrate hydrates and have potential implications for the design of various water-based functional materials.
The new work, published in the journal Nature Communications, provides insights applicable to the scalable design of related water-based functional materials, such as clathrates of group 14 elements, surfactants, and functional polymers.
Physical chemist David Wu at Academia Sinica in Taipei, Taiwan, who was not involved in the new work, acknowledges the importance of the structure determination and expresses interest in whether these structural motifs show up in other semiclathrate materials.
In the stable form of TBAB hydrate, a single bromide ion takes the place of two water molecules, a feature similar to that seen in tetrabutylammonium nitrate. Clathrate hydrates and semiclathrate hydrates can potentially be used in various industrial applications, including gas storage, water purification, heat storage, and advanced air conditioning technology.
The team grew perfect crystals of TBAB hydrate in the stable phase and analyzed them at Japan's Spring-8 synchrotron beamline. This semiclathrate hydrate is the best known and most widely used.
The new research opens up exciting possibilities for the optimisation of applications of TBAB hydrate and potentially allows for more rational design of new materials in the future.
- The new findings on the crystal structure of TBAB hydrate could pave the way for the development of novel functional polymers that make use of the unique features of its water cage framework.
- The study's insights on the TBA cation's ability to adapt to primitive water clusters have implications for the design of medical-condition-treating materials using science and technology, extending beyond clathrate hydrates.
