Observation of an exotic state of water in the hydrophilic nanospace of porous coordination polymers

Fundamental understanding of the confinement of water in porous coordination polymers (PCPs) is important not only with respect to their application, such as gas storage and separation, but also for exploring confinement effects in nanoscale spaces. Here, we report the observation of water in an exotic state in the well-designed hydrophilic nanopores of PCPs. Single-crystal X-ray diffraction finds that nanoconfined water has an ordered structure that is characteristic in ices, but infrared spectroscopy reveals a significant number of broken hydrogen bonds that is characteristic in liquids. We find that their structural properties are quite similar to those of solid-liquid supercritical water predicted in hydrophobic nanospace at extremely high pressure. Our results will open up not only new potential applications of water in an exotic state in PCPs to control chemical reactions, but also experimental systems to clarify the existence of solid-liquid critical points.

Tomoaki Ichii, Takashi Arikawa, Kenichiro Omoto, Nobuhiko Hosono, Hiroshi Sato, Susumu Kitagawa, Koichiro Tanaka