Coordination Chemistry Laboratory, Department of Chemistry, Graduate School of Science, The University of Osaka
Development of Superionic Conduction Framework based on Hydrated Potassium Ions
The reaction of a cysteinato metalloligand, ([Rh(L-cys)3]3-) with ZnII, a spherical anionic multinuclear complex, [Rh4Zn4(L-cys)12O]6-, is obtained. This multinuclear complex is isolated as crystals and were found to have a supramolecular framework with interstices filled with hydrated potassium cations.
The ionic conductivity of the crystals at room temperature was measured and found to exhibit an exceptionally high value of 1.3×10-2 S/cm, comparable to that of a 0.01 M KCl(aq). Further investigation by varying the alkaline metal cation revealed that the ionic conductivity increases in the order of Li+ < Na+ < K+, in contrast to the trend typically observed in conventional ionic conductors. Through judicious experimensts, it was found that K+ migrate in the form of hydrated K+ species, in which the ions are coordinated by water molecules, resulting in a larger effective ionic species. This material represents the first superionic conductor in which hydrated K+ act as the charge carriers.
Press release on our first in the world Hydrated Potassium ion based Superionic Conducting Framework
Further investigation involving the replacement of rhodium ion with other earth-abundant metal ions had been carried out and we have confirmed that it exhibits ionic conductivity comparable to that of the aforementioned compound.
This work is supported by the funding from JKA Foundation, Auto Race (2024)
Besides L-cysteine, we are also exploring other cluster compound with potential superionic conductivity with D-penicillamine ligands.
This work is supported by the funding from JKA Foundation, Keirin (2025)
In addition to superionic conductivity, we have found that the [Rh4Zn4(L-cys)12O]6- supramolecular crystals undergo facile cation exchange through a single-crystal to single-crystal manner. Simply soaking the crystals in lanthanide containing solution enables the facile formation of cubane type lanthanide hydroxo cluster within the interstices of the supramolecular framework.
The incorporation and assembly of other types of metal clusters within the interstices of this supramolecular framework are currently under investigation.
For more information on our lanthanide cubane clusters formation, please refer to our press release The easy way to get a square deal