Metal organic nanotubes offer higher synthetic tunability and 1-D nanoconfinement of solvent molecules that can be utilized for advanced membrane technologies. Nanoconfinement of solvent, like water molecules, leads to unusual phase behavior and diffusion rates, that have yet to be fully understood.  In the current study, we utilize a metal organic nanotube (UMONT) with pore diameter of 1.2 nm that has previously been noted to contain a hexagonal ice (I<sub>h</sub>) like water molecular arrangement along the channel. Crystallographic data which is collected at 100 K has shown anomalous residual electron density between the hexagonal water arrays that can be linked to an additional partially occupied water site and suggests the presence of stacked disordered ice in this system. We further evaluated changes in the residual electron density changes with varying temperatures and equilibration times. Our data suggest that the phase transition of hexagonally arranged water structure occurs in the temperature range of 200 K - 250 K at different equilibration times, which may suggest a glassy transition state.

Effects of temperature on water ordering within metal-organic nanotubes

ACS Spring 2022

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