Y(HPO4)(NO3)(H2O)·2H2O: A Solvent-Responsive Inorganic Layered Material with Reversible Phase Transitions and Optically Active Proton Conductivity

A two-dimensional (2D) inorganic phosphate compound, Y(HPO 4 )(NO 3 )(H 2 O)·2H 2 O (YH2H), was synthesized via a slow evaporation method and structurally characterized by single-crystal X-ray diffraction. YH2H crystallizes in the orthorhombic space group, Pbcm and features a layered structure composed of edge-sharing YO 8 polyhedra. The interlayer space is stabilized by two types of lattice water molecules, which form an extended hydrogen-bonding network critical to both structural integrity and functionality. Upon heating, YH2H undergoes a reversible two-step dehydration process, forming a contracted dehydrated phase (YH). Real-time in situ powder X-ray diffraction captured these sequential phase transitions. Notably, YH spontaneously rehydrates under ambient conditions, fully restoring the original framework. Methanol intercalation into the YH phase leads to the formation of an expand…