Guanidinium Intercalation into Layered Zirconium Phosphates and Phosphonates: Synthesis, Structure, and Ionic Conductivity

Guanidinium-intercalated derivatives of α- and γ-zirconium hydrogen phosphate, zirconium 2-sulfoethylphosphonate, and zirconium 4-sulfophenylphosphonate were successfully synthesized by treatment of the host materials with aqueous guanidine carbonate solutions at room temperature. In contrast, hydrothermal treatment at 180 °C proved unsuitable for the preparation, as guanidine underwent decomposition, leading predominantly to the formation of ammonium-intercalated phases and, in some cases, partial degradation of the host structure. The synthesized materials were characterized by powder X-ray diffraction, elemental analysis, thermogravimetric analysis, and infrared spectroscopy. The combined results confirmed the incorporation of guanidinium ions into the interlayer space together with variable amounts of co-intercalated water. Spectroscopic data further indicated the formation of extensive hydrogen-bonding networks involving guanidinium ions, water molecules, and acidic groups of the host frameworks. Proton conductivity measurements revealed a pronounced dependence on relative humidity, with conductivity increasing as the water content of the materials increased. Nevertheless, the conductivities of all guanidinium intercalates remained lower than those of the corresponding parent zirconium phosphates and phosphonates. Temperature-dependent conductivity measurements suggested that proton transport proceeds predominantly via a vehicle mechanism in both hydrated and dehydrated states. The prepared intercalates exhibited reversible dehydration and rehydration behavior and retained their structural integrity during conductivity measurements.