Solvent Guest-Induced Guanidine Organophosphonate Inclusion Complex for <i>Para</i> -Xylene Encapsulation and Proton Conduction

The inductive effect of the solvent is not only a key means of regulating the material structures but also an important way to enhance the material properties. This is especially true for the crystalline porous materials formed by weak interactions such as hydrogen bonding, π conjugation, and van der Waals forces. Herein, two guanidine organophosphonate compounds were successfully obtained using 4,4′-biphenyl diphosphate acid (H4L) and guanidine hydrochloride (G) through hydrogen-bonded interactions, with formulae [(H4L)G]·0.5p-xyl (GP-1) and (H4L)G (GP-2). Interestingly, the structures of the two materials exhibited completely different structural characteristics. Among them, GP-1 is a three-dimensional pillared-layer structure formed by the stacking mode of two-dimensional layers connected through hexagonal cages. On the other hand, GP-2 is a densely packed structure formed by guanidine cations connecting the upper and lower phosphonic acid layers. Meanwhile, due to the structure with a cage that well matched the shape of p-xyl, GP-1 exhibited the ability of para-xylene (p-xyl) encapsulation. The abundant continuous hydrogen-bond chains in the two structures provided the precondition to achieve proton conduction. At 80 °C and 98% relative humidity, their proton conductivity values were 5.27 × 10–6 and 2.75 × 10–6 S cm–1, respectively. The rigid connection between the phosphonic acid group and the skeleton, as well as the insufficient proton source in the structure, resulted in the poor proton conductivity of both materials.