Synthesis and characterization of two layered aluminophosphates [R-C8H12N]8[H2O]2·[Al8P12O48H4] and [S-C8H12N]8[H2O]2·[Al8P12O48H4] with a mirror symmetric feature and their proton conductivity

Abstract

The template effect of chiral organic molecules to aluminophosphate open frameworks was investigated by the syntheses of two layered structures, [R-C₈H₁₂N]₈[H₂O]₂·[Al₈P₁₂O₄₈H₄] and [S-C₈H₁₂N]₈[H₂O]₂·[Al₈P₁₂O₄₈H₄] (denoted as AlPO-CJ72-R and -S), with a mirror symmetric feature. The two structures are obtained separately, which is the first instance in inorganic open-framework materials to our knowledge, by α-methylbenzylamine with homochirality. Single-crystal X-ray diffraction analysis reveals that the structure of either AlPO-CJ72-R or AlPO-CJ72-S crystallizes in the chiral triclinic space group P1, and the existence of AAAA-stacked Al₂P₃O₁₂³⁻ layers made up of alternating AlO₄ and PO₃(O) or PO₂(O)(OH) tetrahedra to form a 4 × 6 network. Their structures show self-assembled chiral H-bond chains, the chiralities of which are transferred to adjacent helical T–O (T = Al and P) chains. The frameworks are mirror symmetric to each other. The performance of AlPO-CJ72 regarding proton conductivity was tested. It shows an excellent result up to 3.01 × 10⁻³ S cm⁻¹ (363 K, 98% RH), which might be attributed to the H-bond chains in the structure.