High proton conductivity in metalloring-cluster based metal-organic nanotubes

Two novel anionic single-walled metal-organic nanotubes (MONTs), [(CH₃)₂NH₂][In(cdc)(thb)]·2DMF·9.5H₂O (FJU-105) and [(CH₃)₂NH₂][In(cdc)(H-btc)]·2DMA·11H₂O (FJU-106) (H₂cdc = 9H-carbazole-3,6-dicarboxylic acid, H₂thb = 2,5-thiophene dicarboxylic acid, H₃btc = 1,3,5-benzene tricarboxylic acid), are achieved by employing [In₆(cdc)₆]⁶⁺ metalloring cluster with largest diameter as the secondary building blocks (SBUs). The inner surface of FJU-106 is functionalized by uncoordinated -COOH groups of the H-btc linkers, leading to a higher proton conduction than FJU-105. At 70 °C, FJU-106 displays the proton conduction performances among MONTs, up to 1.80 × 10^-2 S·cm^-1. And FJU-105 and FJU-106 are the first examples of MONT proton conductors operating at subzero temperature.