High proton conductivity behavior in a 2D metal sulfite constructed from a histidine ligand.

In the presence of the amino acid histidine, an inorganic-organic hybrid metal sulfite, Zn 2 (SO 3 ) 2 (C 6 N 3 O 2 H 9 ) 2 ·H 2 O (1), has been prepared under hydrothermal conditions. Single-crystal X-ray diffraction analysis reveals that 1 shows a 2D layer framework built up from a classical second building unit (S4R), and bridged histidine molecule. Notably, it is the first report of a metal sulfite in the presence of an amino acid molecule. A 1D H-bonding array can be constructed by the H-bonding interaction between histidine molecules and sulfite groups. Moreover, a new function of metal sulfite for proton conduction was investigated by alternating-current impedance analysis. The results demonstrate that compound 1 shows a high proton conductivity of approximately 10 -3 S cm -1 at 348 K and 98% relative humidity.