Proton Conductivity Control by Ion Substitution in a Highly Proton-Conductive Metal–Organic Framework

Proton conductivity through two-dimensional
(2-D) hydrogen-bonding
networks within a layered metal–organic framework (MOF) (NH4)2(H2adp)­[Zn2(ox)3]·3H2O (H2adp = adipic acid; ox = oxalate)
has been successfully controlled by cation substitution. We synthesized
a cation-substituted MOF, K2(H2adp)­[Zn2(ox)3]·3H2O, where the ammonium ions in
a well-defined hydrogen-bonding network are substituted with non-hydrogen-bonding
potassium ions, without any apparent change in the crystal structure.
We successfully controlled the proton conductivity by cleavage of
the hydrogen bonds in a proton-conducting pathway, showing that the
2-D hydrogen-bonding networks in the MOF truly contribute to the high
proton conductivity. This is the first example of the control of proton
conductivity by ion substitution in a well-defined hydrogen-bonding
network within a MOF.