A thermal-stable praseodymium(III) metal-organic framework from a naphthyl acylthiourea-carboxylate ligand: Synthesis, crystal structure and proton conductive properties

Abstract

Compared with other traditional proton-conducting materials, the structures of metal-organic frameworks (MOFs) are more advantageous in terms of designability and tunability. Considering the strong and flexible coordination ability of carboxylate-based thiourea ligands, we synthesized a [3-(naphthalene-2-carbonyl)-thioureido]-acetic acid (H3L) ligand, and successfully obtained {[Pr(H2L)2(NO3)(H2O)2]·2H2O·MeOH}n (1). 1 is a 1D framework, in which the Pr(III) atoms are bridged by carboxyl oxygen, and then form a three-dimensional solid-state structure under the action of intermolecular hydrogen bonds and π-π stacking interactions. AC impedance measurements uncover that proton conductivity (σ) of 1 has a significant positive temperature and humidity dependence. The σ of MOF 1 can attain 3.41 ​× ​10−4 ​S/cm under 100 ​°C and 98% RH. In addition, the proton-conductive mechanism was discussed based on the structural analysis, H2O vapor adsorption curve and the activation energies evaluated by fitting the Arrhenius equation.