Two stable phenyl acyl thiourea carboxylate-based MOFs: Syntheses, crystal structures and proton conductive properties

The phenyl-substituted acylthiourea-carboxylic acid ligand has several coordination sites and strong coordination ability. The MOFs constructed by these ligands are flexible and stable, which is very beneficial to the study of proton conductivity. In this paper, we designed and synthesized two MOFs, [Mn(H2BBT)2(H2O)2]n (H3BBT = N-benzoyl-N′-(4-benzoxy)thiourea) (1), and [Cd(H2BBT)2]n (2) by the solvent evaporation method. Their molecular structures were characterized by single-crystal X-ray diffraction. The high water and chemical stability of the two MOFs were confirmed by X-ray powder diffraction. The AC impedance spectra of them show that the proton conductivity increases with the increase in temperature and humidity. The best proton conductivities of 1 and 2 are 1.69 ​× ​10-5 and 1.79 ​× ​10-4 ​S ​cm-1 under 98% RH and 100 ​°C, respectively. The proton conduction mechanisms of the two MOFs were highlighted based on the calculated activation energy, structural characteristics, N2 and H2O vapor adsorption determinations, and so on.