A Comparative Study of Proton Conduction Between a 2D Zinc(II) MOF and Its Corresponding Organic Ligand

Abstract

Until now, comparative studies on proton conductivity between organic ligands and related metal−organic frameworks (MOFs) have been very limited. Herein, a stable 2D Zn(II) MOF, [Zn(L)Cl] n (1), has been successfully synthesized by using a zwitterionic-type organic ligand, 2-(1-(carboxymethyl)-1H-benzo[d]imidazol-3-ium-3-yl)acetate (HL). It is found that there are a large amount of free carboxyl groups and hydrogen bonds in the solid-state structure of HL, and a large number of chlorine ions are aligned in the channels of 1, which is favorable to the efficient proton transfer. Correspondingly, the proton conductivity values of 1 and HL are almost of the same order of magnitude under the same conditions. Moreover, the optimal σ value of 1 (4.72 × 10 −3 S/cm at 100 °C and 98% relative humidity) is almost four times higher than that (1.36 × 10 −3 S/cm) of the HL ligand. On the basis of the crystal data, SEM images, and calculated E a values, we discuss the differences on proton conductivities and conduction mechanisms of 1 and HL. This report provides an inspiration for the preparation of highly conductive materials with free carboxyl groups and chloride ions.

A confinement of N-heterocyclic molecules in a metal–organic framework for enhancing significant proton conductivity

“…[27][28][29][30] The fact revealed that the high-level proton movement relating to the enormous number of protons signicantly enhanced the proton conductivity in MOFs. This is addressed through modifying the void space of the frameworks and organic linkers by functional groups (e.g., -COOH, -OH, and -SO 3 H) [29][30][31][32][33] or introducing guest molecules such as ammonia, 34,35 water, 36 and N-heterocyclic molecules (e.g., triazole, 37 histamine, 30,38 and imidazole 29,39,40 ). The imidazole derivatives are chosen as the efficient proton carrier agents due to their high polarity, which can favourably uptake water molecules from the external medium, leading to the optimal proton conduction pathway formation.…”

Proton conductive Zr-based MOFs

“…Recently, the research of an important family of crystalline solid materials, such as metal-organic frameworks (MOFs), [8][9][10][11][12][13][14][15][16][17][18][19][20] covalent organic frameworks (COFs), [21][22][23][24] and hydrogenbonded organic frameworks (HOFs) [25][26][27][28][29][30] acting as promising conductors has attracted great attention. In addition to the structural modifying ability and functional modulability of such crystalline materials, which are well known to us, they also have high crystallinity, which provides a good material basis for the in-depth study of the proton conduction mechanism.…”

Multifunctional Viologen-Derived Supramolecular Network with Photo/Vapochromic and Proton Conduction Properties

“…In contrast to the large number of chromic MOFs, supramolecular networks containing bipyridinium carboxylate unit are still rare [ 16 , 17 ], and the further research to understand the chromic mechanism and enhance the chromic properties of supramolecular networks is highly desirable [ 18 ]. On the other hand, supramolecular networks possessing hydrophilic groups (such as -COOH, -SO 3 H and -PO 3 H 2 ) and well-defined hydrogen bond paths may be eligible proton conductors for hydrogen fuel-cell applications [ 19 , 20 ]. Nevertheless, the related reports on the crystalline supramolecular networks are inadequate [ 21 ].…”