Straightforward Loading of Imidazole Molecules into Metal–Organic Framework for High Proton Conduction

Abstract

A one-step straightforward strategy has been developed to incorporate free imidazole molecules into a highly stable metal-organic framework (NENU-3, ([Cu(BTC)(HO)][HPWO])·Guest). The resulting material Im@(NENU-3) exhibits a very high proton conductivity of 1.82 × 10 S cm at 90% RH and 70 °C, which is significantly higher than 3.16 × 10 S cm for Im-Cu@(NENU-3a) synthesized through a two-step approach with mainly terminal bound imidazole molecules inside pores. Single crystal structure reveals that imidazole molecules in Im-Cu@(NENU-3a) isolate lattice water molecules and then block proton transport pathway, whereas high concentration of free imidazole molecules within Im@(NENU-3) significantly facilitate successive proton-hopping pathways through formation of hydrogen bonded networks.

A Highly Stable Two‐Dimensional Copper(II) Organic Framework for Proton Conduction and Ammonia Impedance Sensing

“…However,s ome peaks from 9.5 to 258 slightly shift towardlower anglesc ompared with the simulated ones, which showsa ne xpansion of the lattice after absorption of water molecules. Thus, it leads to the optimized protonconductivity for 1 of 1.50 10 À3 Scm À1 .A sl isted in Ta ble 2, althought he optimized conductivity value is smaller than that of severalr ecent MOFs, [38][39][40][41] this value can be compared to that of some previousM OFs under similar tested conditions, [41][42][43][44][45][46] and is remarkably highert han that of four imidazole dicarboxylate-based Co II MOFs and other MOFs. [27,28,47] It is illustrated again that the structural advantage of MOF 1 is the a large amount of uncoordinated carboxylate units between the layers forprotontransfer.…”

Metal–Organic Frameworks and Other Crystalline Materials for Ultrahigh Superprotonic Conductivities of 10−2 S cm−1 or Higher

“…By applying this strategy, Zhang and Chen et al. showed a simple and straightforward approach to install a high density of free imidazoles into the pores of an ultra‐stable MOF (NENU‐3, [[Cu 12 (BTC) 8 (H 2 O) 12 ] [HPW 12 O 40 ]) ⋅ host) . Imidazole molecules in activated NENU‐3, Im‐Cu(NENU‐3a) (synthesized in a two‐step process), isolate coordinated water molecules from the framework and thus block the proton‐transport pathways, as demonstrated by single‐crystal diffraction measurement studies.…”

“…[ O 40 ])·host). [17] Imidazole molecules in activatedN ENU-3, Im-Cu(NENU-3a) (synthesized in at wo-step process), isolate coordinated water molecules from the framework and thus block the proton-transport pathways, as demonstrated by single-crystal diffraction measurement studies. On the other hand, the high density of free imidazole molecules within Im@(NENU-3) (synthesized in as imple one-step process) significantly facilitatess ubsequent proton-jump pathways throught he formation of hydrogen bonds.…”

“…It is interesting to notet hat higherc onductivity was achieved when imidazoles were simply loadedi nto the cavity (not in coordination)for Im@(NENU-3). [17] However,when imidazoles were coordinated with metal centers for Im-Fe-MOF, [18] ac onductivity superior to simply cavity-loaded Im@Fe-MOF was observed. This observation might be attributed to the significantly different frameworksw ithv arying pore sizes and interconnections within the frameworks, as speculated by the authors.…”

“…This observation might be attributed to the significantly different frameworksw ithv arying pore sizes and interconnections within the frameworks, as speculated by the authors. [17,18] The isostructural UiO-66 family has been considerably exploredf or protonc onductivity to establish an approach for enhancing conductivity through systematic design and tailoring of the hostf ramework. Hong et al synthesized ad ithiol derivative, UiO-66(SH) 2 ,w ith free thiol groups to chemically anchor ÀSO 3 Hg roups throughp ostsynthetic oxidationt og enerate of UiO-66(SO 3 H) 2 .…”