Proton conduction in a hydrogen-bonded complex of copper(ii)-bipyridine glycoluril nitrate

Abstract

Bipyridine glycoluril (BPG), a urea-fused bipyridine tecton, forms a square-pyramidal secondary building unit with copper(ii) which further self-assembles to give a porous hydrogen-bonded complex. This complex displays a high proton conductivity of 4.45 × 10 S cm at 90 °C and 95% relative humidity (RH). Chains consisting of coordinated water, solvent water and nitrate anions embedded in the complex are responsible for high proton conduction. The proton conduction pathway was corroborated by ab initio electronic structure calculations with molecular dynamics (MD) simulations using the Nudged Elastic Band (NEB) method. The theoretical activation energy estimated to be 0.18 eV is in close agreement with the experimental value of 0.15 eV which evidences a Grotthuss proton hopping mechanism. We thus demonstrate that the hydrogen-bonded complex encapsulating appropriate counter ions, coordinated water and solvent water molecules exhibts superprotonic conductivity.

A robust zirconium amino acid metal-organic framework for proton conduction

“…This value is among the highest conductivities reported for other water-mediated proton-conducting MOFs, including UiO - 66-(SO 3 H) 2 34 , (Hpy) 2 [Zn 2 (ox) 3 ].nH 2 O 51 , VNU-15 52 , JLU-Liu44 53 , Fe-CAT-5 5 , PCMOF2 1 / 2 8 , and PCMOF20 31 , and converges towards the performances of the benchmark Nafion based polymer 54 . Furthermore, MIP-202(Zr) is the best proton conductor among the MOFs showing a cationic framework, such as the Zn-(4-carboxyphenyl)imidazolium-based solid with a σ = 2.3 × 10 −3 S cm −1 at 298 K/95% RH 55 , and the Cu-bipyridine glycoluril (BPG) based MOF with a σ = 4.4 × 10 −3 S cm −1 at 363 K/95% RH 56 . In addition, the conductive performances of MIP-202(Zr) are well maintained over one week of experiments performed at 363 K and 95% RH (Supplementary Figure 14 ).…”

Proton-Conducting Hydrogen-Bonded Organic Frameworks

“…In the same year, Kim et al reported the proton conductivity of a porous SOF of cucurbit[6]­uril (CB[6]) crystallized in acidic medium . Since 2016, the proton conductivity of HOFs has been extensively investigated, − and many reports have been published within a short period realizing the different strategies of designing building blocks and the synthesis processes to achieve superprotonic conductivity on HOFs (Table and Table S1 in the Supporting Information).…”

Lewis Acid Guests in a {P8W48} Archetypal Polyoxotungstate Host: Enhanced Proton Conductivity via Metal‐Oxo Cluster within Cluster Assemblies

“…[17c,23] Therefore,t he incorporated nitrate functions in KNaLi-1 may behave like SO 3 Hg roups in Nafion and so as proton accepters,w hich could further connect with the free and coordinated water molecules as well as the hydroxy groups by hydrogen bonds,p aving an extremely hydrophilic channel as aproton-transport route (Figure 4b). [24] In conclusion, af acile solution reaction of Al III / Ga III ions as guests with the super-lacunary…”

“…Beyond that, it has been well established that the existence of Brønsted acids (e.g., H 2 SO 4 and H 3 PO 4 ) could easily deliver protons along the conduction pathways on account of their strong acidity and low volatility . Therefore, the incorporated nitrate functions in KNaLi‐1 may behave like SO 3 H groups in Nafion and so as proton accepters, which could further connect with the free and coordinated water molecules as well as the hydroxy groups by hydrogen bonds, paving an extremely hydrophilic channel as a proton‐transport route (Figure b) …”