ABSTRACT
The proton-conducting performances of a microporous Ti-based metal-organic framework (MOF), MIP-207, were successfully tuned using a multicomponent ligand replacement strategy to gradually introduce a controlled amount of sulfonic acid groups as a source of Brönsted acidic sites while keeping the robustness and ecofriendly synthesis conditions of the starting material. Typically, multivariate sulfonic-based solids MIP-207-(SO3H-IPA)x-(BTC)1-x were prepared by combining various ratios of trimesate 1,3,5-benzenetricarboxylate (BTC) moieties and 5-SO3H-isophthalate (SO3H-IPA). The best sulfonic-MOF candidate that combines structural integrity with high proton conductivity values (e.g., σ = 2.6 × 10-2 S cm-1 at 363 K/95% relative humidity) was further investigated using ab initio molecular dynamics simulations. These calculations supported that the -SO3H groups act as proton donors and revealed that the proton transfer mechanism results from the solvation structure of protons through the fast Zundel/hydronium interconversion along the continuous H-bonded network connecting the adsorbed water molecules.
ABSTRACT
Crystalline B-N-H compounds of low molecular weight have been intensively investigated over the past two decades owing to their promises for chemical hydrogen storage. Hydrazine borane NH2-NH2-BH3 is one of the most recent examples of this family of materials. In the present work, we explored its structural behaviour under mechanical stimulus by synchrotron high pressure X-ray diffraction. It has been evidenced that hydrazine borane shows a gradual pressure-induced decrease of its unit cell dimension and the process is reversible when the applied pressure is released. The compressibility of this material was established to be relatively low (high bulk modulus) and highly anisotropic. As revealed by molecular simulations based on Density Functional Theory calculations, the mechanical behaviour of NH2-NH2-BH3 was correlated to the pressure-induced changes of its crystal structure in terms of intra- and intermolecular bond lengths and angles parameters.
