Evaluation of Brønsted acidity and proton topology in Zr- and Hf-based metal–organic frameworks using potentiometric acid–base titration

Abstract

Potentiometric acid–base titration is introduced as a method to evaluate pKa values (Brønsted acidity) of protons present in the nodes of water stable Zr6- and Hf6-based metal–organic frameworks (MOFs), including UiO-type MOFs, NU-1000, and MOF-808.

When defects turn into virtues: The curious case of zirconium-based metal-organic frameworks

“…Table 2 summarizes all the different scenarios proposed so far on the basis of experimental observations. prepared with the same procedure can in fact be distinguished and quantified by acid-base titration [120]. Other works from the same group assumed the same type of model, justified by experimental observations [115,121].…”

“…In virtue of their superior robustness, Zr-MOFs are ideal MOF platforms for introduction of Brønsted acidic sites. Defect-free Zr-MOFs have a weak Brønsted acid character due to the presence of µ 3 -OH groups in the clusters, but additional sites can be introduced by creation of defects.Acid-base titration experiments were carried out on perfect samples of UiO-67, observing a single equivalent point at pH = 7.1 and calculating a pK a of 3.44[120]. The titration curve of a defective sample of UiO-66 reveals three apparent inflection points at pH 5.44, 7.56 and 9.51, corresponding to pK a values of 3.52, 6.79 and 8.30, respectively(Figure 18).…”

Photoresponsive spiropyran-functionalised MOF-808: postsynthetic incorporation and light dependent gas adsorption properties

“…5 The zirconium-based MOF-808 25,26 (Fig. 31,32 Herein we also report the novel synthesis of a spiropyran through multi-step PSM inside MOF-808, and explore the guest sorption properties of the resulting photoactive framework. 14Å for SP length and ca.…”

Hybridization of Pd Nanoparticles with UiO‐66(Hf) Metal‐Organic Framework and the Effect of Nanostructure on the Catalytic Properties

“…[16] The m 3 -OH groupsp resent on Hf 6 -secondaryb uildingu nits(SBUs) (Scheme 1) exhibits Brønsted acidity. [17] The synergetic catalytic properties arousedo ut of hybridization of Pd with UiO-66(Hf) were established for dehydrogenation of ammonia borane(AB) (widely investigated as solid hydrogen storage material) and also for transfer semi-hydrogenation of phenylacetylene(PA). It is intriguing to note that both these reactions are yet to be explored using Pd-MOF hybrid catalysts.…”