Structuralization of Ca²⁺-Based Metal–Organic Frameworks Prepared via Coordination Replication of Calcium Carbonate

The emergence of metal–organic frameworks (MOFs) as potential candidates to supplant existing adsorbent types in real-world applications has led to an explosive growth in the number of compounds available to researchers, as well as in the diversity of the metal salts and organic linkers from which they are derived. In this context, the use of carbonate-based precursors as metal sources is of interest due to their abundance in mineral deposits and their reaction chemistry with acids, resulting in just water and carbon dioxide as side products. Here, we have explored the use of calcium carbonate as a metal source and demonstrate its versatility as a precursor to several known frameworks, as well as a new flexible compound based on the 2,5-dihydroxybenzoquinone (H₂dhbq) linker, Ca­(dhbq)­(H₂O)₂. Furthermore, inspired by the ubiquity and unique structures of biomineralized forms of calcium carbonate, we also present examples of the preparation of superstructures of Ca-based MOFs via the coordination replication technique. In all, the results confirm the suitability of carbonate-based metal sources for the preparation of MOFs and further expand upon the growing scope of coordination replication as a convenient strategy for the preparation of structuralized materials

Synthesis and Hydrogen Storage Properties of Be₁₂(OH)₁₂(1,3,5-benzenetribenzoate)₄

Synthesis and Hydrogen Storage Properties of Be12(OH)12(1,3,5-benzenetribenzoate)4</sub

Synthesis and Hydrogen Storage Properties of Be₁₂(OH)₁₂(1,3,5-benzenetribenzoate)₄

Synthesis and Hydrogen Storage Properties of Be12(OH)12(1,3,5-benzenetribenzoate)4</sub

Impact of Molecular Clustering inside Nanopores on Desorption Processes

Understanding the sorption kinetics of nanoporous systems is crucial for the development and design of novel porous materials for practical applications. Here, using a porous coordination polymer/quartz crystal microbalance (PCP/QCM) hybrid device, we investigate the desorption of various vapor molecules featuring different degrees of intermolecular (hydrogen bonding) or molecule-framework interactions. Our findings reveal that strong intermolecular interactions lead to the desorption process proceeding via an unprecedented metastable state, wherein the guest molecules are clustered within the pores, causing the desorption rate to be temporarily slowed. The results demonstrate the considerable impact of the chemical nature of an adsorbate on the kinetics of desorption, which is also expected to influence the efficiency of certain processes, such as desorption by gas purge

Application of a High-Throughput Analyzer in Evaluating Solid Adsorbents for Post-Combustion Carbon Capture via Multicomponent Adsorption of CO₂, N₂, and H₂O

Despite the large number of metal–organic frameworks that have been studied in the context of post-combustion carbon capture, adsorption equilibria of gas mixtures including CO₂, N₂, and H₂O, which are the three biggest components of the flue gas emanating from a coal- or natural gas-fired power plant, have never been reported. Here, we disclose the design and validation of a high-throughput multicomponent adsorption instrument that can measure equilibrium adsorption isotherms for mixtures of gases at conditions that are representative of an actual flue gas from a power plant. This instrument is used to study 15 different metal–organic frameworks, zeolites, mesoporous silicas, and activated carbons representative of the broad range of solid adsorbents that have received attention for CO₂ capture. While the multicomponent results presented in this work provide many interesting fundamental insights, only adsorbents functionalized with alkylamines are shown to have any significant CO₂ capacity in the presence of N₂ and H₂O at equilibrium partial pressures similar to those expected in a carbon capture process. Most significantly, the amine-appended metal organic framework mmen-Mg₂(dobpdc) (mmen = <i>N</i>,<i>N</i>′-dimethylethylenediamine, dobpdc ^4– = 4,4′-dioxido-3,3′-biphenyldicarboxylate) exhibits a record CO₂ capacity of 4.2 ± 0.2 mmol/g (16 wt %) at 0.1 bar and 40 °C in the presence of a high partial pressure of H₂O

Neutron Scattering and Spectroscopic Studies of Hydrogen Adsorption in Cr₃(BTC)₂A Metal−Organic Framework with Exposed Cr²⁺ Sites

Microporous metal−organic frameworks possessing exposed metal cation sites on the pore surface are of particular interest for high-density H2 storage at ambient temperatures, owing to the potential for H2 binding at the appropriate isosteric heat of adsorption for reversible storage at room temperature (ca. −20 kJ/mol). The structure of Cr3(BTC)2 (BTC3− = 1,3,5-benzenetricarboxylate) consists of dinuclear paddlewheel secondary building units connected by triangular BTC3− bridging ligands to form a three-dimensional, cubic framework. The fully desolvated form of the compound exhibits BET and Langmuir surface areas of 1810 and 2040 m2/g, respectively, with open axial Cr2+ coordination sites on the paddlewheel units. Its relatively high surface area facilitates H2 uptakes (1 bar) of 1.9 wt % at 77 K and 1.3 wt % at 87 K, and a virial-type fitting to the data yields a zero-coverage isosteric heat of adsorption of −7.4(1) kJ/mol. The detailed hydrogen loading characteristics of Cr3(BTC)2 have been probed using both neutron powder diffraction and inelastic neutron scattering experiments, revealing that the Cr2+ site is only partially populated until a marked elongation of the Cr−Cr internuclear distance occurs at a loading of greater than 1.0 D2 per Cr2+ site. Below this loading, the D2 is adsorbed primarily at the apertures of the octahedral cages. The H−H stretching frequency corresponding to H2 molecules bound to the primary site is observed in the form of an ortho−para pair at 4110 and 4116 cm−1, respectively, which is significantly shifted compared to the frequencies for free H2 of 4155 and 4161 cm−1. The infrared data have been used to compute a site-specific binding enthalpy for H2 of −6.7(5) kJ/mol, which is in agreement with the zero-coverage isosteric heat of adsorption derived from gas sorption isotherm data

Impact of Metal and Anion Substitutions on the Hydrogen Storage Properties of M‑BTT Metal–Organic Frameworks

Microporous metal–organic frameworks are a class of materials being vigorously investigated for mobile hydrogen storage applications. For high-pressure storage at ambient temperatures, the M₃[(M₄Cl)₃(BTT)₈]₂ (M-BTT; BTT^3– = 1,3,5-benzenetristetrazolate) series of frameworks are of particular interest due to the high density of exposed metal cation sites on the pore surface. These sites give enhanced zero-coverage isosteric heats of adsorption (<i>Q</i>_st) approaching the optimal value for ambient storage applications. However, the <i>Q</i>_st parameter provides only a limited insight into the thermodynamics of the individual adsorption sites, the tuning of which is paramount for optimizing the storage performance. Here, we begin by performing variable-temperature infrared spectroscopy studies of Mn-, Fe-, and Cu-BTT, allowing the thermodynamics of H₂ adsorption to be probed experimentally. This is complemented by a detailed DFT study, in which molecular fragments representing the metal clusters within the extended solid are simulated to obtain a more thorough description of the structural and thermodynamic aspects of H₂ adsorption at the strongest binding sites. Then, the effect of substitutions at the metal cluster (metal ion and anion within the tetranuclear cluster) is discussed, showing that the configuration of this unit indeed plays an important role in determining the affinity of the framework toward H₂. Interestingly, the theoretical study has identified that the Zn-based analogs would be expected to facilitate enhanced adsorption profiles over the compounds synthesized experimentally, highlighting the importance of a combined experimental and theoretical approach to the design and synthesis of new frameworks for H₂ storage applications