Rare Earth -MOFs: From Synthesis to Their Deployment for Amine-Sensing Application in Aqueous Media

The pursuit of developing sensors, characterized by their fluorescence-intensity enhancement or "turn-on" behavior, for accurately detecting noxious small molecules, such as amines, at minimal levels remains a significant challenge. Metal-organic frameworks (MOFs) have emerged as promising candidates as sensors as a result of their diverse structural features and tunable properties. This study introduces the rational synthesis of a new highly coordinated (6,12)-connected rare earth (RE) alb-MOF-3, by combining the nonanuclear 12-connected hexagonal prismatic building units, [RE9(μ3-O)2(μ3-X)12(OH)2(H2O)7(O2C-)12], with the 6-connected rigid trigonal prismatic extended triptycene ligand. The resulting Y-alb-MOF-3 material is distinguished by its high microporosity and Brunauer-Emmett-Teller surface area of approximately 1282 m2/g, which offers notable hydrolytic stability. Remarkably, it demonstrates selective detection capabilities for primary aliphatic amines in aqueous media, as evidenced by fluorescence turn-on behavior and photoluminescence (PL) titration measurements. This work emphasizes the potential of MOFs as sensors in advancing their selectivity and sensitivity toward various analytes.

Tunable Low-Relative Humidity and High-Capacity Water Adsorption in a Bibenzotriazole Metal-Organic Framework

Materials capable of selectively adsorbing or releasing water can enable valuable applications ranging from efficient humidity and temperature control to the direct atmospheric capture of potable water. Despite recent progress in employing metal-organic frameworks (MOFs) as privileged water sorbents, developing a readily accessible, water-stable MOF platform that can be systematically modified for high water uptake at low relative humidity remains a significant challenge. We herein report the development of a tunable MOF that efficiently captures atmospheric water (up to 0.78 g water/g MOF) across a range of uptake humidity (27-45%) employing a readily accessible Zn bibenzotriazolate MOF, CFA-1 ([Zn5(OAc)4(bibta)3], H2bibta = 1H,1H'-5,5'-bibenzo[d][1,2,3]triazole), as a base for subsequent diversification. Controlling the metal identity (zinc, nickel) and coordinating nonstructural anion (acetate, chloride) via postsynthetic exchange modulates the relative humidity of uptake, facilitating the use of a single MOF scaffold for a diverse range of potential water sorption applications. We further present a fundamental theory dictating how continuous variation of the pore environment affects the relative humidity of uptake. Exchange of substituents preserves capacity for water sorption, increases hydrolytic stability (with 5.7% loss in working capacity over 450 water adsorption-desorption cycles for the nickel-chloride-rich framework), and enables continuous modulation for the relative humidity of pore condensation. This combination of stability and tunability within a synthetically accessible framework renders Ni-incorporated M5X4bibta3 promising materials for practical water sorption applications.

Reticular Chemistry for the Construction of Highly Porous Aluminum-Based -Metal-Organic Frameworks

Edge-transitive nets are regarded as appropriate blueprints for the practice of reticular chemistry, and in particular, for the rational design and synthesis of functional metal-organic frameworks (MOFs). Among edge-transitive nets, type I edge-transitive nets have unique coordination figures, offering only one edge-transitive target for their associated expressed net-cBUs. Here, we report the reticulation of the binodal edge-transitive (6, 6)-c nia net in MOF chemistry, namely, the deliberate assembly of trinuclear aluminum clusters and 6-connected hexacarboxylate ligands into highly porous nia-MOFs. Further studies reveal that Al-nia-MOF-1 shows promising attributes as a storage media for oxygen (O₂) at high-pressure adsorption studies.

Reticular Chemistry at Its Best: Directed Assembly of Hexagonal Building Units into the Awaited Metal-Organic Framework with the Intricate Polybenzene Topology, pbz-MOF

The ability to direct the assembly of hexagonal building units offers great prospective to construct the awaited and looked-for hypothetical polybenzene (pbz) or "cubic graphite" structure, described 70 years ago. Here, we demonstrate the successful use of reticular chemistry as an appropriate strategy for the design and deliberate construction of a zirconium-based metal-organic framework (MOF) with the intricate pbz underlying net topology. The judicious selection of the perquisite hexagonal building units, six connected organic and inorganic building blocks, allowed the formation of the pbz-MOF-1, the first example of a Zr(IV)-based MOF with pbz topology. Prominently, pbz-MOF-1 is highly porous, with associated pore size and pore volume of 13 Å and 0.99 cm³ g^-1, respectively, and offers high gravimetric and volumetric methane storage capacities (0.23 g g^-1 and 210.4 cm³ (STP) cm^-3 at 80 bar). Notably, the pbz-MOF-1 pore system permits the attainment of one of the highest CH₄ adsorbed phase density enhancements at high pressures (0.15 and 0.21 g cm^-3 at 35 and 65 bar, respectively) as compared to benchmark microporous MOFs.

MOF Crystal Chemistry Paving the Way to Gas Storage Needs: Aluminum-Based soc-MOF for CH4, O2, and CO2 Storage

The molecular building block approach was employed effectively to construct a series of novel isoreticular, highly porous and stable, aluminum-based metal–organic frameworks with soc topology. From this platform, three compounds were experimentally isolated and fully characterized: namely, the parent Al-soc-MOF-1 and its naphthalene and anthracene analogues. Al-soc-MOF-1 exhibits outstanding gravimetric methane uptake (total and working capacity). It is shown experimentally, for the first time, that the Al-soc-MOF platform can address the challenging Department of Energy dual target of 0.5 g/g (gravimetric) and 264 cm³ (STP)/cm³ (volumetric) methane storage. Furthermore, Al-soc-MOF exhibited the highest total gravimetric and volumetric uptake for carbon dioxide and the utmost total and deliverable uptake for oxygen at relatively high pressures among all microporous MOFs. In order to correlate the MOF pore structure and functionality to the gas storage properties, to better understand the structure–property relationship, we performed a molecular simulation study and evaluated the methane storage performance of the Al-soc-MOF platform using diverse organic linkers. It was found that shortening the parent Al-soc-MOF-1 linker resulted in a noticeable enhancement in the working volumetric capacity at specific temperatures and pressures with amply conserved gravimetric uptake/working capacity. In contrast, further expansion of the organic linker (branches and/or core) led to isostructural Al-soc-MOFs with enhanced gravimetric uptake but noticeably lower volumetric capacity. The collective experimental and simulation studies indicated that the parent Al-soc-MOF-1 exhibits the best compromise between the volumetric and gravimetric total and working uptakes under a wide range of pressure and temperature conditions.