Chiral Lanthanum Metal-Organic Framework with Gated CO2 Sorption and Concerted Framework Flexibility

Precise Modulation of CO2 Sorption in Ti8Ce2-Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

Investigating the structure-property correlation in porous materials is a fundamental and consistent focus in various scientific domains, especially within sorption research. Metal oxide clusters with capping ligands, characterized by intrinsic cavities formed through specific solid-state packing, demonstrate significant potential as versatile platforms for sorption investigations due to their precisely tunable atomic structures and inherent long-range order. This study presents a series of Ti8Ce2-oxo clusters with subtle variations in coordinated linkers and explores their sorption behavior. Notably, Ti8Ce2-BA (BA denotes benzoic acid) manifests a distinctive two-step profile during the CO2 adsorption, accompanied by a hysteresis loop. This observation marks a new instance within the metal oxide cluster field. Of intrigue, the presence of unsaturated Ce(IV) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between the CO2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating metal-oxo clusters with structural flexibility and provides profound insights into their host-guest interaction motifs. These insights hold substantial promise across diverse fields and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships.

Flexible Microporous Framework for One-Step Acquisition of Ethylene from Ternary C2 Hydrocarbons

One-step purification of ethylene (C2H4) from ternary C2 hydrocarbon mixtures is a crucial task and an enduring challenge because of their similar molecular size and physical properties. Owing to their intriguing structural dynamics, flexible MOFs have attracted more attention for gas adsorption and separation. Herein, we report a flexible MOF FJI-W-66 that exhibits rarely seen "breathing" behaviors for C2 hydrocarbons. Upon activation, the channels of guest-free FJI-W-66a significantly contract to a nearly closed-pore state. FJI-W-66a shows the stepwise adsorption isotherms for C2 hydrocarbons, which suggests the occurrence of structural transformation between less open and more open phases. Breakthrough experiments provide evidence that FJI-W-66a can selectively separate C2H4 from C2H2/C2H4/C2H6 mixtures with different ratios under ambient conditions, realizing the one-step acquisition of C2H4 from ternary C2 hydrocarbons.

Reticular Synthesis of Flexible Rare-Earth Metal-Organic Frameworks: Control of Structural Dynamics and Sorption Properties Through Ligand Functionalization

An exciting direction in metal-organic frameworks involves the design and synthesis of flexible structures which can reversibly adapt their structure when triggered by external stimuli. Controlling the extent and nature of response in such solids is critical in order to develop custom dynamic materials for advanced applications. Towards this, it is highly important to expand the diversity of existing flexible MOFs, generating novel materials and gain an in-depth understanding of the associated dynamic phenomena, eventually unlocking key structure-property relationships. In the present work, we successfully utilized reticular chemistry for the construction of two novel series of highly crystalline, flexible rare-earth MOFs, RE-thc-MOF-2 and RE-teb-MOF-1. Extensive single-crystal to single-crystal structural analyses coupled with detailed gas and vapor sorption studies, shed light onto the unique responsive behavior. The development of these series is related to the reported RE-thc-MOF-1 solids which were found to display a unique continuous breathing and gas-trapping property. The synthesis of RE-thc-MOF-2 and RE-teb-MOF-1 materials represents an important milestone as they provide important insights into the key factors that control the responsive properties of this fascinating family of flexible materials and demonstrates that it is possible to control their dynamic behavior and the associated gas and vapor sorption properties.

Hydrogenation of Carbon Dioxide to Formate by Noble Metal Catalysts Supported on a Chemically Stable Lanthanum Rod-Metal-Organic Framework

The conversion of carbon dioxide to formate is of great importance for hydrogen storage as well as being a step to access an array of olefins. Herein, we have prepared a JMS-5 metal-organic framework (MOF) using a bipyridyl dicarboxylate linker, with the molecular formula [La₂(bpdc)_3/2(dmf)₂(OAc)₃]·dmf. The MOF was functionalized by cyclometalation using Pd(II), Pt(II), Ru(II), Rh(III), and Ir(III) complexes. All metal catalysts supported on JMS-5 showed activity for CO₂ hydrogenation to formate, with Rh(III)@JMS-5a and Ir(III)@JMS-5a yielding 4319 and 5473 TON, respectively. X-ray photoelectron spectroscopy of the most active catalyst Ir(III)@JMS-5a revealed that the iridium binding energies shifted to lower values, consistent with formation of Ir-H active species during catalysis. The transmission electron microscopy images of the recovered catalysts of Ir(III)@JMS-5a and Rh(III)@JMS-5a did not show any nanoparticles. This suggests that the catalytic activity observed was due to Ir(III) and Rh(III). The high activity displayed by Ir(III)@JMS-5a and Rh(III)@JMS-5a compared to using the Ir(III) and Rh(III) complexes on their own is attributed to the stabilization of the Ir(III) and Rh(III) on the nitrogen and carbon atom of the MOF backbone.

Control over Phase Transformations in a Family of Flexible Double Diamondoid Coordination Networks through Linker Ligand Substitution

In this work, we present the first metal-organic framework (MOF) platform with a self-penetrated double diamondoid (ddi) topology that exhibits switching between closed (nonporous) and open (porous) phases induced by exposure to gases. A crystal engineering strategy, linker ligand substitution, was used to control gas sorption properties for CO₂ and C3 gases. Specifically, bimbz (1,4-bis(imidazol-1-yl)benzene) in the coordination network X-ddi-1-Ni ([Ni₂(bimbz)₂(bdc)₂(H₂O)]_n, H₂bdc = 1,4-benzenedicarboxylic acid) was replaced by bimpz (3,6-bis(imidazol-1-yl)pyridazine) in X-ddi-2-Ni ([Ni₂(bimpz)₂(bdc)₂(H₂O)]_n). In addition, the 1:1 mixed crystal X-ddi-1,2-Ni ([Ni₂(bimbz)(bimpz)(bdc)₂(H₂O)]_n) was prepared and studied. All three variants form isostructural closed (β) phases upon activation which each exhibited different reversible properties upon exposure to CO₂ at 195 K and C3 gases at 273 K. For CO₂, X-ddi-1-Ni revealed incomplete gate-opening, X-ddi-2-Ni exhibited a stepped isotherm with saturation uptake of 3.92 mol·mol^-1, and X-ddi-1,2-Ni achieved up to 62% more gas uptake and a distinct isotherm shape vs the parent materials. Single-crystal X-ray diffraction (SCXRD) and in situ powder X-ray diffraction (PXRD) experiments provided insight into the mechanisms of phase transformation and revealed that the β phases are nonporous with unit cell volumes 39.9, 40.8, and 41.0% lower than the corresponding as-synthesized α phases, X-ddi-1-Ni-α, X-ddi-2-Ni-α, and X-ddi-1,2-Ni-α, respectively. The results presented herein represent the first report of reversible switching between closed and open phases in ddi topology coordination networks and further highlight how ligand substitution can profoundly impact the gas sorption properties of switching sorbents.

Two novel metal-organic frameworks functionalised with pentamethylcyclopentadienyl iridium(III) chloride for catalytic conversion of carbon dioxide to formate

Hydrogenation of CO₂ to formate is a vital reaction, because formate is an excellent hydrogen carrier, which yields blue hydrogen. Blue hydrogen is comparatively cheaper and attractive as the world envisions the hydrogen economy. In this work, two isostructural lanthanide-based MOFs (JMS-6 and JMS-7 [Ln(bpdc)_3/2(dmf)₂(H₂O)₂]_n) were prepared and used as support materials for molecular catalysts. The bipyridyl MOF backbone were functionalised using pentamethylcyclopentadienyl iridium(III) chloride to give Ir(III)@JMS-6a and Ir(III)@JMS-7a. XPS of the functionalised MOFs show downfield shifts in the N 1s binding energy indicating successful grafting of the complex to the MOF. Hydrogenation experiments in the presence of an organic base showed that the functionalised MOFs were active towards converting CO₂ to formate. Ir(III)@JMS-6a and Ir(III)@JMS-7a exhibited the highest turnover numbers of 813 and 621 respectively. ICP-OES indicated insignificant leaching during catalysis. TEM images and XPS data of the recovered catalyst ruled out the presence of Ir(0), confirming that the activity observed was attributed to the molecular Iridium(III) centres.

Chiroptical Activity of An Achiral Emissive Eu Metal-Organic Framework

Chiroptical activity of achiral crystals is theoretically allowed but very unusual. There is a particularly scarcity of empirical studies on optically active achiral metal-organic frameworks (MOFs). Herein we report an achiral emissive Eu MOF and its chiroptical properties both in the ground and excited states. The framework crystallizes in an achiral space group (Pna2₁ ) belonging to the polar point group (mm2), where the asymmetric arrangement of racemic trinuclear Eu-oxo clusters is responsible for the optical activity. A pair of circular dichroisms (CD) and circularly polarized luminescence (CPL) peaks with opposite signs were observed for single crystals. Importantly, the luminescence dissymmetry factor can reach up to 1.1×10^-3 , which is comparable in magnitude to the value of most of the chiral-linker-bridged MOFs. This work gives the first example of achiral MOFs with CPL response and should be instructive for the discovery of more CPL emitters from racemic MOF family.

A hexagon based Mn(II) rod metal-organic framework - structure, SF6 gas sorption, magnetism and electrochemistry

A manganese(II) metal-organic framework based on the hexatopic hexakis(4-carboxyphenyl)benzene, cpb^6-: [Mn₃(cpb)(dmf)₃], was solvothermally prepared showing a Langmuir area of 438 m² g^-1, rapid uptake OF sulfur hexafluoride (SF₆) as well as electrochemical and magnetic properties, while single crystal diffraction reveals an unusual rod-MOF topology.

A Novel Instantaneous Self-Assembled Hollow MOF-Derived Nanodrug for Microwave Thermo-Chemotherapy in Triple-Negative Breast Cancer

Hollow materials derived from metal-organic frameworks (MOFs) have emerged in the biomedical field due to their unique properties, and different synthesis methods have been proposed. However, so far, the large-scale use of hollow MOFs is mostly limited by the timeliness of synthesis methods. Herein, we propose a new ultrasonic aerosol flow strategy for the instantaneous synthesis of a Zr-MOF-derived hollow sphere complex (ZC-HSC) in only one step. Through rapid transient heating, the coordination between metal salts and organic ligands occurs along with prompt evaporation of the solvent. The whole process lasts for only about 21 s, compared with several steps that take hours or even days for conventional synthesis methods. Based on the ZC-HSC, we designed a nanodrug with the functions of manipulating the tumor microenvironment, which can reshape the tumor microenvironment by improving tumor hypoxia and inflammatory microenvironment and promoting antiangiogenic therapy. Combined with microwave thermo-chemotherapy, the nanodrugs effectively treat triple-negative breast cancer (the tumor cell survival rate was only 34.76 and 31.05% in normoxic and hypoxic states, respectively, and the tumor inhibition rate reached 87.9% at the animal level), providing a new theoretical basis for the treatment of triple-negative breast cancer. This rapid, one-step, and continuous ultrasonic aerosol flow strategy has bright prospects in the synthesis of MOF-derived hollow materials and promotes the further development of large-scale applications of biological nanomaterials.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.