Isoreticular Series Research Articles

Ultrastable Carboxyl-Functionalized Pore-Space-Partitioned Metal-Organic Frameworks for Gas Separation.

Isoreticular chemistry, which enables property optimization by changing compositions without changing topology, is a powerful synthetic strategy. One of the biggest challenges facing isoreticular chemistry is to extend it to ligands with strongly coordinating substituent groups such as unbound -COOH, because competitive interactions between such groups and metal ions can derail isoreticular chemistry. It is even more challenging to have an isoreticular series of carboxyl-functionalized MOFs capable of encompassing chemically disparate metal ions. Here, with the simultaneous introduction of carboxyl functionalization and pore space partition, a family of carboxyl-functionalized materials is developed in diverse compositions from homometallic Cr3+ and Ni2+ to heterometallic Co2+/V3+, Ni2+/V3+, Co2+/In3+, Co2+/Ni2+. Cr-MOFs remain highly crystalline in boiling water. Unprecedentedly, one Cr-MOF can withstand the treatment cycle with 10m NaOH and 12m HCl, allowing reversible inter-conversion between unbound -COOH acid form and -COO- base form. These materials exhibit excellent sorption properties such as high uptake capacity for CO2 (100.2 cm3g-1) and hydrocarbon gases (e.g., 142.1 cm3g-1 for C2H2, 110.5 cm3g-1 for C2H4) at 1 bar and 298K, high benzene/cyclohexane selectivity (up to ≈40), and promising separation performance for gas mixtures such as C2H2/CO2 and C2H2/C2H4.

Advancing Pore‐Space‐Partitioned Metal–Organic Frameworks with Isoreticular Cluster Concept

AbstractTrigonal planar M3(O/OH) trimers are among the most important clusters in inorganic chemistry and are the foundational features of multiple high‐impact MOF platforms. Here we introduce a concept called isoreticular cluster series and demonstrate that M3(O/OH), as the first member of a supertrimer series, can be combined with a higher hierarchical member (double‐deck trimer here) to advance isoreticular chemistry. We report here an isoreticular series of pore‐space‐partitioned MOFs called M3M6 pacs made from co‐assembly between M3 single‐deck trimer and M3x2 double‐deck trimer. Important factors were identified on this multi‐modular MOF platform to guide optimization of each module, which enables the phase selection of M3M6 pacs by overcoming the formation of previously‐always‐observed same‐cluster phases. The new pacs materials exhibit high surface area and high uptake capacity for CO2 and small hydrocarbons, as well as selective adsorption properties relevant to separation of industrially important mixtures such as C2H2/CO2 and C2H2/C2H4. Furthermore, new M3M6 pacs materials show electrocatalytic properties with high activity.

Advancing Pore-Space-Partitioned Metal-Organic Frameworks with Isoreticular Cluster Concept.

Trigonal planar M3(O/OH) trimers are among the most important clusters in inorganic chemistry and are the foundational features of multiple high-impact MOF platforms. Here we introduce a concept called isoreticular cluster series and demonstrate that M3(O/OH), as the first member of a supertrimer series, can be combined with a higher hierarchical member (double-deck trimer here) to advance isoreticular chemistry. We report here an isoreticular series of pore-space-partitioned MOFs called M3M6 pacs made from co-assembly between M3 single-deck trimer and M3x2 double-deck trimer. Important factors were identified on this multi-modular MOF platform to guide optimization of each module, which enables the phase selection of M3M6 pacs by overcoming the formation of previously-always-observed same-cluster phases. The new pacs materials exhibit high surface area and high uptake capacity for CO2 and small hydrocarbons, as well as selective adsorption properties relevant to separation of industrially important mixtures such as C2H2/CO2 and C2H2/C2H4. Furthermore, new M3M6 pacs materials show electrocatalytic properties with high activity.

Engineering of an Isoreticular Series of CALF-20 Metal–Organic Frameworks for CO2 Capture

Engineering of an Isoreticular Series of CALF-20 Metal–Organic Frameworks for CO₂ Capture

Electrochromism in Isoreticular Metal-Organic Framework Thin Films with Record High Coloration Efficiency.

The power of isoreticular chemistry has been widely exploited to engineer metal-organic frameworks (MOFs) with fascinating molecular sieving and storage properties but is underexplored for designing MOFs with tunable optoelectronic properties. Herein, three dipyrazole-terminated XDIs (X = PM (pyromellitic), N (naphthalene), or P (perylene); DI = diimide) with different lengths and electronic properties are prepared and employed as linkers for the construction of an isoreticular series of Zn-XDI MOFs with distinct electrochromism. The MOFs are grown on fluorine-doped tin oxide (FTO) as high-quality crystalline thin films and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Due to the constituting electronically isolated XDI linkers, each member of the isoreticular thin film series exhibits two reversible one-electron redox events, each at a distinct electrochemical potential. The orientation of the MOFs as thin films as well as their isoreticular nature results in identical cation-coupled electron hopping transport rates in all three materials, as demonstrated by comparable apparent electron diffusion coefficients, Deapp. Upon electrochemical reduction to either the [XDI]•- or [XDI]2- state, each MOF undergoes characteristic changes in its optical properties as a function of linker length and redox state of the linker. Operando spectroelectrochemistry measurements reveal that Zn-PDI@FTO (PDI = perylene diimide) thin films exhibit a record high coloration efficiency of 941 cm2 C-1 at 746 nm, which is attributed to the maximized Faradaic transformations at each electronically isolated PDI unit. The electrochromic response of the thin film is retained to more than 99% over 100 reduction-oxidation cycles, demonstrating the applicability of the presented materials.

A GPT-4 Reticular Chemist for Guiding MOF Discovery.

We present a new framework integrating the AI model GPT-4 into the iterative process of reticular chemistry experimentation, leveraging a cooperative workflow of interaction between AI and a human researcher. This GPT-4 Reticular Chemist is an integrated system composed of three phases. Each of these utilizes GPT-4 in various capacities, wherein GPT-4 provides detailed instructions for chemical experimentation and the human provides feedback on the experimental outcomes, including both success and failures, for the in-context learning of AI in the next iteration. This iterative human-AI interaction enabled GPT-4 to learn from the outcomes, much like an experienced chemist, by a prompt-learning strategy. Importantly, the system is based on natural language for both development and operation, eliminating the need for coding skills, and thus, make it accessible to all chemists. Our collaboration with GPT-4 Reticular Chemist guided the discovery of an isoreticular series of MOFs, with each synthesis fine-tuned through iterative feedback and expert suggestions. This workflow presents a potential for broader applications in scientific research by harnessing the capability of large language models like GPT-4 to enhance the feasibility and efficiency of research activities.

A GPT‐4 Reticular Chemist for Guiding MOF Discovery**

AbstractWe present a new framework integrating the AI model GPT‐4 into the iterative process of reticular chemistry experimentation, leveraging a cooperative workflow of interaction between AI and a human researcher. This GPT‐4 Reticular Chemist is an integrated system composed of three phases. Each of these utilizes GPT‐4 in various capacities, wherein GPT‐4 provides detailed instructions for chemical experimentation and the human provides feedback on the experimental outcomes, including both success and failures, for the in‐context learning of AI in the next iteration. This iterative human‐AI interaction enabled GPT‐4 to learn from the outcomes, much like an experienced chemist, by a prompt‐learning strategy. Importantly, the system is based on natural language for both development and operation, eliminating the need for coding skills, and thus, make it accessible to all chemists. Our collaboration with GPT‐4 Reticular Chemist guided the discovery of an isoreticular series of MOFs, with each synthesis fine‐tuned through iterative feedback and expert suggestions. This workflow presents a potential for broader applications in scientific research by harnessing the capability of large language models like GPT‐4 to enhance the feasibility and efficiency of research activities.

Role of Transition Metals in Metal-Organic Frameworks as Nanoporous Ion Emitters for Thermal Ionization Mass Spectrometry.

Thermal ionization mass spectrometry is a powerful analytical technique that allows for precise determination of isotopic ratios. Analysis of low abundance samples, however, can be limited by the ionization efficiency. Following an investigation into a new type of metal-organic hybrid material, nanoporous ion emitters (nano-PIEs), devised to promote the emission of analyte ions and reduce traditional sample loading challenges, this work evaluates the impact that changing the metal in the material has on the ionization of uranium (U). Being derived from metal-organic frameworks (MOFs), nano-PIEs inherit the tunability of their parent MOFs. The MOF-74 series has been well studied for probing the impact various framework metals (i.e., Mg, Mn, Co, Ni, Cu, Zn, and Cd) have on material properties, and thus, a series of nano-PIEs with different metals were derived from this isoreticular MOF series. Trends in ionization efficiency were studied as a function of ionization potential, volatility, and work function of the framework metals to gain a better understanding of the mechanism of analyte ionization. This study finds a correlation between the analyte ionization efficiency and nano-PIE framework metal volatility that is attributed to its tunable thermal stability and degradation behavior.

Structure–Activity Relationships in Ni- Carboxylate-Type Metal–Organic Frameworks’ Metamorphosis for the Oxygen Evolution Reaction

Metal–organic frameworks (MOFs) have been reported to catalyze the oxygen evolution reaction (OER). Despite the established links between the pristine MOFs and their derived metal hydroxide electrocatalysts, several limitations still preclude understanding of the critical factors determining the OER performance. Of prime importance appears the choice of MOF and how its compositions relate to the catalyst stability and in turn to the reconstruction or metamorphosis mechanisms into the active species under OER conditions. An isoreticular series of Ni-carboxylate-type MOFs [Ni2(OH)2L] was chosen to elucidate the effects of the carboxylate linker length expansion and modulation of the linker–linker π–π interactions (L = 1,4-benzodicarboxylate, 2,6-napthalenedicarboxylate, biphenyl-4,4′-dicarboxylate, and p-terphenyl-4,4″-dicarboxylate). Degradation and reconstruction of MOFs were systematically investigated. The linker controls the transformation of Ni-MOF into distinct nickel hydroxide phases, and the conversion from α-Ni(OH)2 to β-Ni(OH)2, thus correlating the Ni-MOF composition with the OER activity of the Ni-MOF-derived metastable nickel hydroxide phase mixture.

Large Degree of Variation in Sorption Properties within a System of Isoreticular, Mixed-Ligand Ni- and Co-Based 2-Periodic Metal–Organic Frameworks

Two Ni-based and two Co-based mixed-ligand metal–organic frameworks (MOFs), which are all isoreticular with each other, are shown to have a large variation in nitrogen, carbon dioxide, hydrogen, and water vapor sorption properties, despite their similar structures. The MOFs have 1,2-bis(4-pyridyl)ethane (bpe) as the common ligand with the second ligand being either 2-nitroterephthalate (2-nta) or 2-bromoterephthalate (2-bta) for the Ni-based MOFs or 2-nta or 2-aminoterephthalate (2-ata) for the Co-based MOFs. The four MOFs have the formula [Ni(2-nta)(bpe)(H2O)2]n·2(DMA)n (1), [Ni(2-bta)(bpe)(H2O)2]n·2.8(DMF)n (2), [Co(2-nta)(bpe)(H2O)2]n·2(DMA)n (3), and [Co(2-ata)(bpe)(H2O)2]n·3(DMA)n·(H2O)n (4), respectively, where DMA = N,N′-dimethylacetamide and DMF = N,N′-dimethylformamide. Variable-temperature powder X-ray diffraction (VT-PXRD) studies indicate that the activated MOF structures are different from those of the as-synthesized MOFs, showing that the 2-periodic layers are dynamic upon desolvation. For the same metal ion, the MOF involving the 2-nta ligand has higher sorption, while sorption for the Ni-based MOFs is higher than for the Co-based MOFs. MOF 1 has the highest sorption within the isoreticular series and also has the highest sorption (the highest for water vapor) compared to other MOFs with the same or related ligands.

Al‐based Isoreticular Metal‐Organic Frameworks with MIL‐53 Topology as Effective Adsorbents in Methane Purification

AbstractIn the present investigation, an isoreticular series of Al‐based metal‐organic frameworks (MOFs) with MIL‐53 topology namely, MIL‐53(Al)‐FA, MIL‐53(Al)‐BDC, MIL‐53(Al)‐NDC and MIL‐53(Al)‐BPDC formed by organic linkers with different molecular size and correlated porosity were examined for their adsorption capacity for C3H8, C3H6, C2H4, and CH4, and C3H8/CH4, C3H6/CH4, C2H4/CH4 separation selectivity. C3H8 and C3H6 adsorption is found to be sensitive to van der Waals forces and increases with increasing micropore volume of the MOFs. Ideal Adsorption Solution Theory (IAST) has been applied to estimate binary C3H8/CH4, C3H6/CH4 (C3/C1), and C2H4/CH4 (C2/C1) selectivity. The MOFs investigated have shown high C3/C1 selectivity with MIL‐53(Al)‐FA exhibiting exceptional C3H8/CH4 and C3H6/CH4 selectivity of 330 and 246, respectively, for the 5 : 95 (v/v) mixtures. MIL‐53(Al)‐FA also exhibited the highest C2/C1 selectivity among them. The high affinity of MIL‐53 Al‐based MOFs for C3 and C2 hydrocarbons over C1 make them suitable as adsorbents for methane purification.

Isoreticular Series of Two-Dimensional Covalent Organic Frameworks with the kgd Topology and Controllable Micropores.

Two-dimensional (2D) covalent organic frameworks (COFs) possess designable pore architectures but limited framework topologies. Until now, 2D COFs adopting the kgd topology with ordered and rhombic pore geometry have rarely been reported. Here, an isoreticular series of 2D COFs with the kgd topology and controllable pore size is synthesized by employing a C6-symmetric aldehyde, i.e., hexa(4-formylphenyl)benzene (HFPB), and C3-symmetric amines i.e., tris(4-aminophenyl)amine (TAPA), tris(4-aminophenyl)trazine (TAPT), and 1,3,5-tris[4-amino(1,1-biphenyl-4-yl)]benzene (TABPB), as building units, referred to as HFPB-TAPA, HFPB-TAPT, and HFPB-TABPB, respectively. The micropore dimension down to 6.7 Å is achieved in HFPB-TAPA, which is among the smallest pore size of reported 2D COFs. Impressively, both the in-plane network and stacking sequence of the 2D COFs can be clearly observed by low-dose electron microscopy. Integrating the unique kgd topology with small rhombic micropores, these 2D COFs are endowed with both short molecular diffusion length and favorable host-guest interaction, exhibiting potential for drug delivery with high loading and good release control of ibuprofen.

Tuning Adsorption-Induced Responsiveness of a Flexible Metal–Organic Framework JUK-8 by Linker Halogenation

Flexible stimuli-responsive metal–organic frameworks have become promising candidates for numerous applications in gas-related technologies; however, the methods of fine tuning their responses are still limited and sought after. In this work, we demonstrate control over the adsorption properties of a flexible platform by incorporating halogen substituents (X = F, Cl, Br, I) into an eightfold interpenetrated isoreticular series [Zn(oba)(X-pip)]n (JUK-8X; X-pip = 4-pyridyl-functionalized benzene-1,3-dicarbo-5-halogenohydrazide; oba2– = 4,4′-oxydibenzoic carboxylate). The introduced halogen atoms allow for precise tuning of CO2 gate-opening pressures from p/p0 = 0.08 for the parental JUK-8 to 0.78 for the chlorine-functionalized JUK-8Cl. The presence of fluorine or chlorine substituent in the X-pip linker practically does not influence the maximum molar CO2 uptake as compared to JUK-8, whereas larger bromine or iodine atoms increase this uptake by 59 and 48%, respectively. Utilizing in situ powder X-ray diffraction (PXRD) during CO2 adsorption for a model JUK-8F, we propose a detailed mechanism of phase transitions including positions of the adsorbed gas molecules for the two loaded phases. Density functional theory calculations supported by in situ PXRD measurements at a saturation pressure shed light on the unusual CO2 adsorption properties of JUK-8Br and JUK-8I. Overall, our report demonstrates the use of halogen interactions for the control of a gas-responsive system and provides insightful guidance for the further development of flexible, adaptable materials.

Interlayer Interactions as Design Tool for Large-Pore COFs.

Covalent organic frameworks (COFs) with a pore size beyond 5 nm are still rarely seen in this emerging field. Besides obvious complications such as the elaborated synthesis of large linkers with sufficient solubility, more subtle challenges regarding large-pore COF synthesis, including pore occlusion and collapse, prevail. Here we present two isoreticular series of large-pore imine COFs with pore sizes up to 5.8 nm and correlate the interlayer interactions with the structure and thermal behavior of the COFs. By adjusting interlayer interactions through the incorporation of methoxy groups acting as pore-directing “anchors”, different stacking modes can be accessed, resulting in modified stacking polytypes and, hence, effective pore sizes. A strong correlation between stacking energy toward highly ordered, nearly eclipsed structures, higher structural integrity during thermal stress, and a novel, thermally induced phase transition of stacking modes in COFs was found, which sheds light on viable design strategies for increased structural control and stability in large-pore COFs.

Modelling adsorption based on an isoreticular MOF‐series of IFPs–Part I: Collection of physical properties and single component equilibria

AbstractAn isoreticular series of metal organic frameworks (MOFs) of IFPs (IFP, imidazolate frameworks Potsdam) is investigated for their morphological properties and adsorption behaviour. The materials are characterized phenomenologically with respect to their particle size and tendency of agglomerate formation, and with respect to their internal structure. For this purpose, material densities, pore size distributions, specific inner surfaces, and porosities are determined. The main part of the investigation is based on the analysis of gravimetrically determined adsorption equilibria for carbon dioxide (CO2) and methane (CH4) and their modelling. In this context, two different approaches for the consideration of the buoyancy of the sample are compared. The adjusted measurement data are globally approximated as sets of isotherms at different temperatures with two different modifications of the Langmuir model. Results show that both models are well suited for the interpolation of the experimental data in the temperature range under consideration. Comparison of the heats of adsorption derived from the isosteric method with values extracted from the model equations confirms them as physically consistent. This provides the opportunity to numerically simulate the dynamic separation of CO2/CH4‐mixtures under consideration of the heat tone based on the single component data. The IFPs can be divided phenomenologically into two categories. One is exclusively microporous (IFP‐4, ‐6, ‐7, and ‐8), while the other exhibits hierarchical structures of micropores coupled with mesopores (IFP‐1, ‐2, ‐3, and ‐5). Equilibrium data indicate that the latter are better suited for the separation of CO2/CH4‐mixtures due to their higher selectivities and capacities.

Frontispiece: Host–Guest Interactions in a Metal–Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction

Metal–Organic Frameworks In their Communication on page 17854, Julien Warnan, Roland A. Fischer et al. report the rational engineering of a series of metal–organic frameworks for photocatalytic solar fuel production.

Topological Insulating Phase in Single-Layer Pentagonal Covalent Organic Frameworks: A Reticular Design Using Metal Phthalocyanine

Organic topological insulators have received tremendous attention lately due to their designability and highly chemical diversity. In this work, we propose an isoreticular series of single-layer π-conjugated covalent organic frameworks with the Cairo pentagonal tiling, termed mcm-ZnPc-1, mcm-ZnPc-2, mcm-ZnPc-3, and mcm-ZnPc-3N, where mcm is the crystal net’s symbol and ZnPc stands for zinc phthalocyanine. First-principles calculations using density functional theory show that mcm-ZnPc-1 and mcm-ZnPc-2 are trivial insulators with band gaps of 0.96 and 1.18 eV, respectively. Interestingly, expanding the π-conjugated system of mcm-ZnPc-2, followed by a chemical substitution, results in mcm-ZnPc-3 and mcm-ZnPc-3N with a distorted Dirac point and a quadratic band-crossing point in their band structures, respectively. The topological analyses indicate that mcm-ZnPc-3N is a Z2 topological insulator with a nontrivial gapless edge state. Our tight-binding model for the pentagonal lattice suggests that the topologically trivial-to-nontrivial transition can be attributed to the sufficient electronic coupling between two adjacent linkers and to the fact that the band-crossing point locates at the Fermi level. Remarkably, we show that replacing Zn in mcm-ZnPc-3N with Cd and Hg can substantially enlarge the nontrivial band gap from 0.3 meV up to 10 meV due to strong spin–orbit coupling strengths although a biaxial strain is necessary to tune the Fermi level of mcm-HgPc-3N in order to enter its topological insulating phase. Our proposed materials are predicted to be dynamically, thermally, and mechanically stable, thus paving the way for their experimental realization. This work not only introduces the pentagonal lattice as a building motif for framework structures but also demonstrates a strategy to engineer the exotic band structure of organic materials.

Host-Guest Interactions in a Metal-Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction.

A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co‐immobilization of a CO2 reduction catalyst [ReBr(CO)3(4,4′‐dcbpy)] and a photosensitizer [Ru(bpy)2(5,5′‐dcbpy)]Cl2 using the isoreticular series of metal–organic frameworks (MOFs) UiO‐66, ‐67, and ‐68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location—either at the outer MOF particle surface or inside the MOF cavities—affecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.

Wirt‐Gast‐Wechselwirkungen in einer Serie isoretikulärer Metall‐organischer Gerüststrukturen für molekulare photokatalytische CO2‐Reduktion

AbstractEine Strategie zur Verbesserung der Stabilität, Effizienz und Selektivität von homogenen molekularen Katalysatoren ist die Immobilisierung auf Trägeroberflächen oder innerhalb von Matrizes. Hier untersuchen wir die Immobilisierung des CO2‐Reduktionskatalysators [ReBr(CO)3(4,4′‐dcbpy)] und des Photosensibilisators [Ru(bpy)2(5,5′‐dcbpy)]Cl2 unter Verwendung folgender Serie von isoretikulären Metall‐organischen Gerüsten (MOFs): UiO‐66, ‐67 und ‐68. Die spezifische Wahl der Porengröße ermöglicht eine unterschiedliche räumliche Anordnung von Katalysator und Photosensibilisator – entweder an der äußeren Oberfläche der MOF‐Partikel oder im Inneren der MOF‐Kavitäten. Dies beeinflusst die Katalysatorstabilität, die elektronische Kommunikation zwischen Reaktionszentrum und Photosensibilisator und folglich die katalytische Aktivität. Diese Ergebnisse ermöglichen ein rationales Verständnis eines optimierten supramolekularen Zusammenspiels von Katalysator, Photosensibilisator und Wirt.

Multivariate porous platform based on metal-organic polyhedra with controllable functionality assembly

<h2>Summary</h2> The chemical environment of pores is important for various applications of porous solids. Thanks to reticular chemistry, metal-organic frameworks (MOFs) have become a versatile platform targeting numerous applications through multiple functionalizations. Although multivariate MOFs often display novel properties, identifying and manipulating pore types remain a daunting challenge. Here, we present an isoreticular series of Zr-based metal-organic polyhedra (MOPs) as a porous platform to achieve controllable intrinsic pores. Two multivariate synthetic approaches were demonstrated: a mixed-cage strategy, whereby functionalized cages are mixed, compared with the conventional mixed-linker strategy, which yields a random distribution of functionalities. A remarkable difference in functionality assembly was achieved between the strategies, with complexity increasing from binary to senary systems. More interestingly, distinct photophysical properties were observed between mixed-linker and mixed-cage samples and attributed to radiative decay kinetics. This study highlights the potential of MOPs as a unique multivariate platform with tunable component assembly to study the emerging properties of multivariate porous solids.