Heterometallic Metal-organic Frameworks Research Articles

Lithium‐Lanthanide Heterometallic Organic Frameworks with Near‐Unity Photoluminescence Quantum Yields for Single‐Composition White‐Light Emission and Fluorescent Sensing on Nitrobenzene

AbstractLanthanide ion contained metal–organic frameworks (MOFs) have garnered significant attention in the fields of solid‐state lighting and chemical sensing due to their porous structure and distinctive optical properties. However, they also present challenges because of the limited photoluminescence (PL) intensity resulting from the parity‐forbidden f–f transitions of lanthanide ions. Herein, the study reports a new heterometallic MOFs Ln3Li2L4 (Li‐Ln‐MOF, Ln = Y, Eu, Tb and Dy, L = deprotonated 1,3,5‐tris(4‐carboxyphenyl)benzene) with a Brunauer‐Emmett‐Teller (BET) surface area of 774.1 m2/g. The porous crystal structure of Li‐Ln‐MOF is characterized by three kinds of channels interpenetrating with each other. By employing ligand alternation and lanthanide ion alloying strategies, Li‐Y1‐xEux‐MOF1 crystal isostructural with Li‐Ln‐MOF is synthesized by using 2,4,6‐tris(4‐carboxyphenyl)‐1,3,5‐triazine (H3TATB) as ligand. The Li‐Y0.7Eu0.3‐MOF1 crystal excels in the comprehensive performance with a BET surface area of 858.8 m2 g−1 and a near‐unity PL quantum yield. The time density functional theory and natural transition orbitals calculations unravel that the outstanding optical properties Li‐Y0.7Eu0.3‐MOF1 originates from the charge transfer between TATB3− and Eu3+. Benefiting from the excellent comprehensive performance of Li‐Y1‐xEux‐MOF1, the study reveals their potentials as single‐composition white‐light emission and fluorescent sensing probe for the detection of nitrobenzene.

Quest for Multifunctionality: Current Progress in the Characterization of Heterometallic Metal-Organic Frameworks.

Metal-organic frameworks (MOFs) are a class of porous, crystalline materials that have been systematically developed for a broad range of applications. Incorporation of two or more metals into a single crystalline phase to generate heterometallic MOFs has been shown to lead to synergistic effects, in which the whole is oftentimes greater than the sum of its parts. Because geometric proximity is typically required for metals to function cooperatively, deciphering and controlling metal distributions in heterometallic MOFs is crucial to establish structure-function relationships. However, determination of short- and long-range metal distributions is nontrivial and requires the use of specialized characterization techniques. Advancements in the characterization of metal distributions and interactions at these length scales is key to rapid advancement and rational design of functional heterometallic MOFs. This perspective summarizes the state-of-the-art in the characterization of heterometallic MOFs, with a focus on techniques that allow metal distributions to be better understood. Using complementary analyses, in conjunction with computational methods, is critical as this field moves toward increasingly complex, multifunctional systems.

Efficient Ethane and Propane Separation from Natural Gas Using Heterometallic Metal-Organic Frameworks with Interpenetrated Structures.

The development of efficient technology for natural gas separation in industrial processes has become imperative. In this regard, the exploration of novel and effective adsorbents has gained significant attention. One promising approach is the metal regulation of metal-organic frameworks (MOFs), particularly heterometallic MOFs, which offer greater potential for gas separation due to their diverse composition. This study presents the synthesis of a series of iron- and vanadium-based heterometallic MOFs (MIL-126), featuring interpenetrated structures, and investigates their adsorption performance for methane (CH4), ethane (C2H6), and propane (C3H8). Experimental results reveal that the choice of metal combinations within the MOF framework significantly influences the adsorption performance of MIL-126. Notably, heterometallic MIL-126(Fe/Ni) exhibits a stronger binding affinity for C3H8, with an impressive uptake of 177 cm3/g. The C3H8/CH4 ideal adsorbed solution theory selectivity of MIL-126(Fe/Ni) surpasses that of MIL-126(Fe) by a factor of 7, reaching a value of 853, second only to the highest reported value. Furthermore, MIL-126(Fe/Ni) exhibits remarkable potential for the recovery of pure CH4 from the equimolar C3H8/CH4 mixture, with the amount of pure CH4 approaching the maximum reported value for MOFs. Insights from isosteric heat at zero loading and Henry's coefficients indicate that the transformation of metal types leads to a change in the interaction energy between C3H8 and the framework. Furthermore, breakthrough experiments validate the effective separation capability of MIL-126(Fe/Ni) for CH4/C2H6/C3H8 mixtures. These findings underscore the remarkable potential of heterometallic MOFs in constructing a wide range of new MOFs with tailorable properties, thereby enhancing their gas separation performance.

Heterometallic MIL-125(Ti-Al) frameworks for electrochemical determination of ascorbic acid, dopamine and uric acid.

The detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA) is not only of great significance in the areas of biomedicine and neurochemistry but also helpful in disease diagnosis and pathology research. Due to their diverse structures, designability, and large specific surface areas, metal-organic frameworks (MOFs) have recently caught considerable attention in the electrochemical field. Herein, a family of heterometallic MOFs with amino modification, MIL-125(Ti-Al)-xNH2 (x = 0%, 25%, 50%, 75%, and 100%), were synthesized and employed as electrochemical sensors for the detection of AA, DA, and UA. Among them, MIL-125(Ti-Al)-75%NH2 exhibited the most promising electrochemical behavior with 40% doping of carbon black in 0.1 M PBS (pH = 7.10), which displayed individual detection performance with wide linear detection ranges (1.0-6.5 mM for AA, 5-100 μM for DA and 5-120 μM for UA) and low limits of detection (0.215 mM for AA, 0.086 μM for DA, and 0.876 μM for UA, S/N = 3). Furthermore, the as-prepared MIL-125(Ti-Al)-75%NH2/GCE provided a promising platform for future application in real sample analysis, owing to its excellent anti-interference performance and good stability.

Dual-Ligand Strategy for the Design and Construction of a Cd-Zn Heterometallic Metal-Organic Framework by One-Pot Synthesis as a Heterogeneous Catalyst for the Epoxidation Reaction of Olefins.

The use of metal-organic frameworks (MOFs) as catalysts is reported in various industrial applications. In contrast to monometallic MOFs, heterometallic MOFs with mixed organic ligands showed enhanced catalytic properties. The catalytic properties of heterometallic MOFs can be enhanced by generating defects and the synergistic effect between the two heterometals at secondary building units. By using a solvothermal technique, a Cd-Zn heterometallic MOF with a new morphology, [Cd2Zn(DPTTZ)0.5(OBA)3(H2O)(HCOOH)] (IUST-4) [DPTTZ = 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole, OBA = 4,4'-oxybis(benzoic acid)], was synthesized via a mixed-ligand strategy and characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared spectroscopy, elemental analysis, and thermogravimetric analysis. X-ray crystallographic analysis showed that IUST-4 is a neutral 3D metal-organic framework crystallized in the monoclinic system with space group C2/c. In this study, the catalytic properties of IUST-4 for the epoxidation of cyclooctene were investigated. IUST-4 was selected as the optimal catalyst for epoxy product production due to its high selectivity and yield. Moreover, the catalytic performance of IUST-4 was maintained despite five recycling cycles without significant degradation. The epoxidation of cyclooctene with IUST-4 has several advantages, including good selectivity, easy recovery, and short-time reaction.

Self-Cascade Ce-MOF-818 Nanozyme for Sequential Hydrolysis and Oxidation.

Mimicking efficient biocatalytic cascades using nanozymes has gained enormous attention in catalytic chemistry, but it remains challenging to develop a nanozyme-based cascade system to sequentially perform the desired reactions. Particularly, the integration of sequential hydrolysis and oxidation reactions into nanozyme-based cascade systems has not yet been achieved, despite their significant roles in various domains. Herein, a self-cascade Ce-MOF-818 nanozyme for sequential hydrolysis and oxidation reactions is developed. Ce-MOF-818 is the first Ce(IV)-based heterometallic metal-organic framework constructed through the coordination of Ce and Cu to distinct groups. It is successfully synthesized using an improved solvothermal method, overcoming the challenge posed by the significant difference in the binding speeds of Ce and Cu to ligands. With excellent organophosphate hydrolase-like (Km = 42.3 µM, Kcat = 0.0208min-1 ) and catechol oxidase-like (Km = 2589µM, Kcat = 1.25s-1 ) activities attributed to its bimetallic active centers, Ce-MOF-818 serves as a promising self-cascade platform for sequential hydrolysis and oxidation. Notably, its catalytic efficiency surpasses that of physically mixed nanozymes by approximately fourfold, owning to the close integration of active sites. The developed hydrolysis-oxidation self-cascade nanozyme has promising potential applications in catalytic chemistry and provides valuable insights into the rational design of nanozyme-based cascade systems.

Ordered Arrangement of Different Metals in Discrete and Infinite Building Blocks for Heterometallic Metal-Organic Frameworks Construction

Ordered Arrangement of Different Metals in Discrete and Infinite Building Blocks for Heterometallic Metal-Organic Frameworks Construction

The application of Na-Bi MOF as a heterometallic coordination polymer and 2,2-dimethoxypropane as an in-situ-generating ternary solvent for the extraction and preconcentration of some phthalate and adipate esters from tap, well, surface, and river water samples

In this study, the first-ever attempt was done to apply a heterometallic metal–organic framework (MOF) called Na-Bi MOF for the extraction and preconcentration of some phthalate and adipate esters. Also for the first time, 2,2-dimethoxypropane was adopted as an efficient in-situ generating ternary solvent for the desorption aim. Diverse real samples including tap, well, surface, and river waters underwent the developed extraction procedure. For performing the process of extraction, only 5 mg of Na-Bi MOF was added into a sodium sulfate-enriched aqueous solution containing the target compounds and vortexed. So, the analytes were adsorbed onto the MOF particles. Centrifugation separated the analyte-loaded MOF from the aqueous solution. The MOF was treated with only 500 µL of 2,2-dimethoxypropane. By centrifugation, the organic phase was separated and subjected to evaporation using a gas splitter device. After the complete evaporation of the organic phase, only 5 µL of 1,2-dibromoethane was applied for the elution of the inner perimeter of the conical bottom glass test tube by vortexing. Eventually, two microliters of the organic phase were injected into a gas chromatograph equipped with flame ionization detection. High enrichment factors (520–800), satisfactory extraction recoveries (52–80 %), low limits of detection and quantification (0.66–1.20 and 2.18–3.97 µg/L, respectively), favorable relative recoveries without dilution (86–117 %), wide linear ranges (3.97–500 µg/L), and high coefficients of determination (0.9903–0.9944) were recorded for the developed method. Low amount use of the MOF and organic solvents, diversity of real samples, no need for dilution, and short chromatographic run (a quarter) are the highlights of the developed method.

Th6-Based Multicomponent Heterometallic Metal-Organic Frameworks Featuring 6,12-Connected Topology for Iodine Adsorption.

Its high coordination number and tendency to cluster make Th4+ suitable for constructing metal-organic frameworks (MOFs) with novel topologies. In this work, two novel thorium-based heterometallic MOF isomers (IHEP-17 and IHEP-18) were assembled from a Th6 cluster, a multifunctional organic ligand [4-(1H-pyrazol-4-yl)benzoic acid (HPyba)], and Cu2+/Ni2+ cations via the one-pot solvothermal synthesis strategy. The framework features a 6,12-connected new topology net and contains two kinds of supramolecular cage structures, Th36M4 and Th24M2, suitable for guest exchange. Both MOF materials can efficiently adsorb I2. X-ray photoelectron spectroscopy, Raman spectroscopy, and single-crystal X-ray diffraction indicate that the adsorbed iodine is uniformly distributed within the Th36M4 cage but not the Th24M2 cage in the form of I3-.

Development of a Mixed Multinuclear Cluster Strategy in Metal-Organic Frameworks for Methane Purification and Storage.

Metal-organic frameworks (MOFs) have attracted extensive attention in methane (CH4) purification and storage. Specially, multinuclear cluster-based MOFs usually have prominent performance because of large cluster size and abundant open metal sites. However, compared to diverse combinations of organic linkers, one MOF with two or more multinuclear clusters is difficult to achieve. In this paper, we demonstrate a mixed multinuclear cluster strategy, which successfully led to three new heterometallic MOFs (SNNU-328-330) with the same common H3TATB [2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine] tritopic linker and six types of multinuclear clusters ([YCd(COO)4(μ2-H2O)], [YCd2(COO)8], [In3(COO)6(μ3-OH)], [In3Eu2(COO)9(μ3-OH)3(μ4-O)], [Y9(COO)12(μ3-OH)14] and [Y2Cd8(COO)16(μ2-H2O)4(μ3-OH)8]). Three MOF adsorbents all show great potentials to remove the impurities (CO2 and C2-hydrocarbons) in natural gas and show prominent high-pressure methane storage capacity. Among them, the ideal adsorbed solution theory separation ratios of equimolar C2H2/CH4, C2H4/CH4, C2H6/CH4, and CO2/CH4 at 298 K for SNNU-328 reach to 29.7-16.0, 19.1-8.2, 33.2-10.3, and 74.3-8.5, which have surpassed many famous MOF adsorbents. Dynamic breakthrough experiments conducted at 273 and 298 K showed that SNNU-330 can separate CH4 from C2H2/CH4, C2H4/CH4, C2H6/CH4, and CO2/CH4 mixtures with the breakthrough interval times of about 48.2, 17.9, 37.2, and 17.1 min g-1 (273 K, 1 bar, v/v = 50/50, 2 mL min-1), respectively. Remarkably, SNNU-329 exhibits extremely high methane storage performance at 298 K with the total uptake and working capacity of 192 cm3 cm-3 (95 bar) and 171 cm3 cm-3 (65 bar) due to the synergistic effects of high surface area, suitable pore sizes, and multiple open metal sites.

Ultrastable Cu-Based Dual-Channel Heterowire for the Switchable Electro-/Photocatalytic Reduction of CO2.

Catalytic conversion of CO2 into high value-added chemicals using renewable energy is an attractive strategy for the management of CO2 . However, achieving both efficiency and product selectivity remains a great challenge. Herein, a brand-new family of 1D dual-channel heterowires, Cu NWs@MOFs are constructed by coating metal-organic frameworks (MOFs) on Cu nanowires (Cu NWs) for electro-/photocatalytic CO2 reductions, where Cu NWs act as an electron channel to directionally transmit electrons, and the MOF cover acts as a molecule/photon channel to control the products and/or undertake photoelectric conversion. Through changing the type of MOF cover, the 1D heterowire is switched between electrocatalyst and photocatalyst for the reduction of CO2 with excellent selectivity, adjustable products, and the highest stability among the Cu-based CO2 RR catalysts, which leads to heterometallic MOF covered 1D composite, and especially the first 1D/1D-type Mott-Schottky heterojunction. Considering the diversity of MOF materials, the ultrastable heterowires offer a highly promising and feasible solution for CO2 reduction.

Orthogonal luminescence lifetime encoding by intermetallic energy transfer in heterometallic rare-earth MOFs

Lifetime-encoded materials are particularly attractive as optical tags, however examples are rare and hindered in practical application by complex interrogation methods. Here, we demonstrate a design strategy towards multiplexed, lifetime-encoded tags via engineering intermetallic energy transfer in a family of heterometallic rare-earth metal-organic frameworks (MOFs). The MOFs are derived from a combination of a high-energy donor (Eu), a low-energy acceptor (Yb) and an optically inactive ion (Gd) with the 1,2,4,5 tetrakis(4-carboxyphenyl) benzene (TCPB) organic linker. Precise manipulation of the luminescence decay dynamics over a wide microsecond regime is achieved via control over metal distribution in these systems. Demonstration of this platform’s relevance as a tag is attained via a dynamic double encoding method that uses the braille alphabet, and by incorporation into photocurable inks patterned on glass and interrogated via digital high-speed imaging. This study reveals true orthogonality in encoding using independently variable lifetime and composition, and highlights the utility of this design strategy, combining facile synthesis and interrogation with complex optical properties.

Molecular insight into the structure of heterometallic metal-organic frameworks MIL-53-M (M = Al and Ga) and their intermolecular interaction with pyridine: A periodic density functional theory

Heterometallic metal-organic frameworks (MOFs) as part of functional materials possess interesting functionalities which may benefits for many potential applications. In this study, quantum mechanical approach was used to investigate the effect of multi metal ion nodes of Al3+ and Ga3+ in a famous breathing MOF of MIL-53. The ratio of Al3+ to Ga3+ was modulated to give bimetallic MIL-53(Al/Ga). The presence of Al3+ and Ga3+ in MIL-53(Al/Ga) induces the structural changes as evidence from the calculated unit cell parameters, where increasing the concentration of Al3+ generally reduces the size of the unit cell dimension. The electronic properties have been identified to give small fine tuning of the band gap energy where the presence of Al3+ shows a dominant factor to shift the edge of the conductance band according to the density of states plots. The band gap energy of MIL-53(Ga) was calculated to be 3.47 eV and it decreases when Ga3+ was substituted by Al3+ to give band gap energy of 3.33 eV for MIL-53(Al). Therefore, the bandgap energy can be fine-tuned by modulating the ratio of Al3+ to Ga3+ in bimetallic MIL-53(Al/Ga). The nature of the bonding within various MIL-53(Al/Ga) was also identified using electron localization maps indicating a possible ionic characteristic for metal ions to ligand interaction. In addition, the adsorption of pyridine within MIL-53(Al/Ga) provides an insight into the Bronsted acidity of MIL-53(Al/Ga) due to the presence of bridging -µOH. In this case, adsorbed pyridine in MIL-53-2Al2Ga shows the lowest adsorption energy compared to the other configurations indicating a stronger Bronsted acidity of the -µOH site. This is also in correlation with the more positively charge of pyridine molecules inside MIL-53-2Al2Ga due to the hydrogen bonding interaction with hydrogen of -µOH. This study gives an insight into the functional material design in term of the electronic properties as well as the behavior towards guest molecules.

Simpler is better: A heterometallic (Mn-Na) metal organic framework (MOF) with a rare myc topology synthesized from bench chemicals for selective adsorption and separation of organic dyes

A low cost heterometallic (Mn-Na) coordination polymer with rare myc topology is designed and exploited for cationic dye adsorption selectivity and separation. • A low cost new heterometallic ( Mn-Na ) metal organic framework (MOF) is synthesized. • The crystallography reveals presence of two metal ions in the asymmetric unit i.e, Mn and Na. • Topological analysis shows a rare myc topology of the MOF which is very uncommon among the coordination polymers. • The resulting Mn-Na shows excellent selectivity, in the aqueous phase, for adsorption and separation of cationic dye, methylene blue (MB) with adsorption capacity to be 46.22 mg g −1 . • The present material showed excellent structural stability and recyclability with pseudo-second-order kinetics for adsorption. • The plausible mechanism suggests that HSAB concept is responsible for the adsorption process. The present work summarizes the design of a new heterometallic ( Mn-Na ) metal organic framework (MOF) synthesized under solvothermal conditions. The single crystal X-Ray analysis uncovers its composition as [MnNa(HCOO) 3 ] n . The crystallography reveals the presence of two metal ions in the asymmetric unit i.e., Mn and Na which are connected through a bridging formate ligand. Both Mn(II) and Na(I) are coordinated by six oxygen atoms thus forming a distorted octahedral geometry around each metal ion. The HCOO - ligand acts as a bridge to propagate the structure along the three axis resulting in a 3D MOF. Each oxygen of the formate is coordinated to both Mn and Na. Topological analysis shows a rare myc topology of the MOF which is very uncommon among the coordination polymers reported so far. The resulting Mn-Na shows excellent selectivity, in the aqueous phase, for adsorption and separation of cationic dye, methylene blue (MB) with an adsorption capacity to be 46.22 mg g −1 . Moreover, this adsorbent material showed excellent structural stability and recyclability; and the pseudo-second-order kinetics for adsorption. The plausible mechanism suggests that the HSAB concept is responsible for the adsorption process. Hard donors of dye molecules build strong interactions with hard Na + ions embedded in MOF. Thus, the designed MOF is the first example in heterometallic MOF chemistry to show dye adsorption and is established as a simple, easy to prepare and low-cost polymer for environmental protection for future endeavours.

Trends in Siting of Metals in Heterometallic Nd-Yb Metal-Organic Frameworks and Molecular Crystals.

Several studies suggest that metal ordering within metal-organic frameworks (MOFs) is important for understanding how MOFs behave in relevant applications; however, these siting trends can be difficult to determine experimentally. To garner insight into the energetic driving forces that may lead to nonrandom ordering within heterometallic MOFs, we employ density functional theory (DFT) calculations on several bimetallic metal-organic crystals composed of Nd and Yb metal atoms. We also investigate the metal siting trends for a newly synthesized MOF. Our DFT-based energy of mixing results suggest that Nd will likely occupy sites with greater access to electronegative atoms and that local homometallic domains within a mixed-metal Nd-Yb system are favored. We also explore the use of less computationally extensive methods such as classical force fields and cluster expansion models to understand their feasibility for large system sizes. This study highlights the impact of metal ordering on the energetic stability of heterometallic MOFs and crystal structures.

Adapting UFF4MOF for Heterometallic Rare-Earth Metal-Organic Frameworks.

Heterometallic metal-organic frameworks based on rare-earth metals (RE-MOFs) have potential in a number of applications where energy transfer between nearby metal atoms is required. This observation implies that it is important to understand the level of local mixing that is achieved between metals of different types during synthesis of RE-MOFs. Density functional theory calculations can give quantitative information on the relative energy of different configurations of RE-MOFs, but these calculations cannot be applied to the full range of medium- and long-range orderings that are possible in heterometallic materials. This limitation can be overcome using force field (FF)-based calculations if appropriate FFs are available. We show that an existing generic FF for MOFs, UFF4MOF, does not accurately predict energies of mixing in heterometallic Nd/Yb MOFs and introduce a modified FF to address this shortcoming. The resulting FF is used to explore metal orderings in large simulation volumes for a Nd/Yb MOF, illustrating the complexities that can arise in the structure of heterometallic RE-MOFs.

Nanochannel-Based Heterometallic {CoIITbIII}-Organic Framework for Fluorescence Recognition of Tryptophan and Catalytic Cycloaddition of Epoxides with CO2

To pave the way for the salient application of metal–organic frameworks (MOFs) as realistic sensors, it is critical to screen or design the customized functional structure with specified prominent synergistic effects provided by its constituents, voids, specific surfaces, functional sites, etc. This prompts us to study the sensing performance of a honeycomb nanochannel of heterometallic MOFs previously invented. This structure has excellent physical and chemical properties of high specific surface area, good chemical stability, and highly open coexistence of Lewis acid–base sites. In this work, the highly robust sky-blue [CoTb(CO2)6(OH2)]-based heterometallic framework of {[(CH3)2NH2][CoTb(TDP)(H2O)]·3H2O·4DMF}n (NUC-31; H6TDP = 2,4,6-tri(2′,4′-dicarboxyphenyl)pyridine) was synthesized. The results of the fluorescence recognition experiment show that, compared with other amino acids, NUC-31 has an ultrastrong fluorescence quenching for tryptophan with a detection limit as low as 0.11 mM, which means that NUC-31 can be used as a potential fluorescence probe for the targeted detection of tryptophan of ecosystems. In addition, the catalytic experiment results indicated that NUC-31 has high activity for catalyzing the cycloaddition reaction of epoxides with CO2 under 75 °C and 1 atm. It is precisely due to NUC-31 having extremely unsaturated tetracoordinated Co(II) and hepta-coordinated Tb(III) metal ions as well as a high pore volume (65.1%), which makes the catalytic reaction conditions relatively mild. Therefore, this work certificated that nanoporous MOFs assembled from a multifunctional ligand with the highly open coexistent Lewis acid–base sites had a potential application not only in monitoring tryptophan in clinical scenarios but also as an effective heterogeneous catalyst.

Europium-cadmium organic framework with zwitterionic ligand exhibiting tunable luminescence, CO2 adsorption and dye degradation

Porous lanthanide-transition heterometallic metal-organic frameworks (MOFs) as a subclass of porous hybrid materials have attracted considerable attention as a new advance in the research on MOFs. However, rationally designing and constructing heterometallic MOFs with desirable properties remains a challenging task. In this work, involving the heterometallic cooperative crystallization method, a novel europium-cadmium MOF based on a zwitterionic carboxylate ligand, [EuCd(pbbp)2(SO4)2Cl2(H2O)3] (1), (H2pbbp·2Cl ​= ​1,1'-(1,4-phenylene-bis(methylene))-bis(3-carboxy pyridinium) dichloride), has been solvothermally synthesized. Complex 1 was characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, and thermogravimetric analysis. The structure of complex 1 consists of Eu–Cd heterometallic chains with one-dimensional channels. Complex 1 shows interesting excitation-dependent luminescence at room temperature. The gas adsorption studies show that complex 1 exhibits highly selective adsorption of CO2 over N2 and H2 under ambient conditions, which may be caused by the stronger interaction of CO2 with the positively charged pyridinium functional groups. In addition, the photocatalytic activity studies indicate that complex 1 shows good activity in rhodamine B dye degradation.

Non-Calcined Layer-Pillared Mn0.5Zn0.5 Bimetallic-Organic Framework as a Promising Electrocatalyst for Oxygen Evolution Reaction.

Electrocatalytic generation of oxygen is of great significance for sustainable, clean, and efficient energy production. Multiple electron transfer in oxygen evolution reaction (OER) and its slow kinetics represent a serious hedge for efficient water splitting, requiring the design and development of advanced electrocatalysts with porous structures, high surface areas, abundant electroactive sites, and low overpotentials. These requisites are common for metal-organic frameworks (MOFs) and derived materials that are promising electrocatalysts for OER. The present work reports on the synthesis and full characterization of a heteroleptic 3D MOF, [Zn2(μ4-odba)2(μ-bpdh)]n·nDMF (Zn-MUM-1), assembled from 4,4'-oxydibenzoic acid and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh). Besides, a series of heterometallic MnZn-MUM-1 frameworks (abbreviated as Mn0.5Zn0.5-MUM-1, Mn0.66Zn0.33-MUM-1, and Mn0.33Zn0.66-MUM-1) was also prepared, characterized, and used for the fabrication of working electrodes based on Ni foam (NF), followed by their exploration in OER. These noble-metal-free and robust electrocatalysts are stable and do not require pyrolysis or calcination while exhibiting better electrocatalytic performance than the parent Zn-MUM-1/NF electrode. The experimental results show that the Mn0.5Zn0.5-MUM-1/NF electrocatalyst features the best OER activity with a low overpotential (253 mV at 10 mA cm-2) and Tafel slope (73 mV dec-1) as well as significant stability after 72 h or 6000 cycles. These excellent results are explained by a synergic effect of two different metals present in the Mn-Zn MOF as well as improved charge and ion transfer, conductivity, and stability characteristics. The present study thus widens the application of heterometallic MOFs as prospective and highly efficient electrocatalysts for OER.

Heterometallic Metal-Organic Framework Based on [Cu4I4] and [Hf6O8] Clusters for Adsorption of Iodine.

Heterometallic metal-organic framework (MOF) as a kind of porous material is very important because of its excellent properties in catalysis, magnetic, sensor, and adsorption fields, but the reasonable design and syntheses of these are still challenging. Herein, we prepared one heterometallic MOF with the formula [Hf6(μ 3-OH)8(OH)8][(Cu4I4) (ina)4]2·22DMF (NS-1, ina = isonicotinate). Single-crystal X-ray diffraction analysis revealed that NS-1 is a three-dimensional network with flu topology, constructed from 8-connected [Hf6(μ 3-OH)8(OH)8]8+ and 4-connected [Cu4I4] clusters as second building units (SBUs). To our best knowledge, NS-1 is a rare example with two different metal clusters as SBUs in heterometallic Hf-based MOFs. Interestingly, NS-1 exhibits a reversible adsorption performance for iodine in the cyclohexane solution, the adsorption kinetics fits well with the pseudo-second-order equation, and the Freundlich model relating to multilayer adsorption better describes the process of iodine absorption.