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.

3D vs. turbostratic: controlling metal-organic framework dimensionality via N-heterocyclic carbene chemistry

Using azolium-based ligands for the construction of metal-organic frameworks (MOFs) is a viable strategy to immobilize catalytically active N-heterocyclic carbenes (NHC) or NHC-derived species inside MOF pores. Thus, in the present work, a novel copper MOF referred to as Cu-Sp5-BF4, is constructed using an imidazolinium ligand, H2Sp5-BF4, 1,3-bis(4-carboxyphenyl)-4,5-dihydro-1H-imidazole-3-ium tetrafluoroborate. The resulting framework, which offers large pore apertures, enables the post-synthetic modification of the C2 carbon on the ligand backbone with methoxide units. A combination of X-ray diffraction (XRD), solid-state nuclear magnetic resonance (ssNMR) and electron microscopy (EM), are used to show that the post-synthetic methoxide modification alters the dimensionality of the material, forming a turbostratic phase, an event that further improves the accessibility of the NHC sites promoting a second modification step that is carried out via grafting iridium to the NHC. A combination of X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) methods are used to shed light on the iridium speciation, and the catalytic activity of the Ir-NHC containing MOF is demonstrated using a model reaction, stilbene hydrogenation.

Selective N-Alkylation of Amines with DMC over Biogenic Cu-Zr Bimetallic Nanoparticles

Herein, we report the green synthesis of copper-zirconium bimetallic nanoparticles (Cu-Zr BNPs) from aqueous solutions using Azadirachta indica leaf extract as a reducing and stabilizing agent. The CuO, ZrO2 NP, and Cu-Zr BNP samples were characterized by X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy, and the morphologies of the samples were analyzed by high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction analysis (SAED). The synthesized Cu-Zr BNPs have been employed as efficient catalysts for the selective N-methylation of aromatic and aliphatic amines with dimethyl carbonate. The effect of process conditions on the percentage conversion of benzylamine with dimethyl carbonate as a model reaction has been investigated. The Cu-Zr bimetallic nanoparticle catalytic system in a 1:2 molar ratio was able to convert amines into the corresponding N-methylated amines with a selectivity up to 91% at 180 °C in 4 h. The analysis of catalytic reusability confirmed that the reported heterogeneous catalyst can be used for five consecutive cycles without much loss in activity. Thus, the current protocol can be considered as a simpler, reproducible, and environmentally benign approach for N-methylation of amines.

Cyclometalation of lanthanum(iii) based MOF for catalytic hydrogenation of carbon dioxide to formate

The hydrogenation of carbon dioxide (CO2) to formic acid is of great importance due to its useful properties in the chemical industry. In this work, we have prepared a novel metal-organic framework (MOF), JMS-1, using bipyridyl dicarboxylate linkers, with molecular formula [La2(bpdc)3(DMF)3] n . Network analysis of JMS-1 revealed a new 7-connected topology (zaz). The MOF backbone of the activated phase (JMS-1a) was functionalized by cyclometalation using [RuCl2(p-cymene)]2 to produce Ru(ii)@JMS-1a. Both JMS-1a and Ru(ii)@JMS-1a were able to convert CO2 in the presence of hydrogen to formate. Ru(ii)@JMS-1a displayed outstanding conversion evidenced by a yield of 98% of formate under optimized conditions of total pressure 50 bar (CO2/H2 = 1 : 4, temperature 110 °C, time 24 h, 5 mmol KOH, 8 mL ethanol). This work is significant in providing new strategies of incorporating active catalytic centres in MOFs for efficient and selective conversion of CO2 to formate.

Syntheses, structural diversity and photocatalytic properties of three coordination polymers assembled by different N-heterocyclic ligands

The diversity of ligands and central metal ions plays an important role not only in coordination modes and final products but also in their photocatalytic activities.

Two Chemically Stable Cd(II) Polymers as Fluorescent Sensor and Photocatalyst for Aromatic Dyes

Two new 2D Cd(II)-based coordination polymers (CPs), viz. [Cd₂(H₂L)₂(2,2'-bipy)₂] (1) and [Cd(L)0.5(phen)·0.5H₂O] (2), have been constructed using ethylene glycol ether bridging tetracarboxylate ligand 5,5'(4,4'-phenylenebis(methyleneoxy)) diisophthalic acid (H₄L). Both CPs behaved as profound fluorescent sensor for Fe3+ ion and nitro-aromatics (NACs), specifically 2,4,6-trinitrophenol (TNP). The stability at elevated temperature and photocatalytic behaviors of both 1 and 2 for photo-decomposition of aromatic dyes have also been explored. An attempt has been made to explore the plausible mechanism related with the decrease in fluorescence intensity of 1 and 2 in presence of NACs using theoretical calculations. Additionally, the probable mechanism of photo catalysis by 1 and 2 to photo-degrade aromatic dyes has been explained using density of states (DOS) calculations.

A metal–organic framework based multifunctional catalytic platform for organic transformation and environmental remediation

Given the need for an efficient reaction platform, a multifunctional material has been developed through the integration of iodine into a Cd²⁺ based MOF as a new catalytic system for organic transformation.

Ethylene oligomerization in metal–organic frameworks bearing nickel(ii) 2,2′-bipyridine complexes

The metal–organic frameworks Zr₆O₄(OH)₄(bpydc)₆ (1; bpydc²⁻ = 2,2′-bipyridine-5,5′-dicarboxylate) and Zr₆O₄(OH)₄(bpydc)_0.84(bpdc)_5.16 (2; bpdc²⁻ = biphenyl-4,4′-dicarboxylate) were readily metalated with Ni(DME)Br₂ (DME = dimethoxyethane) to produce the corresponding metalated frameworks 1(NiBr₂)₆ and 2(NiBr₂)_0.84. Both nickel(ii)-containing frameworks catalyze the oligomerization of ethylene in the presence of Et₂AlCl. In these systems, the pore environment around the active nickel sites significantly influences their selectivity for formation of oligomers over polymer. Specifically, the single-crystal structure of 1(NiBr₂)_5.64 reveals that surrounding metal–linker complexes enforce a steric environment on each nickel site that causes polymer formation to become favorable. Minimizing this steric congestion by isolating the nickel(ii) bipyridine complexes in the mixed-linker framework 2(NiBr₂)_0.84 markedly improves both the catalytic activity and selectivity for oligomers. Furthermore, both frameworks give product mixtures that are enriched in shorter olefins (C_4–10), leading to deviations from the expected Schulz–Flory distribution of oligomers. Although these deviations indicate possible pore confinement effects on selectivity, control experiments using the nickel-treated biphenyl framework Zr₆O₄(OH)₄(bpdc)₆(NiBr₂)_0.14 (3(NiBr₂)_0.14) reveal that they likely arise at least in part from the presence of nickel species that are not ligated by bipyridine within 1(NiBr₂)_5.64 and 2(NiBr₂)_0.84.

Design and synthesis of coordination polymers with chelated units and their application in nanomaterials science

The advances and problems associated with the preparation, properties and structure of coordination polymers with chelated units are presented and assessed.

Cluster-based MOFs with accelerated chemical conversion of CO2 through C–C bond formation

We report here two cluster-based MOFs I and II as excellent heterogeneous catalysts in the carboxylation reactions of CO₂ and terminal alkynes under 1 atm and mild conditions. This is the first time for MOFs materials to catalyze this type of reactions.

Syntheses, structural diversity and photocatalytic properties of various Co(ii) coordination polymers based on a “V”-shaped 1,3-di(4′-carboxyl-phenyl)benzene acid and different imidazole bridging ligands

Various polymeric structures of complexes 1–4.

Synthesis, structure, and magnetic and catalytic properties of metal frameworks with 2,2′-dinitro-4,4′-biphenyldicarboxylate and imidazole-containing tripodal ligands

Four new MOFs with mixed ligands were successfully synthesized, and their magnetic, adsorption and catalytic properties were investigated.

Design of amine-functionalized metal–organic frameworks for CO2 separation: the more amine, the better?

A total of 41 825 metal–organic frameworks (MOFs) were computationally screened toward the design of amine-functionalized MOFs for CO₂ separation.

Single-crystal-to-single-crystal metalation of a metal-organic framework: a route toward structurally well-defined catalysts

Metal-organic frameworks featuring ligands with open chelating groups are versatile platforms for the preparation of a diverse set of heterogeneous catalysts through postsynthetic metalation. The crystalline nature of these materials allows them to be characterized via X-ray diffraction, which provides valuable insight into the structure of the metal sites that facilitate catalysis. A highly porous and thermally robust zirconium-based metal-organic framework, Zr6O4(OH)4(bpydc)6 (bpydc(2-) = 2,2'-bipyridne-5,5'-dicarboxylate), bears open bipyridine sites that readily react with a variety of solution- and gas-phase metal sources to form the corresponding metalated frameworks. Remarkably, Zr6O4(OH)4(bpydc)6 undergoes a single-crystal-to-single-crystal transformation upon metalation that involves a change in space group from Fm3̅m to Pa3̅. This structural transformation leads to an ordering of the metalated linkers within the framework, allowing structural characterization of the resulting metal complexes. Furthermore, Zr6O4(OH)4(bpydc)6 yields an active heterogeneous catalyst for arene C-H borylation when metalated with [Ir(COD)2]BF4 (COD = 1,5-cyclooctadiene). These results highlight the unique potential of metal-organic frameworks as a class of heterogeneous catalysts that allow unparalleled structural characterization and control over their active sites.

Assembly of a series of d10 coordination polymers based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene: from syntheses, structural diversity, luminescence, to photocatalytic properties

Six d¹⁰ coordination polymers with different architectures based on W-shaped 1,3-di(2′,4′-dicarboxyphenyl)benzene (H₄DDB) have been prepared. Their photoluminescence and photocatalytic properties were also investigated.

Crystal engineering, structure–function relationships, and the future of metal–organic frameworks

After twenty years of vigorous R&D, where are MOFs headed?

Functionalising metal–organic frameworks with metal complexes: the role of structural dynamics

The impact of dynamics in the functionalisation of metal–organic framework UiO-67 with an Ir-complex has been studied. Highly functionalised Ir-UiO-67 can be only trapped as kinetic products, which lose metals and exchange species to gain stability.

Structural diversity and magnetic properties of six metal–organic polymers based on semirigid tricarboxylate ligand of 3,5-bi(4-carboxyphenoxy)benzoic acid

Six new metal–organic complexes with structural diversities constructed from 3,5-bi(4-carboxyphenoxy)benzoic acid and metal ions were synthesized and characterized.

Structures and properties of coordination polymers involving asymmetric biphenyl-3,2′,5′-tricarboxylate

The conformation stability and coordination modes of an asymmetric polycarboxylate ligand (H₃bptc) and the properties of its compounds have been investigated.

A 3-D diamondoid MOF catalyst based on in situ generated [Cu(L)2] N-heterocyclic carbene (NHC) linkers: hydroboration of CO2

A new MOF, [Zn₄O{Cu(L)₂}₂], with 14 Å channels lined by in situ generated [Cu(L)₂] N-heterocyclic carbene linkers catalyses the hydroboration of CO₂.

Syntheses, structures, and properties of a series of 2D and 3D coordination polymers based on trifunctional pyridinedicarboxylate and different (bis)imidazole bridging ligands

Hydrothermal reactions based on two trifunctional pyridinedicarboxylate carboxylates and transitional metal cations in the presence of three (bis)imidazole bridging ligands afford ten 2D and 3D coordination polymers.

Syntheses, structures, and luminescence properties of four metal–organic polymers with undocumented topologies constructed from 3,5-bis((4′-carboxylbenzyl)oxy)benzoate ligand

Four 3D metal–organic polymers with new topologies based on 3,5-bis((4′-carboxylbenzyl)oxy)benzoic acid were synthesized and characterized.

Post-synthetic metalation of metal–organic frameworks

Post-synthetic metalation (PSMet) offers expansive scope for a targeted approach to tailoring the properties of MOFs.

Syntheses, structures, and magnetic properties of six coordination polymers based on 4,5-di(4′-carboxylphenyl)phthalic acid and different bis(imidazole) bridging linkers

Six multi-dimensional metal–organic polymers based on 4,5-di(4′-carboxylphenyl)phthalic acid and bis(imidazole) bridging linkers were synthesized and characterized.

Syntheses, topologies, and luminescence of four Ln–organic polymers constructed from aromatic tetracarboxylic acids

Four interesting Ln coordination polymers based on tetracarboxylate acids have been hydrothermally synthesized through the linker extension strategy.

Rare-earth carboxylates, [Ln2(iii)(μ3-OH)(C4H4O5)2(C4H2O4)]·2H2O [Ln = Ce, Pr and Nd]: synthesis, structure and properties

Three new three-dimensional hybrid compounds, Ln₂(μ₃-OH)(C₄H₄O₅)₂(C₄H₂O₄)]·2H₂O, (Ln = Ce, Pr and Nd) (I²O¹-type) exhibiting proton conductivity and multi-photon up-conversion behaviour have been described.

Syntheses, structures, and magnetic properties of five coordination polymers constructed from biphenyl-3,4′,5-tricarboxylic acid and (bis)imidazole linkers

Five coordination polymers (CPs) based on biphenyl-3,4′,5-tricarboxylic acid and bis(imdizole) bridging linkers were synthesized under hydrothermal conditions.