LITERATURE REVIEW
Introduction of Metal-Organic Framework
Metal-organic frameworks (MOFs) are a significant category of porous crystalline materials formed by the combination of metal ions or metal-containing clusters, known as secondary building units (SBUs), with rigid organic linkers The geometry and connectivity of these organic linkers and metal clusters play a crucial role in determining the structure of the resulting MOFs.
In 1998, Omar Yaghi began exploring the potential of polytopic carboxylate-based bridging linkers, highlighting their ability to deprotonate for charge balance, which eliminates the need for extra-framework counterions These linkers can bind metals in various ways, similar to N-donor linkers One notable material, MOF‐2 (Zn(BDC)(H2O)), features Zn2(–COO)4(H2O)2 paddlewheel-like secondary building units and ditopic BDC linkers, resulting in a two-dimensional network with a Langmuir surface area ranging from 270 to 310 m²/g.
To date, more than 70,000 different MOFs being reported and studied (Figure
2) The organic units are ditopic or polytopic organic carboxylates which linked to metal-containing units, yield architecturally robust crystalline MOF structures with
Figure 1 Crystal structure of MOF ‐ 2 Color code: black, C; red, O; blue polyhedra, Zn
2 the surface area values typically range from 1000 to 10,000 m 2 /g, thus exceeding those of traditional porous materials such as zeolites and carbons 4
Figure 2 Growth of the CSD and MOF entries since 1972 The inset shows the MOF self-assembly process from building blocks: metals (red spheres) and organic linkers (blue struts) 4
1.1.1 Secondary Building Units (SBUs) and Topology
Metal-Organic Frameworks (MOFs) consist of two secondary building units (SBUs): the first is an organic linker that can be ditopic, tritopic, or polytopic, and the second is a metal atom or a polyatomic inorganic cluster containing two or more metal atoms These metal-containing SBUs can be generated in situ or predesigned by carefully selecting reaction conditions such as solvent system, temperature, molar concentration, and pH The components of MOFs are interconnected through coordination bonds, along with various weak interactions like pi-electron, hydrogen bonds, and Van der Waals forces.
3 der Waals interaction), which provide more flexibility to crystalline material and add to the usefulness of MOFs among porous materials
In the topological analysis of Metal-Organic Frameworks (MOFs), the shapes of inorganic secondary building units (SBUs) are characterized by their connectivity with organic linker SBUs, which can be represented as polyhedra, polygons, or infinite rods For instance, in MOF-5, the tetrazinc acetate cluster is simplified into an octahedral building unit featuring six points of extension, while the ditopic BDC linker acts as a connecting element Consequently, the overall topology of MOF-5 is identified as pcu, representing a simple cubic network with six-coordinated (6-c) vertices.
Figure 3 Examples of inorganic and organic SBUs 5
Figure 4 SBUs of MOF-5 Atom code: C, black; O, red; Zn, blue polyhedral Hydrogen atoms are omitted for clarity
The ultilization of approriate organic linkers and inorganic buiding units allows the chemists to design and target specific structures that display an interesting topology
1.1.2 Advantage Properties of Metal Organic Frameworks
High porosity: many MOFs possess surface area larger than 2000 m 2 /g, and some of them are remarkably higher than 5000 m 2 /g, such as NU-110 7 (7140 m 2 /g), MOF-
Large pore volume: many MOFs possess pore volume more than 1 cc/g, and some of them are larger than 2 cc/g, such as NU-110 (4.4 cc/g) 7 , UMCM-2 (2.32 cc/g) 10 , MOF-210 (3.60 cc/g) 8 , etc
Organic SBU Metal-Containg SBU
Metal organic framework pcu net
Figure 5 Crystal structures of highly porous MOFs 9
Control pore size: the size of pore is well defined ranging from microporous channel to mesoporous cage by enhancing the linker’s length
Plentiful supply of organic parts in MOFs makes post-synthesis modification possible
The discovery of numerous metal-organic frameworks (MOFs) has been driven by the modification of inorganic building units and organic linkers, leading to a significant increase in related publications As a result, the total number of MOFs is expected to surpass that of any other porous materials, offering an extensive array of candidates for diverse applications.
Designable the target structures: we can design and synthesize the target structures with the knowledge of topology, crystallography, and solid geometry
Due to these important advantages, MOFs have attracted much promise in a wide range of applications, including gas storage and separations 11 , heterogeneous catalysis 12 , conductivity 13 as well as water storage 14
Multitopic Carboxylate based Metal Organic Frameworks
1.2.1 Tetratopic Carboxylate Linker based MOFs
In MOF chemistry, tetratopic linkers featuring either a planar or tetrahedral branching point are commonly utilized Upon structural analysis, these tetratopic linkers can be interpreted as two 3-c branch points rather than a single 4-c branch point This approach allows for a clearer differentiation of potential derived nets that may exhibit identical symmetry while maintaining an understanding of the fundamental net structure.
From topological side, table 1 lists some basic nets and derived nets that can be obtained from tetratopic linkers and 4-c, 6-c, 8-c and 12-c inorganic SBUs
1.2.1.1 MOFs constructed from tetratopic linker and Lanthanide ions
The lanthanides, part of the f-block elements, predominantly form trivalent cations (Ln³⁺), which is their most stable oxidation state Their electronic configuration is typically represented as [Xe] 4fⁿ, where n ranges from 0 to 14 While trivalent states are common, some lanthanides, such as samarium, neodymium, and promethium, can also exist in +2 or +4 oxidation states due to their ability to achieve empty, half-filled, or fully-filled 4f shells.
Figure 6 The limiting shapes of tetratopic linker with one 4-c branch or two 3-c branch points
7 europium, thulium, and ytterbium can form stable divalent ions Moreover, cerium, praseodymium, dysprosium, and terbium can form stable tetravalent ions
Table 1 Some basic nets and derived nets from tetratopic linkers
Shapes of tetratopic linker Inorganic SBUs Basic Net Derived Net
4-c paddle wheel or other square SBUs nbo lvt cds ssa ssb fof, fog, tfb lil, lim gwg sty stj, stx, stu, stw
6-c stp soc ttp, ttx edq, cdj
8-c scu csq tty xly, xlz
Tetrahedral paddle wheel pts sur, tfk, dmd, tfi, pth phw, phx
Lanthanide metal ions possess larger ionic radii than first-row transition metal ions, leading to a high coordinative demand characterized by elevated coordination numbers and connectivity Consequently, lanthanide metal-organic frameworks (Ln-MOFs) exhibit a diverse range of stable three-dimensional structures and showcase a variety of intriguing properties Notably, the unsaturated Lewis acidic metal sites within Ln-MOFs offer potential for catalytic reactions.
The choice of linker system is important for the constitution of a framework structure as well as for its properties Lanthanide ion are hard and strong ionic
8 character Due to the high oxophilicity of lanthanides, carboxylate linkers are the by far the largest group of linkers
Metal-organic frameworks (MOFs) featuring lanthanide ions and tetracarboxylate linkers are uncommon, with one notable example being the (4,8)-connected networks that utilize the methylenediisophthalate (MDIP) linker In these structures, [Ln2(COO)8]2– units are interconnected via eight MDIP linkers, resulting in a three-dimensional open framework characterized by elliptical channels.
Figure 7 (A) [Ln 2 (COO) 8 ] 2 cluster, (B) The coordination modes of MDIP linker, (C) The framework of the compound is viewed along the [001] direction 19
1.2.1.2 Overview of MOFs constructed from Benzoimidephenanthroline tetracarboxylic acid (H 4 BIPA-TC)
The tetratopic linker, benzoimidephenanthroline tetracarboxylic acid (H4BIPA-TC), features a planar, π-acidic naphthalene core with diimide functionality that enhances π–π stacking interactions The naphthalene diimide (NDI) core exhibits high electron affinity, excellent charge carrier mobility, and remarkable thermal and oxidative stability, making NDI-based materials strong candidates for applications in organic electronics, photovoltaic devices, and flexible displays However, only a limited number of metal-organic frameworks (MOFs) have been developed using H4BIPA-TC.
TC linker (Table 2) and their applications were less studied
Table 2 Published MOFs from H 4 BIPA-TC (L) linker
Metals Linker MOFs Properties Ref
[M2(L)(MeOH)(H2O)4]n fcu like framework, trans-stilbene epoxidation
Ca [Ca2(L)(DMF)4].2DMF 7-connected {3 6 4 9 5 6 } net, reversible photochromic properties
Mg Mg–NDI selective organic amine (electron rich) sensing in solid state
1.2.2 Hexatopic Carboxylate Linker based MOFs
Hexatopic linkers used in metal-organic framework (MOF) synthesis typically exhibit highly symmetric geometries, including trigonal prismatic, octahedral, or planar hexagonal shapes The most commonly observed configuration for these linkers is a planar hexagon Nevertheless, a detailed analysis of the branching points in hexatopic linkers can reveal more complex and improved representations of their shapes within the resulting MOFs.
Hexatopic linker synthesis is generally a straightforward process, often utilizing a triangular-based core and employing Suzuki-coupling reactions, although these methods are not strictly required.
Figure 8 Some topologies and shapes for hexatopic linkers
From topological side, table 4 lists some basic nets and derived nets that can be obtained from hexatopic linkers and 4-c, 6-c inorganic SBUs
Currently, approximately thirty-two hexatopic carboxylic linker-based Metal-Organic Frameworks (MOFs) have been identified Certain MOFs in this category are easily expandable, resulting in structures that demonstrate exceptional porosity and distinctive pore systems, making them ideal for gas sorption applications.
The most interesting 3D frameworks from hexacarboxylate linkers are constructed by linking Cu2 or Zn2 paddle-wheel SBUs with essentially planar linkers 15, 26-28
Table 3 Some basic nets and derived nets from hexatopic linkers
Shapes of hexatopic linker Inorganic SBUs Basic Net Derived Net hexagon (6 branch)
The article discusses various geometric shapes, including the hexagon, triangular prism, and octahedron, alongside specific models like the 3-c SBU kgd paddle wheel and the hexagon (3 branch) paddle wheel It highlights the significance of these shapes in design and structure, emphasizing their applications in different contexts The text also mentions the paddle wheel's role in enhancing functionality and performance in various systems.
4-c SBU cor tfu soc hey toc tot
Zou et al introduced the compound Zn-TPBTM, synthesized through a solvothermal reaction involving the C3 symmetric facial linker H6TPBTM and Zn(NO3)2·6H2O in dimethylacetamide (DMA) This compound features a cuboctahedral structure composed of 24 isophthalate moieties and 12 dinuclear Zn2(COO)4 paddlewheel units, where the cuboctahedron serves as a 24-connected node The structure is further enhanced by the tritopic node from the linker, TPBTM, resulting in a (3,24-c) rht topology 3D network Additionally, when hexacarboxylate linkers are simplified to create 3-c vertices, while maintaining the paddlewheel centers as 4-c vertices, a trinodal (3,4)-c ntt net is formed This approach provides a clearer and more systematic understanding of the linker modifications and their structural implications.
The rht net features a diverse array of relative cavity sizes, characterized by the packing of three types of metal-organic polyhedra in a 1:2:1 ratio This includes a cuboctahedron (cub-Oh), a truncated tetrahedron (T-Td) composed of 4 TPBTM linkers and 12 Zn2(COO)4 units, and a truncated octahedron (T-Oh).
Figure 9 The representative hexatopic ligands used to construct porous MOFs
The Zn-TPBTM framework consists of 8 TPBTM linkers and 12 Zn2(COO)4 units, forming a highly porous structure In this arrangement, one truncated tetrahedron connects to four cuboctahedra, while a truncated octahedron links to six cuboctahedra by sharing their triangular and square windows However, the stability of the Zn-TPBTM framework is compromised upon the removal of methanol, resulting in a loss of crystallinity and transforming the desolvated sample into a nonporous material.
This strategy has led to the development of various isoreticular (3,24)-connected rht-type metal-organic frameworks (MOFs) that exhibit high surface areas and impressive gas storage capacities Notable examples include PMOFs, PCNs, NOTTs, NUs, rht-MOFs, and several others.
A novel hexatopic linker, 1',2',3',4',5',6'-hexa(4-carboxyphenyl)benzene (H6CPB), has been developed with a highly symmetrical, star-shaped structure This design features local C2 axes on the aryl faces that are oriented at 60° angles to each other, enhancing its symmetry properties.
The illustration depicts the connection between the hexagonal BHEHPI linker and the paddlewheel Cu(CO2)4, resulting in the formation of NU-110 with an ntt topology In the color-coded representation, zinc and copper are shown as blue polyhedra, while carbon, oxygen, and nitrogen atoms are represented in black, red, and blue, respectively For clarity, all hydrogen atoms, except those involved in hydrogen bonding, have been omitted from the diagram.
Post-Combustion Carbon Dioxide (CO 2 ) Separation in MOFs Chemistry
CO2 is a key greenhouse gas significantly contributing to global climate change, with its atmospheric concentration rising due to increased fossil fuel use for energy This highlights the urgent need for effective materials to remove CO2 from gas mixtures Metal-organic frameworks (MOFs) are promising candidates for CO2 separation, thanks to their highly porous and diverse structures MOFs can facilitate four main types of CO2 capture: post-combustion capture, pre-combustion capture, oxy-fuel combustion, and direct air capture.
1.3.1 MOFs for Post-Combustion CO 2 Separations
For post-combustion capture, the flue gas generated in current power plants is comprised of N2 (73–77 %), CO2 (15–16 %) and other minor components, such as
H2O, O2, CO, NOx, and SOx, with a total pressure of approximately 1 bar (Table 4) 58 After removal of the impurities, the partial pressure of CO2 is approximately 0.15 bar
(15 kPa) and the principal separation is CO2 form a N2-rich gas stream
Metal-organic frameworks (MOFs) designed for CO2 capture should demonstrate exceptional selectivity for CO2 compared to N2, possess high CO2 adsorption capacities, require minimal energy for regeneration, maintain long-term stability under operational conditions, and allow for rapid gas diffusion through the adsorbent material.
Table 4 Benchmark parameters showing typical compositions of gases (by weight) in postcombustion and the kinetic diameter of the gas molecules 58
Selectivity in separation processes is influenced by various factors, such as the molecular sieving effect, thermodynamic equilibrium, and kinetic effects In kinetic separation, the similar kinetic diameters of CO2 (3.30 Å) and N2 play a significant role.
Metal-organic frameworks (MOFs) with pore sizes around 3.64 Å may restrict gas diffusion, impacting their efficiency in gas separation In thermodynamic separation processes, the selectivity of adsorbents is influenced by chemical interactions between gas mixture components and the MOF's surface functionalities Notably, carbon dioxide (CO2) exhibits higher polarizability (29.1 × 10 –25 cm -3) and quadrupole moment (13.4 × 10 -40 Cãm 2) compared to nitrogen (N2), which has polarizability of 17.4 × 10 –25 cm -3 and quadrupole moment of 4.7 × 10 -40 Cãm 2 This disparity results in a greater affinity of MOFs for CO2, enhancing their effectiveness in selective gas adsorption.
1.3.2 Strategies to Improve the CO 2 /N 2 Selectivity
Enhancing selectivity can be achieved by optimizing pore sizes and modifying the chemical environment of framework components, including the metal sites—such as open metal sites and doped foreign metals—and the organic linkers, which feature uncoordinated nitrogen atoms and amine functionalities.
According to the size-selective mechanism, microporous MOFs with pore/window sizes in the range of 3–4 Å, which is close to the kinetic diameter of
CO2 molecules are promising candidates for selective capture at low pressures Research by Eddaoudi et al has focused on the ultra-microporous SIFSIX-3-M series (M = Zn, Cu, Ni), which features pyrazine linkers This series exhibits pore sizes ranging from 3.5 to 4 Å and a moderate surface area, yet demonstrates exceptional CO2/N2 selectivity under low-pressure conditions.
CO2 adsorption uptake can rapidly reach 2.3 mmol g -1 at 0.15 bar and 298 K 59
The pore size tuning of channel structures in SIFSIX materials reveals significant variations in their properties For SIFSIX-2-Cu-i, the pore size is 5.15 Å with a Brunauer–Emmett–Teller (BET) apparent surface area of 735 m²/g, determined through nitrogen adsorption In contrast, SIFSIX-3-Zn exhibits a smaller pore size of 3.84 Å and a BET surface area of 250 m²/g, as measured from CO₂ adsorption isotherms at 298 K Meanwhile, SIFSIX-3-Cu has an even smaller pore size of 3.50 Å, with a BET and Langmuir surface area of approximately 300 m²/g, also assessed via CO₂ adsorption at the same temperature.
To reduce the pore size of metal-organic frameworks (MOFs), modifying the linkers with suitable substituents is essential Huang et al synthesized UiO-66-(CH3)2 and evaluated its CO2 uptake in comparison to UiO-66 and other functionalized variants The UiO-66-(CH3)2 variant exhibited smaller pore sizes, approximately 4.2 Å, attributed to the presence of two methyl groups on its structure.
UiO-66-(CH3)2 demonstrates a significant enhancement in CO2 adsorption capacity and selectivity for CO2 over N2, attributed to the presence of 17 linkers and the stronger interactions between CO2 molecules and the framework, outperforming other UiO-66 materials.
At 1 bar, the amount of CO2 adsorbed in UiO-66-(CH3)2 reaches ca 130 cm 3 g −1 (25.6 wt%) at 273 K, which represents an enhancement of ∼33% compared with the non- modified UiO-66 60
One effective technique for minimizing pore sizes is through pore space partitioning, which entails anchoring metal ions or clusters at the centers of cages or channels Additionally, this method involves introducing functional groups to the metal sites within the frameworks.
Figure 12 presents the structural details of CPM-4, showcasing a 3D indium−BTC framework characterized by one-dimensional hexagonal channels aligned along the c axis The illustration includes both top and side views of a hexagonal channel, which features captured paddlewheel cobalt dimers.
Unsaturated open metal sites significantly enhance the gas separation properties of metal-organic frameworks (MOFs) due to their strong affinity for CO2, driven by dipole–quadrupole interactions A prominent example is the M-MOF-74 series, also known as M-CPO-27, which includes various metals such as Mg(II), Zn(II), Mn(II), Fe(II), and Ni(II) with the ligand 2,5-dioxidoterephthalate (2,5-DOT) Among these, Mg-MOF-74 exhibits the highest CO2 uptake capacity, reaching 37.8 wt%, marking a notable achievement in gas storage under standard conditions.
18 conditions (298 K and 1 bar) 65 The other isostructural analogues, such as Ni-MOF-
The CO2 adsorption capacity of Zn-MOF-74 and Co-MOF-74 is significantly lower, particularly at low pressures This reduced capacity can be attributed to the increased ionic character of the Mg-O bond, in addition to the presence of open metal sites Furthermore, the surface area and pore volume vary among MOFs with the same structure but different metal nodes Poloni et al conducted a theoretical study on two series of metal-organic frameworks (MOFs), specifically BTT and MOF-74, examining the effects of Ca, Mg, and nine divalent transition-metal cations.
Research indicates that Ti and V-based metal-organic frameworks (MOFs) exhibit the highest CO2 binding energy, unexpectedly reaching twice the anticipated value derived from pure electrostatic interactions The authors attribute this phenomenon to the unique electronic configuration of the divalent cations and the symmetry of the metal coordination site during CO2 binding.
The single crystal structure of Mg-MOF-74 is created through the reaction of the DOT linker with Mg(NO3)2·6H2O This structure features one-dimensional inorganic rods interconnected by DOT, resulting in linear hexagonal channels In the representation, carbon atoms are depicted in gray, oxygen atoms in red, six-coordinate magnesium atoms and terminal ligands in pink, while five-coordinate magnesium atoms are shown in blue For clarity, hydrogen atoms and terminal ligands in the top right fragment are omitted.
19 was proposed that a strong CO2 affnity with open metal sites could be expected when the σ* anti-bonding orbitals between the CO2 lone electron pair and metal d orbitals are empty 67
The lanthanide‐based MOFs were also prepared due to the high coordination value of La, which showed a high volumetric CO2 capacity of 44 cm 3 g -1 at 273 K and 1 bar 67
Catalytic Applications in MOFs Chemistry
Metal-organic frameworks (MOFs) serve as host materials that create reaction chambers, allowing substrates to interact and react effectively When selecting MOFs, it is essential to consider specific criteria and desirable properties to optimize their performance in various applications.
The framework must be robust enough to maintain its chemical and physical stability, structure and porosity
The MOF as a catalyst should be recyclable and show high turn over number, TON (number of cycles that one mole of catalyst can run through before if deactivates)
The guest and solvents molecules must be removed completely to generate the accessible active sites and void space
It is important to make sure and prove that the catalytic reaction takes place inside the porous material and not only on the outer surface The best way to
20 prove the interaction between catalytic site and substrate is by using single crystal X-ray diffraction (SCXRD)
The size of the particles affects the reaction rates The smaller the particles, the larger the accessible surfaces and thereby the higher catalytic activity and reaction rate
In MOFs, the metallic component, the organic linker, and the pore system play an important role as catalytically active sites 72
1.4.1.1 Catalysis at The Metal Nodes
Metal ions serve a crucial structural role as nodes in frameworks and exhibit notable catalytic activity in organic transformations, including cyanosilylation and Lewis acid-catalyzed reactions, as well as the oxidation of alcohols, thiols, and thioethers Transition metal metal-organic frameworks (MOFs), particularly copper (Cu) MOFs, have proven effective in catalyzing a diverse array of organic reactions.
Table 5 Cu-MOFs used for catalytic reaction 73
Cu(2-pymo)2] Aerobic oxidation of olefin
Cu(bpy)( H2O)2(BF4)2(bpy) Ring-opening of epoxide
Cu(D-asp)bpe0.5and Cu(L-asp)bpe0.5] Methanolysis of epoxide
(Cu(Ac)2(pbbm))CH3OH
Cu3(btc)2 Isomerization; cyclization; rearrangement
Oxidation of polyphenol Cyanosilylation of aldehyde
Cu2(papa)2Cl2 Biginelli reaction; 1,2-addition of a,b- unsaturated ketones
Cu3(pdtc)(pvba)2(H2O)3 Henry reaction
Three-component couplings of amines, aldehydes and alkynes
Cu(tcba)(DMA) Epoxidation of olefins
Cu2(bpdc)2(bpy) Cross-dehydrogenative coupling reaction
Cu2I2(bttp4) Three-component coupling of azides, alkynes, and amines Cu-MOF-SiF6 and Cu-MOF-NO3 Oxidation of benzylic compounds
The ketalization reactions of CuPhos-Br, CuPhos-Cl, and CuPhos-PF6 involve various ligands such as 2-hydroxypyrimidinolate (pymo), 4,4′-bipyridine (bpy), and D-aspartate (D-asp) Key components include trans-1,2-bis(4-pyridyl)ethylene (bpe), (4-formylphenoxy)acetic acid (L2), and 2-[2-[[(2-aminoethyl)imino]methyl]phenoxy]acetic acid (L3) Additional ligands like 1,1′-(1,5-pentanediyl)bis(1H-benzimidazole) (pbbm), benzene-1,3,5-tricarboxilate (btc), and (S)-3-hydroxy-2-((pyridin-4-ylmethyl)amino)propanoic (papa) play significant roles in the reactions Other important compounds include pyridine-2,3,5,6-tetracarboxylic acid (pdtc), 4,4′,4″-nitrilotris([1,10-biphenyl]-4-carboxylic) (tcba), (E)-4-(2-(pyridin-4-yl)vinyl)benzoic acid (pvba), biphenyldicarboxylate (bpdc), and benzene-1,3,5-triyl triisonicotinate (bttp4).
A highly crystalline Cu-MOF, specifically Cu3(BTC)2, was synthesized using an electrochemical method, resulting in a sky blue precipitate that was dried at 120 °C for 12 hours and activated at 200 °C for 2 hours This activation process altered the color from sky blue to dark blue, indicating a change in the coordination number of copper from six to four The high copper content, characterized by exposed open-structured copper in the paddle wheel structure of Cu3(BTC)2, plays a crucial role in the efficient conversion of p-nitrophenol to p-aminophenol, achieving a remarkable rate constant of 8.69 x 10 -2 s -1 for the reduction reaction.
Scheme 1 (A) Schematic representation of coordinated and decoordinated forms of water in
Cu 3 (btc) 2 ; (B) Reduction scheme of p-nitrophenol to p-aminophenol 74
Scheme 2 Functionalization of HKUST–1 with palladium complexes 75
Scheme 3 Postsynthetic cation exchange of UiO-66 76
Unsaturated sites can serve as effective grafting locations, as demonstrated by Arnanz et al., who created a bifunctional metal-organic framework (MOF) by integrating a palladium complex into aminopyridine compounds at the unsaturated sites of HKUST–1 This innovative catalyst facilitates the tandem Sonogashira/click reaction.
23 starting from 2-iodobenzylbromide, sodium azide and alkynes to produce 8H- [1,2,3]triazolo[5,1-a]isoindoles with good yields under mild reaction conditions 75
The post-synthetic exchange of metal clusters enables the creation of metal-organic frameworks (MOFs) that incorporate multiple metal centers, serving both as structural components and catalytic active sites Kim et al successfully synthesized the first titanium(IV) analogue of the robust UiO-66(Zr) framework through postsynthetic metal ion exchange.
1.4.1.2 Catalysis at The Organic Linker
The accessibility of functional groups on organic bridging linkers can be customized for specific applications in heterogeneous catalysis, where various organic functional groups act as active sites in the catalytic process.
Incorporating functional groups such as amino, pyridyl, and amide into solid catalysts can significantly enhance their activity A notable example is UiO-66-NH2, which has been successfully utilized as a solid catalyst in the Knoevenagel condensation of aromatic aldehydes with ethyl cyanoacetate and malononitrile, achieving over 90% conversion in the reaction.
Figure 14 UiO-66-NH 2 as bifunctional acid-base catalyst for Knoevenagel condensation 77
The mixed-linker MOFs (MIXMOFs) are versatile, introducing multifunctional features within one MOF Numerous studies have been carried out by varying two or more distinct functionalities in one MOF 78
For instance, a MIXMOF based on the [Cu3(BTC)2] was prepared in which the benzene-1,3,5-tricarboxylate (H3BTC) linkers have been partially replaced by 10,
20, 30, 40, 50, and 90 mol% pyridine-3,5- dicarboxylate (H2PyDC) 79 Both catalysts
The study demonstrated that 24 effectively catalyzed the hydroxylation of toluene in both acetonitrile and neat conditions, revealing distinct selectivity for the desired o- and p-cresol as well as other oxidation products Notably, [Cu3(BTC)2] and [Cu(BTC)0.5(PyDC)0.5] exhibited different selectivity profiles, influencing the formation of products such as benzaldehyde, benzyl alcohol, and methylbenzoquinone.
Figure 15 (Left) Illustration of replacing btc by pydc; (Right) Reaction scheme for the oxidation of toluene 79
1.4.2 MOFs as Heterogeneous Catalysts for The Oxidative Carboxylation of Olefins
The one-pot synthesis of cyclic carbonates from olefins and CO2, known as oxidative carboxylation, offers a cost-effective method by utilizing readily available olefins without the need for prior epoxide synthesis Despite its advantages, the reaction faces challenges such as low catalytic efficiency and the formation of side products, which hinder its broader application Currently, only a limited number of effective catalytic systems, including homogeneous rhodium salts and heterogeneous metal oxides like Nb2O5, MgO, Fe2O3, and V2O5, have been developed for this transformation, often in conjunction with O2.
CO2 gave quite low (17%–20%) carbonate selectivity under harsh reaction conditions
Scheme 4 Synthesis of cyclic carbonates through oxidative carboxylation of alkenes
Direct oxidative carboxylation combines alkene epoxidation with CO2 cycloaddition to the formed epoxide, necessitating compatible reaction conditions and catalysts for both steps Recent studies show that using tert-butyl hydroperoxide (TBHP) as an oxidant and tetrabutylammonium bromide (TBAB) as a carboxylation catalyst enhances carbonate selectivity to 42-43%, although it still requires high CO2 pressures ranging from 10 to 40 bar Additionally, Sun et al have proposed a detailed reaction mechanism for this process.
The process involves five key steps: first, the catalytic oxidation of bromide (Br-) using tert-butyl hydroperoxide (TBHP) generates hypobromite (OBr-) Next, in the presence of water, bromination of the olefin occurs, resulting in the formation of bromohydrin This is followed by a base-promoted dehydrobromination of the bromohydrin, which leads to the creation of an epoxide The subsequent step involves the ring opening of the epoxide through a nucleophilic attack by the bromide ion, yielding an oxy anion species Finally, carbon dioxide (CO2) attacks this species to produce the cyclic carbonate.
Scheme 5 A proposed mechanism for the direct synthesis of styrene carbonate from styrene and CO2 in TBAB with TBHP 123
Metal-Organic Frameworks (MOFs) are distinguished by their exceptional properties, including a high surface area, large pore sizes, and a significant density of accessible metal sites Their tunable pore sizes and functionalities enable them to effectively adsorb substantial quantities of gases.
Zalomaeva et al demonstrated that Cr-MIL-101 serves as an effective catalyst for the solvent-free cycloaddition of CO2 to epoxides, achieving high yields of styrene and propylene carbonates (95% and 82%, respectively) under mild conditions (8 bar CO2, 25 °C) with TBAB as a cocatalyst However, the inclusion of Cr-MIL-101 in the oxidative carboxylation of styrene led to an increase in the side product benzaldehyde, thereby decreasing carbonate selectivity Additionally, Han et al introduced a novel asymmetric auto-tandem epoxidation/cycloaddition reaction using chiral POMOFs, which effectively converts light olefins into valuable enantiomerically pure cyclic carbonates in a single-step process with high enantioselectivity.
1.4.3 MOFs as Lewis Acid Catalysts for the Friedel–Crafts Alkylation
The Friedel–Crafts reaction of aromatic compounds plays a crucial role in producing intermediates across various industries, including petroleum, pharmaceuticals, fragrances, flavors, dyes, and agrochemicals Traditionally, homogeneous Lewis acid catalysts like AlCl3, FeCl3, ZnCl2, and strong mineral acids such as HF have been utilized in these reactions However, to enhance catalyst recovery, recycling, and product separation, numerous solid acid catalysts have been explored Additionally, metal-organic frameworks (MOFs) such as Zn-MOF-5, Cu-MOF-74, Zr-MOF, and Fe-MOF have been investigated for their potential in these reactions.
Scope of This Dissertation
Metal-Organic Frameworks (MOFs) consist of two types of secondary building units (SBUs) The first SBU is the organic linker, which can be classified as ditopic (with two types of coordinating functionalities), tritopic (with three types), or polytopic (with more than three types).
SBU, or secondary building unit, refers to a metal atom or a polyatomic inorganic cluster composed of two or more metal atoms Recent advancements have led to the discovery of numerous metal-organic frameworks (MOFs) by altering the inorganic building units and organic linkers, resulting in a significant increase in related publications.
With over 70,000 structures, the extensive variety of Metal-Organic Frameworks (MOFs) surpasses that of any other porous materials, offering countless possibilities for diverse applications such as gas storage and separation, catalysis, and drug delivery.
Tetratopic and hexatopic linkers exhibit high coordination numbers and symmetry, making them ideal for developing new topological metal-organic frameworks (MOFs) that feature large surface areas, unique pore systems, and enhanced thermal and chemical stability Additionally, these linkers help prevent the formation of interpenetrated structures.
In this dissertaion, we have studied on the tetratopic linker, H4BIPA-TC and hexatopic linker, H6CPB as polytopic organic SBUs to contruct new topology MOFs
The obbject of this work is four-fold: (i) Ration design and synthesis of new MOFs,
(ii) Descriptions and comparisons of these structures Consequently, the homogeneous phase, chemical and thermal stability will be evaluated and detailed
(iii) The investigation of the relationship between the new structures and CO2 separation application, (iv) The investigation of catalytic acitivy of these new MOFs
EXPERIMENTAL
Materials and General Procedures
Lathanum (III) nitrate hydrate (La(NO3)3·xH2O, 99.9% trace metals basis), europium (III) nitrate pentahydrate (Eu(NO3)3·5H2O, 99.9%), and neodymium (III) nitrate hexahydrate (Nd(NO3)3·6H2O, 99.9%) are essential chemical compounds sourced from Sigma-Aldrich, alongside 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA) and glacial acetic acid (≥99.85%) Additional reagents include copper(I) iodide (CuI, ≥99.5%), 1,8-diazabicycloundec-7-ene (DBU, ≥99.0%), sodium hydroxide (NaOH, reagent grade, ≥98%), hydrochloric acid (HCl, 1 M), and copper(II) nitrate trihydrate (Cu(NO3)2·3H2O, >99%) Terbium (III) nitrate hydrate (Tb(NO3)3·xH2O, 99.9% REO) was procured from Alfa Aesar Other notable chemicals include 5-aminoisophthalic acid (≥98%), methyl-4-iodobenzoate (98%), bis(triphenylphosphine)palladium(II) chloride (PdCl2(PPh3)2, 98%), diethylamine (DEA, 99.5%), trimethylsilylacetylene (98%), dicobalt octacarbonyl (Co2(CO)8, 95%), 2,2'-bipyridine-5,5'-dicarboxylic acid (H2bpydc, 97%), and 2,5-dihydroxyterephthalic acid (H2DOT, 98%), along with N,N-dimethylacetamide (DMA, 99.8%).
High-purity solvents and reagents were sourced for the study, including anhydrous 1,4-dioxane, tetrahydrofuran (THF), dichloromethane (DCM), methanol (MeOH), ethanol (EtOH), and toluene, with purity levels exceeding 99.5% and 99.85%, respectively, all purchased from Acros Organics Additionally, cerium (III) nitrate hexahydrate with a purity of ≥98.5%, glacial acetic acid (≥99.8%), ammonium chloride, and anhydrous sodium sulfate were acquired from Merck Chemical.
Dimethylacetamide (DMA) was sourced from Fisher Chemical Co., while deuterated solvents such as CDCl3, DMSO-d6, and DCl (20% in D2O) were obtained from Cambridge Isotope Laboratories in Andover, MA, and utilized without additional purification Additionally, diethylamine and ultrapure deionized water, with a resistivity of 17.8 MΩ·cm, were employed in the experiments.
The chemicals obtained from a Barnstead Easypure II system were degassed with nitrogen for 5 minutes before being added to the Sonogashira coupling reactions All chemicals were utilized without additional purification unless specified.
H4BIPA-TC and H6CPB was prepared, with slight modifications, according to a previously reported procedure.(Appendix 1-12)
Indole (99%), benzaldehyde (99%), 4-methylbenzaldehyde (97%), 4- methoxybenzaldehyde (98%), 4-tert-butylbenzaldehyde (97%), 4-nitrobenzaldehyde (98%), 4-fluorobenzaldehyde (98%), 4-chlorobenzaldehyde (97%), 4- bromobenzaldehyde (99%), 3-fluorobenzaldehyde (97%), 3-bromobenzaldehyde (97%), 2-fluorobenzaldehyde (97%), 2-bromobenzaldehyde (98%), 4- imidazolecarboxaldehyde (98%), aluminum chloride hexahydrate (AlCl3ã6H2O ,
The article lists various high-purity chemicals and solvents sourced from reputable suppliers Key materials include iron(III) chloride (FeCl3, 97%), hafnium(IV) chloride (HfCl4, 99%), and copper(II) oxide (CuO, 98%), alongside oxides such as zinc oxide (ZnO, ≥99%) and titanium(IV) oxide (TiO2, ≥99%) Additionally, several anhydrous solvents are highlighted, including toluene (99.8%), methanol (99.8%), and acetonitrile (99.8%) Other notable compounds include styrene (99.5%), 5-nitroindole (98%), and copper(II) sulfate (CuSO4, 99%) The materials were primarily obtained from Sigma-Aldrich and Merck Chemical Co., ensuring high quality and reliability for various applications.
31 from Cambridge Isotope Laboratories (Andover, MA) and used without further purification
MOF-177 (Basolite Z377), ZIF-8 (Basolite Z1200), MIL-53(Al) (Basolite A100), and HKUST-1 (Basolite C300) were purchased from Sigma-Aldrich To yield guest-free material, HKUST-1, MOF-177, and ZIF-8 were activated under vacuum
(10 -3 Torr) and heated at 120 °C for 24 h MIL-53(Al) was immersed in anhydrous methanol (5 mL) for 1 day before activated under vacuum at ambient temperature for
12 h, followed by heating at 100 °C under vacuum for an additional 24 h
The synthesis of Mg-MOF-74 (Mg2(DOT)(H2O)2) involved preparing a solution of 4.5 mL DMF, 0.30 mL EtOH, and 0.30 mL H2O in an 8 mL vial containing 0.011 g of 2,5-dihydroxyterephthalic acid (H2DOT) and 0.047 g of Mg(NO3)2⋅6H2O This mixture was sonicated and heated at 120 °C for 48 hours, resulting in a yellow powder After decanting the mother liquor, the solid was washed with DMF (3 × 5 mL) daily for three days and subsequently immersed in anhydrous methanol (3 × 5 mL) daily for another three days The solvent-exchanged sample was activated under vacuum at room temperature for 12 hours, followed by heating at 150 °C under vacuum for 24 hours The structure and porosity of the synthesized material were confirmed through powder X-ray diffraction and N2 adsorption measurements.
The synthesis of single crystal UiO-67-bpydc (Zr6O4(OH)4(bpydc)6) was performed with slight modifications to an established method A 0.10 M stock solution of ZrCl4 in DMA (0.90 mL) was combined with 16 mg of H2bpydc in an 8 mL vial, followed by the addition of 0.85 mL of a 10 M benzoic acid solution in DMA and 2.25 mL of anhydrous DMF The mixture was sonicated and heated at 140 °C for three days, resulting in colorless octahedron-shaped single crystals The crystals were washed with DMF (3 × 5 mL) daily for three days and then immersed in anhydrous methanol (3 × 5 mL) daily for an additional three days.
The exchanged sample underwent activation in a vacuum at room temperature for 12 hours, followed by a 24-hour heating period at 120 °C under vacuum The structural integrity and porosity of the sample were validated through powder X-ray diffraction and N2 adsorption measurements conducted at 77 K.
The synthesis of Nd-BDC, specifically Nd2(BDC)3(DMF)3·H2O, was performed with slight modifications to a previously established method An 8 mL vial was prepared with a solution containing 2.5 mL DMF, 0.50 mL ethanol, and 0.50 mL water, along with 4.0 mg of H2BDC and 10.9 mg of Nd(NO3)3·6H2O The mixture was sonicated and heated at 85 °C for 48 hours, resulting in a violet crystalline powder After decanting the mother liquor, the solid was washed with DMF (3 × 5 mL) over three days, followed by immersion in anhydrous ethanol (3 × 5 mL) for an additional three days The solvent-exchanged sample was then activated under vacuum at 50 °C for 24 hours, with its structure and porosity confirmed by powder X-ray diffraction.
Powder X-ray diffraction (PXRD) patterns were obtained using a Bruker D8 Advance diffractometer with Ni-filtered Cu Kα radiation (λ = 1.54178 Å), operating at 40 kV and 40 mA (1,600 W) at the Inomar Center, VNU-HCM The system included an anti-scattering shield to prevent diffuse radiation from affecting the detector Metal-organic framework (MOF) samples were placed on zero background holders and flattened with a spatula PXRD measurements were performed over a 2θ range of 3 to 50°, with a step size of 0.02° and a fixed count time of 1 second per step.
Optical microscope images were obtained using a Nikon SMZ1000 Zoom Stereomicroscope at the Inomar Center, VNU-HCM Elemental microanalyses (EA) for MOF-891 were conducted at UC Berkeley's Microanalytical Laboratory with a Perkin Elmer 2400 Series II CHNS elemental analyzer, while the EAs for MOF-588, -589, -590, -591, -592, and -894 were performed at the Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) utilizing a LECO CHNS-932 Additionally, Fourier Transform Infrared (FT-IR) spectra were collected at the Inomar Center.
The analysis was conducted at the Inomar Center, VNU-HCM, using a Bruker Vertex 70 spectrometer, where samples were well-dispersed in KBr pellets The output signals were categorized as very strong (vs), strong (s), medium (m), shoulder (sh), weak (w), very weak (vw), or broad (br) Additionally, thermal gravimetric analysis (TGA) was performed on a TA Q500 thermal analysis system, with samples placed in a platinum pan and subjected to a continuous flow of air.
Low-pressure adsorption isotherms for N2, CO2, and CH4 were obtained using a Micromeritics 3Flex, with helium utilized to estimate dead space Measurements at 77 K were conducted in a liquid nitrogen bath, while temperatures of 273, 283, and 298 K were achieved using a circulating ethylene glycol/water bath (1/1, v/v) Breakthrough measurements were carried out with an L&C Science and Technology PSA-300-LC Analyzer, featuring a bed column measuring 14 × 0.635 cm (length × inner diameter) The system was equipped with a ThermoStar GSD320 mass spectrometer to monitor CO2 and N2 levels.
H2O, and O2 from the gaseous effluent goes through the sample bed Ultrahigh purity grade N2, CH4, and He gases (99.999% purity) and high purity grade CO2 (99.995%) were used for all sorption experiments
1H and 13C nuclear magnetic resonance (NMR) spectra were recorded using a Bruker Advance II 500 MHz spectrometer at the University of Science, VNU-HCM, with chemical shifts expressed in parts per million (ppm) relative to the solvent peak or tetramethylsilane (TMS) at 0 ppm Peak patterns were denoted as singlet (s) or doublet (d), and coupling constants (J) were measured in Hertz (Hz) High-resolution electrospray-ionization mass spectrometry (HR-ESI-MS) was performed in negative ionization mode on an Agilent 1200 Series high-performance liquid chromatography system coupled with a Bruker micrOTOF-QII mass spectrometer Additionally, gas chromatography (GC) analyses were conducted using an Agilent GC System 19091s-433: 93.92873 equipped with a mass selective detector (Agilent 5973N) and a capillary HP-5MS 5% Phenyl Methyl Silox column (30 m × 250 µm × 0.25 µm) to assess the products of the catalytic reaction, focusing on conversion and selectivity.
Catalytic reaction yields were analyzed using an Agilent GC System 123-0132, featuring a flame ionization detector (FID) and a capillary DB-1ms column (30 m × 320 µm × 0.25 µm), with biphenyl as the internal standard The GC program commenced at 50 °C for 1 minute, ramped at 15 °C/min to 300 °C, and held for 20 minutes, with an injection volume of 0.5 µL, a split ratio of 50:1, a solvent delay of 3 minutes, and a mass range of 80-500 amu Ultrasonic irradiation was conducted using an Elma S30H Ultrasonic cleaning unit, operating at a frequency of 37 kHz, with a nominal power of 280 W and an output of 80 W Additionally, inductively coupled plasma mass spectroscopy (ICP-MS) data was obtained using an Agilent ICP-MS 7700x at the University of Science, VNU-HCM, while field-emission scanning electron microscopy (FE-SEM) was performed with a Hitachi S-4800 FE-SEM, utilizing ultralow voltage imaging at an accelerating voltage of 1 kV.
Synthesis of MOFs
2.2.1 Synthesis of tetratopic linker based MOFs: MOF-588, MOF-589, MOF-
A 0.01 M stock solution of lanthanum (III) nitrate hydrate was prepared in deionized water and added to an 8 mL vial, followed by the addition of 1 mL of 0.01 M H4BIPA-TC in DMA, 1 mL of deionized water, and 400 µL of CH3COOH The mixture was sonicated and heated at 120 °C for 15 hours, then filtered to obtain yellow rectangular flat-shaped crystals The synthesized sample was washed with DMF for three days and then immersed in anhydrous ethanol, exchanging the solvent three times daily over three days After decanting the solvent, it was removed under vacuum for 24 hours, followed by annealing at 60 °C for 24 hours to produce the activated sample Elemental analysis was conducted for the activated sample, calculated for LaC30H19N2O16 = [La(HBIPA-TC)(DMA)(H2O)3]·2H2O.
C, 45.00; H, 3.33; N, 4.63 Found: C, 45.41; H, 2.89; N, 4.13 FT-IR (KBr, 4000–400 cm -1 ):
3425 (s, br), 1714 (s), 1678 (vs), 1618 (s), 1578 (s), 1552 (w), 1447 (m), 1417 (vw), 1388 (m), 1350 (vs, sh), 1256 (s, sh), 1199 (w), 1120 (w).
A 0.01 M stock solution of cerium (III) nitrate hexahydrate in deionized water (1 mL) was added to an 8 mL vial This was followed by the addition of 1 mL solution H4BIPA-
To synthesize MOF-589, a mixture of TC in DMA (0.01 M), 1 mL of deionized water, and 300 μL of CH3COOH was heated at 120 °C for 15 hours, followed by filtration to obtain yellow block crystals The as-synthesized sample was washed with DMF (3 × 10 mL) over three days and then immersed in anhydrous ethanol, exchanging the solvent three times daily for three days After decanting the solvent, it was removed under vacuum at ambient temperature for 24 hours, followed by annealing at 60 °C for 24 hours to produce the activated sample Elemental analysis of the activated sample, calculated for CeC30H19N2O16 = [Ce(HBIPA-TC)(H2O)3]·H2O, showed C at 44.84%, H at 2.38%, and N at 3.49%, with found values of C at 45.56%, H at 2.36%, and N at 3.49% FT-IR analysis was conducted in the range of 4000–400 cm⁻¹.
3431 (s, br), 1714 (s), 1678 (vs), 1619 (s), 1579 (s), 1553 (w), 1447 (m), 1418 (vw), 1389 (m), 1350 (vs, sh), 1256 (s, sh), 1199 (w), 1120 (w).
A 0.04 M stock solution of Nd(NO3)3·6H2O was prepared and added to a tube, followed by the addition of 1 mL of 0.04 M H4BIPA-TC in DMA, 4 mL of deionized water, and 100 µL of CH3COOH The mixture was sealed, sonicated for 30 minutes, and heated at 120°C for three days, after which the hot solution was filtered to obtain yellow block crystals of MOF-590 The as-synthesized sample underwent washing with DMA for three days, followed by immersion in anhydrous ethanol, with solvent exchange three times daily over three days After decanting the solvent, it was removed under vacuum at ambient temperature for 24 hours, and the sample was subsequently annealed at 120°C for 24 hours to yield the activated sample Elemental analysis of the activated sample indicated a composition of Nd2C45H30.5N3O25.
= [Nd2(BIPA-TC)1.5]ã7H2O: C, 41.52; H, 2.36; N, 3.23 Found: C, 41.26; H, 2.84; N, 3.52 FT-IR (KBr, 4000–400 cm -1 ): 3430 (s, br), 1715 (s), 1678 (vs), 1620 (s), 1548 (s), 1451 (m),
A 0.043 M stock solution of Europium (III) nitrate pentahydrate in deionized water (0.6 mL) was added to a 4 mL vial, which preloaded with H4BIPA-TC (15 mg, 0.025 mmol)
This was followed by the addition of DMF (1 mL), deionized water (0.2 mL) and CH3COOH
A reaction mixture of 250 µL was sonicated and heated at 100 °C for 24 hours, followed by filtration to obtain yellow block crystals of Eu-imide-MOF The synthesized sample was washed with DMF (3 × 10 mL) over three days and then immersed in anhydrous ethanol, with exchanges occurring three times daily for an additional three days After decanting the solvent, it was removed under vacuum at ambient temperature for 24 hours, followed by annealing at 50 °C for 24 hours to yield the activated sample Elemental analysis of the activated sample revealed the following composition: C, 45.83; H, 3.39; N, 4.44, closely matching the calculated values of C, 45.84; H, 3.29; N, 4.45 for EuC48H41N4O27 [Eu(H2BIPA-TC)1.5]·8H2O·DMF FT-IR analysis showed characteristic peaks at 3428 (s, br), 1713 (s), 1676 (vs), 1615 (s), 1577 (s), 1451 (m), 1389 (m), 1349 (vs, sh), 1295 (s, sh), 1196 (w), and 1120 (w) cm⁻¹.
A 0.08 M stock solution of Terbium (III) nitrate hydrate was prepared by adding 0.6 mL to a 4 mL vial containing 15 mg (0.025 mmol) of H4BIPA-TC Subsequently, 1 mL of DMF, 0.2 mL of deionized water, and 200 µL of acetic acid (CH3COOH) were added to the mixture.
The reaction mixture was sonicated and heated to 100 °C for 24 hours, resulting in the formation of yellow block crystals of MOF-592, which were filtered from the hot solution The as-synthesized sample underwent a thorough washing with DMF over three days, followed by immersion in anhydrous ethanol, with solvent exchanges occurring three times daily for an additional three days After decanting the solvent, the sample was subjected to vacuum removal at ambient temperature for 24 hours, followed by annealing at 50 °C for another 24 hours to obtain the activated sample Elemental analysis of the activated sample revealed values close to the calculated percentages for TbC48H35N4O24 [Tb(H2BIPA-TC)1.5]·5H2O·DMF, with carbon, hydrogen, and nitrogen found to be 47.28%, 3.21%, and 4.60%, respectively FT-IR analysis indicated significant absorption peaks at 3425, 1712, 1677, 1615, 1578, 1450, 1384, 1349, 1252, 1199, and 1120 cm⁻¹.
2.2.2 Synthesis of hexatopic linker based MOFs: MOF-891 and MOF-894 2.2.2.1 Synthesis of MOF-891
A 0.02 M stock solution of copper nitrate trihydrate (0.5 mL) was combined with 20 mg (0.025 mmol) of H6CPB in an 8 mL vial, followed by the addition of 3 mL of deionized water The mixture was heated at 85 °C for 16 hours, resulting in the formation of blue, block-shaped crystals.
The crystals were washed with DMF (3 × 10 mL) daily for three days to ensure purity To achieve guest-free material, the DMF-washed MOF-891 was subsequently immersed in methanol (3 × 10 mL) each day for four days The solvent-exchanged sample underwent activation under vacuum at ambient temperature for 24 hours, followed by heating at 180 °C under vacuum for an additional 24 hours Elemental analysis revealed that the calculated values for [Cu3(CPB)(DEF)0.4]∙3.8H2O were C, 54.98; H, 3.32; N, 0.51%, while the found values were C, 54.67; H, 2.97.
N,