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. 2022 Jul 11;61(29):11084–11094. doi: 10.1021/acs.inorgchem.2c00825

Synthesis, Structure, and Thermal Stability of a Mesoporous Titanium(III) Amine-Containing MOF

Timothy Steenhaut 1,*, Séraphin Lacour 1, Gabriella Barozzino-Consiglio 1, Koen Robeyns 1, Robin Crits 1, Sophie Hermans 1,*, Yaroslav Filinchuk 1,*
PMCID: PMC9328077  PMID: 35817416

Abstract

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The first mesoporous bimetallic TiIII/Al metal–organic framework (MOF) containing amine functionalities on its linkers has been selectively obtained by converting the cheap commercially available (TiCl3)3AlCl3 into Ti3–xAlxCl3(THF)3 and reacting this complex with 2-aminoterephthalic acid in dimethylformamide (DMF) under soft solvothermal conditions. This compound is structurally related to the previously described NH2-MIL-101(M) (M = Cr, Al, and Fe) MOFs. Thermal gravimetric analyses and in situ powder X-ray diffraction (PXRD) measurements demonstrated that this highly air-sensitive TiIII-containing MOF is structurally stable up to 200 °C. Nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and inductively coupled plasma (ICP) revealed that NH2-MIL-101(TiIII) contains trinuclear Ti3(μ3-O)Cl(DMF)2(RCOO)6 clusters with strongly bound DMF molecules and a small amount of aluminum. Sorption experiments revealed a higher affinity of this MOF for hydrogen compared to the previously described monometallic unfunctionalized MIL-101(TiIII) MOF.

Short abstract

A new mesoporous TiIII-based MOF containing amine functions on its linkers, NH2-MIL-101(Ti), has been selectively synthesized in a reproducible manner. This MOF is isostructural to its previously reported Cr, Fe, and Al analogues. Its thermal stability has been assessed through variable-temperature X-ray diffraction, and the local structure around the clusters has been determined by a combination of elemental analysis and NMR spectroscopy. NH2-MIL-101(Ti) possesses a slightly improved affinity for H2 compared to MIL-101(Ti).

Introduction

Metal–organic frameworks, also known as MOFs, are well-established materials with currently more than 90,000 experimentally obtained structures and more than 500,000 predicted ones.1 The most interesting feature of such compounds, formed by the interconnection of metal centers or clusters through organic bridging linkers,2 is that they can possess permanent porosity, enabling many applications in adsorption, separation, and catalysis, among others.3−7

Amidst the vast variety of existing MOFs, the ones with the so-called MTN topology are particularly interesting. The topology of these frameworks is derived from that of the zeolite Socony Mobil Thirthy-Nine (ZSM-39)8 and consists of an assembly of two types of large interconnected mesopores that are accessible through hexagonal and pentagonal windows (Figure 1A,B). The vast majority of these MOFs (although a few exceptions are known)9 are built from trinuclear M3-μ3-oxo clusters bearing six carboxylate functions from the organic linkers and additional anions (F–, OH–, Cl–, etc.) for charge balancing when needed, together with solvent molecules to complete the coordination spheres of the metal centers (Figure 1C). The linkers interconnect four metal cluster units to form microporous supertetrahedra of which they form either edges or faces, depending on whether they are ditopic or tritopic (i.e., linkers having two or three carboxylate functions, respectively).10 The most representative members of this series of MOFs are MIL-101(M) and MIL-100(M), built respectively from terephthalate (BDC2–) or trimesate (BTC3–) linkers (Figure 1D,E) and contain chromium,11,12 iron,13,14 or aluminum15−17 as metal centers. Several reports also mention the use of vanadium,18,19 indium,20 manganese,21 scandium,22 or, more recently, titanium(IV)23 or a combination of several metals (e.g., Ni2+, Co2+, Zn2+, or even lanthanides)24−26 for the construction of such frameworks. However, there are very few reports on MTN MOFs containing titanium in the +III oxidation state27−29 or more generally reports on the incorporation of TiIII in metal–organic frameworks,30−32 although Ti3+ open-metal centers in other types of materials are known to be efficient sites for hydrogen sorption, catalysis, or other applications.33−36

Figure 1.

Figure 1

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(A, B) Assembly of the supertetrahedra into large and small mesoporous cages forming MOFs with MTN topology. The structure of microporous supertetraedra in previously described TiIII-based MOFs with MTN topology containing the (C) [Ti3O(solv)y(X)3–y(CO2R)6] cluster based on (D) BDC2–, (E) BTC3– linkers or their extended versions, (F) BPDC2–, and (G) TATB3–. (H) Supertetrahedron of the new MOF described in this work; NH2-MIL-101(TiIII) is represented in the inset, with an enlargement around the amine function. Color code: deep blue, Ti; red, O; gray, C; marine blue, N; white, H; large pink spheres, micropores formed by the supertetrahedra.

Mason et al. obtained the first TiIII-based MOF, MIL-101(TiIII) (Figure 1C) in 2015 using a solvothermal approach consisting of heating H2BDC and TiCl3 in a 10:1 mixture of dimethylformamide (DMF) and ethanol.27 The obtained purple solid was shown to be crystallographically pure MIL-101(TiIII) having chemical formula Ti3O(OEt)(BDC)3(DMF)2, with DMF being partly exchangeable by tetrahydrofuran (THF). This MOF was not only the first reported TiIII-based one but also the first-ever described compound containing carboxylate-bridged titanium-oxo clusters of the Ti3O(O2CR)6L3 type (Figure 1A). Activation of MIL-101(TiIII) by washing with THF followed by heating at 150 °C allowed to remove coordinated solvent molecules from one out of the three Ti centers, creating open-metal sites, whereas washing the MOF with methanol or ethanol instead of THF led to the decomposition of the framework. Furthermore, the activated MOF showed high and irreversible reactivity with oxygen by forming peroxide and superoxide species, evidencing its particular sensitivity.

After this first investigation, the area of TiIII-based MOFs remained largely unexplored, likely due to their air-sensitive nature. However, quite recently, Antonio et al. developed a procedure based on the in situ generation of TiCl3 as a precursor for the synthesis of such compounds.28 This procedure was first used to synthesize MIL-101(TiIII) by electrochemically reducing TiCl4, which is cheaper and available in higher-purity grades than commercial TiCl3. This was carried out in a mixture of DMF and ethanol in the presence of terephthalic acid and NBu4PF6 as the electrolyte. The obtained solution with the freshly generated Ti3+ was then solvothermally treated to yield the desired MOF. In their study, the authors also extended their synthesis approach to various other MOFs with the MTN topology having tritopic and extended linkers. In this way, they were able to obtain MIL-100(TiIII) (Figure 1E), MIL-101(TiIII)-BPDC (Figure 1F), and MIL-100(TiIII)-TATB (Figure 1G) (BPDC = 4,4′-biphenyldicarboxylate; TATB = 4,4′,4″-[1,3,5]triazine-2,4,6-triyl-tris-benzoate).

Interestingly, the MOFs obtained by this electrochemical-mediated approach were compared with products obtained solvothermally from commercial TiCl3 in the absence of NBu4PF6. In addition to higher crystallinity and porosity, X-ray photoelectron spectroscopy analysis indicated that the electrochemically obtained MOFs contain F– as charge counterbalancing anions, whereas the solvothermally obtained ones seemed to contain Cl–. This latter observation, based on the results of surface analysis, is in disagreement with the report of Mason et al.,27 who used a very similar procedure to obtain their MIL-101(TiIII) with an ethoxide charge balancing anion. To the best of our knowledge, until now, there have been no reports on TiIII-MOFs that contain functionalities within their linkers. Adding such functionalities could not only have an important impact on the properties of the resulting MOFs for various applications in fields such as gas adsorption or catalysis37,38 but also open the door for further postfunctionalization of the materials to modify their properties.39−41 For these reasons, we have decided to focus on the development of NH2-MIL-101(TiIII) (Figure 1H), a derivative of MIL-101(TiIII) with amine functionalities on its linkers.42

The MOF described in this work contains a small amount of aluminum, from the titanium(III) precursor used for the synthesis, and is thus a bimetallic MOF. Interestingly, only one previous literature report concerns the synthesis of Ti-based bimetallic MOFs with the MTN (MIL-100 (Figure 1E) or PCN-333 (another name for MIL-100-TATB, Figure 1G)) topology, containing scandium as a second metal.43 However, the previously reported strategy relied on the exchange of the very expensive Sc3+ in the presynthesized monometallic Sc-based MOFs by Ti3+. Our bimetallic NH2-MIL-101(TiIII, Al) MOF is obtained by a much cheaper, facile, one-pot synthesis strategy.

Materials and Methods

Chemicals and Syntheses

(TiCl3)3AlCl3 (76.0–78.5% TiCl3) and acetyl chloride (98%) were purchased from Alfa Aesar. Dry toluene (99.85%, extra dry, AcroSeal), 4-bromoacetophenone (98%), potassium pyrosulfate (98%), n-BuLi (1.6 M in hexanes), and 2,4,6-trimethylaniline (97%) were purchased from Acros Organics. Dry THF (≥99.9%, with 250 ppm of butylated hydroxytoluene (BHT) as an inhibitor), aluminum chloride (99.9%), and 2-aminoterephthalic acid (99%) were purchased from Sigma-Aldrich. DMF (HiPerSolv, CHROMANORM), dichloromethane (DCM) (HiPerSolv, CHROMANORM), sulfuric acid (96%), chloroform (HiPerSolv, CHROMANORM), concentrated hydrochloric acid (37%), glacial acetic acid (ACS reagent grade), and ethanol (technical grade) were purchased from VWR. The acetone used was of technical grade. Triethylamine (99.7%) was purchased from Fisher Chemicals. CDCl3, NaOD (40% w/w in D2O, ≥99.00%), and D2O were purchased from Eurisotop. Carbon dioxide (Alphagaz 1) was purchased from Air Liquide. Potassium permanganate crystals were purchased from J.T. Baker Chemicals N.V. (Holland).

Synthesis of Ti3–xAlxCl3(THF)3

TiCl3(THF)3 was synthesized from (TiCl3)3AlCl3 according to a reported procedure.44 In brief, in a glovebox, 20 g of (TiCl3)3AlCl3 was loaded into a 250 mL custom-made Schlenk flask equipped with a glass-frit filter (see Figure S1) containing a magnetic stirring bar, and the flask was closed with a rubber septum. Outside the glovebox, maintaining the flask under an argon atmosphere (using a Schlenk line), 10 mL of dry toluene was added to the flask, which was subsequently cooled down to −63 °C using a CHCl3/liquid nitrogen mixture. Dry THF (200 mL) was then added to the mixture, which was subsequently stirred at room temperature for 1 h, allowing the formation of a pale blue solid. The product was then isolated by filtration under vacuum, and the solid was washed several times with degassed (by argon bubbling) hexane and dried under vacuum to yield pale blue crystalline TiCl3(THF)3. The analysis of the obtained solid by inductively coupled plasma optical emission spectroscopy (ICP-OES) revealed some residual aluminum; the compound can be formulated as Ti0.93Al0.07Cl3(THF)3 (see the Supporting Information).

Synthesis of NH2-MIL-101(TiIII, Al)

A yellow solution containing 0.126 (or 0.63) g of 2-aminoterephthalic acid in 15 (or 75) mL of DMF was introduced into a 500 mL GL32 glass bottle equipped with a magnetic stirring bar. A B29/32 rubber septum from which the collar had been previously cut off (see Figure S2A) was then used to close the bottle, and the solution was degassed by passing argon through it with the help of a long needle. Separately, a dark blue solution containing 0.556 (or 2.78) g of Ti0.93Al0.07Cl3(THF)3 (weighed in a glovebox, see the preparation above) in 15 (or 75) mL of degassed (argon bubbling) DMF was prepared using Schlenk techniques. This TiIII-containing solution was then added to the linker solution via a cannula under stirring, yielding a dark blue solution. A heat-resistant (180 °C) screw cap with a flat interior (see Figure S2A) was then fitted on the glass bottle to secure the rubber septum. The glass bottle was then placed inside a preheated oven at 130 °C to allow crystallization of the MOF for 18 h (without stirring). The solution was then allowed to cool down to room temperature, and the septum was removed carefully (Attention! Internal pressure is possible at this stage and the rubber septum might pop off the bottle. It is recommended to insert a needle into the septum just after removal of the screw cap to remove excess pressure). The solution was then filtered over a nylon membrane under a continuous flux of argon (see the experimental setup in Figure S2B) to separate the brown MOF from the dark blue solution. The product was then washed several times with degassed (by argon bubbling) DMF and acetone until a clear filtrate was obtained. Special care was taken at this stage to never allow the product to dry completely or pass air through it (oxidation by air resulting in a color change of the MOF from chocolate to yellow). After a final wash with acetone, the still slightly wet product (the solvent in the pores allows to exclude oxygen) was quickly transferred to a round bottom flask with a large (B29/32) neck that was fitted to a glass stopcock and the product was then put under vacuum. This last step must be performed quickly as the product may not dry in the air; otherwise, quick oxidation and degradation of the MOF occur. The MOF was then dried under vacuum and heated at 130 °C for about 10 min to give NH2-MIL-101(TiIII, Al) as a dark brown (chocolate) powder that can be stored in an argon-filled glovebox. Alternatively, the filtration step might be performed in a dedicated glovebox; however, because DMF dissolves most types of plastic (and can therefore cause damage to the transparent windows of gloveboxes), this is not recommended and is at the risk to the experimentalist.

Activation of NH2-MIL-101(TiIII, Al) in Boiling DCM

Inside an argon-filled glovebox, about 1 g of as-synthesized NH2-MIL-101(TiIII, Al) was loaded in a large 100 mL glass test tube with a ground glass joint, together with a magnetic stirring bar. The glass tube was then closed with a rubber septum and removed from the glovebox. On a Schlenk line, about 40 mL of CH2Cl2 (DCM) degassed by Ar bubbling was added to the solid. The tube was immersed in a beaker containing hot water (∼50 °C) and stirring was started. The DCM was allowed to boil for 5–10 min, after which the beaker with hot water was removed and stirring was stopped to allow decantation of the solid. The supernatant was then removed via a cannula. Freshly degassed DCM was then added for the second washing. This procedure was repeated five times. After the fifth wash and removal of DCM, the product was dried under vacuum and then transferred to a glovebox for storage prior to further analyses.

Synthesis of MIL-101(Al)-NH2

Crystallographically pure MIL-101(Al)-NH2 was obtained through a slightly modified procedure taken from the literature.45 In brief, a solution of 0.63 g of 2-aminoterephthalic acid in 75 mL of DMF was heated to 130 °C in a 500 mL round-bottomed flask equipped with a magnetic stirrer. Then, a clear solution containing 1.81 g of previously dissolved aluminum chloride hexahydrate in 75 mL of DMF (slow dissolution) was added dropwise with the help of an addition funnel over a period of 1 h. The mixture was then stirred further at 130 °C for 14 h. The yellow precipitate was recovered through centrifugation and washed several times with DMF and acetone until a clear supernatant was obtained. The MOF was recovered as a yellow powder upon drying in a vacuum oven at 60 °C for about 1 h. To avoid any degradation from moisture, the MOF was stored in an argon-filled glovebox.

Synthesis of Complementary Linkers

1,3,5-Tris(carboxyphenyl)benzene

1,3,5-Tris(carboxyphenyl)benzene was synthesized according to a previously described procedure.46 In brief, 3.04 g of 4-bromoacetophenone and 4.09 g of potassium pyrosulfate were finely ground with a mortar and pestle and subsequently introduced into a 100 mL round-bottomed flask equipped with a magnetic stirring bar. Concentrated sulfuric acid (0.2 mL, 96%) was then added dropwise under stirring. The reaction mixture was heated at 180 °C for 16 h using an oil bath. After cooling down the reaction mixture to room temperature, 25 mL of ethanol was added and the mixture was refluxed for 2 h. The solid was then filtered off and washed two times with ethanol. The solid was subsequently introduced into a 100 mL round-bottomed flask and refluxed in water for 1 h, followed by filtration and two times washing with water. The product was finally recrystallized in chloroform to yield the 1,3,5-tris(4-carboxyphenyl)benzene intermediate. The obtained 1,3,5-tris(4-carboxyphenyl)benzene (0.84) was then introduced into a dry three-necked flask equipped with an entrance and exit for CO2 and a rubber septum. Dry THF (100 mL) was added to the reaction medium, which was cooled down to −78 °C (acetone/dry ice bath) under stirring. About 2.35 mL of a 1.6 M solution of n-BuLi in hexanes was then added dropwise through the rubber septum and reacted further for 5 min. Gaseous CO2 was then bubbled through the reaction medium to precipitate the product, and the reaction was quenched by addition of 20 mL of a 50:50 mixture of acetic acid and water. Concentrated (37%) hydrochloric acid was added slowly until no more product precipitated. The obtained powder was recrystallized in hot acetic acid and dried at 120 °C under vacuum. The final linker was obtained in 50% yield. 1H NMR (CDCl3, 300 MHz, δ): 7.69 ppm, s, 3H; 7.63–7.52 ppm, m, 12 H.

N-Mesitylacetamide

N-Mesitylacetamide was obtained through a previously described procedure.47 In brief, 10.5 mL of 2,4,6-trimethylaniline was introduced under argon in a flame-dried 500 mL round-bottomed flask equipped with a Teflon stir bar and a rubber septum. CH2Cl2 (100 mL) was added to the flask, and the mixture was cooled down to 0 °C (ice bath). Acetyl chloride (5.6 mL) was added dropwise by a syringe, followed by 11 mL of triethylamine. After 2 h of reaction, the mixture was filtered. The solid was then suspended in water and stirred for 30 min. The solid was then collected by filtration and dried under vacuum. 2-Aminobenzene-1,3,5-tricarboxylic acid (2-aminotrimesic acid, H3BTCNH2) was also obtained through a previously described procedure.47 In brief, 5 g of obtained N-mesitylacetamide and 165 mL of water were introduced into a 500 mL round-bottomed flask, followed by the portion-wise addition of 0.55 g of sodium hydroxide. Then, 34 g of KMnO4 was added in portions (∼5 portions) for ∼2 h under vigorous stirring. The flask was then equipped with a condenser, and the solution was heated under stirring at 85 °C for 72 h. The reaction mixture was then filtered through filter paper, and MnO2 was rinsed with ∼200 mL of hot water. The obtained filtrate was acidified with 40 mL of HCl, and the mixture was refluxed overnight (100 °C). The obtained white solid was then filtered and rinsed with ice-cold water. 1H NMR (CDCl3, 300 MHz, δ): 6.93 ppm, s, 2H; 2.29 ppm, s, 3H; 2.25 ppm, s, 6H; 1.73 ppm, s, 3H.

Analysis

Inductively coupled plasma optical emission spectroscopy (ICP-OES) and chlorine analysis (Schöniger flask method) were performed by Medac Ltd.

PXRD patterns were measured in glass capillaries (0.7 mm diameter, Hilgenberg GmbH) that were filled with the samples in a glovebox and sealed with grease. Before analysis, the capillaries were cut and instantly placed into molten wax on goniometric heads and the measurements were performed immediately after preparation to avoid air from entering. The analysis was performed using a MAR345 image plate detector and an Incoatec Microfocus SourceHIGHBRILLIANCE (IμSHIGHBRILLIANCE) Mo ELM47 operating at 50 kV and 1000 μA. The samples were exposed to X-rays for 5 min during which the capillary with the sample was rotated by 180°. Diffraction data was integrated by Fit2D software (using data from a 0.1 mm diameter capillary filled with LaB6 as a calibrant). Variable-temperature PXRD (VT-PXRD) was performed by heating the sample-containing capillary with a Leister LE MINI SENSOR KIT hot air blower (Leister Technologies Benelux B.V.). The air blower was calibrated by a thermocouple housed in a capillary; the determined error on the sample temperature was ±5 °C. Alternatively, PXRD measurements were collected on a STOE STADI P Combi diffractometer using Cu Kα1 radiation (40 kV, 40 mA) (graphite primary monochromator). The diffracted beam was recorded on a DECTRIS MYTHEN 1K strip detector. Samples were loaded in 0.7 mm diameter capillaries, aligned to the geometric center of the diffractometer, and measured in transmission mode, with independent 2-theta movement.

FTIR spectra were measured with a Bruker Alpha spectrometer equipped with a Platinum ATR sample holder (diamond crystal, single bounce) housed in an argon-filled glovebox.

Nitrogen physisorption measurements were performed on an ASAP2020 device from Micromeritics at 77 K. The sample tube was filled inside a glovebox to avoid degradation.

Thermogravimetric analysis (TGA) measurements were performed using a Netszch STA 449 F3 TGA/DSC equipped with a stainless steel oven hosted in an argon-filled glovebox. Conventional TGA was run with a heating speed of 10 K/min under an argon atmosphere until 500 °C, followed by air/argon flow (reactive/protective gas) from 500 to 900 °C.

1H NMR spectra were recorded at room temperature (296 K) on a Bruker Avance 500 spectrometer operating at 500.13 MHz using a BBFO {1H, X} probehead equipped with a z-gradient coil. The measurements were performed using the standard Bruker zg pulse program. The acquisition time was fixed to 1.6 s, the number of scans was fixed to 16, and the relaxation delay was 30 s. About 5 mg of activated MOF was weighed in a glovebox and introduced into a 4 mL screw-capped vial. Outside the glovebox, 0.2 mL of concentrated NaOD was added to the sample, followed by 1.0 mL of D2O (allowing air to enter the vial to oxidize paramagnetic TiIII to TiIV). The suspension was then shaken, heated with a heat gun, and sonicated until a white suspension, formed by dissolved organic species and sodium salts together with solid titanium oxides/hydroxides, was obtained. The suspension was filtered using a poly(tetrafluoroethylene) (PTFE) syringe filter (0.45 μm) to obtain a clear solution. The obtained solution (0.6 mL) was used for NMR determination. Reference solutions of “digested” formic acid and DMF (spectra not shown) were obtained by the same procedure.

The electron paramagnetic resonance (EPR) spectra of activated NH2-MIL-101(TiIII, Al) were recorded on a Bruker 200D-SRC spectrometer. Prior to the measurement, the activated sample was loaded into a high-quality Suprasil quartz tube in a glovebox where it was sealed under the argon atmosphere. The tube was inserted in the double rectangular TE104 cavity of the EPR spectrometer, which was cooled by liquid nitrogen to a temperature of 150 K. Parameters for acquisition are set as follows: microwave power, 200 mW; microwave frequency, 9.57 GHz; modulation amplitude, 4.47 G; center field, 3400 G; sweep width, 1600 G.

Hydrogen sorption isotherms were measured on a Micromeritics ASAP2020 device, according to Application Note 136 of the manufacturer (www.micromeritics.com). A degassing temperature different from that in the application note (100 °C instead of 300 °C) was used to avoid sample degradation. Measurements were performed at 77 K in the pressure range between 0 and 620 mbar with Alphagaz 1 grade hydrogen from Air Liquide.

Results and Discussion

Synthesis of NH2-MIL-101(TiIII) and Attempts with Other Linkers

Most TiIII complexes are quite expensive precursors and therefore unsuitable for synthesizing large amounts of TiIII-based MOFs. Therefore, the cheap commercially available (TiCl3)3AlCl3 was investigated as a metal source for synthesizing TiIII-containing NH2-MIL-101(M) MOFs (M = Ti and/or Al). The synthesis was performed by making two solutions of each of the precursors (metal and linker) in DMF as the only solvent, which easily dissolves all of the reactants. These were then mixed together under argon, and the resulting solution was subsequently heated in a closed glass vial at 130 °C, well below the boiling point of DMF. Care was taken to do so by excluding air from entering (see the experimental part and Figure S2), as TiIII oxidizes easily. Unfortunately, attempts when directly using the bimetallic (TiCl3)3AlCl3 precursor resulted in a very fine powder that was unrecoverable through filtration and readily oxidized in air. In the same reaction conditions, using pure AlCl3, we obtained an amorphous material, as revealed by powder X-ray diffraction (PXRD) (not shown), that could only be isolated by centrifugation. As we expected that Al was responsible for the small particle size obtained when using (TiCl3)3AlCl3, we reacted this bimetallic precursor with THF to form a light blue solid, likely TiCl3(THF)3, which is insoluble in alkanes, allowing us to easily eliminate soluble AlCl3 through simple filtration, according to Jones et al.44 Although the obtained TiCl3(THF)3 still contained some residual aluminum, as determined by ICP analysis (the obtained complex was determined as being Ti0.93Al0.07Cl3(THF)3, see Table S3), we were able to obtain crystallographically pure TiIII-containing NH2-MIL-101 from this precursor (Figures S3 and 2). We performed this successful synthesis twice, in a reproducible manner. The product’s crystal structure has been assessed by PXRD, showing that it is isostructural to other MIL-101 MOFs (Figures 3 and S3), and its infrared spectrum showed the characteristic features of NH2-MIL-101 frameworks, as well as the absence of reactants in the obtained MOF (Figure S4). ICP-OES analysis (Table S6) revealed that the obtained MOF is bimetallic in nature, having a Ti/Al ratio of 85:15, which indicates that Al is preferentially incorporated into the framework compared to TiIII, as the precursor contains a 93:7 Ti/Al ratio. This is in accordance with the fact that the filtrate after synthesis was of blue color, indicating that some TiIII used for the synthesis was not incorporated into the MOF. The obtained MOF is thus named NH2-MIL-101(TiIII, Al) further in this work.

Figure 2.

Figure 2

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Conversion of (A) (TiCl3)3AlCl3 into (B) Ti0.93Al0.07Cl3(THF)3 complex and its reaction with 4-aminoterephthalic acid in DMF at 130 °C to yield (C) NH2-MIL-101(TiIII, Al), from which (D) physisorbed DMF and acetone were exchanged for DCM. Attempts to obtain similar MOFs in DMF at 130 °C by either engaging (E) (TiCl3)3AlCl3 or (F) AlCl3 as a metal source or (G) nonfunctionalized terephthalic acid as a linker source did not yield the desired material.

Figure 3.

Figure 3

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Variable-temperature PXRD patterns and (insets) thermal gravimetric analysis curves of (A) as-synthesized and (B) DCM-exchanged NH2-MIL-101(TiIII, Al). TGA curves were recorded at a heating speed of 10 K/min under argon until 500 °C, followed by oxidation under air from 500 to 900 °C (indicated by the “oxidation” dashed line on the TGA curves). The schemes show the large mesopores of the MOF with (A) acetone and DMF and (B) DCM molecules.

It is worth noting that using terephthalic acid instead of 4-aminoterephthalic acid as a linker source resulted in a mixture of crystalline phases including MIL-101(TiIII) (Figure S5), evidencing that the presence of an amine function is essential for selectively obtaining the desired topology under the used conditions. Interestingly, one of the phases in this latter attempt seems isostructural to MOF-235 (Figure S5A), which has been reported only with a limited number of metals, including Fe48 and Al for which it has been described only with an amine function on the linker.49 In addition, the way of performing the mixing is of importance for the outcome of the reaction. This was demonstrated in the case of the reaction with AlCl3 as a precursor, for which pure NH2-MIL-101(Al) could be obtained by slowly adding a solution of 4-aminoterephthalic acid to a preheated solution of AlCl3 (Figure S6) but not by heating a cold solution of both reactants. This is intrinsically linked to the formation mechanism of NH2-MIL-101(Al), which is discussed in one of our review articles.50 The slow addition of the aluminum chloride solution to the preheated solvent mixture, which is a small but important modification compared to the previously described syntheses, even allowed obtaining an NH2-MIL-101(Al) MOF with the highest surface area yet described for this MOF (SBET = 3440 m2/g, Tables 1 and S2). Amorphous materials were also obtained when using tritopic linker precursors such as trimesic acid (H3BTC) or 1,3,5-tris(carboxyphenyl)benzene (H3BTB) or in the presence of water (Figure S5B,C). Interestingly, the use of 2-aminotrimesic acid (H3BTCNH2) as a trimeric linker allowed obtaining a MOF with the MTN topology (MIL-100), although the important broadening of the peaks in the PXRD pattern could indicate the presence of a large number of defects or small crystallites (Figure S5D). This last synthesis further indicates that the presence of an amine function seems to facilitate the synthesis of MOFs with the MTN topology using TiCl3(THF)3 as a precursor. However, owing to the difficulty of analyzing defects,51 this last MOF has not been analyzed further due to the extreme sensitivity of the product toward air. All of the tested synthetic parameters and outcomes of the reactions are given in Table S1.

Table 1. Decomposition Temperatures and Surface Areas of Various Reported MIL-101(M) and NH2-MIL-101(M) MOFs, Together with Those of NH2-MIL-101(TiIII, Al) Described in This Work.

  decomposition temperature (°C)
 surface area (m2/g)
  
MOF TGA VT-PXRD BET Langmuir reference
MIL-101(Cr) n/a n/a 2800–4230 n/a (12)
  ∼350 n/a 2134 n/a (54)
NH2-MIL-101(Cr) 250 n/a 2070 n/a (55)
MIL-101(Fe) n/a n/a 2123 n/a (56)
  n/a n/a 1420 n/a (57)
NH2-MIL-101(Fe) n/a n/a 2572 n/a (56)
MIL-101(V) 300 n/a 3600 5700 (19)
MIL-101(Sc) 450 n/a 155–640 n/a (58)
NH2-MIL-101(Sc) 300a n/a n/aa n/aa (57)
NH2-MIL-101(Al) n/a ∼150 3440 4799 this work
  n/a n/a 2074 n/a (56)
  >377 n/a 2100 n/a (16)
  >500 n/a 2530 n/a (53)
MIL-101(TiIII) n/a n/a 2970 3890–4440 (27)
  n/a n/a 3285 4360 (28)
NH2-MIL-101(TiIII, Al) n/a 200 2024–2146 2792–2966 this work
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a

Cannot be activated, structural transformation to NH2-MIL-88(Sc) upon heating.

Thermal Stability and Porosity

The thermal stability of NH2-MIL-101(TiIII, Al) was evaluated by means of thermogravimetric analysis by heating the sample at 10 K/min under argon from room temperature to 500 °C and under air from 500 to 900 °C to be able to calculate the theoretical weight losses after calcination. PXRD analysis of the oxidation product was performed to confirm that TiO2, as a mixture of essentially rutile with small amounts of anatase (see Figure S7), was the final combustion residue, together with some Al2O3, which is not visible in the PXRD pattern either because of the small proportion or tiny crystallite size in the combustion residue or because it is obtained as an amorphous phase or due to the microabsorption effect. The theoretical TiO2/Al2O3 ratio should be 92:8, according to the ICP-determined proportion of both metals in the MOF (Ti/Al = 2.54:0.46, see Table S6). The TGA results (Figure 3A, inset) highlight a constant weight loss over the complete temperature range under argon with no well-defined plateau, indicating that removal of solvents is overlapping with framework decomposition.

The MOF’s decomposition temperature was therefore determined by in situ variable-temperature PXRD (VT-PXRD). From these experiments (Figure 3A), it appeared that the framework remains stable at least up to 150 °C, after which decomposition occurs, as shown by the intensity decrease of diffraction peaks from 200 °C, to yield an amorphous compound at higher temperatures. This quite low observed thermal stability compared to that of some other NH2-MIL-101(M) MOFs (see Table 1) could be due to the removal of residual solvents with high surface tension (i.e., residual DMF from the synthesis), which causes the framework to collapse. To remove any remaining DMF from the pores, the as-synthesized MOF was activated by refluxing five times in degassed boiling dichloromethane (DCM) (see the experimental part), which is a solvent having low surface tension.3,52 Fourier transform infrared (FTIR) spectroscopy indicated that this procedure enabled a successful exchange of the solvent molecules (Figure S4). VT-PXRD was then performed on the DCM-activated MOF to evaluate changes in the thermal stability (Figure 3B). However, the overall stability remained unchanged, as diffraction peaks started to vanish away at 200 °C, yielding an amorphous material at 210 °C. The observed thermal stability is lower than those previously observed for this type of material with other metals (Table 1) but is higher than the one of NH2-MIL-101(Al), which we determined experimentally to be around 150 °C through VT-PXRD (Figure S6). It should be noted that for NH2-MIL-101(Al), this decomposition temperature is much lower than 370–500 °C that has been reported even in most recent literature works (see Table 1) but whose determination was based on TGA data only. This indicates that TGA might overestimate the structural thermal stability of this type of MOFs, as this analysis only reflects the temperature at which the linker combustion occurs.16,53 Noteworthy, in both cases (as-synthesized and DCM-activated MOF), the color of the powder changed from chocolate to caramel after framework decomposition. The main change on the TGA curve of the DCM-activated MOF compared to the as-synthesized material is reflected by the plateau after solvent removal at around 150 °C, indicating facilitated solvent removal from this sample, due to the lower boiling point of DCM, and the stability of the sample with emptied pores until 200 °C. Furthermore, the intensities of the diffraction peaks of the activated material (Figures 3 and S8) are higher than for the as-synthesized one, indicating better crystallinity. This is likely due to the more efficient removal of the solvent. Indeed, solvent molecules create disorder in the structure and their removal can thus lead to diffraction peaks of higher intensity. This is reflected by the increasing peak intensity under progressive heating before the frameworks start to decompose. Therefore, the DCM-activated sample was used for further experiments.

The accessible surface area of NH2-MIL-101(TiIII, Al) was probed by nitrogen physisorption at 77 K after activation of the sample under vacuum at 100 and 150 °C (Figure S9). During thermal activation at these two temperatures, the sample lost 26.0 and 28.8% of its initial weight, respectively (for calculations, see Table S4). The results show that thermal activation at 100 °C led to a BET surface area of 2024 m2/g (SLangmuir, 2792 m2/g), whereas increasing the activation temperature to 150 °C increased the BET surface area to 2146 m2/g (SLangmuir, 2966 m2/g). The determined specific surface areas are in a similar range as those previously reported for similar MOFs based on other metals (Table 1). FTIR analysis performed on the samples after nitrogen physisorption shows that the activation procedure efficiently removed DCM from the MOF’s pores (Figure S4).

Determination of the Cluster Structure

To determine the presence of organic species coordinating with the metal clusters of the thermally activated MOF, some amount of sample was digested in a NaOD/D2O mixture and the obtained solution was analyzed by 1H NMR. The spectra (Figure S10) showed the characteristic signals of the aromatic protons of 2-aminoterephthalate (7.3, 6.9, and 6.8 ppm), together with two singlets at 8.1 and 1.9 ppm. Those singlets are attributed to sodium formate and dimethylamine, which are both products of the hydrolysis of DMF in NaOD.59 Since the integration of both signals gives a ratio close to 6 (NH(CH3)2/HCOO–), it was deduced that those signals originated from DMF present inside the framework prior to digestion. It should be noted that the ratio of both integrals is always slightly inferior to 6, which can be explained by the high volatility of dimethylamine. Quantification based on the integration of these signals, and especially the one of the nonvolatile sodium formate, compared to the signal of the 2-aminoterephthalate linker allowed us to determine that after activation slightly less than two molecules of DMF were present per trinuclear cluster (Table S5). These results indicate a very strong affinity between the DMF molecules used for the synthesis and the titanium metal centers. However, as the number of DMF molecules per cluster determined by 1H NMR seemed to decrease when the MOF was activated at 150 °C (1.4 DMF/cluster) instead of 100 °C (1.7 DMF/cluster), it seems that thermal activation can at least remove some of the coordinated solvent, leading to the formation of coordinatively unsaturated metal centers (Figure 4B).

Figure 4.

Figure 4

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(A) Structure of the Ti3O(EtO)(DMF)2(COOR)6 cluster composing MIL-101(TiIII) and activation mechanism as proposed by Mason et al. (part of the DMF can be replaced by THF).27 (B) Structure of the Ti3OCl(DMF)2(COOR)6 cluster of NH2-MIL-101(TiIII) obtained in this work and its activation. Color code: deep blue, Ti; red, O; gray, C; marine blue, N; white, H; green, Cl.

As no other species were detected by 1H NMR, we excluded the presence of organic anions balancing the residual positive charge of the clusters. Based on the results of 1H NMR, ICP analysis, and Cl analysis by the Schöniger flask method (Table S6), we concluded that the composition of the activated MOF is Ti2.54Al0.46OCl(DMF)1.7(BDCNH2)3. The charge balancing anion on the clusters is thus chloride, unlike the MIL-101(TiIII) MOF obtained by Mason et al., in which an ethoxide anion ensures the neutrality of the clusters (Figure 4A), which can be explained by the absence of ethanol in the reaction medium for our synthesis.27 Given the significant amount of TiIII compared to Al in the framework, it is reasonable to assume that some of the clusters composing the MOF are monometallic and of the Ti3O(Cl)(DMF)2(COOR)6 type (Figure 4B), whereas some clusters are of the Ti2AlO(Cl)(DMF)2(COOR)6 type. The +III oxidation state of Ti in the MOF has been evidenced by means of electron paramagnetic resonance (EPR) measurements. NH2-MIL-101(TiIII, Al) activated at 100 °C is EPR active at room temperature, and the signal was enhanced upon cooling to 150 K, at which temperature it was recorded as a very intense signal (Figure 5). This is in contrast with the reported MIL-101(TiIII), which is EPR silent in its activated form at room temperature. The absence of signal for this MOF has been explained by strong antiferromagnetic coupling between the TiIII centers in the trinuclear Ti3IIIO clusters through d orbital overlap as the TiIII–O–TiIII angle is close to 120°.27 The signal observed for our activated NH2-MIL-101(TiIII, Al) is due to the presence of paramagnetic TiIII, which is not antiferromagnetically coupled. Indeed, the measured g values correspond to the ones reported for TiIII in Ti-oxo clusters as well as for oxidized MIL-101(Ti) that contains Ti2IVTiIIIO units without antiferromagnetic coupling due to the presence of only one TiIII per cluster (Table 2).27,60 In the case of activated NH2-MIL-101(TiIII, Al), we do not observe any signal of superoxides bound to TiIV, such as those previously reported for oxidized MIL-101(Ti). This is expected, as the MOF has not been exposed to oxygen and therefore likely does not contain TiIV species. The absence of antiferromagnetic coupling between TiIII centers could be due to the presence of TiIIIAl2O clusters, which are however statistically not favored, or to the presence of distorted Ti2IIIAlO clusters having a TiIII–O–TiIII angle that is significantly higher than 120°, not allowing d orbital overlap. It should be noted that the presence of Al3O clusters in the framework cannot be excluded, even if highly improbable, based on the available data. The verification of this hypothesis, as well as the quantification of each type of bimetallic cluster, requires highly specialized techniques and would be very challenging due to the complex structure, high sensitivity of the MOF toward air, and the paramagnetic nature of TiIII and is therefore outside the scope of this work. The air sensitivity of the framework is evidenced by the color change of the MOF from chocolate to yellow upon exposure to traces of air (Figure S11), leading to an amorphous product.

Figure 5.

Figure 5

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X-band EPR spectrum of NH2-MIL-101(TiIII, Al) activated at 100 °C and recorded at 150 K. The measured g values correspond to TiIII species in Ti-oxo clusters.

Table 2. EPR g Values for Activated NH2-MIL-101(TiIII, Al) Compared to Reported Values for TiIII in Oxidized MIL-101(TiIII/IV) and in a Ti6O4 Cluster.

  activated NH2-MIL-101(TiIII, Al) TiIII in oxidized MIL-101(TiIII/IV)27 TiIII in a Ti6O4 cluster60
g1 1.953 1.952 1.968
g2 1.935 1.939 1.943
g3 1.918 1.923 1.923
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Thermogravimetric analysis of the sample after nitrogen physisorption analysis (Figure S12) was performed to further confirm the above conclusions. Based on the determined structure, a weight loss of 73.1% is expected upon transformation of the framework into TiO2 and Al2O3. The experimental weight loss of the activated MOF after combustion is very close to the theoretical value and thus confirms our findings. Furthermore, the slightly higher weight loss on combustion for the DCM-washed sample activated at 100 °C (73.11%) compared to the same sample activated at 150 °C (72.68%) further indicates that higher activation temperatures allow for increased removal of the coordinated DMF.

Hydrogen Sorption

The hydrogen sorption isotherm of NH2-MIL-101(TiIII, Al) at 77 K was recorded after activation at 100 °C (Figure 6). Interestingly, the uptake is quite steep at low pressures, especially when compared to H2 sorption in MIL-101(TiIII) as previously described by Mason et al.27 This steep uptake might be indicative of interaction between the coordinatively unsaturated TiIII centers of the MOF and hydrogen. Remarkably, when normalized to the surface area, the uptake capacity of NH2-MIL-101(TiIII, Al) is nearly twice as high as for MIL-101(TiIII), which further confirms that stronger interactions exist for this bimetallic amine-containing MOF. This improved adsorption performance might indicate that tuning the nature of the functionalities on the MOF’s linkers might be an effective way of tuning the hydrogen sorption properties of TiIII-based MOFs, in a similar way as to previous observations made for various MOFs based on other metals.61 However, it should be stated that NH2-MIL-101(TiIII, Al) is still far from being the best performing MOF for hydrogen sorption, mainly due to its high sensitivity, and also because it adsorbs less H2 than some well-known MOF materials for this application (e.g., HKUST-1 adsorbs slightly more than 9.5 mmol/g H2 at 600 mbar and 77 K).62

Figure 6.

Figure 6

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Hydrogen adsorption isotherms (77 K) of MIL-101(TiIII) reported by Mason et al.27 (SBET = 2970 m2/g) and NH2-MIL-101(TiIII, Al) from this work (2024 m2/g), expressed in (A) mmol H2/g and (B) relative to the Brunauer–Emmett–Teller (BET) surface area (μmol/m2). The inset shows the TiIII open-metal site on which H2 is likely to interact.

Conclusions

We developed a synthesis strategy for obtaining bimetallic NH2-MIL-101(TiIII, Al) in a reproducible manner, by reacting Ti0.93Al0.07Cl3(THF)3 with 4-aminoterephthalic acid in DMF at 130 °C, through a direct one-pot synthesis strategy. All other reaction conditions screened with changes in used linkers or metal sources all yielded amorphous materials or structures that did not correspond to the MTN topology or to low-crystallinity materials. The thermal stability of this air-sensitive MOF was determined to be around 200 °C by means of thermogravimetric analysis and variable-temperature PXRD. 1H NMR and chloride determination by the Schöniger flask method revealed that the new MOF is composed of clusters having a Cl– charge neutralizing anion, of the Ti3OCl(DMF)2(O2CR)6 type, from which less than one DMF molecule can be thermally removed to create TiIII open-metal sites. Surprisingly, the obtained NH2-MIL-101(TiIII, Al) has a better affinity for hydrogen than the previously described MIL-101(TiIII) material, indicating that linker functionalization can have a positive impact on the H2 sorption properties of TiIII-based MOFs. We anticipate that the properties of TiIII-containing NH2-MIL-101(TiIII, Al) could further be modulated through linker postsynthesis modification through amine chemistry, similar to previous work on NH2-MIL-101(M) structures based on other metals or by varying the nature and amount of the second metal. For example, the amount of Al could be increased to render the MOF less prone to degradation in the presence of oxygen.

Acknowledgments

The authors thank the FNRS for the FRIA fellowship to T.S. and the EQP and CdR projects (T.0169.13, U.N036.15, U.N022.19, J.0073.20). Jean-François Statsyns is acknowledged for technical support and hydrogen sorption measurements and Benjamin Van Meerbeek for the synthesis of the 1,3,5-tris(carboxyphenyl)benzene linker. The authors acknowledge Giacomo Romolini, Bjorn Dieu, Pr. Bernard Gallez, Dr. Lionel Mignion, and Véronique Louppe for EPR measurements and discussion.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.inorgchem.2c00825.

  • Photographs of setups used for syntheses; PXRD patterns; FTIR spectra, variable-temperature PXRD patterns, and TGA curves of NH2-MIL-101(Al); nitrogen physisorption isotherms; NMR spectra; reaction parameters for screening; reported and experimental surface areas of NH2-MIL-101(Al); ICP-OES results; weight loss calculations; NMR integrations and calculations; and elemental analyses (PDF)

The authors declare no competing financial interest.

Supplementary Material

ic2c00825_si_001.pdf (1.5MB, pdf)

References

  1. Moosavi S. M.; Nandy A.; Jablonka K. M.; Ongari D.; Janet J. P.; Boyd P. G.; Lee Y.; Smit B.; Kulik H. J. Understanding the Diversity of the Metal-Organic Framework Ecosystem. Nat. Commun. 2020, 11, 4068 10.1038/s41467-020-17755-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Batten S. R.; Champness N. R.; Chen X.-M.; Garcia-Martinez J.; Kitagawa S.; Öhrström L.; O’Keeffe M.; Paik Suh M.; Reedijk J. Terminology of Metal–Organic Frameworks and Coordination Polymers (IUPAC Recommendations 2013). Pure Appl. Chem. 2013, 85, 1715–1724. 10.1351/PAC-REC-12-11-20. [DOI] [Google Scholar]
  3. Kirchon A.; Feng L.; Drake H. F.; Joseph E. A.; Zhou H. C. From Fundamentals to Applications: A Toolbox for Robust and Multifunctional MOF Materials. Chem. Soc. Rev. 2018, 47, 8611–8638. 10.1039/c8cs00688a. [DOI] [PubMed] [Google Scholar]
  4. Wang B.; Xie L. H.; Wang X.; Liu X. M.; Li J.; Li J. R. Applications of Metal–Organic Frameworks for Green Energy and Environment: New Advances in Adsorptive Gas Separation, Storage and Removal. Green Energy Environ. 2018, 3, 191–228. 10.1016/j.gee.2018.03.001. [DOI] [Google Scholar]
  5. Pascanu V.; González Miera G.; Inge A. K.; Martín-Matute B. Metal-Organic Frameworks as Catalysts for Organic Synthesis: A Critical Perspective. J. Am. Chem. Soc. 2019, 141, 7223–7234. 10.1021/jacs.9b00733. [DOI] [PubMed] [Google Scholar]
  6. Wei Y. S.; Zhang M.; Zou R.; Xu Q. Metal-Organic Framework-Based Catalysts with Single Metal Sites. Chem. Rev. 2020, 120, 12089–12174. 10.1021/acs.chemrev.9b00757. [DOI] [PubMed] [Google Scholar]
  7. Li H.; Wang K.; Sun Y.; Lollar C. T.; Li J.; Zhou H. C. Recent Advances in Gas Storage and Separation Using Metal–Organic Frameworks. Mater. Today 2018, 21, 108–121. 10.1016/j.mattod.2017.07.006. [DOI] [Google Scholar]
  8. Schlenker J. L.; Dwyer F. G.; Jenkins E. E.; Rohrbaugh W. J.; Kokotailo G. T.; Meier W. M. Crystal Structure of a Synthetic High Silica Zeolite—ZSM-39. Nature 1981, 294, 340–342. 10.1038/294340a0. [DOI] [Google Scholar]
  9. Fang Q.; Zhu G.; Xue M.; Sun J.; Wei Y.; Qui S.; Xu R. A Metal-Organic Framework with the Zeolite MTN Topology Containing Large Cages of Volume 2.5 Nm3. Angew. Chem., Int. Ed. 2005, 44, 3845–3848. 10.1002/anie.200462260. [DOI] [PubMed] [Google Scholar]
  10. Lu W.; Wei Z.; Gu Z. Y.; Liu T. F.; Park J.; Park J.; Tian J.; Zhang M.; Zhang Q.; Gentle T.; Bosch M.; Zhou H. C. Tuning the Structure and Function of Metal-Organic Frameworks via Linker Design. Chem. Soc. Rev. 2014, 43, 5561–5593. 10.1039/c4cs00003j. [DOI] [PubMed] [Google Scholar]
  11. Férey G.; Serre C.; Mellot-Draznieks C.; Millange F.; Surblé S.; Dutour J.; Margiolaki I. A Hybrid Solid with Giant Pores Prepared by a Combination of Targeted Chemistry, Simulation, and Powder Diffraction. Angew. Chem. 2004, 116, 6461–6301. 10.1002/ange.200460592. [DOI] [PubMed] [Google Scholar]
  12. Llewellyn P. L.; Bourrelly S.; Serre C.; Vimont A.; Daturi M.; Hamon L.; Weireld G.; De; Chang J.; Hong D.; Hwang Y. K.; Jhung S. H. High Uptakes of CO2 and CH4 in Mesoporous Metals Organic Frameworks MIL-100 and MIL-101. Langmuir 2008, 18, 7245–7250. [DOI] [PubMed] [Google Scholar]
  13. Yoon J. W.; Seo Y. K.; Hwang Y. K.; Chang J. S.; Leclerc H.; Wuttke S.; Bazin P.; Vimont A.; Daturi M.; Bloch E.; Llewellyn P. L.; Serre C.; Horcajada P.; Grenèche J. M.; Rodrigues A. E.; Férey G. Controlled Reducibility of a Metal-Organic Framework with Coordinatively Unsaturated Sites for Preferential Gas Sorption. Angew. Chem., Int. Ed. 2010, 49, 5949–5952. 10.1002/anie.201001230. [DOI] [PubMed] [Google Scholar]
  14. Barbosa A. D. S.; Julião D.; Fernandes D. M.; Peixoto A. F.; Freire C.; de Castro B.; Granadeiro C. M.; Balula S. S.; Cunha-Silva L. Catalytic Performance and Electrochemical Behaviour of Metal–Organic Frameworks: MIL-101(Fe) versus NH2-MIL-101(Fe). Polyhedron 2017, 127, 464–470. 10.1016/j.poly.2016.10.032. [DOI] [Google Scholar]
  15. Volkringer C.; Popov D.; Loiseau T.; Férey G.; Burghammer M.; Riekel C.; Haouas M.; Taulelle F. Synthesis, Single-Crystal X-Ray Microdiffraction, and NMR Characterizations of the Giant Pore Metal-Organic Framework Aluminum Trimesate MIL-100. Chem. Mater. 2009, 21, 5695–5697. 10.1021/cm901983a. [DOI] [Google Scholar]
  16. Serra-Crespo P.; Ramos-Fernandez E. V.; Gascon J.; Kapteijn F. Synthesis and Characterization of an Amino Functionalized MIL-101(Al): Separation and Catalytic Properties. Chem. Mater. 2011, 23, 2565–2572. 10.1021/cm103644b. [DOI] [Google Scholar]
  17. Steenhaut T.; Filinchuk Y.; Hermans S. Aluminium-Based MIL-100(Al) and MIL-101(Al) Metal-Organic Frameworks, Derivative Materials and Composites: Synthesis, Structure, Properties and Applications. J. Mater. Chem. A 2021, 9, 21483–21509. 10.1039/D1TA04444C. [DOI] [Google Scholar]
  18. Lieb A.; Leclerc H.; Devic T.; Serre C.; Margiolaki I.; Mahjoubi F.; Lee J. S.; Vimont A.; Daturi M.; Chang J. S. MIL-100(V) - A Mesoporous Vanadium Metal Organic Framework with Accessible Metal Sites. Microporous Mesoporous Mater. 2012, 157, 18–23. 10.1016/j.micromeso.2011.12.001. [DOI] [Google Scholar]
  19. Carson F.; Su J.; Platero-Prats A. E.; Wan W.; Yun Y.; Samain L.; Zou X. Framework Isomerism in Vanadium Metal-Organic Frameworks: MIL-88B(V) and MIL-101(V). Cryst. Growth Des. 2013, 13, 5036–5044. 10.1021/cg4012058. [DOI] [Google Scholar]
  20. Dou Z.; Cai J.; Cui Y.; Yu J.; Xia T.; Yang Y.; Qian G. Preparation and Gas Separation Properties of Metal-Organic Framework Membranes. Z. anorg. allg. Chem. 2015, 641, 792–796. 10.1002/zaac.201400574. [DOI] [Google Scholar]
  21. Reinsch H.; Stock N. Formation and Characterisation of Mn-MIL-100. CrystEngComm 2013, 15, 544–550. 10.1039/c2ce26436f. [DOI] [Google Scholar]
  22. Mitchell L.; Gonzalez-Santiago B.; Mowat J. P. S.; Gunn M. E.; Williamson P.; Acerbi N.; Clarke M. L.; Wright P. A. Remarkable Lewis Acid Catalytic Performance of the Scandium Trimesate Metal Organic Framework MIL-100(Sc) for C-C and C=N Bond-Forming Reactions. Catal. Sci. Technol. 2013, 3, 606–617. 10.1039/c2cy20577g. [DOI] [Google Scholar]
  23. Castells-Gil J.; Padial N. M.; Almora-Barrios N.; Da Silva I.; Mateo D.; Albero J.; García H.; Martí-Gastaldo C. De Novo Synthesis of Mesoporous Photoactive Titanium(Iv)-Organic Frameworks with MIL-100 Topology. Chem. Sci. 2019, 10, 4313–4321. 10.1039/C8SC05218B. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Giménez-Marqués M.; Santiago-Portillo A.; Navalón S.; Álvaro M.; Briois V.; Nouar F.; Garcia H.; Serre C. Exploring the Catalytic Performance of a Series of Bimetallic MIL-100(Fe, Ni) MOFs. J. Mater. Chem. A 2019, 7, 20285–20292. 10.1039/C9TA01948K. [DOI] [Google Scholar]
  25. Castells-Gil J.; M Padial N.; Almora-Barrios N.; Gil-San-Millán R.; Romero-Ángel M.; Torres V.; da Silva I.; Vieira B. C. J.; Waerenborgh J. C.; Jagiello J.; Navarro J. A. R.; Tatay S.; Martí-Gastaldo C. Heterometallic Titanium-Organic Frameworks as Dual-Metal Catalysts for Synergistic Non-Buffered Hydrolysis of Nerve Agent Simulants. Chem 2020, 6, 3118–3131. 10.1016/j.chempr.2020.09.002. [DOI] [Google Scholar]
  26. Steenhaut T.; Hermans S.; Filinchuk Y. Green Synthesis of a Large Series of Bimetallic MIL-100(Fe,M) MOFs. New J. Chem. 2020, 44, 3847–3855. 10.1039/d0nj00257g. [DOI] [Google Scholar]
  27. Mason J. A.; Darago L. E.; Lukens W. W.; Long J. R. Synthesis and O2 Reactivity of a Titanium(III) Metal-Organic Framework. Inorg. Chem. 2015, 54, 10096–10104. 10.1021/acs.inorgchem.5b02046. [DOI] [PubMed] [Google Scholar]
  28. Antonio A. M.; Rosenthal J.; Bloch E. D. Electrochemically Mediated Syntheses of Titanium(III)-Based Metal-Organic Frameworks. J. Am. Chem. Soc. 2019, 141, 11383–11387. 10.1021/jacs.9b05035. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Brozek C. K.; Dincă M. Ti 3+ -, V 2+/3+ -, Cr 2+/3+ -, Mn 2+ -, and Fe 2+ -Substituted MOF-5 and Redox Reactivity in Cr- and Fe-MOF-5. J. Am. Chem. Soc. 2013, 135, 12886–12891. 10.1021/ja4064475. [DOI] [PubMed] [Google Scholar]
  30. Bueken B.; Vermoortele F.; Vanpoucke D. E. P.; Reinsch H.; Tsou C. C.; Valvekens P.; De Baerdemaeker T.; Ameloot R.; Kirschhock C. E. A.; Van Speybroeck V.; Mayer J. M.; De Vos D. A Flexible Photoactive Titanium Metal-Organic Framework Based on a [TiIV3(M3-O)(O)2(COO)6] Cluster. Angew. Chem., Int. Ed. 2015, 54, 13912–13917. 10.1002/anie.201505512. [DOI] [PubMed] [Google Scholar]
  31. Zou L.; Feng D.; Liu T. F.; Chen Y. P.; Yuan S.; Wang K.; Wang X.; Fordham S.; Zhou H. C. A Versatile Synthetic Route for the Preparation of Titanium Metal-Organic Frameworks. Chem. Sci. 2016, 7, 1063–1069. 10.1039/c5sc03620h. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Ji P.; Song Y.; Drake T.; Veroneau S. S.; Lin Z.; Pan X.; Lin W. Titanium(III)-Oxo Clusters in a Metal-Organic Framework Support Single-Site Co(II)-Hydride Catalysts for Arene Hydrogenation. J. Am. Chem. Soc. 2018, 140, 433–440. 10.1021/jacs.7b11241. [DOI] [PubMed] [Google Scholar]
  33. Kang S.; Klebanoff L. E.; Baker A. A.; Cowgill D. F.; Stavila V.; Lee J. R. I.; Nielsen M. H.; Ray K. G.; Liu Y.-S.; Wood B. C. Assessing the Reactivity of TiCl 3 and TiF 3 with Hydrogen. Int. J. Hydrogen Energy 2018, 43, 14507–14519. 10.1016/j.ijhydene.2018.05.128. [DOI] [Google Scholar]
  34. Liu N.; Xu M.; Yang Y.; Zhang S.; Zhang J.; Wang W.; Zheng L.; Hong S.; Wei M. Au δ – – O v – Ti 3 + Interfacial Site: Catalytic Active Center toward Low- Temperature Water Gas Shift Reaction. ACS Catal. 2019, 9, 2707–2717. 10.1021/acscatal.8b04913. [DOI] [Google Scholar]
  35. Yang X.; Qu J.; Wang L.; Luo J. In-Plasma-Catalysis for NO x Degradation by Ti 3. RSC Adv. 2021, 11, 24144–24155. 10.1039/d1ra02847b. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Qing Y.; Li Y.; Li W.; Yao H. Ti3+ Self-Doped Dark TiO2 Nanoparticles with Tunable and Unique Dielectric Properties for Electromagnetic Applications. J. Mater. Chem. C 2021, 9, 1205–1214. 10.1039/d0tc05112h. [DOI] [Google Scholar]
  37. Lin Y.; Kong C.; Chen L. Amine-Functionalized Metal-Organic Frameworks: Structure, Synthesis and Applications. RSC Adv. 2016, 6, 32598–32614. 10.1039/c6ra01536k. [DOI] [Google Scholar]
  38. Xu C.; Fang R.; Luque R.; Chen L.; Li Y. Functional Metal–Organic Frameworks for Catalytic Applications. Coord. Chem. Rev. 2019, 388, 268–292. 10.1016/j.ccr.2019.03.005. [DOI] [Google Scholar]
  39. Cohen S. M. Postsynthetic Methods for the Functionalization of Metal-Organic Frameworks. Chem. Rev. 2012, 112, 970–1000. 10.1021/cr200179u. [DOI] [PubMed] [Google Scholar]
  40. Wu S.; Chen L.; Yin B.; Li Y. “Click” Post-Functionalization of a Metal-Organic Framework for Engineering Active Single-Site Heterogeneous Ru(III) Catalysts. Chem. Commun. 2015, 51, 9884–9887. 10.1039/c5cc02741a. [DOI] [PubMed] [Google Scholar]
  41. Kalaj M.; Cohen S. M. Postsynthetic Modification: An Enabling Technology for the Advancement of Metal-Organic Frameworks. ACS Cent. Sci. 2020, 6, 1046–1057. 10.1021/acscentsci.0c00690. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Steenhaut T.; Lacour S.; Barozzino-Consiglio G.; Robeyns K.; Crits R.; Hermans S.; Filinchuk Y.. Synthesis, Structure and Thermal Stability of a Mesoporous Titanium(III) Amine Containing MOF with Improved Hydrogen Sorption Properties. ChemRxiv, 2021, 10.26434/chemrxiv-2021-8rdgv. [DOI] [PMC free article] [PubMed]
  43. Zou L.; Feng D.; Liu T.-F.; Chen Y.-P.; Yuan S.; Wang K.; Wang X.; Fordhama S.; Zhou H.-C. A Versatile Synthetic Route for the Preparation of Titanium Metal–Organic Frameworks. Chem. Sci. 2016, 7, 1063–1069. 10.1039/c5sc03620h. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Jones N. A.; Liddle S. T.; Wilson C.; Arnold P. L. Titanium(III) Alkoxy-N-Heterocyclic Carbenes and a Safe, Low-Cost Route to TiCl3(THF)3. Organometallics 2007, 26, 755–757. 10.1021/om060486d. [DOI] [Google Scholar]
  45. Morel F. L.; Ranocchiari M.; Bokhoven J. A. Van. Synthesis and Characterization of Phosphine-Functionalized Metal – Organic Frameworks Based on MOF - 5 and MIL-101 Topologies. Ind. Eng. Chem. Res. 2014, 53, 9120–9127. 10.1021/ie403549v. [DOI] [Google Scholar]
  46. Rana U.; Mondal S.; Sannigrahi J.; Sukul P. K.; Amin M. A.; Majumdarb S.; Malik S. Aromatic Bi-, Tri- and Tetracarboxylic Acid Doped Polyaniline Nanotubes: Effect on Morphologies and Electrical Transport Properties. J. Mater. Chem. C 2014, 2, 3382–3389. 10.1039/c3tc32152e. [DOI] [Google Scholar]
  47. Rubin H. N.; Reynolds M. M. Functionalization of Metal-Organic Frameworks To Achieve Controllable Wettability. Inorg. Chem. 2017, 56, 5266–5274. 10.1021/acs.inorgchem.7b00373. [DOI] [PubMed] [Google Scholar]
  48. Yoon J. H.; Choi S. B.; Oh Y. J.; Seo M. J.; Jhon Y. H.; Lee T. B.; Kim D.; Choi S. H.; Kim J. A Porous Mixed-Valent Iron MOF Exhibiting the Acs Net: Synthesis, Characterization and Sorption Behavior of Fe3O(F4BDC)3(H2O)3·(DMF)3.5. Catal. Today 2007, 120, 324–329. 10.1016/j.cattod.2006.09.003. [DOI] [Google Scholar]
  49. Goesten M. G.; Stavitski E.; Juan-Alcañiz J.; Martiñez-Joaristi A.; Petukhov A. V.; Kapteijn F.; Gascon J. Small-Angle X-Ray Scattering Documents the Growth of Metal-Organic Frameworks. Catal. Today 2013, 205, 120–127. 10.1016/j.cattod.2012.08.044. [DOI] [Google Scholar]
  50. Steenhaut T.; Filinchuk Y.; Hermans S. Aluminium-Based MIL-100(Al) and MIL-101(Al) Metal–Organic Frameworks, Derivative Materials and Composites: Synthesis, Structure, Properties and Applications. J. Mater. Chem. A 2021, 9, 21483–21509. 10.1039/D1TA04444C. [DOI] [Google Scholar]
  51. Steenhaut T.; Grégoire N.; Barozzino-Consiglio G.; Filinchuk Y.; Hermans S. Mechanochemical Defect Engineering of HKUST-1 and Impact of the Resulting Defects on Carbon Dioxide Sorption and Catalytic Cyclopropanation. RSC Adv. 2020, 10, 19822–19831. 10.1039/c9ra10412g. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Ma J.; Kalenak A. P.; Wong-Foy A. G.; Matzger A. J. Rapid Guest Exchange and Ultra-Low Surface Tension Solvents Optimize Metal–Organic Framework Activation. Angew. Chem. 2017, 129, 14810–14813. 10.1002/ange.201709187. [DOI] [PubMed] [Google Scholar]
  53. Babar M.; Mubashir M.; Mukhtar A.; Saqib S.; Ullah S.; Bustam M. A.; Show P. L. Sustainable Functionalized Metal-Organic Framework NH2-MIL-101(Al) for CO2 Separation under Cryogenic Conditions. Environ. Pollut. 2021, 279, 116924 10.1016/j.envpol.2021.116924. [DOI] [PubMed] [Google Scholar]
  54. Chen M. L.; Zhou S. Y.; Xu Z.; Ding L.; Cheng Y. H. Metal-Organic Frameworks of MIL-100(Fe, Cr) and MIL-101(Cr) for Aromatic Amines Adsorption from Aqueous Solutions. Molecules 2019, 24, 3718 10.3390/molecules24203718. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Jiang D.; Keenan L. L.; Burrows A. D.; Edler K. J. Synthesis and Post-Synthetic Modification of MIL-101 (Cr) -NH 2 via a Tandem Diazotisation Process W. Chem. Commun. 2012, 48, 12053–12055. 10.1039/c2cc36344e. [DOI] [PubMed] [Google Scholar]
  56. Taha A. A.; Huang L.; Ramakrishna S.; Liu Y. MOF [NH2-MIL-101(Fe)] as a Powerful and Reusable Fenton-like Catalyst. J. Water Process Eng. 2020, 33, 101004 10.1016/j.jwpe.2019.101004. [DOI] [Google Scholar]
  57. Karimi Alavijeh R.; Akhbari K. Biocompatible MIL-101(Fe) as a Smart Carrier with High Loading Potential and Sustained Release of Curcumin. Inorg. Chem. 2020, 59, 3570–3578. 10.1021/acs.inorgchem.9b02756. [DOI] [PubMed] [Google Scholar]
  58. Santiago B. G.Synthesis and Properties of Scandium Carboxylate Metal-Organic Frameworks. Dissertation, University of St Andrews, 2015. [Google Scholar]
  59. Buncel E.; Symons E. A. The Inherent Instability of Dimethylformamide-Water Systems Containing Hydroxide Ion. J. Chem. Soc. D 1970, 0, 164–165. 10.1039/C29700000164. [DOI] [Google Scholar]
  60. Wu Y.-Y.; Luo W.; Wang Y.; Pu Y.; Zhang X.; You L.; Zhu Q.; Dai J. Titanium–oxo–Clusters with Dicarboxylates: Single-Crystal Structure and Photochromic Effect. Inorg. Chem. 2012, 51, 8982–8988. 10.1021/ic301092b. [DOI] [PubMed] [Google Scholar]
  61. Deng H.; Doonan C. J.; Furukawa H.; Ferreira R. B.; Towne J.; Knobler C. B.; Wang B.; Yaghi O. M. Multiple Functional Groups of Varying Ratios in Metal-Organic Frameworks. Science 2010, 327, 846–850. 10.1126/science.1181761. [DOI] [PubMed] [Google Scholar]
  62. Xiao B.; Wheatley P. S.; Zhao X.; Fletcher A. J.; Fox S.; Rossi A. G.; Megson I. L.; Bordiga S.; Regli L.; Thomas K. M.; Morris R. E. High-Capacity Hydrogen and Nitric Oxide Adsorption and Storage in a Metal-Organic Framework. J. Am. Chem. Soc. 2007, 129, 1203–1209. 10.1021/ja066098k. [DOI] [PubMed] [Google Scholar]

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