WO2015177511A1

WO2015177511A1 - Method of preparing a metal organic framework

Info

Publication number: WO2015177511A1
Application number: PCT/GB2015/051383
Authority: WO
Inventors: Hong-cai ZHOU; Dawei Feng; Kecheng Wang; Jian Tian
Original assignee: Jason Ornstein; Texas A&M University System; Texas A&M University
Current assignee: Jason Ornstein; Texas A&M University System; Texas A&M University
Priority date: 2014-05-23
Filing date: 2015-05-11
Publication date: 2015-11-26
Anticipated expiration: 2016-11-23

Abstract

The present invention relates to a method of preparing a metal organic framework comprising metal ions and carboxylate ligands; the method comprises: reacting (i) a source of metal ions, with (ii) a carboxylic acid precursor of a the carboxylate ligands, in an organic solvent consisting of one or more carboxylic acid solvents, at a temperature of about 75°C or greater, optionally in the presence of water. The present invention also relates to the same method for preparing monocrystalline metal organic frameworks as well as the metal organic frameworks obtained from such methods.

Description

Method of Preparing a Metal Organic Framework

This application claims the benefit of U.S. provisional application number 62/002,620, filed on 23 May 2014, the entire contents of which are incorporated by reference.

This invention was made with government support under DE-AR0000073 awarded by U.S. Dept of Energy. The government has certain rights in the invention

Field of the Invention

The invention relates to methods of preparing metal organic frameworks, in particular to methods of preparing monocrystalline metal organic frameworks as well as metal organic frameworks obtained/obtainable from such methods.

US 8,431,744 B2 describes a solvent-free process for preparing a magnesium-based porous metal organic framework starting from magnesium metal or magnesium oxide. US 8,524,932 B2 describes a process for preparing a porous metal organic framework in which the reaction is carried out in an alkaline aqueous medium. Nevertheless, there remains a need for alternative methods of preparing metal organic frameworks as well as methods that provide advantages over the prior art.

Summary of the Invention

Accordingly, in one aspect, the invention provides a method of preparing a metal organic framework comprising metal ions and carboxylate ligands;

the method comprises:

reacting (i) a source of metal ions, with (ii) a carboxylic acid precursor of the carboxylate ligands, in an organic solvent consisting of one or more carboxylic acid solvents, at a temperature of about 75°C or greater, optionally in the presence of water.

The method of the invention is more economical, and allows recycling of the solvents employed and therefore reduces solvent waste. The method of the invention also provides a way of preparing metal organic frameworks in monocrystalline form.

The method of the invention employs carboxylic acid solvents, such as acetic acid. In particular, the method of the invention employs one or more carboxylic acids in the absence of other organic solvents. Previous methods for preparing metal organic frameworks have employed organic solvents such as DMF. In contrast, organic solvents that are not carboxylic acid solvents, such as DMF, are not employed in the method of the present invention. The inventors have surprisingly found that in the absence of other organic solvents, the carboxylic acid solvents employed in the method of the invention can be recycled/re-used. Moreover, the inventors have surprisingly found that the use of carboxylic acid solvents, such as acetic acid, in the absence of other organic solvents, provides a method delivering unexpected performance with regard to other aspects of the method, e.g. yield, purity, crystallinity.

In one embodiment, the method employs an organic solvent consisting of one or more carboxylic acid solvents, the organic solvent is essentially free of other organic solvents that are not carboxylic acid solvents.

The carboxylic acid solvent may be any carboxylic acid solvent. In particular, the one or more carboxylic acid solvents may be selected from a substituted or unsubstituted Ci_-4 carboxylic acid. Examples of suitable carboxylic acid solvents include, but are not limited to, acetic acid, formic acid, propionic acid, and trifluroacetic acid. Preferred carboxylic acids are formic acid and acetic acid. Particularly preferred is acetic acid.

In addition to one or more carboxylic acid solvents, the reaction maybe carried out in the presence of water. For example, the volume ratio of carboxylic acid solvent to water maybe greater than or equal to 1:5. For example, the volume ratio of carboxylic acid solvent to water may range from about 99:1 to about 1:5, from about 50:1 to about 1:3, from about 20:1 to about 1:2, from about 10:1 to about 1:1, from about 5:1 to about 1:1, or from about 2:1 to about 1:1. In one embodiment, the volume ratio of carboxylic acid solvent to water is about 1:1.

The metal ions which are part of the metal organic framework are derived from the source of metal ions. For example, the metal ions may comprise metal ions selected from the transition metals of the periodic table, such as selected from Fe, Al, Cr, V, Sc, Zr, Ti, Ga and In metal ions. Alternatively, the metal ions may be selected from Fe, Al, Zr, and Ti. In one embodiment, the metal ions comprise Fe or Zr metal ions.

In one embodiment, the metal ions comprise only one metal. For example, the metal ions may be Fe, Al, Zr, or Ti. In alternative embodiment, the metal ions further comprise metal ions selected from Group 2 through Group 16 metal ions. For example, the metal ions may comprise a metal cation mixture of M metal ions and X metal ions; wherein M is a transition metal ion, and X is selected from the group consisting of Group 2 through Group 16 metal ions.

For example, M may be selected from Fe, Al, Cr, V, Sc, Ti, Zr and In metal ions.

For example, X may be a metal ion selected from Al, Fe, Co, Ni, Mn, Zn, Mg, Cr, V, Sc, Ca, Ba, and In metal ions. More specifically, X may be selected from Al(III), Fe(II), Fe(III), Co(II), Ni(II), Mn(II), Zn(II), Mg(II), Cr(III), V(III), Sc(III), Ca(II), Ba(II) and In(III) metal ions, preferably X is a metal ion selected from Fe(II), Fe(III), Co(II), Ni(II), Mn(II), Zn(II), and Mg(II) metal ions. In one embodiment, the metal ions comprise a metal cation mixture of formula M₂X.

In one embodiment, the method provides a metal organic framework comprising Fe³⁺ ions and carboxylate ligands. The metal organic framework may include only Fe³⁺ ions or may include a metal cation mixture of Fe³⁺ and X²⁺ ions; wherein X is a metal ion selected from the group consisting of Group 2 through Group 16 metals. For example, X may be a metal ion selected from Al(III), Fe(II,III), Co(II), Ni(II), Mn(II), Zn(II), Mg(II), Cr(III), V(III), Sc(III), Ca(II), Ba(II) or In(III), preferably X is a metal ion selected from Fe(II,III), Co(II), Ni(II), Mn(II), Zn(II), and Mg(II). The metal ions may comprise M²⁺ metal ions, M³⁺ metal ions, or M⁴⁺ metal ions.

The source of metal ions may be in the form of a metal salt, a metal ion coordination complex, or a hydrate thereof. Suitable metal salts include but are not limited to a salt selected from a halide salt (e.g. a chloride salt), a nitrate salt (e.g. N0₃ ), acetate salts, sulphate salts or hydrates of the same. In particular, the metal salt may be an iron salt such as an iron nitrate, an iron halide, or a hydrate thereof. Specific examples of metal salts include but are not limited to FeCl₃, Fe(N0₃)₃.9H₂0, A1C1₃, A1(N0₃)₃, ZrCl₄ and VC1₃. A preferred metal salt is Fe(N0₃)₃.9H₂0. Suitable metal ion coordination complexes include but are not limited to acetate complexes, and hydrates of the same. For example, suitable metal ion coordination complexes include but are not limited to Fe₃0(CH₃COO)6 and Fe₂CoO(CH₃COO)6.

Specific examples of metal ion coordination complexes include but are not limited to iron (III) acetate, i.e. [Fe₃0(OAc)6(H₂0)₃]OAc, and FeM₂0(CH₃COO)₆, wherein each M is independently selected from Fe, Al, Cr, V, Sc, and In. The carboxylate ligands of the metal organic framework are derived from the carboxylic acid precursor (or salt thereof) employed in the method of the invention. For the purposes of the present invention, the term "derived" means that the carboxylic acid compounds are present in partly deprotonated or fully deprotonated form. The carboxylic acid may be any carboxylic acid. The carboxylic acid may be any di-, tri-, tetra-, hexa-, or octa-carboxylic acid. The carboxylic acids may be substituted or unsubstituted. For example, the carboxylic acids may be substituted by one or more substituents independently selected from -OH, -NH₂, -OCH₃, -NH(CH₃), -N(CH₃)₂, - CN and halides (e.g. -CI, -F, -I). One suitable example is:

In one embodiment, the carboxylic acid precursor is 3,5-dicarboxyl-(3,5- dicarboxylazophenyl)benzene (ABTC), ([5,io,i5,20-Tetrakis(4- methoxycarbonylphenyl)porphyrinato]-Co(II)), i.e. Co-TCPP, SiTD, or BTC. Further examples of suitable carboxylic acids are provided below.

The reaction is carried out at an elevated temperature. In particular, the reaction is carried out under reflux conditions. For example, the reaction may be carried out at a temperature of about 120°C or greater, preferably at a temperature of about 150°C or greater.

The reaction may be carried out at about atmospheric pressure (101.325 kPa;

approximately 1 bar) or greater. The reaction is preferably carried out at a pressure of less than or equal to about 400 kPa (about 4 bar), more preferably less than or equal to about 200 kPa (about 2 bar). As stated above, the reaction may be carried out at atmospheric pressure. In this case, however, slightly over pressures or under pressures may be employed due to the apparatus. Therefore, in the context of the present invention, the term "atmospheric pressure" is to be taken to mean a pressure range which results from the actual atmospheric pressure ± 15 kPa (150 mbar). The method of the invention provides a new way of preparing metal organic

frameworks comprising metal ions and carboxylate ligands in monocrystalline or polycrystalline forms. Particularly useful is the fact that the method of the present invention provides a new way of preparing such metal organic frameworks in monocrystalline form.

Accordingly, the method of the invention may be employed to prepare monocrystalline metal organic frameworks comprising metal ions and carboxylate ligands.

A monocrystalline metal organic framework prepared by a method of the invention may have a crystal size of greater than about 0.05mm, 0.1mm, 0.2mm, 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, or 0.9mm. For example, the crystal size may range from about 0.1mm to about 5mm, preferably from about 0.3mm to about 4mm, more preferably from about 0.5mm to about 2mm, more preferably from about imm to about 3mm.

In a further aspect, the present invention provides a monocrystalline metal organic framework obtained/obtainable by the method of the present invention.

The metal-organic frameworks according to the invention have a wide range of applications.

According to one aspect, the invention provides a method comprising uptaking at least one substance by a metal-organic framework of the present invention. For example, the substance may be hydrogen, methane, carbon dioxide, oxygen or nitrogen.

According to one aspect, the invention provides a method of storing a gas in a metal- organic framework according to the present invention. Alternatively, the invention provides the use of a metal-organic framework according to any embodiment of the present invention for storing a gas. This may be achieved by binding the gas in a plurality of linker channel sites present in the metal-organic framework, for example using van der Waals forces.

The use/method of storing gases in this way may optimise gas storage density and volumetric gas storage.

For example, the gas may be hydrogen, methane, carbon dioxide, oxygen or nitrogen.

In the above embodiments of the invention, the metal-organic framework may be configured to store methane or hydrogen, for example for fuelling vehicles.

In a further aspect, the present invention provides the use of any metal-organic framework according to the invention for adsorbing a guest molecule, for example a gas molecule such as hydrogen, methane, carbon dioxide, oxygen or nitrogen. In this respect, the invention also provides a method of adsorbing a guest molecule, for example a gas molecule such as hydrogen, methane, carbon dioxide, oxygen or nitrogen, comprising contacting a metal-organic framework of the invention with a guest molecule source. Accordingly, the invention also provides a metal-organic framework according to any embodiment of the present invention, further comprising one or more than one type of guest molecule.

The guest molecule may be a gas molecule such as hydrogen, methane, carbon dioxide, oxygen or nitrogen.

In fact, in the context of any of the embodiments described herein, the substance, gas molecule, or gas maybe selected from: (a) H₂, N₂, Ar, 0₂, C0₂, NO, N0₂ or CO; or

(b) an alkane (Ci-6), alkene (C2-4), alkyne (C2-6), alcohol (Ci-6), arene (C6-8) or a substituted version of any of these;

wherein the alkane may be selected from CH₄, C₂H₆, C₃Hs, C₄H₁₀, C₅H₁₂ or ΟόΗ₁₄; or a cycloalkane (C3-6) selected from the group consisting of C₃H6, C₄H8, C₅H₁₀ and ΟόΗ₁₄;

wherein the alkene may be C₂H₄, C₃H6, C₄Hs, C₅H₁₀ or 0όΗ₁₂; wherein the alkyne may be C₂H₂;

wherein the alcohol may be methanol, ethanol, n-propanol, isopropanol, n-butanol or isobutanol; or

wherein the arene may be a substituted arene (C6-8) such as is nitrobenzene, 1,2-dinitrobenzene, 1,3-dinitrobenzene, 1,4-dinitrobenzene,

1,2,4-trinitrobenzene or 1,3,5-trinitrobenzene.

Description of the Figures

The invention will now be described further with reference to the following non- limiting examples and the accompanying Figures, in which:

Figure 1 illustrates the differences between amorphous, polycrystalline, and

monocrystalline materials. Figure 2 shows an optical microscope image of PCN-250-Fe.

Figure 3 shows the N₂ adsorption isotherms of PCN-250-Fe.

Figure 4 shows the powder x-ray diffraction pattern (PXRD) of PCN-250-Fe.

Figure 5 shows the thermogravimetric (TG) analysis for PCN-250-Fe. Figure 6 shows an optical microscope image of PCN-224-Zr. Figure 7 shows the N₂ adsorption isotherms of PCN-224-Zr.

Figure 8 shows the powder x-ray diffraction pattern (PXRD) of PCN-224-Zr. Figure 9 shows the thermogravimetric (TG) analysis for PCN-224-Zr.

Figure 10 shows the powder x-ray diffraction pattern (PXRD) of PCN-651-Fe. Figure 11 shows the powder x-ray diffraction pattern (PXRD) of PCN-652-Fe.

Detailed Description of the Invention A monocrystalline MOF (or a single crystal MOF) consists of a MOF in which the crystal lattice of the entire solid is continuous, unbroken (with no grain boundaries) to its edges. Monocrystalline is opposed to amorphous material, in which the atomic order is limited to short range order only. Polycrystalline materials lie between these two extremes; they are made up of small crystals. A polycrystalline solid or polycrystal is comprised of many individual grains or crystallites. There is no relationship between the grains. Therefore, on a large enough length scale, there is no periodicity across a polycrystalline sample. They are different from monocrystalline materials. Large single crystals are very rare in nature and can be difficult to produce in the laboratory. It is desired that metal organic framework materials should be free from objectionable or incompatible impurities which detrimentally affect the crystal structure or the physical properties of the crystal. The material should be finely divided and uniform in size. Due to the absence of the defects associated with grain boundaries,

monocrystalline metal organic frameworks have high surface areas and provide control over the crystallization process. The differences between amorphous, polycrystalline and (mono)crystalline are illustrated in Figure l.

In preferred embodiments of the invention, the monocrystalline metal organic frameworks comprise a low occurrence of twinning. For example, the monocrystalline metal organic frameworks may comprise less than about 5% twinning crystals. Most preferred, the monocrystalline metal organic frameworks comprise no twinning crystals.

A carboxylic acid precursor is employed in the method of the present invention. This carboxylic acid forms the carboxylate ligands. The carboxylic acid may be any suitable carboxylic acid including but not limited to carboxylic acids having two or more carboxylic acid groups. For example, the carboxylic acid maybe a dicarboxylic acid, a tricarboxylic acid, a tetracarboxylic acid, a hexacarboxylic acid, or an octacarboxylic acid.

The carboxylic acids may be substituted or unsubstituted. For example, the carboxylic acids maybe substituted by one or more substituents independently selected from - OH, -NH₂, -OCH₃, -NH(CH₃), -N(CH₃)₂, -CN and halides (e.g. -CI, -F, -I). Likewise, the carboxylate ligands may be derived from any such carboxylic acids. For example, the carboxylic acid may be a dicarboxylic acid, such as, for instance, oxalic acid, succinic acid, tartaric acid, 1,4-butanedicarboxylic acid, 1,4-butenedicarboxylic acid, 4-oxopyran-2,6-dicarboxylic acid, 1,6-hexanedicarboxylic acid,

decanedicarboxylic acid, 1,8-heptadecanedicarboxylic acid, 1,9- heptadecanedicarboxylic acid, heptadecanedicarboxylic acid, acetylenedicarboxylic acid, 1,2-benzene-dicarboxylic acid, 1,3-benzenedicarboxylic acid, 2,3- pyridinedicarboxylic acid, pyridine-2,3-dicarboxylic acid, i,3-butadiene-i,4- dicarboxylic acid, 1,4-benzene-dicarboxylic acid, p-benzenedicarboxylic acid, imidazole-2,4-dicarboxylic acid, 2-methylquinoline-3,4-dicarboxylic acid, quinoline- 2,4-dicarboxylic acid, quinoxaline-2,3-dicarboxylic acid, 6-chloroquinoxaline-2,3- dicarboxylic acid, 4,4'-diaminophenylmethane-3,3'-dicarboxylic acid, quinoline-3,4- dicarboxylic acid, 7-chloro-4-hydroxyquinoline-2,8-dicarboxylic acid,

diimidedicarboxylic acid, pyridine-2,6-dicarboxylic acid, 2-methylimidazole-4,5- dicarboxylic acid, thiophene-3,4-dicarboxylic acid, 2-isopropylim idazole-4,5- dicarboxylic acid, tetrahydropyran-4,4-dicarboxylic acid, perylene-3,9-dicarboxylic acid, perylenedicarboxylic acid, Pluriol E 200-dicarboxylic acid, 3,6- dioxaoctanedi carboxylic acid, 3,5-cyclo-hexadiene-i,2-di carboxylic acid,

octanedicarboxylic acid, pentane-3,3-dicarboxylic acid, 4,4'-diamino-i,i'-diphenyl-3,3'- dicarboxylic acid, 4,4'-diaminodiphenyl-3,3'-dicarboxylic acid, benzidine-3,3'- dicarboxylic acid, i,4-bis(phenylamino)benzene-2,5-dicarboxylic acid, 1,1'- binaphthyidicarboxylic acid, 7-chloro-8-methylquinoline-2,3-dicarboxylic acid, 1 - anilinoanthraquinone-2,4'-dicarboxylic acid, poly-tetrahydrofuran-250-dicarboxylic acid, i,4-bis(carboxymethyl)piperazine-2,3-dicarboxylic acid, 7-chloroquinoline-3,8- dicarboxylic acid, i-(4-carboxy)phenyl-3-(4-chloro)phenylpyrazoline-4,5-dicarboxylic acid, 1,4,5,6,7, 7-hexachloro-5-norbornene-2,3-dicarboxylic acid,

phenylindanedicarboxylic acid, i,3-dibenzyl-2-oxoimidazolidine-4,5-dicarboxylic acid, 1,4-cyclohexanedi carboxylic acid, naphthalene-i,8-dicarboxylic acid, 2- benzoylbenzene-i,3-dicarboxylic acid, i,3-dibenzyl-2-oxoimidazolidine-4,5-cis- dicarboxylic acid, 2,2'-biquinoline-4,4'-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, 3,6,9-trioxaundecanedicarboxylic acid, hydroxybenzophenonedicarboxylic acid, Pluriol E 300-di carboxylic acid, Pluriol E 400-dicarboxylic acid, Pluriol E 600- dicarboxylic acid, pyrazole-3,4-di carboxylic acid, 2,3-pyrazinedicarboxylic acid, 5,6- dimethyl-2,3-pyrazine-dicarboxylic acid, 4,4'-diamino(diphenyl

ether)diimidedicarboxylic acid, 4,4'-diaminodiphenylmethanediimidedicarboxylic acid, 4,4'-diamino(diphenyl sulfone)diimidedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,3-adamantanedicarboxylic acid, 1,8- naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 8-methoxy-2,3- naphthalenedicarboxylic acid, 8-nitro-2,3-naphthalenedicarboxylic acid, 8-sulfo-2,3- naphthalenedicarboxylic acid, anthracene-2,3-dicarboxylic acid, 2',3'-diphenyl-p- terphenyl-4,4"-dicarboxylic acid, (diphenyl ether)-4,4'-dicarboxylic acid, imidazole-4,5- dicarboxylic acid, 4(iH)-oxothiochromene-2,8-dicarboxylic acid, 5-tert-butyl-i,3- benzenedicarboxylic acid, 7,8-quinolinedicarboxylic acid, 4,5-imidazoledicarboxylic acid, 4-cyclohexene-i,2-dicarboxylic acid, hexatriacontanedicarboxylic acid, tetradecanedicarboxylic acid, 1,7-heptane-dicarboxylic acid, 5-hydroxy-i,3- benzenedicarboxylic acid, 2,5-dihydroxy-i,4-dicarboxylic acid, pyrazine-2,3- dicarboxylic acid, furan-2,5-dicarboxylic acid, i-nonene-6,9-dicarboxylic acid, eicosenedicarboxylic acid, 4,4'-dihydroxy-diphenylmethane-3,3'-dicarboxylic acid, 1- amino-4-methyl-9,io-dioxo-9,io-dihydroanthracene-2,3-dicarboxylic acid, 2,5- pyridinedicarboxylic acid, cyclohexene-2,3-dicarboxylic acid, 2,9-dichlorofluorubin- 4,11-dicarboxylic acid, 7-chloro-3-methylquinoline-6,8-dicarboxylic acid, 2,4- dichlorobenzophenone-2',5'-dicarboxylic acid, 1,3-benzenedicarboxylic acid, 2,6- pyridinedicarboxylic acid, i-methylpyrrole-3,4-dicarboxylic acid, l-benzyl-iH-pyrrole- 3,4-dicarboxylic acid, anthraquinone-i,5-dicarboxylic acid, 3,5-pyrazoledicarboxylic acid, 2-nitro-benzene-i,4-dicarboxylic acid, heptane-i,7-dicarboxylic acid, cyclobutane- 1,1-dicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 5,6-dehydronorbomane-2,3- dicarboxylic acid, 5-ethyl-2,3-pyridinedicarboxylic acid or camphordicarboxylic acid.

For example, the carboxylic acid may be a tricarboxylic acid, such as for instance 2- hydroxy-i,2,3-propanetricarboxylic acid, 7-chloro-2,3,8-quinolinetricarboxylic acid, 1,2,3-, 1,2,4-benzenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 2-phosphono- 1,2,4-butanetricarboxylic acid, 1,3,5-benzenetricarboxylic acid, l-hydroxy- 1,2,3- propanetricarboxylic acid, 4,5-dihydro-4,5-dioxo-iH-pyrrolo[2,3-F]quinoline-2,7,9- tricarboxylic acid, 5-acetyl-3-amino-6-methyl-benzene-i,2,4-tri carboxylic acid, 3- amino-5-benzoyl-6-methylbenzene-i ,2,4-tricarboxylic acid, 1,2,3-propanetricarboxylic acid or aurintri carboxylic acid.

For example, the carboxylic acid may be a tetracarboxylic acid, such as, for instance, i,i-dioxidoperylo[i,i2-BCD]thiophene-3,4,9,io-tetracarboxylic acid, perylene- tetracarboxylic acids such as perylene-3,4,9,io-tetracarboxylic acid or perylene-1,12- sulfone-3,4,9,io-tetracarboxylic acid, butanetetracarboxylic acids such as 1,2,3,4- butanetetracarboxylic acid or meso-i,2,3,4-butanetetracarboxylic acid, decane-2,4,6,8- tetracarboxylic acid, i,4,7,io,i3,i6-hexaoxacyclooctadecane-2,3,n,i2-tetracarboxylic acid, 1,2,4,5-benzenetetracarboxylic acid, 1,2,11,12-dodecanetetracarboxylic acid, 1,2,5,6-hexanetetracarboxylic acid, 1,2,7,8-octane-tetracarboxylic acid, 1,4,5,8- naphthalenetetracarboxylic acid, 1,2,9,10-decanetetracarboxylic acid,

benzophenonetetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, tetrahydrofurantetracarboxylic acid or cyclopentanetetracarboxylic acids such as cyclopentane-i,2,3,4-tetracarboxylic acid.

The ligands may also be derived from a carboxylic acid selected from compounds of formula Li to L30 and combinations thereof:

L15 L16 L17 L18

L19 L20 L21 L22

L26

Specific combinations of ligands include ligands derived from L31 and L32:

L32

Alternatively, the ligand may be derived from a carboxylic acid selected from the following compounds or combinations thereof:

In the invention, the carboxylate ligands maybe selected from but not limited t< tri-, and tetra-carboxylate ligands. For example, the carboxylate ligands may b< derived from ₂',3",5",6'-tetramethyl-[i,i':4',i":4",i'"-quaterphenyl] 3,3'",5,5"' - - ι₅ - tetracarboxylic acid, 1,3,5-benzenetribenzoic acid, or 4,4',4"-s-triazine-2,4,6- triyltribenzoic acid.

2',3",5",6'-tetramethyl-[i,i':4',i":4",i"'-quaterphenyl] 3,3"',5,5"' -tetracarboxylic acid has chemical structure:

TMQPTC

1,3,5-benzenetribenzoic acid has the chemical structure:

4,4',4"-s-triazine-2,4,6-triyltribenzoic acid has the chemical structure:

In one embodiment, the carboxylic acid is L22 (also referred to as ABTC): 3,5- dicarboxyl-(3,5-dicarboxylazophenyl)benzene:

ABTC

An example synthesis of L22 is described below. An alternative synthesis is set out in Wang et al, "Metal Organic Frameworks based on double-bond-coupled di-isophthalate linkers with high hydrogen and methane uptakes", Chemistry of Materials 2008, 20,

3145·

The present invention is described in more detail below in the context of specific examples. However, the invention should not be construed so as to be limited by these specific examples.

Examples

Synthesis ofL22 CABTC): $,^-dicarboxyl-($,^-dicarboxylazophenyl)benzene

A mixture of 5-nitroisophthalic acid (2.1 g, 10 mmol), Zn (1.3 g, 20 mmol), and NaOH (0.8 g, 20 mmol) in a mixture of ethanol (50 mL) and water (20 mL) was heated under reflux. After the mixture was refluxed for 12 h, a yellow solid was obtained and collected by filtration. The resultant solid was dissolved in 50 mL of NaOH (aq, 1 M) and filtered to remove any insoluble solids. The filtrate was acidified to pH=3 with 3M HC1 (aq) to afford 2.8 g of 3,5-dicarboxyl (3',5'-dicarboxyl-azophenyl)benzene as an orange precipitate (yield: 78%).

Alternative synthesis ofL22 iABTC): s.^-dicarboxyl-is.^- dicarboxylazophenyDbenzene

A mixture of 5-nitroisophthalic acid (19 g, 90 mmol) and NaOH (50 g, 1250 mmol) in 250 mL of distilled water was placed into a lL 3-neck round bottom flask and stirred vigorously at 333 K. To this slurry, 100 g of D-glucose dissolved in 150 mL of distilled water was slowly added. The resulting brown mixture was cooled down to room temperature, and air was bubbled for 4 hours always under stirring. The reaction mixture was cooled in an ice-bath and the sodium salt of Tazb recovered by filtration and washed with small amount of cold water. The resulting yellow solid was then dissolved in 200mL of distilled water and this solution was acidified down to pH = 1 by the addition of HCl 37 %. The resulting orange solid was recovered by filtration, washed with distilled water and dried at 373 K under vacuum. Yield 70%. Synthesis ofCo-TCPP Ci^.io.i^.20-TetrakisC4- methoxycarbonul henuD or h rinatol-CoCIW:

To refluxed propionic acid (100 mL) in a 500-mL three necked flask were added pyrrole (3.0, 0.043 rnol) and methyl p-formylbenzoate (6.9 g, 0.042 mol), and the solution was refluxed for I2h in darkness. After the reaction mixture was cooled to room

temperature, crystals were collected by suction-filtration to afford 5,10,15,20- Tetrakis(4-methoxycarbonylphenyl)porphyrin (TPPCOOMe) as purple crystals (i-9g, 2.24mmol, 21.3% yield).

A solution of TPPCOOMe 0.854 g (i-0 mmol) and CoCl2-6H20 (3.1 g, 12.8 mmol) in 100 mL of DMF was refluxed for 6 h. After the mixture was cooled to room

temperature, 150 mL of H2O was added. The resultant precipitate was filtered and washed with 50 mL of H2O for two times. The obtained solid was dissolved in CHCI3, followed by washing three times with water. The organic layer was dried over anhydrous magnesium sulfate and evaporated to afford quantitative red crystals.

The obtained ester (0.75 g) was stirred in THF (25 mL) and MeOH (25 mL) mixed solvent, to which a solution of KOH (2.63 g, 46.95 mmol) in H2O (25 mL) was introduced. This mixture was refluxed for 12 h. After cooling down to room

temperature, THF and MeOH were evaporated. Additional water was added to the resulting water phase and the mixture was heated until the solid was fully dissolved, then the homogeneous solution was acidified with lM HC1 until no further precipitate was detected. The red solid was collected by filtration, washed with water and dried in vacuum.

Synthesis ofSiTD

A 100 ml round-bottomed flask was fitted with a Claisen adapter on which a condenser was attached. The flask was charged with 0.88 g (127 mmol) of Li, 20 ml of anhydrous diethyl ether and a magnetic stirring bar. The system was flushed with N2 and 10.34 ^ml (60.3 mmol) of 4-bromotoluene in 30 ml of anhydrous diethyl ether was added slowly with rapid stirring. An immediate exothermic reaction caused the ether to start boiling. The mixture was stirred for 30 min and 1.14 ml (10 mmol) of silicon tetrachloride was added dropwise. The mixture was stirred for an additional 30 min and quenched by the slow addition of 5 ml of water at o °C. Diethyl ether was removed by rotary evaporation and the product was isolated by vacuum filtration. Recrystallization from cyclohexane gave 3.59 g (92%) of tetra-p-tolylsilane as white solid.

To the solution of tetra-p-tolylsilane (1.00 g, 2.55 mmol) in water (2.5 mL) and pyridine (3.4 mL) was added KMn0₄ (4.83 g, 30.6 mmol). The reaction temperature was maintained at 95 °C for 4 hr and then KMn0₄ (4.83 g, 30.6 mmol), water (2.5 mL) and pyridine (3.4 mL) were added at room temperature. The reaction temperature was maintained at 95 °C for 16 hr. Excess permanganate was quenched by adding methanol. Mn0₂ being formed was removed by suction filtration and washed with hot water. The filtrate was acidified with cone. HC1 till pH = 1. The solid precipitated from the filtrate was collected, redissolved in aqueous NaOH (5 %) and filtrated again to remove insoluble impurity. The solution was then acidified with cone. HC1 to give the product as white solid (0.66 g, 50 %).

1,3,5-benzenetricarboxylic acid (BTC) was purchased from Alfa Aesar.

BTC:

L22 (10 mg), Fe(N03)3.9H20 (40 mg) and acetic acid (1 ml) in 2 ml of DMF were ultrasonically dissolved in a Pyrex vial. The mixture was heated in 150°C oven overnight. After cooling down to room temperature, dark brown crystals

(monocrystalline) were harvested by filtration. Yield: ~8o%.

L22 (10 mg), Fe(N03)3.9H20 (40 mg) in 2 ml of acetic acid were ultrasonically dissolved in a Pyrex vial. The mixture was heated in 150°C oven overnight. After cooling down to room temperature, dark brown (monocrystalline) crystals were harvested by filtration. Yield: ~8o%.

Fe(N0₃)₃.9H₂0 (40mg), L22 (lomg), H₂0(imL), acetic acid(imL), 150°C overnight. Yield: ~8o%

ABTC (10 mg), Fe(N03)3.9H20 (40 mg) in 2 ml of acetic acid/H20 (v:v=i:i) solvent were ultrasonically dissolved in a Pyrex vial. The mixture was heated in 150°C oven overnight. After cooling down to room temperature, dark brown (monocrystalline) crystals were harvested by filtration. Yield: ~8o%.

[Fe₃0(OH)(OOCCH₃)₆](io mg) and ABTC (10 mg) were dissolved in 2 mL of acetic acid. After being ultrasoniced, the mixture was heated in 200 °C oven for 24 h. After cooling down to room temperature, dark crystals were harvested by filtration.

Figure 2 shows an optical microscope image of PCN-250-Fe.

Figure 3 shows the N₂ adsorption isotherms of PCN-250-Fe. Figure 4 shows the powder x-ray diffraction pattern (PXRD) of PCN-250-Fe.

Figure 5 shows the thermogravimetric (TG) analysis for PCN-250-Fe.

Example 4 - Preparation of PCN-224-Zr

ZrCl4 (10 mg) and Co-TCPP (10 mg) in 2 mL of acetic acid were ultrasonically dissolved in a 4 mL Pyrex vial. The mixture was heated in 120 °C oven for 12 h. After cooling down to room temperature, dark crystals were harvested by filtration.

Figure 6 shows an optical microscope image of PCN-224-Zr.

Figure 7 shows the N₂ adsorption isotherms of PCN-224-Zr. Figure 8 shows the powder x-ray diffraction pattern (PXRD) of PCN-224-Zr. Figure 9 shows the thermogravimetric (TG) analysis for PCN-224-Zr.

Example - Preparation of PCN-6^i-Fe

[Fe₃0(OH)(OOCCH₃)₆](20 mg) and SiTD (20 mg) were dissolved in 2 mL of acetic acid. After being ultrasoniced, the mixture was heated in 220 °C oven for 24 h. After cooling down to room temperature, dark dark crystals were harvested by filtration.

Figure 10 shows the powder x-ray diffraction pattern (PXRD) of PCN-651-Fe. Example 6 - Preparation of PCN-6 2-Fe

[Fe₃0(OH)(OOCCH₃)₆](io mg) and BTC (10 mg) were dissolved in 2 mL of acetic acid. After being ultrasoniced, the mixture was heated in 200 °C oven for 12 h. After cooling down to room temperature, dark dark crystals were harvested by filtration.

Figure 11 shows the powder x-ray diffraction pattern (PXRD) of PCN-652-Fe. Results

As can be seen from the examples above, the use of a carboxylic acid solvent (without other organic solvents) surprisingly provides a metal organic framework in comparable yield to the method described in the reference example. The solvents employed in the methods of the invention can also be recycled and reused in a subsequent method of preparing a metal organic framework. In contrast, the solvents employed in the method of the reference example cannot be recycled and reused. This represents a significant advantage of the present invention compared to the methods that have been described earlier. Without wishing to be bound by theory, the applicants believe that organic solvents such as DMF undergo decomposition and hence cannot be recycled but carboxylic acid solvents are not being decomposed and therefore can be recycled and reused.

Furthermore, the method of the invention (exemplified by Examples 1 and 2) provides metal organic frameworks exhibiting a high degree of crystallinity. In particular, the methods of the invention provide monocrystalline metal organic frameworks comprising metal ions and carboxylate ligands. Without wishing to be bound by theory, it is believed that the carboxylic acid acts as a modulator and competing controlling reagent, which helps grow single crystal products. In other words, the presence of the carboxylic acid (e.g. acetic acid) slows down the reaction of the carboxylic acid ligand precursor with the source of metal ions (e.g a metal salt or a metal ion coordination complex). This reduction in the reaction rate allows crystals to grow slower and larger.

Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the scope of the invention as set forth in the following claims.

Claims

1. A method of preparing a metal organic framework comprising metal ions and carboxylate ligands;

the method comprises:

reacting (i) a source of metal ions, with (ii) a carboxylic acid precursor of a the carboxylate ligands, in an organic solvent consisting of one or more carboxylic acid solvents, at a temperature of about 75°C or greater, optionally in the presence of water.

2. The method of claim 1, wherein the metal ions comprise metal ions selected from the transition metals of the periodic table.

3. The method of claim 2, wherein the metal ions comprise metal ions selected from Fe, Al, Cr, V, Sc, Zr, Ti and In metal ions.

4. The method of claim 3, wherein the metal ions comprise metal ions selected from Fe and Zr.

5. The method of any one of claims 2 to 4, wherein the metal ions comprise only one metal.

6. The method of any one of claims 2 to 4, wherein the metal ions further comprise metal ions selected from Group 2 through Group 16 metal ions.

7. The method of claim 1, wherein the metal ions comprise a metal cation mixture of M metal ions and X metal ions; wherein M is a transition metal ion, and X is selected from the group consisting of Group 2 through Group 16 metal ions.

8. The method of claim 7, wherein the metal ions comprise a metal cation mixture of formula M₂X.

9. The method of claim 7 or claim 8, wherein M is selected from Fe, Al, Cr, V, Sc, Ti, Zr, and In metal ions.

10. The method of any one of claims 7 to 9, wherein X is selected from Al(III), Fe(II), Fe(III), Co(II), Ni(II), Mn(II), Zn(II), Mg(II), Cr(III), V(III), Sc(III), Ca(II), Ba(II) and In(III) metal ions.

11. The method of claim 10, wherein X is selected from Fe(II), Fe(III), Co(II), Ni(II), Mn(II), Zn(II), and Mg(II) metal ions.

12. The method of any one of claims claim 7 to 11, wherein the metal ions comprise M²⁺ metal ions, M3+ metal ions, or M4+ metal ions.

13. The method of any one of the preceding claims, wherein the source of metal ions is a metal salt, a metal ion coordination complex, or a hydrate thereof.

14. The method of claim 13, wherein the metal salt is selected from FeCl₃, ZrCl₄, Fe(N0₃)₃.9H₂0, A1C1₃, A1(N0₃)₃, and VC1₃.

15. The method of claim 13, wherein the metal ion coordination complex is selected from [Fe₃0(OAc)₆(H₂0)₃]OAc and a complex of formula FeM₂0(CH₃COO)₆ wherein each M is independently selected from Mn, Fe, Co, Ni, and Zn.

16. The method of any one of the preceding claims, wherein the carboxylic acid precursor is a dicarboxylic acid, a tricarboxylic acid, or a tetracarboxylic acid.

17. The method of claim 16, wherein the carboxylic acid is 3,5-dicarboxyl-(3,5- dicarboxylazophenyl)benzene:

18. The method of any one of the preceding claims, wherein the organic solvent is selected from acetic acid, propionic acid, or trifluoroacetic acid.

19. The method of claim 18, wherein the organic solvent is acetic acid.

20. The method of any one of the preceding claims, wherein the reaction is carried out in the presence or absence of water.

21. The method of any one of the preceding claims, wherein the reaction is carried out at a temperature of about 120°C or greater, preferably at a temperature of about 150°C or greater.