METAL-INORGANIC FRAMEWORKS

Abstract

Metal-inorganic frameworks (“MIFs”) having enhanced adsorption capabilities to hydrogen, CO, CO.sub.2, hydrocarbons, and a variety of other guest molecules are disclosed. All linkers in the MIFs contain metal complexes, comprising metal atoms and inorganic or organic ligands, instead of only organic ligands as linkers in metal-organic frameworks (MOFs). Compared to their MOF counterparts, MIFs with carbon-free or carbon-deficient chemical structure are expected to possess enhanced thermal stability, higher catalytic activity, and higher gas affinity and selectivity.

Claims

1. A metal-inorganic framework (MIF) coordination polymer comprising: a plurality of metal clusters, each metal cluster comprising one or more metal ions; and a plurality of linking complexes connecting adjacent metal clusters.

2. The MIF of claim 1, wherein the one or more metal ions comprises Zr.sup.4+, Zn.sup.2+, Ni.sup.2+, Mn.sup.2+, or a combination thereof.

3. The MIF of claim 1, wherein the linking complexes are linear/two-coordinate, trigonal planar/three-coordinate, or square planar/four-coordinate, or combinations thereof.

4. The linking complexes of claim 3, wherein the linking complexes are oligomeric or polymeric associative linker aggregates.

5. The MIF of claim 1, wherein the metal-inorganic framework comprises a [Pt.sub.2(P.sub.2O.sub.5H.sub.2)].sup.4− dimeric 4-coordinate/square planar complex linker.

6. The MIF of claim 1, wherein the metal-inorganic framework comprises a trinuclear gold(I) 2-coordinate/linear complex linker.

7. The MIF of claim 1, wherein the metal-inorganic framework comprises a [Au(TPPTS).sub.3].sup.8− 3-coordinate/trigonal planar complex linker.

8. The MIF of claim 1, wherein the MIF is carbon-free.

9. The MIF of claim 1, wherein the MIF has one or more cavities suitable for containing one or more gas molecules.

10. The MIF of claim 1, wherein the MIF has an average pore size of about 10 Å.

11. The MIF of claim 1, wherein the MIF has a pore volume of 0.13 cm.sup.3/g.

12. The MIF of claim 1, wherein the MIF has a maximum pore volume of 0.1325 cm.sup.3/g.

13. The MIF of claim 1, wherein the MIF has a surface area of at least about 80 m.sup.2/g as measured by the BET method.

14. A method of storing a gas within a metal-inorganic framework (MIF) comprising: contacting a MIF having an average pore size of 10 Å with a gas; wherein the gas is at a pressure ranging from 14.5 to 725 psi.

15. The method of claim 14, wherein the MIF comprises a [Pt.sub.2(P.sub.2O.sub.5H.sub.2)].sup.4− dimeric four-coordinate/square planar complex linker.

16. The method of claim 14, wherein the MIF comprises a trinuclear gold(I) two-coordinate/linear complex linker.

17. The method of claim 14, wherein the MIF comprises a [Au(TPPTS).sub.3].sup.8− three-coordinate/trigonal planar complex linker.

18. The method of claim 14, wherein the MIF is carbon-free.

19. The method of claim 14, wherein the gas is hydrogen, carbon monoxide, carbon dioxide, a hydrocarbon, nitrogen, oxygen, ammonia, chlorine, a noble gas, hydrogen sulfide, or a solvent vapor.

20. The method of claim 14, wherein said step of contacting the MIF having an average pore size of 10 Å with a gas is performed at a temperature ranging from 50 to 85 Kelvin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 demonstrates the building blocks of the carbon-free MIF series MIF-1 through MIF-4.

[0021] FIGS. 2A-2C. FIG. 2A depicts a reaction scheme for building blocks of a MIF-II series (M=Pt.sup.2+), a MIF-III series (M=Pd.sup.2+), and a MIF-IV series (M=Ni.sup.2+), and MIF-V series (M=Cu.sup.2+). FIG. 2B depicts a reaction scheme for the synthesis of a 5-(pyridine-2-yl)-4H-1,2,4-triazole-3-carboxylic acid ligand. The ligand coordinates to the M linker in FIG. 2A with R=COOH. FIG. 2C depicts a reaction scheme for the synthesis of a 4-(5-(pyridine-2-yl)-4H-1,2,4-triazol-3-yl) benzoic acid ligand. The ligand coordinates to the M linker in FIG. 2A with R=p-C.sub.6H.sub.4-COOH. Sub-series are defined by x for the linker's metal M, AB for the R group, and number for the second metal M′; e.g., “MIF-III-B-1” denotes the sub-series with M=Pd.sup.2+, R=COOH, and M′=Zr.sup.4+

[0022] FIG. 3 illustrates building blocks of the MIF-VI series (top: representative embodiments MIF-VI-1 through MIF-VI-4) and the MIF-VII series (bottom: MIF-VII-A through MIF-VII-C).

[0023] FIG. 4 illustrates building blocks of the MIF-VIII series MIF-VIII-1 through MIF-VIII-4.

[0024] FIGS. 5A-5B. FIG. 5A is a plot of nitrogen adsorption isotherms at 77 K for MIF-1 (BET surface area=266.5 m.sup.2/g; approximate pore size=10 Å). FIG. 5B is a plot of nitrogen adsorption isotherms at 77 K for MIF-4 (BET surface area=86.3 m.sup.2/g).

[0025] FIGS. 6A-6C. FIG. 6A is an image of MIF-1, MIF-2, and NaPtPOP starting material/precursor. FIG. 6B is an image illustrating enhancements in the photoluminescence quantum yield. MIF-1=1045% enhancement vs Na.sub.4[Pt(POP).sub.4] control. MIF-2=610% enhancement vs Na.sub.4[Pt(POP).sub.4] control. FIG. 6C is an image illustrating stability upon extended storage in air for MIF-1 and MIF-2 vs the NaPtPOP starting material/precursor as a control.

[0026] FIG. 7 is a graph of the solid-state absorption spectra for MIF-3 and MIF-4 vs MIF-1 along with photographs of each solid sample at ambient room light.

[0027] FIGS. 8A-8C. FIG. 8A illustrates the linear geometry of a 2-coordinate MIF linker. FIG. 8B illustrates the trigonal geometry of a 3-coordinate MIF linker. FIG. 8C illustrates the square-planar geometry of a 4-coordinate MIF linker.

DETAILED DESCRIPTION

[0028] Currently available MOFs are lacking with respect to thermal stability, catalytic activity, gas affinity, and gas selectivity. This leads to performance and cost inefficiencies when using such membranes in applications such as hydrogen gas storage.

[0029] It has now been discovered that inorganic complexes may be used to synthesize porous frameworks. The metal-inorganic frameworks possess enhanced thermal stability, higher catalytic activity, and higher gas affinity and selectivity.

[0030] Disclosed herein is a new class of porous materials and coordination polymers called “metal-inorganic frameworks” or “MIFs” having internal channels and cavities in a variety of configurations that are capable of adsorbing small guest molecules. The MIFs are connected by inorganic complexes instead of organic molecules as linkers or building blocks.

[0031] The MIFs disclosed herein possess a variety of low-dimensional linear, trigonal-planar, square-planar, and/or macrocyclic-planar oligomeric clusters and 2-dimensional infinite-sheet assembly geometries with a variety of metal atoms bridging the inorganic linkers. H.sub.2 molecules can adsorb much more strongly in MIFs than they do in typical MOFs. Therefore, ambient and near-ambient storage of H.sub.2 can be achieved in MIFs.

[0032] A. Carbon-Free MIFs

[0033] A carbon-free MIF series is depicted in FIG. 1. The carbon-free MIFs are synthesized by a metathesis reaction that replaces the cation from a non-coordinating counter-ion such as Na.sup.+ or K.sup.+ in Na.sub.4[Pt.sub.2(P.sub.2O.sub.5H.sub.2)].2H.sub.2O (sodium dihydrotetrakis (pyrophosphito) platinum(II), “NaPtPOP”) or K.sub.4[Pt.sub.2(P.sub.2O.sub.5H.sub.2)].2H.sub.2O (potassium dihydrotetrakis (pyrophosphito) platinum(II), “KPtPOP”). The MIFs are synthesized using a microwave-assisted procedure (Satumtira, 2012), with a coordinating metal ion such as Zr.sup.4+, Zn.sup.2+, Mn.sup.2+, or Ni.sup.2+, leading to the isolation of representative embodiments MIF-1, MIF-2, MIF-3, and MIF-4, respectively.

[0034] B. Methods of Making MIFs

[0035] The MIF-II, MIF-III, MIF-IV, and MIF-V series identified in FIG. 2 are synthesized by a novel synthetic scheme. FIG. 2A shows the inorganic synthesis of the building blocks of the MIF-II series (M=Pt.sup.2+), MIF-III series (M=Pd.sup.2+), and MIF-IV series (M=Ni.sup.2+), and MIF-V series (M=Cu.sup.2+). FIG. 2B shows the synthesis of a ligand that coordinates to the M atoms in the linker with R=COOH. FIG. 2C shows the synthesis of a ligand that coordinates to the M atoms in the linker with R p-C.sub.6H.sub.4COOH. Subsequent coordination of the inorganic linkers to coordinating metal ions (M′) such as Zr.sup.4+, Zn.sup.2+, Mn.sup.2+, or Ni.sup.2+leads to the isolation of representative embodiments MIF-x-A/B-1, MIF-x-A/B-2, MIF-x-A/B-3, and MIF-x-A/B-4, respectively, e.g., “MIF-V-A-3” denotes the sub-series with M=Cu.sup.2+, R=p-C.sub.6H.sub.4COOH, and M′=Mn.sup.2+.

[0036] The MIF-VI and MIF-VII series shown in FIG. 3 are synthesized by a metathesis reaction that replaces the acidic COOH protons in the cyclic trinuclear gold(I) complex starting material. The MIF-V and MIF-VI series were synthesized using a previously published procedure (Upadhyay, 2015), with a coordinating, hard, metal ion (M) such as Zr.sup.4+, Zn.sup.2+, Mn.sup.2+, or Ni.sup.2+, leading to the isolation of representative embodiments MIF-x-1, MIF-x-2, MIF-x-3, and MIF-x-4, respectively, with x=VI (MIF-VI series without a second coordinating, soft, M′ metal ion), VII-A (MIF-VII-A series in the presence of a second coordinating, soft, M′ metal ion=Ag.sup.+), VII-B (MIF-VII-B series in the presence of a second coordinating, soft, M′ metal ion=T1.sup.+), or VII-C (MIF-VII-C series in the presence of a second coordinating, soft, M′ metal ion=Pb.sup.2+).

[0037] The MIF-VII series shown in FIG. 4 were synthesized by a metathesis reaction to replace the cation from a non-coordinating counter-ion such as Na.sup.+ in Na.sub.8[Au(TPPTS).sub.3].2H.sub.2O (sodium tris(tris[3,3′,3″-trisulfonatophenyl]phosphine)aurate(I), which was synthesized following a published procedure (Marpu et al., 2010), with a coordinating metal ion such as Zr.sup.4+, Zn.sup.2+, Mn.sup.2+, or Ni.sup.2+, leading to the isolation of representative embodiments MIF-VIII-1, MIF-VIII-2, MIF-VIII-3, and MIF-VIII-4, respectively.

[0038] C. Applications

[0039] In contrast to the MOFs described above, the MIFs disclosed herein possess a variety of low-dimensional (linear, trigonal-planar, square-planar, macrocyclic-planar, oligomeric clusters of all the above, and 2-dimensional infinite-sheet assemblies of all the above) geometries with a variety of metal atoms within the inorganic linker. One advantage of the presently claimed MIFs is that they can absorb H.sub.2 molecules can adsorb much more strongly typical MOFs. Therefore, ambient and near-ambient storage of H.sub.2 can be achieved in MIFs.

[0040] D. Examples

[0041] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

[0042] Example 1

[0043] Nitrogen Adsportion Isotherms

[0044] Nitrogen adsorption isotherms at 77 K, shown in FIG. 5, reveal that MIF-1 and MIF-4 are porous with a BET surface area of at least 266.5 m.sup.2/g and 86.3 m.sup.2/g, respectively; the approximate pore size of MIF-1 was 10 Å, whereas MIF-2 and MIF-3 attained lower porosity parameters. These results validate the concept of attaining permanent porosity in this series of carbon-free MIFs and demonstrate that the extent of porosity can be tuned with the alteration of the coordinating ion to the linker. Optimization of the activation process to remove water/solvent molecules improves the aforementioned lower limits prior to investigating the gas uptake of H.sub.2, CH.sub.4, and other gases and guest species at variable pressure, temperature, and other experimental conditions relevant to different applications.

[0045] Example 2

[0046] Optical Properties and Shelf-Life Enhancement

[0047] The MIF formation mechanism gives rise to dramatic enhancement in the photoluminescence quantum yield (Φ) and shelf-life (stability upon extended storage in air) for MIF-1 and MIF-2 vs the NaPtPOP starting material/precursor as a control. As illustrated in FIG. 6B, >1000% enhancement in CD was attained for MIF-I, whereas a >600% enhancement was attained for MIF-2.

[0048] The shelf-life improved dramatically as evidenced by visual inspection of all MIF samples that maintained their original color even upon multiple months of exposure to storage under ambient air/light/moisture conditions, whereas the NaPtPOP control sample has undergone rather clear discoloration indicating its decomposition under the same storage conditions. Compare appearance of original samples (FIG. 6A) to samples after multiple months of exposure to ambient air/light/moisture conditions (FIG. 6C). Exposed MIF-1 and MIF-2 resemble original samples MIF-1 and MIF-2 in appearance. The appearance of exposed NaPtPOP control sample is significantly different from the original NaPtPOP control sample, indicating that some decomposition has occurred.

[0049] Another manifestation of the sensitivity of the photoluminescence properties of the MIF series to chemical composition is the quenching of the photoluminescence in the presence of paramagnetic ions such as Mn.sup.2+(d.sup.5) and Ni.sup.2+(d.sup.8), leading to non-luminescent MIF-3 and MIF-4 solids, unlike the situation for the MIF-1 and MIF-2 frameworks that contain diamagnetic Zr.sup.4+)(d.sup.0) and Zn.sup.2+ (d.sup.10) metal ions, respectively. These differences are illustrated in the solid-state absorption spectra for MIF-3 and MIF-4 vs MIF-1, as shown in FIG. 7. Thus, the weak features at long wavelengths for MIF-3 and MIF-4 are due to dd ligand-field transitions responsible for the quenching of their photoluminescence, whereas these features are absent in MIF-1. By contrast, the sharp signal decline at short wavelengths in MIF-1 is due to its strong photoluminescence, whereas this decline is absent in the non-luminescent MIF-3 and MIF-4 solid samples.