# Patent

## Title
Zn3(BDC)3[Cu(SalPycy)] and Zn3(CDC)3[Cu(SalPycy)]—enantiopure mixed metal-organic frameworks for selective separations and enantioselective recognition

## Abstract

Disclosed herein are mixed metal-organic frameworks, Zn3(BDC)3[Cu(SalPycy)] and Zn3(CDC)3[Cu(SalPycy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:




These are useful for applications such as selective gas storage, selective molecular separations, and selective detection of molecules, including enantioselective applications thereof.

## Background
This application claims the benefit of U.S. Provisional Patent Application No. 61/632,061, filed Jan. 17, 2012, the entirety of which is incorporated herein by reference.


This invention was made with government support under grant number CHE 0718281 from the National Science Foundation. The government has certain rights in the invention.


BACKGROUND OF THE INVENTION
I. Field of the Invention
The present disclosure relates generally to the fields of chemistry and materials science. More particularly, it concerns metal-organic frameworks, compositions thereof and methods use thereof, including for storing, detecting, and separating of gas and/or liquid molecules.
II. Description of Related Art
Microporous metal-organic frameworks (MOFs) have been rapidly emerging as new type of porous materials for gas storage, separation, sensing and heterogeneous catalysis. The tunable pores and the immobilized functional sites within such microporous MOFs have enabled them to direct specific recognition of certain molecules, and thus for their highly selective guest sorption and separation. The diverse metal ions and/or metal-containing clusters as the nodes and a variety of organic linkers as the bridges to construct the porous coordination polymers (PCPs) by the coordination bonds have led to a series of porous MOFs from ultramicroporous to mesoporous domains. Although thousands of MOFs have been synthesized and structurally characterized over the past two decades, those exhibiting permanent porosity and thus being classified as porous MOFs are still of few percentage. This is primarily due to the labile coordination geometries of the metal ions and/or metal-containing clusters, and the flexibility of the bridging organic linkers which cannot sustain the frameworks under vacuum and/or thermal activation. One efficient strategy to stabilize the PCPs and thus to construct porous MOFs is to make use of rigid clusters (Fang et al., 2006a; Fang et al., 2006b; Bai et al., 2008; Wang et al., 2009), as exemplified in those MOFs with the binuclear paddle-wheel M2(COO)6 (M=Cu2+, Co2+, Ni2+ and Zn2+) and tetranuclear Zn4O(COO)6 as the secondary building units (Eddaoudi et al., 2000). Another strategy to stabilize the frameworks is to make use of the framework interpenetration and/or interwoven to enforce the framework interactions (Ma and Lin, 2009; Kesanli et al., 2005). This approach has been successful in constructing interpenetrated MOFs with higher permanent porosity than their non-interpenetrated analogues (Ma et al., 2007; Ma et al., 2008).
Precise control of pore sizes and pore surfaces within porous materials is very important for their highly selective recognition and thus separation of small molecules, but very challenging and difficult to be realized in traditional zeolite materials (Kuznicki et al., 2001). The situation has been changing since the emerging of the new type of porous materials, so-called microporous metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) over the past two decades. This is because the pores within such porous MOFs, particularly those within isoreticular metal-organic frameworks whose structures are pre-determined by the coordination geometries of the secondary building blocks (SBUs), can be systematically modified simply by the change of different organic bridging linkers and the control of the framework interpenetration (Deng et al., 2010; Chen et al., 2010; Ma et al., 2010; Horike et al., 2009). Furthermore, the pore surfaces within such porous MOFs can be functionalized by the immobilization of different recognition sites such as the open metal sites, the Lewis basic/acidic sites, and chiral pockets to direct their specific recognition of small molecules (Britt et al., 2009; Shimomura et al., 2010; Rabone et al., 2010; Devic et al., 2010; Seo et al., 2000; Morris and Bu, 2010; Chen et al., 2009; Yang et al., 2009; Xie et al., 2010). In fact, to systematically tune the micropores to induce their size specific encapsulation of small gas molecules and to immobilize functional sites to direct their different interactions with the substrates, various series of microporous metal-organic framework materials have been emerging as the promising microporous media for the recognition and separation of small molecules (Kitaura et al., 2004; Chen et al., 2004; Cho et al., 2006; Liu et al., 2010; Murray et al., 2010; Ma et al., 2009; McKinlay et al., 2008; Dubbeldam et al., 2008; Chen et al., 2006; Finsy et al., 2008; Bae et al., 2010; Zhang et al., 2008; Dybtsev et al., 2004; Li et al., 2009; Vaidhyanathan et al., 2006; Nuzhdin et al., 2007; Dybtsev et al., 2006; Chen et al., 2008).
Kitagawa pioneered the research on construction of porous mixed-metal-organic frameworks (M′MOFs) by making use of M-Salen metalloligands in 2004 (Kitaura et al., 2004; Chen et al., 2004). Such a novel approach eventually led to few porous M′MOFs for heterogeneous asymmetric catalysis and enantioselective separation (Ma et al., 2010; Cho et al., 2006; Liu et al., 2010). More recently, this metalloligand or pre-constructed building block approach has been successfully developed to construct porous metal-organic frameworks, and realized the first such mixed-metal-organic framework (M′MOF) Zn3(BDC)3[Cu(SalPyen)].(G)x (M′MOF-1; BDC=1,4-benzenedicarboxylate; SalPyenH2=Schiff base condensed from 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde and ethylenediamine; G=guest molecules) with permanent porosity clearly established by both gas and vapor sorption (Chen et al., 2008). This new M′MOF approach has provided us with a new dimension to tune and functionalize the micropores within this series of isoreticular M′MOFs by (a) the incorporation of different secondary organic linkers, (b) the immobilization of different metal sites other than Cu2+, (c) the introduction of chiral pockets/environments through the usage of chiral diamines, and (d) the derivatives of the precursor through the usage of other organic groups such as t-butyl instead of methyl group, and thus to explore novel functional microporous M′MOFs for their recognition and separation of small molecules.
Although thousands of MOFs and M′MOFs have been synthesized and structurally characterized over the past two decades, the ones with open metal sites are still relatively few (Chen et al., 2010; Dinca and Long, 2008), this is mainly because such open metal sites are typically very reactive and tend to bind the atoms from the neighboring ligands to form the condensed structures. Also, few MOFs have been shown to be useful for selective sorption, separation and/or sensing of guest molecules. Accordingly, identifying and developing new MOFs and/or M′MOFs that exhibit one or more of these useful properties is desirable.
SUMMARY OF THE INVENTION
Disclosed herein are new mixed-metal organic frameworks (M′MOFs) comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:




In some embodiments, the repeat unit is of the formula Zn3(BDC)3[Cu(SalPyCy)]. In some embodiments, the repeat unit is of the formula Zn3(CDC)3[Cu(SalPyCy)].
In some embodiments, the M′MOFs further comprises one or more than one type of guest molecule. In some embodiments, one type of guest molecules is a solvent molecule. In some embodiments, the solvent molecule is water. In some embodiments, the solvent molecule is N,N′-diethylformamide. In some embodiments, the M′MOFs further comprise about five N,N′-diethylformamide and four water molecules per repeat unit.
In some embodiments, one type of guest molecules is 1-phenylethanol. In some embodiments, the 1-phenylethanol is at least 80% R-1-phenylethanol. In some embodiments, the 1-phenylethanol is at least 80% S-1-phenylethanol. In some embodiments, the M′MOFs further comprise about five N,N′-diethylformamide and one 1-phenylethanol per repeat unit.
In some embodiments, one type of guest molecule is a gas molecule. In some embodiments, the gas molecule is H2, N2, Ar, O2, CO2, NO, NO2 or CO.
In some embodiments, one type of guest molecule is an alkane(C1-6), alkene(C2-4), alkyne(C2-6), alcohol(C1-6), arene(C6-8) or a substituted version of any of these. In some embodiments, one type of guest molecule is an alkane(C1-6). In some embodiments, the alkane(C1-6) is C2H6, C3H, C4H10, C5H12 or C6H14. In some embodiments, the alkane(C1-6) is a cycloalkane(C3-6) selected from the group consisting of C3H6, C4H8, C5H10 and C6H12.
In some embodiments, one type of guest molecule is an alkene(C2-6). In some embodiments, the alkene(C2-6) is C2H4, C3H6, C4H8, C5H10 or C6H12. In some embodiments, the alkene(C2-6) is C2H4.
In some embodiments, one type of guest molecule is an alkyne(C2-6). In some embodiments, the alkyne(C2-6) is C2H2.
In some embodiments, one type of guest molecule is an alcohol(C1-6). In some embodiments, the alcohol(C1-6) is methanol, ethanol, n-propanol, isopropanol, n-butanol or isobutanol.
In some embodiments, the M′MOF is substantially free from any solvent molecules.
In some embodiments, the M′MOFs have a weight percentage at least 90% attributable to repeat units of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)]. In some embodiments, the M′MOFs have a weight percentage at least 95% attributable to repeat units of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)]. In some embodiments, the M′MOFs have a weight percentage at least 99% attributable to repeat units of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)].
In some embodiments, the stereochemistry of the SalPyCy ligand is further defined as:




wherein R indicates the stereochemical conformation of the indicated carbon atoms.

In another aspect, the present invention provides methods of storing a compound within a mixed-metal-organic framework (M′MOF) comprising:

    (a) obtaining an M′MOF comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:






and

    (b) combining the M′MOF with a first compound such that the first compound is contained within the M′MOF.


In another aspect, the present invention provides methods detecting a compound using an M′MOF comprising:

    (a) obtaining an M′MOF comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:






    (b) combining the M′MOF with a first compound such that the first compound enters the M′MOF to form an M′MOF.guest complex; and
    (c) comparing the photoluminescence intensity of the M′MOF with the photoluminescence intensity of the M′MOF.guest complex so as to detect the first compound.


In another aspect, the present invention provides methods separating two or more compounds using an M′MOF comprising:

    (a) obtaining a mixed-metal-organic framework (M′MOF) comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:






    (b) combining the M′MOF with a mixture comprising a first compound and a second compounds; and
    (c) separating the two or more compounds based on their differential diffusion rate within the M′MOF.


In some embodiments, the first compound is independently selected from the group consisting of alkane(C1-6), alkene(C2-4), alkyne(C2-6), alcohol(C1-6), arene(C6-8) and a substituted version of any of these, provided that the first and the second compound are not the same. In some embodiments, the first compound is an alkane(C1-6). In some embodiments, the alkane(C1-6) is CH4, C2H6, C3H8, C4H10, C5H12 or C6H14.
In some embodiments, the first compound is an alkene(C2-6). In some embodiments, the alkene(C2-6) is C2H4, C3H6, C4H8, C5H10 or C6H12. In some embodiments, the alkene(C2-6) is C2H4.
In some embodiments, the first compound is an alkyne(C2-6). In some embodiments, the alkyne(C2-6) is C2H2.
In some embodiments, the first compound is a gas molecule. In some embodiments, the gas molecule is H2, N2, Ar, O2, CO2, NO, NO2 or CO. In some embodiments, the gas molecule is CO2.
In some embodiments, the second compound is independently selected from the group consisting of alkane(C1-6), alkene(C2-4), alkyne(C2-6), alcohol(C1-6), arene(C2-6) and a substituted version of any of these, provided that the second and the second compound are not the same. In some embodiments, the second compound is an alkane(C1-6). In some embodiments, the alkane(C1-6) is CH4, C2H6, C3H8, C4H10, C5H12 or C6H14. In some embodiments, the second compound is an alkene(C2-6). In some embodiments, the alkene(C2-6) is C2H4, C3H6, C4H8, C5H10 or C6H12. In some embodiments, the alkene(C2-6) is C2H4. In some embodiments, the second compound is an alkyne(C2-6). In some embodiments, the alkyne(C2-6) is C2H2.
In some embodiments, the stereochemistry of the SalPyCy ligand is further defined as:




wherein R indicates the stereochemical conformation of the indicated carbon atoms.

Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.



BRIEF DESCRIPTION OF THE DRAWINGS
The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present disclosure. The invention may be better understood by reference to one of these drawings in combination with the detailed description of specific embodiments presented herein.
FIGS. 1a-d show X-ray crystal structures of M′MOF-3 showing (a) the hexagonal primitive network topology (Schäfli symbol 36418536) and (b) the 3D pillared framework with chiral pore cavities, and M′MOF-3⊃S-PEA showing (c) the hexagonal primitive network topology and (d) the 3D pillared framework exclusively encapsulating S-PEA molecules (Zn, pink; Cu, cyan; O, red; C, grey; N, blue; H, white).
FIG. 2 shows gas sorption isotherms of CO2 on M′MOFs-2a (blue solid square) and -3a (red solid circle) at 195 K. Solid symbols indicate adsorption; empty symbols indicate desorption.
FIGS. 3a & b show adsorption isotherms of acetylene (green solid square) and ethylene (blue solid triangle) on (a) M′MOF-2a and (b) M′MOF-3a at 195 K. Solid symbols indicate adsorption; empty symbols indicate desorption.
FIGS. 4a & b show adsorption isotherms of acetylene (blue solid square), CO2 (red solid circle) and ethylene (green solid triangle) on M′MOF-2a at 273 K (FIG. 4a) and 295 K (FIG. 4b). Solid symbols indicate adsorption; empty symbols indicate desorption.
FIGS. 5a & b show adsorption isotherms of acetylene (blue solid square), CO2 (red solid circle) and ethylene (green solid triangle) on M′MOF-3a at 273 K (FIG. 5a) and 295 K (FIG. 5b).
FIGS. 6a-f show the comparison of the enthalpies for adsorption of ethylene (a, d), acetylene (b, e) and carbon dioxide (c, f) on M′MOF-2a (FIGS. 6a-c) and M′MOF-3a (FIGS. 6d-f) from two methods: the linear extrapolation (solid blue diamond) and virial equation (empty red square).
FIG. 7 shows both the synthesis of enantiopure M′MOF Zn3(BDC)3[Cu(SalPycy)].(G)x (M′MOF-2) and M′MOF Zn3(CDC)3[Cu(SalPycy)].(G)x (M′MOF-3). It also compares the relative abilities of these MOFs to separate acetylene from ethylene, as well as their relative abilities to enantioselectively recognize chiral 1-phenylethyl alcohol (PEA).



DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
Disclosed herein are mixed metal-organic frameworks having chiral pores. These may be used for applications such as selective gas storage, selective gas detection, selective gas sorption and selective gas separation.
I. Definitions
M′MOF-1 corresponds to the formula Zn3(BDC)3[Cu(SalPyen)].(G)x, wherein G is a guest molecule.
BDC is 1,4-benzenedicarboxylate.
CDC is 1,4-cyclohexanedicarboxylate.
DMF refers to N,N′-dimethylformamide.
“Guest molecule,” or “G” in the context of a chemical formula, refers to a molecule, including a solvent molecule or a gas molecule, that is enclosed within the pores or open sites of a framework material such as an MOF or M′MOF. Examples of guest molecules include, for example, methane, water, N,N′-dimethylformamide, N,N′-diethylformamide, ethanol and nitrobenzene.
“Metal-organic frameworks” (MOFs) are framework materials, typically three-dimensional, self-assembled by the coordination of metal ions with organic linkers exhibiting porosity, typically established by gas adsorption. The MOFs discussed and disclosed herein are at times simply identified by their repeat unit (see below), that is without brackets or the subscript n. A mixed-metal-organic frameworks (M′MOF) is a subset of MOFs having two of more types of metal ions.
A “repeat unit” is the simplest structural entity of certain materials, for example, frameworks and/or polymers, whether organic, inorganic or metal-organic. In the case of a polymer chain, repeat units are linked together successively along the chain, like the beads of a necklace. For example, in polyethylene, —[—CH2CH2—]—, the repeat unit is —CH2CH2—. The subscript “n” denotes the degree of polymerisation, that is, the number of repeat units linked together. When the value for “n” is left undefined, it simply designates repetition of the formula within the brackets as well as the polymeric and/or framework nature of the material. The concept of a repeat unit applies equally to where the connectivity between the repeat units extends into three dimensions, such as in metal organic frameworks, cross-linked polymers, thermosetting polymers, etc. Note that for MOFs the repeat unit may also be shown without the subscript n.
“Pores” or “micropores” in the context of metal-organic frameworks are defined as open space within the MOFs; pores become available, when the MOF is activated for the storage of gas molecules. Activation can be achieved by heating, e.g., to remove solvent molecules.
“Multimodal size distribution” is defined as pore size distribution in three dimensions.
“Interpenetrating metal-organic framework” is defined as metal-organic frameworks interlocked with one another.
“Multidentate organic linker” is defined as ligand having several binding sites for the coordination to one or more metal ions.
When used in the context of a chemical group, “hydrogen” means —H; “hydroxy” means —OH; “oxo” means ═O; “halo” means independently —F, —Cl, —Br or —I; “amino” means —NH2, and “nitro” means —NO2.
For the groups and classes below, the following parenthetical subscripts further define the group/class as follows: “(Cn)” defines the exact number (n) of carbon atoms in the group/class. “(C≦n)” defines the maximum number (n) of carbon atoms that can be in the group/class, with the minimum number as small as possible for the group in question, e.g., it is understood that the minimum number of carbon atoms in the group “alkenyl(C≦8)” or the class “alkene(C≦8)” is two. For example, “alkoxy(C≦10)” designates those alkoxy groups having from 1 to 10 carbon atoms (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, or any range derivable therein (e.g., 3 to 10 carbon atoms). (Cn-n′) defines both the minimum (n) and maximum number (n′) of carbon atoms in the group. Similarly, “alkyl(C2-10)” designates those alkyl groups having from 2 to 10 carbon atoms (e.g., 2, 3, 4, 5, 6, 7, 8, 9, or 10, or any range derivable therein (e.g., 3 to 10 carbon atoms)).
The term “alkane” when used without the “substituted” modifier refers to a non-aromatic hydrocarbon consisting only of saturated carbon atoms and hydrogen and having a linear or branched, cyclo, cyclic or acyclic structure. Thus, as used herein cycloalkane is a subset of alkane. The compounds CH4 (methane), CH3CH3 (ethane), CH3CH2CH3 (propane), (CH2)3 (cyclopropane), CH3CH2CH2CH3 (n-butane), and CH3CH(CH3)CH3 (isobutane), are non-limiting examples of alkanes. A “substituted alkane” differs from an alkane in that it also comprises at least one atom independently selected from the group consisting of N, O, F, Cl, Br, I, Si, P, and S. The following compounds are non-limiting examples of substituted alkanes: CH3OH, CH3Cl, nitromethane, CF4, CH3OCH3 and CH3CH2NH2.
The term “alkene” when used without the “substituted” modifier refers to a non-aromatic hydrocarbon having at least one carbon-carbon double bond and a linear or branched, cyclo, cyclic or acyclic structure. Thus, as used herein, cycloalkene is a subset of alkene. The compounds C2H4 (ethylene), CH3CH═CH2 (propene) and cylcohexene are non-limiting examples of alkenes. A “substituted alkene” differs from an alkene in that it also comprises at least one atom independently selected from the group consisting of N, O, F, Cl, Br, I, Si, P, and S.
The term “alkyne” when used without the “substituted” modifier refers to a non-aromatic hydrocarbon having at least one carbon-carbon triple bond and a linear or branched, cyclo, cyclic or acyclic structure. Thus, as used herein, cycloalkyne is a subset of alkyne. The compounds C2H2 (acetylene), CH3C≡CH (propene) and cylcooctyne are non-limiting examples of alkynes. A “substituted alkyne” differs from an alkyne in that it also comprises at least one atom independently selected from the group consisting of N, O, F, Cl, Br, I, Si, P, and S.
The term “alcohol” when used without the “substituted” modifier corresponds to an alkane, as defined above, wherein at least one of the hydrogen atoms has been replaced with a hydroxy group. Alcohols have a linear or branched, cyclo, cyclic or acyclic structure. The compounds methanol, ethanol and cyclohexanol are non-limiting examples of alcohols. A “substituted alcohol” differs from an alcohol in that it also comprises at least one atom independently selected from the group consisting of N, F, Cl, Br, I, Si, P, and S.
The term “arene” when used without the “substituted” modifier refers to an hydrocarbon having at least one six-membered aromatic ring. One or more alkyl, alkenyl or alkynyl groups may be optionally attached to this ring. Also this ring may optionally be fused with other rings, including non-aromatic rings. Benzene, toluene, naphthalene, and biphenyl are non-limiting examples of arenes. A “substituted arene” differs from an arene in that it also comprises at least one atom independently selected from the group consisting of N, O, F, Cl, Br, I, Si, P, and S. Phenol and nitrobenzene are non-limiting examples of substituted arenes.
In addition, atoms making up the compounds of the present invention are intended to include all isotopic forms of such atoms. Isotopes, as used herein, include those atoms having the same atomic number but different mass numbers. By way of general example and without limitation, isotopes of hydrogen include tritium and deuterium, and isotopes of carbon include 13C and 14C. Similarly, it is contemplated that one or more carbon atom(s) of a compound of the present invention may be replaced by a silicon atom(s). Furthermore, it is contemplated that one or more oxygen atom(s) of a compound of the present invention may be replaced by a sulfur or selenium atom(s).
Any undefined valency on a carbon atom of a structure shown in this application implicitly represents a hydrogen atom bonded to the atom.
The use of the word “a” or “an,” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”
Throughout this application, the term “about” is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.
The terms “comprise,” “have” and “include” are open-ended linking verbs. Any forms or tenses of one or more of these verbs, such as “comprises,” “comprising,” “has,” “having,” “includes” and “including,” are also open-ended. For example, any method that “comprises,” “has” or “includes” one or more steps is not limited to possessing only those one or more steps and also covers other unlisted steps.
The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.
The term “hydrate” when used as a modifier to a compound means that the compound has less than one (e.g., hemihydrate), one (e.g., monohydrate), or more than one (e.g., dihydrate) water molecules associated with each compound molecule, such as in solid forms of the compound.
An “isomer” of a first compound is a separate compound in which each molecule contains the same constituent atoms as the first compound, but where the configuration of those atoms in three dimensions differs.
The term “saturated” when referring to an atom means that the atom is connected to other atoms only by means of single bonds.
The above definitions supersede any conflicting definition in any of the reference that is incorporated by reference herein. The fact that certain terms are defined, however, should not be considered as indicative that any term that is undefined is indefinite. Rather, all terms used are believed to describe the invention in terms such that one of ordinary skill can appreciate the scope and practice the present invention.
II. Synthetic Methods
Disclosed herein are the synthesis, structures, sorption and chiral recognition studies of two new M′MOFs Zn3(BDC)3[Cu(SalPycy)].(G)x (M′MOF-2) and Zn3(CDC)3[Cu(SalPycy)].(G)x (M′MOF-3). As shown in FIG. 7, enantiopure M′MOF Zn3(BDC)3[Cu(SalPycy)].(G)x (M′MOF-2) can be readily assembled, for example, by the solvothermal reaction of the chiral Cu(SalPyCy) with Zn(NO3)2 and H2BDC.
The new Salen-type chiral Schiff base of pyridine derivative H2SalPyCy was prepared by condensation of 5-methyl-4-oxo-1,4-dihydropyridine-3-carbaldehyde with (1R,2R)-cyclohexanediamine. Reaction of Cu(NO3)2.2.5H2O with H2SalPyCy formed the preconstructed building block Cu(H2SalPyCy)(NO3)2 that was incorporated into M′MOF-2 and M′MOF-3 by the solvothermal reactions with Zn(NO3)2.6H2O and H2BDC or H2CDC in DMF at 373 K as dark blue thin plates, respectively. They were formulated as Zn3(BDC)3[Cu(SalPyCy)].5DMF.4H2O (M′MOF-2) and Zn3(CDC)3[Cu(SalPyCy)].5DMF.4H2O (M′MOF-3) by elemental microanalysis and single-crystal X-ray diffraction studies, and the phase purity of the bulk material was independently confirmed by powder X-ray diffraction (PXRD). The desolvated M′MOFs-2a and -3a for the adsorption studies was prepared from the methanol-exchanged samples followed by the activation under ultra-high vacuum at room temperature, where M′MOFs-2a and -3a are used to describe the desolvated form of M′MOFs-2 and -3. The XRD profiles of desolvated M′MOFs-2a and -3a indicates that they maintains the crystalline framework structures (see Supporting Information).
X-ray single crystal structures reveal that M′MOF-2 and M′MOF-3 are isostructural three-dimensional frameworks in which Zn3(COO)6 SBUs are bridged by BDC or CDC anions to form the 36 two-dimensional tessellated Zn3(BDC)3 or Zn3(CDC)3 sheets that are further pillared by the Cu(SalPyCy) (FIGS. 1a-d). Topologically, M′MOF-2 and M′MOF-3 can be described as a hexagonal primitive networks (Schäfli symbol 36418536) which are the same as its achiral analogue Zn3(BDC)3[Cu(SalPyen)]; (O'Keeffe et al., 2008) however, the incorporation of chiral metallo-ligand Cu(SalPycy)] leads to enantiopure M′MOF-2 and M′MOF-3, exhibiting two chiral pore cavities of about 6.4 Å in diameter (FIGS. 1a-b). The chiral pore cavities are filled with the disordered solvent molecules in which M′MOF-2 and M′MOF-3 have the pore accessible volume of 51.7% and 48.1%, respectively, calculated using the PLATON program (Spek, 2001).
Further details related to the syntheses and characterization of these M′MOFs is provided in the Examples section below. The methods described herein can be further modified, optimized and scaled up using the principles and techniques of chemistry and/or materials science as applied by a person skilled in the art. Such principles and techniques are taught, for example, in Chen et al. (2005), which is incorporated by reference herein.
III. Properties and Uses of MOFs
C2H2/C2H4 separation is a very important industrial separation task as both acetylene and ethylene are essential reagents for a lot of chemical products and materials. The current approaches through partial hydrogenation of acetylene into ethylene over a supported Pd catalyst and through solvent extraction of cracked olefins using an organic solvent are costly and energy consuming. Adsorption technology might provide the resolution to separate these two important chemicals; however, no example of microporous materials exhibiting highly selective adsorption of C2H2/C2H4 has been realized so far because of their comparable molecular sizes. In some embodiments, the MOFs described herein may be used to selectively separation of C2H2/C2H4.
More generally, the MOFs disclosed herein may be used for molecular separations, molecule detection (including stereochemical recognition) and/or molecular storage. Many of these applications result from the unique micropores of the MOFs. M′MOF-2 is isostructural to the nonchiral Zn3(BDC)3[Cu(SalPyen)].(G)x (M′MOF-1). M′MOF-2 was found to have chiral cavities. Such chiral cavities can be tuned by the incorporation of different bicarboxylate CDC(CDC=1,4-cyclohexanedicarboxylate) for their enhanced recognition and separation of small molecules. In some embodiments, M′MOF-3 was found to exhibit significantly enhanced selective separation of C2H2/C2H4 and improved enantioselective recognition of 1-phenylethyl alcohol (PEA) than M′MOF-2. Both represent examples of microporous materials for the highly selective separation of molecules, including C2H2/C2H4, which represents a very important industrial separation.
To establish the permanent porosity, the methanol-exchanged M′MOFs-2 and -3 may be activated under high vacuum at room temperature overnight to form the desolvated M′MOF-2a and -3a. Nitrogen adsorption on the activated M′MOFs-2a and -3a at 77.3 K was very slow due to activated diffusion effects. Therefore, CO2 adsorption at 195 K was used for their pore characterization. Surprisingly, they exhibit remarkably different sorption isotherms attributed to the different dicarboxylates. The uptake of M′MOF-2a (158 cm3/g) is about twice that that of M′MOF-3a (86 cm3/g) at P/P0 of 1 (FIG. 2). Both M′MOF-2a and -3a show hysteretic sorption behaviors, indicating their framework flexibility and the existence of the meta-stable intermediate frameworks which have been also observed in other flexible porous MOFs (Horike et al., 2009). The Langmuir (BET) surface areas calculated from the first step adsorption isotherms are 598(388) and 237(110) m2/g, respectively, for M′MOF-2a and -3a within the pressure range of 0.05<P/P0<0.3. Assuming that the second step isotherms still fit into the monolayer coverage model, the overall Langmuir surface areas of M′MOF-2a and -3a are 939 and 551 m2/g. Their total pore volumes from the highest P/P0 values and pore volumes corresponding to the intermediate isotherm step are 0.301 (0.189) and 0.164 (0.049) cm3/g for M′MOF-2a and M′MOF-3a, respectively.
The capacities of M′MOF-2a and -3a for their selective separation of C2H2/C2H4 at 195 K were examined. For M′MOF-2a (FIG. 3a), the shapes of the isotherms are complex. Without being bound by theory, these may be attributed to the framework flexibility during adsorption. The total pore volumes were calculated from the highest P/P0 values (P/P0 ̃0.99) using densities of 0.577, 0.726 and 1.032 g cm−3 for the densities of C2H4, C2H2 and CO2, respectively. The total pore volumes were 0.306, 0.309 and 0.301 cm3 g−1 for C2H4, C2H2 and CO2, respectively; which are basically the same, indicating that all three gas molecules can have the full access to the pores within M′MOF-2a. M′MOF-3a, while exhibiting significantly different sorption behaviors with respect to C2H4 and C2H2. M′MOF-3a can take up the acetylene up to 147 cm3/g with a one-step hysteresis loop, while only small amount of ethylene (30.2 cm3/g) without the marked loop at 1 atm and 195 K (FIG. 3b). Accordingly, the total pore volumes were different, of 0.066, 0.236 and 0.165 cm3 g−1 for C2H4, C2H2 and CO2, respectively, as calculated from their highest P/P0 values, indicating that the three gas molecules have differential degree of access to the pores at 1 atm and 195 K when the pores within M′MOF-3a become smaller. Such subtle pore control is very important for these kinds of porous materials to exhibit highly selective molecular separation. In fact, M′MOF-2a can only slightly differentiate C2H2 from C2H4 with a low selectivity of 1.6, while M′MOF-3a displays significantly higher selectivity of 25.5 and thus can exclusively separate C2H2 from C2H4 (Table 1). In the diffusion of molecules into spherical or rectangular pores both cross sectional dimensions are typically important. In contrast, for slit shaped pores only the smallest dimension is typically important in determining selectivity. Without being bound by theory, such significantly enhanced separation capacity of M′MOF-3a over M′MOF-2a may be attributed to the smaller micropores within M′MOF-3a which favors its higher size-specific separation effect on the C2H2/C2H4 separation. The narrower molecular size of C2H2 (3.32×3.34×5.70 Å3) compared with that of C2H4 (3.28×4.18×4.84 Å3) has enabled the full entrance of the C2H2 into the micropores in M′MOF-3a, while C2H4 molecules are basically blocked or the kinetics are very slow.







TABLE 1







The Henry's constants or the product of the Langmuir equation constants


(qm × b) and the equilibrium selectivity for different gases on the two M′MOFs.










(a) M′MOF-2a
(b) M′MOF-3a













Temp
195 K
273 K
295 K
195 K
273 K
295 K










Henry's Constants K or qm × b (cm3 g−1 torr−1)













C2H2
239.37 × 0.0057
55.76 × 0.0078
55.09 × 0.0044
179.99 × 0.0058
50.36 × 0.0071
48.30 × 0.0058


CO2
194.65 × 0.0064
49.57 × 0.0044
43.14 × 0.0030
 98.64 × 0.0089
30.18 × 0.0025
27.75 × 0.0012


C2H4
178.88 × 0.0048
38.72 × 0.0073
39.71 × 0.0031
710.17 × 5.75 × 10−5
21.90 × 0.0040
12.45 × 0.0043







Selectivity α12













C2H2/CO2
1.10
2.00
1.89
 1.18
4.74
8.41


CO2/C2H4
1.46
0.77
1.02
21.60
0.86
0.62


C2H2/C2H4
1.61
1.54
1.93
25.53
4.08
5.23









The adsorption isotherms of C2H2, C2H4 and CO2 on M′MOF-2a and M′MOF-3a were further measured at 273 K and 295 K (FIGS. 4a & b and 5a & b). They showed Type I sorption isotherms with very little hysteresis. The selectivities toward C2H2/C2H4 on M′MOF-2a at 273 K and 295 K were 1.5 and 1.9, respectively. Again, M′MOF-3a exhibited enhanced C2H2/C2H4 selectivities of 4.1 and 5.2 at 273 K and 295 K, respectively, which are 2.5 times higher than the corresponding values for M′MOF-2a (Table 1).
The unique and temperature-dependent gas separation capacities of M′MOF-3a are attributed both to thermodynamically and kinetically controlled framework flexibility (Horike et al., 2009; Zhang et al., 2008). Without being bound by theory, the more flexible nature of CDC in M′MOF-3 has enabled the framework M′MOF-3 to be more flexible, thus resulting in narrower pores in activated M′MOF-3a than those in M′MOF-2a, as shown in their PXRD patterns. In order to open pore entrances for the C2H2 uptake, the gate pressure of 166 mmHg typically needs to be applied on the thermodynamically flexible framework M′MOF-3a at 195 K. At higher temperatures of 273 and 295 K, the rotation/swing of the organic linker and metalloligand within M′MOF-3a has enlarged the pore apertures for the access of both C2H2 and C2H4 molecules. Such kinetically controlled framework flexibility has been also revealed in several other porous metal-organic frameworks and utilized for their temperature-dependent gas separation (Ma et al., 2009; Zhang et al., 2008).







TABLE 2







Summary of the parameters and the enthalpies of gas adsorption


on M′MOFs at 273 and 295 K obtained from the virial equation.



















Qst, n=0/kJ


Compounds
Adsorbate
T/K
A0/ln(mol g−1 Pa−1)
A1/g mol−1
R2
mol−1





M′MOF-2a
C2H4
273
−15.234 ± 0.059
−1770.328 ± 6.856 
0.99975
32.7




295
−16.302 ± 0.054
−1551.378 ± 7.704 
0.99946



C2H2
273
−14.070 ± 0.012
−1621.285 ± 11.438
0.99950
37.7




295
−15.300 ± 0.011
−1353.201 ± 11.133
0.99892



CO2
273
−15.591 ± 0.013
−1070.628 ± 35.231
0.99247
32.5




295
−16.652 ± 0.007
 −939.937 ± 15.613
0.99697



C2H4
273
−17.020 ± 0.003
−2143.060 ± 6.940 
0.99983
27.3




295
−17.906 ± 0.018
−2199.728 ± 94.199
0.99452


M′MOF-3a
C2H2
273
−14.203 ± 0.026
−2056.965 ± 25.871
0.99811
27.1




295
−15.087 ± 0.042
−1693.176 ± 41.686
0.99158



CO2
273
−16.679 ± 0.026
 −3117.335 ± 137.777
0.99031
40.5




295
−17.999 ± 0.007
−1902.594 ± 33.455
0.99753









The coverage-dependent adsorption enthalpies of the M′MOFs to acetylene, ethylene and CO2 were calculated based on the virial method and the van't Hoff isochore. The virial graphs for adsorption of C2H4, C2H2 and CO2 on M′MOF-2a and M′MOF-3a at 273 and 295K. It is apparent that the virial graphs have very good linearity in the low pressure region. The parameters and the enthalpies obtained from the virial equation are summarized in Table 2. For M′MOF-2a, C2H4 adsorption had A1 values increasing from −1770 to −1551 g mol−1 from 273 to 295 K, which has a similar trend of A1 values on a carbon molecular sieve increasing from −2480 to −1821 g mol−1 from 303 to 343 K (Reid et al., 1998); C2H2 adsorption had A1 values increasing from −1621 to −1353 g mol−1 from 273 to 295 K, which also has a similar trend of A1 values on a carbon molecular sieve increasing from −1444 to −1302 g mol−1 from 303 to 343 K. It is apparent that the virial parameters for C2H4 and C2H2 adsorption have similar values and trends. CO2 adsorption on M′MOF-2a had A1 values from −1071 to −940 g mol−1 from 273 to 295 K without well defined trend, which has been also observed in CO2 adsorption on a carbon molecular sieve with the A1 values ranging from −1000 to −1045 g mol−1 from 303 to 343 K. The trends in the A1 parameters for C2H4, C2H2 and CO2 adsorption on M′MOF-2a are consistent with the adsorbate-adsorbate interactions decreasing with increasing temperature. In comparison with those for C2H4 and C2H2 adsorption on M′MOF-2a, the virial parameters for C2H4 and C2H2 adsorption on M′MOF-3a are more negative due to its smaller pores, but still have similar values and trends from 273 to 295 K. The fact that the A1 values for C2H4 adsorption on M′MOF-3a are not obviously changed indicates that the adsorbate-adsorbate interactions may be independent of temperature from 273 to 295 K.
The Qst,n=0 values were 32.7, 37.7 and 32.5 kJ mol−1 for C2H4, C2H2 and CO2 adsorption on M′MOF-2a over the temperature range of 273-295 K. The Qst,n=0 values for C2H2 and CO2 were comparable to those obtained for their adsorption on a carbon molecular sieve (35.0 kJ mol−1 (C2H2) and 28.2 kJ mol−1 (CO2)), while the value of 32.7 kJ mol−1 for C2H4 adsorption on M′MOF-2a was significantly lower than the value (50.1 kJ mol−1) obtained for C2H4 adsorption on a carbon molecular sieve in the temperature range of 303 to 343 K. The comparison of the results from the two methods, the linear extrapolation and the virial equation shows that there is a very good agreement (FIGS. 6a-f). In all cases the isosteric enthalpies of adsorption gradually decreased with the increasing surface coverage. The isosteric enthalpies of adsorption are significantly higher than the enthalpies of vaporization of 17, 14 and 16.5 kJ mol−1 for C2H4, C2H2 and CO2, respectively (Chickos and Acree, 2003). The isosteric enthalpies of adsorption for C2H2, C2H4 and CO2 on M′MOF-2a are characteristic of their interactions with the hydrophobic pore surfaces presented in carbon molecular sieves.
The Qst,n=0 for C2H4, C2H2 and CO2 adsorption on M′MOF-3a were 27.4, 27.1 and 40.5 kJ/mol, respectively, over the temperature range from 273 K to 295 K. The systematically lower Qst,n=0 values for C2H4 and C2H2 adsorption on M′MOF-3a than those observed on M′MOF-2a (32.7 kJ/mol for C2H4 and 37.7 kJ/mol for C2H2) may be attributed to the deficiency of π-π interactions between these molecules and CDC moieties on surfaces of pores in M′MOF-3a. The results derived from the linear extrapolation are in very good agreement with those obtained from the virial equation (FIGS. 6a-f). It needs to be mentioned that the Qst values for C2H4 and C2H2 adsorption on M′MOF-3a are almost the same, indicating that the selective C2H2/C2H4 separation cannot be realized by their differential interactions with the pore surfaces, thus the unique gas separation characteristics for M′MOF-3a are mainly attributed to size-exclusive effect.
It needs to be mentioned that C2H2/C2H4 separation is a very important while challenging industrial separation task. Ethylene, the lightest olefin and the largest volume organic chemical, is largely stocked in petrochemical industry and is widely used to produce polymers and other chemicals (Sundaram et al., 1995). The typical ethylene produced in steam crackers contains on the order of 1% of acetylene (U.S. Pat. No. 4,126,645), while a ppm level of acetylene (>5 ppm) in ethylene can poison Ziegler-Natta catalyst during ethylene polymerizations and can also lower the product quality of the resulting polymers (Huang et al., 2007). Moreover, the acetylenic compounds are often converted into solid, thus blocking the fluid stream and even leading to explosion (Molero et al., 1999). There are mainly two commercial approaches to remove acetylenes in ethylene: partial hydrogenation of acetylene into ethylene over a noble metal catalyst such as a supported Pd catalyst (Choudary et al., 1999; Khan et al., 2006), and solvent extraction of cracked olefins using an organic solvent to obtain pure acetylene (Weissermel and Arpe, 2003). However, the former process suffers from the catalyst price and the loss of olefins due to the overhydrogenation to paraffins, while the latter is also disadvantageous in terms of technical and economical aspects, partially, due to the low selectivities of acetylene over olefins and also to the significant loss of solvent after multiple operations. Apparently, there is a significant need to develop novel alternative C2H2/C2H4 separation approaches. Some recent attempts, hydrogenation by non-precious metal alloy catalysts (Studt et al., 2008), ionic liquid extraction (Palgunadi et al., 2010), and x-complexation (Wang and Stiefel, 2001), have been made to reduce the cost or to enhance the selectivities.
In some embodiments, the MOFs disclosed herein may be used to effect such challenging separations. For example, M′MOF-3a may be used in some embodiments for a C2H2/C2H4 separation at moderate pressures over 200 mmHg at 195 K. In order to realize high C2H2/C2H4 separation at low pressures at 195 K, the gate pressure for the entrance of C2H2 may need to be further reduced. In some embodiments, it may be accomplished by the combinatorial approach. In any case, with a C2H2/C2H4 separation selectivity of 5.23, M′MOF-3a is a practical material for this important separation even at room temperature.
The enantiopure pore environments within M′MOF-2 and -3 were further explored for use in chiral recognition and enantioselective separation processes. Unlike the achiral M′MOF-1 Zn3(BDC)3[Cu(SalPyen)], which encapsulates both R- and S-1-phenylethyl alcohol (PEA) to form Zn3(BDC)3[Cu(SalPyen)]⊃R/S-PEA, the enantiopure M′MOF-3 exclusively takes up S-PEA to form M′MOF-3⊃S-PEA ((Zn3(CDC)3[Cu(SalPyCy)].S-PEA). The symbol “⊃” indicates encapsulating. In fact, the solvothermal reaction of the corresponding reaction mixture of Zn(NO3)2.6H2O, H2CDC and Cu(H2SalCy)(NO3)2 in the presence of certain amount of racemic PEA in DMF at 100° C. readily formed the enantiopure M′MOF-3 which exclusively encapsulates S-PEA (FIG. 1d). The incorporated S-PEA can be easily extracted by immersing the as-synthesized M′MOF-3⊃S-PEA in methanol.
The chiral recognition and enantioselective separation of M′MOF-2 and -3 for the R/S-PEA racemic mixture were examined using the bulky as-synthesized materials. The as-synthesized M′MOF-2 and -3 were exchanged with methanol and then immersed in the racemic mixture to selectively encapsulate the S-PEA. Once such PEA-included M′MOF-2 and -3 were immersed in methanol, the encapsulated PEA within the enantiopure M′MOF-2 and -3 can be readily released from the chiral pores, making their potential application for enantioselective separation of R/S-PEA. Chiral HPLC analysis of the desorbed PEA from the PEA-included M′MOF-2 yielded an ee value of 21.1%, and the absolute S configuration for the excess was confirmed by comparing its optical rotation with that of the standard sample. It must be noted that the used M′MOF-2 keeps high crystallinity and can be regenerated simply by the immersion into the excess amount of methanol, and thus for further resolution of racemic R/S-PEA. The second and third such regenerated M′MOF-2 provide an ee value of 15.7% and 13.2%, respectively. The low enantioselectivity of the enantiopure M′MOF-2 for the separation of R/S-PEA might be attributed to its large chiral pore environments which have limited its high recognition of S-PEA. The smaller chiral pores within the enantiopure M′MOF-3 have significantly enhanced its enantioselectivity for the separation of R/S-PEA with the much higher ee value of 64%. The regenerated M′MOF-3 can also be further utilized for the separation of R/S-PEA with the slightly lower ee value of 55.3% and 50.6%, respectively. Without being bound by theory the chiral pores within M′MOF-2 and M′MOF-3 correspond to the size of S-PEA, which makes these MOFs well suited to separate enantiomers of this molecule.
The two M′MOFs, Zn3(BDC)3[Cu(SalPycy)].(G)x (M′MOF-2) and Zn3(CDC)3[Cu(SalPycy)].(G)x (M′MOF-3) differ, for example, in their pore size. The slightly smaller pores within M′MOF-3 may be at least in part responsible for the activated M′MOF-3a to exhibit higher separation selectivities with respect to both C2H2/C2H4 and enantioselective separation of S-1-phenylethyl alcohol (PEA) than M′MOF-2a. As will be readily apparent to a person skilled in the art, these MOFs can be used for the separation of other molecules and stereoisomers.
IV. Examples
The following examples are included to demonstrate particular embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute particular modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.
Materials and Methods.
All reagents and solvents employed in synthetic studies were commercially available and used as supplied without further purification. 5-Methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde was synthesized according to the literature procedure (Arya et al., 1983).
Synthesis of Cu(H2SalPyCy)(NO3)2 
A solution of (1R,2R)-(−)-1,2-cyclohexanediamine (0.846 g, 7.41 mmol) in EtOH (20 mL) was added dropwise to a solution of 5-methyl-4-oxo-1,4-dihydro-pyridine-3-carbaldehyde (1.794 g, 14.82 mmol) in EtOH (130 mL), and the resulting mixture was refluxed for two hours to form a clear light brown solution. To this solution, a solution of Cu(NO3)2.2.5H2O (1.798 g, 7.73 mmol) in EtOH (20 mL) was added, forming a blue precipitate of Cu(PyenH2)(NO3)2 that was collected by filtration, washed with EtOH and air dried (2.035 g, 51%).
Synthesis of Zn3(BDC)3[Cu(SalPyCy)].5DMF.4H2O
(M′MOF-2) A mixture of Zn(NO3)2.6H2O (0.236 g, 0.79 mmol), H2BDC (0.131 g, 0.79 mmol), and Cu(H2SalPyCy)(NO3)2 (0.143 g, 0.24 mmol) was dissolved in 100 mL DMF, and heated in a vial (400 mL) at 373 K for 24 hours. The dark blue thin plates formed were collected and dried in the air (0.21 g, 57%). Elemental analysis (%): Calcd. for Zn3(BDC)3[Cu(SalPyCy)].5DMF.4H2O (C59H77N9O23CuZn3): C, 46.02; H, 5.04; N, 8.19. Found: C, 45.97; H, 4.98; N, 8.24.
Synthesis of Zn3(CDC)3[Cu(SalPyCy)].5DMF.4H2O
(M′MOF-3) A mixture of Zn(NO3)2.6H2O (0.236 g, 0.79 mmol), H2CDC (0.136 g, 0.79 mmol), and Cu(H2SalPyCy)(NO3)2 (0.143 g, 0.24 mmol) was dissolved in 100 mL DMF, and heated in a vial (400 mL) at 373 K for 24 hours. The dark blue thin plates formed were collected and dried in the air (0.23 g, 62%). Elemental analysis (%): Calcd. for Zn3(BDC)3[Cu(SalPyCy)].5DMF.4H2O(C59H95N9O23CuZn3): C, 45.48; H, 6.15; N, 8.09. Found: C, 45.35; H, 6.23; N, 7.96.
Synthesis of Zn3(CDC)3[Cu(SalPyCy)].S-PEA.5DMF
(M′MOF-3⊃S-PEA): A mixture of Zn(NO3)2.6H2O (0.018 g, 0.06 mmol), H2CDC (0.01 g, 0.06 mmol), and Cu(H2SalPyCy)(NO3)2 (0.016 g, 0.30 mmol) was dissolved in 3 mL DMF and 2 mL D,L-1-phenylethyl alcohol (PEA), and heated in a vial (23 mL) at 373 K for 24 hours. The purple platelet crystals were collected and dried in the air (0.01 g, 31%). Elemental analysis (%): Calcd. for Zn3(CDC)3[Cu(SalPyCy)].S-PEA.5DMF (C67H97CuN9O20Zn3): C, 50.04; H, 6.08; N, 7.84. Found: C, 50.12; H, 6.15; N, 7.96.
Synthesis of Zn3(BDC)3[Cu(SalPyen)].R/S-PEA.5DMF
(M′MOF-1⊃R/S-PEA): A mixture of Zn(NO3)2.6H2O (0.018 g, 0.06 mmol), H2BDC (0.01 g, 0.06 mmol), and Cu(H2SalPyen)(NO3)2 (0.015 g, 0.03 mmol) was dissolved in 3 mL DMF and 2 mL D,L-1-phenylethyl alcohol (PEA), and heated in a vial (23 mL) at 373 K for 24 hours. The purple platelet crystals were collected and dried in the air (0.01 g, 32%). Elemental analysis (%): Calcd. for Zn3(BDC)3[Cu(SalPyen)].R/S-PEA.5DMF (C63H73CuN9O20Zn3): C, 49.26; H, 4.79; N, 8.21. Found: C, 49.55; H, 4.85; N, 8.30.
Adsorption Studies.
After the bulk of the solvent was decanted, the freshly prepared sample of M′MOF-2 or M′MOF-3 (ca. 0.15 gram) was soaked in ca. 10 mL methanol for 1 hours, and then the solvent was decanted. Following the procedure of methanol soaking and decanting for 10 times, the solvent-exchange samples were activated by vacuum at room right overnight till the pressure of 5 μmHg. CO2, ethylene and acetylene adsorption isotherms were measured on ASAP 2020 for the activated M′MOFs. As the center-controlled air condition was set up at 22.0° C., a water bath of 22.0° C. was used for adsorption isotherms at 295.0 K, while dry ice-acetone and ice-water bathes were used for the isotherms at 195 K and 273 K, respectively.
All of the methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.
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The following references, and those listed in the Appendix, to the extent that they provide exemplary procedural or other details supplementary to those set forth herein, are specifically incorporated herein by reference.

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## Claims

1. A mixed-metal-organic framework (M′MOF) comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:

2. The M′MOF of claim 1, wherein the repeat unit is of the formula Zn3(BDC)3[Cu(SalPyCy)].

3. The M′MOF of claim 1, wherein the repeat unit is of the formula Zn3(CDC)3[Cu(SalPyCy)].

4. The M′MOF of claim 1, wherein the stereochemistry of the SalPyCy ligand is further defined as:




wherein R indicates the stereochemical conformation of the indicated carbon atoms.

5. The M′MOF of claim 1, further comprising one or more than one type of guest molecule.

6. The M′MOF of claim 5, wherein one type of guest molecules is a solvent molecule.

7. The M′MOF of claim 6, wherein the solvent molecule is water.

8. The M′MOF of claim 6, wherein the solvent molecule is N,N′-dimethylformamide.

9. The M′MOF of claim 6, wherein one type of guest molecules is 1-phenylethanol.

10. The M′MOF of claim 5, wherein one type of guest molecule is a gas molecule.

11. The M′MOF of claim 10, wherein the gas molecule is H2, N2, Ar, O2, CO2, NO, NO2 or CO.

12. The M′MOF of claim 5, wherein one type of guest molecule is an alkane(C1-6), alkene(C2-4), alkyne(C2-6), alcohol(C1-6), arene(C6-8) or a substituted version of any of these.

13. The M′MOF of claim 12, wherein one type of guest molecule is an alkene(C2-6).

14. The M′MOF of claim 13, wherein the alkene(C2-6) is C2H4, C3H6, C4H8, C5H10 or C6H12.

15. The M′MOF of claim 14, wherein the alkene(C2-6) is C2H4.

16. The M′MOF of claim 5, wherein one type of guest molecule is an alkyne(C2-6).

17. The M′MOF of claim 16, wherein the alkyne(C2-6) is C2H2.

18. A method of storing a compound within a mixed-metal-organic framework (M′MOF) comprising:
(a) obtaining an M′MOF comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:





and
(b) combining the M′MOF with a first compound such that the first compound is contained within the M′MOF.

19. A method of detecting a compound using an M′MOF comprising:
(a) obtaining an M′MOF comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:




(b) combining the M′MOF with a first compound such that the first compound enters the M′MOF to form an M′MOF.guest complex; and
(c) comparing the photoluminescence intensity of the M′MOF with the photoluminescence intensity of the M′MOF.guest complex so as to detect the first compound.

20. A method of separating two or more compounds using an M′MOF comprising:
(a) obtaining a mixed-metal-organic framework (M′MOF) comprising a repeat unit of the formula Zn3(BDC)3[Cu(SalPyCy)] or Zn3(CDC)3[Cu(SalPyCy)], wherein BDC is 1,4-benzenedicarboxylate, CDC is 1,4-cyclohexanedicarboxylate, and SalPyCy is a ligand of the formula:




(b) combining the M′MOF with a mixture comprising a first compound and a second compounds; and
(c) separating the two or more compounds based on their differential diffusion rate within the M′MOF.