This invention relates to the provision of metal organic frameworks (MOFs) as solid sorbents to selectively capture gas molecules from the atmosphere or other gases, in particular to capture CO ₂ and even more specific in the presence of H ₂ O.

In recent years, carbon capture, utilization and storage (CCUS) processes have been one of the most active research and business areas aiming to reduce worldwide carbon emissions. One of the most important goals in CCUS processes is to develop new stable microporous solid sorbents that can adsorb CO ₂ in flue gas or industrial CO ₂ sources and ideally remove CO ₂ from the atmosphere via direct air capture (DAC). Due to the fact that both atmosphere and flue gas have competing water content, this competition between CO ₂ and H ₂ O molecules has been a significant challenge for application of physisorbent MOF materials to selectively capture CO ₂ molecules.

Many porous solids have potential to be used as solid sorbents for CO ₂ capture, metal organic frameworks (MOFs) being one of them. MOFs generally prefer physisorption of H ₂ O over CO ₂ molecules. In order to capture CO ₂ in flue gas or in another gas mixture, a MOF must be able to selectively capture (physisorb) CO ₂ over H ₂ O.

The requirements for the MOFs that can be used to selectively capture CO ₂ are high. The desired MOF must be stable in humid conditions, acidic and alkaline conditions and survive at high temperatures. In general, MOFs are known to have weak chemical stabilities and thermal stabilities in the presence of humidity and high temperatures. Thus, they will lose their functionality and selectivity under most conditions which are harsher than e.g. at room temperature or any slightly enhanced temperatures as well as at increased percentages of humidity. A further limitation to the use of MOFs is to contact them with gases which are not dry.

Typically, MOFs are composed of metal binding functional groups, i.e., carboxylic acids, pyridines, azolates, quinoids that are also capable creating relatively stronger hydrogen bonds with H ₂ O molecules. Carboxylate MOFs are the most widely studied MOF family and they are generally known to hydrolyze in the presence of water. One example of MOFs as potential solid sorbents to selectively capture CO ₂ molecules in atmosphere and in flue gas, an MOF as sorbent for CO ₂ in the presence of water is described in EP 2971 277. The MOF described therein is known as Calf-20 which is composed of oxalic acid triazolate functional groups (a carboxylate MOF) with molecular formula [Zn ₂ (l,2,4- triazolate) ₂ (oxalate)].

Calf-20 is known to perform selective physisorption of CO ₂ molecules in the presence of water. However, beginning at 10% relative humidity (RH) the CO ₂ loading gradually decreases until it is almost negligible at RH > 30%. Selectivity of Calf-20 for H ₂ O and CO ₂ becomes equal at 40% RH. Consequently, it is state of the art, MOFs usually use organophosphonate building blocks which were not known to selectively capture CO ₂ molecules in the presence of H ₂ O even if there are only traces of H ₂ O.

The object of the present invention is to provide solid CO ₂ sorbents comprising MOFs. This object of the present invention is solved by the provision of MOF as organophosphonates and organoarsonates, and in particular a solid CO ₂ sorbent comprising a phosphonate MOF with one of the following molecular formulas [{M ₂ (4,4’-bipyridine) _0.5 }(l,4-naphthalenediphosphonate)], [{M ₂ (4,4’-bipyridine) _0.5 }(l,4-naphthalenediarsonate)], [{M ₂ (l,4-Bis(4-pyridyl)benzene) ₀₅ }(l,4- naphthalenediphosphonate)], [{M ₂ (l,4-Bis(4-pyridyl)benzene) ₀₅ }(l,4-naphthalenediarsonate)], [{M ₂ (4,4 ^Z -[1,1 ^Z -Biphenyl]-4,4 ^Z -diylbis[pyridine] ) ₀₅ }(l,4-naphthalenediphosphonate)] or [{M ₂ (4,4 ^Z -[1,1 ^Z -Biphenyl]-4,4 ^Z -diylbis[pyridine] ) ₀₅ }(l,4-naphthalenediarsonate)], wherein the metal is a divalent kation M ²⁺ e,g. copper(ll), zinc(ll) , cadmium(ll) , ferrum(ll), nickel(ll), cobalt(ll), manganese(ll), berylliu m(l I), magnesium(ll), calcium(ll), strontium(ll) or barium(ll). The units of the secondary building unit (SBU) and the metal organic framework are preferably unsubstituted, but may be also partially and/or totally substituted by halogenides.

Unexpectedly, the MOFs of the present invention were found to selectively capture CO ₂ under harsh conditions. Such conditions are e.g. the presence of H ₂ O in a gas with 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100% RH.

It was found further that MOFs of the present invention are stable until 360°C allowing the use of hot gases and or industrial waste gases containing CO ₂ . In the present invention MOFs can operate from -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°, C130°C, 140°C, 150°C, 160°, C 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C or 360°C or in any range in between these values.

Additionally, also a high content of acidic gases, like SO ₂ , SO ₃ , H ₂ S, H ₂ SO ₃ , H ₂ SO ₄ , HF, HCl, HNO ₂ , HNO ₃ , NO, NO ₂ , NO _X in a range from 0 % up to 20 %, alternatively 0.1 - 18%, alternatively 0.5 - 10%, alternatively 0.5 - 15%, alternatively 5 - 15%, alternatively 5 - 10%, alternatively 10 - 15 %, or alternatively 10 - 18%, which would be considered as corrosive or harsh conditions, will be still suitable conditions for the MOFs of the invention and do not destroy the bonds of the compound.

In one embodiment of the invention the solid sorbent comprises [{Cu ₂ (4,4’-bipyridine) _0.5 }(l,4- naphthalenediphosphonate)], named hereafter GY-75, is a MOF which selectively captures CO ₂ in flue gas. It was found that [{Cu ₂ (4,4’-bipyridine) _0.5 }(l,4- ^na phthalenediphosphonate)] (GY-75) has particularly in presence of H ₂ O much higher preference for CO ₂ capturing molecules compared to any MOF known in the state of the art . Additionally, it has got even the highest affinity expectation in CO ₂ capturing for industry compared to the standards in literature.

In another embodiment the solid sorbent comprises [{Cu ₂ (l,4-Bis(4-pyridyl)benzene) _0.5 }(l,4- naphthalenediphosphonate)], named hereafter GY-76, and is a MOF which selectively captures CO ₂ in flue gas (see Figure IF). GY-76 is obtained after isoreticular expansion of GY-75 with 1,4- Bis(4-pyridyl)benzene linker (see Figure 2D). Isoreticular expansion of void channels in GY-75 retains the same hydrophobic properties of GY-75 in void channels of GY-76. GY-76 has a larger surface area up to 500 m ² /g compared to GY-75 and GY-76 retains the same hydrophobic environment observed in GY-75. Similar to GY-75, GY-76 also crystallizes in C 2/c space group. The crystal structure of GY-76 was solved using three dimensional (3D) electron diffraction.

In another embodiment the solid sorbent comprises [{Cu ₂ (4,4'-[l,l'-Biphenyl]-4,4'- diylbis[pyridine] ) ₀₅ }(l,4- ^na phthalenediphosphonate)], named hereafter GY-77, and is a MOF which selectively captures CO ₂ in flue gas. Also, GY-77 is obtained after isoreticular expansion of GY-75 with 4,4'-[l,l'-Biphenyl]-4,4'-diylbis[pyridi ne] linker (see Figure 2E). GY-77 has a larger surface area compared to GY-75 and GY-76. GY-77’s void channels retain the same hydrophobic environment observed in GY-75 and GY-76. GY-76 has larger surface area compared to GY-75 and GY-76. Similar to GY-75 and GY-76, GY-77 also crystallizes in C 2/c space group. Further compounds that can be used as MOFs in the solid CO ₂ sorbent of the present invention are MOFs having the same coordination environment in the secondary building unit of GY-75, GY-76 and GY-77 and possessing divalent metal ions, such as Zn ²⁺ , Cd ²⁺ , Ni ²⁺ , Co ²⁺ , Mn ²⁺ , Be ²⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Ba ²⁺ or Fe ²⁺ for example.

Furthermore, different modifications for MOFs of the present invention are possible such as isoreticularly increasing of the surface area, while keeping the identity of the secondary building units, by increasing the tether length of 4,4’-bipyridine units, such as to 1,4-Bis(4- pyridyl)benzene and 4,4'-[l,l'-Biphenyl]-4,4'-diylbis[pyridine] (see Figures 2D and 2E).

Isostructural [{Cu ₂ (4,4’-bipyridine) _0.5 }(l,4- ^na phthalenediarsonate)] (GY-75-As), [{M ₂ (l,4-Bis(4- pyridyl)benzene) ₀₅ }(l,4-naphthalenediarsonate)] (GY-76-As), [{M ₂ (4,4'-[l,l'-Biphenyl]-4,4'- diylbis[pyridine] ) ₀₅ }(l,4- ^na phthalenediarsonate)] (GY-77-As) have similar properties as GY-75, GY-76 and GY-77 (Figure 8) and they can be synthesized under the same conditions respectively.

MOFs of the present invention, its use for CO ₂ capturing and the method for selectively separating CO ₂ from gas mixtures will now be explained in detail on the example of GY-75. Additionally, its exceptional thermally stability over e.g. Calf-20 which increases the range of their applicability will be shown in the following sections.

The structure and the hydrothermal synthesis of MOF [{Cu ₂ (4,4’-bipyridine) _0.5 }(l,4- naphthalenediphosphonate)] for its use in semiconductors was previously published in K. Siemensmeyer et al., “Phosphonate Metal-Organic Frameworks: A Novel Family of Semiconductors. Adv Mater 32, e2000474 (2020). In this publication susceptibility of the MOFs is described but there is no hint of their ability of capturing CO ₂ .

Up to now 300,000 MOFs are screened in databases e.g. MOFXDB API Databases as a MOF for capturing CO ₂ , GY-75 has not been identified, without being bound by this hypothesis, probably due to its hydrophilic sections forms hydrogen bonding and has thus a higher melting point. Alternatively, it may also be that the covalently bonded atoms e.g. in the GY-75 and even more stability than hydrogen bonded atoms and thus show these unexpected characteristics and advantages due to its overwhelmingly deviations of the normal MOF behavior.

As seen in Figure lA and IB, the secondary building units of GY-75 are connected by 4,4’- bipyridine and fully deprotonated 4,4’-naphthalenediphosphonic organic linkers or building blocks to form the three-dimensional MOF structure with rod shaped void channels. In more detail, each secondary building unit is composed of a central copper(ll)oxide dimer chain. As seen in Figure IB, each of the Cu ²⁺ ions in the central copper(ll)oxide dimer chains has an additional copper(ll)oxide side dimer with Cu ²⁺ ions. 4,4’-bipyridine organic linkers or building blocks are coordinately bound to the Cu ²⁺ ions forming the side copper(ll)oxide dimers, which are bound to the central copper(ll)oxide dimer chain. Fully deprotonated 1,4- naphthalenediphosphonic acid organic linkers or building blocks are coordinately bound to each of the Cu ²⁺ ions via phosphonic acid oxygens.

Due to the presence of three oxygen atoms and two hydrogen atoms in an organophosphonic acid functional group (R-PO ₃ H ₂ ), phosphonate MOFs are known to be hydrophilic. Therefore, within phosphonate MOF pores, competition between CO ₂ and H ₂ O physisorption would be expected to favor H ₂ O due to the multiple hydrogen bonding possibilities between phosphonate functional groups and H ₂ O molecules.

Surprisingly, pores of GY-75 are composed of hydrophobic phenyl side of fully deprotonated 1,4-naphthalenediphosphonic acid (1,4-naphthalenediphosphonate) building blocks and 4,4’- bipyridine moieties. Unsubstituted or substituted hydrophobic phenyl side of 1,4- naphthalenediphosphonate groups of GY-75 are facing inside the pores of GY-75, which increases the hydrophobic nature of the pore sites providing more preferred physisorption environment for CO ₂ molecules in GY-75 pore sites. It seems, without being bound by the theory, that this protects the hydrophilic sections of GY-75 from H ₂ O access, which limits the hydrogen bonding or van der Waals interactions between H ₂ O molecules and GY-75 pores.

Due to the hydrophilic nature of phosphonates, phosphonate-MOFs and non-porous phosphonate metal organic solids are usually synthesized with water of crystallization in the pores. Due to the unique structure of GY-75, presence of no water of crystallization is observed. This is also another indicator of GY-75’s hydrophobicity of its pores.

GY-75 can, thus, incorporate further hydrophobic gases like methane or hydrogen.

GY-75 is synthesized under autogenous pressure and acidic hydrothermal reaction conditions in water at 200°C. Therefore, GY-75 is an extremely stable MOF that can survive under autogenous pressure in water at 200°C. Despite its synthesis under hydrothermal reaction conditions, and cooling down in presence of water, after its synthesis, no water molecules are present in the pores of GY-75 based on GY-75’s crystal structure obtained by single crystal X-ray diffraction. Surprisingly, it was found that GY-75 has much higher selectivity for C0 ₂ capture via physisorbing in the presence of H ₂ 0 compared to Calf-20. Calf-20 is known to be selective for C0 ₂ capture below 40% RH, but Calf-20 starts losing its selectivity for CO ₂ capture in the presence of H ₂ O starting from a RH of around 30% and higher.

At 10% RH Calf-20 starts adsorbing H ₂ O, while GY-75 starts adsorbing H ₂ O at 80% RH still has a selectivity for adsorbing CO ₂ . At RH of around 40 % Calf-20’s selectivity of adsorbing H ₂ O vapor and CO ₂ gas becomes equal. Above 40% relative humidity Calf-20 is more selective for H ₂ O vapor.

Interestingly, the inventor found as shown in Figure 3 that GY-75 can selectively capture much better CO ₂ and particularly much better at the presence of H ₂ O in a RH of above 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70% and up to 80% RH including any ranges in between, than Calf-20 or any other MOF known.

In particular, GY-75 can also selectively capture CO ₂ over H ₂ O at RH higher than 80%.

One of the advantages of GY-75 compared to the current state of the art is its exceptional chemical and thermal stability. GY-75 is synthesized at 200°C in water under hydrothermal reaction conditions and under autogenous pressure, as well as acidic pH conditions. Even under harsh conditions like in acids and alkalines GY-75 is stable, at room temperature over 5-10 years. E.g. GY-75 is stable in 0,1 M KOH at pH 13 while it dissociates to form CuO and Cu(OH) ₂ species at about 5 M KOH and can be easily disposed.

When in use, GY-75 can be recycled hundreds of times and adsorb and desorb CO ₂ as many times as the recycling stages can be performed.

The pressure for recycling and releasing CO ₂ is lowered, a technique that is known and used as Pressure Swing Adsorption (PSA). Same result is achieved by lowering or increasing the temperature known as Temperature Swing Adsorption (TSA). Using Vacuum Swing Adsorption (VSA) is possible to recycle the MOF and release CO ₂ , too.

As seen in Figure 6, Thermo Gravimetric Analysis (TGA) of GY-75 indicates that organic components of GY-75 are stable till 400°C.

Furthermore, the pores of GY-75 can be activated at350°C for 24 hours in vacuum without losing its crystal structure, which is proven by complementary PXRD (Powder X-Ray Diffraction) experiments. The measurements of the structure experiments of the powder of GY-75 show the distribution of the molecules and therefore the pores in the molecule and giving proof that the “binding sites” are free for physisorbing molecules like CO ₂ .

The activation of MOF is performed to open and unblock pores so that maximum amount of CO ₂ can be adsorbed. After their synthesis most MOFs include reactants or solvents inside their pores, or they can adsorb water vapor and atmospheric gases while they are exposed to air. For example, pores of GY-75 might be partially occupied by unreacted 4,4’-bipyridines, which were needed to remove to activate the MOF for CO ₂ adsorption. As 4,4’-bipyridine has a boiling point of 304.8°C the GY-75 has also a high thermal stability and thus it is possible to activate GY-75 at 350°C and above. Activation for gas molecules can be also done at lower pressures and a temperature range between 0°C and 360°C.

As seen in Figure 7, GY-75 retains its crystal structure after 24 hours at 350°C while Calf-20 has been shown to be stable in air only up to 150°C.

Furthermore, it has been proven that the crystal structure of GY-75, GY-76 and GY-77 can and will stay intact for many years at room temperature and the correlating relative humidity.

GY-76 and GY-77 are synthesized at temperatures above 220 °C under hydrothermal conditions. They are synthesized free of solvents in their pore channels. Although, they are synthesized under hydrothermal reaction conditions no crystallization of water was observed in their pore channels due to the retained hydrophobicity of the pore channels after isoreticular expansions.

Although phosphonate-MOFs are composed of hydrophilic compartments, the skilled practitioner never thought to store CO ₂ . Surprisingly, it was found that the unique pore structure of GY-75, GY-76 and GY-77 make it possible that GY-75, GY-76 and GY-77 have higher affinities for CO ₂ molecules compared to H ₂ O molecules. Due to its high selectivity for CO ₂ molecules in the presence of water molecules up to 80% RH, GY-75, GY-76 and GY-77 are advantageous to capture CO ₂ both in flue gas, natural gas and/or via direct air capture from the atmosphere or biogas.

The MOFs according to the invention are thus highly suitable to capture hydrophobic gases. For example, GY-75, GY-76 and GY-77 can adsorb and store hydrophobic gases preferably carbon dioxide, methane or hydrogen.

In one embodiment the invention provides, thus, a method for selectively separating carbon dioxide from a gas mixture with RH from 30%, 40%, 50%, 60%, 70% and up to RH of 80%, and even above 80% RH and towards 100% RH comprising the step of contacting the gas mixture with at least one sorbent as provided herein. Typically, a gas mixture from which the MOFs of the invention can effectively separate hydrophobic gases are atmospheric gases, greenhouse gases, biogases, natural gas or industrial waste gases which contain, in addition to carbon dioxide and water vapor, at least one gas selected from the group consisting of nitrogen, oxygen, methane, hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen dioxide, and any mixture of the foregoing.

The claimed sorbent is further particularly suitable to selectively absorb CO ₂ in a gas mixture having a temperature in the range of -60°C to 360°C, and in particular at a temperature of -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C or 360°C.

According to the method the reaction conditions at which CO ₂ is released include the step of releasing the CO ₂ comprises heating the sorbent (with or without pressure) up to temperatures of 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 150°C, 200°C, 350°C or even up to 400°C.

Pressure Swing Adsorption, Temperature Swing Adsorption and Vacuum SwingTechnologies are used for CO ₂ gases, GY-75 has an isosteric enthalpy of adsorption of -36,5 kJ/mol whereas Calf-20 has -39 kJ/mol. The moderate value of -36,5 kJ/mol is very suitable for industrial applications of CO ₂ capture and release when needed using these methods.

According to one further embodiment the released CO ₂ is then collected for further use, described as e.g. carbon capture utilization and storage (CCUS).

Additionally, the method of the invention is particularly useful for separating CO ₂ from gas mixture containing at least one additional gas selected from the group consisting of nitrogen, oxygen, methane, hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, nitrogen dioxide, and any mixture of the foregoing. Such gas mixtures are typically found as or defined as natural gas, air, shale gas, biogas and flue gas.

MOFs according to the invention are synthesized by solvothermal method that means the reaction is in a closed vessel under autogenous pressure above the boiling point of the solvent. Such solvothermal method usually includes a hydrothermal method and an organic solvothermal method.

The reaction conditions for forming MOFs according to the invention is directed by heating/temperature, molar ratio of initial ion to ligand, pH, solvent, time and pressure. By using these parameters in combination with choosing a suitable and wanted ligand the structure of the formed MOFs such as size, surface, pore size and morphology is controlled. As solvents for generating MOFs of the invention are most commonly used N,N-dimethylformamide, ethanol, methanol and water.

MOFs with divalent transition metal ions like Zn ²⁺ and Cu ²⁺ and further divalent metal ions as Ca ²⁺ , Mn ²⁺ , Mg ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cd ²⁺ , Ba ²⁺ are composed with linear or Y-shaped or X-shaped or tetrahedral shaped linkers as polycarboxylate, carboxylates or phosphonates or nitrogen donating linkers to build structure types of high crystallinity with mono-/bi-/tri-/tetra-nuclear oxoclusters and chains.

Reaction conditions for GY-75 are starting with

1,4-naphthalenediphosphonic acid + CuSO ₄ *5H ₂ O + 4,4’-bipyridine + H ₂ O above 220 °C, 4d, Ap

Reaction conditions for GY-77 are starting with

1,4-naphthalenediphosphonic acid + CuSO ₄ *5H ₂ O + 4,4'-[l,l'-Biphenyl]-4,4'- diylbis[pyridine] + H ₂ O GY-77 above 220 °C, 4d, Ap

For the hydrothermal reactions Teflon lined Parr Acid Digestion Vessels were used starting at a pH of 2.

1,4-naphthalenediphosphonic acid (0.100 g, 0.35 mmol), CuSO4*5H2O (0.150 g, 0.60 mmol), 4,4’- bipyridine (0.040 g, 0.256 mmol) and H ₂ 0 (10.084 g, 560 mmol) reacted for 4 days at 200°C under autogeneous pressure. GY-76 and GY-77 are synthesized using 0.256 mmol l,4-Bis(4-pyridyl)benzene and + 4,4'-[l,l'-Biphenyl]-4,4'-diylbis[pyridine] using the same reaction conditions as for GY-75 respectively. Needle-shaped green crystals were received and purified in acetone and air-dried. GY-75, GY-76 and GY-77 can also be synthesized using mechanochemistry, either solvent free or with solvents, and microwave synthesis at large scales.

For further MOFs it is summarized of the invention to use mixed divalent metal MOF synthesis and solvent free synthesis. When using divalent metals with nitrogen containing ligands such as triazole, tetrazole, imidazole and pyrazole MOFs are formed that are more chemically robust against hydrolysis.

Phosphonic acids are known to be stable against hydrolysis, decomposition under UV light and thermal decomposition up to 400°C. When phosphonic acids and arsonic acids are fully deprotonated they have -2 negative charge R-PO ₃ ² ' and R-AsO ₃ ² ' respectively. Therefore, they can form stronger metal binding resulting in better stability compared to the other organic linker families (carboxylates, sulfonates, azolates, pyridines, imines, quinoids, etc.), which are used in MOF synthesis.

Copper(ll)salts as CuSO ₄ *5H ₂ 0 and other divalent meta 1(1 l)sa Its such containing Zn ²⁺ , Mg ²⁺ , Ba ²⁺ , Ca ²⁺ , Co ²⁺ , Ni ²⁺ and Cd ²⁺ can be used. Examples mentioned but not limited exclusively to that are ZnSO ₄ *7H ₂ O, Zn ₃ (PO ₄ ) ₂ *4H ₂ O, Ca ₃ (PO ₄ ) ₂ and divalent metals hereafter as M (I I) in the formula abbreviated like M (I l)(OAc) ₂ , M (I I) (NO ₃ ) ₂ , M (I I) (BF ₄ ) ₂ , M (I l)Cl ₂ and similar metal salts can be used to form MOFs.

Figure description:

Figure 1A: One dimensional (or rod shaped) Secondary building unit (SBU) of [{Cu ₂ (4,4’- bpy)0.5](l,4-N DPA)] (1,4-NDPA is 1,4-naphthalenediphosphonate) (GY-75) expanding.

Figure IB: The perspective view of rectangular void channels along with the top view of the one-dimensional or rod shaped SBU, where the band gap of the compound is 1.4 eV.

Figure 1C: Side view of the rod shaped SBU consisting of a zigzag chain of corner-sharing copper dimers, with Cu-Cu distances of less than 3 A. Dimers are based on their Cu-Cu bond distances.

As it can be seen in Figure ID, according to the density functional theory (DFT) CO ₂ molecules are situated more in the center of GY-75 pore channels with CO ₂ binding energy of -36.8 kJ/mol. As seen in Figure IE, H ₂ 0 molecules are more oriented towards hydrophilic secondary building units but side phenyl groups of the 1,4-napthalenediphoshonate is blocking its complete orientation towards hydrophilic compartments. Therefore, water molecules in GY-75 pores cannot generate stronger non- covalent interactions, such as hydrogen bonds with the hydrophilic compartments of GY-75.

Figure IF shows the crystal structure of GY-76, which is the isoreticular expansion of GY-75 into GY-76 by usingthe longer tethered linker l,4-Bis(4-pyridyl)benzene. The structure of GY-76 is obtained from three-dimensional electron diffraction.

Figure 2A: 1,4-naphthalenediphosphonic acid. Figure 2B: 1,4-naphthalenediphosphonate, fully deprotonated 1,4-naphthalenediphosphonic acid. Figure 2C: 4,4’-bipyridine.

Furthermore, surface area of GY-75 can be increased isoreticularly via increasing the tether length of 4,4’-bipyridine units to l,4-Bis(4-pyridyl)benzene and 4,4'-[l,l'-Biphenyl]-4,4'- diylbis[pyridine] (See Figure 2D and 2E respectively).

Figure 3 confirms in a Monte Carlo simulation that the MOF, GY-75, is highly selective for capturing CO ₂ up to 80% RH, while Calf-20 is capturing only up to 40% RH usingthe same parameters.

Figure 4 shows CO ₂ adsorption isotherms of GY-75 at different temperatures. As expected at higher temperatures CO ₂ capture capacity is reduced. Data derived from Figure 4 shows the pores of GY-75 have an isosteric enthalpy of adsorption of -36,5 kJ/mol whereas Calf-20 has -39 kJ/mol. The moderate value of -36,5 kJ/mol is very suitable for industrial applications of CO ₂ capture and release when needed.

Experimental results of heat adsorption led to similar results within the expected error margin. GY-75 has high affinity for CO ₂ , on the other hand, CO ₂ affinity of GY-75 is low enough to release CO ₂ molecule when needed for carbon separation, recycling and/or storage processes.

Further data confirm that GY-75 has an -28,1 kJ/mol isosteric enthalpy of adsorption for H ₂ O molecules, which indicates that GY-75 has less affinity for H ₂ O molecules compared to the CO ₂ molecules.

Figure 5A shows the structure of GY-76 with exemplary atoms labeled.

Figure 5B summarizes the isoreticular expansions of GY-75 into GY-76, GY-77 and longer tethered versions of 4,4’-bipyridine, where n= 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.

Figure 6, shows a Thermo Gravimetric Analysis (TGA) of GY-75 indicating that organic components of GY-75 are stable under oxygen, RH (relative humidity) and temperatures of above 400 °C. Figure 7 shows GY-75 retains its crystal structure after 24 hours at 350°C while its competitor Calf-20 has been shown to be stable in air only up to 150°C. Figure 7 shows further powder XRD pattern. According to Figure 7, the structure of GY-75 is not altered after its activation at 350°C. Calf-20 was instable much earlier. Figure 8 shows molecule 1,4-naphthalenediarsonate.