UTSA-74: A MOF-74 Isomer with Two Accessible Binding Sites per Metal Center for Highly Selective Gas Separation

Supramolecular Cu(ii)–dipyridyl frameworks featuring weakly coordinating dodecaborate dianions for selective gas separation

Several novel weakly coordinating dodecaborate anion hybrid supramolecular Cu(ii)–dipyridyl frameworks were synthesized and characterized by single crystal analysis with one potential for selective C₂H₂/C₂H₄ and C₂H₂/CO₂ separation.

Engineering ligand conformation by substituent manipulation towards diverse copper-tricarboxylate frameworks with tuned gas adsorption properties

To expand the structural diversity and optimize the material performance, it is essential but challenging to regulate MOF structures in a predictable and controllable manner. In this work, by manipulating the substituents to engineer the ligand conformations, we designed and synthesized two asymmetric tricarboxylate ligands, and used them to successfully target two copper-tricarboxylate frameworks with diversified topologies depending on the ligand conformations. Besides, the ligand asymmetry induced the formation of two uncommon kinds of copper-carboxylate clusters, thus greatly expanding the library of copper-carboxylate secondary building units. Furthermore, the two compounds also displayed tunable gas adsorption properties pertinent to C2H2 separation and purification. At 298 K and 1 atm, the uptake capacity of C2H2 varies from 79.5 to 104.6 cm3 (STP) g-1, while the adsorption selectivities of C2H2 with respect to CO2 and CH4 are in the range of 2.3-3.8 and 15.3-21.6 for the equimolar components, respectively. Compared to the nitro counterpart, the methoxy MOF features higher C2H2 uptake capacity, larger C2H2/CO2 and C2H2/CH4 adsorption selectivities, and lower regeneration energy. This work demonstrates that simple ligand modification can be used to engineer the structures and tune gas adsorption properties of the resulting MOFs.

A novel CdII-based metal–organic framework as a multi-responsive luminescent sensor for Fe3+, MnO4−, Cr2O72−, salicylaldehyde and ethylenediamine detection with high selectivity and sensitivity

A luminescent Cd^II-based MOF has been synthesized.

High Adsorption Capacity and Selectivity of SO2 over CO2 in a Metal-Organic Framework

Herein, we report a new metal-organic framework (MOF), namely, ECUT-77, which is built on rod-shaped secondary building units, showing a high Brunauer-Emmett-Teller surface area of 760.3 cm²/g, a pore volume of 0.4 cm³/g, and an aperture of about 1 nm. This MOF enables both high SO₂ adsorption capacity up to 8.0 mmol/g at 0.92 bar and room temperature and a high SO₂/CO₂ selectivity of 44, resulting in excellent SO₂ separation upon a ECUT-77 column from a SO₂/CO₂ mixture containing 2000 ppm of SO₂.

Structural Isomerism of Two Ce-BTC for Fabricating Pt/CeO2 Nanorods toward Low-Temperature CO Oxidation

Metal-organic frameworks (MOFs) have attracted enormous research interest as precursors/templates to prepare catalytic materials. However, the effect of structural isomerism of MOFs on the catalytic performance has rarely been studied. In this contribution, two topologically different Ce-benzene tricarboxylate (Ce-BTC) based on the same ligands and metal centers (viz., "MOF isomers") are prepared and used as porous supports to load Pt nanoparticles (NPs), which shows distinct differences in porosities and loading behaviors of Pt. Strikingly, an irreversible framework transformation from tetragonal Ce-BTC to monoclinic isomer is observed during water soaking treatment. The results give clear evidence that Pt/CeO₂ derived from tetragonal Ce-BTC inclines to produce more Pt⁰ and smaller Pt NPs, which eventually improve the catalytic performance for CO oxidation (T₁₀₀ = 80 °C). In situ diffuse reflectance infrared Fourier transform spectroscopy analyses demonstrate that the adsorbed CO-Pt⁰ is the dominant intermediate for CO oxidation, rather than CO-Pt^{σ +} at the low temperature. Furthermore, MOF isomers based on the same structural units are also found in other Ln-MOFs, such as Er-BTC, Eu-BTC, Y-BTC, and Ce/Y-BTC. Overall, this study affords a fundamental understanding of the effect of MOF structural isomers on the catalytic performance of the derived composites.

Efficient C2Hn Hydrocarbons and VOC Adsorption and Separation in an MOF with Lewis Basic and Acidic Decorated Active Sites

To help address efficient separation of C₂H_n light hydrocarbons and C₂H₂/CO₂ in the chemical industry, the self-assembly via an azolate-carboxylate ligand and Co(II) ion gave rise to a new porous MOF material, [Co(btzip)(H₂btzip)]·2DMF·2H₂O (1) (H₂btzip = 4,6-bis(triazol-1-yl)isophthalic acid). In the MOF, the pores are modified by rich uncoordinated triazolyl Lewis basic N atoms and acidic -COOH groups, which strengthen interactions with C₂H_n hydrocarbons and CO₂ molecules, leading to high adsorption amounts for C₂H_2, C₂H₄, C₂H₆, and CO₂ and remarkable separation efficiency for C₂H_n-CH₄, CO₂-CH₄, and C₂H₂-CO₂ mixtures, as confirmed by breakthrough experiments on the realistic gas mixtures. The MOF also reveals outstanding selective adsorption ability for benzene/toluene, methanol/1-propanol, methanol/2-propanol, and 2-propanol/1-propanol isomers. Molecular simulations disclose the different adsorption sites in the MOF for various adsorbates.

Optimizing ibuprofen concentration for rapid pharmacokinetics on biocompatible zinc-based MOF-74 and UTSA-74

Metal-organic frameworks (MOFs) have potential as drug carriers on the basis of their surface areas and pore volumes that allow for high loading and fast release. This study investigated two biocompatible MOFs - Zn MOF-74 and UTSA-74 - for ibuprofen delivery. The effect of drug loading was studied by impregnating the MOFs with 30, 50, and 80 wt% ibuprofen. The samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ physisorption. From SEM, the MOF structures were maintained at 30 wt% ibuprofen, however, became agglomerated at 50-80 wt% loading, as the drug deposited on the surface and adhered the particles to one another. In the physisorption measurements, the Zn MOF-74 samples decreased in surface area with ibuprofen loading, until they became zero at 80 wt%. In UTSA-74, the drug impregnation was less effective, as 35% of the original surface area was retained in the 80 wt% sample. On the basis of our drug release measurements, 50 wt% ibuprofen loading was found to be optimal on Zn MOF-74, as it gave rise to fast kinetics (k = 0.27 h^-1/2) and high drug concentrations within the first 10 h. In UTSA-74, the fastest release rate was observed at 30 wt% loading (k = 0.22 h^-1/2), as the poor impregnation efficiency blocked diffusion through the MOF pores at higher loading. Color changes of phosphate buffer saline (PBS) solutions at different time intervals also suggested that Zn MOF-74 decomposed during drug release, as it produced yellowing of the PBS solution. On the other hand, UTSA-74 did not discolor the PBS solution, and was concluded to not have dissolved during drug release. From these results, it was concluded that Zn MOF-74 was the superior drug carrier, as it could effectively deliver higher ibuprofen loadings and would dissolve in the process of drug release, thereby reducing its invasiveness in the human body.

Bimetallic Rod-Packing Metal-Organic Framework Combining Two Charged Forms of 2-Hydroxyterephthalic Acid

Although many rod-packing metal-organic frameworks are known, few are based on ordered heterometallic rod building unit. We show here the synthesis of CPM-76 based on an unprecedented Zn-Mg bimetallic rod with crystallographically distinguishable metal sites. The configuration of the rod offers two types of coordination site with trigonal bipyramidal and octahedral sites selectively occupied by Zn and Mg, respectively. Also unusual is the inter-connection mode between the rods, which is based on dual-charged forms (-3 and -2) of the 2-hydroxyterephthalic acid (H₃ OBDC) ligand. Interestingly, each metal site in CPM-76 binds one solvent molecule, leading to a high density of solvent binding sites.

Coordination-driven assembly of a 3d-4f heterometallic organic framework with 1D Cu4I4 and Eu-based chains: syntheses, structures and various properties

A three-dimensional porous 3d-4f heterometallic organic framework, namely, {[Eu3(Cu4I4)3(INA)9(DMF)4]·3DMF}n (YNU-2), was successfully prepared under solvothermal conditions. There are two different one-dimensional metal chains in the structure, namely, Cu4I4 and EuIII-based chains, resulting in an excellent stability of the prepared sample. A N2 sorption isotherm at 77 K revealed that the activated sample exhibits a Brunauer-Emmett-Teller surface area of 371 m2 g-1, while, YNU-2 can adsorb obviously higher CO2 amounts than CH4 at 273 K and 298 K under 1 atm because of the stronger interaction force between CO2 and the porous skeleton. Furthermore, YNU-2 is highly efficient heterogeneous catalyst for chemical fixation of the CO2 and epoxides into cyclic carbonates with a preferable recyclability. Taking into account its excellent stability, the prepared sample can be used to construct an electrochemical adapter sensor for detecting cocaine with a detection limit of 0.27 pg mL-1 in the wide range of 0.001-0.5 ng mL-1.

Boosting Selective Adsorption of Xe over Kr by Double-Accessible Open-Metal Site in Metal-Organic Framework: Experimental and Theoretical Research

Obtaining highly valuable Xe from air or other sources is highly important but still seriously restricted by its inherent inert nature and the great difficulty in separation from other inert gases, especially for Xe and Kr that show comparable size. In this work, we show both experimental and theoretical research of how to boost the selective adsorption of Xe over Kr by double-accessible open-metal site in metal-organic framework (MOF). The MOF, namely, UTSA-74, shows a high Xe uptake up to 2.7 mmol/g and a lower Kr uptake of 0.58 mmol/g at 298 K and 1 bar, leading to a high selectivity of 8.4. The effective Xe/Kr separation was further confirmed by both transient breakthrough simulation and experimental breakthrough. The separation mechanism, as unveiled by the grand canonical Monte Carlo simulation and dispersion-corrected density functional theory calculation, is due to the unique double-accessible open-metal site in UTSA-74 that affords stronger interaction toward Xe than Kr.

A porous Zn(ii)-coordination polymer based on a tetracarboxylic acid exhibiting selective CO2 adsorption and iodine uptake

A porous Zn(ii)-coordination polymer, namely {[Zn2(μ8-abtc)(betib)]·DMF}n (1), was solvothermally synthesized from 3,3',5,5'-azobenzenetetracarboxylate (abtc4-) and 1,4-bis(2-ethylimidazol-1-yl)butane (betib) ligands and {[Zn2(μ8-abtc)(betib)]·H2O}n (2) was obtained through the immersion of 1 in methanol. Compounds 1 and 2 were structurally characterized via numerous techniques. Both compounds displayed a 3D porous framework with a 3,6-connected sqc5381 net. Compound 2a obtained at 140 °C from 2 exhibited gas and iodine adsorption properties. Interestingly, the compound adsorbed selectively CO2 with the uptake capacity of 54.02 cm3 g-1 (13.26%) over N2 (5.43 cm3 g-1) and CH4 (14.53 cm3 g-1) at 273 K. The compound also adsorbed iodine with the weights of 19.99% and 30.26% in solution and vapor phases, respectively. The single crystal X-ray result and Raman spectra showed the presence of iodine units in the pores of the framework.

Crystal engineering of porous coordination networks to enable separation of C2 hydrocarbons

Crystal engineering, the field of chemistry that studies the design, properties, and applications of crystals, is exemplified by the emergence over the past thirty years of porous coordination networks (PCNs), including metal-organic frameworks (MOFs) and hybrid coordination networks (HCNs). PCNs have now come of age thanks to their amenability to design from first principles and how this in turn can result in new materials with task-specific features. Herein, we focus upon how control over the pore chemistry and pore size of PCNs has been leveraged to create a new generation of physisorbents for efficient purification of light hydrocarbons (LHs). The impetus for this research comes from the need to address LH purification processes based upon cryogenic separation, distillation, chemisorption or solvent extraction, each of which is energy intensive. Adsorptive separation by physisorbents (in general) and PCNs (in particular) can offer two advantages over these existing approaches: improved energy efficiency; lower plant size/cost. Unfortunately, most existing physisorbents suffer from low uptake and/or poor sorbate selectivity and are therefore unsuitable for trace separations of LHs including the high volume C2 LHs (C₂H_x, x = 2, 4, 6). This situation is rapidly changing thanks to PCN sorbents that have set new performance benchmarks for several C2 separations. Herein, we review and analyse PCN sorbents with respect to the supramolecular chemistry of sorbent-sorbate binding and detail the crystal engineering approaches that have enabled the exquisite control over pore size and pore chemistry that affords highly selective binding sites. Whereas the structure-function relationships that have emerged offer important design principles, several development roadblocks remain to be overcome.

Rational Design of Microporous MOFs with Anionic Boron Cluster Functionality and Cooperative Dihydrogen Binding Sites for Highly Selective Capture of Acetylene

Separation of acetylene (C₂ H₂ ) from carbon dioxide (CO₂ ) or ethylene (C₂ H₄ ) is important in industry but limited by the low capacity and selectivity owing to their similar molecular sizes and physical properties. Herein, we report two novel dodecaborate-hybrid metal-organic frameworks, MB₁₂ H₁₂ (dpb)₂ (termed as BSF-3 and BSF-3-Co for M=Cu and Co), for highly selective capture of C₂ H₂ . The high C₂ H₂ capacity and remarkable C₂ H₂ /CO₂ selectivity resulted from the unique anionic boron cluster functionality as well as the suitable pore size with cooperative proton-hydride dihydrogen bonding sites (B-H^δ- ⋅⋅⋅H^δ+ -C≡C-H^δ+ ⋅⋅⋅H^δ- -B). This new type of C₂ H₂ -specific functional sites represents a fresh paradigm distinct from those in previous leading materials based on open metal sites, strong electrostatics, or hydrogen bonding.

Metrics for Evaluation and Screening of Metal-Organic Frameworks for Applications in Mixture Separations

For mixture separations, metal-organic frameworks (MOFs) are of practical interest. Such separations are carried out in fixed bed adsorption devices that are commonly operated in a transient mode, utilizing the pressure swing adsorption (PSA) technology, consisting of adsorption and desorption cycles. The primary objective of this article is to provide an assessment of the variety of metrics that are appropriate for screening and ranking MOFs for use in fixed bed adsorbers. By detailed analysis of several mixture separations of industrial significance, it is demonstrated that besides the adsorption selectivity, the performance of a specific MOF in PSA separation technologies is also dictated by a number of factors that include uptake capacities, intracrystalline diffusion influences, and regenerability. Low uptake capacities often reduce the efficacy of separations of MOFs with high selectivities. A combined selectivity-capacity metric, Δq, termed as the separation potential and calculable from ideal adsorbed solution theory, quantifies the maximum productivity of a component that can be recovered in either the adsorption or desorption cycle of transient fixed bed operations. As a result of intracrystalline diffusion limitations, the transient breakthroughs have distended characteristics, leading to diminished productivities in a number of cases. This article also highlights the possibility of harnessing intracrystalline diffusion limitations to reverse the adsorption selectivity; this strategy is useful for selective capture of nitrogen from natural gas.

Ultrafast assembly of swordlike Cu3(1,3,5-benzenetricarboxylate)n metal-organic framework crystals with exposed active metal sites

Owing to their large surface area and high uptake capacity, metal-organic frameworks (MOFs) have attracted considerable attention as potential materials for gas storage, energy conversion, and electrocatalysis. Various strategies have recently been proposed to manipulate the MOF surface chemistry to facilitate exposure of the embedded metal centers at the crystal surface to allow more effective binding of target molecules to these active sites. Nevertheless, such strategies remain complex, often requiring strict control over the synthesis conditions to avoid blocking pore access, reduction in crystal quality, or even collapse of the entire crystal structure. In this work, we exploit the hydrodynamics and capillary resonance associated with acoustically-driven dynamically spreading and nebulizing thin films as a new method for ultrafast synthesis of swordlike Cu₃(1,3,5-benzenetricarboxylate)_n (Cu-BTC) MOFs with unique monoclinic crystal structures (P2₁/n) distinct to that obtained via conventional bulk solvothermal synthesis, with 'swordlike' morphologies whose lengths far exceed their thicknesses. Through pulse modulation and taking advantage of the rapid solvent evaporation associated with the high nebulisation rates, we are also able to control the thicknesses of these large aspect ratio (width and length with respect to the thickness) crystals by arresting their vertical growth, which, in turn, allows exposure of the metal active sites at the crystal surface. An upshot of such active site exposure on the crystal surface is the concomitant enhancement in the conductivity of the MOF, evident from the improvement in its current density by two orders of magnitude.

A robust Th-azole framework for highly efficient purification of C2H4 from a C2H4/C2H2/C2H6 mixture

Separation of C2H4 from C2H4/C2H2/C2H6 mixture with high working capacity is still a challenging task. Herein, we deliberately design a Th-metal-organic framework (MOF) for highly efficient separation of C2H4 from a binary C2H6/C2H4 and ternary C2H4/C2H2/C2H6 mixture. The synthesized MOF Azole-Th-1 shows a UiO-66-type structure with fcu topology built on a Th6 secondary building unit and a tetrazole-based linker. Such noticeable structure, is connected by a N,O-donor ligand with high chemical stability. At 100 kPa and 298 K Azole-Th-1 performs excellent separation of C2H4 (purity > 99.9%) from not only a binary C2H6/C2H4 (1:9, v/v) mixture but also a ternary mixture of C2H6/C2H2/C2H4 (9:1:90, v/v/v), and the corresponding working capacity can reach up to 1.13 and 1.34 mmol g-1, respectively. The separation mechanism, as unveiled by the density functional theory calculation, is due to a stronger van der Waals interaction between ethane and the MOF skeleton.

A Chemically Stable Hofmann-Type Metal-Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture

The realization of porous materials for highly selective separation of acetylene (C₂ H₂ ) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal-organic framework (MOF), Co(pyz)[Ni(CN)₄ ] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C₂ H₂ capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C₂ H₂ capture capacity (49 cm³ g^-1 at 0.01 bar and 296 K) and thus ultrahigh selectivity for C₂ H₂ /CO₂ (36.5), C₂ H₂ /C₂ H₄ (24.2), and C₂ H₂ /CH₄ (1312.9) separation at ambient conditions, respectively, of which the C₂ H₂ /CO₂ selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C₂ H₂ molecule, thus leading to its ultrahigh C₂ H₂ capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C₂ H₂ /CO₂ , 1/99 C₂ H₂ /C₂ H₄ , and 50/50 C₂ H₂ /CH₄ mixtures under ambient conditions.

The Fluorescence Property of Zirconium-Based MOFs Adsorbed Sulforhodamine B

Sulforhodamine B (SRB) is widely utilized for cell staining and laser field. But its application is limited by aggregation-caused quenching (ACQ). In this work, we evaluated the use of UiO-66 and UiO-67 of Zr-based metal organic frameworks (Zr-MOFs) as the host to adsorb SRB molecules due to the high stabily and good loading capacity of Zr-MOFs. The fluorescence properties of the compounds were then discussed respectively. Due to the aperture difference between UiO-66 and UiO-67, they showed distinct fluorescence properties after loading SRB. When the concentration reaches 5 ppm, fluorescence quenching begins to occur in SRB@UiO-66, while it occurs in SRB@UiO-67 at 2 ppm. The solution of quenching phenomenon could open new avenues for the extensive use of SRB.

General Approach for Constructing Mechanoresponsive and Redox-Active Metal-Organic and Covalent Organic Frameworks by Solid-Liquid Reaction: Ferrocene as the Versatile Function Unit

We report for the first time the construction of mechanoresponsive and redox-active metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) by anchoring ferrocene (Fc) pendants as mechanophores in the pore wall. This work outlines a simple, general, and low-cost route to tailor MOFs and COFs by a Fc unit for mechanoresponsive nature, the release of Fe ions, redox behavior, and modulation of the skeleton charge together.

Optimizing Multivariate Metal-Organic Frameworks for Efficient C2H2/CO2 Separation

Adsorptive separation of acetylene (C₂H₂) from carbon dioxide (CO₂) promises a practical way to produce high-purity C₂H₂ required for industrial applications. However, challenges exist in the pore environment engineering of porous materials to recognize two molecules due to their similar molecular sizes and physical properties. Herein, we report a strategy to optimize pore environments of multivariate metal-organic frameworks (MOFs) for efficient C₂H₂/CO₂ separation by tuning metal components, functionalized linkers, and terminal ligands. The optimized material UPC-200(Al)-F-BIM, constructed from Al³⁺ clusters, fluorine-functionalized organic linkers, and benzimidazole terminal ligands, demonstrated the highest separation efficiency (C₂H₂/CO₂ uptake ratio of 2.6) and highest C₂H₂ productivity among UPC-200 systems. Experimental and computational studies revealed the contribution of small pore size and polar functional groups on the C₂H₂/CO₂ selectivity and indicated the practical C₂H₂/CO₂ separation of UPC-200(Al)-F-BIM.

Rational Construction of Porous Metal-Organic Frameworks for Uranium(VI) Extraction: The Strong Periodic Tendency with a Metal Node

Although metal-organic frameworks (MOFs) have been reported as important porous materials for the potential utility in metal ion separation, coordinating the functionality, structure, and component of MOFs remains a great challenge. Herein, a series of anionic rare earth MOFs (RE-MOFs) were synthesized via a solvothermal template reaction and for the first time explored for uranium(VI) capture from an acidic medium. The unusually high extraction capacity of UO₂²⁺ (e.g., 538 mg U per g of Y-MOF) was achieved through ion-exchange with the concomitant release of Me₂NH₂⁺, during which the uranium(VI) extraction in the series of isostructural RE-MOFs was found to be highly sensitive to the ionic radii of the metal nodes. That is, the uranium(VI) adsorption capacities continuously increased as the ionic radii decreased. In-depth mechanism insight was obtained from molecular dynamics simulations, suggesting that both the accessible pore volume of the MOFs and hydrogen-bonding interactions contribute to the strong periodic tendency of uranium(VI) extraction.

Mixed Metal-Organic Framework with Multiple Binding Sites for Efficient C2 H2 /CO2 Separation

The separation of C2 H2 /CO2 is particularly challenging owing to their similarities in physical properties and molecular sizes. Reported here is a mixed metal-organic framework (M'MOF), [Fe(pyz)Ni(CN)4 ] (FeNi-M'MOF, pyz=pyrazine), with multiple functional sites and compact one-dimensional channels of about 4.0 Å for C2 H2 /CO2 separation. This MOF shows not only a remarkable volumetric C2 H2 uptake of 133 cm3  cm-3 , but also an excellent C2 H2 /CO2 selectivity of 24 under ambient conditions, resulting in the second highest C2 H2 -capture amount of 4.54 mol L-1 , thus outperforming most previous benchmark materials. The separation performance of this material is driven by π-π stacking and multiple intermolecular interactions between C2 H2 molecules and the binding sites of FeNi-M'MOF. This material can be facilely synthesized at room temperature and is water stable, highlighting FeNi-M'MOF as a promising material for C2 H2 /CO2 separation.

Coordinated Water as New Binding Sites for the Separation of Light Hydrocarbons in Metal-Organic Frameworks with Open Metal Sites

Metal-organic frameworks with open metal sites are promising materials for gas separations. Particularly, the M₂(dobdc) (dobdc^4- = 2,5-dioxidobenzenedicarboxylate, M²⁺ = Co²⁺, Mn²⁺, Fe²⁺, ...) framework has been the Drosophila of this research field and has delivered groundbreaking results in terms of sorption selectivity. However, many studies focus on perfect two-component mixtures and use theoretical models, e.g., the ideal adsorbed solution theory, to calculate selectivities. Within this work, we shed light on the comparability of these selectivities with values obtained from propane/propene multicomponent measurements on the prototypical Co₂(dobdc) framework, and we study the impact of impurities like water on the selectivity. Despite the expected capacity loss, the presence of water does not necessarily lead to a decreased selectivity. Density functional theory calculations of the binding energies prove that the water molecules adsorbed to the metal centers introduce new binding sites for the adsorbates.