Alkaline Earth Metal Organic Frameworks Research Articles

Square-planar Tetranuclear Cluster-based Alkaline Earth Metal-organic Frameworks with Enhanced Proton Conductivity.

Alkaline earth (AE) metal complexes have garnered significant interest in various functional fields due to their nontoxicity, low density, and low cost. However, there is a lack of systematic investigation into the structural characteristics and physical properties of AE-metal-organic frameworks (MOFs). In this research, we synthesized isostructural MOFs consisting of AE4(μ4-Cl) clusters bridged by benzo-(1,2;3,4;5,6)-tris(thiophene-2'-carboxylic acid) (BTTC3-) ligands. The resulting structure forms a truncated octahedral cage denoted as [AE4(m4-Cl)]6(BTTC)8, which further linked to a porous three-dimensional framework. Among the investigated AE ions (Ca, Sr, and Ba), the Ca4-MOF demonstrated good chemical stability in water compared to Sr4-MOF and Ba4-MOF. The N2 adsorption and solid-state UV-vis-NIR absorption behaviors were evaluated for all AE4-MOFs, showing similar trends among the different metal ions. Additionally, the proton conduction study revealed that the Ca4-MOF exhibited ultra-high proton conductivity, reaching 3.52×10-2 S cm-1 at 343 K and 98 % RH. Notably, the introduction of LiCl via guest exchange resulted in an improved proton conduction of up to 6.36×10-2 S cm-1 under similar conditions in the modified LiCl@Ca4-MOF. The findings shed light on the regulation of physical properties and proton conductivity of AE-MOFs, providing valuable insights for their potential applications in various fields.

Efficient modulation of a barium metal-organic framework using amino acids.

In recent years, significant advances have been made in the precise control of the physical properties of metal-organic frameworks (MOFs) via the linker-modulated method in which modulators compete with linkers and impose kinetic limitations through crystal growth. In this regard, the structure of a new barium-organic framework [Ba(H2BTC)2(H2O)4]n, BaBTC (BTC = 1,3,5-benzene tricarboxylic acid) is introduced, which allows the competitive coordination strategy and growth orientation of an alkaline-earth metal-organic framework (AEMOF) to be probed without sacrificing phase purity, porosity and crystallinity. The modulator effect of an assortment of amino acids on the particle size and morphology of BaBTC is investigated. Additionally, another new MOF [Ba(BTC)2(H2O)3]n.nH2O, BaBTC-2, is synthesized through a change in the ligand concentration. This work gives a successful example of a modulation method for AEMOF synthesis by amino acids that may contribute towards targeting future avenues of nanomaterial synthesis.

Sr(II) and Ba(II) Alkaline Earth Metal-Organic Frameworks (AE-MOFs) for Selective Gas Adsorption, Energy Storage, and Environmental Application.

Two new alkaline earth metal-organic frameworks (AE-MOFs) containing Sr(II) (UPJS-15) or Ba(II) (UPJS-16) cations and extended tetrahedral linker (MTA) were synthesized and characterized in detail (UPJS stands for University of Pavol Jozef Safarik). Single-crystal X-ray analysis (SC-XRD) revealed that the materials are isostructural and, in their frameworks, one-dimensional channels are present with the size of ~11 × 10 Å2. The activation process of the compounds was studied by the combination of in situ heating infrared spectroscopy (IR), thermal analysis (TA) and in situ high-energy powder X-ray diffraction (HE-PXRD), which confirmed the stability of compounds after desolvation. The prepared compounds were investigated as adsorbents of different gases (Ar, N2, CO2, and H2). Nitrogen and argon adsorption measurements showed that UPJS-15 has SBET area of 1321 m2 g-1 (Ar) / 1250 m2 g-1 (N2), and UPJS-16 does not adsorb mentioned gases. From the environmental application, the materials were studied as CO2 adsorbents, and both compounds adsorb CO2 with a maximum capacity of 22.4 wt.% @ 0 °C; 14.7 wt.% @ 20 °C and 101 kPa for UPJS-15 and 11.5 wt.% @ 0°C; 8.4 wt.% @ 20 °C and 101 kPa for UPJS-16. According to IAST calculations, UPJS-16 shows high selectivity (50 for CO2/N2 10:90 mixture and 455 for CO2/N2 50:50 mixture) and can be applied as CO2 adsorbent from the atmosphere even at low pressures. The increased affinity of materials for CO2 was also studied by DFT modelling, which revealed that the primary adsorption sites are coordinatively unsaturated sites on metal ions, azo bonds, and phenyl rings within the MTA linker. Regarding energy storage, the materials were studied as hydrogen adsorbents, but the materials showed low H2 adsorption properties: 0.19 wt.% for UPJS-15 and 0.04 wt.% for UPJS-16 @ -196 °C and 101 kPa. The enhanced CO2/H2 selectivity could be used to scavenge carbon dioxide from hydrogen in WGS and DSR reactions. The second method of applying samples in the area of energy storage was the use of UPJS-15 as an additive in a lithium-sulfur battery. Cyclic performance at a cycling rate of 0.2 C showed an initial discharge capacity of 337 mAh g-1, which decreased smoothly to 235 mAh g-1 after 100 charge/discharge cycles.

Alkaline Earth Metal-Organic Frameworks Based on Tetratopic Anthraquinone-Based Linkers: Synthesis, Characterization, and Photochemical Applications.

A tetratopic bis(diphenylamino)anthraquinone linker is presented, and its physicochemical properties are evaluated. The linker is shown to successfully coordinate alkaline earth metals leading to four new reported metal-organic frameworks (MOFs), which have been fully characterized, including single-crystal X-ray diffraction. The physicochemical and emissive properties of the MOF materials are investigated and compared to those of the uncoordinated ligand. Finally, the catalytic behavior of the ligand and the MOF materials toward the photooxidation of sulfides is described.

Three Amino‐functionalized Alkaline Earth Metal‐Organic Frameworks as Catalysts for Knoevenagel Condensation

AbstractThree amino‐functionalized alkaline earth Metal‐Organic Frameworks (MOFs), including Mg‐ABDC [Mg(ABDC)(DMF)], Ca‐ABDC [Ca(ABDC)(DMF)] and Sr‐ABDC [Sr(ABDC)(DMF)]( ABDC=2‐aminobenzene‐1,4‐dicarboxylate anion), were synthesized under solvothermal conditions. The incorporation of alkaline earth metals and N‐containing ligands is an effective way to increase the basicity of MOFs. To explore catalytic activity of three alkaline earth MOFs, they were applied to catalyze the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate to produce ethyl (E)‐α‐cyanocinnamate. All three alkaline earth MOFs had high catalytic performance, among which Mg‐ABDC showed the best performance. The activity of catalyst was expressed by the conversion rate and selectivity. The conversation rate was up to 94.7 % and the selectivity was nearly 100 % by adding Mg‐ABDC. Mg‐ABDC was proved to be an efficient, stable and heterogeneous catalyst through hot filtration and recycling tests.

Novel alkaline earth metal–organic frameworks with thiophene groups for selective detection of Fe3+

This work demonstrates that the alkaline earth ion radii play an important role in coordination numbers and topologies for constructing MOFs, and these MOFs can be used as fast-response fluorescence sensors for the detection of Fe3+.

A series of four novel alkaline earth metal-organic frameworks constructed of Ca(ii), Sr(ii), Ba(ii) ions and tetrahedral MTB linker: structural diversity, stability study and low/high-pressure gas adsorption properties.

A series of four novel microporous alkaline earth metal–organic frameworks (AE-MOFs) containing methanetetrabenzoate linker (MTB) with composition {[Ca4(μ8-MTB)2]·2DMF·4H2O}n (UPJS-6), {[Ca4(μ4-O)(μ8-MTB)3/2(H2O)4]·4DMF·4H2O}n (UPJS-7), {[Sr3(μ7-MTB)3/2]·4DMF·7H2O}n (UPJS-8) and {[Ba3(μ7-MTB)3/2(H2O)6]·2DMF·4H2O}n (UPJS-9) (UPJS = University of Pavol Jozef Safarik) have been successfully prepared and characterized. The framework stability and thermal robustness of prepared materials were investigated using thermogravimetric analysis (TGA) and high-energy powder X-ray diffraction (HE-PXRD). MOFs were tested as adsorbents for different gases at various pressures and temperatures. Nitrogen and argon adsorption showed that the activated samples have moderate BET surface areas: 103 m2 g−1 (N2)/126 m2 g−1 (Ar) for UPJS-7′′, 320 m2 g−1 (N2)/358 m2 g−1 (Ar) for UPJS-9′′ and UPJS-8′′ adsorbs only a limited amount of N2 and Ar. It should be noted that all prepared compounds adsorb carbon dioxide with storage capacities ranging from 3.9 to 2.4 wt% at 20 °C and 1 atm, and 16.4–13.5 wt% at 30 °C and 20 bar. Methane adsorption isotherms show no adsorption at low pressures and with increasing pressure the storage capacity increases to 4.0–2.9 wt% of CH4 at 30 °C and 20 bar. Compounds displayed the highest hydrogen uptake of 3.7–1.8 wt% at −196 °C and 800 Torr among MTB containing MOFs.

Alkaline Earth Metal–Organic Frameworks with Tailorable Ion Release: A Path for Supporting Biomineralization

An innovative application of metal-organic frameworks (MOFs) is in biomedical materials. To treat bone demineralization, which is a hallmark of osteoporosis, biocompatible MOFs (bioMOFs) have been proposed in which various components, such as alkaline-earth cations and bisphosphonate molecules, can be delivered to maintain normal bone density. Multicomponent bioMOFs that release several components simultaneously at a controlled rate thus offer an attractive solution. We report two new bioMOFs, comprising strontium and calcium ions linked by p-xylylenebisphosphonate molecules that release these three components and display no cytotoxic effects on human osteosarcoma cells. Varying the Sr2+/Ca2+ ratio in these bioMOFs causes the rate of ions dissolving into simulated body fluid to be unique; along with the ability to adsorb proteins, this property is crucial for future efforts in drug-release control and promotion of mineral formation. The one-pot synthesis of these bioMOFs demonstrates the utility of MOF design strategies.

Four alkaline earth metal (Mg, Ca, Sr, Ba)-based MOFs as multiresponsive fluorescent sensors for Fe3+, Pb2+ and Cu2+ ions in aqueous solution

A series of new alkaline earth-metal organic frameworks (AE-MOFs), i.e. {[Mg2(μ6-L)(μ2-OH2)(H2O)4]·DMF}n (1), [Ca2(μ10-L)(EtOH)]n (2), [Sr(μ6-H2L)(MeOH)]n (3) and {[Ba1.5(μ5-H2L)(μ4-H3L)(H2O)3]·2(H2O)}n(4) were synthesized under solvothermal reaction by employing a symmetrical V-shaped multicarboxylic acid ligand H4L (H4L = 5,5′-oxydiisophthalic acid), resulting in versatile coordination modes as well as various topologies. 1 forms a uninodal 4-connected (66)-dia 3D topology based on dinuclear Mg2(COO)2(μ2-OH2) clusters. 2 displays an unprecedented 3-nodal (5,5,10)-connected 3D net with (424·621)(48·62)2 topology based on 1D [Ca(COO)]n chains and dinuclear Ca2(COO)2 clusters. 3 indicates a uninodal 6-connected 3D net with (410·65)-sma topology based on 1D [Sr(COO)]n chains. 4 features a new 4-nodal (4,5,6,6)-connected net with (43·63)2(46·64)2(46·68·8)(46·69)2 topology based on two types of 1D chains. 1-4 show solid-state fluorescent properties at ambient temperature. Especially, 1 and 2 have multiresponsive recognition of Fe3+ and Pb2+ ions, Fe3+ and Cu2+ ions, respectively, while 3 and 4 show single selective detection for Fe3+ ion, signifying that they could be potential fluorescent sensors for specific heavy metal ions in water system. The sensing mechanism has also been discussed in detail.

Synthesis and Structure of Three New Alkaline Earth Metal–Organic Frameworks with High Thermal Stability as Catalysts for Knoevenagel Condensation

Three new alkaline earth metal–organic frameworks (MOFs), [Mg2(BDC-OH)2(DMF)3] (Mg-HBDC), [Ca(BDC-OH)(DMF)2] (Ca-HBDC), and [Sr(BDC-OH)(DMF)] (Sr-HBDC) (BDC-OH = 2-hydroxyterephthalate(2−) anion and DMF = N,N-dimethylformamide), were synthesized by the assembly of BDC-OH and nitrate salts of the metal ions under solvothermal conditions. Single-crystal structure analysis revealed that Ca-HBDC and Sr-HBDC are isostructural to their corresponding MOFs containing 2,5-dihydroxyterephthalalate(2−) anion (H2dhtp) and terephthalate(2−) anion (BDC), respectively. The MOFs were also characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and powder X-ray diffraction. The obtained MOFs were applied as heterogeneous basic catalysts for the Knoevenagel condensation reaction at room temperature. The catalysts showed good catalytic activity and structural stability in the condensation reaction and could be reused without observable loss of activity.

Two new alkaline earth metal organic frameworks with the diamino derivative of biphenyl-4,4′-dicarboxylate as bridging ligand: Structures, fluorescence and quenching by gas phase aldehydes

Alkaline earth metal ion organic frameworks (AEMOFs) represent a relatively underexplored subcategory of MOFs. Two new MOFs [Ca6(bpdc-(NH2)2)5(μ3-HCO2)2(H2O)2.5(DMF)0.5]·0.5H2O·2.5DMF (1) and [Sr4(bpdc-(NH2)4)(μ2-DMF)2(DMF)1/3]·2/3(DMF) (2) [H2bpdc-(NH2)2 = 2,2′-diamino-[1,1′-biphenyl]-4,4′-dicarboxylic acid); DMF = N,N-dimethylformamide] are presented here. These MOFs display structural variety with diverse topologies and new structural features. Luminescence studies revealed that both MOFs display ligand based fluorescence with small differences in emission profiles possibly attributable to the difference in charge density of the metal ions combined with the different conformation adopted by the ligand in the crystal structures of 1 and 2. Furthermore, initial sensing studies reveal that both MOFs can potentially function as fluorescent sensors for gas phase aldehydes.

Synthesis, crystal structures, and fluorescence properties of porphyrin alkaline earth MOFs

Two porphyrin based alkaline earth metal organic frameworks (MOFs) have been constructed from a multicarboxylate ligand tetra(4-carboxyphenyl)porphyrin (H4TCPP). Hydrothermal reaction between H4TCPP and Sr(II)/Ba(II) led to the formation of alkaline-earth MOFs [Sr4(TCPP)2(DMF)8]n (1) and [Ba4(TCPP)2(DMF)8]n (2). Single crystal X-ray diffraction analysis of 1 and 2 reveals that the two isomorphous compounds display a 3D supramolecular network structure constructed by mutually staggered TCPP ligands and metal ions. Both 1 and 2 exhibit excellent fluorescence properties and the fluorescence emission intensities and the maximum emission peak position of 2 in a variety of organic solvents are closely related to the dielectric constant of the solvents.

Three alkaline earth metal-organic frameworks based on fluorene-containing carboxylates: syntheses, structures and properties

Three metal-organic frameworks, {[Mg2(MFDA)2(DMF)3]∙0.5H2O} n ( 1 ), {[Ca(MFDA)(DMF)(H2O)]∙0.5DMF} n ( 2 ) and [Ca(MFDA)(DMF)2] n ( 3 ) (DMF= N , N -dimethylformamide) have been synthesized by the solvothermal reactions between the ligand 9,9-dimethylfluorene-2,7-dicarboxylic acid (H2MFDA) and the corresponding metal salts, respectively. The single crystal X-ray structural analyses reveal that compounds 1 – 3 display three-dimensional structures based on the M(II)–O–C chains. It is interesting that the MFDA ligands in 1 – 3 have different dihedral angles between the two carboxylate groups ranging from 9.9(1)° to 41.8(2)°. All of compounds exhibit strong ligand-centered blue emissions under UV lights. Their thermal properties have also been studied.

Syntheses, structures and characteristics of four alkaline-earth metal-organic frameworks (MOFs) based on benzene-1,2,4,5-tetracarboxylicacid and its derivative ligand

Two new pillar-layered Ba(II)-based 3D frameworks and two new Ca(II)-based 3D supramolecular frameworks, [Ba2(dbtec)(H2O)2]n (1), [Ca2(dbtec)(H2O)8]n (2), {[Ba2(H2btec)·H2O]·0.5H2O}n (3) and [Ca(H2btec)·H2O]n (4) (H4dbtec = 3,6-dibromobenzene-1,2,4,5-tetracarboxylic acid; H4btec = benzene-1,2,4,5-tetracarboxylic acid), have been synthesized under similar reaction conditions and stoichiometry. Single crystal X-ray diffraction study reveals axial-orientation Br···π supramolecular interactions exist in the crystal structure of 1, which keeps an 3D binodal network with the (32.412.510.62.72)(32.46.56.6)2 topology. Whereas in 2, intramolecular and intermolecular H-bonding interactions with the ligated water molecules promote the formation of 3D supramolecular frameworks network. For 3, a new 3D 3-nodal network occurs in the structure and some rare coordination modes for the H4btec are observed. There is a 2D double layer with the thickness of 7.60 Å in 4. In addition, besides the high thermal stability, the FTIR spectra, PXRD patterns and the photoluminescent of these compounds are also discussed.

Mechanochemical Synthesis, Characterization, and Structure Determination of New Alkaline Earth Metal-Tetrafluoroterephthalate Frameworks: Ca(pBDC-F4)·4H2O, Sr(pBDC-F4)·4H2O, and Ba(pBDC-F4)

New fluorinated alkaline earth metal–organic frameworks were successfully synthesized by milling of metal hydroxides M(OH)2 with tetrafluoroterephthalic acid H2pBDC-F4. Both calcium- and strontium-tetrafluoroterephthalates are tetrahydrated, while the barium tetrafluoroterephthalate is free of coordinating water molecules. The two isomorphic structures Ca(pBDC-F4)·4H2O and Sr(pBDC-F4)·4H2O were solved from the powder diffraction data by ab initio structure determination and subsequent Rietveld refinement. The products were thoroughly characterized by elemental analysis, thermal analysis, magic-angle spinning NMR, Fourier transform infrared spectroscopy, scanning electron microscopy imaging, and Brunauer–Emmett–Teller measurements. Our findings suggest that the mechanochemical synthesis route is a promising approach for the preparation of new fluorinated alkaline earth metal–organic frameworks.

Insight into Lewis Acid Catalysis with Alkaline‐Earth MOFs: The Role of Polyhedral Symmetry Distortions

We propose a multidisciplinary approach to face the interpretation of heterogeneous catalysis with alkaline-earth metal-organic frameworks (MOFs). Their oxygen-based polyhedra, which do not exhibit regular geometries, do act as very active Lewis acid sites. Four novel alkaline-earth MOFs that belong to three different structural types-Mg-AEPF-11, Mg-APF-12, Ca-AEPF-13 and Sr-APF-13-are reported, together with their net topologies, and a study of the symmetry distortions around the alkaline-earth metal polyhedra by using a continuous shape mapping (CShM) description. These MOFs are good catalysts in the selective hydrogenation of styrene. Even more, Sr-AEPF-13 shows the best conversions ever published with alkaline-earth MOFs for the hydrogenation of activated alkenes under mild conditions. A combination of crystallographic and topological analysis and theoretical calculations, together with experimental catalytic results, has been applied to understand the catalytic activity of these four novel alkaline-earth MOFs. This work demonstrates that the presence of symmetry-distorted alkaline-earth polyhedra gives rise to highly catalytic-active MOFs in the hydrogenation of activated alkenes.

Alkaline earth metal–organic frameworks supported by ditopic carboxylates

Hydrothermal reactions of alkaline earth metal nitrates with two ditopic carboxylic acids, trans-1,4-cyclohexanedicarboxylic acid (H2CDC) and 1,4-phenylenedipropionic acid (H2PDP), generate two 3-D metal–organic frameworks (MOFs) with empirical formulas [Ca(CDC)(H2O)2]·H2O (1) and [Sr(PDP)(H2O)] (2), respectively. Compound 1 consists of Ca–COO–H2O chains cross-linked through the –C6H10– spacers of the CDC anions, showing slightly open 1-D channels along the crystallographic c axis that accommodate the guest water molecules. Compound 2 exhibits a MOF consisting of wavy 2-D Sr–COO–H2O nets linked by –CH2CH2C6H4CH2CH2– tethers, and the condensed structure appears to arise from conformational flexibility of the ligand spacer.

Synthesis, X-ray crystal structure, and solution studies of two novel supramolecular coordination polymers of barium(II) and copper(II) based on chelidamic acid

Two homometal–organic coordination polymers, [Ba(C7H3NO5)2(H2O)4Ba(H2O)3]n·(2H2O)n and [[Cu(C7H2NO5)(C5H6N2)2]2Cu(C5H6N2)2(H2O)2]n·(6H2O)n, have been synthesized and characterized by X-ray single-crystal diffraction. In the barium compound (the first example of chelidamic acid introduced into the alkaline earth metal organic framework), two independent barium ions are coordinated by water and chelidamic acid molecules in monocapped and bicapped square anti-prismatic geometries. The two independent chelidamic acid molecules bridge several alkaline earth metal ions assembling a layered metal organic structure. In the copper compound, chelidamic acid shows its versatility as a ligand since it bridges three copper ions, with the carboxylate O atoms, the hydroxyl O atom, and the pyridine N atom coordinating the 3D metal ions. 4-Aminopyridine and water as ligands complete the coordinating sphere of the two independent Cu ions in distorted octahedral geometries. The equilibrium constants for the chelidamic acid-4-aminopyridine proton transfer system and the stoichiometry and stability of complexation of this system with Cu(II) and Ba(II) ions in aqueous solution were investigated by potentiometric pH titration method. The stoichiometry of some complex species in solution was found to be similar to the cited crystalline metal ion complexes.

A magnesium-based multifunctional metal–organic framework: synthesis, thermally induced structural variation, selective gas adsorption, photoluminescence and heterogeneous catalytic study

Three magnesium based carboxylate framework systems were prepared through a temperature-dependent synthesis. The compounds were synthesized by a hydrothermal method and characterized by single crystal X-ray diffraction analysis. A stepwise increase in the temperature of the medium resulted a stepwise increase in the dimensionality of the network, ultimately leading to the formation of a new 2D layered alkaline earth metal-organic framework (MOF) compound, {[Mg2(HL)2(H2O)4]·H2O}n (1) (H3L = pyrazole-3,5-dicarboxylate). Compound 1 selectively adsorbs hydrogen (H2) (ca. 0.56 wt% at 77 K) over nitrogen at 1 atm and demonstrates a strong blue fluorescent emission band at 480 nm (λ(max)) upon excitation at 270 nm. Notably, the 2D framework compound efficiently catalyzes the aldol condensation reactions of various aromatic aldehydes with ketones in a heterogeneous medium under environmentally friendly conditions. The catalyst can be recycled and reused several times without any significant loss of activity.

Barium Carboxylate Metal–Organic Framework – Synthesis, X‐ray Crystal Structure, Photoluminescence and Catalytic Study

AbstractA new 3D alkaline earth metal–organic framework (MOF), [Ba(Hdcp)H2O]n (1) (H3dcp = 3,5‐pyrazoledicarboxylic acid), has been hydrothermally synthesized and structurally characterized by single‐crystal X‐ray diffraction analysis. A crystallographic study reveals that each metal ion in 1 is coordinated by eight O atoms and one N atom. Each 3,5‐pyrazoledicarboxylato (Hdcp2–) ligand coordinates to six alkaline earth metal centers through two carboxylate groups, each of which adopts a μ3‐η2:η1‐bridging coordination mode to afford a 3D network. Thermogravimetric analysis reveals that 1 is thermally stable up to ca. 230 °C. An emission band at ca. 466 nm (λmax) was observed in the photoluminescence spectrum of 1 in the solid state at room temperature. Compound 1 heterogeneously catalyzes the aldol condensation reactions of various aromatic aldehydes with acetone, cyclohexanone, acetophenone, and cyclopentanone.