Lewis Acid Base Sites Research Articles

Chemorobust 4p-5p {InPb}-organic framework for efficiently catalyzing cycloaddition of CO2 with epoxides and deacetalization-Knoevenagel condensation

Due to that the high charge density and small radius render In3+ cation a stronger Lewis acidity, multifunctional nanoporous In-MOFs have become one of the most promising catalysts for their high activity. Herein, the solvothermal self-assembly by employing 2,4,6-tri (2,4-dicarboxyphenyl)pyridine (H6TDP) as organic linker leads to a robust honeycomb skeleton of {[(CH3)2NH2][InIIIPbII(TDP) (H2O)]⋅3DMF⋅3H2O}n (NUC-52) with the merits of nanoscopic channels, high porosity (61.3%), large specific surface area, and thermal stability. To the best of our knowledge, this is the first 4p-5p heterometallic {InIIIPbII} cluster-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 7-coordinated Pb2+ ions, 4-coordinated In3+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Performed catalytic experiments exhibited that activated NUC-52 owned the high catalytic activity on the cycloaddition reactions of styrene oxide with CO2 under mild conditions with excellent turnover number (2475) and turnover frequency (619 h−1). Moreover, activated NUC-52 could greatly accelerate the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile. Hence, this work lays down the groundwork for constructing heterometallic cluster-based nanoporous MOFs with excellent Lewis acidic catalysis and chemical stability, which should be ascribed to the reasonable coordination arrangement between organic ligands and distinct metal ions according to the hard–soft acid–base (HSAB) theory.

Nanoporous {Y2}-Organic Frameworks for Excellent Catalytic Performance on the Cycloaddition Reaction of Epoxides with CO2 and Deacetalization-Knoevenagel Condensation.

Stable metal-organic frameworks containing periodically arranged nanosized pores and active Lewis acid-base active sites are considered as ideal candidates for efficient heterogeneous catalysis. Herein, the exquisite combination of [Y2(CO2)7(H2O)2] cluster (abbreviated as {Y2}) and multifunctional linker of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) led to a nanoporous framework of {[Y2(TDP)(H2O)2]·5H2O·4DMF}n (NUC-53, NUC = North University of China), which is a rarely reported binuclear three-dimensional (3D) framework with hierarchical tetragonal-microporous (0.78 nm) and octagonal-nanoporous (1.75 nm) channels. The inner walls of these channels are aligned by {Y2} clusters and plentifully coexisted Lewis acid-base sites of YIII ions and Npyridine atoms. Furthermore, NUC-53 has a quite large void volume of ∼65.2%, which is significantly higher than most documented 3D rare-earth-based MOFs. The performed catalytic experiments exhibited that activated NUC-53 showed a high catalytic activity on the cycloaddition reactions of CO2 with styrene oxide under mild conditions with excellent turnover number (TON: 1980) and turnover frequency (TOF: 495 h-1). Moreover, the deacetalization-Knoevenagel condensation reactions of benzaldehyde dimethyl acetal and malononitrile could be efficiently prompted by the heterogeneous catalyst of NUC-53. These findings not only pave the way for the construction of nanoporous MOF based on rare-earth clusters with a variety of catalytic activities but also provide some new insights into the catalytic mechanism.

A nanocaged cadmium-organic framework with high catalytic activity on the chemical fixation of CO2 and deacetalization-knoevenagel condensation

Heterogeneous MOFs catalysts have attracted great attention due to the efficient combination of heterogeneity (easy post-reaction separation and recyclability) and homogeneity (active sites and porosity), which inspire us to explore functional MOFs materials with higher catalytic activity on the chemical fixation of CO2 and deacetalization-Knoevenagel condensation. Herein, the self-assembly of Cd2+ and H6TDP under acidic solvothermal condition generated one cadmium-organic framework of {[(CH3)2NH2]2 [Cd2 (TDP) (H2O)2]⋅3DMF⋅2H2O}n (NUC-29, H6TDP = 2,4,6-tris(2,4-dicarboxyphenyl)pyridine) with nano-caged voids and hierarchical microporous channels, which were built on the combination of two kinds of mononuclear units of [Cd (1) (COO)3(H2O)] and [Cd (2) (COO)3(H2O)]. After the removal of solvent molecules by activation, NUC-29 possesses the coexistence of Lewis acid-base sites on the inner surface of channels including all exposed Cd2+ sites and Npyridine sites, which render it an excellent recyclable heterogeneous catalyst to facilitate the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation under mild conditions.

Selectively Regulating Lewis Acid–Base Sites in Metal–Organic Frameworks for Achieving Turn‐On/Off of the Catalytic Activity in Different CO2Reactions

AbstractRegulating Lewis acid–base sites in catalysts to investigate their influence in the chemical fixation of CO2is significant but challenging. A metal–organic framework (MOF) with open metal Co sites, {(NH2Me2)[Co3(μ3‐OH)(BTB)2(H2O)]⋅9 H2O⋅5 DMF}n(1), was obtained and the results of the catalytic investigation show that1can catalyze cycloaddition of CO2and aziridines to give 99 % yield. The efficiency of the cyclization of CO2with propargyl amines is only 32 %. To improve the catalytic ability of1, ligand XN with Lewis base sites was introduced into1and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF2({(NH2Me2)[Co3(μ3‐OH)(NHMe2)(BTB)2(XN)]⋅8 H2O⋅4 DMF}n). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from2treated with acid solution support this conclusion. This work illuminates a MOF‐construction strategy that produces efficient catalysts for CO2conversion.

Selectively Regulating Lewis Acid-Base Sites in Metal-Organic Frameworks for Achieving Turn-On/Off of the Catalytic Activity in Different CO2 Reactions.

Regulating Lewis acid-base sites in catalysts to investigate their influence in the chemical fixation of CO2 is significant but challenging. A metal-organic framework (MOF) with open metal Co sites, {(NH2 Me2 )[Co3 (μ3 -OH)(BTB)2 (H2 O)]⋅9 H2 O⋅5 DMF}n (1), was obtained and the results of the catalytic investigation show that 1 can catalyze cycloaddition of CO2 and aziridines to give 99 % yield. The efficiency of the cyclization of CO2 with propargyl amines is only 32 %. To improve the catalytic ability of 1, ligand XN with Lewis base sites was introduced into 1 and coordinated with the open Co sites, resulting in a decrease of the Lewis acid sites and an increase in the Lewis base sites in a related MOF 2 ({(NH2 Me2 )[Co3 (μ3 -OH)(NHMe2 )(BTB)2 (XN)]⋅8 H2 O⋅4 DMF}n ). Selective regulation of the type of active centers causes the yield of oxazolidinones to be enhanced by about 2.4 times, suggesting that this strategy can turn on/off the catalytic activity for different reactions. The catalytic results from 2 treated with acid solution support this conclusion. This work illuminates a MOF-construction strategy that produces efficient catalysts for CO2 conversion.

Effects of Lewis acid-base site and oxygen vacancy in MgAl minerals on peroxymonosulfate activation towards sulfamethoxazole degradation via radical and non-radical mechanism

Radicals of SO4•-, OH•, non-radical of 1O2 and even direct oxidation all occurred in peroxymonosulfate (PMS) activation process. Hence, to regulate the above radical or non-radical mechanism is of great significance for the treatment of organic pollutants in practical water. In this work, MgAl-minerals exhibited a satisfied performance in controlling the contribution of radicals (SO4•-, OH•) and non-radical (1O2) towards PMS activation based on results of reactive oxygen species scavenger experiments and electron spin resonance spectra. Compared with MgAl-1(61.8%) and MgAl-2 (61.4%) (Al/Mg = 1, 2), MgAl-3 (Al/Mg = 3) exhibited the highest sulfamethoxazole (SMX) removal efficiency (92.5%). Moreover, the contribution of radical and non-radical to SMX degradation were 56.7% and 30.1%, which was different from that of MgAl-1(7.8% and 39.5%) and MgAl-2 (5.2% and 41.6%). The roles of Lewis acid-base site and oxygen vacancies (OVs) in MgAl-minerals on radical and non-radical processes were detailed investigated. Lewis acid sites and OVs can enrich SMX and PMS at the solid-water interface. Simultaneously, OVs promote electron transfer from SMX to PMS acts as electron media, resulting in more SO4•- and OH• generation. While the basic sites favored the generation of 1O2 via PMS self-decomposition mechanism. Therefore, in PMS activation process over MgAl-minerals, the involved reactive oxygen species can be regulated via controlling the amounts of Lewis acid-base sites and oxygen vacancies. This finding provided new insights into PMS oxidation over non-transition metal-based catalysts and water remediation with complex water characteristics.

Nanochannel-based {BaZn}-organic framework for catalytic activity on the cycloaddition reaction of epoxides with CO2 and deacetalization-Knoevenagel condensation.

Herein, the rare combination of BaII (5s) and ZnII (3d) in the presence of the structure-oriented TDP6- ligand generated the nanochannel-based hybrid material {[(CH3)2NH2]2[BaZn(TDP)(H2O)]·DMF·5H2O}n (NUC-51, H6TDP = 2,4,6-tri(2,4-dicarboxyphenyl)pyridine), which possesses excellent physicochemical characteristics such as nanoscopic channels, high porosity, large specific surface area, and high heat/water-resistance. To the best of our knowledge, this is the first 3D [BaIIZnII(CO2)6(H2O)]-based nano-porous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including 4-coordinated Zn2+ ions, 7-coordinated Ba2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. Catalytic experiments exhibited that activated NUC-51a possesses a high catalytic activity on the cycloaddition reactions of epoxides with CO2 at 55 °C, which can be ascribed to its structural advantages of nanoscale channels and rich bifunctional active sites. Moreover, NUC-51a could significantly accelerate the deacetalization-Knoevenagel condensation reaction in DMSO solvent at 70 °C.

Ultrathin In‐Plane Heterostructures for Efficient CO2 Chemical Fixation

AbstractChemical fixation of carbon dioxide (CO2) into value‐added organics is regarded as a competitive and viable method in large scale industrial production, during which the catalysts with promoting CO2 activation ability are needed. Herein, we proposed an in‐plane heterostructure strategy to construct Lewis acid–base sites for efficient CO2 activation. By taking ultrathin in‐plane Cu2O/Cu heterostructures as a prototype, we show that Lewis acid‐base sites on heterointerface can facilitate a mixed C and O dual coordination on surface, which not only strengthen CO2 adsorption, but also effectively activate the inert molecules. As revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and quasi in situ X‐ray photoelectron spectroscopy (XPS), Lewis acid‐base sites could readily activate CO2 to .CO2− species, which is the key intermediate radical for CO2 fixation. As a result, abundant Lewis acid–base sites endow Cu2O/Cu nanosheets with excellent performances for dimethyl carbonate generation, a high conversion yield of 28 % with nearly 100 % selectivity under mild conditions. This study provides a model structure for CO2 fixation reactions.

Ultrathin In‐Plane Heterostructures for Efficient CO2 Chemical Fixation

AbstractChemical fixation of carbon dioxide (CO2) into value‐added organics is regarded as a competitive and viable method in large scale industrial production, during which the catalysts with promoting CO2 activation ability are needed. Herein, we proposed an in‐plane heterostructure strategy to construct Lewis acid–base sites for efficient CO2 activation. By taking ultrathin in‐plane Cu2O/Cu heterostructures as a prototype, we show that Lewis acid‐base sites on heterointerface can facilitate a mixed C and O dual coordination on surface, which not only strengthen CO2 adsorption, but also effectively activate the inert molecules. As revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and quasi in situ X‐ray photoelectron spectroscopy (XPS), Lewis acid‐base sites could readily activate CO2 to .CO2− species, which is the key intermediate radical for CO2 fixation. As a result, abundant Lewis acid–base sites endow Cu2O/Cu nanosheets with excellent performances for dimethyl carbonate generation, a high conversion yield of 28 % with nearly 100 % selectivity under mild conditions. This study provides a model structure for CO2 fixation reactions.

Highly Robust {Ln4}-Organic Frameworks (Ln = Ho, Yb) for Excellent Catalytic Performance on Cycloaddition Reaction of Epoxides with CO2 and Knoevenagel Condensation

Due to the high electron charge, large ion radius, and plentiful outer hybrid orbitals of LnIII cations, microporous Ln-MOFs can be used as Lewis acidic catalysts with high catalytic activity for a variety of organic reactions, which prompts us to explore cluster-based nanoporous Ln-MOFs by employing structure-oriented ligands. Herein, the exquisite combination of coplanar [Ln4(μ3–OH)2(μ2–HCO2)(H2O)2] clusters (abbreviated as {Ln4}) and the structure-oriented multifunctional ligand of 2,6-bis(2,4- dicarboxylphenyl)-4-(4-carboxylphenyl)pyridine (H5BDCP) led to two isomorphic nanoporous frameworks of {(Me2NH2)[Yb4(BDCP)2(μ3–OH)2(μ2–HCO2)(H2O)2]·5DMF·H2O}n (NUC-38Yb) and {(Me2NH2)[Ho4(BDCP)2(μ3–OH)2(μ2– HCO2)(H2O)2]·6DMF·3H2O}n (NUC-38Ho). To the best of our knowledge, NUC-38Ho and NUC-38Yb are rarely reported {Ln4}-based three-dimensional (3D) frameworks with embedded hierarchical triangular-microporous and hexagonal-nanoporous channels, which are shaped by six rows of coplanar {Ln4} clusters and characterized by plentiful coexisting Lewis acid–base sites on the inner wall including open LnIII sites, Npyridine atoms, μ3–OH, and μ2–HCO2. Catalytic experiments performed using NUC-38Yb as the representative exhibited that NUC-38Yb possessed a high catalytic activity on the cycloaddition reactions of epoxides with CO2 under mild conditions, which can be ascribed to its structural advantages including nanoscale channels, rich bifunctional active sites, large surface areas, and chemical stability. Moreover, NUC-38Yb, as a heterogeneous catalyst, could greatly accelerate the Knoevenagel condensation reactions of aldehydes and malononitrile. Hence, this work paves the way for the construction of functional Ln-cluster-based nanoporous metal–organic frameworks (MOFs) by elaborately designing functional ligands with transnormal connection modes.

Acetic acid-regulated mesoporous zirconium-furandicarboxylate hybrid with high lewis acidity and lewis basicity for efficient conversion of furfural to furfuryl alcohol

The synthesis of porous material endowed with high Lewis acid-base sites for catalytic transfer hydrogenation (CTH) of carbonyl compounds to their corresponding alcohols has become a hot topic. Herein, a mesoporous metal-organic hybrid (Zr-FDCA) was prepared through facile self-assembly of biomass-based 2,5-furandicarboxylic acid (FDCA) and zirconium by using acetic acid as the modulator. Its catalytic activity was tested by CTH of furfural (FAL) to furfuryl alcohol (FOL) in isopropanol. The characterization results revealed that Zr-FDCA displayed higher Lewis acid-base sites due to the competition between acetic acid and FDCA, thus exhibiting an outstanding catalytic performance to give a FOL yield up to 100% at 150 °C in 3 h. Based on the experimental results, a kinetic model describing this reaction has been established and shown a good correlation between the measured and predicted data, which can provide an effective tool to monitor the process and tailor the process conditions to obtain the desired product. More gratifyingly, Zr-FDCA displayed good recyclability, which can be easily separated from the reaction mixture and repetitively used at least five runs without an obvious loss of activity.

Synthesis of Methyl Mercaptan on Mesoporous Alumina Prepared with Hydroxysafflor Yellow A as Template: The Synergistic Effect of Potassium and Molybdenum

K-promoted Mo-based catalysts showed great promise for the hydrogenation of CS2 to methyl mercaptan (CH3SH). However, the research on the synergistic effect of K and Mo, and the active site of CS2 hydrogenation to CH3SH were unexplored widely. To solve this problem, the synergistic effect of K and Mo in the K-promoted Mo-based catalysts for CS2 hydrogenation to prepare CH3SH was investigated. The mesoporous alumina was the support and loaded the active components potassium and molybdenum to prepare the catalyst. The results suggested that the active components K and Mo can not only cooperatively regulate the acid-base sites on the catalyst surface, but also stabilize the molybdate species at +5 valence during the reduction process and increase the Mo unsaturated coordination sites. Combined with the results of the catalytic activity evaluation, indicating that the main active site of the catalysts is the weak Lewis acid-base site, and the strong acidic site and strong alkaline site are not conducive to the formation of CH3SH. Moreover, the possible catalytic mechanism of CS2 hydrogenation to CH3SH on the weak Lewis acid-base sites of the catalysts was proposed. The research results of this paper can provide an experimental basis and theoretical guidance for the design of high-performance CH3SH synthesis catalyst and further mechanism research.

Synergistic Lewis acid-base sites of ultrathin porous Co3O4 nanosheets with enhanced peroxidase-like activity

Synergistic Lewis acid-base sites of ultrathin porous Co3O4 nanosheets with enhanced peroxidase-like activity

Template-Induced {Mn2}-Organic Framework with Lewis Acid-Base Canals as a Highly Efficient Heterogeneous Catalyst for Chemical Fixation of CO2 and Knoevenagel Condensation.

The target for the self-assembly of functional microporous metal-organic frameworks (MOFs) could be realized by employing ligand-directed and/or template-induced strategies, which prompted us to explore the synthetic technique of d10 secondary-building-unit-based nanoporous frameworks. Here, the exquisite combination of a paddle-wheel [Mn2(CO2)6(OH2)2] cluster and a TDP6- ligand contributes one robust honeycomb framework of {(Me2NH2)2[Mn2(TDP)(H2O)2]·3H2O·3DMF}n (NUC-31; DMF = N,N-dimethylformamide), whose activated state with the removal of associated aqueous molecules characterizes the outstanding physicochemical properties of nanochannels, penta- and tetracoordinated Mn2+ serving as highly open metal sites, rich Lewis base sites (rows of C═O groups and Npyridine atoms), and excellent thermal stability. Moreover, it is worth mentioning that Lewis acid-base sites on the inner surface of the channels in activated NUC-31 successfully form one unprecedented canal-shaped acid-base confined space with evenly distributed open metal sites of Mn2+ and Npyridine atoms as the canal bottom as well as two rows of C═O groups serving as dyke dams. Catalytic experiments displayed that activated NUC-31 could serve as an efficient heterogeneous catalyst for the chemical fixation of CO2 with epoxides into cyclic carbonates under mild conditions. Furthermore, NUC-31 could effectively catalyze the reaction Knoevenagel condensation, which should be ascribed to the synergistic polarization effect aroused from its plentiful Lewis base sites in the confined channel space. Hence, these results demonstrate that the employment of ligand-directed and template-dependent strategies could overcome the self-assembled barriers of functional microporous MOFs and achieve unexpected frameworks.

Modification of the properties of γ-alumina as a support for nickel and molybdate catalysts by addition of silica

Commercial pure γ-Al2O3 and SiO2 (1−30 wt.%) doped γ-Al2O3 were characterized as acid catalysts in ethanol conversion and used as supports for NiO and MoO3. Supported catalysts were prepared by incipient wetness impregnation. All catalytic materials were characterized by BET, XRD, FE-SEM microscopy, UV–vis and IR spectroscopies. Pure and silica-doped NiO/Al2O3 materials were used as precursors of metal catalysts for CO2 hydrogenation. Pure and silica-doped MoO3/Al2O3 materials were used as catalysts for ethanol oxidative dehydrogenation to acetaldehyde.These data show that the addition of silica in moderate amounts selectively influences a part of the alumina surface and strongly modifies the dispersing properties of alumina support. In particular, silica preferentially bonds over the strongest Lewis acid-base sites of γ-Al2O3, where also Ni2+ and molybdate species tend to interact. Being the SiO2-Al2O3 interaction stronger than the NiO-Al2O3 interaction and the MoO3-Al2O3 interaction, silica displaces nickel and molybdate species to less preferential sites where their interaction with exposed alumina is weaker. This results in more easily reducible Ni2+ species and larger Ni metal particles for silica doped Ni/Al2O3, and more monomeric and less polymeric molybdate species for silica doped MoO3/Al2O3.

6s-3d {Ba3Zn4}-Organic Framework as an Effective Heterogeneous Catalyst for Chemical Fixation of CO2 and Knoevenagel Condensation Reaction.

The exquisite combination of Ba2+ and Zn2+ with the aid of 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) under the condition of solvothermal self-assembly generates one highly robust [Ba3Zn4(CO2)12(HCO2)2(OH2)2]-organic framework of {[Ba3Zn4(TDP)2(HCO2)2(OH2)2]·7DMF·4H2O}n (NUC-27), in which adjacent 2D layers are interlaced via hydrogen-bonding interactions to form a 3D skeleton with peapod-like channels and nano-caged voids. It is worth emphasizing that both Ba2+ and Zn2+ ions in NUC-27 display the extremely low coordination modes: hexa-coordinated [Ba(1)] and tetra-coordinated [Ba(2), Zn(1), and Zn(2)]. Furthermore, to the best our knowledge, NUC-27 is one scarcely reported 2D-based nanomaterial with an unprecedented Z-shaped hepta-nuclear heterometallic cluster of [Ba3Zn4(CO2)12(HCO2)2(OH2)2] as SBUs, which not only has plentiful low-coordinated open metal sites but also has the excellent physicochemical properties including omni-directional opening pores, ultrahigh porosity, larger specific surface area, and the coexistence of Lewis acid-base sites. Just as expected, thanks to its rich active metal sites and pyridine groups as strong Lewis acid-base roles, completely activated NUC-27 displays high catalytic efficiency on the chemical transformation of epoxides with CO2 into cyclic carbonates under mild conditions and effectively accelerates the reaction process of Knoevenagel condensation.

Hf-MOF catalyzed Meerwein−Ponndorf−Verley (MPV) reduction reaction: Insight into reaction mechanism

Hf-MOF-808 exhibits excellent activity and specific selectivity on the hydrogenation of carbonyl compounds via a hydrogen transfer strategy. Its superior activity than other Hf-MOFs is attributed to its poor crystallinity, defects and large specific surface area, thereby containing more Lewis acid-base sites which promote this reaction. Density functional theory (DFT) computations are performed to explore the catalytic mechanism. The results indicate that alcohol and ketone fill the defects of Hf-MOF to form a six-membered ring transition state (TS) complex, in which Hf as the center of Lewis stearic acid coordinates with the oxygen of the substrate molecule, thus effectively promoting hydrogen transfer process. Other reactive groups, such as –NO2, C = C, -CN, of inadequate hardness or large steric hindrance are difficult to coordinate with Hf, thus weakening their catalytic effect, which explains the specific selectivity Hf-MOF-808 for reducing the carbonyl group.

Nanochannel-based heterometallic {ZnIIHoIII}-organic framework with high catalytic activity for the chemical fixation of CO2.

The exquisite combination of ZnII and HoIII generated the highly robust [ZnHo(CO2)6(OH2)]-based heterometallic framework of {[ZnHo(TDP)(H2O)]·5H2O·3DMF}n (NUC-30, H6TDP = 2,4,6-tri(2′,4′-dicarboxyphenyl)pyridine), which featured outstanding physicochemical properties, including honeycomb nanochannels, high porosity, large specific surface area, the coexistence of highly open Lewis acid–base sites, good thermal and chemical stability, and resistance to most organic solvents. Due to its extremely unsaturated metal tetra-coordinated Zn(ii) ions, hepta-coordinated Ho(iii) and high faveolate void volume (61.3%), the conversion rate of styrene oxide and CO2 into cyclic carbonates in the presence of 2 mol% activated NUC-30 and 5 mol% n-Bu4NBr reached 99% under the mild conditions of 1.0 MPa and 60 °C. Furthermore, the luminescence sensing experiments proved that NUC-30 could be used as a fast, sensitive and highly efficiency sensor for the detection of Fe3+ in aqueous solution. Therefore, these results prove that nanoporous MOFs assembled from pyridine-containing polycarboxylate ligands have wide applications, such as catalysis and as luminescent materials.

Highly Robust 3s-3d {CaZn}-Organic Framework for Excellent Catalytic Performance on Chemical Fixation of CO2 and Knoevenagel Condensation Reaction.

In terms of ligand-directed synthetic strategy, multifunctional metal-organic frameworks (MOFs) could be assembled by employing organic ligands with nitrogen-containing heterocycles, which could serve as Lewis base sites in crystallized porous frameworks. Here, the acidic one-pot hydrothermal reaction of CaCl2, Zn(NO3)2, and 2,4,6-tri(2,4-dicarboxyphenyl)pyridine (H6TDP) generates one robust honeycomb-shaped double-walled material of {[(CH3)2NH2]2[CaZn(TDP)(H2O)]·3DMF·3H2O}n (NUC-21), which has the excellent physicochemical characteristics of nanoscopic channels, high porosity (58.3%), large specific surface area, and high heat/water-resisting property. To the best of our knowledge, this is the first 3s-3d dinuclear [CaZn(CO2)6(OH2)]-based nanoporous host framework, whose activated state possesses the coexistence of Lewis acid-base sites including four-coordinated Zn2+ ions, four-coordinated Ca2+ ions, uncoordinated carboxyl oxygen atoms, and Npyridine atoms. As expected, because of the coexistence of Lewis acid-base nature, desolvated NUC-21 displays satisfactory catalytic activity on the chemical cycloaddition of various epoxides with CO2 into the corresponding alkyl carbonates under comparatively mild conditions. Furthermore, the efficient conversion of benzaldehydes and malononitrile confirms that NUC-21 is simultaneously a bifunctional heterogeneous catalyst for Knoevenagel condensation reactions. Hence, the achievements broaden the way for assembling nanoporous multifunctional MOFs by employing ligand-directed synthetic strategy, which can accelerate the transformation from simple structural research to socially demanding applications.

Formic Acid Dehydration Rates and Elementary Steps on Lewis Acid–Base Site Pairs at Anatase and Rutile TiO2 Surfaces

Formic acid (HCOOH) decomposition is often used to assess the acid–base properties of oxide surfaces. Its reverse reaction forms HCOOH and formate species that can act as intermediates in CO2/CO/H2...