Carboxylic Acid Ligands Research Articles

An unexpected and robust nickel (II)-based ether-bonded homogeneous system: Effective for photocatalytic CO2-to-CO transformation in visible light

Three halogen-containing pyridine carboxylic acid ligands (6-fluoropicolinic acid, 6-chloropicolinic acid, and 6-bromopicolinic acid) were combined with nickel to form three types of complexes: Ni-O ((6,6′-oxydipicoline acid) Ni(H2O)2), Ni-(OH)2((6,6′-hydroxydipicoline acid) Ni(H2O)2) and Ni-Br2((6,6′-bromodipicoline acid) Ni(H2O)2). Interestingly, the nickel salt reacted with 6-fluoropicolinic acid to form the ether-type complex Ni-O, with 6-chloropicolinic acid to form the hydroxy-type complex Ni-(OH)2, and with 6-bromopicolinic acid to form a Ni-Br2 complex with unchanged ligands. The Ni-O and Ni-(OH)2 complexes are novel in structure and especially the Ni-O show an excellent catalytic performance on reduction of CO2 to CO. After 12 h of irradiation, the Ni-O complexes attained a CO turnover number (TON) of 5664.3 and 86.7 % selectivity. The configurations of the complex catalysts have been demonstrated to play a major role in photocatalysis, by integrating analysis of high resolution mass spectrometry (HRMS) as well as density-functional theory (DFT). A potential proton-coupled electron transfer (PCET) mechanism of two-stage photocatalytic process is proposed.

Interior and Exterior Surface Modification of Zr-Based Metal-Organic Frameworks for Trace Benzene Removal.

The emission of volatile organic compounds (VOCs) significantly contributes to air pollution and poses a serious threat to human health. Benzene, one of the most toxic VOCs, is difficult for the human body to metabolize and is classified as a Group 1 carcinogen. The development of efficient adsorbents for removing trace amounts of benzene from ambient air is thus of great importance. In this work, we studied the benzene adsorption properties of four Zr-based metal-organic frameworks (Zr-MOFs) through static volumetric and dynamic breakthrough experiments. Two previously reported Zr-MOFs, BUT-12 and STA-26, were prepared with a tritopic carboxylic acid ligand (H3L1) functionalized with three methyl groups, and STA-26 is a 2-fold interpenetrated network of BUT-12. Two new isoreticular Zr-MOFs, BUT-12-Et and STA-26-Et, were synthesized using a similar ligand, H3L2, where the methyl groups are replaced with ethyl groups. There are mesopores in BUT-12 and BUT-12-Et and micropores in STA-26 and STA-26-Et. The four Zr-MOFs all showed high stability in liquid water and acidic aqueous solutions. The microporous STA-26 and STA-26-Et showed much higher benzene uptakes than mesoporous BUT-12 and BUT-12-Et at room temperature under low pressures. Particularly, the benzene adsorption capacity of STA-26-Et was high up to 2.21 mmol/g at P/P0 = 0.001 (P0 = 12.78 kPa), higher than those of the other three Zr-MOFs and most reported solid adsorbents. Breakthrough experiments confirmed that STA-26-Et could effectively capture trace benzene (10 ppm) from dry air; however, its benzene capture capacity was reduced by 90% under humid conditions (RH = 50%). Coating of the crystals of STA-26-Et with polydimethylsiloxane (PDMS) increased the hydrophobicity of the exterior MOF surfaces, leading to a more than 2-fold improvement in its benzene capture capacity in the breakthrough experiment under humid condition. PDMS coating of STA-26-Et likely slowed down the water adsorption process, and thus, the adsorbent afforded more efficient capture of benzene. This work demonstrates that modifying both the interior and exterior surfaces of MOFs can effectively enhance their performance in capturing trace benzene from ambient air, even under humid conditions. This finding is meaningful for the development of new adsorbents for effective air purification applications.

Investigation on fluorescent sensing properties of Cd(II)-coordination polymers synthesized by nitrogen-containing carboxylic acid ligand

In this study, two-dimensional (2D) cadmium-based coordination polymer (CP) (Cd-1, [Cd4L8]n) and one-dimensional (1D) cadmium-based CP (Cd-2, [CdL(H2O)(NO3)·H2O]n) have been obtained by mixing 1-(4-benzoic acid)-3-(pyrazinyl)-1H-1,2,4-triazole (HL) as organic ligand and CdCO3 as a source of metal ions in hydrothermal/solvent-thermal reaction. The structures and properties of two examples of Cd(II) CPs were characterized and analyzed. The results from infrared spectroscopy, thermogravimetric analysis, and X-ray single-crystal diffraction analysis indicated that the CPs have a stable framework structure and better thermal stability. In addition, in the study of fluorescence properties, two Cd(II)-CPs were found to have high sensitivity to the specific recognition of Fe3+, CrO42− and Cr2O72− ions in metal nitrate and anionic aqueous solutions, and the stability and recyclability of which were further demonstrated through cycling tests, which are expected to be used for the development of the new Cd(II)-CPs and to be an excellent fluorescent probe material.

Two coordination polymers based on conjugated pyrazine aromatic carboxylic acid ligands: Structural and magnetic research

Two new coordination polymers [M(L)(H2O)2]n (M=Co (1) and Mn (2)) (H2L=5-(pyrazin-2-yl) isophthalic acid) were synthesized by hydrothermal method and systematically characterized. The two compounds were analyzed in depth by x-ray single crystal diffraction, elemental analysis, IR spectroscopy, PXRD and thermal analysis. The x-ray single crystal diffraction results indicate that compound 1 is a 3D framework structure. Through the carboxyl oxygen atoms and pyrazine nitrogen atoms on different L2− ligands, two interesting infinitely extended right helix chains are formed along the c-axis, and the two helix chains are combined to form a 3D framework structure of 1. In compound 2, the adjacent Mn2+ is bridged with four carboxyl oxygen groups in the ligand to form a binuclear structure unit {Mn2O4}. Each {Mn2O4} is linked to six organic ligands, and each ligand is linked to three {Mn2O4}, which together form a (3,6) linked 3D coordination polymer material. It is noteworthy that the interconnections between the layers form a lantern-like structure when viewed from the b-axis direction. Additionally, compounds 1 and 2 demonstrated temperature-dependent magnetic susceptibility (dc) and negative values of θ (equal to -10.59 K and -6.38 K), which are indicates the presence of weak antiferromagnetic interactions in both compounds 1 and 2.

Imidazole/pyridine-based ionic liquids modified metal-organic frameworks for efficient adsorption of Congo red in water

In this work, a metal-organic framework (MOF), {[Ba2L(NO3) (DMF)2] (DMF·H2O)}n, denoted as HBU-167, was synthesized under solvothermal conditions. HBU-167 obtained a 3D layer framework comprising the imidazole carboxylic acid ligand and Ba2+ as nodes. It was demonstrated to have an adsorption capacity for Congo red (CR), with an adsorption capacity of 407.37 mg•g−1 and a removal rate of 65.46 %. To improve the adsorption capacity of HBU-167, simply impregnated three imidazole/pyridine-based ionic liquids (ILs) onto HBU-167 to obtain IL@HBU-167 for efficient CR adsorption. The results of Powder X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy revealed that ILs successfully bonded to HBU-167. Adsorption experiments on CR revealed that IL@HBU-167 exhibited increased stability as well as improved adsorption capacity. The adsorption capabilities of the IL@HBU-167 were 440.70 mg•g−1, 491.23 mg•g−1, and 544.56 mg•g−1, respectively, while the removal rates were 72.96 %, 75.00 %, and 83.28 %, respectively. Batch experiments were applied to analyze the impact of factors such as contact time, initial concentration, pH, temperature, and ionic strength on the adsorption of CR by IL@HBU-167. The maximum adsorption capacity was observed at 25 °C and pH = 6. The kinetic data indicated that the adsorption conformed to the pseudo-second-order kinetic model. The Langmuir isothermal model accurately described isothermal data. Furthermore, the adsorption capacity of IL@HBU-167 was investigated in real water samples from various sources. The results showed that IL@HBU-167 can be used as an innovative and inexpensive adsorbent for the removal of CR from water. The adsorption capacity was mainly derived from π-π, electrostatic interactions, and hydrogen bonding between IL@HBU-167 and CR.

Transition metal coordination polymers based on imidazole/triazole carboxylic acid ligands for efficient detection of Fe3+ ions and adsorption of dyes

Five new coordination polymers (CPs), namely [Zn(L1)2·(H2O)2]n (1), [Cd(L1)2(H2O)2]n (2), [Cd(L1)Cl]n (3), [Cu(L1)2(H2O)2]n (4) and [Cd(L2)2(H2O)2]n (5) [HL1=4-(((1H-1,2,4-triazol-3-yl)amino)methyl)benzoic acid, HL2=4-((4-(1H-imidazol-1-yl)benzyl)amino)benzoic acid] based on imidazole/triazole carboxylic acid ligands were synthesized by adjusting the structure of the ligands, synthesis temperatures and solvents. CPs 1, 2, 4 and 5 display 1D chain structures with different shapes, and 3 is a 4-connected crb network structure. The fluorescence sensing properties and dye adsorption of those CPs were studied, the results showed that 1–3 can sensitively detect Fe3+ by turn-off effect and the limits of detection were 0.269, 0.024 and 0.06 μM, respectively. The study of the mechanism showed that energy transfer, competitive absorption and weak interaction are the reasons of fluorescent quenching. CP 5 exhibited adsorption performance for malachite green (MG) with adsorption capacity of 1428.6 mg g−1 and has good reusability, and the hydrogen bond and π-π interactions have been proved to be the main factors for the adsorption of MG by 5.

A novel porphyrin MOF catalyst for efficient conversion of CO2 with propargyl amines.

The capture and conversion of carbon dioxide (CO2) into valuable chemical products under mild conditions is an important and challenging approach for contemporary industry. Carboxylic acid ligands are widely used in the development of functionalized metal organic framework materials due to their excellent stability. Herein, a novel mixed-metal organic framework Cu-TCPP(Fe) was assembled from iron-(Fe)-porphyrin ligands, which can efficiently catalyze the reaction of propargylic amines and CO2 to synthesize 2-oxazolidinones.

Regulation engineering of lignin-derived N-doped carbon-supported FeNi alloy particles towards efficient electrocatalytic oxygen evolution

The electrocatalytic hydrogen production technology using green energy can reduce the dependence on traditional fossil fuels and the net emission of carbon dioxide. However, the high overpotential and low efficiency of the oxygen evolution reaction (OER) on the anode limit the overall water splitting. Here, carboxylic acid ligands with coordination function were designed and synthesized by modifying the surface functional groups of lignin. Bimetallic functionally-doped lignin-derived carbon materials (Fe4Ni4@NC) were synthesized by continuous ion layer adsorption and pyrolysis process using Fe and Ni transition metals as source and template. The catalyst requires only 214 mV of overpotential to produce 10 mA·cm−2, which has much faster catalytic kinetics. Theoretical calculation shows that the energy barrier of rate-determining step in OER is reduced by appropriate feed ratio and nano-size. The facile strategy opens up an economical and efficient solution for designing OER electrocatalysts with high catalytic activity and excellent stability.

Selective detection of Fe3+ and Congo red adsorption properties studies of Ln-complexes based on imidazopyridine carboxylic acid ligand

Five new Ln-complexes [Ln(L)2(OH)(H2O)3]n (1 and 2) and {[Ln2(L)2(HL)2(H2O)8]Cl4·7H2O}n (3–5) [Ln = Nd (1), Sm (2), Eu (3), Ho (4), Er (5), HL = 4-(1H-imidazo[4,5-c]pyridin-2-yl)benzoic acid] were synthesized under solvothermal conditions. The single crystal X‑ray diffraction showed that Ln-complexes 1–5 were one-dimensional (1D) structures. Interestingly, the sensing experimental showed that 1–5 could be considered as promising specificity fluorescent sensor for Fe3+ ions with good reusability and high sensitivity, and the detection limits were 7.14 × 10−6, 3.21 × 10−6, 7.28 × 10−6, 6.74 × 10−6 and 7.42 × 10−6 M, respectively. Ln-complexes 1–5 exhibited excellent adsorption performance to dye Congo red (CR), and the adsorption capacities were 2792 mg·g−1, 2551 mg·g−1, 2858 mg·g−1, 2752 mg·g−1 and 2654 mg·g−1, respectively. Adsorption kinetics and adsorption isotherms showed that the adsorption of 1–5 belongs to the chemical adsorption process, the hydrogen bonding and π-π interactions between the 1–5 host and CR guest molecules resulted in high adsorption capacity.

Relativistic DFT Calculations of Cadmium and Selenium Solid-State NMR Spectra of CdSe Nanocrystal Surfaces.

Solid-state NMR spectra have been used to probe the structure of CdSe nanocrystals and propose detailed models of their surface structures. Density functional theory (DFT)-optimized cluster models that represent probable molecular structures of carboxylate-coordinated surface sites have been proposed. However, to the best of our knowledge, 113Cd and 77Se chemical shifts have not been calculated for these surface models. We performed relativistic DFT calculations of cadmium and selenium magnetic shielding tensors on model compounds with previously measured solid-state NMR spectra with (i) the four-component Dirac-Kohn-Sham (DKS) Hamiltonian and (ii) the scalar and (iii) spin-orbit levels within the ZORA Hamiltonian. Molecular clusters with Cd and Se sites in varying bonding environments were used to model CdSe (100) and CdSe(111) surfaces capped with carboxylic acid ligands. Our calculations identify the observed 113Cd isotropic chemical shifts δ(iso) of -465, -318, and -146 ppm arising from CdSeO3, CdSe2O2, and CdSe3O surface groups, respectively, with very good agreement with experimental measurements. The 113Cd chemical shifts linearly decrease with the number of O-neighbors. The calculated spans (δ11 - δ33) encompass the experimental values for CdSe3O and CdSe2O2 clusters but are slightly larger than the measured value for CdSeO3 clusters. Relativistic DFT calculations predicted a one-bond 113Cd-77Se scalar coupling of 258 Hz, which is in good agreement with the experimental values of 250 Hz. With a dense coverage of carboxylic acid ligands, the CdSe (100) surface shows a distribution of Cd-Se bond lengths and J-couplings. Relativistic DFT simulations thus aid in interpretation of NMR spectra of CdSe nanocrystals and related nanomaterials.

Imide-functionalized Cu-MOF: Biomimetic peroxidase activity and detection of hydrogen peroxide and ascorbic acid

The synthesis of MOF with imide-functionalized aromatic conjugated carboxylic acid ligands has been a hot topic of field. A novel biomimetic peroxidase material (Cu-BDCPPI) was designed, synthesized and characterized by combining imide-functionalized aromatic conjugated carboxylic acid ligands N, N′-bis (3,5-dicarboxyphenyl) homophthalic diimide (H4BDCPPI) and catalytically active copper ions. The potential catalytic effect of Cu-H4BDCPPI on peroxidase-like activity was found firstly. It can catalyze the typical colorimetric substrate 3,3′,5,5′-tetramethylbenzyl (TMB) from colorless to blue ox-TMB in the presence of H2O2, and its enzymatic catalytic activity is similar to that of natural horseradish peroxidase (HRP). So, based on the catalytic performance of Cu-BDCPPI, a colorimetric method and test strips can be established for the detection of H2O2 and ascorbic acid (AA). This work provides a feasible strategy for synthesizing MOF materials with peroxidase like properties, expanding the application of MOF materials in the field of biological analysis.

A series of lanthanide complexes with different aromatic carboxylic acid ligands: Synthesis, supramolecular structure, thermal properties and luminescence behaviors

Six noble two-dimensional lanthanide complexes [Ln(2,4-DFBA)3(terpy)·H2O]·H2O (Ln = Tb(1), Dy(2)), [Pr(2,4,6-TMBA)3(terpy)·H2O] (3) [Nd(2,4,6-TMBA)3(terpy)·H2O]·C2H5OH·H2O(4) and [Ln(2,4,6-TMBA)3(terpy)·H2O]·1.5H2O (Ln = Dy(5), Ho(6) (2,4-DFBA = 2,4-difluorobenzoate, 2,4,6-TMBA = 2,4,6-trimethylbenzoate, terpy = 2,2 ': 6′, 2 ''- terpyridine) were synthesized by conventional solution method with 2,4-difluorobenzoic acid and 2,4,6-trimethylbenzoic acid as main ligands and 2,2 ': 6′, 2 ''- terpyridine as auxiliary ligands. The complexes were characterized by infrared spectroscopy and Raman spectroscopy, and the thermal decomposition mechanism of the complex was studied by TG-DTG-DSC/FTIR coupling technology. The solid fluorescence test was also carried out for complexes 1,2 and 4. It was found that the complexes have good fluorescence properties, and the fluorescence lifetime of complex 1 was 0.541 ms.

Immobilization of horseradish peroxidase on metal-organic framework to improve enzyme activity for enhanced chemodynamic therapy

Bio-enzymes have the advantages of strong substrate specificity, high catalytic efficiency, and minimal toxic side effects, making them promising drugs in cancer therapy. However, the poor stability and cellular penetrability of uncoated protein in the physiological environment severely restricts the direct application of Bio-enzyme. To address it, we report a metal-organic framework (MOF), Hf-DBA (H2DBA, biphenyl carboxylic acid ligands). The morphology of the Hf-DBA was revealed by TEM and the diameter was in the range of 200 to 350 nm. Hf-DBA acted a carrier for intracellular delivery and protection of horseradish peroxidase (HRP). The prepared HRP@Hf-DBA can catalyze the excess H2O2 in the tumor cells to generation of •OH for chemodynamic therapy (CDT). Compared with free HRP, the catalytic activity of HRP@Hf-DBA is significantly improved, and the optimal catalytic conditions are explored. The catalytic stability of HRP@Hf-DBA remained above 70% after 12 cycles of catalysis. After treatment with HRP@Hf-DBA, the apoptosis rates of A549 and Hela cells was 71.64%, and 76.86%. The results in vitro show that HRP@Hf-DBA can effectively inhibit the growth of tumor cells through enhanced CDT.

New complexes based on reduced Schiff base carboxylic acid ligand: Electric properties, fluorescence properties and detection of Fe3+

Two kinds of complexes [M(L)(H2O)]n(1–3) [M = Cd(1), Co(2), Mn(3)] and {[Ln(L)(HL)]·(H2O)3}n (4–6) [Ln = Sm(4), Gd(5), Tm(6)] were dexterously constructed via reduced Schiff base carboxylic acid ligand (H2L=5-((4-(1H-imidazol-1-yl)benzyl)amino)isophthalic acid) under solvothermal reactions. Complexes 1–3 are two-dimensional (2D) framework consisted of binuclear [M2O10N2] building unit. Complexes 4–6 are three-dimensional (3D) network structure with ecu topological net. Importantly, with the 2D layered structure complex 3 as the electrode material for a supercapacitor has a maximum specific capacitance is 412.3 F·g−1 at a current density of 1 A·g−1, and even at 5 A·g−1, the specific capacitance retention is about 59.2 % of the initial capacitance. The electrochemical property ascribed attributed to the inherent properties of complex 3, including its layered structure and favorable exposed facets. Remarkably, the exploration of luminescence studies demonstrated that complex 1 has an outstanding capacity for detecting Fe3+ with excellent selectivity and sensitivity, where individual quenching efficiency Ksv (1.18 × 103 M−1) and detection limit (2.1 × 10−5 M) were regarded as the excellent coordination polymers sensors for detecting Fe3+.

Metal ion assistant transformation strategy to synthesize catechol-based metal–organic frameworks from Ti3C2Tx precursors

Chemical transformation strategy is capable of fabricating nanomaterials with well-defined structures and fascinating performance via controllable crystallization kinetics in the phase transformation. V2CTx MXene has been used as precursors to fabricate vanadium porphyrin metal–organic frameworks (V-PMOFs) via the coordination of deprotonated carboxylic acid ligands. However, the rational and in-depth exploration of synthesis mechanism with the aim of enriching the variety of MXene (i.e., Ti3C2Tx) and organic ligands (i.e., catechol-based) to design new MOFs is rarely reported. Herein, we have first developed a metal ion assistant transformation strategy to synthesize three-dimensional catechol-based TiCu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) MOFs with a non-interpenetrating SrSi2 (srs) framework using two-dimensional Ti3C2Tx as precursors. The unique synergetic transformation mechanism involves the electron transfer from Ti3C2Tx to electrostatically adsorbed Cu2+ ion for redox reaction, the subsequent Ti–C bond rupture for Ti4+ ion release, and the continuous chelation coordination between Ti4+/Cu2+ and HHTP. Ti3C2Tx precursors and auxiliary metal ion could be rationally substituted by V2CTx and Mn+ (e.g., Ni2+, Co2+, Mn2+, and Zn2+), respectively. This strategy lays the foundation for the design and synthesis of innovative and multifarious MOFs derived from MXene or other unconventional metal precursors.

Studied on highly sensitive fluorescent sensors for Fe3+, Nitrobenzene and dye adsorption properties of Ln-MOFs based on benzimidazole carboxylic acid ligand

Five new lanthanide metal-organic frameworks (Ln-MOFs) {[Ln(L)(H2O)5]·Cl}n (1–5), ([Ln=Pr(1), Nd(2), Eu(3), La(4), Ce(5)] based on benzimidazole carboxylic acid ligand [H2L = 2-(4-carboxyphenyl)-1H-benzo[d] imidazole-6-carboxylic acid]) with the same two-dimensional planar structure were synthesized by solvothermal method. Ln-MOFs 1–3 exhibited the good adsorption performance for the anionic dye Congo red (CR) and the adsorption capacities were 468, 449 and 438 mg·g−1, respectively. The adsorption kinetics indicated that the adsorption was chemical adsorption and the hydrogen bonds and π···π interactions between 1–3 hosts and CR guest molecules resulted in high adsorption capacities. Ln-MOFs 4 and 5 were developed for the exploration of fluorescence sensing performance. The results show that 4 and 5 can be used as fluorescent sensor for Fe3+ with good reusability, high sensitivity and selective detection, the detection limits were 1.1 × 10−5 and 4.3 × 10−6 M, respectively. Research shows that the quenching mechanism of Fe3+belongs to fluorescence resonance energy transfer (FRET). Meanwhile, 4 and 5 also have good detection effect on nitrobenzene (NB) and the detection limits were 1.6 × 10−6 and 2.4 × 10−7 M, respectively.

Sensitive detection of chloramphenicol and efficient adsorbent for conge red of lanthanide complexes based on lactam carboxylic acid ligands

Two lanthanide metal complexes [M(H4L)Cl(OH) (H2O)2]n [M = La (1), Ce (2)] were constructed via lactam carboxylic acid ligand (2-(5-amino-2,5-dihydro-1H-imidazole-4-yl)-4-oxo-3,4-dihydroquinazoline-7-carboxylic acid) (H5L) under solvothermal condition. Complexes 1 and 2 could sensitively, selectively and repeatedly detect chloramphenicol (CAP) through the fluorescence quenching effect with a quenching constant (Ksv) of 1.87 × 103 and 1.52 × 104 Μ−1, respectively, and the detection limit (LOD) were 1.23 × 10−6 and 2.03 × 10−7 M, respectively. Density functional theory (DFT) calculations indicate that the LUMO energy level of the CAP quenched was lower than that of the ligand, so the photoelectron energy transfer (PET) between complexes and CAP leads to fluorescence quenching. Moreover, 1 and 2 exhibited excellent adsorption performance to Congo red (CR) and adsorption capacity were 3448.3 mg g−1 and 1886.5 mg g−1, respectively. Adsorption kinetics experiments showed that this kind of adsorption belonged to chemisorption, the hydrogen bonding and π-π interactions between the complex host and CR guest molecules resulted in high adsorption capacity.

Acidity of Carboxylic Acid Ligands Influences the Formation of VO2(A) and VO2(B) Nanocrystals under Solvothermal Conditions.

Vanadium dioxide (VO2) can adopt many different crystal structures at ambient temperature and pressure, each with different, and often desirable, electronic, optical, and chemical properties. Understanding how to control which crystal phase forms under various reaction conditions is therefore crucial to developing VO2 for various applications. This paper describes the impact of ligand acidity on the formation of VO2 nanocrystals from the solvothermal reaction of vanadyl acetylacetonate (VO(acac)2) with stoichiometric amounts of water. Carboxylic acids examined herein favor the formation of the monoclinic VO2(B) phase over the tetragonal VO2(A) phase as the concentration of water in the reaction increases. However, the threshold concentration of water required to obtain phase-pure VO2(B) nanocrystals increases as the pKa of the carboxylic acid decreases. We also observe that increasing the concentration of VO(acac)2 or the concentration of acid while keeping the concentration of water constant favors the formation of VO2(A). Single-crystal electron diffraction measurements enable the identification of vanadyl carboxylate species formed in reactions that do not contain enough water to promote the formation of VO2. Increasing the length of the carbon chain on aliphatic carboxylic acids did not impact the phase of VO2 nanocrystals obtained but did result in a change from nanorod to nanoplatelet morphology. These results suggest that inhibiting the rate of hydrolysis of the VO(acac)2 precursor either by decreasing the ratio of water to VO(acac)2 or by increasing the fraction of water molecules that are protonated favors the formation of VO2(A) over VO2(B).

Syntheses, Structures, and Photoluminescence Properties of Two New Zinc(II) Coordination Polymers Constructed by Rigid Carboxylic Acid Ligand

Syntheses, Structures, and Photoluminescence Properties of Two New Zinc(II) Coordination Polymers Constructed by Rigid Carboxylic Acid Ligand

The effect of replacing linker with carboxylic acid ligands on the oxygen evolution performance of metal-organic frameworks

Metal-organic frameworks (MOFs) are versatile platforms for developing various applications, owing to their structural diversity and functional tunability. The catalytic performance of metal-organic frameworks (MOFs) can be improved by introducing defects using monocarboxylate ligands, but the role of these ligands remains unclear. Herein, we show how doping MOFs with electron-withdrawing or electron-donating monocarboxylate ligands affects their oxygen evolution reaction (OER) performance. We further demonstrate that ferrocene derivatives as doped ligands can significantly enhance the OER performance of MOFs, owing to the strong synergistic effects between ferrocene derivatives and MOFs. Different from other doping MOF, ferrocene derivatives doped MOFs (1,1'-Fc-Ni-BDC) exhibit remarkable electrocatalytic activity with a low overpotential of 387 mV at 10 mA cm−2, and possess good electrochemical stability. Density functional theory (DFT) calculations reveal that the active sites are not on ferrocene derivatives, but rather on MOFs, and that ferrocene derivatives facilitate the formation of OER intermediates. Our findings provide new insights into the role of ligands in modulating the OER performance of MOFs. This work offers a new perspective to develop efficient MOF-based electrocatalysts by introducing electronegative metallocene ligands.