Monocarboxylate Ligands Research Articles

Enhancing CO2 electroreduction to ethylene via microenvironment regulation in boron-imidazolate frameworks.

Using the structure-induced effect of KBH(mim)3 ligand, four 2-dimensional (2D) boron imidazolate frameworks with identical body framework and different dangling monocarboxylate ligands, have been synthesized. Electrocatalytic results indicate that the surrounding microenvironment regulation could effectively affect the activity and selectivity towards C2H4. BIF-151 showed the highest electrocatalytic performances with the Faraday efficiency (FE) of 25.94% for C2H4 at -1.4 V vs. RHE.

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.

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Gut microbial short-chain fatty acids-mediated olfactory receptor 78 stimulation promotes anorexigenic gut hormone peptide YY secretion in mice

Olfactory receptor 78 (Olfr78), which is also known as a receptor for short-chain fatty acids (SCFAs) produced via gut microbial fermentation from indigestible polysaccharides such as dietary fibers, is expressed in the enteroendocrine cells of the colon. However, the role of Olfr78 in gut hormone secretion remains unknown. Here, we aimed to investigate the function and mechanism of action of Olfr78 in vivo and in vitro. Toward this, we assessed the expression of Olfr78 in several tissues, affinity of Olfr78 to various monocarboxylates, and the secretion of anorexigenic gut hormone peptide YY (PYY) via Olfr78 using various molecular and biochemical techniques. Olfr78 was abundantly expressed in the colon and mouse enteroendocrine cell line STC-1 and showed specific affinity to SCFAs such as acetate and propionate, but not butyrate, in a monocarboxylate ligand screening assay using a heterologous expression system. Acetate promoted PYY secretion in STC-1 cells via Olfr78-protein kinase A signaling, whereas the effects were abolished by Olfr78 RNA interference. Colonic SCFAs production via oral administration of fructo-oligosaccharide significantly increased plasma PYY levels, whereas this effect was abolished in Olfr78-deficient and germ-free mice. These results suggested that the SCFA receptor Olfr78 is important for anti-obesity and anorexigenic effects of the gut microbiota and dietary fibers.

Thermal analysis combined with X-ray diffraction/Rietveld method, FT-IR and UV-vis spectroscopy: Structural characterization of the lanthanum and cerium (III) polycrystalline complexes

In this work, structural, spectroscopical and thermal studies of lanthanum(III) and cerium(III) complexes with the 3,5-dimethoxybenzoate (DMBz) monocarboxylate ligand were performed. The metal-ligand minimum stoichiometry and polymeric arrangement of the complexes were respectively defined by TGA-DSC and X-ray powder diffraction as [M(DMBz)3.n]x, wherein “M” represents the lanthanides, “n” the water molecules in the lanthanum compound and “x” the basic unit of repetition in monoclinic polycrystalline system with space group P21/c. The products of the thermal decomposition of the material were also monitored by TGA-DSC/FT-IR both in air and N2 atmospheres in order to suggest the thermal decomposition mechanism. Theoretical calculations based in experimental results were performed to assess the coordination mode and spectroscopic properties of lanthanide complexes involving a monocarboxylate ligand. From theoretical calculations it was possible to generate FT-IR theoretical vibrational spectra and relate the level of correspondence to the experimental data inherent to the metal-ligand coordination mode. From the HOMO/LUMO orbitals obtained by TD-DFT calculations, the main electronic transitions responsible for the absorption and emission bands of the complexes were determined.

Two Gd2 cluster complexes with monocarboxylate ligands displaying significant magnetic entropy changes

Two Gd2 cluster complexes with the formulas of [Gd2(dnba)6(phen)2] (1) and [Gd2(Hnsa)2(nsa)2(phen)2(H2O)2] (2) (Hdnba = 3,5-dinitrobenzoic acid, H2nsa = 5-nitrosalicylic acid and phen = 1,10-phenanthroline) respectively have been successfully synthesized under hydrothermal conditions. The GdIII ions of 1 are bridged by four carboxylates with syn-syn-μ2-η1:η1 and syn-syn-μ2-η1:η2 modes, while the GdIII ions of 2 are linked by two carboxylate ligands with only syn-syn-μ2-η1:η2 mode. Magnetic studies indicate that weak antiferromagnetic and ferromagnetic interactions exist between the adjacent GdIII ions within Gd2 clusters, respectively. Complexes 1 and 2 display distinct magnetocaloric effects induced by different magnetic interactions and magnetic densities. Notably, the maximum magnetic entropy changes (−ΔSmmax) of 1 and 2 reach 16.8 J kg−1 K−1 and 22.2 J kg−1 K−1 with ΔH = 7 T at 2 K and 3.5 K, respectively.

Synthesis and structural characterization of homochiral coordination polymers with imidazole-based monocarboxylate ligands.

Chiral Na[(S)-LR] (R = Me, 1a; iPr, 1b; CH2iPr, 1c, and (S)-secBu, 1d) and Na[(R)-LR] (R = Me, 1a') compounds were synthesised following standard procedures. New compounds 1d and 1a' were analytically and spectroscopically characterised. 1a and 1c were structurally identified by single-crystal X-ray diffraction methods as homochiral 2D coordination polymers, {Na(H2O)[(S)-LMe]}n and {Na[(S)-LCH2iPr]}n, respectively. Both (S)-2alkyl,2-(1H-imidazol-1-yl)acetate anions displayed unprecedented coordination modes in these coordination polymers: μ3κ2OκO' for 1a and μ4κ2Oκ2O' for 1c. Enantiomeric species 1a', {Na(H2O)[(R)-LMe]}n, showed the same X-ray powder diffractogram (XRPD) as 1a, in agreement with a similar crystal structure. DFT calculations on the [LR]- anions confirmed their coordination capabilities as ditopic linkers. In fact, the reaction of Na[LR] with several metal salts yielded the following coordination polymers: {Ag[(S)-LMe]}n, 2a, {Ag[(R)-LMe]}n, 2a', {Cu[(S)-LR]2}n (R = Me, 3a; iPr, 3b), {Cu[(R)-LMe]}n, 3a', {Zn[(S)-LR]2}n (R = Me, 4a; iPr, 4b; (S)-secBu, 4d) and {Zn[(R)-LMe]2}n, 4a'. For the known compounds 3a and 4a, this procedure is a new synthetic route that avoided high temperature reaction conditions. New complexes 2, 3a', b, and 4a', b, d were characterised by elemental analysis, infrared and XRPD methods and complex 2a by single-crystal X-ray diffraction. This complex is also a two-dimensional coordination polymer in which the [(S)-LMe]- anion acts as a μ4κN,κ2O,κ2O' bridging ligand. Compounds 1-4a' are the first examples of homochiral coordination polymers with imidazole-monocarboxylate ligands based on non-natural amino acids. Preliminary studies on the metal-catalysed preparation of chiral α-aminophosphonates were carried out but, unfortunately, no enantioselectivity was observed.

Solution and Solid State Structural Chemistry of Th(IV) and U(IV) 4-Hydroxybenzoates.

Organic ligands with carboxylate functionalities have been shown to affect the solubility, speciation, and overall chemical behavior of tetravalent metal ions. While many reports have focused on actinide complexation by relatively simple monocarboxylates such as amino acids, in this work we examined Th(IV) and U(IV) complexation by 4-hydroxybenzoic acid in water with the aim of understanding the impact that the organic backbone has on the solution and solid state structural chemistry of thorium(IV) and uranium(IV) complexes. Two compounds of the general formula [An6O4(OH)4(H2O)6(4-HB)12]· nH2O [An = Th (Th-1) and U (U-1); 4-HB = 4-hydroxybenzoate] were synthesized via room-temperature reactions of AnCl4 and 4-hydroxybenzoic acid in water. Solid state structures were determined by single-crystal X-ray diffraction, and the compounds were further characterized by Raman, infrared, and optical spectroscopies and thermogravimetry. The magnetism of U-1 was also examined. The structures of the Th and U compounds are isomorphous and are built from ligand-decorated oxo/hydroxo-bridged hexanuclear units. The relationship between the building units observed in the solid state structure of U-1 and those that exist in solution prior to crystallization as well as upon dissolution of U-1 in nonaqueous solvents was investigated using small-angle X-ray scattering, ultraviolet-visible optical spectroscopy, and dynamic light scattering. The evolution of U solution speciation as a function of reaction time and temperature was examined. Such effects as well as the impact of the ligand on the formation and evolution of hexanuclear U(IV) clusters to UO2 nanoparticles compared to prior reported monocarboxylate ligand systems are discussed. Unlike prior reported syntheses of Th and U(IV) hexamers where the pH was adjusted to ∼2 and 3, respectively, to drive hydrolysis, hexamer formation with the HB ligand appears to be promoted only by the ligand.

Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions

AbstractInvited for the cover of this issue is Anton Savchenkov from Samara National Research University, Russian Federation. The cover image shows the heteronuclear uranyl clusters evolving from a typical mononuclear anionic complex unit with aliphatic monocarboxylate ligands.

Front Cover: Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions (Eur. J. Inorg. Chem. 18/2018)

Front Cover: Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions (Eur. J. Inorg. Chem. 18/2018)

Two chain-based TbIII/DyIII complexes derived from m-nitrobenzoic acid with totally different structures and magnetic properties

Two LnIII complexes derived from one aromatic monocarboxylate ligand, namely [Tb2(mnba)6(H2O)4]n (1) and [Dy2(mnba)4(μ3-OH)2(H2O)]n (2) (Hmnba = m-nitrobenzoic acid), have been prepared by similar synthetic procedures and structurally characterized. Complex 1 contains two identical one-dimensional (1D) chains with the syn,syn-carboxylate as linkers, while complex 2 takes the 1D chain structure with μ3--OH and carboxylate as bridge. Magnetic studies indicate that ferromagnetic interactions between intra-chain metal centers exist in 1 and 2 and only complex 2 exhibits field-induced slow magnetic relaxation behavior.

Unusual Heteronuclear Uranyl Clusters with Aliphatic Monocarboxylate Ligands and Coordination Modes of Crotonate, Butyrate, and Valerate Ions

Two compounds with unusual architectures of uranyl complexes were synthesized and then studied by single‐crystal X‐ray diffraction and FTIR spectroscopy. Compound Ba2[UO2(C3H5COO)3]4·2C3H5COOH·7H2O (I) is constructed of neutral hexanuclear clusters {Ba2[UO2(C3H5COO)3]4(C3H5COOH)2(H2O)4} containing crotonate ions. Compound Sr(H2O)6{Na[UO2(i‐C3H7COO)3]3} (II) is constructed of anionic tetranuclear clusters {Na[UO2(i‐C3H7COO)3]3}2– containing isobutyrate ions. These and other examples of heteronuclear clusters imply that the alkali and alkaline‐earth metal atoms in these structures are not just charge‐balancing ions, but truly drive the formation of polynuclear units. The analysis of the coordination modes of crotonate, butyrate, and valerate ions in the crystal structures of all coordination compounds from the Cambridge Structural Database (CSD) allowed the identification of the structural role of these ligands. The results of the analysis show that the bridging function is in fact the most common function for crotonate, butyrate, and valerate ions in known crystal structures. Information on the possible and preferred coordination modes of ligands is extremely important for crystal structure prediction and crystal engineering.

Tri- (M = CuII) and hexanuclear (M = NiII, CoII) heterometallic coordination compounds with ferrocene monocarboxylate ligands: Solid-state structures and thermogravimetric, electrochemical and magnetic properties

The synthesis and characterization of the hexanuclear [M2(κO-O2CFc)2(µ-O2CFc)2(µ-H2O)(κ2N,N′-tmeda)2] (MII=Ni, 5; Co, 6; Fc=ferrocenyl, (η5-C5H4)(η5-C5H5)Fe; tmeda=N,N,N′,N′-tetramethylethylendiamine) and the trinuclear [Cu(κ2N,N′-tmeda)(κ2O,O′-O2CFc)2 2] (7) coordination compounds are described. Compounds 5–7 were prepared by the consecutive reaction of ferrocene carboxylic acid (FcCO2H; 1) with [nBu4N]OH followed by treatment of in situ formed [nBu4N][FcCO2] with the metal salts [M(tmeda)(NO3)2] (M=Ni, 2; Co, 3; Cu, 4). The structures of 5–7 in the solid state were determined by single crystal X-ray diffraction analysis. Isostructural 5 and 6 crystallise in the triclinic P1¯ (5) and in the monoclinic space group P21/n (6). The two MII(tmeda) entities of 5 and 6 with MII=Ni, Co, respectively, are syn, syn-bridged by two FcCO2− functionalities and one µ-bridging water molecule. Additionally, two FcCO2− ligands are κO-coordinated to each MII ion to form octahedral MN2O4 coordination setups. A related MN2O4 coordination setup is observed for 7 as well, whereby the CuII ion is coordinated by two O2CFc and one tmeda ligand. Electrochemical investigations reveal that all individual Fc units of 5–7 are oxidized separately. Thermogravimetric analysis showed that 5 and 6 start to decompose at 110 and 125°C and thus at significantly lower temperatures compared to 7 (200°C). The mass residues obtained after decomposition are composed of Fe2O3, FeNi3 and Fe0.64Ni=Ni0.36 (5), Fe and Co3O4 (6) and Cu2O and CuFeO2 (7), as determined by powder X-ray diffraction analysis (PXRD). Thermal susceptibility measurements of 5 and 6 determined a weak antiferromagnetic coupling in 5 and 6 with J=1.1K and J=1.9K, respectively.

Synthesis, structures and magnetocaloric properties of two dinuclear GdIII clusters derived from monocarboxylate ligands

Two dinuclear GdIII clusters, namely [Gd2(piv)6(phen)2] (1) and {[Gd2(2-TCA)6(phen)2]·2H2O} (2) (Hpiv=pivalic acid, 2-TCA=Thiophene-2-carboxylic acid and phen=1,10-phenanthroline), have been synthesized under hydrothermal conditions. Complex 1 features dinuclear structure with two syn-syn-μ2-η1:η1 carboxylates bridging, while 2 exhibits dinuclear structure bridged by four carboxylates with syn-syn-μ2-η1:η1 and syn-syn-μ2-η1:η2 modes. Magnetic studies indicate that weak antiferromagnetic interactions between adjacent GdIII ions exist in 1 and 2. They exhibit relatively large magnetocaloric effects with −ΔSmmax=19.1Jkg−1K−1 and 21.8Jkg−1K−1 for ΔH=70kOe, respectively, influenced by relatively high magnetic density and weak magnetic interaction.

Partitioning of humic acids between aqueous solution and hydrogel. 3. Microelectrodic dynamic speciation analysis of free and bound humic metal complexes in the gel phase.

The hydrogel/water partitioning of the various species in the cadmium(II)/soil humic acid (HA) system is studied for two types of gel, using in situ microelectrodic voltammetry. Under the conditions of this work, with HA particles of ca. 25 and 125 nm radius, the CdHA complex is shown to be close to nonlabile toward a 12.5 μm radius microelectrode. This implies that its kinetic contribution to Cd(2+) reduction at the medium/microelectrode interface is practically negligible. The polyacrylamide (PAAm) gels equilibrate with the aqueous medium under significant sorption of HA at the gel backbone/gel medium interface, which in turn leads to induced sorption of Cd(II) in the form of immobilized gel-bound CdHA. The rather high total Cd content of the PAAm gel suggests that the binding of Cd(2+) by the hydrophobically gel-bound HA is stronger than that for dispersed HA particles. Still, the intraparticulate speciation of Cd(II) over Cd(2+) and CdHA corresponds to an intrinsic stability constant similar to that for simple monocarboxylate ligands such as acetate. Alginate gels are negatively charged, and their free [Cd(aq)(2+)] is higher than that in the medium by the corresponding Donnan coefficient. On top of that, Cd(2+) is specifically sorbed by the gel backbone/gel medium interface to reach accumulation factors as high as a few tens. HA and CdHA accumulate in the outer 20 μm film of gel at the gel/water interface of both gels, but they do not penetrate into the bulk of the alginate gel. Overall, the gel/water interface dictates drastic changes in the speciation of Cd/HA as compared to the aqueous medium, with distinct features for each individual type of gel. The results have broad significance, for example, for predictions of reactivity and bioavailability of metal species which inherently involve partitioning and diffusion into diverse gel layers such as biointerfacial cell walls, biofilm matrices, and mucous membranes.

The first example of a zirconium-oxide based metal-organic framework constructed from monocarboxylate ligands.

This work reports the first example of a Zr-based MOF which is exclusively constructed from the monocarboxylate ligand formate. Despite the low surface area, the new material exhibits an unexpectedly favourable affinity for carbon dioxide over nitrogen at room temperature.

Homochiral luminescent lanthanide dinuclear complexes derived from a chiral carboxylate

A family of chiral Ln2clusters based on a chiral monocarboxylate ligand has been successfully constructedviaa diffusion method, and Eu, Tb and Dy analogues display good luminescent properties.

Tuning the magnetic behaviors in [FeIII12LnIII4] clusters with aromatic carboxylate ligands

Six new Fe–Ln clusters composed of a Fe12Ln4 core derived from two monocarboxylate ligands have been successfully obtained with a step-by-step strategy. Magnetic analyses suggest that 1–6 show different magnetic properties, and 2 and 6 display SMM-like behaviors.

Tuning pore size in a zirconium–tricarboxylate metal–organic framework

The water-stable frameworks, [Zr6O4(OH)4(X)6(btc)2]·nH2O, where X = formate, acetate, or propionate, exhibit tunable porosity by virtue of systematic modulation of the chain length of the monocarboxylate ligand X.

Heavy Atom Effect Driven Organic Phosphors and Their Luminescent Lanthanide Metal-Organic Frameworks.

This investigation demonstrates the heavy atom effect (HAE) concept in developing new organic phosphors and engineering the excited-state energy levels in lanthanide metal ion suprastructures. This was accomplished by coupling two independent energy-transfer photophysical processes: enhancing the electronic population in the excited triplet state through intersystem crossing (ISC) and transferring the triplet energy to the excited state of the lanthanide ions. A new series of iodo-substituted carboxylic ligands were synthesised through a tailor-made approach and complexes with Eu3+ ions to give one- and three-dimensional metal-organic frameworks (MOFs). Single-crystal structures of the europium complexes revealed the formation of a 1D linear coordination polymer for the monocarboxylate ligand and 3D MOFs for the dicarboxylate ligand. The HAE quenches the S1 →S0 transition (self-fluorescence) in these ligands and promotes S1 →T processes for building enhanced excited triplet electronic states. Single-crystal structures of iodo-substituted complexes proved that the ligand molecules were held together by strong π stacking. The π stack restricted vibration relaxation and, as a result, these ligands turned into white or yellowish solid-state organic phosphors. In Eu3+ ion complexes, the solid-state phosphorescence of the ligands was completely quenched and the triplet excitation energy was channelled into ligand-to-metal energy transfer. Thus, the current approach opens up a new strategy for designing luminescent MOFs based on the HAE principle by controlling the excited-state energy levels.