Carboxylate Precursors Research Articles

Colloidal Synthesis of Laterally Confined Blue-Emitting 3.5 Monolayer CdSe Nanoplatelets.

The typical synthesis protocol for blue-emitting CdSe nanoplatelets (NPLs) yields particles with extended lateral dimensions and large surface areas, resulting in NPLs with poor photoluminescence quantum efficiency. We have developed a synthesis protocol that achieves an improved control over the lateral size, by exploiting a series of long-chained carboxylate precursors that vary from cadmium octanoate (C8) to cadmium stearate (C18). The length of this metallic precursor is key to tune the width and aspect ratio of the final NPLs, and for the shorter chain lengths, the synthesis yield is improved. NPLs prepared with our procedure possess significantly enhanced photoluminescence quantum efficiencies, up to 30%. This is likely due to their reduced lateral dimensions, which also grant them good colloidal stability. As the NPL width can be tuned below the bulk exciton Bohr radius, the band edge blue-shifts, and we constructed a sizing curve relating the NPL absorption position and width. Further adjusting the synthesis protocol, we were able to obtain even thinner NPLs, emitting in the near-UV region, with a band-edge quantum efficiency of up to 11%. Results pave the way to stable and efficient light sources for applications such as blue and UV light-emitting devices and lasers.

Safety Assessment of Benzyne Generation from a Silyl Triflate Precursor.

Silyl triflate precursors to benzyne and related intermediates have emerged as valuable synthetic building blocks. However, data addressing the safety of employing these silyl triflate precursors are lacking. We report the calorimetric analysis of a typical Kobayashi procedure for forming and trapping benzyne using a silyl triflate precursor. Our findings suggest that, unlike benzenediazonium carboxylate precursors to benzyne, silyl triflates may be employed under mild conditions without severe concern for runaway reaction.

Locating and Controlling the Zn Content in In(Zn)P Quantum Dots

Zinc is routinely employed in the synthesis of InP quantum dots (QDs) to improve the photoluminescence efficiency and carrier mobility of the resulting In(Zn)P alloy nanostructures. The exact location of Zn in the final structures and the mechanism by which it enhances the optoelectronic properties of the QDs are debated. We use synchrotron X-ray absorbance spectroscopy to show that the majority of Zn in In(Zn)P QDs is located at their surface as Zn carboxylates. However, a small amount of Zn is present inside the bulk of the QDs with the consequent contraction of their lattice, as confirmed by combining high-resolution high-angle annular dark-field imaging scanning transmission electron microscopy with statistical parameter estimation theory. We further demonstrate that the Zn content and its incorporation into the QDs can be tuned by the ligation of commonly employed Zn carboxylate precursors: the use of highly reactive Zn acetate leads to the formation of undesired Zn3P2 and the final nanostructures being characterized by broad optical features, whereas Zn carboxylates with longer carbon chains lead to InP crystals with much lower zinc content and narrow optical features. These results can explain the differences between structural and optical properties of In(Zn)P samples reported across the literature and provide a rational method to tune the amount of Zn in InP nanocrystals and to drive the incorporation of Zn either as surface Zn carboxylate, as a substitutional dopant inside the InP crystal lattice, or even predominantly as Zn3P2.

The impact of polyol structure on the formation of Zn0.6Co0.4Fe2O4 spinel-based pigments

The formation of Zn0.6Co0.4Fe2O4 spinel-based pigments by sol–gel method and post-annealing pathway and the impact of polyol structure on their properties were investigated. The phase evolution and mass changes of gels during annealing were assessed by thermal analysis. The differential thermal analysis revealed that above 400 °C the carboxylate precursors decompose to ZnFe2O4, CoFe2O4, and Zn2SiO4. X-ray diffraction pattern showed the presence of crystalline ZnFe2O4, CoFe2O4, Zn2SiO4, and SiO2, while Fourier transform infrared spectra confirmed the formation of metal-carboxylates and SiO2 matrix at 200 °C and formation of ZnFe2O4, CoFe2O4, and Zn2SiO4 at 1200 °C. The atomic force microscopy images showed spherical nanoparticles of size and shape varying with the polyol structure. The coloring properties and the potential ceramic applications of the obtained dark gray powders were tested by their embedding in opaque and transparent tile glazes and their application on ceramic tile.

Influence of polyol structure and molecular weight on the shape and properties of Ni0.5Co0.5Fe2O4 nanoparticles obtained by sol-gel synthesis

This paper presents the formation and decomposition of silica embedded metal carboxylates obtained using Co-, Fe- and Ni- nitrates and polyols with different structure and molecular weight (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2,3-propanetriol). The thermal behavior of carboxylate precursors (oxalic, malonic, lactic, hydroxymalonic and succinic) is similar for all used polyols, both the formation and decomposition of precursors occurring in two stages. However, the mass loss slightly increases with increasing of the diol chain length and significantly increases with the presence of a supplementary, nonreactive secondary hydroxyl group. X-ray diffraction shows the formation of NiO single phase or NiO and CoFe2O4 mixtures below 750 °C, and of mixed Co-Ni ferrite single phase at 1000 °C, while Fourier transformed infrared spectroscopy confirms the formation of silica matrix and the formation and decomposition of carboxylate precursors. Transmission electron microscopy shows spherical nanoparticles of different size. The Ni0.5Co0.5Fe2O4 nanocrystallites size (4.3–28.1 nm) and relative crystallinity (4–100 a.u.) increase with the annealing temperature, the diol chain length and the distance between hydroxyl groups. The coercive field (0.015–0.6 T) and saturation magnetization (21.5–25 emu/g) of gels annealed at 1000 °C also increase for longer chain length diols.

From a volatile molecular precursor to twin-free single crystals of bismuth.

A highly volatile molecular precursor, dibismuth(ii) (tetra)trifluoroacetate, was successfully utilized for the gas phase growth of twin-free single crystals of bismuth. This allowed high-quality single-crystal X-ray diffraction data to be collected, providing accurate structural parameters for elemental bismuth under ambient conditions.

Role of aliphatic ligands and solvent composition in the solvothermal synthesis of iron oxide nanocrystals

This paper describes a new method for controlling nanocrystal size and crystal phase in solvothermal syntheses of iron oxide nanocrystals by altering the carbon chain length of aliphatic iron(III) carboxylate precursors and reaction solvent composition, respectively. Hematite (α-Fe2O3) nanocrystals were synthesized from iron(III) carboxylate precursors in a 2:1 water:ethanol mixture in the presence of free aliphatic carboxylic acids or aliphatic primary amine ligands. In the presence of amine, increasing the length of the carbon chain of the iron(III) carboxylate precursor from two to eighteen carbons produced pseudocubic nanocrystals with size dispersities of ∼10% and diameters that decreased from 65 nm to 25 nm. Changing the chain length of the amine does not affect the size of the nanocrystals. In contrast, free carboxylic acid ligands produce polydisperse, polycrystalline hematite nanoparticles. The crystal structure of the iron oxide nanocrystals synthesized by this method depends on the mole-fraction of water (xwater) in the water/ethanol solvent mixture: xwater = 0 produces maghemite (γ-Fe2O3), xwater = 0.67 produces hematite, and xwater = 1 produces a mixture of goethite (α-FeOOH) and hematite. The dependence of the nanocrystal size on ligand chain length is attributed to decreasing solubility of partially hydrolyzed iron(III) carboxylate precursors in the reaction solvent mixture with increasing chain length. The dependence of nanocrystal phase on solvent composition is attributed to the different reactivities of water and ethanol toward hydrolysis of the iron(III) carboxylate precursors.

Colloidal Synthesis of Double Perovskite Cs2AgInCl6 and Mn-Doped Cs2AgInCl6 Nanocrystals.

We show here the first colloidal synthesis of double perovskite Cs2AgInCl6 nanocrystals (NCs) with a control over their size distribution. In our approach, metal carboxylate precursors and ligands (oleylamine and oleic acid) are dissolved in diphenyl ether and reacted at 105 °C with benzoyl chloride. The resulting Cs2AgInCl6 NCs exhibit the expected double perovskite crystal structure, are stable under air, and show a broad spectrum white photoluminescence (PL) with quantum yield of ∼1.6 ± 1%. The optical properties of these NCs were improved by synthesizing Mn-doped Cs2AgInCl6 NCs through the simple addition of Mn-acetate to the reaction mixture. The NC products were characterized by the same double perovskite crystal structure, and Mn doping levels up to 1.5%, as confirmed by elemental analyses. The effective incorporation of Mn ions inside Cs2AgInCl6 NCs was also proved by means of electron spin resonance spectroscopy. A bright orange emission characterized our Mn-doped Cs2AgInCl6 NCs with a PL quantum yield as high as ∼16 ± 4%.

Base-Free Generation of Organic Electron Donors from Air-Stable Precursors.

Organic electron donors (OEDs) are powerful reducing agents recognized for their potential in the reduction of challenging substrates and in original applications. Nonetheless, their low stability in atmospheric oxygen or over time complicates their manipulation and storage. To overcome these constraints and enhance OED practicality, new air- and moisture-stable aminopyridinium carboxylate and carbonate precursors were synthesized and thermally activated to generate the potent electron donor in situ. Carboxylate adducts proved to be excellent latent OED systems, enabling the facile and efficient reduction of challenging substrates. Their reduction properties were correlated to their structural characteristics by thermogravimetric and spectroscopic analysis.

Influence of the cobalt nitrate:ethylene glycol molar ratio on the formation of carboxylate precursors and cobalt oxides

Influence of the cobalt nitrate:ethylene glycol molar ratio on the formation of carboxylate precursors and cobalt oxides

Alumina/activated carbon nano-composites: Synthesis and application in sulphide ion removal from water

An investigation of adsorption of sulphide ion (S2−) in water onto carbon/alumina nano-composites synthesized from aluminium carboxylate precursors, in presence of HCl, NaOH, NaCl and surfactant is reported in this paper. A controlled oxygen free pyrolytic technique has been adopted for the synthesis of nano-composites, using acetate, acetyl acetonate, lactate and distearate of aluminium and activated carbon. XRD, SEM and TEM studies of the composites show that they contain clusters made of nano carbon particles of size 50–130nm into which nano alumina particles of size around 10nm are dispersed. While applying the adsorption data in Langmuir, Freundlich, Temkin and Dubinin-Raduskevich isotherm models, the data fit well with Langmuir model. All composites have increased porosity and decreased surface area compared to bare carbon. The adsorption capacity of composites obtained from acetate and lactate are higher and are found to be in the range of 71–200mg/g.

An updated synthesis of [11 C]carfentanil for positron emission tomography (PET) imaging of the μ-opioid receptor.

[11 C]Carfentanil ([11 C]CFN) is a selective radiotracer for in vivo positron emission tomography imaging studies of the μ-opioid system that, in our laboratories, is synthesized by methylation of the corresponding carboxylate precursor with [11 C]MeOTf, and purified using a C2 solid-phase extraction cartridge. Changes in the commercial availability of common C2 cartridges have necessitated future proofing the synthesis of [11 C]CFN to maintain reliable delivery of the radiotracer for clinical imaging studies. An updated synthesis of [11 C]CFN is reported that replaces a now obsolete purification cartridge with a new commercially available version and also substitutes the organic solvents used in traditional production methods with ethanol.

Harnessing Organic Ligand Libraries for First-Principles Inorganic Discovery: Indium Phosphide Quantum Dot Precursor Design Strategies

Indium phosphide quantum dots (QDs) represent promising replacements for more toxic QDs, but InP QD production lags behind other QD materials due to limited understanding of how to tune InP QD growth. We carry out a first-principles, computational screen of the tuning of In carboxylate precursor chemistry to alter the kinetics of elementary steps in InP QD growth. We employ a large database normally used for discovery of therapeutic drug-like molecules to discover design rules for these inorganic complexes while maintaining realism (i.e., stable, synthetically accessible substituents) and providing diversity in a 210-molecule test set. We show the In–O bond cleavage energy, which is tuned through ligand functionalization, to be a useful proxy for In–P bond formation energetics in InP QD synthesis. Energy decomposition analysis on a 32-molecule subset reveals that lower activation energies correlate to later transition states, due to stabilization from greater In–P bond formation and more favorable reactio...

Synthesis and characterization of silver nanoparticles from (bis)alkylamine silver carboxylate precursors

A comparative study of amine and silver carboxylate adducts [R1COOAg-2(R2NH2)] (R1 = 1, 7, 11; R2 = 8, 12) as a key intermediate in NPs synthesis is carried out via differential scanning calorimetry, solid-state FT-infrared spectroscopy, 13C CP MAS NMR, powder X-ray diffraction and X-ray photoelectron spectroscopy, and various solution NMR spectroscopies (1H and 13C NMR, pulsed field gradient spin-echo NMR, and ROESY). It is proposed that carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination as opposed to bridging bidentate coordination of pure silver carboxylates resulting from the formation of dimeric units. All complexes are packed as lamellar bilayer structures. Silver carboxylate/amine complexes show one first-order melting transition. The evidence presented in this study shows that phase behavior of monovalent metal carboxylates are controlled, mainly, by head group bonding. In solution, insoluble silver salt is stabilized by amine molecules which exist in dynamic equilibrium. Using (bis)amine-silver carboxylate complex as precursor, silver nanoparticles were fabricated. During high-temperature thermolysis, the (bis)amine-carboxylate adduct decomposes to produce silver nanoparticles of small size. NPs are stabilized by strongly interacting carboxylate and trace amounts of amine derived from the silver precursor interacting with carboxylic acid. A corresponding aliphatic amide obtained from silver precursor at high-temperature reaction conditions is not taking part in the stabilization. Combining NMR techniques with FTIR, it was possible to follow an original stabilization mechanism.Graphical abstractThe synthesis of a series (bis)alkylamine silver(I) carboxylate complexes in nonpolar solvents were carried out and fully characterized both in the solid and solution. Carboxyl moieties in the presence of amine ligands are bound to silver ions via chelating bidentate type of coordination. The complexes form layered structures which thermally decompose forming nanoparticles stabilized only by aliphatic carboxylates.

Experimental and theoretical assessment of the mechanism and site requirements for ketonization of carboxylic acids on oxides

Ketonization of carboxylic acids removes O-atoms and forms new CC bonds, thus providing routes from sustainable carbon feedstocks to fuels and chemicals. The elementary steps involved and their kinetic relevance, as well as the number and nature of the active sites on active TiO2 and ZrO2 catalysts, remain matters of active discourse. Here, site titrations demonstrate the requirement for coordinatively-unsaturated M-O-M sites (M=Ti, Zr) with specific geometry and intermediate acid-base strength. The measured site densities allow rigorous reactivity comparisons among catalysts based on turnover rates and activation free energies, as well as the benchmarking of mechanistic proposals against theoretical assessments. Kinetic, isotopic, spectroscopic, and theoretical methods show that C2C4 acids react on anatase TiO2 via kinetically-relevant CC coupling between 1-hydroxy enolate species and coadsorbed acids bound at vicinal acid-base pairs saturated with active monodentate carboxylates. Smaller TiTi distances on rutile TiO2 lead to the prevalence of unreactive bidentate carboxylates and lead to its much lower ketonization reactivity than anatase. The prevalent dense monolayers of chemisorbed acid reactants reflect their strong binding at acid-base pairs and their stabilization by H-bonding interactions with surface OH groups derived from the dissociation of the carboxylic acids or the formation of 1-hydroxy enolates; these interactions also stabilize CC coupling transition states preferentially over their carboxylate precursors; high coverages favor sequential dehydration routes of the α-hydroxy-γ-carboxy-alkoxide CC coupling products over previously unrecognized concerted six-membered-ring transition states. Infrared spectra show that ubiquitous deactivation, which has precluded broader deployment of ketonization in practice and unequivocal mechanistic inquiries, reflects the gradual formation of inactive bidentate carboxylates. Their dehydration to ketene-like gaseous species is faster on anatase TiO2 than on ZrO2 and allows the effective scavenging of bidentate carboxylates via ketene hydrogenation to alkanals/alkanols on a Cu function present within diffusion distances. These strategies make anatase TiO2, a more effective catalyst than ZrO2, in spite of its slightly lower initial turnover rates. This study provides details about the mechanism of ketonization of C2C4 carboxylic acids on TiO2 and a rigorous analysis of the sites required and of active and inactive bound species on TiO2 and ZrO2. The preference for specific distances and for intermediate acid-base strength in M-O-M species is consistent with the structure and energy of the proposed transition states and intermediates; their relative stabilities illustrate how densely-covered surfaces, prevalent during ketonization catalysis, represent an essential requirement for the achievement of practical turnover rates.

Effect of Zinc Incorporation on the Performance of Red Light Emitting InP Core Nanocrystals.

This report presents a systematic study on the effect of zinc (Zn) carboxylate precursor on the structural and optical properties of red light emitting InP nanocrystals (NCs). NC cores were assessed using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), energy-dispersive X-ray spectroscopy (EDX), and high-resolution transmission electron microscopy (HRTEM). When moderate Zn:In ratios in the reaction pot were used, the incorporation of Zn in InP was insufficient to change the crystal structure or band gap of the NCs, but photoluminescence quantum yield (PLQY) increased dramatically compared with pure InP NCs. Zn was found to incorporate mostly in the phosphate layer on the NCs. PL, PLQY, and time-resolved PL (TRPL) show that Zn carboxylates added to the precursors during NC cores facilitate the synthesis of high-quality InP NCs by suppressing nonradiative and sub-band-gap recombination, and the effect is visible also after a ZnS shell is grown on the cores.

Continuous Growth of Metal Oxide Nanocrystals: Enhanced Control of Nanocrystal Size and Radial Dopant Distribution.

The ability to precisely control the composition of nanocrystals, similar to the way organic chemists control the structure of small molecules, remains an important challenge in nanoscience. Rather than dictating nanocrystal size through the nucleation event, growth of nanocrystals through continuous precursor addition would allow fine structural control. Herein, we present a method of growth for indium oxide nanocrystals that relies on the slow addition of an indium carboxylate precursor into hot oleyl alcohol. Nanocrystal size and structure can be governed at a subnanometer scale, and it is possible to precisely control core size over a range of three to at least 22 nm with dispersities as low as 7%. Growth can be stopped and restarted repeatedly without aggregation or passivation. We show that the volume of the nanocrystal core (and thus molecular weight) increases linearly with added monomer and the number of nanocrystals remains constant throughout the growth process, yielding an extremely predictable approach to size control. It is also possible to place metal oxide shells (e.g., Sn-doped In2O3 (ITO)) at various radial positions within the nanocrystal, and we use this approach to synthesize ITO/In2O3 core/shell nanocrystals as well as In2O3/ITO/In2O3 core/shell/shell nanocrystals.

Nanosized GdVO4 powders synthesized by sol–gel method using different carboxylic acids

Nanosized GdVO4 powders were synthesized via a sol–gel method using different carboxylic acids as chelating agent, followed by calcination at 600 °C for 3 h. The effect of different carboxylic acids such as citric acid, malic acid, and tartaric acid on the characteristics of the nanosized GdVO4 powders was investigated. The GdVO4 powder was also synthesized without carboxylic acid for comparison. The thermal decomposition process of the carboxylate precursors was investigated by thermogravimetric differential thermal analysis (TG-DTA). X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and surface area measurement data were used to confirm the formation of nanocrystalline GdVO4 powders. It is found that the synthesis using the carboxylic acid with higher heat of combustion results in the powder with larger crystallite size. The difference in the steric effect of the acids used, which was evaluated by a computational method, also affects the degree of agglomeration of the synthesized powders.

Palladium-catalyzed C-H bond carboxylation of acetanilides: an efficient usage of N,N-dimethyloxamic acid as the carboxylate source.

N,N-Dimethyloxamic acid can be successfully employed as a carboxylate precursor in the palladium-catalyzed direct C-H carboxylation of acetanilides. The reaction proceeds smoothly under mild conditions over a broad range of substrates with high functional group tolerance, affording substituted N-acyl anthranilic acids in moderate to high yields.

Solution design for low-fluorine trifluoroacetate route to YBa2Cu3O7 films

We present our work in the preparation of metallorganic precursor solutions with reduced fluorine content, able to fulfil the requirements for high-performance superconducting YBCO epitaxial layers as a promising approach to low cost and scalable coated conductors. Six different solutions using different quantities of fluorine and non-fluorine carboxylate precursors with a total amount of fluorine from 10 to 50% that of standard trifluoroacetic acid (TFA) solutions. For stabilization purposes different coordinating agents have been used and the solution rheology has been modified for proper substrate wettability. Thermal decomposition analysis and infrared spectroscopy performed directly in films, have revealed that the decomposition takes place in two consecutive stages around 265 and 310 °C respectively, and nuclear magnetic resonance (NMR) analysis could unveil the chemical reactions taking place in the solution. Using the solutions with 20% fluorine and upon optimization of the growth process parameters, YBCO layers with Tc and Jc(77 K) of 90 K and 4 MA cm−2 are obtained.