Metal Oxalates Research Articles

Solvent-free synthesis of new metal sulfate–oxalates containing chain-like building blocks

Four new metal sulfate–oxalates were synthesized under solvent-free conditions. These compounds have single-layered, double-layered, and three-dimensional structures containing metal oxalate chains as building blocks. Topological analyses reveal that they have hcb, mog, and kgd topologies, respectively. Possible build-up processes for the formation of the hybrid frameworks were proposed.

Synthesis, spectroscopic, thermal and XRD studies of aminoguanidinium copper and cadmium oxalates

New aminoguanidinium metal oxalate complexes with the formulae (AmgH)2[Cu(C2O4)2] and (AmgH)2[Cd(C2O4)2(H2O)2] have been synthesized and characterized. The copper compound loses aminoguanidine exothermically at 240 °C in DTA, whereas aminoguanidine is lost endothermically at 200 °C in cadmium. Both cases decompose exothermically via their respective metal oxalate intermediates to give metal oxide as the end product. It was also observed that hydrazine is lost exothermically in the hydrazinium copper oxalate hydrate. The single-crystal X-ray diffraction study of the copper complex revealed that aminoguanidinium ions are not involved in coordination but act as charge-compensating cations. It is interesting to note that both oxalates act as bidentate chelating ligands. One oxalate bridges the neighbouring copper atom through its carbonyl oxygen with a bond length of 2.561 A to form square pyramidal geometry around the copper atom.

Micro FTIR imaging for the investigation of deteriorated organic binders in wall painting stratigraphies of different techniques and periods

This work deals with the detection and imaging of metal oxalates/carboxylates in the paint layers of ancient wall paintings and with the investigation of their possible association with the ageing of organic substances used as binding media in the original painting. This assumption is investigated employing Fourier transform infrared (FTIR) imaging on several case studies; starting with a thin section of the paint stratigraphy extracted from extensively deteriorated post-Byzantine murals, painted with an oil binder. Metal carboxylates and oxalates show their maximum concentration at the interface of free fatty acids and pigment particles, indicating a possible origin of their formation. Then, the methodology was applied in paint thin sections, originating from Prehistoric, Roman and Hellenistic wall paintings. In these case studies, metal oxalates detected within the paint layers were explored regarding their relation to the use of an organic binder in the wall paintings. The chemical images of calcium oxalates in the paint layers of the Prehistoric wall paintings was a trigger for further laborious investigation on numerous samples, which resulted in revealing the spectrum of an aged proteinaceous binding medium. Thereafter, the distribution of metal oxalates within the paint layers of the samples from the Roman and Hellenistic wall paintings, unaffected by any later intervention, was assumed as an indirect indication of the use of an original organic binder.

Structural Chemistry and Properties of Metal Oxalates Containing a Long-Spanning Dipyridyl Ligand: Chain, Interpenetrated Diamondoid, Threaded-Loop Layer, and Self-Penetrated Topologies

Hydrothermal reaction of metal oxalate (ox) salts and bis(4-pyridylmethyl)piperazine (bpmp) afforded a series of coordination polymers that were structurally characterized by single-crystal X-ray diffraction. {[Cd(H2O)4(bpmp)](ox)}n (1) and {[Co(H2O)4(bpmp)](ox)}n (2) show isostructural cationic one-dimensional (1D) coordination polymer chain motifs with unligated ox anions. A higher temperature polymorph of 2, {[Co(ox)(bpmp)]·3H2O}n (3), possesses a system of threefold interpenetrated three-dimensional (3D) diamondoid nets. {[Mn(H2O)4(bpmp)] [Mn2(ox)3]·5H2O}n (4) manifests a unique 1D + 2D → 3D polyrotaxane coordination polymer structure with 1D cationic [Mn(H2O)4(bpmp)]n chains threaded through apertures coursing through parallel stacks of anionic [Mn2(ox)3]n two-dimensional (2D) hexagonal layers. {[Cu2(ox)2(bpmp)]·6H2O}n (5) possesses 2D [Cu2(ox)2]n layers pillared by bpmp ligands into a 3D [Cu2(ox)2(bpmp)]n coordination polymer network with an unprecedented 4,4-connected self-penetrated (5383)2(5482) topology. Variable temperature magnetic susceptibility studies showed weak antiferromagnetic coupling along [Co(ox)]n chain submotifs in 3 with concomitant zero-field splitting (J = −4.1(7) cm–1, D = 34.5(6) cm–1), weak antiferromagnetic coupling within the [Mn2(ox)3]n hexagonal layers in 4 (J ∼ −0.5 cm–1), and strong antiferromagnetic coupling within the 2D [Cu2(ox)2]n layers in 5 (J = −220(6) cm–1).

One-pot solvothermal synthesis of Co1−xMnxC2O4 and their application as anode materials for lithium-ion batteries

A facile one-pot solvothermal route has been developed to synthesize phase pure MxC2O4⋅2H2O (M=Mn, Co; 0<x⩽1) microstructures without employing any hard/soft template and their electrochemical performance in lithium-ion batteries has been systematically investigated. Morphology, microstructure and composition of the synthesized materials are characterized by field emission-scanning electron microscopy, X-ray diffraction and energy-dispersive X-ray spectroscopy. Anhydrous micron-sized MnC2O4 and CoC2O4 exhibits specific reversible discharge capacity of ∼800 and 950mAhg−1 respectively, at 1C-rate. MnC2O4 exhibited good cycling stability while CoC2O4 showed severe capacity fading phenomenon after 40 cycles, thereafter attaining 400–600mAhg−1 for all C-rates. Interestingly, mixed solid solution having Co0.52Mn0.48C2O4 composition improved the specific reversible discharge capacity to a stable value of ∼1000mAhg−1 (1C-rate), which is one of the highest reported values for such oxalates. The cycling stability of this mixed metal oxalate is remarkably better than its individual constituents at most C-rates. The Mn2+ substitution into CoC2O4 lattice has led to the synergistic modification of the electrochemical performances, thus making it a promising anode candidate for future LIBs.

Synthesis and Characterization of Ultrafine and Porous Structure of Magnesium Ferrite Nanospheres

Porous sphere-shaped magnesium (MgFe 2 O 4 ) spinel ferrite particles were synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal synthesis route starting from an aqueous suspension of coprecipitated metal oxalates. The structural and morphological properties of the prepared materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, infrared spectroscopy and N 2 adsorption-desorption measurement. Results show that the obtained MgFe 2 O 4 particles are nearly spherical in shape and about 100-250 nm in mean diameter. Every magnetic microsphere is made of many ultrafine MgFe 2 O 4 nanoparticles and porous in structure. The obtained sphere-shaped products exhibited a saturation magnetization of 70.25 emu/g and a coercivity of 326.41 Oe at room temperature.

Averrhoa carambola: A Renewable Source of Oxalic Acid for the Facile and Green Synthesis of Divalent Metal (Fe, Co, Ni, Zn, and Cu) Oxalates and Oxide Nanoparticles

A green, simple, and environmentally benign synthetic approach has been utilised to obtain some bivalent metal oxalates from Averrhoa carambola juice extract, without any purification or special treatment of the juice. The main acid components (oxalic acid and ascorbic acid) of the juice were identified by HPLC technique. The effect of temperature on the purity of the product has been investigated. The as-synthesized metal oxalates were thermally decomposed at low temperatures to their respective metal oxide nanoparticles. The metal oxalates and their respective thermal decomposition products were characterized by Fourier Transform Infrared spectroscopy, X-ray diffraction analysis, and thermogravimetry.

Vibrational spectra of the two hydrates of strontium oxalate

The infrared and Raman spectra of the two hydrates of strontium oxalate, SrC2O4⋅H2O and SrC2O4⋅2H2O, were recorded and discussed on the basis of their structural peculiarities and in comparison with the spectra of the related calcium oxalates and other previously investigated metallic oxalates.

Comparative Electrochemical Study of Metal Oxalate As Anode for Lithium Batteries

Rechargeable lithium ion batteries (LIB) are the most advanced power sources for portable electronic devices, hybrid electric vehicles, transportation sectors and military applications. Metal oxalate is technologically important and functional material, because of its applications for use in energy storage such for Li ion batteries. Thus, these materials have been investigated as alternative negative materials for LIB owing to high capacity (700 ~ 1,000 mAhg-1) based on a conversion mechanism.Several metals based oxalates with different aspect ratios have been synthesized by hydrothermal reaction of metals (= Ni, Co, Mn) with Na2C2O4 and H2O in the presence of ethylene glycol (EG). Control over the aspect ratios of oxalates were achieved by adjusting the hydrothermal reaction temperature and time.The electrode was fabricated by mixing 70 wt% active material, 10 wt% carbon black (electronic conductive additive) and polyacrylic acid (PAA, binder) in N-methylpyrrolidinone (20 wt%). A solution of 1 M LiPF6 dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (3 : 7 weight ratio) was used as the electrolyte in the cell. Electrochemical test was carried out in coin type cell. Galvanostatic electrochemical charge and discharge test were made between 0V and 3.0V at 100 mAg-1 current at room temperature.The hydrothermal method is useful to synthesize metal oxalate with particles and crystallization. Nickel and manganese oxalate crystallize in the monoclinic phase, while the cobalt compound adopts the orthorhombic phase. The as-prepared metal oxalates demonstrate a high performance as anode material for LIB. Among them, nickel oxalate showed a high initial discharge capacity of 1321 mAhg-1. The first charge capacity of the as-prepared electrode at a current density of 100 mAg-1 reach 786 mAhg-1 with good capacity retention.

Coprecipitates Synthesis of CaIn2O4 and Its Photocatalytic Degradation of Methylene Blue by Visible Light Irradiation

Visible light-activated photocatalyst calcium indate (CaIn2O4) has been successfully prepared by a new approach with lower temperature calcinations. The sub-micrometer-sized samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectroscopy. High-purity CaIn2O4 particles were synthesized by controlling the sintering temperature and their photocatalytic performance were evaluated. Under visible light irradiation, 10 ppm of methylene blue solution was effectively degraded in 3.0 h. The excellent photocatalytic activity of CaIn2O4 is attributed to the high purity, small particle size, and large surface area because of lower sintering temperature by thermal decomposition of metal oxalate precursor.

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt (CoFe2O4), nickel (NiFe2O4), zinc (ZnFe2O4) and manganese (MnFe2O4) spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of coprecipitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining coprecipitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low temperature of 75 °C and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction (XRPD), while X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy (TEM) observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer (SQUID) revealing hard and soft ferrimagnetic behavior, respectively.

Synthesis and characterization of hollow spherical cathode Li1.2Mn0.54Ni0.13Co0.13O2 assembled with nanostructured particles via homogeneous precipitation-hydrothermal synthesis

Two different kinds of hollow spherical materials Li1.2Mn0.54Ni0.13Co0.13O2 which are assembled by the nanoplate-shaped particles and the quasi-sphere shaped particles, have been prepared through the homogeneous precipitation of metal oxalate precursor and subsequent solid state reaction with lithium nitrate. X-ray diffraction (XRD) pattern shows the two as-prepared samples have a good layered structure and solid solution characteristic. As the lithium-ion battery cathode, the as-prepared sample exhibits an initial discharge capacity of 286.4 mAh g−1 at 0.1 C between 2.0 and 4.8 V, and a discharge capacity of 240.9 mAh g−1 can be retained after 50 cycles. The structure of hollow spherical material is assembled with nanoplate-shaped particles, which is beneficial for improving the rate performance. It is due to the shortened transmission distance for Li+ from the cathode materials to electrolyte. At the charge–discharge rate of 1.0 C, a stable discharge capacity of 170.5 mAh g−1 also can be reached after 112 cycles with capacity retention of 86.2%. Meanwhile, the relationship of structure and electrochemical performance is also discussed in detail.

Magnetic studies on mixed metal oxalate bridged compounds NBu4MAIInFeII1–n[FeIII(ox)3] (MA = Mn, Zn)

The mixed metal oxalate bridged compounds NBu4MAIInFeII1–n[FeIII(ox)3](MA = Mn, Zn) were investigated by magnetic measurements. The temperature dependence of the compounds NBu4ZnIInFeII1–n[FeIII(OX)3] (n = 0. 04, 0·08, 0·10) shows two temperature compensation points in the temperature range of 32–41·5 K and multiple magnetic pole reversals are observed in the material. When n≧0·1 the temperature compensation point disappears, the value of M increases and exhibits weak irreversibility in the field cooled (FC) magnetisation curves. At the same time, spin glass state is founded below 35 K and the bifurcation of the zero field cooled and FC plots below the Neel temperature of 30 K indicates irreversibility. At the Neel temperature of 39·9 K, a compensation temperature and a spin canting are observed in the compound NBu4FeII0·97MnII0·03[FeIII(OX)3].

The influence of heat treatment on the formation and transport current density of DyBa2Cu3O7-δ ceramics superconductor synthesized from nano-coprecipitated powders

DyBa2Cu3O7-δ superconducting ceramic has been prepared from nano metal oxalate precursors with average grain size <30 nm using the coprecipitation method. Four sintering temperatures were applied for the same time period. XRD showed a single phase of an orthorhombic structure for all samples with small amount of 211 phase which was detected for samples sintered above 930°C. The sintered samples also exhibited metallic behaviour with TC(R=0) = 89 K–90 K and the transport critical current density (JC) values enhanced from 4.35 A/cm2 to 12.9 A/cm2 as the sintering temperature increased. The SEM micrographs showed grains of large size that are randomly distributed and have irregular structure. The compaction between the grains was improved as sintering temperature increased and thus resulted in reducing the weak links effect. In conclusion, Reducing the gaps between the grain and the formation of 211 phase as pinning centers might be explain the enhancement in the transport current properties of Dy123 in a way to be used in the HTSC device applications.

Preparing high performance of LiFe(1−x)MxPO4 by using Fe(1−x)MxC2O4 as raw material precipitated from ferrochrome alloy leaching solution

To separate ferrum from chromium in the leaching sulfate solution of ferrochrome alloy, the oxalic acid was employed to precipitate the ferrum as the form of FeC2O4 and Cr was left in the solution. In this route, small amount of nickel, cobalt and manganese exited in ferrochrome alloy were also precipitated simultaneously together with ferrous oxalate. Analysis from ICP shows that the molar percent of Fe in oxalic precipitate is 97.9% and the main doped elements are Ni (1.1%) and Mn (0.4%).The mixed metal oxalate Fe(1−x)MxC2O4 was used as a raw material to prepare doped LiFePO4 cathode material of lithium ion batteries. The obtained LiFe(1−x)MxPO4/C was a single olivine-type phase with higher crystallinity and presents the well-distributed fine particles. It shows an outstanding electrochemical performance with a discharge capacity of 162mAh/g at the rate of 0.1C, 136mAh/g at 1C and 103mAh/g at 5C. When cycled at 1C for 50 times, the capacity retention is 98.2%.

Flux and surfactant directed facile thermal conversion synthesis of hierarchical porous MgO for efficient adsorption and catalytic growth of carbon nanotubes

Three-dimensional (3D) hierarchical porous structures have attracted extensive attention owing to their versatile applications. Herein, 3D hierarchical porous MgO superstructures with a well faceted profile and high crystallinity were successfully obtained via a facile flux and surfactant directed decomposition of metal oxalates. As a nonionic surfactant, NP-9 served as the dispersing agent and prevented the porous MgO particles from aggregating with each other. The flux NaCl induced vapor migration through the porous structure, favoring the in situ crystallization of MgO after the phase conversion from the oxalate precursor, enhancing the toughness of the backbone and further realizing the preservation of the polyhedron-like morphology. The as-obtained hierarchical porous MgO superstructures were very efficient and effective as adsorbents for methylene blue (MB) and a catalyst support for single-walled carbon nanotube (SWCNTs) growth. The as-obtained SWCNTs afford an ultrahigh surface area of 1232 m2 g−1. Such superstructures could be employed as great potential candidates in dye-containing water treatment as well as heterogeneous catalysis.

From 1D chain to 2D layer and 3D network: Solvent-free syntheses of new metal oxalates

Four metal oxalates, Hdpa⋅Cr(ox)2 (1), (Hdpa)2⋅Zn2(ox)3⋅2H2O (2), Zn(H2O)(ox) (3), and (Hgua)(H3O)⋅Cd(C2O4)2 (4), have been synthesized under solvent-free conditions, where dpa=diisopropylamine, ox=oxalate, and gua=guanidine. These compounds have extended structures varying from 1D chain (for 1), to 2D layer (for 2 and 3), and 3D framework network (for 4). The temperature dependence of the magnetic susceptibility of compound 1 indicates the existence of antiferromagnetic interactions between the chromium ions. Upon excitation at 230nm, compound 3 exhibits an extensive luminescence with a peak centered at 501nm.

Oxalate precursor preparation of Li1.2Ni0.13Co0.13Mn0.54O2 for lithium ion battery positive electrode

Li1.2Ni0.13Co0.13Mn0.54O2 powders have been prepared through co-precipitation of metal oxalate precursor and subsequent solid state reaction with lithium carbonate. X-ray diffraction pattern shows that the massive rock-like structure has a good layered structure and solid solution characteristic. Scanning electron microscope and transition electron microscope images reveal that the Li1.2Ni0.13Co0.13Mn0.54O2 composed of nanoparticles have the size of 1–2 μm. As a lithium ion battery positive electrode, the Li1.2Ni0.13Co0.13Mn0.54O2 has an initial discharge capacity of 285.2 mAh g−1 at 0.1 C within 2.0–4.8 V. When the cutoff voltage is decreased to 4.6 V, the cycling stability of product can be greatly improved, and a discharge capacity of 178.5 mAh g−1 could be retained at 0.5 C after 100 cycles. At a high charge–discharge rate of 5 C (1,000 mAh g−1), a stable discharge capacity of 121.4 mAh g−1 also can be reached. As the experimental results, the Li1.2Ni0.13Co0.13Mn0.54O2 prepared from oxalate precursor route is suitable as lithium ion battery positive electrode.

EFFECT OF HEAT TREATMENT OF HoBa2Cu3O7-δ CERAMICS SUPERCONDUCTOR SYNTHESIZED FROM NANO-COPRECIPITATED POWDERS

Nano-sized metal oxalate precursors was thermally treated and investigated to produce high temperature superconducting ceramics with a formula of HoBa 2 Cu 3 O 7-δ ( Ho -123). The nano metal oxalate powders were subjected to different heat treatments at various temperatures for the phase formation study. The high-TC phase was observed for all samples as an evidence for the single step transition of (R–T) curves. The TC(R = 0) for Ho 123 is 91 K and 90 K for samples sintered at 920°C, 930°C and 88 K for samples sintered at 940°C and 950°C, respectively. XRD data showed single phase of an orthorhombic structure where a small amount of none superconducting phase Ho 2 BaCuO 5( Ho 211) phase was detected. The Ho 211 phase was increased as sintering temperature increased due to the decomposition process and affected the transport properties. SEM micrographs showed large grain sizes that are randomly distributed. However, the grain size decreased as the sintering temperature increased which resulted in the formation of weak-links and hence decreases the transport properties. Using nano-sized metal oxalate precursors simplified the formation of HTSC materials with less processing temperatures which could be beneficial in superconducting tape industry. In addition, control of the sintering temperature lead to the formation of Ho 123 phase with optimum amount of Ho 211 phase which acts as pinning centers and improves the transport properties.

Theoretical studies of electronic structure and structural properties of anhydrous alkali metal oxalates

The theoretical analysis of electronic structure and bonding properties of anhydrous alkali metal oxalates, based on the results of DFT FP-LAPW calculations, Bader’s QTAIM topological properties of electron density, Cioslowski and Mixon’s topological bond orders [reported in the first part of this paper by Koleżyński (doi: 10.1007/s10973-013-3126-z )] and Brown’s Bond Valence Model calculations, carried out in the light of thermal decomposition pathway characteristic for these compounds are presented. The obtained results shed some additional light on the origins of the complex pathway observed during thermal decomposition process (two stage process, first the formation of respective carbonate and then decomposition to metal oxide and carbon dioxide). For all structures analyzed, strong similarities in electronic structure and bonding properties were found (ionic-covalent bonds in oxalate anion with C–C bond as the weakest one in entire structure and almost purely ionic between oxalate group and alkali metal cations), allowing us to propose the most probable pathway consisting of consecutive steps, leading to carbonate anion formation with simultaneous cationic sublattice relaxations, which results in relative ease of respective metal carbonate formation.