Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

The reactions of ethylene glycol with manganese oxalates MnC₂O₄ · 2 H₂O and MnC₂O₄ · 3H₂O on heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from oxalates to give a new solvate compound according to the reaction MnC₂O₄ · nH₂O + HOCH₂CH₂OH = MnC₂O₄(HOCH₂CH₂OH) + nH₂O↑. The crystals of the solvates retain the morphology of the initial oxalates, which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC₂O₄ · 3H₂O and MnC₂O₄(HOCH₂CH₂OH) having quasi-unidimensional structure gave Mn₃O₄ and Mn₂O₃ nanowhiskers in air and MnO in an inert gas environment. Heating of MnC₂O₄ · nH₂O in ethylene glycol at temperatures above 100°C results in anhydrous manganese oxalate.     

Thermogravimetric analysis of wheatleyite Na<Subscript>2</Subscript>Cu<Superscript>2+</Superscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>·2H<Subscript>2</Subscript>O

Evidence for the existence of primitive life forms such as lichens and fungi can be based upon the formation of oxalates. These oxalates form as a film like deposit on rocks and other host matrices. The anhydrous oxalate mineral moolooite CuC₂O₄ as the natural copper(II) oxalate mineral is a classic example. Another example of a natural oxalate is the mineral wheatleyite Na₂Cu²⁺(C₂O₄)₂·2H₂O. High resolution thermogravimetry coupled to evolved gas mass spectrometry shows decomposition of wheatleyite at 255°C. Two higher temperature mass losses are observed at 324 and 349°C. Higher temperature mass losses are observed at 819, 833 and 857°C. These mass losses as confirmed by mass spectrometry are attributed to the decomposition of tennerite CuO. In comparison the thermal decomposition of moolooite takes place at 260°C. Evolved gas mass spectrometry for moolooite shows the gas lost at this temperature is carbon dioxide. No water evolution was observed, thus indicating the moolooite is the anhydrous copper(II) oxalate as compared to the synthetic compound which is the dihydrate.     

Two bismuth oxalate hydrates and revision of their chemical formulae

The crystal structures of two bismuth(III) oxalate hydrates, previously described as `Bi<sub>2</sub>(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>·H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>' and `Bi₂(C₂O₄)₃·7H₂O', were solved and refined from single‐crystal X‐ray diffraction data. The results led to the revised chemical formulae Bi₂(C₂O₄)₃·6H₂O and Bi₂(C₂O₄)₃·8H₂O, respectively. Both dibismuth(III) trioxalate hexahydrate (tetra­aqua­tri‐μ‐oxalato‐dibismuth(III) dihydrate, {[Bi₂(C₂O₄)₃(H₂O)₄]·2H₂O}_n) and dibismuth(III) trioxalate octahydrate (tetra­aqua­tri‐μ‐oxalato‐dibismuth(III) tetrahydrate {[Bi₂(C₂O₄)₃(H₂O)₄]·4H₂O}_n) are characterized by a three‐dimensional network of Bi atoms connected by tetradentate oxalate groups. All ligand and `free' water mol­ecules are located in channels and voids. The mean Bi—O bond lengths are ∼2.51 Å. The lone electron pairs on all Bi³⁺ cations are stereochemically inactive.     

Thermal analysis of some polynuclear coordination compounds as precursors of iron garnets (M3Fe5O12, M=Y3+ or Er3+)

The thermal behaviour of four coordination compounds (NH₄)₆[Y₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·12H₂O, (NH₄)₆[Y₃Fe₅(C₆O₇H₁₀)₆(C₆O₇H₉)₆]·8H₂O, (NH₄)₆[Er₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·10H₂O and (NH₄)₆[Er₃Fe₅(C₄O₆H₄)₆(C₄O₆H₃)₆]·22H₂O has been studied to evaluate their suitability for garnet synthesis. The thermal decomposition and the phase composition of the resulted decomposition compounds are influenced by the nature of metallic cations (yttrium-iron or erbium-iron) and ligand anions (malate or gluconate).     

3D Coordination Polymer Incorporating Discrete Molecular Octahedra

Copper(II) oxalate coordination polymer [{Cu₄(C₂O₄)₄(L)₄}₃ · {Cu₃(C₂O₄)₃(L)₆}₂ · 3L · 25H₂O]_n (L = 3,3′,5,5′‐tetramethyl‐4,4′‐bipyrazole) reveals a structure that is related to the Pt₃O₄ net topology. The 3D linkage is sustained with copper‐oxalate squares and copper‐bipyrazole triangles sharing vertices. The framework supports giant icosahedral cages and entraps discrete molecular octahedra formed by two molecular complexes Cu₃(C₂O₄)₃(L)₆ associated by means of NH‐‐‐N hydrogen bonding. The coexistence of the discrete and 3D portions formed by the same components suggests self‐templation as a key feature of the system. Simpler copper oxalate compounds [Cu(C₂O₄)(L)₂(H₂O)] · CH₃OH · 3.75H₂O and [Cu₂(C₂O₄)₂(L)₅] · L · 11H₂O are concomitant products of the reaction mixture and they exist in the form of molecular mono‐ and binuclear complexes.     

Three yttrium crotonate complexes with diimines

The synthesis and crystal structures of three new yttrium crotonate (crot) compounds, associated with three different nitro­genous bases, namely 1,10‐phenanthroline (phen), 4‐­methyl‐1,10‐phenanthroline (mphen) and 2,2′‐bipyridyl­amine (bpa), are presented. All three compounds organize as centrosymmetric dimers, to give tetra‐μ‐crotonato‐bis[croto­nato(1,10‐phenanthroline)yttrium(III)] dihydrate, [Y₂(C₄H₅O₂)₆(C₁₂H₈N₂)₂]·2H₂O or [Y(crot)₃(phen)]₂·2H₂O, (I), tetra‐μ‐crotonato‐bis­[crotonato(4‐methyl‐1,10‐phenan­throline)­yttrium(III)] dihydrate, [Y₂(C₄H₅O₂)₆(C₁₃H₁₀N₂)₂]·2H₂O or [Y(crot)₃(mphen)]₂·2H₂O, (II), and tetra‐μ‐crot­onato‐bis­[di­aqua(crotonato)yttrium(III)] 2,2′‐bipyridyl­amine tetrasolvate, [Y₂(C₄H₅O₂)₆(H₂O)₄]·4C₁₀H₉N₃ or [Y(crot)₃(aq)₂]₂·4(bpa), (III). Complexes (I) and (II) are isomorphous, with the bases acting as chelating ligands. In complex (III), the coordination sphere is built up of carboxyl­ate and aqua ligands, with the non‐coordinated di­imine acting as included solvent.     

Template-directed syntheses of two 3D metal oxalates: in situ N-methylation and crystal structures

Two isomorphic organically templated zinc/cobalt oxalates, (dmdabco)[Zn₂(C₂O₄)₃]·4H₂O (1), and (dmdabco)[Co₂(C₂O₄)₃]·4H₂O (2) (C₂O₄^2? = oxalate; dmdabco = N,N′-dimethyl-1,4-diazabicyclo[2,2,2]octane), have been prepared under solvothermal conditions and characterized by X-ray structural analyses. The dmdabco²⁺ templating agent was derived from simple in situ N-alkylation between methanol and 1,4-diazabicyclo[2,2,2]octane (dabco). Distinct from conventional Eschweiler-Clarke methylation containing excess formic acid and formaldehyde, such one-step methylation from methanol molecules is convenient. Both 1 and 2 exhibit a uninodal 3-connected 3-D interrupted open-framework, in which oxalate ligands have in-plane and out-of-plane connection modes.     

Thermal decomposition of mixed Ce and Gd oxalates and thermal properties of mixed Ce and Gd oxides

The aim of the present work is to study the thermal decomposition of the mixed oxalates (Ce_1–xGd_x)₂(C₂O₄)₃·nH₂O. The mechanisms of decomposition of Ce and Gd oxalate are different, and mixed oxalates behave in an intermediate way. Their dehydration stages are more similar to those of Gd oxalate, as not all the molecules of water are equivalent like the cerium oxalate. The decomposition leads to (Ce_1–xGd_x)O_2–x/2. For x close to 0 or to 1 two solid solutions exist, while for the central composition, the presence of a biphasic region can not be excluded.     

Molten potassium pyrosulfate: The reactions of seven metal oxalates

The reactions of Li₂C₂O₄, Na₂C₂O₄, K₂C₂·H₂O, CaC₂·H₂O, ZnC₂O₄, La₂(C₂O₄)₃ and K₂TiO(C₂O₄)₂· 2H₂O with K₂S₂O₇ were investigated using thermal methods of analysis. Reaction products were analysed by various techniques. It was found that anhydrous oxalates reacted with K₂S₂O₇, evolving a mixture of CO₂ and CO with the formation of K₂SO₄ and the corresponding metal sulfates, which, in the reactions of ZnC₂O₄ and K₂TiO(C₂O₄)₂ 2H₂O, probably existed as K₂[Zn(SO₄)₂] and K₄[Ti(SO₄)₄], respectively. Water was found to be an additional product in the hydrated metal oxalate reactions. The stoichiometries of these reactions have been established from the thermogravimetric and acidimetric results.     

Synthesis,open-framework structure and thermal behaviour of ammonium tin oxalate,Sn2(NH4)2(C2O4)3·3H2O

A new mixed ammonium tin oxalate trihydrate, Sn₂(NH₄)₂(C₂O₄)₃·3H₂O, has been prepared from evaporation of a solution of tin and ammonium oxalates. Its crystal structure has been solved from single-crystal diffraction data. The symmetry is orthorhombic, space group Pnma (No. 62), cell dimensions a=15.1821(5) Å, b=11.7506(2) Å, c=10.8342(3) Å, and Z=4. The structure consists of macroanionic layers built from [Sn(C₂O₄)₃]^2– groups. The SnO₆ polyhedron can be described as a pseudo pentagonal bipyramid, with the lone pair of electrons presumably occupying one apex. The resulting framework displays holes in which the water molecules and ammonium groups are located. The thermal behaviour of the mixed ammonium tin oxalate has been investigated with temperature-dependent X-ray powder diffraction and conventional thermal analysis. The degradation process has been completely explained, as well as that of oxammite, a phase always obtained in the preparations. The thermal decomposition of oxammite leads to (NH₄)₂C₂O₄ and a new acid salt, NH₄HC₂O₄. The mixed ammonium tin oxalate decomposes successively into the amorphous compounds, Sn₂(NH₄)₂(C₂O₄)₃·H₂O and Sn₂(NH₄)₂(C₂O₄)₃, SnC₂O₄ and, finally, cassiterite SnO₂.     

Oxalato‐ und Quadratato‐Komplexe hochkoordinierter Metallionen: Die Raumnetzstrukturen von La2(C2O4)(C4O4)2(H2O)8 · 2,5 H2O und K[Bi(C2O4)2] · 5 H2O

Oxalato‐ and Squarato‐Bridged Threedimensional Networks: The Crystal Structures of La₂(C₂O₄)(C₄O₄)₂(H₂O)₈ · 2.5 H₂O and K[Bi(C₂O₄)₂] · 5 H₂O The title compounds have been formed by hydrolysis of amino‐ and thioderivatives of squaric acid in the presence of La^III and Bi^III ions. Both compounds are threedimensional coordination polymers in the solid state, as shown by single crystal X‐ray crystallography. In La₂(C₂O₄)(C₄O₄)₂(H₂O)₈ · 2.5 H₂O oxalato‐bridged pairs of LaO₉ polyhedra are connected with identical neighbouring polyhedra by squarate ions. In K[Bi(C₂O₄)₂] · 5 H₂O each Bi atom is fourfold linked to other Bi atoms by the oxalate ions. The resulting 3D network shows a diamond‐like topology with square‐shaped channels. In both structures the channels are partially filled by water molecules.     

Hydrothermal synthesis,structures and magnetic properties of two new holmium(III) oxalato complexes

Two new holmium (Ho) oxalato complexes have been synthesized under hydrothermal conditions and structurally characterized. [Ho(OH)₂]₂(C₂O₄) (1) has a 3-D structure with Ho-(μ₃-OH) hydroxide layers connected by μ₄-bridging oxalate ligands forming a unique hybrid structure. Sr(H₂O)₄[Ho(C₂O₄)₂(H₂O)]₂·2H₂O (2) has a 3-D structure built through μ₂-bridging oxalate ligands connecting hexagonal Ho oxalate layers with hydrated Sr²⁺ ions in the channels. Different oxalate ligand arrangements around the metal ions control the structural alterations among the lanthanoid double oxalates even with similar formulas. Both structures have been discussed and compared to the existing lanthanoid oxalato complexes. In addition, their vibration modes, thermal stabilities, electronic structures, and magnetic properties have been further investigated and reported. Both 1 and 2 show the deviation of the magnetic behaviors from the Curie–Weiss law due to the crystal field effects.     

Di­aqua­tris­(pentane‐2,4‐dionato‐O,O′)­holmium(III) mono­hydrate and di­aqua­tris­(pentane‐2,4‐dionato‐O,O′)holmium(III) 4‐hydroxy­pentan‐2‐one solvate dihydrate

The structures of the title compounds, [Ho(C₅H₇O₂)₃(H₂O)₂]·H₂O and [Ho(C₅H₇O₂)₃(H₂O)₂]·C₅H₈O₂·2H₂O, both show an eight‐coordinate holmium(III) ion in a square antiprismatic configuration. The packing of these structures consists of an infinite two‐dimensional network of hydrogen‐bonded mol­ecules. In both structures, the same hydrogen‐bonded chain of Ho^III complexes is found.     

Separate Crystallization of Lanthanide Oxalates and Calcium Oxalates from Nitric Acid Solutions

The separation of lanthanides from calcium compounds in the form of oxalates from hot nitric acid solutions of Ln(NO₃)₃ and Ca(NO₃)₂ with the insertion of oxalic acid and a Ln₂(C₂O₄)₃ · nH₂O crystal seed was studied by mass-spectrometric, atomic emission, microscopic, X-ray diffraction, and fluorescence analyses. The produced single-phase precipitate was found to contain an isomorphic impurity of La–Sm oxalates, while calcium oxalate remained in the hot nitric acid solution (95°С) saturated with oxalic acid. This facile and efficient method provides Ln₂(C₂O₄)₃ · nH₂O (n = 9.5 mol) in one step in a 80.1 rel. % yield, with the major phase being at least 99.4 wt %. The unit cell parameters were determined for the crystals of the isomorphic lanthanide oxalate mixture: a = 11.243(2) Å, b = 9.591(2) Å, c = 10.306(2) Å; α = γ = 90°, β = 114.12(1)°; Z = 2; V = 1013.7(5) ų.     

Coordination Chemistry of [Nb2(S2)2]4+ Clusters: Preparation and Crystal Structures of K4[Nb2(S2)2(C2O4)4] · 6 H2O and (NH4)6[Nb2(S2)2(C2O4)4](C2O4)

Bis(disulfido)bridged Nb^IV cluster oxalate complexes [Nb₂(S₂)₂(C₂O₄)₄]^4– were prepared by ligand substitution reaction from the aqua ion [Nb₂(μ‐S₂)₂(H₂O)₈]⁴⁺ and isolated as K₄[Nb₂(S₂)₂(C₂O₄)₄] · 6 H₂O ( 1 ), (NH₄)₆[Nb₂(S₂)₂(C₂O₄)₄](C₂O₄) ( 2 ) and Cs₄[Nb₂(S₂)₂(C₂O₄)₄] · 4 H₂O ( 3 ). The crystal structures of 1 and 2 were determined. The crystals of 1 belong to the space group P1, a = 720.94(7) pm, b = 983.64(10) pm, c = 1071.45(10) pm, α = 109.812(1)°, β = 91.586(2)°, γ = 105.257(2)°. The crystals of 2 are monoclinic, space group C2/c, a = 1567.9(2) pm, b = 1906.6(3) pm, c = 3000.9(4) pm, β = 95.502(2)°. The packing in 2 shows alternating layers of cluster anions and of ammonium/uncoordinated oxalates perpendicular to the [1 0 1] direction. Vibration spectra, electrochemistry and thermogravimetric properties of the complexes are also discussed.     

Oxalate-2-ethanolamine complexes of some bivalent cations (Mn,Co, Ni,Cu, Zn and Cd)

On the refluxing ofM(II) oxalate (M=Mn, Co, Ni, Cu, Zn or Cd) and 2-ethanolamine in chloroform, the following complexes were obtained: MnC₂O₄·HOCH₂CH₂NH₂·H₂O, CoC₂O₄·2HOCH₂CH₂NH₂, Ni₂(C₂O₄)₂·5HOCH₂CH₂NH₂·3H₂O, Cu₂(C₂O₄)₂·5HOCH₂CH₂NH₂, Zn₂(C₂O₄)₂·5HOCH₂CH₂NH₂·2H₂O and Cd₂(C₂O₄)₂·HOCH₂CH₂NH₂·2H₂O. Following the reaction ofM(II) oxalate with 2-ethanolamine in the presence of ethanolammonium oxalate, a compound with the empirical formula ZnC₂O₄·HOCH₂CH₂NH₂·2H₂O¹ was isolated. The complexes were identified by using elemental analysis, X-ray powder diffraction patterns, IR spectra, and thermogravimetric and differential thermal analysis. The IR spectra and X-ray powder diffraction patterns showed that the complexes obtained were not isostructural. Their thermal decompositions, in the temperature interval between 20 and about 900°C, also take place in different ways, mainly through the formation of different amine complexes. The DTA curves exhibit a number of thermal effects.     

Thermal decomposition features of calcium and rare-earth oxalates

Thermal decomposition of Ln₂(C₂O₄)₃ · 9H₂O concentrate (Ln = La, Ce, Pr, Nd) in the presence of CaC₂O₄ · H₂O was studied by X-ray diffraction, thermogravimetry, and chemical analysis. Annealing at temperatures above 374°C in the absence of calcium oxalate gives rise to the solid solution of CeO₂-based rare-earth oxides. Calcite CaCO₃ is formed in the presence of calcium oxalate at annealing temperatures above 442°C, which impedes the formation of lanthanide oxide solid solution and favors crystallization of oxides as individual La₂O₃, CeO₂, Pr₆O₁₁, and Nd₂O₃ phases. An increase in temperature above 736°C is accompanied by decomposition of calcium carbonate to give rise to an individual CaO phase and an individual phase of CeO₂-based lanthanide oxide solid solution.     

Sur un nouveau Complexe entre l'oxyfluorure d'antimoine et l'oxalate. Structure cristalline de (NH4)4H2(C2O4)3(SbOF) 2 · H2O

On a New Complex of Antimony Oxide Fluoride and Oxalate. Crystal Structure of (NH₄)₄H₂(C₂O₄)₃(SbOF) ₂ · H₂O The crystal structure of (NH₄)₄H₂(C₂O₄)₃(SbOF) ₂ · H₂O has been fixed by X-ray diffraction on single crystal (R = 0.025 for 2124 planes). The antimony atom is complexed by the oxalate anions which are bidendate chelates. Antimony coordination is seven (five oxygen atoms, one fluorine atom, and the lone pair E). Antimony environment is a pentagonal bipyramid, one of the axial positions is occupied by the lone pair, the other one by the fluorine atom.     

Nuclear magnetic resonance of 27Al in single crystals of NaMgAl(C2O4)3·xH2O

Nuclear magnetic resonance of ²⁷Al nuclei was used to determine the quadrupole splitting constants ν_Q of the Al³⁺ ion in the oxalate complexes of NaMgAl(C₂O₄)₃·8H₂O and NaMgAl(C₂O₄)₃·9H₂O. The eightfold-hydrated crystal was obtained by annealing a ninefold-hydrated crystal. The resonance spectrum of the ninefold-hydrated crystal is split and the asymmetry parameter η amounts to 0.076.     

Magnetic properties of nanocrystalline CuFe2O4 and kinetics of thermal decomposition of precursor

CuFe₂(C₂O₄)₃·4.5H₂O was synthesized by solid-state reaction at low heat using CuSO₄·5H₂O, FeSO₄·7H₂O, and Na₂C₂O₄ as raw materials. The spinel CuFe₂O₄ was obtained via calcining CuFe₂(C₂O₄)₃·4.5H₂O above 400 °C in air. The CuFe₂(C₂O₄)₃·4.5H₂O and its calcined products were characterized by thermogravimetry and differential scanning calorimetry, Fourier transform FT-IR, X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectrometer, and vibrating sample magnetometer. The result showed that CuFe₂O₄ obtained at 400 °C had a saturation magnetization of 33.5 emu g^?1. The thermal process of CuFe₂(C₂O₄)₃·4.5H₂O experienced three steps, which involved the dehydration of four and a half crystal water molecules at first, then decomposition of CuFe₂(C₂O₄)₃ into CuFe₂O₄ in air, and at last crystallization of CuFe₂O₄. Based on KAS equation, OFW equation, and their iterative equations, the values of the activation energy for the thermal process of CuFe₂(C₂O₄)₃·4.5H₂O were determined to be 85 ± 23 and 107 ± 7 kJ mol^?1 for the first and second thermal process steps, respectively. Dehydration of CuFe₂(C₂O₄)₃·4.5H₂O is multistep reaction mechanisms. Decomposition of CuFe₂(C₂O₄)₃ into CuFe₂O₄ could be simple reaction mechanism, probable mechanism function integral form of thermal decomposition of CuFe₂(C₂O₄)₃ is determined to be 1 ? (1 ? α)^1/4.