Mössbauer studies of solid state photolysis of barium and strontium tris(oxalato) ferrates (III)

Solid state photolysis of strontium and barium tris(oxalato) ferrate(III) was done under a medium pressure lamp and investigated with Mössbauer spectroscopy. The product [Fe^II(C₂O₄) (H₂O)₂]^2? formed during photolysis is found to be quite stable and does not convert to ferric state on long standing in air.     

Preparation of sodium ferrite from the thermolysis of sodium tris(maleato/fumarato)ferrates(III)

Thermal decomposition of sodium tris(maleato)ferrate(III) hexahydrate, Na₃[Fe(C₄H₂O₄)₃]·6H₂O and sodium tris(fumarato)ferrate(III) heptahydrate, Na₃[Fe(C₄H₂O₄)₃]·7H₂O has been studied upto 973 K in static air atmosphere employing TG, DTG, DSC, XRD, Mössbauer and infrared spectroscopic techniques. Dehydration of the maleate complex is complete at 455 K and the anhydrous complex immediately undergoes decomposition till α-Fe₂O₃ and sodium carbonate are formed at 618 K. In the final stage of remixing of cations, a solid state reaction between α-Fe₂O₃ and sodium carbonate leads to the formation of α-NaFeO₂ at a temperature (773 K) much lower than for ceramic method. Almost similar mode of decomposition has been observed for the fumarate complex. A comparison of the thermal stability shows that the fumarate precursor decomposes at a higher temperature than the maleate complex due to the trans geometry of the former.     

Mössbauer study of the thermal decomposition of alkali tris(oxalato)ferrates(III)

The thermal decomposition of alkali (Li,Na,K,Cs,NH₄) tris(oxalato)ferrates(III) has been studied at different temperatures up to 700°C using Mössbauer, infrared spectroscopy, and thermogravimetric techniques. The formation of different intermediates has been observed during thermal decomposition. The decomposition in these complexes starts at different temperatures, i.e., at 200°C in the case of lithium, cesium, and ammonium ferrate(III), 250°C in the case of sodium, and 270°C in the case of potassium tris(oxalato)ferrate(III). The intermediates, i.e., Fe¹¹C₂O₄, K₆Fe¹¹₂(ox)₅. and Cs₂Fe¹¹ (ox)₂(H₂O)₂, are formed during thermal decomposition of lithium, potassium, and cesium tris(oxalato)ferrates(III), respectively. In the case of sodium and ammonium tris(oxalato)ferrates(III), the decomposition occurs without reduction to the iron(II) state and leads directly to α-Fe₂O₃.     

Crystal structure and spectroscopic behavior of three new tris-oxalatoferrate(III) salts

A new general synthetic procedure for preparation of Na₃[Fe(C₂O₄)₃]·5H₂O (1), Rb₃[Fe(C₂O₄)₃]·3H₂O (2), and Cs₃[Fe(C₂O₄)₃]·2H₂O (3) was developed. The crystal structures of these salts have been determined by single crystal X-ray diffraction. Salt 1 crystallizes in the monoclinic space group C2/c with Z = 8, salt 2 in P2₁/c with Z = 4, and salt 3 in P2₁/n with Z = 4. The three new salts and K₃[Fe(C₂O₄)₃]·3H₂O, prepared for comparative purposes, were further characterized by infrared and ⁵⁷Fe-Mössbauer spectroscopy. These spectra are discussed in comparison with those of related oxalato complexes.     

Mössbauer study on solid state photolysis of alkali tris(malonato)ferrates(III)

Solid state photolysis of alkali tris(malonato)ferrates(III), i.e., M₃[Fe(CH₂C₂O₄)₃]xH₂O (M=Li, Na, K, NH₄) has been studied employing Mössbauer, infrared and reflectance spectroscopic techniques. The complexes were irradiated for 300 hours using a medium pressure mercury vapour lamp of 250 W, Photodecomposition led to the formation of an iron(II) intermediate, M₂[Fe^II(CH₂C₂O₄)₂(H₂O)₂] (M=Li, Na, K) which on prolonged standing in air oxidized to M[Fe^III(CH₂C₂O₄)₂(H₂O)₂]. However, in case of ammonium complex, Fe^IICH₂C₂O₄·2H₂O once formed remained stable. The extent of photoreduction showed the sequence: NH₄, K>Li>Na. The results have been compared with those of alkali tris (oxalato) ferrates(III).     

Kinetics of thermal decomposition of iron(III) dicarboxylate complexes

Summary Tris(dicarboxylate) complexes of iron(III) with oxalate, maleate, malonate and phthalate viz. K₃[Fe(C₂O₄)₃]×3H₂O (1), K₃[Fe(OOCCH₂COO)₃]×3H₂O (2), K₃[Fe(OOCCH=CHCOO)₃]×3H₂O (3), K₃[Fe(OOC-1,2-(C₆H₄)-COO)₃]×3H₂O (4) have been synthesized and characterized using a combination of physicochemical techniques. The thermal decomposition behaviour of these complexes have been investigated under dynamic air atmosphere upto 800 K. All these complexes undergo a three-step dehydration/decomposition process for which the kinetic parameters have been calculated using Freeman-Carrol model as well as using different mechanistic models of the solid-state reactions. The trisoxalato and trismalonato ferrate(III) complexes undergo rapid dehydration at lower temperature below 470 K. At moderately higher temperatures (i.e. >600 and 500 K, respectively) they formed bis chelate iron(III) complexes. The trismalonato and trismaleato complexes dehydrate with almost equal ease but the latter is much less stable to decomposition and yields FeCO₃ below 760 K. The cis-dicarboxylate complexes particularly with maleate(2-) and phthalate(2-) ligands are highly prone to the loss of cyclic anhydrides at moderately raised temperatures. The thermal decomposition of the tris(dicarboxylato)iron(II) to iron oxide was not observed in the investigated temperature range up to 800 K. The dehydration processes generally followed the first or second order mechanism while the third decomposition steps followed either three-dimensional diffusion or contracting volume mechanism.     

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.     

Tricaesium tris(oxalato‐κ2O1,O2)chromate(III) dihydrate

The title compound, Cs₃[Cr(C₂O₄)₃]·2H₂O, has been synthesized for the first time and the spatial arrangement of the cations and anions is compared with those of the other members of the alkali metal series. The structure is built up of alternating layers of either the d or l enantiomers of [Cr(oxalate)₃]³⁻. Of note is that the distribution of the [Cr(oxalate)₃]³⁻ enantiomers in the Li⁺, K⁺ and Rb⁺ tris(oxalato)chromates differs from those of the Na⁺ and Cs⁺ tris(oxalato)chromates, and also differs within the corresponding BEDT‐TTF [bis(ethylenedithio)tetrathiafulvalene] conducting salts. The use of tris(oxalato)chromate anions in the crystal engineering of BEDT‐TTF salts is discussed, wherein the salts can be paramagnetic superconductors, semiconductors or metallic proton conductors, depending on whether the counter‐cation is NH₄⁺, H₃O⁺, Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺. These materials can also be superconducting or semiconducting, depending on the spatial distribution of the d and l enantiomers of [Cr(oxalate)₃]³⁻.     

Thermal dehydration and decomposition of M[M(C2O4)2]·xH2O (x=3 forM=Sr(II) andx=6 forM=Hg(II))

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C₂O₄)₂]·3H₂O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C₂O₄)₂]·6H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO₃ was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO₃ and SrC₂O₄ around 455°C. Sharp phase transition from γ-SrCO₃ to β-SrCO₃ indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E ^*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C₂O₄)₂]·3H₂O has been proposed.     

Solid state photodecomposition of alkaline earth tris/malonato/ferrates/III/

Solid state photolysis of alkaline earth tris/malonato/ferrates/III/, i.e., M₃[Fe(CH₂C₂O₄)₃]₂.xH₂O /M=Mg, Ca, Sr, Ba/ has been investigated employing Mössbauer, infrared and reflectance spectroscopic techniques. The complexes were irradiated for 400 h using a medium pressure mercury vapour lamp of 250 Watts. Photoreduction led to the formation of M[Fe^II(CH₂C₂O₄)₂(H₂O)₂]. The extent of photoreduction showed the following order: Ca>Sr>Mg>Ba. The results have been compared with those of analogous alkaline earth tris/oxalato/ferrates/III/.     

Physico-chemical Studies on Thermal Decomposition of Alkali Tris(maleato)ferrates(III)

The thermal decomposition of alkali tris(maleato)ferrates(III), M₃ [Fe(C₂ H₂ C₂ O₄ )₃ ] (M =Li, Na, K) has been studied isothermally and non-isothermally employing simultaneous TG-DTG-DTA, XRD, Mössbauer and IR spectroscopic techniques. The anhydrous complexes decompose in the temperature range 215–300°C to yield Fe(II)maleate as an intermediate followed by demixing of the cations forming α-Fe₂ O₃ and alkali metal maleate/oxalate in successive stages. In the final stage of remixing of the cations (430–550°C) a solid state reaction occurs between α-Fe₂ O₃ and alkali metal carbonate leading to the formation of fine particles of respective ferrites. The thermal stabilities of the complexes have been compared with that of alkali tris(oxalato)ferrates(III).     

Thermal Investigations of M[La(C2O4)3]⋅xH2O (M=Cr(III) and Co(III))

The complexes M[La(C₂O₄)₃]⋅xH₂O (x=10 for M=Cr(III) and x=7 forM=Co(III)) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR, reflectance and powder X-ray diffraction (XRD) studies. Thermal investigations using TG, DTG and DTA techniques in air of chromium(III)tris(oxalato)lanthanum(III)decahydrate, Cr[La(C₂O₄)₃]⋅10H₂O showed the complex decomposition pattern in air. The compound released all the ten molecules of water within ∼170°C, followed by decomposition to a mixture of oxides and carbides of chromium and lanthanum, i.e. CrO₂, Cr₂O₃, Cr₃O₄, Cr₃C₂, La₂O₃, La₂C₃, LaCO, LaCrO_x (2<x<3) and C at ∼1000°C through the intermediate formation of several compounds of chromium and lanthanum at ∼374, ∼430 and ∼550°C. Thecobalt(III)tris(oxalato)lanthanum(III)heptahydrate, Co[La(C₂O₄)₃]⋅7H₂O becomes anhydrous around 225°C, followed by decomposition to Co₃O₄, La₂(CO₃)₃ and C at ∼340°C and several other mixture species of cobalt and lanthanum at∼485°C. The end products were identified to be LaCoO₃, Co₃O₄, La₂O₃, La₂C₃, Co₃C, LaCO and C at ∼ 2>1000°C. DSC studies in nitrogen of both the compounds showed several distinct steps of decomposition along with ΔH and ΔSvalues. IR and powder XRD studies have identified some of the intermediate species. The tentative mechanisms for the decomposition in air are proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mössbauer studies on the thermolysis of manganese tris(malonato)ferrate(III)hexahydrate

Summary The thermal decomposition of manganese tris(malonato)ferrate(III) hexahydrate, Mn₃[Fe(CH₂C₂O₄)₃]₂ ^. 6H₂O has been investigated from ambient temperature to 600 °C in static air atmosphere using various physico-chemical techniques, i.e., simultaneous TG-DTG-DSC, XRD, M?ssbauer and IR spectroscopic techniques. Nano-particles of manganese ferrite, MnFe₂O₄, have been obtained as a result of solid-state reaction between a-Fe₂O₃ and MnO (intermediate species formed during thermolysis) at a temperature much lower than that for ceramic method. SEM analysis of final thermolysis product reveals the formation of monodisperse manganese ferrite nanoparticles with an average particle size of 35 nm. Magnetic studies show that these particles have a saturation magnetization of 1861G and Curie temperature of 300 °C. Lower magnitude of these parameters as compared to the bulk values is attributed to their smaller particle size.     

Synthesis and some properties of anionic chloranilate complexes of iron(iii). Crystal and molecular structure of rubidium and cesium chloranilatoferrates

New anionic chloranilate complexes of iron(iii) Cs[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (1), Rb[Fe(C₆O₄Cl₂)₂(H₂O)₂]·4H₂O (2), Rb₂[Fe(C₆O₄Cl₂)₂(H₂O)₂]₂·5H₂O (3), Cs₃Fe(C₆O₄Cl₂)₃ (4), (Bu₄N)Fe(C₆O₄Cl₂)₂ (5), (Bu₄N)₄Fe₂(C₆O₄Cl₂)₅ (6), and (R₄N)₃Fe(C₆O₄Cl₂)₃ (R = Pr (7), Bu (8), C₅H₁₁ (9)) were synthesized in an aqueous medium. The Mössbauer spectra of the synthesized chloranilatoferrates are characteristic of the high-spin state of Fe^III in an octahedral oxygen coordination. The crystal and molecular structures of compounds 1–3 were determined by X-ray diffraction. The complex anions [Fe(C₆O₄Cl₂)₂(H₂O)₂]^2? involved in these compounds are composed of two chelate chloranilate ions and two water molecules trans-(1,2) or cis-coordinated (3) to the iron atom. Since tetraalkylammonium tris(chloranilato)ferrates 7–9 and binuclear complex 6 are soluble in many organic solvents, they are promising precursors for the synthesis of metal-organic coordination polymers. Tetrabutylammonium bis(chloranilato)ferrate (Bu₄N)Fe(C₆O₄Cl₂)₂ (5) is the first example of the preparation of an anionic chloranilate complex of iron(iii) with a plausible chain structure in an aqueous medium.     

Thermal and structural investigation of some oxalato-niobium complexes

Strontium tris(oxalato)oxoniobate, Sr₃[NbO(C₂O₄)₃]₂ · 8 H₂O has been synthesized and characterized by elemental analysis, infrared spectroscopy and powder X-ray diffraction. A mechanism of thermal decomposition is suggested on the basis of differential thermal analysis. The conditions of strontium metaniobate formation, as final product of the thermal decomposition, have been established.     

Homoleptic 2,2′‐bipyridine metalates(–I) of iron and cobalt,one cocrystallized with an anthracene radical anion and the other with neutral anthracene

Homoleptic 2,2′‐bipyridine (bipy) metalates of iron and cobalt have been synthesized directly from the corresponding homoleptic anthracene metalates. In the iron structure, bis[([2.2.2]cryptand)potassium(I)] tris(2,2′‐bipyridine)ferrate(–I) anthracene(–I), [K(C₁₈H₃₆N₂O₆)]₂[Fe(C₁₀H₈N₂)₃](C₁₄H₁₀), the asymmetric unit contains one potassium complex cation in a general position, the Fe center and one and a half bipy ligands of the ferrate complex on a crystallographic twofold axis that includes the Fe atom, and one half of an anthracene radical anion whose other half is generated by a crystallographic inversion center. The cations and anions are well separated and the geometry about the Fe center is essentially octahedral. In the cobalt structure, ([2.2.2]cryptand)potassium(I) bis(2,2′‐bipyridine)cobaltate(–I) anthracene hemisolvate tetrahydrofuran (THF) disolvate, [K(C₁₈H₃₆N₂O₆)][Co(C₁₀H₈N₂)₂]·0.5C₁₄H₁₀·2C₄H₈O, the asymmetric unit contains the cation, anion, and both cocrystallized THF solvent molecules in general positions, and one half of a cocrystallized anthracene molecule whose other half is generated by a crystallographic inversion center. The cation and anion are well separated and the ligand planes in the cobaltate anion are periplanar. Each anthracene molecule is midway between and is oriented perpendicular to a pair of symmetry‐related bipy ligands such that aromatic donor–acceptor interactions may play a role in the packing arrangement. The lengths of the bonds that connect the bipy rings support the assertion that the ligands are bipy radical anions in the iron structure. However, in the case of cobalt, these lengths are between the known ranges for a bipy radical anion and a bipy dianion, and therefore no conclusion can be made from the crystallography alone. One cocrystallized THF solvent molecule in the cobalt structure was modeled as disordered over three positions with appropriate geometric and thermal restraints, which resulted in a refined component mass ratio of 0.412 (4):0.387 (3):0.201 (3).     

Solid complexes of iron(II) and iron(III) with rutin

Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C₂₇H₂₉O₁₆)·5H₂O, (2) Fe₂OH(C₂₇H₂₇O₁₆)·9H₂O, (3) Fe(OH)₂(C₂₇H₂₉O₁₆)·8H₂O, (4) [Fe₆(OH)₂(4H₂O)(C₁₅H₇O₁₂)SO₄]·10H₂O. The coordination site in a rutin molecule was established on the basis of spectroscopic data (UV–Vis and IR). It was supposed that rutin was bound to the iron ions via 4C=O and 5C—oxygen in the case of (1) and (3). Groups 5C–OH and 4C=O as well as 3′C–OH and 4′C–OH of the ligand participate in binding metals ions in the case of (2). At an excess of iron(III) ions with regard to rutin under the synthesis conditions of (4), a side reaction of ligand oxidation occurs. In this compound, the ligands’ role plays a quinone which arose after rutin oxidation and the substitution of Fe(II) and Fe(III) ions takes place in 4C=O, 5C–OH as well as 4′C–OH, 3′C–OH ligands groups. The magnetic measurements indicated that (1) and (3) are high-spin complexes.     

Synthesis, Characterization and Thermal Decomposition of M1[M2(C2O4)2]xH2O (x=5 for M1=Co and x=4 for M1=Cd; M2=Ni)

Cobalt bis(oxalato)nickelate pentahydrate, Co[Ni(C₂O₄)₂]5H₂O and cadmium bis(oxalato)nickelate tetrahydrate, Cd[Ni(C₂O₄)2]4H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA ) in air showed that both the compound of cobalt and cadmium produced the oxide, MNiO_x (x=3 for M=Co; x=2 for M=Cd ) at 325 and 360°C respectively. DSC studies in nitrogen attributed only the mixture of both the metal at the end. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of lithium tris (malonato) ferrate(III) tetrahydrate

Thermal decomposition of lithium tris (malonato) ferrate (III) tetrahydrate i.e. Li₃[Fe(CH₂C₂O₄)₃].4H₂O has been studied in the temperature range of 353–873 K in static air atmosphere using Mössbauer, infrared spectroscopy and nonisothermal techniques (TG-DTG-DTA). The anhydrous complex decomposed into ferric oxide of varying particle sizes and alkali metal malonates/carbonates in succesive stages. Fimally a solid state reaction between -Fe₂O₃ and alkali metal carbonate gives fine particles of lithium ferrite (LiFeO₂) at a temperature lower than for oxalate precursor and for ceramic method.     

Synthesis,crystal structures and magnetic properties of two iron (II) tris(pyridyl)phosphine selenides complexes

We reported the synthesis of tris(pyridyl)phosphine selenide (TppSe) and tris(4-methylpyridin-2-yl)phosphine selenide (MeTppSe), which were prepared by a simple and straightforward one-pot method with red phosphorus in a KOH/DMSO suspension, and treatment of resulted phosphines with selenium in hot toluene. These compounds were characterized by mass spectroscopy, ¹H, ¹³C and ³¹P NMR spectroscopies and the structure of MeTppSe was characterised by a single-crystal X-ray diffraction. Furthermore, The reactions of selenides with Fe(ClO₄)₂·6H₂O afforded two new iron(II) mononuclear metal complexes [Fe(TppSe)₂][ClO₄]₂·3DMF (1) and [Fe(MeTppSe)₂][ClO₄]₂·2DMF (2). Detailed structural analyses and magnetic susceptibility measurements confirm no spin transition from low-spin to the high-spin state between 2 and 300 K in two iron(II) complexes.