Thermal studies on iron titanate spinel

Thermogravimetry and X-ray analysis show that the iron titanate spinel sample is nonstoichiometric and has the formula Fe_1.76Ti_1.12O₄. On heating in air below 573 K, it undergoes surface oxidation and on further heating DTA and TG show that it undergoes bulk oxidation in three stages. X-ray analysis and resistivity measurements show that while octahedral Fe²⁺ ions are oxidised, the spinel structure is retained and during Fe _tet ²⁺ oxidation a metastable phase is formed and when the oxidation is complete, the pseudobrookite phase is formed.

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Zusammenfassung Durch TG und Röntgendiffraktion zeigte sich, da\ eine EisentitanatSpinellprobe keine stöchiometrische Zusammensetzung, sondern die Formel Fe_1.76Ti_1.12O₄ besitzt. Bei Erhitzen in Luft wird die Probe unterhalb 573 K an der OberflÄche oxidiert. Bei weiterem Erhitzen zeigen DTA- und TG-Daten eine dreistufige Oxidation im gesamten Volumen. Röntgendiffraktions- und Widerstandsuntersuchungen zeigen, da\ bei der Oxidation von oktaedrischen Fe²⁺-Ionen die Spinellstruktur beibehalten wird und bei der Fe _tet ²⁺ Oxidation eine metastabile Phase und nach vollstÄndiger Oxidation eine Pseudobrookitphase gebildet wird.

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The authors wish to thank DST for financial sanction for this work and Durga Basak wishes to thank DST for awarding JRF. The authors also wish to thank Dr. A. K. Kar for his encouragement and help throughout this work.     

Mössbauer studies on one-dimensional iron phthalocyanines

Summary Magnetic moments and⁵⁷Fe Mössbauer spectra at room temperature and at liquid nitrogen temperature of polynuclear ligand-bridged iron phthalocyanines, FePcL (L = pyrazine and 4,4-bipyridyl), are reported. The experimental data are in agreement with a pseudo-octahedral environment around the iron(II) cation. Partially oxidized derivatives, FePc(pz)I_0.26 and FePc(bipy)I_1.06 have been synthesized and their⁵⁷Fe Mössbauer spectra and magnetic moments within the same temperature range obtained. Oxidation is shown to be metal centred and the iodine is found to be in I^– form for FePc(pz)_0.26 and as both I^– and I ₃ ^– species for FePc(bipy)I_1.06. While the magnetic moment of FePc(pz) increases upon oxidation, the opposite occurs for FePc(bipy).     

Adsorption studies of arsenic on Mn-substituted iron oxyhydroxide

Mn-substituted iron oxyhydroxide (Mn(0.13)Fe(0.87)OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m2 g(-1) and a pore volume of 0.35 cm3 g(-1). Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 degrees C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g(-1), respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases, adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15-24 and 45-67 kJ mol(-1) for arsenate and arsenite, respectively.     

Extraction of iron(III) dithizonate

The extraction of iron(III) with dithizone in the presence of different anions, was studied. The complex cation Fe(HDz)₂⁺ formed is extracted in the presence of sodium acetate and tetraphenylborate or capric acid as an ion associate, (Fe(HDz)₂)⁺ X^-, where X^- is the anion of the indicated compounds. In the presence of perrhenate ion, rhenium is coextracted with iron in a 1:1 ratio; the ion associate (Fe(HDz)₂)⁺ (ReO₄)^- is apparently extracted. The isolation of iron from alkali metal chlorides and its atomic-absorption determination is described.     

Adsorption studies of iron(III) on chitin

Adsorption of ferric ions by chitin was studied by the batch equilibration method. The influence of particle size and dosage of the adsorbant, contact time, initial concentration of the adsorbate and temperature were experimentally verified. The effect of anions like chloride, nitrate and sulphate and also of cations like zinc, chromium and copper on the adsorption of iron(III) was determined. The time dependence of fraction of adsorption,Yt, at varying particle sizes and doses of chitin and the intraparticle diffusion rate constants,k _p , of the adsorption process were calculated. Thermodynamic and equilibrium parameters of the reaction were determined to understand the sorption behaviour of chitin. The results revealed that the adsorption of iron(III) by chitin is spontaneous, endothermic and favourable.     

XPES and UVPES studies of iron oxides

X-Ray and uv photoelectron spectra of FeO, Fe₂O₃, and Fe₃O₄ have been studied along with those of a few model compounds. It has been possible to assign distinct bands due to Fe²⁺ and Fe³⁺ in the 3d, 3p, 3s, and 2p bands of Fe₃O₄. The spectra of Fe₃O₄ do not show major changes through the Verwey transition.     

Synthetic and electrochemical studies on alkynyl complexes of iron and ruthenium

Cyclic voltammetric studies on a series of alkynyl complexes [M(CCR)L₂(η- C₅R′₅)] (M = Fe or Ru; R = Ph, Bu_n or Bu_t; L = CO or P-donor ligand; R′ = H or Me) reveal a one-electron oxidation at a glassy carbon electrode in dichloromethane. The chemical reversibility of the oxidation process is dependent upon all four variables (M, L, R and W) considered in this investigation.     

Extraction studies of copper with mesityl oxide

Summary A method has been developed for the extraction of copper(II) both at microgram and milligram level from bromide media using mesityl oxide as an extractant. The copper-bromo complex formed at 3.5 mol/l hydrobromic acid concentration showed quantitative extraction into mesityl oxide. Various experimental parameters such as acid concentration, period of equilibration, stripping agents and diverse ions have been studied. The stripped metal ion is monitored spectrophotometrically or by atomic absorption spectrometry (AAS). The method is applicable to the analysis of pharmaceutical and alloy samples.     

Extraction studies of antimony bromide into benzene

Antimony(III) can be extracted rapidly and quantitatively into benzene from a 10 M H₂SO₄–0.03 M HBr system. The extracted antimony bromide has an antimony to bromine ratio of 1:3. Under the above optimum conditions for extraction of antimony, the behaviour of 35 other elements was studied; As³⁺, Ge⁴⁺, Se⁴⁺, and Sn²⁺ were extracted almost quantitatively, and the percentage extraction of Hg²⁺, Bi³⁺, and Te⁴⁺ was 74.1%, 10% and 5.5% respectively. The extraction of the elements into benzene from a 5 M H₂SO₄–0.01 M KI system was also investigated, A comparison of the two systems is given.     

Spectroscopic studies on iron complexes of different anthracyclines in aprotic solvent systems

Iron complexes of daunorubicin, idarubicin, pirarubicin, and doxorubicin in anhydrous DMF were studied by UV/vis, CD, fluorescence, M?ssbauer, and EPR spectroscopy. Titration studies of the metal-free anthracyclines showed one (UV-detectable) deprotonation step requiring 2 equiv of base, compared to 1 equiv for quinizarine. Metal complexation was studied at three different metal/ligand ratios, and with increasing amounts of base. The results obtained from optical spectroscopy show the existence of two different complex species and give clear indications for the requirements of metal complexation. Complex species I, formed at a low iron-to-ligand ratio, is less dependent on base addition than complex species II formed with equimolar ferric ion. EPR and M?ssbauer experiments provide further insight into the structures of both complex species. Lack of spin density of the M?ssbauer samples in EPR indicates spin coupling between the metal centers. M?ssbauer spectra consist of single quadrupole doublets with values typical for high-spin ferric ion in an octahedral arrangement. The M?ssbauer spectroscopic features at 7 T exclude the presence of S = 0 dimers. Complex I represents a monomeric ferric iron complex whereas complex II is consistent with a more or less aggregrated oligomeric Fe-anthracycline system.     

Structural studies on some iron 8-oxi-quinolinates using Mössbauer spectroscopy

Using Mössbauer spectroscopy the quinolinates of iron/II/ and iron/III/ have been studied. In iron/II/ quinolinate three sublattices were evidenced, two of them being attributed to Fe²⁺ ions and the third to Fe³⁺ impurities. In the iron/III/ quinolinate five structural sublattices were found, two of them containing Fe³⁺ ions, the other two Fe²⁺ ions and the fifth may be attributed to the interstitial Fe³⁺ ions.     

Electrochemical and spectral studies on the reductive nitrosylation of water-soluble iron porphyrin

The reaction of iron(III) (meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(III)TMPyP) with nitric oxide (NO) was studied by electronic absorption spectroscopy, ESR, and electrochemical and spectroelectrochemical techniques in aqueous solutions with pH from 2.2 to 12.0. Fe(III)TMPyP has been found to undergo a reductive nitrosylation in all pHs, and the product of nitric oxide binding to the porphyrin has been determined as iron(II) porphyrin nitrosyl complex ([Fe(II)(NO)TMPyP]). The rate of the reductive nitrosylation exhibits a tendency to get faster with increase in pH. An intermediate species was observed around neutral pH by spectroelectrochemical technique and was proposed to be the iron(II) nitrosyl complex of the mu-oxo dimeric form of FeTMPyP, which is known to be a predominant in neutral solutions.     

Physico-chemical studies on the thermal decompositions of iron(III) phthalates

The thermal decompositions of basic salts of iron(III)o-phthalate sesquihydrate, Fe(C₈H₄O₄)(OH)·1.5H₂O, iron(III)m-phthalate trihydrate, Fe(C₈H₄O₄)(OH)·3H₂O, and iron(III)p-phthalate monhydrate, Fe(C₈H₄O₄)(OH)·H₂O, have been investigated from ambient temperature up to 973 K in air using Mössbauer and infrared spectroscopy, derivatography (DTG-DTA-TG) and X-ray diffraction. The thermal decomposition proceeds without reduction to Iron(II) species in the cases of iron(III)o-phthalate and iron(III)p-phthalate, whereas iron(II) species have been detected in the case of basic iron(III)m-phthalate.-Fe₂O₃ is formed as the end-product. Increase in the particle size of the-Fe₂O₃ with increasing decomposition temperature has also been observed.

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Zusammenfassung Die thermische Zersetzung basischer Salze von Eisen(III)-o-phthalat-Sesquihydrat, Fe(C₈H₄O₄)(OH) · 1,5H₂O, Eisen(III)-m-phthalat-Trihydrat, Fe(C₈H₄O₄)(OH)·3H₂O, und Eisen(III)-p-phthalat-Monohydrat, Fe(C₈H₄O₄)(OH)·H₂O, wurden im Temperaturbereich von Raumtemperatur bis 973 K in Luft mittels Mössbauer- und IR-Spektroskopie, Derivatographie (DTG-DTA-TG) und Röntgendiffraktometrie untersucht. Im Gegensatz zu basischem Eisen(III)-m-phthalat erfolgt bei den entsprechendeno- undp-Phthalatverbindungen im Verlaufe der Zersetzung keine Reduktion zu Eisen(II)-Species.-Fe₂O₃ wird als Endprodukt erhalten. Mit steigender Zersetzungstemperatur nimmt die Größe der-Fe₂O₃-Partikel zu.

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c Fe(C₈H₄O₄)(OH)·vH₂O, x = 1.5,3 1, , -, - n-, 973 . , , ë . - n- , m- . -Fe₂O₃. -Fe₂O₃.

     

Extraction studies of Tabernanthe iboga and Voacanga africana

The root bark of Tabernanthe iboga contains ibogaine as its predominant alkaloid and has been an important source of it. Ibogaine is used experimentally to interrupt drug addiction and allow therapeutic intervention, but is currently unaffordable to doctors in less economically developed countries. To meet this need, an extraction of alkaloids from T. iboga root bark was optimized and simplified to use only diluted vinegar and ammonia, and was successfully applied to related alkaloids from Voacanga africana bark also. The alkaloids were converted to their hydrochlorides and purified, and the minor alkaloids were recovered.     

Polyamine-based anion receptors: Extraction and structural studies

In the discussion that follows some of the more recent progress in the area of anion binding by synthetic polyamine receptors is presented, with emphasis given to work undertaken by the authors’ groups. A continuing theme in these studies has been the relationship between receptor structure and its anion extraction properties.Systematic solvent extraction and structural studies for halide and perrhenate complexes with polyamines of tripodal, macrocyclic and macrobicyclic architecture that contain both aromatic moieties and four to eight amine functions have been performed in order to derive relevant structure-binding/extractability relationships. The results demonstrate that the binding and extraction behaviour of the polyamines towards halides and perrhenate is a complex function of their structural features, degree of protonation and lipophilic properties. The extraction is characterized by the preferred formation of mono- and diprotonated amine species in the organic phase. X-ray structure studies of iodide and perrhenate complexes with open-chain tetraamino derivatives and octaamino cryptands in different protonation states lead to the conclusion that in the first case only limited chelation of the anion occurs and in the second only highly protonated species are able to encapsulate the anion. The structural patterns observed are strongly influenced by the presence of water molecules in the crystals.     

Extraction and spectrophotometric determination of iron as o-phenanthroline-azide mixed ligand complex

Summary The mixed ligand complex, [Fe(Phen)₂(N₃)₂] can be extracted into nitrobenzene giving a molar absorptivity of 16750 at 510 nm. This is the basis of a photometric method for iron which may be either in the trivalent or bivalent state. The new method is free from interference from a number of substances and is more sensitive than the ferroin method.

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Zusammenfassung Der Eisen-Phenanthrolin-Azid-Mischkomplex [Fe(Phen)₂(N₃)₂] ist mit Nitrobenzol extrahierbar und gibt bei 510 nm eine molare Absorption von 16750. Darauf läßt sich eine photometrische Bestimmungsmethode für zweioder dreiwertiges Eisen begründen. Diese wird von vielen Stoffen nicht gestört und ist empfindlicher als die Ferroinmethode.