Bet nitrogen adsorption studies of iron oxides from natural and synthetic sources.

A vacuum microbalance technique has been used to obtain the surface areas and porosities of iron oxyhydroxides derived from Fe(III) and Fe(II) sources. The pore shape of the Fe(III)-derived material was of the wide-bodied, narrow-necked type, whereas the Fe(II)-derived precipitates were composed of parallel plates or slit-shaped pores. The surface area of the Fe(II)-derived material was found to be influenced by the temperature of the precipitate formation. These differences in surface character are discussed in relation to the adsorption of trace constituents at the iron oxyhydroxide-water interface.     

Structural and electronic relationships between conducting iron niobates and iron tungstates

Members of the system FeNbO and FeWO were compared, and their electronic properties were correlated with the structural parameters. The compounds crystallize as ordered variants of the basic α-PbO₂ structure, and the nature of the ordering of the [FeO₆] and [NbO₆] or [WO₆] octahedra determines the conductivity which may be observed for these phases.     

Preparation and characterization of the catalytically active forms of rare earth oxides

Catalytically active forms of the rare earth oxides Ln₂O₃(Ln = La, Sm, Eu, Dy, Ho, and Yb), Pr₆O₁₁, and CeO₂ have been prepared. The dehydration behavior of the precursors of these oxides has been studied by XRD, TG, DTA, TPD-MS, IR, and adsorption-desorption isotherms of N₂ at −196°C. Thermal analyses show that in most cases the dehydration takes place through an intermediate oxyhydroxide LnO (OH) that decomposes to the respective oxide at around 400°C. Strongly held difficult to remove carbonates were present on the surface, e.g., for Yb₂O₃ it was necessary raise the outgassing temperature to 700°C to achieve carbonate decomposition. At temperatures around 500°C these oxides are well crystallized and have moderate specific surface areas (10–40 m²g⁻¹). As a representative of the series, a detailed study of the dehydration and surface decarbonation of Yb₂O₃ was carried out by means of TPD-MS and infrared spectroscopy.     

Preparation and properties of substituted iron tungstates

Polycrystalline samples of members of the systems Fe_2?xCr_xWO₆ and Fe_1?xMn_xWO₄ were prepared and single crystals of Fe_1?xMn_xWO₄ were grown by chemical vapor transport. Their crystallographic parameters and electrical properties were characterized. Fe₂WO₆ crystallizes with the tri-α-PbO₂ structure and is an n-type semiconductor. For 0.3 ≤ x ≤ 2, the system Fe_2?xCr_xWO₆ crystallizes with the inverse trirutile structure and is nonconducting due to blocking of iron(II)-iron(III) conduction paths by chromium(III). For 0 ≤ x ≤ 1, the system Fe_1?xMn_xWO₄ crystallizes with the wolframite structure and shows p-type semiconducting behavior. The nature of the variation of resistivity with x of Fe_1?xMn_xWO₄ suggests that interchain electron transfer may occur in this structure.     

Relative stabilities of layered perovskite and pyrochlore structures in transition metal oxides containing trivalent bismuth

In order to investigate the factors determining the relative stabilities of layered perovskite and pyrochlore structures of transition metal oxides containing trivalent bismuth, several ternary and quaternary oxides have been investigated. While d⁰ cations stabilize the layered perovskite structure, cations containing partially-filled d orbitals (which suppress ferroelectric distortion of MO₆ octahedra) seem to favor pyrochlore-related structures. Thus, the vanadium analogue of the layered perovskite Bi₄Ti₃O₁₂ cannot be prepared; instead the composition consists of a mixture of pyrochlore-type Bi_1.33V₂O₆, Bi₂O₃, and Bi metal. The distortion of Bi_1.33V₂O₆ to orthorhombic symmetry is probably due to an ordering of anion vacancies in the pyrochlore structure. None of the other pyrochlores investigated, Bi₂NbCrO₇, Bi₂NbFeO₇, TlBiM₂O₇ (M = Nb, Ta), shows evidence for cation ordering in the X-Ray diffraction patterns, as indeed established by structure refinement of TlBiNb₂O₇.     

Solvent extraction and spectrophotometric determination of iron(II) with 2,2′-dipyridyl-2-quinolylhydrazone

2,2′-Dipyridyl-2-quinolylhydrazone (DPQH) was used for the spectrophotometric determination of trace amount of iron(II) after the extraction process. Iron(II) reacts with DPQH at pH 3.4–4.5 to form a water-insoluble 1:2 complex, which can be extracted with many kinds of organic solvent. The extracted species with benzene has absorption maxima at 473, 504, and 644 nm and obeyed Beer's law over the range 0–14 μg of iron at 504 nm and 0–33 μg at 644 nm. The molar absorptivities at 504 and 644 nm are 3.14 × 10⁴ and 1.30 × 10⁴M^?1 cm^?1, respectively. DPQH is one of the most sensitive reagents for iron(II) and trace amount of iron(II) can be determined in the presence of fairly large amounts of other ions. Possible equilibria involved in the extraction process were also studied.     

Dielectric studies on sulphonated novolacs

The dielectric constants of novalac type of phenolic resins and their sulphonated derivatives were studied as a function of frequency, temperature and extent of sulphonation. The effect of moisture on the dielectric constant has also been reported. Introduction of —SO₃H groups into the polymer matrix increases the dielectric constant by several orders, while the resin continues to exhibit low losses.     

Synthetic studies relating to acetylergosterol-(tricarbonyl)iron

Acetylergosterol(tricarbonyl)iron has been prepared in good yield using benzylideneacetone(tricarbonyl)iron. The steroidal complex may be hydroborated or subject to osmolysis, to yield potential vitamin D precursors.     

Ferromagnetic resonance studies in some polycrystalline magnesium nickel ferrites

Ferromagnetic resonance measurements were carried out on various compositions of magnesium nickel ferrites prepared by various heat treatments. Corrections were applied for polycrystalline and size effects for calculating the g factor and linewidth. The variation of these parameters has been explained on the basis of the cation distribution in these compounds as obtained from magnetization data assuming a collinear model of spin distribution.     

Mechanistic studies on the photo-oxidation of commercial poly(butadiene)

Products from both the thermal and photo-oxidation of poly-butadiene have been studied using various analytical techniques such as infra-red and ultra-violet spectroscopy, gas-liquid chromatography and phosphorescence emission and phosphorescence excitation spectroscopy. Analyses have allowed a plausible mechanism to be formulated for the photo-oxidation of this polymer, consistent with all the observed physical and chemical changes. Both photo- and thermal oxidative polymer degradation initially result in the formation of α, β-unsaturated carbonyls which, under photo-degrading conditions, are subsequently photolysed to yield the observed final products.     

High-pressure magnetic susceptibility studies of spin-state transition in Fe(II) complexes

High-pressure magnetic susceptibility measurements have been carried out on Fe(dipy)₂(NCS)₂ and Fe(phen)₂(NCS)₂ in the pressure range 1–10 kbar and tempeature range 80–300 K in order to investigate the factors responsible for the spin-state transitions. The transitions change from first order to second or higher order upon application of pressure. The temperature variation of the susceptibility at different pressures has been analysed quantitatively within the framework of available models. It is shown that the relative magnitudes of the ΔG⁰ of high-spin and low-spin conversion and the ferromagnetic interaction between high-spin complexes determines the nature of the transition.     

Thermal studies on oxalate complexes. II. Complexes of iron (III) and chromium (III)

The decomposition of solid K₃[Fe(C₂O₄)₃] · 2 H₂O and K₃[Cr(C₂O₄)₃] · 3 H₂O has been studied using TGA and DSC. After dehydration, the chromium compound was found to decompose by the loss of CO in two steps, the loss of CO₂ and additional CO, and finally the loss of CO₂. The final product appears to be either K₃CrO₃ or the mixed oxides of chromium and potassium. Kinetic parameters and enthalpy data are presented for these reactions. In the case of K₃[Fe(C₂O₄)₃] · 2 H₂O, dehydration is followed by the loss of CO₂ and CO, CO₂ alone, and finally CO. The final product appears to be a basic carbonate of the type K₃[FE(O)₂(CO₃)]. Kinetic and thermal data are presented for most of these decomposition reactions.     

Predicting points of zero charge of oxides and hydroxides

Pauling's electrostatic valence principle has been applied to describe the surface-charging mechanism of oxides in an aqueous environment. This approach has led to the development of an equation with which one can predict the points of zero charge (PZC) of oxides and hydroxides from crystallographic data. The equation proposed in the present work is an improved version of Parks' PZC equation. The improvements are the following: (i) The equation does not incorporate correction terms to take the cation coordination numbers into account; (ii) the PZC of a complex oxide can be predicted directly from crystallographic data instead of from “assumed” PZCs of its component oxides; and (iii) one can use the mean metal-oxygen bond distance of a crystal instead of the ionic radii tabulated by Parks, which are not consistent with the up-to-date values.     

An electron microscopy investigation of tin-molybdenum oxides

Tin-molybdenum oxides prepared by the calcination of precipitates at high temperatures have been investigated by electron microscopy. The solids, which adopt the rutile-related tin(IV) oxide-type structure, are composed of crystalline particles containing planar defects, some of which have been characterized as twin boundaries. Although molybdenum has been found to be concentrated at these planar faults the examination of pure tin(IV) oxide prepared by similar methods shows that their formation is not dependent on the presence of molybdenum. It is suggested that molybdenum segregates to the twin boundaries during the calcination process to accommodate itself in more favorable coordination.     

Solid-state reactions between alkali persulfates and oxides of corundum structure

The effects of three corundum structure oxides, α-Al₂O₃, α-Cr₂O₃, and α-Fe₂O₃, on the thermal decomposition of sodium and potassium peroxodisulfates (persulfates) under non-isothermal static air conditions and using various oxide/persulfate molar ratios, have been thermoanalytically investigated. Compounds such as Na₃Al(SO₄)₃, K₃Al(SO₄)₃, Cr₂(SO₄)₃, K₃Cr(SO₄₃, and Na₃Fe(SO₄)₃ are identified by X-ray diffractometry and conventional chemical analysis. The molar ratios as well as temperatures of the stoichiometric formation for these compounds have been established. At higher temperatures, α-Al₂O₃ acts as a promoter catalyst for the decomposition of pyrosulfate to sulfate, whereas α-Cr₂O₃ behaves as a retarder for the decomposition of persulfate. A eutectic mixture is formed between K₃Al(SO₄) and K₂SO₄ at 675°C. Also, K₃Fe(SO₄)₃ is identified as two crystalline phases.     

The unusual iron complex with a trimethylenemethane type ligand, (η5-cyclopentadienyldicarbonylmanganese)- (phenylmethylene)carbomethaneiron tricarbonyl [Cp(CO)2 MnC(CO)CHPh]Fe(CO)3

The binuclear complex with composition [Cp(CO)₂ MnC(CO)CHPh]Fe(CO)₃ is obtained by interaction of CpMn(CCHPh)(CO)₂ with Fe₂C0)₉. An X-ray study of this complex has shown that besides three carbonyl groups the iron atom is covalently bonded to four atoms, viz. the carbon of a phenylmethylene group, the carbon of a bridging CO group, the manganese atom and the central carbon of the organomanganese ligand lying just above iron. It seems to be the first example of a heteroatomic analogue of trimethylenemethane complexes.