Speciation of Fe(II) and Fe(III) effect on CaCO3 crystallization

The present work was carried out to investigate separately the effect of Fe²⁺ and Fe³⁺ on the precipitation kinetics and the microstructure of CaCO₃. For this an experimental procedure was proposed. Precipitation tests were made by using the dissolved‐CO₂ degassing method. Both air and nitrogen were employed to strip the CO₂ from a Ca(HCO₃)₂ solution initially rich in this gas. At anoxic medium, it was shown that iron (II) prolongs the nucleation step and decelerates the crystalline growth rate. X‐ray diffraction analysis shows that its presence inhibits calcite and promotes aragonite variety. By using air, the reaction medium is rich in oxygen and iron (II) is rapidly oxidized. Seeing the higher solution pH (> 6.5), iron hydroxide forms before the onset of CaCO₃ precipitation and plays a role of seed permitting to initiate CaCO₃ nucleation. So, contrary to the observed effect of iron (II), the presence of iron (III) accelerates the precipitation rate of CaCO₃. As for iron (II), iron (III) inhibits calcite formation but favored the vaterite variety instead of the aragonite one.     

Tetrahedral site of Fe(III) and Cu(II) in renierite

Renierite from Congo is used in the present investigations. It contains only two transition elements iron and copper. EPR results indicate the presence of Fe(III) and Cu(II) with g values 2.03 and 2.40 respectively. Optical absorption spectrum shows several energies in UV‐Vis and NIR region. These energies indicate both Fe(III) and Cu(II) in tetrahedral site. IR spectrum confirms the presence of sulphate and hydroxyl groups in the mineral. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The thermal decomposition of aluminium hydroxide doped with Fe(III) ions

The thermal decomposition of various aluminium hydroxides doped with Fe(III) ions has been studied using ESR. The transition aluminas (η, γ, ϰ-Al₂O₃) formed at low calcination temperatures show the ESR-spectrum characteristic for Fe(III) ions incorporated in low crystalline materials. Spectra of doped reference compounds (ZnAl₂O₄, MgAl₂O₄, (dis)ordered LiAl₅O₈) showed that disorder in the cation sublattice could be responsible for this feature. The ESR spectra of aluminas (θ, x, α-Al₂O₃) formed at high calcination temperatures reveal well-defined and characteristic fine structures. Comparison with reference compounds (β-Ga₂O₃, α-Ga₂O₃) allows to draw conclusions as to the structure. The quality of the spectrum of δ-Al₂O₃ formed in the dehydration sequence of boehmite, was in between that of the low and high temperature aluminas. In order to explain some of the features observed in the various dehydration sequences, a discussion based on the coordination of the anions along lines pointed out by GORTER , has been put forward. To this end, the regularity of the anion coordination is followed within the special packing sequences of the anion layers in the dehydration products.     

The optical constants of quartz,vitreous silica and neutron-irradiated vitreous silica (I)

The infrared reflectivity of three forms of silica, α-quartz, vitreous silica and neutron-irradiated vitreous silica (≈ 2.7 × 10²⁰ neutrons cm^?2) has beenmeasured from 400–2000 cm^?1. These data have been analysed by a Kramers-Kronig transform to give the real and imaginary parts of the complex dielectric constant. Considerable care has been taken to identify and minimize errors arising in the measurements of the reflectivity spectra and in the subsequent analysis. Data are presented for the optical constants, oscillator frequencies, band strengths and halfwidths of each band. The spectra for vitreous silica and neutron-irradiated silica show two regions of absorption which are not present in the crystalline form — a strong band is observed near 950 cm^?1 and a broad band from 600–800 cm^?1. A difference spectrum obtained by subtracting the spectrum of the imaginary part of the dielectric contrast for vitreous silica from the corresponding data for neutron-irradiated silica reveals more detailed structure in the form of a weak but sharp band at 620 cm^?1. Interpretation of these results is contained in a companion paper.     

Crystal structure of bis(isothiocyanato)[2,6-diacetylpyridine bis(4-hydroxybenzoylhydrazone)]Fe(III) Chloride bis(dimethylformamide) solvate

The crystal structure of title compound (Fe[(C₂₅H₂₁N₇O₄S₂)] · 4(C₃NOH₇), where C₃NOH₇ is dimethylformamide, DMF) was determined by the X-ray diffraction method. This compound crystallizes in the monoclinic C2/c space group, Z = 4. Unit cell parameters are: a = 13.6080(5), b = 17.6375(7), c = 19.5571(6) Å, β = 108.753(2)°. The N-H...O and O-H...O interactions stabilize the molecules in the lattice. The structure contains also the solvent dimethylformamide molecules, which are connected with intermoleculer hydrogen bond. The O atoms of DMF molecules take place as acceptor atoms.     

IR-spectral study of vanadate vitreous systems

Some structural conclusions have been reached concerning vanadate glasses according to the influence of the Mⁿ⁺-ions on the vibrations of the isolated V-O-bonds and the location of the bands in the IR-spectra. They may shift with the compositions or preserve their positions.Ions of predominant electrostatic interactions are distributed between the chains and the layers in the glass structure, they interact directly with the isolated V-O bonds. As a result of this the transition from VO₅ into VO₄ is achieved directly or through intermediate complexes.It is likely that ions which participate in covalent bonds fit into vanadate chains of the glass network in substitution positions.     

Synthesis and Characterisation of Scandium (III)-, Yttrium (III)-, and Lanthanum (III) Violurate Complexes

Sc³⁺-, Y³⁺ -and La³⁺ violurate complexes were prepared. The isolated complexes are freely soluble in water, dilute mineral acids, MeOH, Me₂CO, DMF, DMS, partially soluble in AcOH and insoluble in EtOH, CHCl₃ and CCl₄. Molecular compositions of the complexes were formulated on the basis of elemental analysis, molar conductivity and infrared spectra. The IR spectra of violuric acid and its metal complexes reveal that bonding takes place through coordination bond between the central metal ion and the oxygen atom of the oxygen atom of the oximino (C N = O) group and convalenet bond between the central metal ion and oxygen atom of the phenolic (ketonic, C O H) group in the case of 1:2 and 1:3 complexes, and through coordination bond between the central metal ion and C O H and N H groups in the case of 2:3 complexes. All the isomorphous complexes detected by the X-ray powder patterns [the (2:3) Sc³⁺-VA and (2:3) Y³⁺-VA complexes, (1:2) Sc³⁺-VA, (1:2) Y³⁺-VA and (1:2) La³⁺-VA complexes, and the (1:3) Y³⁺-VA and (1:3) La³⁺-VA complexes] have similar X-ray, eletronic and IR spetrograms and chemical formulae. The electronic spectra in DMF and in nujol mulls characterise the octahedral stereochemistry for the investigated complexes.     

ESR study of structural changes in chalcogenide glasses

Structural changes in chalcogenide glasses induced by various processes such as annealing, illumination or application of a high pressure were investigated from a microscopic viewpoint by measuring changes of the ESR spectrum from Mn doped as a probe. Here, Mn incorporated in the glass network exhibits a characteristic ESR signal with g = 4.3 having a hyperfine structure. It is found that the above-mentioned processes cause a change of the lineshape of the hyperfine line and a change of the hyperfine structure constant A, both of which reflect the bonding characteristics around Mn. One of the annealing effects for bulk glasses is the increase of the A-value. The change of the A-value for well-annealed As₂Se₃ and As₄Se₅Ge₁ films occurs reversibly in sequential illumination and annealing cycles, as does the shift of the optical gap. The reversible change of the lineshape is observed for well-annealed As₂Se₃ films in the illumination and annealing cycles. Application of a high pressure to bulk glasses causes changes similar to those by illumination for annealed films. From these results it is concluded that the randomness of amorphous structure decreases by annealing and increases by illumination or application of high pressure.     

Synthesis and Crystal Structure of a Fe(III) Complex with an Isonicotinyl Hydrazone Ligand, [Fe(N-Isonicotinamidosalicylaldimine)Cl<Subscript>2</Subscript>]

Abstract  

A new complex [Fe(N-isonicotinamidosalicylaldimine)Cl₂] has been synthesized by template reaction at room temperature and structurally characterized by X-ray single-crystal analysis. The complex crystallizes in triclinic crystal system, Pī space group, a = 7.273(6) ?, b = 10.015(8) ?, c = 10.479(8) ?, α = 71.067(10)°, β = 89.964(11)°, γ = 75.528(10)°, V = 696.4(9) ?³ and Z = 2. The coordination geometry around the Fe(III) ion is a distorted trigonal bipyramid with a O₂N₁Cl₂ donor set. In the crystal structure, N–H···Cl, C–H···O and C–H···Cl hydrogen bonds and π···π stacking interactions involving aromatic and unclosed π-systems link the molecules to form supramolecular double layers.     

X-ray structures of tris(0-cyclohexyl-dithiocarbonato)bismuth(III) and tris(0-benzyl-dithiocarbonato)bismuth(III)

The crystal structures of two Bi tris xanthates are reported, namely [Bi(S₂CO-c-C₆H₁₁)₃ J and [Bi(S₂COCH₂C₆H₅)₃]. They exist as centrosymmetric dimers, owing to the presence of bridging xanthate ligands, with seven-coordinate Bi atoms. The presence of a stereochemically active lonepair of electrons in each structure distorts the coordination geometry defined by seven S atoms and causes the elongation of some of the Bi-S bond distances. Crystals of both compounds are triclinic, space groupP¯1 with unit cell dimensions for [Bi(S₂CO-c-C₆H₁₁)₃]:a=12.417(3),b=13.571(3),c=9.681(4) Å;=102.30(2),=109.21(2), =66.23(2)° andZ=2; and for [Bi(S₂COCH₂C₆H₅)₃]:a=14.747(2),b=15.966(2),c=5.991(1) Å;=95.08(1),=98.51(1), =104.92(1)° andZ=2. The structures were refined by a full-matrix least-squares procedure to finalR=0.045 using 4274 reflections for [Bi(S₂CO-c-C₆H₁₁)₃] and toR=0.027 using 3993 reflections for [Bi(S₂COCH₂C₆H₅)₃].     

Alkylpyridinium lodobismuthates(III)

Journal of Chemical Crystallography - The reaction of N-alkyl pyridinium iodide salts (RPy+I?, R?=?Me, Et, nPr, nBu) with BiI3 produced various alkyl pyridinium...     

Raman spectroscopic study of hydrogen-containing vitreous silica

It is shown by Raman spectroscopy that high-temperature hydrogen-impregnated vitreous silica contains, in addition to physically dissolved hydrogen, ≡SiOH and ≡SiH groups. A Raman-scattering peak with a wave-number shift of 3685 cm^?1 is assigned to the OH stretching vibration, a peak with a wave-number shift of 2254 cm^?1 to a SiH stretching vibration and a peak with a wave-number shift of 4135 cm^?1 to the presence of physically dissolved hydrogen. When hydrogen was replaced by deuterium, appropriate shifts of the peaks mentioned were found.     

Synthesis and X-ray diffraction study of hexaamminecobalt(III) sodium ethylenediaminetetraacetate 3.5-hydrate

The title compound [Co(NH₃)₆] [Na(EDTA-4H)],3.5H₂O has been synthesized, and its crystal structure has been determined from 2064 independent single-crystal reflections measured on a diffractometer. The crystals are tetragonal, space groupP42₁2, with unit-cell parametersa = 14.618(5) andc = 10.658(4) Å. There are four formula entities in the unit cell givingD _c = 1.562(2) g cm^–3 compared withD _m = 1.56(1) g cm^–3. The structure was solved by conventional Patterson and Fourier techniques, and refined by full-matrix least-squares methods to a final agreement factor of 3.6%. The compound contains two crystallographically independent octahedral [Co(NH₃)₆]³⁺ ions, with an average Co—N distance of 1.966(6) Å, and a seven-coordinate sodium ion which is coordinated to four carboxyl oxygens, two amine nitrogens, and a water molecule which bridges to another sodium ion. The EDTA is therefore acting in its normal hexadentate manner. The range of Na—O distances is 2.25 to 2.93 Å whereas the Na—N distance is 2.46 Å. The crystal structure is additionally stabilized by extensive hydrogen bonding among coordinated ammonias, carboxyl oxygens, and water molecules.     

Crystal structure of chloritopentamminecobalt(III) tetracyanopalladate(II)

The X-ray crystal structure of [(NH₃)₅Co(ClO₂)][Pd(CN)₄]·H₂O consists of two discrete complex ions and a water of hydration. The red crystals are triclinic, P , with lattice parameters a = 7.1992(5), b = 9.4873(7), c = 11.7752(8) Å. = 66.680(1), = 75.784(1), = 82.203(1)°, and Z = 2 giving a cell volume of 715.27(9) ų and a calculated density of 2.043 g/cm³ at 293°. The chlorite ion is O-bonded to the cobalt atom with amine N—Co distances all equal. The chlorite ion is bent with a O—Cl—O angle of 110.8(2)° and the Cl—O distances being 1.601(3) and 1.558(3) Å, the longer value for the O atom also coordinated to Co. The Pd(CN)^–2 ₄ ions are planar, C-coordinated and stack along the x-axis, separated by 3.599(1) Å and alternatively rotated by 29.9(5)°.     

ESR and Mössbauer studies of dispersed states of Fe ions in silica gels

0.01Fe₂O₃---0.99SiO₂ gels were prepared by three different sol-gel methods and the effects of the heat-treatment temperature of the gels on the ESR and Mössbauer parameters were investigated to obtain information about the change in the state of iron ions in the gel. All the gels were found to be amorphous under 600 °C, and among these three methods, the best dispersed state of Fe³⁺ ions was obtained by the method where TEOS was partially hydrolyzed with the same mole content of water before the addition of Fe(OEt)₃. It was indicated that the reaction at the sol-stage plays an important role in the degree of dispersal of Fe³⁺ ions in this system.     

Structural analysis of tris(tetra-n-butylammonium) hexakisisothiocyanatoyttrate(III)

The structural analysis of [(n-C₄H₉)₄N]₃[Y(NCS)₆] (I) using single-crystal diffraction data and full-matrix least squares refinement has been carried out. The hexaisothiocyanate complex crystallizes in the centrosymmetric triclinic space group P (No. 2) with unit cell constants of a = 12.431(1), b = 12.866(1), c = 22.750(2) Å, = 90.78(1), = 92.05(1), = 96.67(1)°, and Z = 2. The molecular unit consists of three separate cationic tetra-n-butylammonium groups and an independent hexakisisothiocyanatoyttrate anionic group in which the six thiocyanate ligands are octahedrally coordinated through the N atom to the Y central ion. Selected bond distances and angles are presented as well as the synthesis and peripheral studies of (I).     

Synthesis, modeling of the structure and kinetic study of the thermal decomposition of La(III) and Nd(III) complexes with 3-hydroxypicolinic acid

Synthesis, spectroscopic studies, prediction of the structure and thermal decomposition of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O (3-OHpic = 3-hydroxypicolinic acid) complexes are described. Elemental analysis and the IR vibrational data are consistent with the complex formulae. The absorption spectra in ethanol of the La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O show maximum absorptions at 214 and 211 nm, respectively, which are shifted to 225 nm in the free ligand. The ab initio method RHF/STO-3G/ECP(MWB52) was used to optimize the geometry and the INDO/S-CI model for calculating the electronic spectra of these complexes. A good agreement between theoretical and experimental UV absorption spectra has been obtained. The thermal decomposition was studied by non-isothermal thermogravimetry. Thermal decomposition reactions of the complexes La(3-OHpic)₃ · 3H₂O and Nd(3-OHpic)₃ · 3H₂O are best described by R2 and R3 kinetic models.