Isomers in the chemistry of iron coordination compounds

The coordination chemistry of iron covers a wide field, as shown by a survey covering the crystallographic and structural data of almost one thousand and three hundred coordination complexes. About 6.7% of these complexes exist as isomers and are summarized in this review. Included are distortion (96.6%) and cis — trans (3.4%) isomers. These are discussed in terms of the coordination about the iron atom, bond length and interbond angles. Distortion isomers, differing only by degree of distortion in Fe-L, Fe-L-Fe and L-Fe-L parameters, are the most common. Iron is found in the oxidation states zero, +2 and +3 of which +3 is most common. The stereochemistry around iron centers are tetrahedral, five — coordinated (mostly trigonal — bipyramid) and six — coordinated. The most common ligands have O and N donor sites.     

A new differential method for determining orders and rates of reactions and its application to solid state reactions. Part I. Some simple decompositions

The thermal dehydroxylation of natural Al-bearing geothite was investigated by IR spectroscopy. Venezuelan lateritic bauxites (which in addition to goethite contain kaolinite, gibbsite, ilmenite and quartz), as well as chemically isolated samples of Al-goethites, were heated to 300, 600 and 1000°C. The spectral features of the iron oxides formed during the thermal treatment depend on the heating temperature, showing that the first dehydroxylation product is Al-bearing protohematite which at temperatures above 600°C is recrystallized to Al-bearing hematite. Part of the aluminum which is occuled in this hematite originates from the gibbsite and to a smaller extent from the kaolinite.     

Ruthenium-mediated Selective Aromatic Thiolation in the Complex [RuII{o-S—C6H4-(p-R-)—N=N—C3H2NN(1)—R′}2]. Synthesis, Spectroscopic, e.p.r., Electro-chemical Characterization and Spectro-electrochemical Correlation

The reaction of ctc-[Ru(RaaiR′)₂Cl₂] (3a–3i) [RaaiR′=1-alkyl-2-(arylazo)imidazole, p-R—C₆H₄—N=N— C₃H₂NN(1)—R′, R=H, OMe, NO₂, R′=Me, Et, Bz] with KS₂COR′′ (R′′=Me, Et, Pr, Bu or CH₂Ph) in boiling dimethylformamide afforded [Ru^II{o-S—C₆H₄(p-R-)—N=N—C₃H₂NN(1)—R′}₂] (4a–4i), where the ortho-carbon atom of the pendant phenyl ring of both ligands has been selectively and directedly thiolated. The newly formed tridentate thiolate ligands are bound in a meridional fashion. The solution electronic spectra exhibit a strong MLCT band near 700 nm and near 550 nm, respectively in DCM. The molecular geometry of the complexes in solution has been determined by H n.m.r. spectroscopy. Cyclic voltammograms show a Ru(II)/Ru(III) couple near 0.4 V and an irreversible oxidation response near 1.0 V due to oxidation of the coordinated thiol group, along with two successive reversible ligand reductions in the range −0.80–0.87 V (one electron), −1.38–1.42 V (one electron). Coulometric oxidation of the complexes at 0.6 V versus SCE in CH₂Cl₂ produced an unstable Ru(III) congener. When R=Me the presence of trivalent ruthenium was proved by a rhombic e.p.r. spectrum having g₁=2.349, g₂=2.310.     

New cage-like metallasiloxane containing Fe<Superscript>III</Superscript> ions in different coordination spheres

The first cage-like ferrophenyl siloxane containing Fe^III ions in different coordination spheres (four iron ions have a trigonal-bipyramidal coordination and two iron ions have a distorted octahedral coordination) was synthesized by the exchange reaction of sodium phenylsilanolate with Fe^III chloride. An exotic lantern-like structure is formed with the involvement of two metal oxide fragments Fe—O—Fe. The structure of this compound was established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 522–524, March, 2007.     

M?ssbauer spectra of iron doped CuCrS2

M?ssbauer spectroscopy is used to study the state of iron atoms in samples with a composition of CuCr_1−x Fe _x S₂ (x = 0.01–0.30). It is shown that at x ≤ 0.02 samples are solid solutions in which iron atoms have an oxidation number of 3+ and replace chromium atoms in octahedral sites. When the iron concentration increases, the second phase — chalcopyrite CuFeS₂ — forms along with the solid solution. The relative iron concentration in this phase increases from 11% at x = 0.03 to 52% at x = 0.30. Original Russian Text Copyright ? 2009 by V. A. Varnek, V. V. Sokolov, I. Yu. Filatova, and S. A. Petrov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 50, No. 2, pp. 365–368, March–April, 2009.     

Catalytic kinetic spectrophotometric determination of iron with (dibromo-<Emphasis Type="Italic">p</Emphasis>-sulfonic acid arsenazo)-potassium bromate-ascorbic acid system

A new method for the determination of traces of iron was developed based on its catalytic effect on the oxidation reaction of dibromo-p-sulfonic acid-arsenazo (DBS-arsenazo, DBS-ASA) by potassium bromate in a 5.0 × 10⁻³ M sulfuric acid medium. The optimum experimental conditions for the determination of iron using iron(III)-dibromo-p-sulfonic acid-arsenazo, (DBS-ASA)-potassium bromate-ascorbic acid system and its kinetic spectrophotometric properties were studied. The absorbance difference (ΔA) is linearly related with the concentration of iron(III) over the range of 0.20–6.0 ng/mL at the maximum absorption wavelength of 520 nm and described by the equation: ΔA = 0.133c (ng/mL) — 0.0133 with a regression coefficient of 0.9966. The detection limit of the method is 0.17 ng/mL. The method has been successfully used in the determination of traces of iron in potato samples. The obtained results agree with those of atomic absorption spectrometry.     

Phytoecdysteroids of the plants of the genusSilene XV. Silenoside F — Brahuisterone 3-O-β-D-glucopyranoside fromSilene brahuica

A new brahuisterone glycoside — silenoside F — has been isolated from the epigeal part ofSilene brahuica Bois. (fam. Caryophyllaceae). Its structure has been established by an analysis of spectral characteristics: 3β,5,14α,22R,25-pentahydroxy-5β-cholest-6-one 3-O-β-D-glucopyranoside. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 734–737, November–December, 1994.     

The effect of ball-milling on the thermal behavior of anatase-doped hematite ceramic system

High energy ball-milling methods were employed in the synthesis of anatase-doped hematite xTiO₂(a) · (1−x)α-Fe₂O₃ (x = 0.1, 0.5, and 0.9) ceramic system. The thermal behavior of as obtained ceramic system was characterized by simultaneous DSC–TG. The pure anatase phase was found to be stable below 800 °C, but there is a 10.36% mass loss due to the water content. Two exothermic peaks on DSC curves of pure anatase indicate the different crystallization rates. The pure hematite partially decomposed upon heating under argon atmosphere. Ball-milling has a strong effect on the thermal behaviors of both anatase and hematite phases. For x = 0.1 and 0.5, there is gradual Ti substitution of Fe in hematite lattice, and the decomposition of hematite is enhanced due to the smaller particle size after ball-milling. The crystallization of hematite was suppressed as the enthalpy values decreased due to the anatase-hematite solid–solid interaction. For x = 0.9, most of the anatase phase converted to rutile phase after long milling time. The thermal behavior of xTiO₂(a) · (1−x)α-Fe₂O₃ showed smaller enthalpy value of the hematite transformation to magnetite and anatase crystallization due to the small fraction of hematite phase in the system and hematite–anatase interaction, while the mass loss upon heating increased as a function of milling time due to more water content absorbed by the smaller particle size.     

Enantioselective hydrogenation of levulinic acid esters in the presence of the Ru<Superscript>II</Superscript>-BINAP-HCl catalytic system

The rate of hydrogenation of γ-ketoesters MeCOCH₂CH₂COOR (R = Et, Prⁱ, Bu^t) in the presence of the chiral Ru^II—BINAP catalyst (BINAP is 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) greatly increases upon the addition of 5–10 equivalents of HCl with respect to ruthenium. In the hydrogenation of ethyl levulinate, the optically active γ-hydroxy ester initially formed would cyclize by ∼95% to give γ-valerolactone with optical purity of 98–99% ee. When the Ru(COD)(MA)₂—BINAP—HCl catalytic system is used (COD is 1,5-cyclooctadiene, MA is 2-methylallyl), complete conversion of the ketoester (R = Et) in EtOH is attained in 5 h at 60 °C under an H₂ pressure of 60–70 atm. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2301–2304, October, 2005.     

Iron speciation related to color of Jurassic sedimentary rocks in Turpan Basin, northwest China

Mesozoic-Cenozoic reddish and green beds are widely distributed in northwest China. Mössbauer spectroscopy revealed that the composition of iron species varies with color in the middle-upper Jurassic sedimentary rocks from the Turpan Basin. Three main kinds of iron species were identified: (1) ferric iron of hematite (hem-Fe³⁺), (2) paramagnetic ferric iron (para-Fe³⁺), and (3) paramagnetic ferrous iron (para-Fe²⁺). Pyrite iron (pyr-Fe²⁺) was revealed only in a few samples. In general, there is a direct correlation between rock color, iron species and total iron content, however, in detail, this relationship is more complicated. The reddish rocks contain higher contents of total iron and hem-Fe³⁺, whereas the gray rocks contain much more para-Fe²⁺. However, relatively low hematite content cannot give red color to rocks, probably due to suppression by other pigments such as organic matter in black or chlorite in green. The dark or green rocks normally contain either only paramagnetic Fe²⁺ and paramagnetic Fe³⁺ species or these two species associated with hematite Fe³⁺, but the relative content of hematite species is lower. The variations of different iron species control lithological properties such as color and also may reflect the sedimentary conditions. Moreover, iron speciation in these rocks is one of the main factors, which result the color features of rocks in remote sensing imagery.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis of nonsymmetrical dialkylamines on the basis of diphenylphosphinic amides

A facile method for the synthesis of nonsymmetrical dialkylamines (CnH2n+1)2NH (n = 1–12) using the Ph2P(O) protecting group was developed. The method includes successive transformation of monoalkylamines to primary diphenylphosphinic N-alkylamides Ph2P(O)NHR’ (R’ = CnH2n+1, n = 1–12) by the Todd—Atherton reaction, phase transfer N-alkylation of these compounds, and hydrolysis of the secondary amides Ph2P(O)NR’R″ thus formed. When the (EtO)2P(O) and Bu2P(O) protecting groups are used, N-alkylation of primary amides is accompanied by the formation of Et—O and P—N bond cleavage products, respectively. A study of the stability of the N-alkylamides R 2P(O)NHR’ (R = Ph, p-MeC6H4, p-CIC6H4, Bu) under strong alkaline conditions used in the phase transfer N-alkylation showed that an increase in the electron-donating ability of substituents at both the nitrogen atom and the phosphorus atom results in a decrease in the degree of P—N bond cleavage. The primary and secondary diphenylphosphinic amides containing a β-hydroxyethyl group at the nitrogen atom are extremely unstable under the alkaline conditions and are converted quantitatively to the diphenylphosphinic acid salt.     

Steroid saponins and sapogenins ofAllium IX. The structure of aginoside

From a methanolic extract of the skins of the bulbs ofAllium giganteum Rgl, a new steroid glycoside has been isolated — aginoside, which is (25R)-5α-spirostan-2α, 3β, 6β-triol 3-0-{[0-β-D-xylopyranosyl-(1→3)-]-[0-β-D-glucopyranosyl-(1→2)]-0-β-D-glucopyranosyl-(1→4)-0-β-D-galactopyranoside}.     

Iron oxide pigmenting powders produced by thermal treatment of iron solid wastes from steel mill pickling lines

Phase changes of iron containing solid wastes from steel mill pickling lines after thermal treatments were investigated aiming the determination of the appropriate conditions for its transformation to be useful for industrial raw materials. Above 275°C, the thermally treated wastes contain a mixture of α-Fe₂O₃ (hematite) and γ-Fe₂O₃ (maghemite) in different proportions, depending on the maximum heating temperature of the thermal treatment. Increasing the maximum temperature the maghemite participation is decreased through its transformation to hematite. Above 850°C hematite is the main constituent, suggesting that thermal treatment of the wastes in this temperature will give a product that could be used as red iron pigment.     

Structural arrangement of layers in some octaorganylsilsesquioxanes

Thick (≈0.2–1 μm) layers of octaorganylsilsesquioxanes [RSiO_1.5]₈, where R is CH₃, C₂H₃, and C₂H₅, were obtained by vacuum deposition and studied by X-ray diffractometry (DRON-3M, R=192 mm, CuK_α radiation). Irrespective of the type of support, the layers are ideally oriented polycrystalline films with the [001] texture axis. Structural arrangement of the layers is analyzed on the basis of the crystal data. Orientation of the terminal atomic groups on the surface of the layer is established. It is shown that it is possible to adjust the scale of the layer pattern. Two-layer compositions— Cu(II) β-diketonates and phthalocyanines on octaorganylsilsesquioxane supports and vice versa — with preserved orientations of the films were obtained. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 5, pp. 923–928, September–October, 1996. Translated by L. Smolina     

Synthesis and spectroscopic characterization of new iron(III) complexes of S-Alkyl/Aryl dithiocarbazates of 5-methyl-3-formylpyrazole and 5-methyl-3-formylpyrazolyl-thiosemicarbazones

New iron (III) complexes of S-methyl-βN-(5-methylpyrazole-3-yl)methylenedithiocarbazate, S-benzyl-β-N-β-(5-methylpyrazole-3-yl)methylenedithiocarbazate, 5-methyl-3-formylpyrazole-3-pyrrolidinylthiosemicarbazone, and 5-methyl-3-formylpyrazole-⁴N-benzylthiosemicarbazone have been synthesized and physicochemically characterized by elemental analyses, magnetic moment measurements (polycrystalline state), electronic, IR, and EPR spectra, as well as conductance measurements, are used to confirm the coordination geometry. The spectral studies reveal the low-spin distorted octahedral structure of the iron (III) complexes containing two uninegative tridentate ligands with NNS donor sites, where the EPR data confirm the presence of a spin — paired iron (III) with d _xz ² d _yz ² d _xy ¹ configuration in the ground state. The article is published in the original.     

Theoretical study on the reactions of trimethylsilane with chlorine and bromine atoms

Theoretical studies are carried out on the multi-channel reactions of SiH(CH₃)₃ with Cl (reaction 1, R1) and Br atoms (R2) by direct dynamics method. The minimum energy path is calculated at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for individual reaction channels, R1a, R1b-in, R1b-out, R1c, R1d, R2a, R2b-in, R2b-out, R2c, and R2d, are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200–1,500 K. The theoretical three-parameter expressions k ₁ (T) = 6.30 × 10⁻¹⁵ T ^1.36exp(704.94/T) and k ₂ (T) = 9.41 × 10⁻²⁶ T ^4.89exp(−1,033.80/T) cm³ molecule⁻¹ s⁻¹ are given. Our calculations indicate that reaction channels R1c and R2c are the major channel.     

Three-parametric equation in evaluation of thermal dissociation of reference compound

Further considerations concerning thermal decomposition of reference material — CaCO₃, described by three-parametric equation in version (3), have been presented. It was established that in linear relationship between coefficients of Eq. (3) a ₂ is the argument of a ₁, which reaches minimal value of thermodynamic character (δH/vR) when a ₂=0 (equilibrium relationship). During thermal decomposition connection between system atmosphere — rich in CO₂ or vacuum, caused by fast evacuation of gaseous products — and activation energy value, as well as maximal temperature of reaction process. Conditions of this kind may be explained by Zawadzki-Bretsznajder law.     

Long-lived phosphorescence of arenes in complexes with cyclodextrins 2. Room-temperature phosphorescence of ternary complexes of naphthalene and phenanthrene with β-cyclodextrin and adamantane derivatives in the presence of oxygen

Long-lived room-temperature phosphorescence (RTP) of arene—β-cyclodextrin (β-CD)— cage hydrocarbon complexes in the presence of oxygen was studied. Naphthalene-d₈, phenanthrene, and fluorene were used as arenes and adamantane, 1,3-dimethyladamantane, diamantane, and diadamantyl were used as the cage hydrocarbons (according to PM3 quantum chemical calculations, the use of these compounds might cause the appearance of long-lived RTP). The RTP lifetime of the naphthalene-d8—β-CD—diadamantyl complex is 11.9 s at 20 °C. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2661–2665, December, 2005.     

Immobilization of Ru — TsDPEN catalyst on functionalized MCM — 41

A Ru — TsDPEN (RuCl[(1S,2S)-N-p-tosyl-1,2-diphenylethylendiamine]p-cymene) catalyst of the Noyori type was immobilized in the channels of MCM — 41 molecular sieve functionalized by (3 — aminopropyl)triethoxysilane (APTES). The resulting compound was tested as a catalyst for the hydrogenation of 1-methyl-3,4-dihydroisoquinoline (MIQ) under laboratory conditions using an azeotropic mixture of formic acid and triethylamine (5:2) as the source of hydrogen and compared to the results acquired in the corresponding system.