Preparation and properties of dispersed iron (III) oxide on rutile

Samples of 5 and 20 mole% α-Fe₂O₃ supported on rutile TiO₂ were prepared by incipient wetness. A temperature of 390°C was found to be necessary for complete decomposition of the nitrates. Below 400°C there appears to be little evidence for strong interactions between α-Fe₂O₃ and the support. However, ternary phase formation was observed at elevated temperature. Magnetic properties of bulk and supported α-Fe₂O₃ are compared and discussed.     

Separation and preconcentration of iron(II) and iron(III) from natural water on a melamine-formaldehyde resin

A combined method for the preconcentration and selective spectrophotometric determination of both valencies of iron, i.e., Fe(II) and Fe(III), down to 0.4 mug l(-1) has been developed. Iron(III) from synthetic and natural water samples has been concentrated on a melamine-formaldehyde resin at pH 5; iron(II) was not retained under identical conditions. The oxidized iron was concentrated on a second resin column. The iron in both columns was eluted with 1 M HCl solution and separately analyzed by the 1,10-phenanthroline-citrate spectrophotometric method. The effect of pH, adsorption and elution rates, and interferences on the developed procedure were investigated. Metal ions that can be retained by the resin at moderate concentrations, e.g., Al(3+), do not cause interference in more dilute solutions encountered in natural water samples. At least 160-fold volume enrichment can be easily obtained using an adsorption flowrate of 50 ml min(-1). A hydrothermal water sample was analyzed by the recommended procedure and by a literature method, and the results were statistically compared by t- and F-tests.     

Preparation and properties of dicyclopentadienylniobium(III) chloride

The preparation of an air-sensitive 16-electron complex, Cp₂NbCl, is described. Its main property is easy transformation to 18-electron mononuclear compounds. Cp₂Nb(=O)Cl and Cp₂Nb(CO)Cl are obtained in oxidation and carbon monoxide gas addition processes, respectively. The physical properties of these complexes are described.     

Preparation and properties of trimethyltris(dimethylphenylphosphine)cobalt(III)

Summary Trimethyltris(dimethylphenylphosphine)cobalt(III) has been prepared by the reaction of dimethyl(2,4-pentanedionato) bis(dimethylphenylphosphine)cobalt(III) with methyllithium in the presence of one equivalent of dimethylphenylphosphine in diethyl ether at 0°. The reaction of the trimethylcobalt(III) complex with 2,4-pentanedione in diethyl ether gave the starting dimethylcobalt complex with evolution of methane (one mol).     

Photoreactivity of iron(III)-aerobactin: photoproduct structure and iron(III) coordination

UV photolysis of the ferric aerobactin complex results in decarboxylation of the alpha-hydroxy carboxylic acid group of the central citrate moiety of aerobactin. The structure determination of the photooxidized ligand shows that decarboxylation occurs at the citrate moiety forming a 3-ketoglutarate moiety. Proton and carbon-13 NMR establish the presence of keto and enol tautomers of the apo-photoproduct, with the enol form prevailing in water. The photoproduct retains the ability to coordinate iron(III). The values of the ligand protonation constants, the pKa of the Fe(III)-ligand complex, and the Fe(III) stability constant of the photoproduct of aerobactin are all close to those of aerobactin. CD spectroscopy suggests that the chirality of the ferric complexes of aerobactin and its photoproduct are similar. Like aerobactin, the photoproduct promotes iron acquisition by the source bacterium, Vibrio sp. DS40M5.     

Spin transition in iron(III) and iron(II) complexes

The main stages of the studies on the spin transitions in iron(III) and iron(II) complexes are considered. The types of the spin transitions and the factors responsible for the latter are reported. The problems arising during experiments in this field are discussed.     

Versatility in the binding of 2-pyrazinecarboxylate with iron. Synthesis, structure and magnetic properties of iron(II) and iron(III) complexes

The synthesis and characterization of two new iron(II) complexes, [Fe(pca)2(py)2].py (1) and {[Fe(pca)2(H2O)].H2O}n (2) and one new iron(III) complex, Na2{[Fe(pca)()]2O}.2H2O.2CH3CN (3) (pca- stands for 2-pyrazinecarboxylate), are reported. Complex 1 is obtained from the reaction of iron powder with 2-pyrazinecarboxylic acid. The reaction of Fe(ClO4)3.10H2O with Hpca in the presence of 3 equiv. of Bu4NOH yields 2, whereas the presence of NaOH yields 3. The molecular structure of 1 contains an iron(II) ion with a pseudo-octahedral environment resulting from the coordination of two pca- ligands in a bidentate chelating fashion and two pyridine molecules; pi-pi stacking interactions between pyridine and pyrazine rings lead to a one-dimensional chain. Complex 2 is an iron(II) coordination polymer with an infinite zig-zag motif and an Fe...Fe separation of 7.1 A. In 2, the pi-pi stacking interactions involving the pyrazine rings and the strong hydrogen bonds between the coordinated water molecule and the carboxylate oxygens of two pca- ligands result in a three-dimensional network structure. Complex 3 consists of an anionic micro-oxo-bridged diiron(III) core with two crystallographically distinct iron(iii) ions; the negative charge is compensated by two sodium cations. Complex 3 is assembled in a three dimensional network structure through coordination of Na(I) and hydrogen bond interactions. Temperature dependent magnetic susceptibility and M?ssbauer spectroscopic studies indicate that 1 and 2 have similar magnetic properties. Both complexes are paramagnetic above 12 K, whereas antiferromagnetic ordering is observed below 12 K. The magnetic properties of reveal strong intramolecular antiferromagnetic interactions between the two iron(III) ions with a J value of -221 cm(-1); no long range intermolecular magnetic coupling is observed between 295 and 4.2 K.     

Catalytic activity of an iron(III) Schiff base complex bound in a polymer resin

An iron(III)–ferrocene complex and its heterogeneous analogue bound in a polymer resin have been prepared and employed as catalysts for the oxidation of various organic substrates. Characterization of the heterogeneous and homogeneous complexes was done by SEM, EDAX, TGA, FT-IR, DRS-UV, and spectroscopy. The catalyst’s activity, stability, and reusability were investigated through industrially relevant oxidation reactions. The solid iron(III)–ferrocene Schiff base complex gave more effective results than the solid-supported ferrocene Schiff base ligand. The antimicrobial activities of the molecular complex and free ligand were studied for Gram-positive and Gram-negative bacteria.     

Thermal decomposition of lanthanide(III) and Y(III) 3,4,5-trihydroxybenzoates: Preparation, properties

Complexes of lanthanides(III) (La-Lu) and Y(III) with 3,4,5-trihydroxybenzoic acid (gallic acid) were obtained and their thermal decomposition, IR spectra and solubility in water have been investigated. When heated, the complexes with a general formula Ln(C₇H₅O₅)(C₇H₄O₅)·nH₂O (n=2 for La-Ho and Y: n=0 for Er-Lu) lose their crystallization water and decompose to the oxides Ln₂O₃, CeO₂, Pr₆O₁₁, and Tb₄O₇, except of lanthanum and neodymium complexes, which additionally form stable oxocarbonates such as Ln₂O₂CO₃. The complexes are sparingly soluble in water (0.3·10^–5–8.3·10^–4 mol dm^–3).This revised version was published online in November 2005 with corrections to the Cover Date.     

Syntheses and magnetic properties of iron(III) complexes with imidazole groups

Iron(III) complexes with the general formula of [Fe (R-Himap)₂]X and [Fe(R-Himat)₂]X (Himap = shiff-base prepared from the condensation of 4-formylimidazole and 2-aminophenol, Himat = shiff base prepared from the condensation of 4-formylimidazole and 2-aminobenzenethiol, and R = H, Me, Ph; X = ClO₄, NO₃, BPh₄) have been synthesized. The complexes have an N₄O₂ donor set or an N₄S₂ donor set. These complexes have 5 and 5 member rings around an iron(III) atom per one chelate ring, that is, "5-5 member rings". The crystal structure, Mössbauer spectra, magnetic properties and absorption spectra of the complexes were examined. In addition, [Fe (Himsa)₂]ClO₄ having "5-6 member rings" of an N₄O₂ donor set and [Fe (Ph-Himap)(Ph-imap)] obtained by the deprotonation of [Fe (Ph-Himap)₂]ClO₄ have been also synthesized, and the Mössbauer spectra and magnetic properties of those complexes were examined. The X-ray structure of a single crystal of [Fe (Himap)₂]BPh₄ was determined: C₄₄H₃₆N₆BO₂Fe, triclinic, space group P(# 2), a = 12.452(2) Å, b = 12.748(2) Å, c = 11.996(2) Å, = 103.97(1)°, = 90.78(1)°, = 84.70(1)° and Z = 2. The moiety of an iron atom of [Fe(Himap)₂]BPh₄ was a pseudo octahedron with an FeN₄O₂ geometry. [Fe(R-Himap)₂]X was in high-spin state (about 5.9 B.M. at 80 K in solid state), and [Fe(R-Himat)₂]X was in low-spin state (about 2.0 B.M. at 293 K). The complex [Fe(Himsa)₂]ClO₄ with "5-6 member rings" and the deprotonated complex [Fe(Ph-Himap)(Ph-imap)] were in the high-spin state (6.0 B.M. at 80 K). It is concluded that the ligand field strength of an N₄S₂ donor set is stronger than that of an N₄O₂ donor set.     

Mössbauer study of the thermal decomposition of iron(III) benzoate and iron(III) fumarate

The thermal decomposition of iron(III) benzoate, Fe(C₇H₅O₂)₃, and iron(III) fumarate pentahydrate, Fe₂(C₄H₂O₄)₃ 5 H₂O, containing uni- and bidentate ligands, respectively, has been investigated at various temperatures for different intervals of time in a static air atmosphere. Thermolysis of these compounds leads directly to the formation of α-Fe₂O₃ in the case of iron(III) benzoate and Fe₃O₄ in the case of iron(III) fumarate as the ultimate products, thus without undergoing reduction to the iron(II) state.     

Spectral and electrochemical properties of deformed short-chain basket-handle iron (III) porphyrins

The spectral and electrochemical properties of series of deformed iron(III) derivatives of short-chain basket-handle porphyrins are reported. 1HNMR and optical studies demonstrated that deformation arises because of the bridging of opposite phenyl groups by short chains. Axial ligation studies indicate that the straps present over both sides of the porphyrin ring do not prevent the entry of small ligands. Electrochemistry in four different solvents suggests the stabilisation of Fe(II) and Fe(I) over Fe(III) in strong coordinating solvents.     

The charge distribution in chromium(III) and iron(III) hexafluoride

Semi-empirical molecular orbital calculations were performed for CrF^3?₆ and FeF^3?₆. The method of calculation is derived from the HF SCF equations using approximations appropriate to the highly ionic transition metal halides. The results of these calculations are shown to be in better agreement than previous semis-empirical calculations with X-ray emission line shifts and atom charges and populations estimated from these shifts.     

Electronic structure of six-coordinate iron(III)-porphyrin NO adducts: the elusive iron(III)-NO(radical) state and its influence on the properties of these complexes

This paper investigates the interaction between five-coordinate ferric hemes with bound axial imidazole ligands and nitric oxide (NO). The corresponding model complex, [Fe(TPP)(MI)(NO)](BF4) (MI = 1-methylimidazole), is studied using vibrational spectroscopy coupled to normal coordinate analysis and density functional theory (DFT) calculations. In particular, nuclear resonance vibrational spectroscopy is used to identify the Fe-N(O) stretching vibration. The results reveal the usual Fe(II)-NO(+) ground state for this complex, which is characterized by strong Fe-NO and N-O bonds, with Fe-NO and N-O force constants of 3.92 and 15.18 mdyn/A, respectively. This is related to two strong pi back-bonds between Fe(II) and NO(+). The alternative ground state, low-spin Fe(III)-NO(radical) (S = 0), is then investigated. DFT calculations show that this state exists as a stable minimum at a surprisingly low energy of only approximately 1-3 kcal/mol above the Fe(II)-NO(+) ground state. In addition, the Fe(II)-NO(+) potential energy surface (PES) crosses the low-spin Fe(III)-NO(radical) energy surface at a very small elongation (only 0.05-0.1 A) of the Fe-NO bond from the equilibrium distance. This implies that ferric heme nitrosyls with the latter ground state might exist, particularly with axial thiolate (cysteinate) coordination as observed in P450-type enzymes. Importantly, the low-spin Fe(III)-NO(radical) state has very different properties than the Fe(II)-NO(+) state. Specifically, the Fe-NO and N-O bonds are distinctively weaker, showing Fe-NO and N-O force constants of only 2.26 and 13.72 mdyn/A, respectively. The PES calculations further reveal that the thermodynamic weakness of the Fe-NO bond in ferric heme nitrosyls is an intrinsic feature that relates to the properties of the high-spin Fe(III)-NO(radical) (S = 2) state that appears at low energy and is dissociative with respect to the Fe-NO bond. Altogether, release of NO from a six-coordinate ferric heme nitrosyl requires the system to pass through at least three different electronic states, a process that is remarkably complex and also unprecedented for transition-metal nitrosyls. These findings have implications not only for heme nitrosyls but also for group-8 transition-metal(III) nitrosyls in general.     

Redox properties of NN′-X-phenylenebis(Y-salicyli-deneiminato)iron(II) complexes and reactivity of the corresponding iron(III) complexes towards catecholates

The electrochemical behaviour of a series of iron(II) complexes with the tetradentate ligand NN′-1,2-phenylenebis(salicylideneimine), [Fe(II)L], was studied in non-aqueous solvents. The redox properties of the complexes were related to the nature of the substituents in the aromatic rings. Attention was devoted to dioxygen reactivity of the complexes. The electrode activity of the catechol—[NN′-1,2-phenylenebis(salicylidene-iminato) iron(III)] system, [Fe(III)L(catH)], was also studied; the results gave evidence that both the electrochemical oxidation and the chemical oxidation by dioxygen of [Fe(II)L] in the presence of catechol lead to the complex [Fe(III)L(catH)].