Metal benzoylpivaloylmethanates. Part III. Manganese(III) and iron(III) chelates

Summary The synthesis and principle properties of several novel tris[1-(4-X-phenyl)-4,4-dimethylpenta-1, 3-dionato]-iron(III) and manganese(III) complexes, where X=MeO, Me, H, F, Cl and NO₂, are described. Magnetic susceptibility measurements in the 4.2–295 K range show a near Curie behaviour and a constant magnetic moment for manganese(III) complexes and for iron complexes, with X=F, Cl or NO₂. Iron complexes with ligands having substituents: X=MeO, Me and H, show weak antiferromagnetic interaction (J=ca.–8 cm^–1 for the two former compounds) and a decrease in magnetic moment with decreasing temperature. In both manganese(III) and iron(III) complexes the diketonate ligand can be easily replaced by chlorine. Equilibrium constants could be evaluated only for substitution of the third diketonate ligand by chloride in the iron complexes on the basis of spectrophotometric measurements. For manganese chelates, the replacement of the second diketonate by chloride is accompanied by reduction of manganese(III) manganese(II) and free organic radical formation is observed.     

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.     

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.     

Binuclear iron(III) acetates

Summary The binuclear iron(III) compound, Fe₂Cl(OH)₂(MeCO₂)₃ 2 AcOH combines with pyridine, -picoline and 2,2-bipyridyl (B) to form Fe₂Cl(OH)₂(AcO)₃·B adducts. The secondary bases, pyrrolidine and diethylamine (RNH), on the other hand, combine with the complete elimination of chlorine to form, Fe₂(NR)(OH)₂(AcO)₃. These products have been characterised by molecular weight, i.r. spectra, magnetic susceptibility and Mössbauer measurements.     

Polynuclear iron(III) pivalates

The formation of magnetically active polynuclear Fe^III pivalates in the FeSO₄·7H₂O-KOOCCMe₃ system was studied. The reaction of FeSO₄·7H₂O (1) with KOOCCMe₃ in EtOH in air afforded the antiferromagnetic trinuclear complex [Fe₃O(OOCCMe₃)₆(H₂O)₃]⁺[OOCCMe₃]^–·3EtOH. A change of the solvent (EtOH) in this system to a 40:1 benzene—THF mixture resulted in the formation of the antiferromagnetic hexanuclear cluster [Fe₆(O)₂(OH)₂(OOCCMe₃)₁₂(HOOCCMe₃)(THF)]·1.5C₆H₆. The addition of trimethylacetic acid to EtOH and recrystallization from hexane gave rise to the antiferromagnetic coordination polymer [K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(H₂O)₂]_n (7). Recrystallization of the latter from acetonitrile afforded the antiferromagnetic tetranuclear complex K₂Fe₄(O)₂(OOCCMe₃)₁₀(HOOCCMe₃)₂(MeCN)₂. The structures of these compounds were established by X-ray diffraction analysis, and their magnetic susceptibilities and thermal decomposition were investigated.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2403–2413, November, 2004.     

Photometric titration of titanium(III) with iron(III)

An oxidimetric titration of titanium(III) with iron(III) with a photometric end-point is proposed. Acetylacetone was used to obtain an intensely coloured titanium(III) complex; titanium(III) was formed by prereduction with chromium(II) or vanadium(II). Amounts of titanium down to 35 μg were determined with fairly good accuracy and precision. Few common elements interfere.     

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.     

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.     

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.     

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.     

Spin-crossover phenomena in tris(trifluoronicotinoylacetonato) iron (III)

Tris(trifluoronicotinoylacetonato) iron(III) has been shown to exhibit spin-crossover phenomenon between ⁶A_1g and ²T_2g terms which are about 322 cm^?1 apart.     

Photometric determination of iron (III)

A sensitive colored reaction of tiron with iron (III) is described. It is based on a complex formation between tiron and iron (III) in basic medium. The method is suitable to determine 0.4–10 ppm of iron (III) with a relative standard deviation of 0.45–1.4% depending on the concentration level, molar absorptivity of 5.7 × 10³ liter mol⁻¹ cm⁻¹, and Sandell sensitivity index of 0.0098 μg/cm².Because of being simple and rapid, this method can certainly be used in routine analysis.     

NIR spectroscopy of selected iron(II) and iron(III) sulphates

A problem exists when closely related minerals are found in paragenetic relationships. The identification of such minerals cannot be undertaken by normal techniques such as X-ray diffraction. Vibrational spectroscopic techniques may be applicable especially when microtechniques or fibre-optic techniques are used. NIR spectroscopy is one technique, which can be used for the identification of these paragenetically related minerals and has been applied to the study of selected iron(II) and iron(III) sulphates. The near-IR spectral regions may be conveniently divided into four regions: (a) the high wavenumber region>7500 cm(-1), (b) the high wavenumber region between 6400 and 7400 cm(-1) attributed to the first overtone of the fundamental hydroxyl stretching mode, (c) the 5500-6300 cm(-1) region attributed to water combination modes of the hydroxyl fundamentals of water, and (d) the 4000-5500 cm(-1) region attributed to the combination of the stretching and deformation modes of the iron(II) and iron(III) sulphates. The minerals containing iron(II) show a strong, broad band with splitting, around 11,000-8000 cm(-1) attributed to (5)T(2g)-->(5)E(g) transition. This shows the ferrous ion has distorted octahedral coordination in some of these sulphate minerals. For each of these regions, the minerals show distinctive spectra, which enable their identification and characterisation. NIR spectroscopy is a less used technique, which has great application for the study of minerals, particularly minerals that have hydrogen in the structure either as hydroxyl units or as water bonded to the cation as is the case for iron(II) and iron(III) sulphates. The study of minerals on planets is topical and NIR spectroscopy provides a rapid technique for the distinction and identification of iron(II) and iron(III) sulphates minerals.     

Gaseous iron(II) and iron(III) complexes with BINOLate ligands

Electrospray ionization (ESI) of dilute solutions of 1,1'-bi-2-naphthol (BINOL) and iron(II) or iron(III) sulfate in methanol/water allows the generation of monocationic complexes of iron and deprotonated BINOL ligands with additional methanol molecules in the coordination sphere, and the types of complexes formed can be controlled by the valence of the iron precursors used in ESI. Thus, iron(II) sulfate leads to [(BINOLate)Fe(CH3OH)n]+ complexes (n=0-3), whereas usage of iron(III) sulfate allows the generation of [(BINOLdiate)-Fe(CH3OH)n]+ cations (n=0-2); here, BINOLate and BINOLdiate stand for singly and doubly deprotonated BINOL, respectively. Upon collision-induced dissociation, the mass-selected ions with n>0 first lose the methanol ligands and then undergo characteristic fragmentations. Bare [(BINOLdiate)Fe]+, a formal iron(III) species, undergoes decarbonylation, which is known as a typical fragmentation of ionized phenols and phenolates either as free species or as the corresponding metal complexes. The bare [(BINOLate)Fe]+ cation, on the other hand, preferentially loses neutral FeOH to afford an organic C20H12O+* cation radical, which most likely corresponds to ionized 1,1'-dinaphthofurane.     

Iodine(III)-mediated ethoxychlorination of enamides with iron(III) chloride

The combination of (diacetoxyiodo)benzene and iron(III) chloride in ethanol allows the efficient regioselective ethoxychlorination of a broad range of enamides. Mechanistic studies tend to rule out the involvement of free radical species and point towards the implication of a mixed [chloro(ethoxy)iodo]benzene intermediate.