Iron(II)-8-mercaptoquinoline,iron(II)-5-chloro-8-mercaptoquino-line and iron(II)-5-bromo-8-mercaptoquinoline complexing in the iron(III) hexacyanoferrate(II) gelatin-immobilized matrix systems

Novel complexing processes in the Fe^II-8-mercaptoquinoline, Fe^II-5-chloro-8-mercaptoquinoline and Fe^II-5-bromo-8-mercaptoquinoline systems, not used previously in coordination chemistry, namely complexing as an iron(III)hexacyanoferrate(II) gelatin-immobilized matrix (GIM) in contact with an aqueous solution of the corresponding ligand, have been observed and analysed. Incorporation of these ligands into the inner coordination sphere is preceded by the decomposition of the immobilized compound KFe[Fe(CN)₆] to form hydroxides or oxohydroxides of Fe^II and Fe^III under the action of OH^- ions. It has been shown that Fe^IIFeIII redox process and the formation of FeB₃ chelates (B^- is a singly deprotonated form of the corresponding ligand) take place during complexing under such conditions.     

Mechanistic information on the reversible binding of NO to selected iron(II) chelates from activation parameters

Mechanistic insight on the reversible binding of NO to Fe(II) chelate complexes as potential catalysts for the removal of NO from effluent gas streams has been obtained from the temperature and pressure parameters for the "on" and "off" reactions determined using a combination of flash photolysis and stopped-flow techniques. These parameters are correlated with those for water exchange reactions on the corresponding Fe(II) and Fe(III) chelate complexes, from which mechanistic conclusions are drawn. Small and positive Delta V(++) values are found for NO binding to and release from all the selected complexes, consistent with a dissociative interchange (I(d)) mechanism. The only exception in the series of studied complexes is the binding of NO to [Fe(II)(nta)(H(2)O)(2)](-). The negative volume of activation observed for this reaction supports the operation of an I(a) ligand substitution mechanism. The apparent mechanistic differences can be accounted for in terms of the electronic and structural features of the studied complexes. The results indicate that the aminocarboxylate chelates affect the rate and overall equilibrium constants, as well as the nature of the substitution mechanism by which NO coordinates to the selected complexes. There is, however, no simple correlation between the rate and activation parameters and the selected donor groups or overall charge on the iron(II) complexes.     

Built-in axial base binding on phenanthroline-strapped zinc(II) and iron(III) porphyrins

In addition to the need for functional models of cytochrome c oxidase, structural models are still required for a better understanding of the small reorganizations occurring during the catalytic cycle. An efficient synthetic approach has been designed to prepare several phenanthroline-strapped porphyrins, two of them bearing two pendant imidazoles. These built-in bases are both potentially able to act as axial bases for the metalloporphyrin and as complementary ligands for copper if necessary. Diamagnetic zinc(II) was used to demonstrate that the distal/proximal selectivity demonstrated by exogenic bases binding studies can be extended to the coordination of iron(III). Combination of EPR and paramagnetic 1H NMR shows that the imidazole binding on the zinc species can be further extended to the iron(III) species in dilute conditions.     

Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination

The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.     

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.     

Solid complexes of iron(II) and iron(III) with rutin

Solid complex compounds of Fe(II) and Fe(III) ions with rutin were obtained. On the basis of the elementary analysis and thermogravimetric investigation, the following composition of the compounds was determined: (1) FeOH(C₂₇H₂₉O₁₆)·5H₂O, (2) Fe₂OH(C₂₇H₂₇O₁₆)·9H₂O, (3) Fe(OH)₂(C₂₇H₂₉O₁₆)·8H₂O, (4) [Fe₆(OH)₂(4H₂O)(C₁₅H₇O₁₂)SO₄]·10H₂O. The coordination site in a rutin molecule was established on the basis of spectroscopic data (UV–Vis and IR). It was supposed that rutin was bound to the iron ions via 4C=O and 5C—oxygen in the case of (1) and (3). Groups 5C–OH and 4C=O as well as 3′C–OH and 4′C–OH of the ligand participate in binding metals ions in the case of (2). At an excess of iron(III) ions with regard to rutin under the synthesis conditions of (4), a side reaction of ligand oxidation occurs. In this compound, the ligands’ role plays a quinone which arose after rutin oxidation and the substitution of Fe(II) and Fe(III) ions takes place in 4C=O, 5C–OH as well as 4′C–OH, 3′C–OH ligands groups. The magnetic measurements indicated that (1) and (3) are high-spin complexes.     

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.     

Copper(II), nickel(II), palladium(II) and iron(III) complexes of 2-(3-phthalhydrazidylazo)-1,3-diketones

Neutral complexes of three phthalhydrazidylazo-1,3-diketones [phthalhydrazidylazo-acetylacetone (H₂PAA),-benzoylacetone (H₂PBA) and-dibenzoylmethane (H₂PDM)] with Cu(II), Ni(II), Pd(II) and Fe(III) have been synthesised and characterized on the basis of their analytical data, magnetic moment, molar conductance and IR and¹H NMR spectral data. Dibasic tridentate coordination of the ligands is brought out by the above spectral data. Half-wave potentials and far IR spectral data of the Cu(II) complexes indicate that the H₂PAA complex is the most stable. M?ssbauer spectra of the Fe(III) complexes reveal that delocalisation of the metald electrons with the chelate ring decreases with increasing capability of the pendant groups of the ring for cross conjugation.     

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.     

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.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

Polarographic determination of iron(II) and iron(III) complexes with edta

The iron(II) and iron(III) complexes with EDTA can be determined separately and in mixtures in acetate-buffered medium at pH 4.0. The E_{$\text{1}\text{2}$}values are in the range ?0.105 to ?0.112 V vs. SCE. Linear calibration plots are obtained over the range 0–1.0 mM for each oxidation state. A sample-handling procedure for avoiding oxidation of iron(II) species is described. It is shown that the acetate buffer system does not affect the stability of the iron-EDTA complexes.     

Novel complexes of 5-(4-carboxyl)phenylene-methanaminophenyl-10,15,20-tri-phenylporphyrin with zinc(II), iron(III), manganese(III) and zinc(II)–iron(III), zinc(II)–manganese(III) supramolecular self-assembly by hydrogen bonding

5-(p-Carboxyl)phenylene-methanaminophenyl-10,15,20-triphenylporphyrin (p-CPTPP) and its Zn^II[Zn(p-CPTPP)], Fe^III[Fe^III(p-CPTPP)Cl], Mn^III[Mn^III(p-CPTPP)Cl] complexes were prepared and characterized by elemental analysis, ¹H-n.m.r., i.r. and u.v.–vis. spectroscopy. The behaviour of the supramolecular self-assemblies, Zn(p-CPTPP)–Fe^III(p-CPTPP)Cl and Zn(p-CPTPP)–Mn^III(p-CPTPP)Cl, were studied by steady-state fluorescence spectroscopic titration and u.v.–vis. spectra. The formation constants were determined from the data of fluorescence spectroscopic titration. The fact that the Zn(p-CPTPP)–Mn^III(p-CPTPP)Cl system has a higher formation constant than the Zn(p-CPTPP)–Fe^III(p-CPTPP)Cl system is discussed.     

Second-sphere contributions to substrate-analogue binding in iron(III) superoxide dismutase

A combination of spectroscopic and computational methods has been employed to explore the nature of the yellow and pink low-temperature azide adducts of iron(III) superoxide dismutase (N(3)-FeSOD), which have been known for more than two decades. Variable-temperature variable-field magnetic circular dichroism (MCD) data suggest that both species possess similar ferric centers with a single azide ligand bound, contradicting previous proposals invoking two azide ligands in the pink form. Complementary data obtained on the azide complex of the Q69E FeSOD mutant reveal that relatively minor perturbations in the metal-center environment are sufficient to produce significant spectral changes; the Q69E N(3)-FeSOD species is red in color at all temperatures. Resonance Raman (RR) spectra of the wild-type and Q69E mutant N(3)-FeSOD complexes are consistent with similar Fe-N(3) units in all three species; however, variations in energies and relative intensities of the RR features associated with this unit reveal subtle differences in (N(3)(-))-Fe(3+) bonding. To understand these differences on a quantitative level, density functional theory and semiempirical INDO/S-CI calculations have been performed on N(3)-FeSOD models. These computations support our model that a single azide ligand is present in all three N(3)-FeSOD adducts and suggest that their different appearances reflect differences in the Fe-N-N bond angle. A 10 degrees increase in the Fe-N-N bond angle is sufficient to account for the spectral differences between the yellow and pink wild-type N(3)-FeSOD species. We show that this bond angle is strongly affected by the second coordination sphere, which therefore might also play an important role in orienting incoming substrate for reaction with the FeSOD active site.     

Direct electrochemical synthesis and characterization of copper(II), iron(II) and iron(III) complexes with 1- and 2-substituted pyridines

Summary The electrochemical oxidation of anodic metals (iron and copper) in MeCN solutions of 2-pyridinone (HOPy), 1-hydroxy-2-pyridinethione (HPT), 2-pyridinemethanethiol-1-oxide (HPMTO) or its dimer 2,2-dithiodimethyldipyridine-1,1-dioxide (PMTO)₂, gave the simple complexes Fe(OPy)₂ · H₂O, Cu(OPy)₂ · 3H₂O, Fe(PT)₂ · 3H₂O, Fe(PT)₃, Cu(PT)₂, Fe(PMTO)₂·3H₂O and Cu(PMTO)₂·H₂O, respectively. When 1,10-phenanthroline (phen) was added to the electrolytic phase, only two mixed complexes were obtained: Cu(OPy)₂phen·3H₂O and Fe(PT)₂phen·2H₂O. The possible molecular structures of the complexes were studied on the basis of their i.r. spectra and magnetic properties.     

O2 and CO binding to tetraaza-tripodal-capped iron(II) porphyrins

A series of tris(2-aminoethylamine) (tren) capped iron(II) porphyrins has been synthesized and characterized and their affinities for dioxygen and carbon monoxide measured. The X-ray structure of the basic scaffold with nickel inserted in the porphyrin is also reported. All the ligands differ by the nature of the group(s) attached to the secondary amine functions of the cap. These various substitutions were introduced to probe if a hydrogen bond with these secondary amine groups acting as the donor could rationalize the high affinity of these myoglobin models. This work clearly indicates that the cage structure of the tren predominates over all the other appended groups with the exception of p-nitrophenol.     

Flow-injection simultaneous determination of iron(III) and copper(II) and of iron(III) and palladium(II) based on photochemical reactions of thiocyanato-complexes

The flow injection analysis systems have been developed for the simultaneous determination of iron(III) and copper(II) and of iron(III) and palladium(II) based on the photochemical reactions of their thiocyanato-complexes. In the first system, a sample solution was injected in to nitric acid solution and mixed with ammonium thiocyanate solution, followed by spectrophotometric monitoring of the thiocyanato-complexes formed. Another aliquot of the same sample solution was injected and the thiocyanato-complexes formed in the same way were irradiated by UV light before spectrophotometric monitoring. In another system, the absorbance of thiocyanato-complexes formed by each sample injection was monitored with two flow cells aligned with the same optical path before and after UV irradiation. The difference in the extent of photochemical decomposition of the thiocyanato-complexes enabled simultaneous determinations of iron(III) and copper(II) and of iron(III) and palladium(II) at levels of several μg ml⁻¹ to some tens μg ml⁻¹ in their admixtures. Sample throughputs are 40 and 20 h⁻¹ by the former and latter systems, respectively.     

Ion-exchanger colorimetry-VII Microdetermination of iron(II) and iron(III) in natural water

A trace method for iron, based on ion-exchanger colorimetry, has been developed. 1,10-Phenanthroline is used as the colour reagent for iron(II) and citrate as the masking reagent for iron(III). Total iron can be determined after reduction of iron(III) to iron(II) with hydroxylamine. It is possible to determine iron at mug/l.-levels in different oxidation states in natural waters.