The Effect of Concentration Parameters on Complexation in the Iron(0)–Iron(II)–Glycine–Water System

The processes of formation of iron(II) complexes in aqueous glycine solutions in the pH range of 1.0–8.0 at 298 K and ionic strength of 1 mol/L (NaClO₄) are studied using Clark and Nikolskii’s oxidation potential method. The type and number of coordinated ligands, the nuclearity, and the total composition of the resulting complexes are determined. The following complex species are formed in the investigated system: [Fe(OH)(H₂O)₅]⁺, [FeHL(H₂O)₅]²⁺, [Fe(HL)(OH)(H₂O)₄]⁺, [Fe(OH)₂(H₂O)₄]⁰, [Fe₂(HL)₂(OH)₂(H₂O)₈]²⁺, and [Fe(HL)₂(H₂O)₄]²⁺. Their formation constants are calculated by the successive iterations method using Yusupov’s theoretical and experimental oxidation function. The model parameters of the resulting coordination compounds are determined.     

Solvation and reactivity of a helical binuclear iron(II) complex with a tetradentate Schiff-base ligand

Reaction of 2-acetylpyridine, hydrazine, and an iron(II) salt gives a low-spin binuclear iron(II) complex, [Fe₂(pmk)₃]⁴⁺, in which three tetradentate Schiff base ligands span the two metal centres to give a complex of helical geometry. We report solubilities of the iodide and perchlorate salts, in H₂O, in aqueous MeOH, and in aqueous DMSO (perchlorate only), up to 60% by vol of organic cosolvent. Transfer chemical potentials for the complex cation from H₂O into the respective mixed solvents have been derived from these solubilities, to give a picture of solvation of this complex in the media studied. Kinetics of base hydrolysis of [Fe₂(pmk)₃]⁴⁺ have been established, in H₂O and in 40% MeOH, 20 and 40% i -PrOH, and 20 and 40% DMSO, at 298.2 K. The reactivity of [Fe₂(pmk)₃]⁴⁺ is discussed in relation to reactivities of a selection of iron(II)-diimine complexes, ranging from [Fe(bipy)₃]²⁺ and [Fe(phen)₃]²⁺ to ligand-encapsulated cage complexes.     

Cyclic voltammetric study of the redox behavior of Fe(II)/Fe(III) systems forming during the oxidation of Fe(II) complexes with saccharin and with saccharin and 1,10-phenanthroline

The electrochemical redox behavior of Fe(II)/Fe(III) systems formed during the oxidation of complexes [Fe(C₇H₄NO₃S)₂(H₂O)₄] · 2H₂O (Fe-sac) and [Fe(C₇H₄NO₃S)₂(C₁₂H₈N₂] · 2H₂O (Fe-sac-phen) have been investigated using cyclic voltammetry in the aqueous medium. In the CVs one pair of well-defined cathodic and anodic peaks appear for the transfer of single electron in the Fe-sac complex. The peak potentials are much wider separated as compared with the free (uncoordinated) Fe(II)/Fe(III) system. The ΔE values demonstrate that the electrode process is irreversible. In the presence of secondary ligand, 1,10-phenanthroline (Fe-sac-phen complex), the redox behavior of iron complexes is quasireversible. The effect of pH on the redox behavior of iron system is studied in acetate buffer. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 12, pp. 1504–1509. The text was submitted by author in English     

New iron(III) nitrate hydrates: Fe(NO3)3·xH2O with x = 4, 5 and 6

Crystals of the title compounds were grown from their hydrous melts or solutions. The crystal structure of iron(III) trinitrate hexahydrate {hexaaquairon(III) trinitrate, [Fe(H₂O)₆](NO₃)₃} is built up from [Fe(H₂O)₆]²⁺ octahedra and nitrate anions connected via hydrogen bonds. In iron(III) trinitrate pentahydrate {pentaaquanitratoiron(III) dinitrate, [Fe(NO₃)(H₂O)₅](NO₃)₂}, one water molecule in the coordination octahedron of the Fe^III atom is substituted by an O atom of a nitrate group. Iron(III) trinitrate tetrahydrate {triaquadinitratoiron(III) nitrate monohydrate, [Fe(NO₃)₂(H₂O)₃]NO₃·H₂O} represents the first example of a simple iron(III) nitrate with pentagonal–bipyramidal coordination geometry, where two bidentate nitrate anions and one water molecule form a pentagonal plane.     

Studies on synthesis,determination of CMC values,kinetics and the mechanism of iron(II) reduction of surfactant–Co(III)–ethylenediamine complexes in aqueous acid medium

The surfactant–Co(III) complexes of the type cis-[Co(en)₂AX]²⁺ (A?=?Tetradecylamine, X?=?Cl^?,?Br^?) were synthesised from corresponding dihalogeno complexes by the ligand substitution method. The critical micelle concentration (CMC) values of these surfactant complexes in aqueous solution were obtained from conductance measurements. The kinetics and mechanism of iron(II) reduction of surfactant–Co(III) complexes, cis-[Co(en)₂(C₁₄H₂₉NH₂)Cl](ClO₄)₂ and cis-[Co(en)₂(C₁₄H₂₉NH₂)Br] (ClO₄)₂ ions were studied spectrophotometrically in an aqueous acid medium by following the disappearance of Co(III) using an excess of the reductant under pseudo-first-order conditions: [Fe(II)]?=?0.25?mol?dm^?3, [H⁺]?=?0.1?mol?dm^?3, [μ]?=?1.0?mol?dm^?3 ionic strength in a nitrogen atmosphere at 303, 308 and 313?K. The reaction was found to be of second order and showed acid independence in the range [H⁺]?=?0.05–0.25?mol?dm^?3. The second-order rate constant increased with surfactant–Co(III) concentration and the presence of aggregation of the complex itself altered the reaction rate. The effects of [Fe(II)], [H⁺] and [μ] on the rate were determined. Activation and thermodynamic parameters were computed. It is suggested that the reaction of [Fe(II)] with Co(III) complex proceeds by an inner-sphere mechanism.     

Novel Complexes of Gallium(III), Indium(III), and Thallium(III) with Pyridine‐Containing Proton Transfer Ion Pairs Obtained from Dipicolinic Acid – Synthesis,Characterization and X‐ray Crystal Structure

Three new complexes of group thirteen metals, gallium(III), indium(III), and thallium(III) with proton transfer compounds, obtained from 2,6‐pyridinedicarboxylic acid (dipicolinic acid), were synthesized and characterized using elemental analysis, IR, ¹H and ¹³C NMR spectroscopy and single crystal X‐ray diffraction. The gallium(III) and indium(III) complexes were prepared using (pydaH₂)(pydc) (pyda = 2,6‐pyridinediamine, pydcH₂ = dipicolinic acid) and thallium(III) complex was obtained from (creatH)(pydcH) (creat = creatinine). The chemical formulae and space groups of the complexes are (pydaH)[Ga(pydc)₂] · 3.25H₂O · CH₃OH, ( 1 ), [In(pydc)(pydcH)(H₂O)₂] · 5H₂O, Pna2₁ ( 2 ) and [Tl₂(pydcH)₃(pydc)(H₂O)₂], ( 3 ). Non‐covalent interactions such as ion‐pairing, hydrogen bonding and π‐π stacking are discussed. The complexation reactions of pyda, pydc, and pyda + pydc with In³⁺ and Ga³⁺ ions in aqueous solution were investigated by potentiometric pH titrations, and the equilibrium constants for all major complexes formed are described.     

Gemischt-Ligand-Komplexe von Eisen(III) mit Brenzkatechin-3,5- disulfonsäure (Tiron) und Thiocyanat in wäßriger Lösung

Mixed-Ligand complexes of Iron(III) with Pyrocatechol-3,5- disulfonie Acid (Tiron) and Thiocyanate in Aqueous Solution In the system iron(III), tiron, thiocyanate two ternary complexes could be detected in acid solution. By spectrophotometric measurements we found the species [Fe(Tiron)(SCN)(H₂O)₃]^2? and [Fe(Tiron)₂(SCN)(H₂O)]^6?. The formation and the optical properties (^λmax,^? max) are discussed.     

Spectroscopic Signature of Dynamical Instability of the Aqueous Complex in the Brown-Ring Nitrate Test**

The chemistry of the brown-ring test has been investigated for nearly a century. Though recent studies have focused on solid state structure determination and measurement of spectra, mechanistic details and kinetics, the aspects of solution structure and dynamics remain unknown. We have studied structural fluctuations of the brown-ring complex in aqueous solution with ab-initio molecular dynamics simulations, from which we identified that the classically established pseudo-octahedral [Fe(H₂O)₅(NO)]²⁺ complex is present along with a square-pyramidal [Fe(H₂O)₄(NO)]²⁺ complex. Based on the inability in multi-reference calculations to reproduce the experimental UV-vis spectra in aqueous solution by inclusion of thermal fluctuations of the [Fe(H₂O)₅(NO)]²⁺ complex alone, we propose the existence of an equilibrium between pseudo-octahedral and square-pyramidal complexes. Despite challenges in constructing models reproducing the solid-state UV-vis spectrum, the advanced spectrum simulation tool motivates us to challenge the established picture of a sole pseudo-octahedral complex in solution.     

Synthesis and characterization of a binuclear iron-μ-peroxo complex of a tetraaza macrocyclic ligand

Summary The dimerization of complex (1), [Fe(TIM)(H₂O)₂]²⁺ (TIM = 2,3,9,10-tetramethyl-1,4,8,11-tetraazacyclotetra-deca-1,3,8,10-tetraene) in aerated aqueous solution results in formation of the binuclear complex (2), [(H₂O)(TIM)-Fe—O—O—Fe(TIM))(H₂O)]⁴⁺. Complex (2) has been characterized by elemental analysis, spectroscopy and electrochemical data.     

Synthesis,electrochemical and antimicrobial studies of mono and binuclear iron(III) and oxovanadium(IV) complexes of [ONO] donor tridentate Schiff-base ligands

Tridentate Schiff bases (H₂L¹ or H₂L²) were derived from condensation of acetylacetone and 2-aminophenol or 2-aminobenzoic acid. Binuclear square pyramidal complexes of the type [M₂(L¹)₂]?·?nH₂O (M?=?Fe–Cl, n?=?0; M?=?VO, n?=?1) were accessed from interaction of H₂L¹ with anhydrous FeCl₃ and VOSO₄?·?5H₂O, respectively. A similar reaction with H₂L², however, produced mononuclear complexes [ML²(H₂O) _x ]?·?nH₂O (M=Fe–Cl, x?=?0, n?=?0; M=VO, x?=?1, n?=?1). The compounds were characterized using elemental analysis, FT-IR, UV-Vis, and NMR (for ligand only), and mass spectroscopies and solution electrical conductivity studies. Magnetic susceptibility measurements suggest antiferromagnetic exchange in binuclear Fe(III) and VO(IV) complexes. Thermo gravimetric analysis (TGA) provided unambiguous evidence for the presence of coordinated as well as lattice water in [VOL²(H₂O)]?·?H₂O. Cyclic voltammetric studies showed well-defined redox processes corresponding to Fe(III)/Fe(II) and VO(V)/VO(IV). In vitro antimicrobial activities of the compounds were investigated against Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas aeroginosa, Escherichia coli, Bacillus subtilis, and Proteus vulgaris. H₂L¹ and its binuclear complexes exhibited pronounced activity against all the microorganisms tested.     

DFT quantum-chemical study of the hydrolysis products of Fe(II) and Fe(III) aqua-complexes

The quantum-chemical DFT calculations of thermodynamic characteristics of the reactions of formation of binuclear dihydroxobridging [Fe(H₂O)₄(μ-OH)₂Fe(H₂O)₄] ⁿ⁺ and oxobridging [Fe(H₂O)₅(μ-O)Fe·(H₂O)₅] ⁿ⁺ (n = 2, 4) cations, the hydrolysis products of cations [Fe(H₂O)₆] ^m+ (m = 2, 3). It is shown that effects of solvation lead to higher energetic stability of the dihydroxobridging binuclear compounds in aqueous solutions.     

An iron(III) 18-metallacrown-6 complex: synthesis,crystal structure,and bioactivity

A macrocyclic hexanuclear iron(III) 18-metallacrown-6 complex, [Fe₆(C₉H₆BrN₂O₃)₆(CH₃OH)₄(H₂O)₂]?·?7CH₃OH?·?4H₂O, has been prepared using a trianionic pentadentate ligand N-acetyl-5-bromosalicylhydrazidate, abshz^3–, and characterized by X-ray diffraction. The crystal structure contains a neutral 18-membered metallacrown ring consisting of six Fe(III) and six abshz^3– ligands. The 18-membered metallacrown ring is formed by combination of six structural moieties, [Fe(III)–N–N]. Due to meridional coordination of ligand to Fe³⁺, the ligand enforces the stereochemistry of the Fe³⁺ ions as a propeller configuration with alternating Δ/Λ forms. Methanol and water are linked with Fe1, Fe1A, Fe,3 and Fe3A. The ratios of methanol to water are 0.76?:?0.24 for Fe1 and Fe1A, and 0.30?:?0.70 for Fe3 and Fe3A, which results in four component crystals of metallacrown rings with ratio of 0.168?:?0.072?:?0.532?:?0.228. Antibacterial screening data showed that the iron metallacrown has moderate antimicrobial activity against Bacillus subtilis.     

[H3tren] templated iron fluorides; synthesis, crystal structures and Mössbauer studies

The hydrothermal synthesis, using tris-(2-ethylamino)amine (tren) as a template, and the crystal structures of three new hybrid iron fluorides, (H₃O)₂·[H₃tren]₂·(FeF₆)₂·(FeF₅(H₂O))·2H₂O (I), [H₃tren]₂·(FeF₆)₂·(FeF₂(H₂O)₄)·8H₂O (II) and [H₃tren]₂·(FeF₆)·(F)₃·H₂O (III), are reported. I, II, and III are triclinic (P-1), monoclinic (P2₁/c) and orthorhombic (I222), respectively. The structure of I is built up from isolated FeF₆ and FeF₅(H₂O) distorted octahedra separated by triprotonated [H₃tren]³⁺ cations, disordered H₃O⁺ cations and H₂O molecules. In II, Fe^IIIF₆ and neutral [Fe^IIF₂(H₂O)₄] octahedra form, together with [H₃tren]³⁺ cations, infinite (100) layers separated by extra water molecules. The structure of III consists of isolated and disordered FeF₆ octahedra, fluoride anions F⁻ connected to [H₃tren]³⁺ cations and extra fluoride anions F⁻ disordered with H₂O molecules. All [H₃tren]³⁺ cations have a “spider” type conformation. ⁵⁷Fe Mössbauer characterization shows that +III valence state can only be considered for iron cations in I and III and preliminary Mössbauer results are consistent with the presence of both +II and +III valences for iron cations in II, in agreement with the crystallographic results.     

Ferric Chloride Complexes in Aqueous Solution: An EXAFS Study

A series of concentrated aqueous solutions of ferric chloride with different chloride:iron(III) ratios has been studied by means of EXAFS to determine the structure around the iron(III) ion of the dominating species in such solutions. The dominating species in dilute acidic aqueous solution of ferric chloride, at less than 1 mmol·dm^?3, are the hydrated iron(III) and chloride ions, while in concentrated aqueous solution and in solutions with an excess of chloride ions, up to 1.0 mol·dm^?3, it is the trans-[FeCl₂(H₂O)₄]⁺ complex. Possible higher chloroferrate(III) or dimeric [Fe₂Cl₆] complexes at room temperature, as proposed in the literature, were not observed in any of the studied solutions in spite of an excess of chloride ions of 1 mol·dm^?3.     

Solvatochromism and solvation of ternary iron-diimine-cyanide complexes

Summary The solvatochromic behaviour of several complexes [Fe(LL)₂(CN)₂] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)₂(CN)₂] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)₄]^– in aqueous solution are described.     

A quantum chemical consideration of ligand exchange in palladium(ii) aqueous and chloride complexes

The behavior of potassium tetrachloropalladate(II) in media simulating biological fluids has been studied. In aqueous solutions of NaCl, the aquation rate is higher than the rate of chloro ligand introduction into the internal coordination sphere of palladium. In HCl solutions, on the contrary, the process of palladium chloro complex formation predominates. The latter is apparently due to protonation of water molecules composing aqua complexes. By means of the ZINDO/1 method, the substitution of ligands – water molecules and hydronium ion – in planar complexes of palladium(II) by chloride ion has been investigated. All complexes containing H₂O and H₃O⁺ ligands, other than [Pd(H₂O)₄]²⁺, have intramolecular hydrogen bonds. In [Pd(H₂O)₃(H₃O)]³⁺ and trans-[Pd(H₂O)₂(H₃O)Cl]²⁺, a “non-classic” symmetric hydrogen bond O ··· H ··· O is established (ZINDO/1, RHF/STO-6G*). By the first three steps the substitution of hydronium ion in the internal sphere of palladium atom is more favorable thermodynamically, compared to water molecules. Logarithms of stepwise stability constants of palladium(II) chloride complexes correlate linearly to enthalpies (ZINDO/1, PM3) of water substitution by chloride ion.     

Kinetic studies of the oxidation of chromium(III) by N-bromosuccinimide

Summary A kinetic study of the oxidation of chromium(III) by N-bromosuccinimide (NBS) in aqueous solutions and H₂O-MeOH solvent mixtures were performed. The kinetics in aqueous solutions obeyed the rate law: d[Cr^VI]/dt = {k ₄ K _h K ₂[NBS][Cr^III]_T}/[₊]{1 + K _h/[H⁺] + (K ₁ + K _h K ₂/[H⁺][NBS])} where K _h, K ₁ and K ₂ are the hydrolysis constant of [Cr^III(H₂O)₆]³⁺, and pre-equilibrium formation constants for the protonated and deprotonated precursor complexes, respectively. An innersphere mechanism is proposed. An argument based on isokinetic correlations among activation parameters for the oxidation of a series of cobalt(II) and chromium(III) complexes including [Cr(H₂O)₆]³⁺ is presented in support of a common mechanism for these reactions. Abstracted from the Ph.D. Thesis (Ain Shams University) of A. E.-D. M. Abdel-Hady.     

Separation and kinetic study of chromium(III) chloro complexes by capillary electrophoresis

Summary Three Cr(III) species (dichlorotetraaquachromium (III), [CrCl₂(H₂O)₄]⁺; monochloropentaaquachromium(III), [CrCl(H₂O)₅]²⁺; and hexaaquachromium(III), [Cr(H₂O)₆]³⁺) have been separated and determined by capillary electrophoresis. The first two complexes could be detected in direct mode in phosphate buffer, but because the absorption of complex [Cr(H₂O)₆]³⁺ is poor in the UV range, indirect UV detection had to be used. For indirect detection 5 mM imidazole was added to the buffer solution. The formation and decomposition of the different Cr(III) complexes were monitored in time after the preparation of solutions of CrCl₃.6H₂O. The slowest process was the decomposition of [CrCl(H₂O)₅]²⁺; 300 h after preparation of a solution of CrCl₃.6H₂O of pH 1 the solution contained only [Cr(H₂O)₆]³⁺. The effects of pH and the content of some matrix ions on the rates of conversion of the complexes were studied. The kinetic characteristics of this complex system could be investigated adequately by means of capillary electrophoresis. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Syntheses,crystal structures,and properties of two dinuclear iron(III) complexes constructed with 1,2,3,5-benzenetetracarboxylic acid and chelating N-donor auxiliary coligands

Two dinuclear Fe(III) metal–organic complexes with tetracarboxylate and chelating N-donor ligands, [Fe(Hbtec)(phen)(H₂O)]₂·2H₂O (1) and [Fe(Hbtec)(bpy)(H₂O)]₂·2H₂O (2) (H₄btec = 1,2,3,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine) have been prepared and characterized by elemental analysis, IR spectroscopic, and X-ray diffraction methods. Both complexes crystallize in the monoclinic space group P2₁/c with two Fe(III) ions bridged by two Hbtec^3? ligands into a dinuclear unit. Hydrogen bonding connects the dinuclear units into a 3-D framework. The dinuclear units are 10-connected nodes that produce a 3-D framework with topology Schläfli symbol as (3¹²·4²⁸·5⁵). Thermal stabilities and luminescent properties of the two complexes have also been investigated.     

Spatial structure and thermodynamic aspects of Dy(III) complex formation with some mono- and dicarboxylic acids

Spatial structures of complexes [DyAc]²⁺, [DyBz]²⁺, [DyAc₂]⁺ and [DyBz₂]⁺ in aqueous solutions (Ac^– and Bz^–, acetate and benzoate anions, respectively) are studied using the paramagnetic double refraction method. The polyhedra of [DyAc(H₂O)₆]²⁺ and [DyBz(H₂O)₆]²⁺ are dodecahedra with ligands coordinated at one of the edges. In the complexes [DyAc₂(H₂O)₄]⁺ and [DyBz₂(H₂O)₄]⁺ the ligands are coordinated at the edges of a square antiprism at an angle of 50 (55)° to the local symmetry axis of higher symmetry.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1038–1040, June, 1993.