Fe(III)Fe(III) and Fe(II)Fe(III) Complexes as Synthetic Analogues for the Oxidized and Reduced Forms of Purple Acid Phosphatases

Novel Fe(III)Fe(III) and Fe(II)Fe(III) complexes [Fe(2)(BBPMP)(&mgr;-OAc)(&mgr;-X)](n)() (1, X = OAc(-), n = 1+; 2, X = OH(-), n = 1+; 3, X = OAc(-), n = 0; 4, X = OH(-), n = 0), where BBPMP(3)(-) is the anion of 2,6-bis[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methylphenol, and OAc(-) is acetate, were prepared in order to provide models for the active site of purple acid phosphatases (PAPs). Complex 1 was obtained by the reaction of H(3)BBPMP with Fe(ClO(4))(2).6H(2)O in methanol and sodium acetate trihydrate under ambient conditions, while complex 3 was synthesized as described for 1, under an argon atmosphere with low levels of dioxygen. 2 was isolated from 1in acetonitrile by a substitution of the bridging acetate group by hydroxide, while 4 was generated in solution during a spectropotentiostatic experiment on 2, under argon. Complex 1, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(2)]ClO(4).H(2)O, has been characterized by X-ray crystallography. Crystal data: monoclinic, space group P2(1)/n, a = 14.863(5) ?, b = 12.315(3) ?, c = 20.872(8) ?, beta = 90.83(3) degrees, Z = 4. IR, M?ssbauer, magnetic, electronic absorption, and electrochemical properties of 1-3 have been investigated, and some of these properties represent a contribution to the understanding of the dinuclear iron center of PAPs. Complexes 2, [Fe(III)(2)(BBPMP)(&mgr;-OAc)(&mgr;-OH)]ClO(4) (lambda(max) = 568 nm/epsilon = 4760 M(-)(1) cm(-)(1)), and 4 [Fe(II)Fe(III)(BBPMP)(&mgr;-OAc)(&mgr;-OH)] (lambda(max) = 516 nm/epsilon = 4560 M(-)(1) cm(-)(1)), constitute good synthetic analogues for the chromophoric site for the oxidized and reduced forms, respectively, of the enzyme.     

Adsorption behavior of Fe(II) and Fe(III) ions on thiourea cross-linked chitosan with Fe(III) as template

A new type of thiourea cross-linked chitosan with Fe(III) as template (TCCTS template) was synthesized. The adsorption of Fe(II) and Fe(III) on this TCCTS template was studied. The factors affecting adsorption such as pH and contact time were considered. The results showed that the optimum pH value for adsorption was pH = 5.0 and the adsorption equilibrium time was about 60 min. The adsorption isotherms and kinetics were investigated, and the equilibrium data agreed very well with the Langmuir model and the pseudo second-order model could describe adsorption process better than the pseudo first-order model. Results also showed that TCCTS template was a favourable adsorbent for Fe(II) and Fe(III) in aqueous solution.     

Cyanido-bridged Fe(III)-Mn(III) heterobimetallic materials built from Mn(III) Schiff base complexes and di- or tri-cyanido Fe(III) precursors

The reaction of [Fe(III)L(CN)(3)](-) (L being bpca = bis(2-pyridylcarbonyl)amidate, pcq = 8-(pyridine-2-carboxamido)quinoline) or [Fe(III)(bpb)(CN)(2)](-) (bpb = 1,2-bis(pyridine-2-carboxamido)benzenate) ferric complexes with Mn(III) salen type complexes afforded seven new bimetallic cyanido-bridged Mn(III)-Fe(III) systems: [Fe(pcq)(CN)(3)Mn(saltmen)(CH(3)OH)]·CH(3)OH (1), [Fe(bpca)(CN)(3)Mn(3-MeO-salen)(OH(2))]·CH(3)OH·H(2)O (2), [Fe(bpca)(CN)(3)Mn(salpen)] (3), [Fe(bpca)(CN)(3)Mn(saltmen)] (4), [Fe(bpca)(CN)(3)Mn(5-Me-saltmen)]·2CHCl(3) (5), [Fe(pcq)(CN)(3)Mn(5-Me-saltmen)]·2CH(3)OH·0.75H(2)O (6), and [Fe(bpb)(CN)(2)Mn(saltmen)]·2CH(3)OH (7) (with saltmen(2-) = N,N'-(1,1,2,2-tetramethylethylene)bis(salicylideneiminato) dianion, salpen(2-) = N,N'-propylenebis(salicylideneiminato) dianion, salen(2-) = N,N'-ethylenebis(salicylideneiminato) dianion). Single crystal X-ray diffraction studies were carried out for all these compounds indicating that compounds 1 and 2 are discrete dinuclear [Fe(III)-CN-Mn(III)] complexes while systems 3-7 are heterometallic chains with {-NC-Fe(III)-CN-Mn(III)} repeating units. These chains are connected through π-π and short contact interactions to form extended supramolecular networks. Investigation of the magnetic properties revealed the occurrence of antiferromagnetic Mn(III)···Fe(III) interactions in 1-4 while ferromagnetic Mn(III)···Fe(III) interactions were detected in 5-7. The nature of these Mn(III)···Fe(III) magnetic interactions mediated by a CN bridge appeared to be dependent on the Schiff base substituent. The packing is also strongly affected by the nature of the substituent and the presence of solvent molecules, resulting in additional antiferromagnetic interdinuclear/interchain interactions. Thus the crystal packing and the supramolecular interactions induce different magnetic properties for these systems. The dinuclear complexes 1 and 2, which possess a paramagnetic S(T) = 3/2 ground state, interact antiferromagnetically in their crystal packing. At high temperature, the complexes 3-7 exhibit a one-dimensional magnetic behavior, but at low temperature their magnetic properties are modulated by the supramolecular arrangement: a three-dimensional antiferromagnetic order with a metamagnetic behavior is observed for 3, 4, and 7, and Single-Chain Magnet properties are detected for 5 and 6.     

Formation of ferrocyanides-III Fe(III), La(III) and Ce(III)

Potassium ferrocyanide forms Fe(4)[Fe(Cn)(6)](3) with Fe(III), KLaFe(CN)(6) with La(III) and KCeFe(CN)(6) with Ce(III). The thermodynamic data for the two lanthanide compounds have been determined.     

Fe(III)-pyruvate and Fe(III)-citrate induced photodegradation of glyphosate in aqueous solutions

The photolysis of Fe(III)-pyruvate and Fe(III)-citrate complexes in water produces hydroxyl radicals in the presence of dissolved oxygen, and can promote the oxidation of organic compounds. The photodegradation of glyphosate with Fe(III)-pyruvate and Fe(III)-citrate complexes was investigated under irradiation at λ?≥?365?nm. The effect of initial concentration of glyphosate, the initial pH value, and the Fe(III)/carboxylate ratio were examined. Upon irradiation of glyphosate aqueous solution with the complexes in the acidic range of natural waters, the bioavailable orthophosphate could be released from degradation of glyphosate. The amount of orthophosphate increased with increasing Fe(III)/carboxylate ratio.     

Field-induced metamagnetic transition in the Fe(III)-Mn(III) bimetallic chain built by a new cyanide-bearing Fe(III) precursor

The use of a new precursor, mer-[Fe(mpzcq)(CN)3]- (1), produced a dimeric molecule, [Fe(mpzcq)(CN)3][Mn(salen)(H2O)] x H2O (2), and a one-dimensional zigzag chain, [Fe(mpzcq)(CN)3][Mn(salcy)] x MeOH x MeCN (3). Antiferromagnetic couplings are operating between magnetic centers through CN ligands, and a field-induced metamagnetic transition is observed in 3.     

Isosaccharinate Complexes of Fe(III)

Prior to this study there were no thermodynamic data for isosaccharinate (ISA) complexes of Fe(III) in the environmental range of pH (>~4.5). This study was undertaken to obtain such data in order to predict Fe(III) behavior in the presence of ISA. The solubility of Fe(OH)₃(2-line ferrihydrite), referred to as Fe(OH)₃(s), was studied at 22?±?2?°C in: (1) very acidic (0.01?mol·dm^?3 H⁺) to highly alkaline conditions (3?mol·dm^?3 NaOH) as a function of time (11?C421?days), and fixed concentrations of 0.01 or 0.001?mol·dm^?3 NaISA; and (2) as a function of NaISA concentrations ranging from approximately 0.0001 to 0.256?mol·dm^?3 and at fixed pH values of approximately 4.5 and 11.6 to determine the ISA complexes of Fe(III). The data were interpreted using the SIT model that included previously reported stability constants for $ {{\text{Fe(ISA}})_{n}}^{3 - n} $ (with n varying from 1 to 4) and Fe(III)?COH complexes, and the solubility product for Fe(OH)₃(s) along with the values for two additional complexes (Fe(OH)₂(ISA)(aq) and $ {\text{Fe(OH)}}_{ 3} ( {{\text{ISA}})_{2}}^{2 - } $ ) determined in this study. These extensive data provided a log₁₀ K ⁰ value of 1.55?±?0.38 for the reaction $ ({\text{Fe}}^{ 3+ } + {\text{ISA}}^{-} + 2 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH}})_{ 2} {\text{ISA(aq}}) + 2 {\text{H}}^{ + } ) $ and a value of ?3.27?±?0.32 for the reaction $ ({\text{Fe}}^{ 3+ } + 2 {\text{ISA}}^{-} + 3 {\text{H}}_{ 2} {\text{O}} \rightleftarrows {\text{Fe(OH)}}_{ 3} ( {\text{ISA}})_{2}^{2 - } + 3 {\text{H}}^{ + } ) $ and show that ISA forms strong complexes with Fe(III) which significantly increase the Fe(OH)₃(s) solubility at pH?<~12. Thermodynamic calculations show that competition of Fe(III) with tetravalent ions for ISA does not significantly affect the solubilities of tetravalent hydrous oxides (e.g., Th and Np(IV)) in ISA solutions.     

Dinuclear triple helical Mn(III), Fe(III) and Co(III) complexes

Synthesis, characterization and physical properties of the dinuclear triple helical complexes [Mn₂(μ-L)₃] (1), [Fe₂(μ-L)₃] (2) and [Co₂(μ-L)₃] (3) with the tetradentate Schiff base (H₂L) derived from 1 mol equiv. of hydrazine and 2 mole equiv. of 2-hydroxy-1-naphthaldehyde are described. Triple helical molecular structures of 2 and 3 have been confirmed by X-ray crystallography. Magnetic susceptibility measurements reveal complex 3 is diamagnetic while a weak antiferromagnetic interaction is operative between the metal centres in both 1 and 2.     

Discrete Rh(III)/Fe(II) and Rh(III)/Fe(II)/Co(III) cyanide-bridged mixed valence compounds

The heterotrinuclear complexes trans- and cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) are unprecedented examples of mixed valence complexes based on ferrocyanide bearing three different metal centers. These complexes have been assembled in a stepwise manner from their {trans-III-L(14S)Co(III)}, {cis-VI-L(15)Rh(III)}, and {Fe(II)(CN)(6)} building blocks. The preparative procedure follows that found for other known discrete assemblies of mixed valence dinuclear Cr(III)/Fe(II) and polynuclear Co(III)/Fe(II) complexes of the same family. A simple slow substitution process of [Fe(II)(CN)(6)](4-) on inert cis-VI-[Rh(III)L(15)(OH)](2+) leads to the preparation of the new dinuclear mixed valence complex [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) with a redox reactivity that parallels that found for dinuclear complexes from the same family. The combination of this dinuclear precursor with mononuclear trans-III-[Co(III)L(14S)Cl](2+) enables a redox-assisted substitution on the transient {L(14S)Co(II)} unit to form [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+). The structure of the final cis-[{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) complex has been established via X-ray diffraction and fully agrees with its solution spectroscopy and electrochemistry data. The new species [{cis-VI-L(15)Rh(III)(μ-NC)}{trans-III-L(14S)Co(III)(μ-NC)}Fe(II)(CN)(4)](2+) and [{cis-VI-L(15)Rh(III)(μ-NC)}Fe(II)(CN)(5)](-) show the expected electronic spectra and electrochemical features typical of Class II mixed valence complexes. Interestingly, in the trinuclear complex, these features appear to be a simple addition of those for the Rh(III)/Fe(II) and Co(III)/Fe(II) moieties, despite the vast differences existent in the electronic spectra and electrochemical properties of the two isolated units.     

Determination of Fe(II)-Fe(III) and Fe(III)-Ni(II) by the two-component potentiometric complexometric titration

Summary The two-component complexometric potentiometric titration has been applied to the simultaneous determination of Fe(III) and Fe(II), and of Fe(III) and Ni(II) in solution. In each case the two analytes were determined by reading the end-points directly from the titration curve. The end-points are determined in a sense arbitrarily, but they are repeatable and easy to be detected precisely. However, the apparent (found) analytical results are biased. They are effectively corrected with the use of a set of two calibration equations (uncomplete second degree polynomials), which approximate the relationship between found endpoints and true concentrations of analytes in solution. The regression coefficients in the equations are determined on the basis of titration data obtained for standard solutions whose compositions correspond to a 2² factorial. Permanent address: Department of Analytical Chemistry, Jagiellonian University, Krakow     

Unequivocal determination of metal atom oxidation state in naked heme proteins: Fe(III)myoglobin, Fe(III)cytochrome c, Fe(III)cytochrome b5, and Fe(III)cytochrome b5 L47R

Unambiguous determination of metal atom oxidation state in an intact metalloprotein is achieved by matching experimental (electrospray ionization 9.4 tesla Fourier transform ion cyclotron resonance) and theoretical isotopic abundance mass distributions for one or more holoprotein charge states. The ion atom oxidation state is determined unequivocally as Fe(III) for each of four gas-phase unhydrated heme proteins electrosprayed from H2O: myoglobin, cytochrome c, cytochrome b5, and cytochrome b5 L47R (i.e., the solution-phase oxidation state is conserved following electrospray to produce gas-phase ions). However, the same Fe(III) oxidation state in all four heme proteins is observed after prior reduction by sodium dithionite to produce Fe(II) heme proteins in solution: thus proving that oxygen was present during the electrospray process. Those results bear directly on the issue of similarity (or lack thereof) of solution-phase and gas-phase protein conformations. Finally, infrared multiphoton irradiation of the gas-phase Fe(III)holoproteins releases Fe(III)heme from each of the noncovalently bound Fe(III)heme proteins (myoglobin, cytochrome b5 and cytochrome b5 L47R), but yields Fe(II)heme from the covalently bound heme in cytochrome c.     

Cyano-bridged Mn(III)-M(III) single-chain magnets with M(III)=Co(III), Fe(III), Mn(III), and Cr(III)

A series of isostructural cyano-bridged Mn(III)(h.s.)-M(III)(l.s.) alternating chains, [Mn(III)(5-TMAMsalen)M(III)(CN)(6)]?4H(2)O (5-TMAMsalen(2-)=N,N'-ethylenebis(5-trimethylammoniomethylsalicylideneiminate), Mn(III)(h.s.)=high-spin Mn(III), M(III)(l.s.)=low-spin Co(III), Mn-Co; Fe(III), Mn-Fe; Mn(III), Mn-Mn; Cr(III), Mn-Cr) was synthesized by assembling [Mn(III)(5-TMAMsalen)](3+) and [M(III)(CN)(6)](3-). The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [-Mn(III)-NC-M(III)-CN-] repeating motif, for which the -NC-M(III)-CN- motif is provided by the [M(III)(CN)(6)](3-) moiety adopting a trans bridging mode between [Mn(III)(5-TMAMsalen)](3+) cations. The Mn(III) and M(III) ions occupy special crystallographic positions: a C(2) axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn-Teller axis of the Mn(III)(h.s.) ion is perpendicular to the N(2)O(2) plane formed by the 5-TMAMsalen tetradentate ligand. These Jahn-Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn-N(axis) -C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter-chain M???M distance being relatively large at 9?? due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5-TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn-Fe and Mn-Mn display intra-chain ferromagnetic interactions, whereas Mn-Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single-chain magnet (SCM) behavior of these three systems, whereas Mn-Co is merely paramagnetic with S(Mn)=2 and D/k(B)=-5.3?K (D being a zero-field splitting parameter). At low temperatures, the Mn-M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite-chain and finite-chain regimes for the SCM behavior. These isostructural hetero-spin SCMs offer a unique series of alternating [-Mn-NC-M-CN-] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits.     

Bemerkenswerte Wirt-Gast-Beziehungen in Tetraphenylphosphoniumsalzen vontris-Trithiocarbonato-Komplexen des As(III), Bi(III) und Fe(III)

Summary The structure and packing of the lattice of the compounds (PPh₄)₃[As(CS₃)₃] (1), (PPh₄)₃[Bi(CS₃)₃] (2), and (PPh₄)₃[Fe(CS₃)₃]·H₂O (3) is discussed in terms of hostguest chemistry in a soft matrix of large cations. The hitherto unknown Fe-complex was characterized by elemental analysis and single crystal structure analysis. Here CS ₃ ^2– acts as a classical bidentate ligand, whereas in the case of the arsenic and bismut complexes, the coordination of this ligand is essentially unidentate due to an interaction with the lone pair on the central atom. For the last two complexes, there seems to be an influence of the packing on the coordination geometry.

Herrn Prof. Dr.E. Hengge zum 65. Geburtstag gewidmet     

Influence of arsenate species on the formation of Fe(III) oxyhydroxides and Fe(II–III) hydroxychloride

Iron(III) oxyhydroxides were prepared by oxidation of aerated aqueous suspensions of Fe(II) hydroxide. The effects of arsenate species on their formation were studied by mixing FeCl₂·4H₂O, NaOH and Na₂HAsO₄ solutions. The intermediate and final products of the oxidation processes were characterised by X-ray diffraction, Infrared and Raman spectroscopy. Arsenate species were not reduced during the process but they influenced both oxidation stages, that is the formation of the intermediate Fe(II–III) compound and its subsequent oxidation into Fe(III) compounds. Arsenate species clearly inhibited the growth and hindered the crystallisation of GR(Cl^?), the Fe(II–III) hydroxychloride that would have formed in the experimental conditions considered here. For the largest arsenate concentrations, the intermediate product was nanocrystalline and more likely consisted of clusters showing an ordering of atoms similar to that of GR(Cl^?), isolated from each other by adsorbed arsenate species. The adsorption of As(V) prevented growth of these clusters into well-crystallised GR(Cl^?). The arsenate species influenced similarly the second reaction stage by inhibiting the formation of well-ordered and crystallised Fe(III) compounds. Lepidocrocite, the final product in the absence of arsenate, was replaced by “6-line” ferrihydrite with increasing As(V) concentration, then “6-line” ferrihydrite was replaced by another poorly ordered compound, feroxyhite. These crystallised compounds were obtained together with an increasing part of nanocrystalline Fe(III) ox(yhydrox)ide(s).     

Characterisation of some polyamino complexes of Fe(II) and Fe(III) imides

Complexes of the types [Fe(imide)₂(Am)₂] and [Fe(imide)₃(Am)(H₂O)](imide = deprotonated malonimide and phthalimide; Am = dipyridyl and o-phenanthroline) have been prepared and characterised on the basis of IR, electronic spectra, conductance, magnetic and Mössbauer studies. The bonding powers of phthalimide and malonimide are almost the same and all the complexes have a distorted octahedral structure.     

Oxidation of Fe(III) to Fe(VI) by ozone in alkaline solutions

The action of ozone on a suspension of Fe(III) hydroxide in alkaline solutions was studied by the spectrophotometric method. A partial conversion of Fe(III) to Fe(VI) is observed at Fe(III) concentrations exceeding 2 mmol l⁻¹. The tenfold increase of the initial Fe(III) concentration raises the Fe(VI) yield by a factor of 2–3. The mechanism of the process includes the decomposition of ozone with the formation of ozonide ions, which oxidize Fe(III) up to Fe(IV), Fe(V), and Fe(VI) in parallel with their conversion to O₂⁻ and HO₂⁻. Fe(VIII) is not formed.     

Tuning the selectivity of two chemosensors to Fe(III) and Cr(III)

Two rhodamine-based chemosensors (1 and 2) were designed, and their sensing behavior toward metal ions was investigated by fluorescence spectroscopies. 1 and 2 achieved tuning the selectivity to Fe(III) and Cr(III) in 100% aqueous solution, whereas other ions including Cd(II), Co(II), Cu(II), Ni(II), Zn(II), Mg(II), Ba(II), Pb(II), Na(I), and K(I) induced basically no spectral change, which constituted a Fe(III)-selective and a Cr(III)-selective fluorescent chemosensor, respectively.     

A new phenanthrene-based bis-oxime chemosensor for Fe(III) and Cr(III) discrimination

The synthesis of two new 2,7-disubstituted phenanthrene-based bis oximes is described. The ability of these two compound for complexing heavy metal cations have been studied and complexation constants and complex stoichiometry for Cr³⁺ and Fe³⁺ complex have been determined. The fluorescent properties of ligand 2 make this compound able to act as a sensor able to discriminate between Cr³⁺ and Fe³⁺. Detection limits for these two cations have been evaluated.