Synthesis,structure and stability of fac-[FeII(CO)3X3]1− (X = Br,I)

fac-[Fe^II(CO)₃X₃]^1? (X = Br, I) are synthesized and their structures have been determined. They are the first crystallographically characterized iron tricarbonyl trihalide complexes. fac-[Fe^II(CO)₃X₃]^1? (X = Br, I) are fairly thermally stable and therefore lead themselves as excellent starting materials for the preparation of various iron carbonyl complexes since both the halide and carbonyl ligands are substitutionally labile.     

Magnetic behavior of polycarbosilazane ?FeII, ?FeIII and mixed‐valence ?FeII–III chloride metallopolymers

Fe^II, Fe^III and mixed‐valence Fe^II–III chlorides were reacted with poly[N,N′‐bis(dimethylsilyl)ethylenedi‐ amine], [? Si(CH₃)₂NHCH₂CH₂NH? ]_n, to form the corresponding Fe‐polycarbosilazane macromolecular complexes. The average chain–chain spacing in these materials was estimated from X‐ray diffraction data and found to be 6.94, 7.29, 7.30 and 7.45 Å in metal‐free and Fe^II? , Fe^III? and Fe^II–III‐containing polycarbosilazanes, respectively. This demonstrates that Fe^II, Fe^III and Fe^II–III chlorides are encapsulated between the polycarbosilazane chains. The chain–chain expansions in the divalent Fe^II and trivalent Fe^III chloride macromolecular complexes are comparable, but less than that in the Fe^II–III chloride analog, which suggests that different chain–chain packings exist in the mixed‐valence macromolecular complex. The magnetic properties of the resulting complexes were investigated by measuring the magnetization in magnetic fields up to 8 kOe and in the temperature range from liquid nitrogen temperature to room temperature. Copyright © 2007 Society of Chemical Industry     

Thermal, Spectroscopic, Cyclic Voltammetric, and Biological Activity Studies of Cobalt(II), Nickel(II), and Copper(II) Complexes of Dicarboxylic Amino Acids and 8-Hydroxyquinoline

Mixed ligand complexes of Co^II, Ni^II and Cu^II with dicarboxylic amino acids (aspartic, glutamic or H₂ADA) as primary ligands and 8-hydroxyquinoline as a secondary ligand were prepared and characterized by elemental analysis, conductivity measurements, thermal analysis, cyclic voltammetry, and electronic and infrared (IR) spectroscopy. Cyclic voltammetry reveals a reversibility of the Cu^II/Cu^I couple, while the reactions of the Co^II and Ni^II complexes are irreversible. All complexes have a metal-to-ligand ratios of 1:1:1 and octahedral structures are suggested to be attained by interactions among both of the amino acids and 8-hydroxyquinoline anions with the metal ions. The reaction orders and activation energies have been computed by means of the Coats–Redfern and Horowitz–Metzger equations. The biological activity of selected complexes as anti-fungal agents has been tested.     

Quantum-chemical calculations of the effect of cycloaliphatic groups in α-diimine and bis(imino)pyridine ethylene polymerization precatalysts on their stabilities with respect to deactivation reactions

For the first time, it is attempted to interpret an experimentally found enhancing effect of cycloaliphatic substituents in aromatic rings of Ni^II- and Pd^II-α-diimine and Fe^II-bis(imino)pyridine ethylene polymerization precatalysts on their catalytic activities at elevated temperatures (60-80 °C), using quantum chemical density functional theory calculations of relative stabilities of the complexes with respect to different deactivation processes, including thermal decomposition and one-electron reduction. It was shown that the effect correlates with the calculated higher thermal stabilities of cycloalkyl-substituted Fe^II-, Ni^II- and Pd^II-complexes as compared to the corresponding alkyl-substituted ones. Ni^II- and Pd^II-α-diimine complexes with cycloalkyl substituents are shown to be more stable than their alkyl-substituted analogues with respect to both thermal decomposition and one-electron reduction. The averaged difference of the thermal decomposition energies between the complexes with cycloaliphatic substituents on one side and aliphatic ones on the other side is ∼2.3 kcal/mol, corresponding to ∼30 times lower equilibrium constant of the thermal decomposition reaction for the cycloalkyl-containing complexes. For the Fe^II- and Pd^II-complexes, the thermal stability correlates with the calculated overlap population of the metal-nitrogen bonds. It was shown that the structure of o-substituents (cycloalkyls vs. alkyls) in the phenyl rings of the ligands does not affect the reaction energies for the transformation reactions of the precatalysts into their corresponding active catalytic cationic forms.     

Preparation and structures of trinuclear manganese(II) complexes with N-2-pyridiylmethylidene-2-hydroxy-5-substituted-phenylamine

The trinuclear manganese(II) complexes, [Mn^II₃(OAc)₄(pap)₂(H₂O)₂] and [Mn^II₃(OAc)₄(5-Cl-pap)₂(MeOH)₂] were prepared by the reaction of tridentate Schiff base ligands X-papH (X=H, Cl), [N-2-pyridiylmethylidene-2-hydroxy-5-substituted-phenylamine], and Mn^II(OAc)₂·2H₂O. In the molecular structures of these complexes, two terminal manganese ions are coordinated with one oxygen and two nitrogen atoms of X-pap, two oxygen atoms of OAc⁻ and a solvent molecule, to form a distorted octahedral structure where the central manganese ion resides on a center of symmetry and is surrounded by an O₆ donor set of four oxygen atoms from four bridging OAc⁻ and two phenolic oxygen atoms of two X-pap ligands.     

Cobalt hexacyanoferrate in PAMAM doped silica matrix. 2. Structural and electronic characterization

A composite of silica sol-gel, generation-4 poly(amidoamine) dendrimer (PAMAM) and cobalt hexacyanoferrate (CoHCF) was synthesized as a potential electrochromic material. The solid-state voltammetry of the material had suggested that the two electroactive sites were present. To elucidate the redox properties, the electronic and the structure in the local atomic environment of Fe and Co was investigated by X-ray absorption spectroscopy (XAS). Although the nominal stoichiometries of the investigated CoHCFs were Co₂^IIFe^II(CN)₆ (or K₂Co^IIFe^II(CN)₆) and KCo^IIFe^III(CN)₆, the spectral data demonstrated that Co^III was present in the composite. Among the supporting evidence for some metal-to-metal electronic transition of Fe^III-CN-Co^II to Fe^II-CN-Co^III was the shortening of the measured Co-N bond length in accord with the formation of Co^III. Further, IR measurements confirm the occurrence of charge transfer between Fe and Co sites in the silica-PAMAM composite.     

Anion-responsive luminescent Eu3+ complexes with ring-like rigid quinoline–amide ligands

Two novel ring-like rigid quinoline–amide ligands, 2-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-N-benzylacetamide (L^I) and 3-[2-(1,3-dioxolan-2-yl)quinolin-8-yloxy]-1,1-diphenylpropan-2-one (L^II), were designed to assemble the anion-responsive luminescent europium complexes. Crystallographic studies of the EuL^I(NO₃)₃ and EuL^II(NO₃)₃ revealed that the tetradentate ligands L^I and L^II cooperatively coordinated with Eu³⁺ ion and some available sites around central europium ions for guest anions were reserved in the complexes. The luminescent properties of the Eu(III) nitrate complexes in acetonitrile solutions were investigated. And the lowest triplet state energy levels of the ligands are well placed to allow energy transfer to the resonance level of Eu(III). At the same time, the luminescence titration experiments and the Job's plot analysis demonstrated the formation of 1:1 complexes in the solutions. The luminescence intensities at 616 nm were enhanced by addition of NO₃^? or Cl^? anion to the mixed acetonitrile solutions of Eu(CF₃SO₃)₃ and the ligands.     

FeIII,CuII and ZnII Complexes of the Rigid 9-Oxido-phenalenone Ligand—Spectroscopy,Electrochemistry, and Cytotoxic Properties

The three complexes [Fe(opo)₃], [Cu(opo)₂], and [Zn(opo)₂] containing the non-innocent anionic ligand opo⁻ (opo⁻ = 9-oxido-phenalenone, Hopo = 9-hydroxyphenalonone) were synthesised from the corresponding acetylacetonates. [Zn(opo)₂] was characterised using ¹H nuclear magnetic resonance (NMR) spectroscopy, the paramagnetic [Fe(opo)₃] and [Cu(opo)₂] by electron paramagnetic resonance (EPR) spectroscopy. While the EPR spectra of [Cu(opo)₂] and [Cu(acac)₂] in dimethylformamide (DMF) solution are very similar, a rather narrow spectrum was observed for [Fe(opo)₃] in tetrahydrofuran (THF) solution in contrast to the very broad spectrum of [Fe(acac)₃] in THF (Hacac = acetylacetone, 2,4-pentanedione; acac⁻ = acetylacetonate). The narrow, completely isotropic signal of [Fe(opo)₃] disagrees with a metal-centred S = 5/2 spin system that is observed in the solid state. We assume spin-delocalisation to the opo ligand in the sense of an opo⁻ to Fe^III electron transfer. All compounds show several electrochemical opo-centred reduction waves in the range of −1 to −3 V vs. the ferrocene/ferrocenium couple. However, for Cu^II and Fe^III the very first one-electron reductions are metal-centred. Electronic absorption in the UV to vis range are due to π–π* transitions in the opo core, giving Hopo and [Zn(opo)₂] a yellow to orange colour. The structured bands ranging from 400 to 500 for all compounds are assigned to the lowest energy π−π* transitions. They show markedly higher intensities and slight shifts for the Cu^II (brown) and Fe^III (red) complexes and we assume admixing metal contributions (MLCT for Cu^II, LMCT for Fe^III). For both complexes long-wavelength absorptions assignable to d–d transitions were detected. Detailed spectroelectrochemical experiments confirm both the electrochemical and the optical assignments. Hopo and the complexes [Cu(opo)₂], [Zn(opo)₂], and [Fe(opo)₃] show antiproliferative activities against HT-29 (colon cancer) and MCF-7 (breast cancer) cell lines in the range of a few µM, comparable to cisplatin under the same conditions.     

A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

To mimic dinuclear active sites of metalloproteins, we have developed a dinucleating ligand system consisting of two tetradentate tripodal ligand compartments with varying terminal donors (carboxylates, phenolates, and pyridines). These ligands provide access to a series of μ-oxo-bridged diferric complexes. The spectroscopic study allows to investigate the molecular structures even in solution, e. g. depending on protonation/deprotonation of coordinated OH⁻ and H₂O ligands or to observe a reversible pH-dependent carboxylate-shift between terminal and bridging binding mode. The electrochemical behavior is strongly influenced by the exogenous ligands, e. g. OH⁻ facilitates oxidation to Fe^IV by 690 mV relative to Cl⁻. Using the terminal carboxylates and a {Fe^III(μ-O)₂Fe^III} core even allows oxidation with O₂ to a high-valent species with Fe^IV (S=2). The implications of this study for further generation of high-valent or peroxo species and their utilization in catalysis is discussed.     

Proteins as Possible Targets for Cytotoxic trans‐Platinum(II) Complexes with Aliphatic Amine Ligands: Further Exceptions to the DNA Paradigm

The reactivity of three cytotoxic trans‐Pt^II complexes bearing aliphatic amine ligands, with transferrin and single‐stranded oligonucleotides as DNA models, was investigated by ESI‐MS and the results obtained are discussed in comparison with cisplatin. Tandem MS studies provided additional information on the preferential Pt binding sites. To determine whether trans‐Pt^II complexes can migrate from a peptide to an oligonucleotide, transfer experiments were also performed using ESI‐MS, and competitive binding of the trans‐Pt^II complexes toward a model peptide and different oligonucleotides was also investigated. Significant differences in the reactivity of the trans complexes with respect to cisplatin were observed. In general, adduct formation with the selected peptide is favored for the trans compounds, whereas cisplatin shows a preference for oligonucleotides, especially if adjacent G–G residues are present. The results are discussed in relation to the possible mechanism of action of the trans‐Pt^II complexes.     

The synthesis of tetrahedral bipyridyl metallo-octupoles with large second- and third-order nonlinear optical properties

Two new 4,4′-bis(donor)-6,6′-diphenyl- 2,2′-bipyridine ligands and their corresponding D_2d (Cu^I, Ag^I, Zn^II) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were investigated. A single crystal X-ray structure was also determined for the bis[4,4′-bis(diethylaminostyryl)-6,6′-diphenyl-bipyridine]copper(I) complex, which revealed a distorded pseudo-tetrahedral geometry. Molecular second-order nonlinear optical properties were determined for the complexes using the Harmonic Light Scatterring technique at 1.91 μm. These metallo-chromophores display large first hyperpolarizabilities β_1.91 in the range of 211-340 × 10⁻³⁰ esu, which increase with the Lewis acidity of the metal ion. The two-photon absorption properties of the bipyridyl ligands and related complexes were determined using either the two-photon emission method for fluorescent compounds or the open aperture Z-scan technique for non emissive ones. The complexes display red-shifted two-photon absorption bands compared to their metal-ion free chromophores, as well as a large increase of the maximum two-photon absorption cross-sections.     

Aqueous radical polymerization of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylacrylamide redox-initiated by aerobically catalytic oxidation of water-soluble tertiary amines

Catalytic oxidation of water-soluble tertiary amines by complexes of Cu^II, Fe^III and Co^II was utilized to initiate radical polymerization of N,N-dimethylacrylamide (DMAAm) in aqueous solution at 70–80 °C. The oxidation of tertiary amines by Cu^II was studied by proton nuclear magnetic resonance spectroscopy and online ultraviolet–visible spectrophotometry. The polymerization kinetics was monitored by gas chromatography, and molecular weight of the PDMAAm was measured by gel-permeation chromatography coupled with multi-angle laser light scattering. Oxidation of tertiary amines occurs predominantly via formation of C_alpha·radicals to initiate polymerization of electron-deficient monomers and N-dealkylation, and redox equilibrium between Cu^I/L and Cu^II/L is established at a faster rate in aqueous media. Fe^III and Cu^II complexes are efficient catalysts as each catalyst molecule could generate above 10 propagating radicals in 5 h, while Co^II complex might involve in oxidation of tertiary amines in non-radical pathway, leading to a low catalytic efficiency. Water-soluble tertiary amines such as N,N-dialkylethanolamine (alkyl = methyl, ethyl etc.) are reducing agents of a higher activity in aqueous media than those primary or secondary analogues. Our strategy renders it possible to prepare polymer of alpha-amino functionality via one-pot process from commercially available commodity reagents under practical conditions with negligible catalyst residue.     

Ethylene oligomerization promoted by group 8 metal complexes containing 2-(2-pyridyl)quinoxaline ligands

Ni^II, Co^II and Fe^II complexes of 2-(2-pyridyl)quinoxaline were synthesized and used in the ethylene oligomerization with methyl-aluminoxane (MAO) as cocatalyst. The nickel complex system mainly produced α-olefins with good activity, while the cobalt and iron complexes showed only marginal activity.     

Preparation of new heteronuclear (NH4)RE[FeII(CN)6]·nH2O complexes (RE = La,Ce, Pr,Nd, Sm,Gd, Dy,Y, Er,Lu) and their low-temperature decomposition for perovskite-type oxide

New heteronuclear (NH₄)RE^III[Fe^II(CN)₆]·nH₂O complexes (RE = La, Ce, Pr, Nd, Sm, Gd, Dy, Y, Er, Lu) were synthesized and their thermal decomposition products were investigated. The crystal structure of (NH₄)RE[Fe^II(CN)₆]·nH₂O would be a hexagonal unit cell (space group: P6₃/m), which was the same as that of La[Fe^III(CN)₆]·5H₂O. The hydration number n = 4 was estimated by TG results for all the RE complexes. The lattice constants depended on the ionic radius of the RE³⁺ ion for the heteronuclear complexes. The single phase of the perovskite type materials was directly obtained by decomposition of the heteronuclear complexes for RE = La, Pr, Nd, Sm, and Gd. A mixture of CeO₂ and Fe₂O₃ was formed for RE = Ce because of its oxidation to Ce⁴⁺. In the case of RE = Dy, Y, Er, and Lu complexes, the perovskite type materials formed at higher temperature via. mixed oxides such as RE₂O₃ and RE₄Fe₅O₁₃ due to the small RE³⁺ ionic radius.     

Oxidative dehydrogenation of n-butene to 1,3-butadiene over multicomponent bismuth molybdate (M9Fe3Bi1Mo12O51) catalysts: Effect of divalent metal (M)

Multicomponent bismuth molybdate (M^II₉Fe₃Bi₁Mo₁₂O₅₁) catalysts with different divalent metal (M^II = Mg, Mn, Co, Ni, and Zn) were prepared by a co-precipitation method, and were applied to the oxidative dehydrogenation of n-butene to 1,3-butadiene. Effect of divalent metal (M^II) on the catalytic performance of M^II₉Fe₃Bi₁Mo₁₂O₅₁ catalysts was investigated. X-ray photoelectron spectroscopy (XPS) measurements were conducted to determine the oxygen mobility of M^II₉Fe₃Bi₁Mo₁₂O₅₁ catalysts. It was found that the catalytic performance of M^II₉Fe₃Bi₁Mo₁₂O₅₁ catalysts was closely related to the oxygen mobility of the catalysts. The yield for 1,3-butadiene was monotonically increased with increasing oxygen mobility of the catalysts. Among the catalysts tested, the Co₉Fe₃Bi₁Mo₁₂O₅₁ catalyst with the highest oxygen mobility showed the best catalytic performance in the oxidative dehydrogenation of n-butene.     

Synthesis,characterization and antitumoral activity of new di-iron(III) complexes containing naphthyl groups: Effect of the isomerism on the biological activity

The synthesis, physico-chemical characterization and cytotoxicity of two di-iron(III) complexes toward three human leukemia cell lines (THP-1, U937 and Molt-4) are reported: [(Cl2)FeIII(μ-HL1)₂FeIII(Cl₂)]·3H₂O (1) and [(Cl2)Fe^III(μ-HL2)₂Fe^III(Cl₂)] (2), where HL1 and HL2 are isomers and contain pyridine, phenol, amine and alcohol moieties with a naphthyl pendant unit. These compounds were characterized by a range of physico-chemical methods. Electrochemical studies reveal the maintenance of the dinuclear arrangement in solution, which is supported by ESI(+)-MS studies. Mossbauer spectra consist of a unique doublet indicating equivalent iron centers in the whole sample. The hyperfine parameters are typical of high-spin iron(III). Complex (1) is more active than complex (2), showing an effect of the isomerism on the antitumoral activity. The comparison between these data and those obtained for complexes containing copper and cobalt reveals that the isomerism of the ligand, the nature of the metal centers, the nuclearity and the kind of cell line exert a great influence on the biological activity.     

An Engineered β-Hairpin Peptide Forming Thermostable Complexes with ZnII,NiII, and CuII through a His3 Site

The three-dimensional structure of a peptide, which determines its function, can denature at elevated temperatures, in the presence of chaotropic reagents, or in organic solvents. These factors limit the applicability of peptides. Herein, we present an engineered β-hairpin peptide containing a His₃ site that forms complexes with Zn^II, Ni^II, and Cu^II. Circular dichroism spectroscopy shows that the peptide−metal complexes exhibit melting temperatures up to 80 °C and remain folded in 6 M guanidine hydrochloride as well as in organic solvents. Intrinsic fluorescence titration experiments were used to determine the dissociation constants of metal binding in the nano- to sub-nanomolar range. The coordination geometry of the peptide−Cu^II complex was studied by EPR spectroscopy, and a distorted square planar coordination geometry with weak interactions to axial ligands was revealed. Due to their impressive stability, the presented peptide−metal complexes open up interesting fields of application, such as the development of a new class of peptide−metal catalysts for stereoselective organic synthesis or the directed design of extremophilic β-sheet peptides.     

Electrocatalytic four-electron reductions of O2 to H2O with cytochrome c oxidase model compounds

Three different complexes, heme-Cu ([(⁶L)Fe^IICu^I]⁺ (1), ⁶L=a binucleating ligand having a heme and covalently tethered copper binding tris(2-pyridyl)methylamine tetradentate moiety), heme complex ((⁶L)Fe^II (4), (with “empty” tethered chelate)), and the “parent” iron-porphyrinate ((F₈TPP)Fe^II (5), F₈TPP=tetrakis(2,6-difluorophenyl)porphyrinate) were employed for the electrocatalytic reduction of O₂. Complexes 1 and 4 reduce O₂ to water (four-electron reduction) with good efficiency (74 and 59%, respectively), but complex 5 exhibited only an ∼20% efficiency, thus primarily the two-electron reduction to hydrogen peroxide occurred. The results of the present electrochemical O₂-reduction studies and the previous studies have elucidated the O₂-binding nature of these three complexes, indicating the formation of quite stable Fe^III(O₂²⁻)Cu^II (peroxo) or Fe^IIIO₂⁻ (superoxo) species. In line with the thinking of other researchers, the fact that both 1 and 4 can well stabilize Fe^IIIO₂⁻ superoxo species may suggest that the formation of the latter is a key to the pathway favoring four-electron reduction of dioxygen to water.     

Polypyridyl CoII-Curcumin Complexes as Photoactivated Anticancer and Antibacterial Agents

Four new Co^II complexes, [Co(bpy)₂(acac)]Cl ( 1 ), [Co(phen)₂(acac)]Cl ( 2 ), [Co(bpy)₂(cur)]Cl ( 3 ), [Co(phen)₂(cur)]Cl ( 4 ), where bpy=2,2’-bipyridine ( 1 and 3 ), phen=1,10-phenanthroline ( 2 and 4 ), acac = acetylacetonate ( 1 and 2 ), cur=curcumin monoanion ( 3 and 4 ) have been designed, synthesized and fully characterized. The X-ray crystal structures of 1 and 2 indicated that the CoN₄O₂ core has a distorted octahedral geometry. The photoactivity of these complexes was tuned by varying the π conjugation in the ligands. Curcumin complexes 3 and 4 had an intense absorption band near 435 nm, which made them useful as visible-light photodynamic therapy agents; they also showed fluorescence with λ_em≈565 nm. This fluorescence was useful for studying their intracellular uptake and localization in MCF-7 breast cancer cells. The acetylacetonate complexes ( 1 and 2 ) were used as control complexes to understand the role of curcumin. The white-light-triggered anticancer profiles of the cytosol targeting complexes 3 and 4 were investigated in detail. These non-dark toxic complexes displayed significant apoptotic photo-cytotoxicity (under visible light) against MCF-7 cells through ROS generation. The control complexes 1 and 2 did not induce significant cell death in the light or dark. Interestingly, 1-4 produced a remarkable antibacterial response upon light exposure. Overall, the reported results here can increase the boundary of the Co^II-based anticancer and antibacterial drug development.     

Electrodeposited Prussian blue films: Annealing effect

The correlation between the temperature-dependent electrochromic (EC) activity and other properties of galvanostatically deposited Prussian Blue (PB) films is presented here. Films subjected to annealing treatment in air at temperatures up to 500 °C were characterized by a variety of techniques which include TGA, XRD, FTIR, UV-vis spectrophotometry, SEM, XPS, cyclic voltammetry etc. The as-deposited X-ray amorphous hydrated PB films were blue in color and had Fe in both Fe^II and Fe^III valence states and were electrochromically active. Consequent to changes in the valence state, degree of hydration and coordination environment of the iron ions upon annealing, EC activity and morphology of the films exhibited dramatic changes. Annealing at moderate temperatures retained the blue color of the films and decreased the EC activity consistent with dehydration and decreased the Fe^II content. Lack of EC activity at higher temperatures was consistent with dehydration and quenching of Fe^II states accompanied with change of color from blue to rust (Fe^III) typical of Fe₂O₃. Independent of the annealing temperature, the films retained their amorphicity, however, prolonged annealing at 500 °C yielded hexagonal Fe₂O₃.