II ) Or Iron Research Articles

Unexpected formation of FeIIFeIIIFeII- and FeIIFeIIFeII-trinuclear hexapyridineoximate helicates: synchrotron single-crystal X-ray structures

Template condensation of 2-acetylpyridineoxime with butyl ester of 1,3-propanediboronic acid in the presence of iron(II) affords a poorly separable mixture of complex products. Similar results were observed when Fe3+ ions were used for cross-linking in place of the diboronic acid. Prolonged crystallization of these mixtures gave crystals of perchlorate salts of a FeIIFeIIIFeII-trinuclear hexapyridineoximate cation and of an analogous FeIIFeIIFeII-intracomplex that crystallize with chloroform and dichloromethane solvent molecules, respectively. Both complexes were characterized by synchrotron single-crystal X-ray diffraction (XRD) experiments. The Fe–N distances of the two ‘terminal’ iron cations are virtually the same between these trinuclear complexes and unambiguously support assignments of oxidation number +2 and low-spin state (S = 0). The centers of the FeN6 -coordination polyhedra adopt geometries resembling trigonal antiprisms with distortion angles φ of approximately 40°. The FeO6 -coordination polyhedra possess an almost ideal Oh geometry with φ close to 60°. Each of these iron(II) or iron(III) µ3 -metallocenters acts as a bifunctional Lewis acid that cross-links two pseudoclathrochelate entities, formed by the ‘terminal’ iron(II) ions, to give an almost linear (the corresponding intramolecular Fe(2)…Fe(1)…Fe(3) angles are close to 180°) helical cation or intracomplex.

Effect of Hofmeister Salts on the LCST of Poly(diethyl vinylphosphonate) and Poly(2‐vinylpyridine‐block‐diethyl vinylphosphonate)

AbstractHerein, the effect of Hofmeister anions on the cloud point of poly(diethyl vinylphosphonate) (PDEVP) homopolymers and poly(2‐vinylpyridine‐block‐diethyl vinylphosphonate) (P(2VP‐b‐DEVP)) block copolymers using their sodium salts is reported. The change in the cloud point temperature (TCP) of these two polymers upon the addition of coordinating transition metal salts is investigated. The TCP of the different solutions is determined by ultraviolet–visible spectroscopy at different temperatures. Additionally, dynamic light scattering (DLS) is applied to investigate the behavior of the block copolymer below and above the TCP. Both polymers follow the trend of the Hofmeister series using the different sodium salts. This indicates that the P2VP block of the copolymer does not affect the TCP when noncoordinating cations are used. In contrast, a linear increase in the TCP is observed when the block copolymer is used in the presence of copper(II) or iron(III), whereas the TCP of the homopolymer in the same concentration range remains unchanged. The cloud point is increased due to an increase in hydrophilicity and electrostatic repulsion, resulting from the transition metal ion coordination. The coordination to the P2VP units is confirmed by the DLS. These findings can lead to potential applications as sensors or in wastewater purification.

Neuronal Proteins as Targets of 3-Hydroxykynurenine: Implications in Neurodegenerative Diseases.

The neurotoxic activity of the tryptophan metabolite 3-hydroxykynurenine (3OHKyn) in neurodegenerative disorders, such as Parkinson's and Alzheimer's diseases, is related to oxidative stress and 3OHKyn interaction with cellular proteins. The pattern of protein modification induced by 3OHKyn involves the nucleophilic side chains of Cys, His, and Lys residues, similarly to the one promoted by dopamine and other catecholamines. In the present work, we have analyzed the reactivity of 3OHKyn toward the neuronal targets α-synuclein (and its N-terminal fragments 1-6 and 1-15) and amyloid-β peptides (1-16 and 1-28) and characterized the resulting conjugates through spectrometric (LC-MS/MS) and spectroscopic (UV-vis, fluorescence, NMR) techniques. The amino acid residues of α-synuclein and amyloid-β peptides involved in derivatizations by 3OHKyn and its autoxidation products (belonging to the xanthommatin family) are Lys and His, respectively. The pattern of protein modification is expanded in the conjugates obtained in the presence of the metal ions copper(II) or iron(III), reflecting a more oxidizing environment that in addition to adducts with protein/peptide residues also favors the fragmentation of the protein. These results open the perspective to using the 3OHKyn-protein/peptide synthetic conjugates to explore their competence to activate microglia cell cultures as well as to unravel their role in neuroinflammatory conditions.

Rat liver mitochondrial dysfunction by addition of copper(II) or iron(III) ions

Increased copper (Cu) and iron (Fe) levels in liver and brain are associated to oxidative stress and damage with increased phospholipid oxidation process. The aim of this work was to assess the toxic effects of Cu2+ and Fe3+ addition to rat liver mitochondria by determining mitochondrial respiration in states 3 (active respiration) and 4 (resting respiration), and phospholipid peroxidation. Both, Cu2+ and Fe3+ produced decreases in O2 consumption in a concentration-dependent manner in active state 3: both ions by 42% with malate-glutamate as complex I substrate (concentration for half maximal response (C50) 60μM Cu2+ and 1.25mM Fe3+), and with succinate as complex II substrate: 64–69% with C50 of 50μM Cu2+ and with C50 of 1.25mM of Fe3+. Respiratory control decreased with Cu2+ (C50 50μM) and Fe3+ (C50 1.25-1-75mM) with both substrates. Cu2+ produced a 2-fold increase and Fe3+ a 5-fold increase of thiobarbituric acid-reactive substances (TBARS) content from 25μM Cu2+ (C50 40μM) and from 100μM Fe3+ (C50 1.75mM). Supplementations with Cu2+ and Fe3+ ions induce mitochondrial dysfunction with phospholipid peroxidation in rat liver mitochondria. Although is proved that a Fenton/Haber Weiss mechanism of oxidative damage occurs in metal-ion induced mitochondrial toxicity, slightly different responses to the metal ions suggest some differences in the mechanism of intracellular toxicity. The decreased rates of mitochondrial respiration and the alteration of mitochondrial function by phospholipid and protein oxidations lead to mitochondrial dysfunction, cellular dyshomeostasis and cell death.

Catalytic aerobic radical polymerization of methyl methacrylate in N,N-dimethylformamide: Stepwise in situ activation of dioxygen to peroxides and further to oxyl radicals

The aerobic radical polymerization of methyl methacrylate (MMA) in N,N-dimethylformamide (DMF) catalyzed by ppm-level complexes of copper(II), cobalt(II), or iron(III), leading to high-molecular-weight polymer (PMMA), was investigated in detail. No active radicals were formed, although DMF could reduce these complexes into their intermediates in the low oxidation state. Oligo(MMA peroxide)s formed in situ as multifunctional initiators decomposed into oxyl radicals to initiate polymerization under catalysis of these complexes. It was further revealed that these complexes undertook two-step O2 activation. They initially catalyzed the interpolymerization of MMA with O2 to afford oligo(MMA peroxide)s and then reduced oligo(MMA peroxide)s into alkyloxyl radicals to initiate polymerization of MMA in DMF, which played a triple role as the O2-rich solvent, the ligand, and the reducing agent.

Abstract 1659: The non-cardiotoxic anticancer drug pixantrone targets topoisomerase II

Abstract Pixantrone is a new non-cardiotoxic aza-anthracenedione anticancer drug structurally related to anthracyclines and anthracenediones such as doxorubicin and mitoxantrone. Pixantrone is approved in the EU for the treatment of relapsed or refractory aggressive B-cell non-Hodgkin lymphoma. This study was undertaken to investigate both the mechanisms of its anticancer activity and its lack of cardiotoxicity. The reduced cardiotoxicity of pixantrone compared to doxorubicin may be due to the fact that it did not bind iron(II) or iron(III). Thus, unlike doxorubicin it would not be able to induce iron-based oxidative stress in the heart. Pixantrone did, however, form a weak complex with Cu(II). Pixantrone was 10-fold less damaging to neonatal rat myocytes than doxorubicin as measured by LDH release. As measured by EPR spectrometry pixantrone generated about two-fold higher levels of its semiquinone free radical than doxorubicin in the hypoxanthine-xanthine oxidase reducing system. Conversely, in intact K562 cells under nitrogen, doxorubicin produced much more semiquinone radical than pixantrone. The reduced myocyte toxicity and semiquinone-forming ability in K562 cells compared to doxorubicin may be due low cell accumulation of dicationic pixantrone. Multidrug resistant Pgp- (ABCB1) overexpressing MDCK/MDR cells were 40-fold cross resistant to pixantrone, compared to parental cells. Pixantrone bound to DNA much more strongly than doxorubicin as determined in a DNA melting point assay. Pixantrone targeted topoisomerase II as evidenced by its ability to inhibit kDNA decatenation, to produce linear double-stranded DNA in a pBR322 DNA cleavage assay, and to form covalent topoisomerase II-DNA complexes in a cellular ICE assay. Pixantrone was 3-fold cross-resistant to K562-derived etoposide-resistant cells. DNA double strand breaks produced by pixantrone assessed in a cellular γH2AX assay were also characteristic of a topoisomerase II-targeted drug. These results support the conclusion that pixantrone displays characteristics that are consistent with targeting topoisomerase II. Support: CIHR; a Canada Research Chair in Drug Development; R01 CA090787. Citation Format: Brian B. Hasinoff, Xing Wu, Daywin Patel, Jack C. Yalowich. The non-cardiotoxic anticancer drug pixantrone targets topoisomerase II. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1659. doi:10.1158/1538-7445.AM2015-1659

Synthesis of Trinuclear Heterobimetallic Cyanido‐Bridged Complexes from the Reaction of [MnI(CN)(CO)(tBuNC)4] with Transition‐Metal Chlorides

AbstractThe reaction of [Mn(CN)(CO)(tBuNC)4] with MnCl2·4H2O, FeCl3·9H2O, NiCl2·6H2O, and CuCl2·2H2O, respectively, led to the formation of trinuclear heterobimetallic complexes that comprised two manganese moieties, with each coordinating the corresponding metal chloride entities through cyanide bridges. The mixed‐valence trinuclear MnI–CN–MnII–NC–MnI complex as well as the MnI–CN–NiII–NC–MnI derivative have been characterized by X‐ray structure analyses. In the case of the copper and iron compounds that exhibit easily reducable central metal ions, intramolecular electron transfer from manganese(I) to copper(II) or iron(III), respectively, is shown by the presence of metal‐to‐metal charge‐transfer (MMCT) bands as well as by EPR spectroscopy. Moreover, the iron complex shows a subsequent disproportionation, which was demonstrated by the isolation and crystallographic characterization of the reduced species with two manganese(I) complex units coordinating one FeIICl2 moiety.

Nitric Oxide Adsorption and Delivery in Flexible MIL-88(Fe) Metal–Organic Frameworks

Adsorption and release of the biologically active nitric oxide (NO) was evaluated over a series of highly flexible iron(III) dicarboxylate MOFs of the MIL-88 structure type, bearing fumaric or terephthalic spacer functionalized or not by polar groups (NO2, 2OH). As evidenced by ex situ X-ray powder diffraction and in situ IR spectroscopy, it appears that if the contracted dried forms of MIL-88 do not expand their structures in the presence of NO, the combination of very narrow pores and trimers of iron polyhedra leads to the adsorption of significant amounts of NO either physisorbed (very narrow pores) and/or chemisorbed [iron(II) or iron(III) coordinatively unsaturated metal sites (CUS)]. The delivery of NO under vapor of water or in simulated body fluid does not exceed 20% range of the total adsorbed amount probably due to a partial release that occurs between the adsorption/desorption setup and the chemiluminescence release tests. Some of these solids nevertheless exhibit a significant release at the biological levels over a long period of time (>16 h) that make these biocompatible and biodegradable MOFs of interest for the controlled release of NO.

Accessibility and Selective Stabilization of the Principal Spin States of Iron by Pyridyl versus Phenolic Ketimines: Modulation of the 6A1 ↔ 2T2 Ground-State Transformation of the [FeN4O2]+ Chromophore

Several potentially tridentate pyridyl and phenolic Schiff bases (apRen and HhapRen, respectively) were derived from the condensation reactions of 2-acetylpyridine (ap) and 2'-hydroxyacetophenone (Hhap), respectively, with N-R-ethylenediamine (RNHCH(2)CH(2)NH(2), Ren; R = H, Me or Et) and complexed in situ with iron(II) or iron(III), as dictated by the nature of the ligand donor set, to generate the six-coordinate iron compounds [Fe(II)(apRen)(2)]X(2) (R = H, Me; X(-) = ClO(4)(-), BPh(4)(-), PF(6)(-)) and [Fe(III)(hapRen)(2)]X (R = Me, Et; X(-) = ClO(4)(-), BPh(4)(-)). Single-crystal X-ray analyses of [Fe(II)(apRen)(2)](ClO(4))(2) (R = H, Me) revealed a pseudo-octahedral geometry about the ferrous ion with the Fe(II)-N bond distances (1.896-2.041 Å) pointing to the (1)A(1) (d(π)(6)) ground state; the existence of this spin state was corroborated by magnetic susceptibility measurements and Mössbauer spectroscopy. In contrast, the X-ray structure of the phenolate complex [Fe(III)(hapMen)(2)]ClO(4), determined at 100 K, demonstrated stabilization of the ferric state; the compression of the coordinate bonds at the metal center is in accord with the (2)T(2) (d(π)(5)) ground state. Magnetic susceptibility measurements along with EPR and Mössbauer spectroscopic techniques have shown that the iron(III) complexes are spin-crossover (SCO) materials. The spin transition within the [Fe(III)N(4)O(2)](+) chromophore was modulated with alkyl substituents to afford two-step and one-step (6)A(1) ↔ (2)T(2) transformations in [Fe(III)(hapMen)(2)]ClO(4) and [Fe(III)(hapEen)(2)]ClO(4), respectively. Previously, none of the X-salRen- and X-sal(2)trien-based ferric spin-crossover compounds exhibited a stepwise transition. The optical spectra of the LS iron(II) and SCO iron(III) complexes display intense d(π) → p(π)* and p(π) → d(π) CT visible absorptions, respectively, which account for the spectacular color differences. All the complexes are redox-active; as expected, the one-electron oxidative process in the divalent compounds occurs at higher redox potentials than does the reverse process in the trivalent compounds. The cyclic voltammograms of the latter compounds reveal irreversible electrochemical generation of the phenoxyl radical. Finally, the H(2)salen-type quadridentate ketimine H(2)hapen complexed with an equivalent amount of iron(III) to afford the μ-oxo-monobridged dinuclear complex [{Fe(III)(hapen)}(2)(μ-O)] exhibiting a distorted square-pyramidal geometry at the metal centers and considerable antiferromagnetic coupling of spins (J ≈ -99 cm(-1)).

Production of coagulant reagents for electro-coagulation processes at low current densities

Abstract In this work, the electrochemical production with low current densities of iron and aluminium reagents for electro-coagulation processes has been studied. It has been found that pH is a very important parameter, being strongly related to the speciation of iron in terms of iron (II) or iron (III) species, and also to the efficiency of the electrochemical reagent-dosing process. Iron (II) species are only significant under acidic conditions because in neutral and alkaline conditions iron (II) is rapidly transformed into iron (III). Efficiencies in the dissolution of the metals are very high and, in some cases, over the value expected for a 100% – efficiency (super-faradaic efficiencies), due to the non-electrolytic dissolution of the electrodes, which is very important for iron under acidic conditions, and even more important for aluminium at alkaline pHs. This significant non-electrolytic contribution explains the different trends observed in the efficiency changes with current density.

Syntheses, crystal structures and magnetic properties of [2 × 1 + 1 × 2] heterotetrametallic and [1 × 1 + 1 × 1] heterodimetallic cocrystals of copper(II) and iron(II/III)

The present work reports syntheses, crystal structures and variable-temperature magnetic properties of three copper(II)–iron(II/III) compounds [{CuIIL1}{FeIIIL1(H2O)2}](ClO4) (1), [{CuIIL1FeII(H2O)3}{CuIIL1}2](ClO4)2 (2) and [{CuIIL2FeII(H2O)3}{CuIIL2}2](ClO4)2·H2O·CH3COCH3 (3), where H2L1=N,N′-ethylenebis(3-ethoxysalicylaldimine) and H2L2=N,N′-o-phenylenebis(3-ethoxysalicylaldimine). Compounds 2 and 3 are tetrametallic [2×1+1×2] cocrystals of one diphenoxo-bridged dinuclear CuIIFeII and two mononuclear CuII moieties, while compound 1 is a dimetallic [1×1+1×1] cocrystal of one mononuclear FeIII and one mononuclear CuII moieties. The overall topology of 1 is one-dimensional. Tetrametallic (in 2 and 3) and one-dimensional (in 1) self-assemblies are generated due to weak noncovalent interactions. Variable-temperature magnetic susceptibility measurements reveal that iron(II) or iron(III) centers in 1–3 remain in high-spin state. Compounds 2 and 3 exhibit weak antiferromagnetic interaction; the J values in the dinuclear core are −22.5 and −13.7cm−1, respectively, compound 1 exhibits very weak antiferromagnetic interaction (J=−0.25cm−1) propagated through the weak noncovalent bonds.

Catalytic oxidation of polyethylene with oxygen under solid‐state conditions

AbstractThe catalytic oxidative degradation of polyethylene in the solid phase was studied. Cobalt(II), manganese(II), or iron(III) acetylacetonates were used as catalysts. The influences of type and amount of catalyst, temperature, and type of oxidizing agent on polyethylene oxidation were investigated. The obtained products were characterized by determination of acid and ester numbers as well as by means of FTIR spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Hydrogen generation by hydrolysis of NaBH4

The hydrolysis of sodium-borohydride (SBH) to produce hydrogen has been studied at various temperatures using salts of nickel (II) or iron (III) as catalyst. Excess of water has been added to a mixture of solid SBH and catalyst to start hydrolysis reaction and the evolved hydrogen measured as a function of time. After a sudden peak a constant hydrogen flow was observed when Ni is used as catalyst. The activation energy has been evaluated from the dependence of the reaction time and of the hydrogen flow on the inverse of temperature. If Ni is substituted by a Fe based catalyst, after the initial increase, a different shape is observed in the hydrogen flow: it reaches a maximum and then monotonously decrease to zero. The different shape has been related to the different activity of the catalyst. The reaction activation energy was evaluated to be 73 KJ/mol.

Intermolecular Enolate Heterocoupling: Scope, Mechanism, and Application

This full account presents the background on, discovery of, and extensive insight that has been gained into the oxidative intermolecular coupling of two different carbonyl species. Optimization of this process has culminated in reliable and scalable protocols for the union of amides, imides, ketones, and oxindoles using soluble copper(II) or iron(III) salts as oxidants. Extensive mechanistic studies point to a metal-chelated single-electron-transfer process in the case of copper(II), while iron(III)-based couplings appear to proceed through a non-templated heterodimerization. This work presents the most in-depth findings on the mechanism of oxidative enolate coupling to date. The scope of oxidative enolate heterocoupling is extensive (40 examples) and has been shown to be efficient even on a large scale (gram-scale or greater). Finally, the method has been applied to the total synthesis of the unsymmetrical lignan lactone (-)-bursehernin and a medicinally important 2,3-disubstituted succinate derivative.

Unexpected high oxidation of cyclohexane by Fe salts and dihydrogen peroxide in acetonitrile

The reaction of cyclohexane (CyH) with 1.5 equivalent of dihydrogen peroxide (30% aqueous solution) in the presence of 1 mol% of an iron(II) or iron(III) salt (without added ligand), at 50 °C in acetonitrile, produces cyclohexanol (Cy OH) and cyclohexanone (Cy O) in high yields (up to 87% of CyH is converted to Cy OH + Cy O). Remarkably, CyH is totally converted within 2 h in the presence of Fe(ClO 4) 2 as catalyst under argon, producing 45% of Cy OH and 42% of Cy O. The addition of a tridentate Schiff-base ligand, namely 2,6-bis-[1-(benzylimino)ethyl]pyridine ( dapb), leads to a clear increase of the selectivity towards Cy OH + Cy O, which are obtained with an overall yield of 93% (and even 100% selectivity to Cy OH and Cy O) in the case of the [Fe(ClO 4) 3/ dapb] catalytic system.

Preparative-scale one-pot syntheses of hexafluoro-1,3-butadiene

Hexafluoro-1,3-butadiene, with its negligible global warming potential, is required in quantities for application in plasma dielectric etching in semiconductor industry and as gaseous microbubble suspension contrast agents in diagnostic ultrasound imaging. Three efficient protocols for the preparation of perfluoro-1,3-butadiene in 62–70% overall yields have been described. They involve the coupling of (1) iodotrifluoroethylene (ITFE) with activated copper, (2) trifluorovinylzinc bromide in the presence of copper (II) or iron (III) salts and (3) trifluorovinylzinc chloride, prepared from 1,1,1,2-tetrafluorethane (HFC 134a) in the presence of copper (II) or iron (III) salts.

Electrochemical and FTIR studies of the mutual influence of lead(II) or iron(III) and phenol on their adsorption from aqueous acid solution by modified activated carbons

Cyclic voltammetry and spectral FTIR studies of the influence of activated carbon surface modification on the co-adsorption of metal cation (lead or iron) and phenol from aqueous acidic solution were carried out. The diversity in surface chemical structure was achieved by applying different procedures of inorganic matter removal and by modifying the carbon samples in various ways: heating under vacuum, aminoxidation in an ammonia–oxygen atmosphere, oxidation with concentrated nitric acid. The quantities of adsorbed metal ions (Pb 2+ or Fe 3+) and phenol from solutions containing cation or phenol separately or in a mixture were determined. The adsorption capacity from acidic aqueous acidic solution depends on the chemical properties of the activated carbon surface (e.g., decrease in phenol adsorption with relative lower basicity of the adsorbent). The electrochemical parameters of electrodes made from the carbon samples were estimated, and some possible electrochemical reactions were determined from voltammograms recorded in acid electrolyte solution containing adsorbed species (separately or as a mixture). Relationships were found between metal ion adsorption and electrochemical behavior of Pb 2+/Pb 4+ and Fe 3+/Fe 2+ couples on the one hand, and the presence of phenol in the solutions tested and the influence of surface chemistry of the carbon electrodes on electrochemical processes on the other. The changes in adsorption capacity with respect to the adsorbates used and the changes in FTIR spectra of the carbons as a result of adsorption and/or coupling phenol molecules are discussed.

Electrocatalytic reduction of oxygen with phenanthroline-strapped porphyrins

The electrochemical behavior of three cytochrome c oxidase models has been investigated. All the models are derived from a phenanthroline-strapped, porphyrin framework that binds zinc(II) or iron(III) chloride in the porphyrin subunit, and copper(I) in the phenanthroline site. The iron complex and the bimetallic zinc(II) copper(I) complex of the parent ligand have been characterized by X-ray diffraction. One model consists of the parent structure on which C 12 alkyl chains have been added. This soluble model achieves electrochemical 2-electron reduction of oxygen in organic solvents without the addition of an exogenous axial base, and in the presence of an organic or inorganic source of protons. The two other models comprise the parent phenanthroline-strapped porphyrin framework, on which two pendant imidazoles have been incorporated. These models adsorbed on ring-disk electrodes with an edge-oriented, pyrolytic graphite (EOPG) disk and a platinum ring, efficiently catalyze the 4-electron reduction of oxygen in dioxygen saturated water at neutral pH.

Perturbations of the Briggs–Rauscher oscillating system by iron–phenanthroline complexes

Perturbations of the oscillatory regime of the Briggs–Rauscher (BR) reaction by the iron(II)–phenanthroline (ferroin) complex were observed in batch conditions. The path of the perturbation (immediate quenching of oscillations – inhibition time – resumption of oscillations) is similar to that provoked by antioxidant free-radical scavengers; however, perturbations occur in a ferroin concentration range much lower than that in which antioxidants act. To investigate this effect, reactions between the iron(II)–or iron(III)–phenanthroline (ferriin) and reagents or intermediates of the BR system were studied in detail. Results of these studies showed that the interaction of the ferroin/ferriin couple with iodine production is responsible for the observed perturbation. A mechanistic interpretation involving HOO radical is proposed.

Proton control of oxidation and spin state in a series of iron tripodal imidazole complexes.

Reaction of iron salts with three tripodal imidazole ligands, H(3)(1), H(3)(2), H(3)(3), formed from the condensation of tris(2-aminoethyl)amine (tren) with 3 equiv of an imidazole carboxaldehyde yielded eight new cationic iron(III) and iron(II), [FeH(3)L](3+or2+), and neutral iron(III), FeL, complexes. All complexes were characterized by EA(CHN), IR, UV, Mössbauer, mass spectral techniques and cyclic voltammetry. Structures of three of the complexes, Fe(2).3H(2)O (C(18)H(27)FeN(10)O(3), a = b = c = 20.2707(5), cubic, I3d, Z = 16), Fe(3).4.5H(2)O (C(18)H(30)FeN(10)O(4.5), a = 20.9986(10), b = 11.7098(5), c = 19.9405(9), beta = 109.141(1), monoclinic, P2(1)/c), Z = 8), and [FeH(3)(3)](ClO(4))(2).H(2)O (C(18)H(26)Cl(2)FeN(10)O(9), a = 9.4848(4), b = 23.2354(9), c = 12.2048(5), beta = 111.147(1) degrees, monoclinic, P2(1)/n, Z = 4) were determined at 100 K. The structures are similar to one another and feature an octahedral iron with facial coordination of imidazoles and imine nitrogen atoms. The iron(III) complexes of the deprotonated ligands, Fe(1), Fe(2), and Fe(3), are low-spin while the protonated iron(III) cationic complexes, [FeH(3)(1)](ClO(4))(3) and [FeH(3)(2)](ClO(4))(3), are high-spin and spin-crossover, respectively. The iron(II) cationic complexes, [FeH(3)(1)]S(4)O(6), [FeH(3)(2)](ClO(4))(2), [FeH(3)(3)](ClO(4))(2), and [FeH(3)(3)][B(C(6)H(5))(4)](2) exhibit spin-crossover behavior. Cyclic voltammetric measurements on the series of complexes show that complete deprotonation of the ligands produces a negative shift in the Fe(III)/Fe(II) reduction potential of 981 mV on average. Deprotonation in air of either cationic iron(II) or iron(III) complexes, [FeH(3)L](3+or2+), yields the neutral iron(III) complex, FeL. The process is reversible for Fe(3), where protonation of Fe(3) yields [FeH(3)(3)](2+).