Aggregation of FeCl2 clusters in supercritical water investigated by molecular dynamics simulations

We have carried out molecular dynamics (MD) simulations of the aggregation of FeCl 2 clusters in supercritical water. The particle formation in systems of 2048 water molecules (rigid SPC/E-model) and 120 Fe (2+) ions and 240 Cl (-) ions has been investigated for 250 ps at five different state points at temperatures from 798 to 873 K and system densities from 0.18 g/cm (3) to 0.13 g/cm (3). We describe the particle growth by means of properties of the largest cluster in a system as well as cluster size averaged and time averaged observables. From preexisting or immediately formed units of Fe (2+)-Cl (-), Fe (2+)-Cl (-) 2, Fe (2+)-Cl (-) 3 etc., the further growth of clusters is dominated by aggregation of such small building blocks. Clusters up to 10 ions in size with large charge imbalances are found during the growth process while a balanced positive to negative charge ratio is found on the average with time and cluster size development. Water molecules are found within the FeCl 2 clusters during the whole time interval covered by the simulations, which is in agreement with the existence of crystal water in FeCl 2 crystals grown from aqueous solutions. The radial distribution functions obtained from the simulation data are in good agreement with experimental results of slightly distorted FeCl 2.4H 2O crystals.     

Transition metal ion-assisted photochemical generation of alkyl halides and hydrocarbons from carboxylic acids

Near-UV photolysis of aqueous solutions of propionic acid and aqueous Fe(3+) in the absence of oxygen generates a mixture of hydrocarbons (ethane, ethylene and butane), carbon dioxide, and Fe(2+). The reaction becomes mildly catalytic (about five turnovers) in the presence of oxygen which converts a portion of alkyl radicals to oxidizing intermediates that reoxidize Fe(2+). The photochemistry in the presence of halide ions (X(-) = Cl(-), Br(-)) generates ethyl halides via halogen atom abstraction from FeX(n)(3-n) by ethyl radicals. Near-quantitative yields of C(2)H(5)X are obtained at ≥0.05 M X(-). Competition experiments with Co(NH(3))(5)Br(2+) provided kinetic data for the reaction of ethyl radicals with FeCl(2+) (k = (4.0 ± 0.5) × 10(6) M(-1) s(-1)) and with FeBr(2+) (k = (3.0 ± 0.5) × 10(7) M(-1) s(-1)). Photochemical decarboxylation of propionic acid in the presence of Cu(2+) generates ethylene and Cu(+). Longer-chain acids also yield alpha olefins as exclusive products. These reactions become catalytic under constant purge with oxygen which plays a dual role. It reoxidizes Cu(+) to Cu(2+), and removes gaseous olefins to prevent accumulation of Cu(+)(olefin) complexes and depletion of Cu(2+). The results underscore the profound effect that the choice of metal ions, the medium, and reaction conditions exert on the photochemistry of carboxylic acids.     

Analysis of problematic complexing behavior of ferric chloride with N,N-dimethylformamide using combined techniques of FT-IR,XPS, and TGA/DTG

A problematic coordination behavior of highly hygroscopic FeCl(3) in DMF solution was studied. From the compositional and structural analyses for the adduct of FeCl(3)/DMF using various techniques such as FTIR, elemental analysis, UV/vis, XPS, and TGA/DTG, it was found that the iron cation exists in the form of an Fe(3+) cation and coordinates via the carbonyl oxygen atom of amide bond in DMF. The analyses of both FT-IR and XPS C 1s spectra for the adduct revealed that 2.1 molecules of DMF coordinate with a more electron-deficient Fe(3+); otherwise 1.2 molecules of DMF coordinated with a relatively electron-rich Fe(3+). The Cl 2p spectrum indicated that the electron-deficient Fe(3+) coordinated with two chlorine ions and the electron-rich Fe(3+) with four chlorines so that the chemical formula of the adduct is of [FeCl(2)(DMF)(1.2)(H(2)O)(2.7)](+)[FeCl(4)(DMF)(2.1)](-). The water molecules in the adduct were found chemisorbed rather than physisorbed, with a singular binding energy.     

Photochemistry of adsorbed nitrate

In the atmosphere, gas-phase nitrogen oxides including nitric acid react with particle surfaces (e.g., mineral dust and sea salt aerosol) to yield adsorbed nitrate, yet little is known about the photochemistry of nitrate on the surface of these particles. In this study, nitrate adsorbed on alumina surfaces, a surrogate for mineral dust aerosol, is irradiated with broadband light (lambda > 300 nm) in the absence and presence of coadsorbed water, at <1% and 45 +/- 2% relative humidity (%RH), respectively, and molecular oxygen. Upon irradiation, the nitrate ion readily undergoes photolysis to yield nitrogen-containing gas-phase products, NO2, NO, and N2O. Although NO2, NO, and N2O form under the different conditions investigated, both coadsorbed water and molecular oxygen change the gas-phase product distribution, with NO being the major product under dry and humid conditions in the absence of molecular oxygen and NO2 the major product in the presence of molecular oxygen. To the best of our knowledge, this is the first study to investigate the role of solvation by coadsorbed water in the photochemistry of adsorbates at solid interfaces and the roles that molecular oxygen, adsorbed water, and relative humidity may have in photochemical processes on aerosol surfaces that have the potential to alter the chemical balance of the atmosphere.     

Polymethylated [Fe(η6-arene)2]2+ dications: methyl-group rearrangements and application of the EINS mechanism

Reactions between the methylated arenes ArMe(n) [where ArMe(n) = C(6)Me(n)H((6-n)), and n = 1-6] and FeCl(2) in heptane at 90 °C in the presence of anhydrous AlCl(3) give, for the arenes with n = 1-5, extensive isomerisations and disproportionations involving the methyl groups on the arene rings, and the formation of mixtures of [Fe(ArMe(n))(2)](2+) dications that defy separation into pure species. GC-MS studies of AlCl(3)/mesitylene and AlCl(3)/durene reactions in the absence of FeCl(2) (90 °C, 2 h) allow quantitative assessments of the rearrangements, and the EINS mechanism (electrophile-induced nucleophilic substitution) is applied to rationalise the phenomena. By contrast, ArMe(n) / FeCl(2) /AlCl(3) reactions in heptane for 24-36 h at room-temperature proceed with no rearrangements, allowing the synthesis of the complete series of pure [Fe(ArMen)](2+) cations in yields of 48-71%. The pure compounds are characterised by (1)H NMR spectroscopy and electrospray-ionization mass-spectrometry (ESI-MS), and the structures of [Fe(m-xylene)(2)][PF(6)](2) and [Fe(durene)(2)][PF(6)](2) are established by single-crystal X-ray diffraction analyses.     

Adsorption of metal halides from ethanol solutions by a 3-n-propylpyridiniumsilsesquioxane chloride-coated silica gel surface

3-n-propylpyridiniumsilsesquioxane chloride polymer, abbreviated as SiPy+Cl-, was used to coat a porous silica gel, SiO2, surface to form the chemically modified solid SiO2/SiPy+Cl-. The resulting polymer film was well adhered to the surface and presented an ion exchange capacity of 0.74 mmol g(-1). Metal halides, MClz [M=Fe(III), Cu(II), and Zn(II)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes described by the equation: mSiO2/SiPy+Cl-+ MClz <=> (SiO2/SiPy+)m[MCl(z+m)]m-, where the [MCl(z+m)]m- species adsorbed on the surface are FeCl4-, ZnCl4(2-), and CuCl4(2-). Accurate estimates of the specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures.     

Unexpected superoxide dismutase antioxidant activity of ferric chloride in acetonitrile

The azobis(isobutyronitrile)-initiated autoxidation of gamma-terpinene in acetonitrile at 50 degrees C yields only p-cymene and hydrogen peroxide (1:1) in a chain reaction carried by the hydroperoxyl radical, HOO. (Foti, M. C.; Ingold, K. U. J. Agric. Food Chem. 2003, 51, 2758-2765). This reaction is retarded by very low (microM) concentrations of FeCl(3) and CuCl(2). The kinetics of the FeCl(3)-inhibited autoxidation are consistent with chain-termination via the following: Fe(3+) + HOO. <==>[Fe(IV)-OOH](3+) and [Fe(IV)-OOH](3+) + HOO. --> Fe(3+) + H2O2 + O2. Thus, FeCl(3) in acetonitrile can be regarded as a very effective (and very simple) superoxide dismutase. The kinetics of the CuCl(2)-inhibited autoxidation indicate that chain transfer occurs and becomes more and more important as the reaction proceeds, i.e., the inhibition is replaced by autocatalysis. These kinetics are consistent withreduction of Cu2+ to Cu+ by HOO. and then the reoxidation of Cu+ to Cu2+ by both HOO.and the H2O2 product. The latter reaction yields HO. radicals which continue the chain.     

Synthesis, structure, and solution properties of [(mim-TASN)FeCl2]+ and its μ-oxo derivative

A series of iron(III) complexes based on the tetradentate ligand 4-((1-methyl-1H-imidazol-2-yl)methyl)-1-thia-4,7-diazacyclononane (L) has been synthesized, and their solution properties investigated. Addition of FeCl(3) to methanol solutions of L yields [LFeCl(2)]FeCl(4) as a dark red solid. X-ray crystallographic analysis reveals a pseudo-octahedral environment around iron(III) with the three nitrogen donors of L coordinated facially. Ion exchange reactions with NaPF(6) in methanol facilitate chloride exchange resulting in a different diastereomer for the [LFeCl(2)](+) cation. X-ray analysis of [LFeCl(2)]PF(6) finds meridional coordination of the three nitrogen donors of L. Electrochemical studies of [LFeCl(2)](+) in acetonitrile display a single Fe(III)/(II) reduction potential at -280 mV versus ferrocenium/ferrocene. In methanol, a broad cathodic wave is observed because of partial exchange of one chloride for methoxide with half-potentials of -170 mV and -440 mV for [LFeCl(2)](+/0) and [LFeCl(OCH(3))](+/0), respectively. The equilibrium constants for chloride exchange are 7 × 10(-4) M(-1) for Fe(III) and 2 × 10(-8) M(-1) for Fe(II). In aqueous solutions chloride exchange yields three accessible complexes as a function of pH. Strongly acidic conditions yield the aqua complex [LFeCl(OH(2))](2+) with a measured pK(a) of 3.8 ± 0.1. Under mildly acidic conditions, the μ-OH complex [(LFeCl)(2)(OH)](3+) with a pK(a) of 6.1 ± 0.3 is obtained. The μ-oxo complex [(LFeCl)(2)(O)](2+) is favored under basic conditions. The diiron Fe(III)/Fe(III) complexes [(LFeCl)(2)(OH)](3+) and [(LFeCl)(2)(O)](2+) can be reduced by one electron to the mixed valence Fe(III)/Fe(II) derivatives at -170 mV and -390 mV, respectively. From pH dependent voltammetric studies, the pK(a) of the mixed valent μ-OH complex [(LFeCl)(2)(OH)](2+) is calculated at 10.3.     

Pentanuclear complexes with unusual structural topologies from the initial use of two aliphatic amino-alcohol ligands in Fe chemistry

Five novel pentanuclear Fe(3+) clusters with the aliphatic amino-alcohol ligands 3-amino-1-propanol (Hap) and 2-(hydroxymethyl)piperidine (Hhmpip) [Fe(5)(μ(3)-Ο)(2)(L)(4)(O(2)CR)(7)] [L = ap(-), R = Ph (1); L = ap(-), R = C(CH(3))(3) (2); L = hmpip(-), R = Ph (3); L = hmpip(-), R = C(CH(3))(3) (4)] and [Fe(5)(μ(4)-Ο)(μ(3)-Ο)(O(2)CC(CH(3))(3))(8)(ap)(2)Cl(HO(2)CC(CH(3))(3))] (5) are reported. Compounds 1-4 were prepared from reactions of preformed trinuclear Fe(3+) clusters with the ligands in a molar ratio 1 : 5 in MeCN (1, 3, 4) or DMF (2), whereas compound 5 was prepared from the reaction of FeCl(3) with Hap in the presence of HO(2)CC(CH(3))(3) in a molar ratio 1 : 3 : 2 in MeCN. To the best of our knowledge, 1-5 are the first examples of Fe(3+) complexes with the ligands Hap and Hhmpip. The structures of 1-4 are composed of a quasi-planar [Fe(5)(μ(3)-O)(2)](11+) core which consists of two vertex-sharing [Fe(3)(μ(3)-O)](7+) triangles. The structure of 5 is based on the [Fe(5)(μ(4)-O)(μ(3)-O)](11+) core, in which the five Fe(3+) ions adopt a monocapped trigonal pyramidal topology. Variable-temperature magnetic susceptibility measurements on powdered microcrystalline samples of 1 and 5 revealed the existence of antiferromagnetic interactions which led to an S = 5/2 ground state. M?ssbauer spectroscopy studies on powdered microcrystalline samples of 1 and 5 confirmed that all iron ions of both complexes are in the Fe(3+) (S = 5/2) state. The variation of the ligand environment in the various iron sites was reflected in their different quadruple splitting parameters. At T < 50 K the M?ssbauer spectra indicated the onset of spin relaxation effects in the time scale of the technique (10(-7)-10(-8) s).     

Selective Ion Pair Adsorption of Cobalt and Copper Salts on Cationically Produced Poly(1,3-divinylimidazolid-2-one)/Silica Hybrid Particles

For quantitative metal salt adsorption, poly(1,3-divinylimidazolid-2-one)/silica [poly BVU(cat.)/silica] particles with different polymer contents have been synthesized by a cationic surface polymerization of 1,3-divinylimidazolid-2-one onto silica. Preliminary experiments with the metal ion salts CoCl(2), CoI(2), CuCl(2), and FeCl(3) on poly-BVU(cat.)/silica particles, a radically produced poly-BVU(rad.) resin, and a cationically produced poly-BVU(cat.) resin have been carried in acetone solution to check the suitability of the adsorbents. The adsorption mechanism for Co(2+) and Cu(2+) on poly-BVU(cat.)/silica is in accordance with the Langmuir model for monolayer adsorption as shown by quantitative adsorption measurements by means of UV/vis spectroscopy. An ion pair adsorption mechanism is suggested for CoCl(2), CoI(2), and CuCl(2) on poly-BVU(cat.)/silica because both environments cationically produced poly-BVU and residual silanol groups are required for linking the cation and anion. ESR spectroscopic results of CoCl(2)-, CuCl(2)-, and FeCl(3)-poly-BVU(cat.)/silica hybrid adsorbates show selective adsorption for Co(2+) and Cu(2+). However, two different adsorption sites are indicated for Fe(3+) on poly-BVU(cat.)/silica. Copyright 2001 Academic Press.     

Binding of pi-acceptor ligands to (triamine)iron(II) complexes

A series of (Me3TACN)FeII derivatives with soft coligands have been investigated, where Me3TACN is N,N',N"-trimethyl-1,4,7-triazacyclononane. Treatment of Me3TACN with FeCl2 afforded a compound with the empirical formula (Me3TACN)FeCl2 (1). Compound 1, which is a versatile precursor reagent, was shown by single-crystal X-ray diffraction to be the salt [(Me3TACN)2Fe2Cl3][(Me3TACN)FeCl3], containing isolated [(Me3TACN)2Fe2Cl3]+ and [(Me3TACN)FeCl3]- subunits. Treatment of 1 with NaBPh4 gave the known [(Me3TACN)2Fe2Cl3]BPh4, while the addition of Me3TACN to FeCl4(2-) gave [(Me3TACN)FeCl3]-. Oxygenation of 1 afforded [(Me3TACN)FeCl2]2(mu-O), which was shown crystallographically to be centrosymmetric with a pair of distorted octahedral Fe centers. The Fe-N bond trans to the Fe-O bond is elongated by 02 A relative to the other Fe-N distances. Solutions of 1 and thiolates absorb CO to give [(Me3TACN)Fe(SPh)(CO)2]BPh4 and (Me3TACN)Fe(S2C2H4)(CO) (nu CO = 1896 cm-1). Treatment of 1 with excess CN- afforded [(Me3TACN)Fe(CN)3]-, isolated as its PPh4+ salt 5. Crystallographic and spectroscopic studies show that 5 is low spin with a C3v structure; its Fe-N distances contracted by 023 A relative to those in [(Me3TACN)FeCl3]-. Aqueous solutions of 1 bind CO upon the addition of CN- to produce (Me3TACN)Fe(CN)2(CO) (6) Analogous to 6 is (Me3TACN)Fe(CN)2(CNMe), prepared by methylation of 5. The metastable dicarbonyl [(Me3TACN)FeI(CO)2]I was prepared by treatment of FeI2(CO)4 with Me3TACN and was crystallographically characterized as its BPh4- salt. Values of E1/2 for [(Me3TACN)FeCl3]-, 5, and 6 are -0409, -0640, and 0533 V vs Fc/Fc+, respectively.     

Iron-catalyzed oxidative coupling of alkylamides with arenes through oxidation of alkylamides followed by Friedel-Crafts alkylation

FeCl(3) in combination with t-BuOOt-Bu as an oxidant was found to be an efficient catalyst for oxidation of alkylamides to α-(tert-butoxy)alkylamides. FeCl(2) and CuCl showed, respectively, almost the same and slightly lower activities compared with FeCl(3) in the tert-butoxylation of N-phenylpyrrolidone (1a), whereas no tert-butoxylated product was obtained by use of Fe(OTf)(3), RuCl(3), or Zr(OTf)(4). FeCl(3) was found to be effective also as a catalyst for the Friedel-Crafts alkylation with thus obtained α-(tert-butoxy)alkylamides. The Friedel-Crafts alkylation proceeded smoothly also in the presence of a catalytic amount of Fe(OTf)(3), RuCl(3), or Zr(OTf)(4). In contrast, FeCl(2) and CuCl, which showed certain activity toward the tert-butoxylation, failed to promote the Friedel-Crafts alkylation. Among the transition metal complexes thus far examined, only FeCl(3) showed high catalytic activities for both the oxidation and the Friedel-Crafts alkylation. The bifunctionality of FeCl(3) was utilized for the oxidative coupling of alkylamides with arenes through a tandem reaction consisting of oxidation of alkylamides to α-(tert-butoxy)alkylamides and the following Friedel-Crafts alkylation. The FeCl(3)-catalyzed oxidative coupling is applicable to a wide variety of alkylamides and arenes, though a combination of FeCl(3) with Fe(OTf)(3) was found to be effective for the reaction of arenes with low nucleophilicity. A Fe(II)-Fe(III) catalytic cycle is concerned with the tert-butoxylation, whereas a Fe(III) complex as a Lewis acid catalyzes the Friedel-Crafts alkylation.     

GA-KBrO3-H2SO4体系化学振荡的研究

研究了GA(没食子酸)-KBrO_3-H_2SO_4体系的诱导期τ、振荡周期T_2与反应物起始浓度的依赖关系, 302 K时的经验式为τ=22.8 c~(-2.23)_(H_2SO_4) c~(-2.17)_(KBrO_3) c~(0.795)_(GA) (mol.dm~(-3))~(4.25)·sT_2=0.84 c~(-2.28)_(H_2SO-4)c~(-1.97)_(KBrO_3) exp{(0.000147(mol.dm~(-3))~2/c~2_(GA)}(mol.dm~(-3))~(4.25)·sτ及T_2都随~CGA的增加而增长, 这与B-Z反应中关于有机物的结论不同。用循环伏安法研究该体系的结果表明, GA在诱导期结束时就基本上都被氧化为中间物, GA并不象前人所认为的是维持振荡的物种, 实际参与振荡的是由GA生成的物质。本文还研究了Fe(Phen)_3~(2+)对GA-KBrO_3-H_2SO_4体系振荡的影响, 发现Br~-振荡行为随Fe(Phen)_3~(2+)的浓度而变。低~CFe(phen)_3~(2+)时,Br~-的振荡行为与GA-KBrO_3-H_2SO_4体系的基本相似, 其特征是每个振荡周期内, Br~-振荡脉冲发生前是逐渐积累的。随着~CFe(phen)_3~(2+)的增大, Br~-出现另一特征的振荡行为, 在每个振荡周期内, Br~-振荡脉冲发生前是逐渐减小。我们认为, GA-KBrO_3-H_2SO_4-Fe(Phen)_3~(2+)体系的振荡不能单一地用OKN机理加以解释, 它可能是两套振荡机理耦合的振荡。     

Iron(III) chemistry with ferrocene-1,1'-dicarboxylic acid (fdcH2): an Fe7 cluster with an oxidized fdc(-) ligand

The synthesis and properties are reported of a new Fe(7) cluster obtained from the reaction of ferrocene-1,1'-dicarboxylic acid (fdcH(2)) with FeCl(2)·4H(2)O in MeOH under ambient light conditions. The compound is the mixed-anion salt [Fe(7)O(3)(OMe)(fdc)(6)(MeOH)(3)][FeCl(4)]Cl(2) (1; 8Fe(III)), containing six (fdc(n-)) groups as peripheral ligands. The cation of 1 has virtual C(3) symmetry and contains a central [Fe(4)(μ(3)-O)(3)(μ(3)-OMe)](5+) cubane unit whose three oxide ions each become μ(4) by attaching to a fourth Fe atom outside the cubane. The resulting [Fe(7)(μ(3)-O(3))(μ(3)-OMe)](14+) core is surrounded by six fdc(n-) (n = 1, 2) groups, which divide into two sets by virtual symmetry. The blue color of the complex suggested that some of these ligands are in their oxidized fdc(-) ferricenium (Fe(III)) state, and various data point to there being one fdc(-) ligand in the compound, the initial example of the group acting as a ligand in inorganic chemistry. Variable-temperature, solid-state DC and AC susceptibility measurements reveal the cation to be antiferromagnetically coupled, as expected for high-spin Fe(III), and to have an S = 2 ground state, consistent with an S = (5)/(2) Fe(7) inner core coupled antiferromagnetically to the one paramagnetic fdc(-) (S = (1)/(2)) ligand. Complex 1 displays multiple reductions and oxidations when investigated by electrochemistry in MeCN. (57)Fe Mo?ssbauer spectroscopy supports the presence of only five fdc(2-) ligands, but cannot resolve the signals from the various Fe(III) sites.     

过渡金属离子液体[C2mim][FeCl4]的溶解热

在干燥氩气氛下, 用等摩尔的高纯无水FeCl3和氯化1-甲基-3-乙基咪唑([C2mim][Cl])直接搅拌混合, 制备棕色透明的含过渡金属铁的离子液体[C2mim][FeCl4]. 在298.15 K下, 利用具有恒温环境的溶解反应热量计测定了这种离子液体的摩尔溶解焓(ΔsHm). 针对[C2mim][FeCl4]溶解于水后即分解的特点, 在Pitzer电解质溶液理论基础上, 提出了确定这种离子液体标准摩尔溶解焓的新方法, 得到了[C2mim][FeCl4]的标准摩尔溶解焓(ΔsH 0—m=-76.6 kJ/mol), 以及Pitzer焓参数组合: β(0)LFe,Cl+β(0)L[C2mim], Cl+ΦLFe,[C2mim]=0.072209和β(1)LFe,Cl+β(1)L[C2mim], Cl=0.15527. 借助热力学循环和Glasser离子液体晶格能理论, 用Fe3+, Cl-和[C2mim]+的离子水化焓数据以及[C2mim][FeCl4]标准摩尔溶解焓, 估算得到了配离子[FeCl4]-(g)解离成Fe3+(g)和4Cl-(g)的解离焓为5659 kJ/mol. 这个结果揭示了离子液体[C2mim][FeCl4]的标准摩尔溶解焓绝对值并不很大的原因, 即很大的离子水化焓被很大的[FeCl4]-(g)的解离焓相互抵消.     

n-Propylpyridinium chloride-modified poly(dimethylsiloxane) elastomeric networks: preparation, characterization, and study of metal chloride adsorption from ethanol solutions

An n-propylpyridinium chloride-modified PDMS elastomeric network, PDMS/Py(+)Cl(-), was prepared from linear PDMS chains containing Si(CH(3))(2)OH end-groups cross-linked by 3-chloropropyltrimethoxysilane and posterior reaction with pyridine. PDMS/Py(+)Cl(-) material was structurally characterized by infrared spectroscopy (IR) and solid state (13)C and (29)Si NMR. Thermogravimetric analysis of the product showed good thermal stability, with the initial temperature of weight loss at 450 K. The ion-exchange capacity of the PDMS/Py(+)Cl(-) was 0.65 mmol g(-1). Metal halides, MCl(z) [M=Fe(3+), Cu(2+), and Co(2+)], were adsorbed by the modified solid from ethanol solutions as neutral species by forming the surface anionic complexes MCl(z+n)(n-). The nature of the anionic complex structure was proposed by UV-vis diffuse reflectance spectra. The species adsorbed were FeCl(-)(4), CuCl(2-)(4), and CoCl(2-)(4). The specific sorption capacities and the heterogeneous stability constants of the immobilized metal complexes were determined with the aid of computational procedures. The trend in affinities of PDMS/Py(+)Cl(-) for the metal halides were found to be FeCl(3)>CuCl(2) approximately CoCl(2).     

Kinetics and mechanism of the reactions of [FeCl4]- with PhS- or PhSH in MeCN, and the role of cations containing N-H groups

The kinetics of the reactions between [FeCl4]- and an excess of PhS- have been studied using stopped-flow spectophotometry. The associated absorbance-time curves can be fitted to two exponentials, and these first and second phases correspond to the formation of [FeCl3(SPh)]- and [FeCl2(SPh)2]-, respectively. It seems likely that the steps involving formation of [FeCl(SPh)3]- and [Fe(SPh)4]- are associated with much smaller changes in absorbance and so are not detected. The kinetics of the first phase exhibit a non-linear dependence on the concentration of PhS- indicating an associative mechanism in which PhS- rapidly binds to [FeCl4]- to form [FeCl4(SPh)]2- prior to rate-limiting dissociation of chloride and formation of [FeCl3(SPh)]-. The kinetics indicate that at high concentrations of PhS-, the five-coordinate intermediate attains stoichiometric concentrations. This is confirmed by the spectroscopic changes. The second phase shows analogous kinetics. The kinetics of the reactions between [FeCl4]- and an excess of PhSH have also been studied. For the first phase the reaction occurs at a rate independent of the concentration of PhSH, consistent with an associative mechanism in which the solvent (MeCN) is the nucleophile to form [FeCl3(NCMe)]. Subsequent rapid replacement of the coordinated solvent by PhSH yields [FeCl3(SHPh)]. The kinetics of the second phase of the reaction with PhSH exhibits a non-linear dependence on the concentration of PhSH, analogous to the kinetics observed with PhS- and consistent with an associative mechanism. The cations [NHEt3]+, [NH2Et2]+ and [lutH]+ (lut = 2,6-dimethylpyridine) form ion pairs with [FeCl4]- which undergo substitution more rapidly than free [FeCl4]-.     

Theoretical study of negatively charged Fe(-)-(H2O)(n ≤ 6) clusters

Interactions of a singly negatively charged iron atom with water molecules, Fe(-)-(H(2)O)(n≤6), in the gas phase were studied by means of density functional theory. All-electron calculations were performed using the B3LYP functional and the 6-311++G(2d,2p) basis set for the Fe, O, and H atoms. In the lowest total energy states of Fe(-)-(H(2)O)(n), the metal-hydrogen bonding is stronger than the metal-oxygen one, producing low-symmetry structures because the water molecules are directly attached to the metal by basically one of their hydrogen atoms, whereas the other ones are involved in a network of hydrogen bonds, which together with the Fe(δ-)-H(δ+) bonding accounts for the nascent hydration of the Fe(-) anion. For Fe(-)-(H(2)O)(3≤n), three-, four-, five-, and six-membered rings of water molecules are bonded to the metal, which is located at the surface of the cluster in such a way as to reduce the repulsion with the oxygen atoms. Nevertheless, internal isomers appear also, lying less than 3 or 5 kcal/mol for n = 2-3 or n = 4-6. These results are in contrast with those of classical TM(+)-(H(2)O)(n) complexes, where the direct TM(+)-O bonding usually produces high symmetry structures with the metal defining the center of the complex. They show also that the Fe(-) anions, as the TM(+) ions, have great capability for the adsorption of water molecules, forming Fe(-)-(H(2)O)(n) structures stabilized by Fe(δ-)-H(δ+) and H-bond interactions.     

Isolation and detailed characterization of the trans-[(H2O)2FeCl4](-) anion: stabilization of novel iron(III) species by large organic cations

1,2-Diaminoethane (en) and FeCl3 give (enH2) [FeCl5(H2O)] (1) in concentrated HCl, extending the aquapentachloroferrate(III) series. For 1: C2H12N2Cl5OFe, orthorhombic, P2(1)2(1)2(1), a = 14.531(6) A, b = 10.772(4) A, c = 6.888(2) A, Z = 4. Diazabicyclo[2.2.2]octane dihydrochloride (DABCO-2HCl) and FeCl3 in concentrated HCl form a tetrachloroferrate(III) derivative whose subsequent ethanol treatment (restricted water access) results in the formation of a compound of composition (DABCOH2)2 [FeCl4(H2O)2]Cl3 (2). This contains the trans-[FeCl4(H2O)2](-) anion, in which the trans-Fe-O distances are 2.049(4) A. For 2: C12H32N4Cl7O2Fe, orthorhombic, Pnma, a = 16.378(3) A, b = 7.3323(6) A, c = 19.431(3) A, Z = 4. A combination of 57Fe M?ssbauer spectroscopy and ac susceptibility data confirm uncanted 3D antiferromagnetic ground states with T(Néel) approximately 3.4 K for (enH2)[FeCl5(H2O)] and approximately 2.0 K for [DABCOH2]2[FeCl4(H2O)2]Cl3.     

Monitoring reaction intermediates in the FeCl3-catalyzed michael reaction by nuclear inelastic scattering

We present a study of the metal-centered vibrations in the first step of the Fe(III)-catalyzed Michael reaction. Nuclear inelastic scattering of synchrotron radiation was carried out on a shock-frozen solution of FeCl3.6H2O in 2-oxocyclopentane ethylcarboxylate (CPEH), as well as on the solid reference compounds FeCl3.6H2O, [N(CH3)4][FeCl 4], and Fe(acac) 3. In addition to the vibrations of the FeCl4(-) anion at 133 and 383 cm(-1), a multitude of modes associated with the complex Fe(CPE)2(H2O)2 could be identified. Normal-mode analysis on different isomers of the simplified model complex Fe(acac)2(H2O)2 as well as that of the full complex carrying two entire CPE ligands was carried out using density functional calculations. Comparison with experiment suggests that the facial bis(diketonato) isomer probably dominates in the reaction mixture. Thus, we have identified for the first time the isomeric structure of an iron-based intermediate of a homogeneous catalytic reaction using nuclear inelastic scattering.