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1.
The mechanism of photoinduced intra- and intermolecular protolytic interactions ofortho-hydroxy derivatives of 2,5-diphenyloxazole in an aqueous alcohol medium was studied over a wide range of acidity from pH
∼13 toH
0 of ∼−7. The spectral parameters of protolytic forms and equilibrium constants were obtained, and rate constants for the primary
photochemical processes (excited-state intra- and intermolecular proton transfer reactions) were evaluated. It was shown that
the spectral characteristics of oxazoleortho-hydroxy derivatives in an acidic medium are formed as a result of competition and interchange of intra- and intermolecular
protolytic interactions. The phototautomeric form in strongly acidic solutions was found to be produced by dissociation of
the cationic form with the protonated oxazole ring. 相似文献
2.
The aquation of chromium(III)-isocinchomeronato and quinolinato complexes, mer-[Cr(icaH)3]0 and mer-[Cr(quinH)3]0 (where icaH− and quinH− are N,O-bonded isocinchomeronic and quinolinic acid anion, respectively) was studied in NaOH solutions. The process leads
to successive ligand liberation in the fully deprotonated species. The kinetics of the first ligand liberation were studied
spectrophotometrically in the visible region. A mechanism is proposed in which the rate of the chelate-ring opening at the
Cr–N bond is much faster than the rate of the Cr–O bond breaking. The rate-determining step is described by the rate law:
k
obs1 = k
OH(1) + k
O
Q
2 [OH−], where k
OH(1) and k
O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and
Q
2 is an equilibrium constant between these two protolytic forms. The first pseudo-first-order rate constants (k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. The results are compared with those determined
in acidic medium. Kinetics of the second and third ligand liberation were also studied and values of successive pseudo-first-order
rate constants (k
obs2, k
obs3) are [OH−] independent. Effect of chromium(III)-quinolinato and isocinchomeronato complexes on 3T3 fibroblast proliferation was evaluated.
Cytotoxicity of these complexes is low, suggesting they may be promising candidates as novel dietary supplements. 相似文献
3.
Wagner José Barreto Sonia Regina Giancoli Barreto Waleria Pickina Silva 《Transition Metal Chemistry》2009,34(6):677-681
The reaction between Fe(III) and dopamine in aqueous solution in the presence of Na2S2O3 was followed through UV–Vis spectroscopy, pH and oxy-reduction potential (Eh) measurements. The formation and quick disappearing
of the complex [Fe(III)HL1−]2+, HL1− = monoprotonated dopamine was observed with or without S2O3
2− at pH 3. An unexpected reaction occurs in presence of thiosulfate forming the stable anion complex [Fe(III)(L2−)2]1−, L2− = dopacatecholate (λ = 580 nm) and the auto-increasing of the pH, from 3 to 7. It was proposed that H+ and molecular oxygen are consumed by free radical thiosulfate formed during the reaction. 相似文献
4.
The reactions of e−
aq, H-atoms, OH radicals and some one electron oxidants and reductants were studied with dithio-oxamide (DTO) in aqueous solutions
using pulse radiolysis technique. The transient species formed by the reaction of e−
aq with DTO at pH 6.8 has an absorption band with λ
max at 380 nm and is reducing in nature. H-atom reaction with DTO at pH 6.8 also produced the same transient species. The semi-reduced
species was found to be neutral indicating that the electron adduct gets protonated quickly. However at pH 1, the species
produced by H-atom reaction had a different spectrum with λ
max at 360 and 520 nm. Reaction of acetone ketyl radicals and CO2
− radicals with DTO at pH 6.8 gave transient spectra which were identical to that obtained by e−
aq reaction. However at pH 1, the spectrum obtained by the reaction of acetone ketyl radicals with DTO was similar to that obtained
by H-atom reaction at that pH. The transient species formed by OH radical reaction with DTO in the pH range 1–9.2 also has
two absorption maxima at 360 and 520 nm. This spectrum was identical with the spectrum obtained by H-atom reaction at pH 1.
This means that all these radicals viz. OH, H-atom and (CH3)2COH radicals react with DTO at pH 1 by H-abstraction mechanism. The transient species produced was found to be sensitive to
the presence of oxygen. One-electron oxidizing radicals such as Br2
−· and SO4
−· radicals reacted with DTO at neutral pH to give the same species as produced by OH radical reaction having absorption maxima
at 360 to 520 nm. At acidic pHs, only Br2
−· and Cl2
−· radicals were able to oxidize DTO to give the same species as produced by OH radical reaction. The semioxidized species is
a resonance stabilized species with the electron delocalized over the-N-C-S bond. This species was found to be neutral and
non-oxidizing in nature. 相似文献
5.
Summary Manganese(III) acetate was prepared by the electrolytic oxidation of Mn(OAc)2 in aqueous AcOH. The electro-generated manganese(III) species was characterised by spectroscopic and redox potential studies.
The kinetics of oxidation of pyridoxine (PRX) by manganese(III) in aqueous AcOH were investigated and is first order with
respect to [MnIII]. The effects of varying [MnIII], [PRX], added manganese(II), pH and added anions such as AcO−, F−, Cl− and ClO
inf4
sup−
and SO
inf4
sup2−
were studied. The rate decreased slowly with increasing [H+] up to 0.2 mol dm−3 and increased steeply thereafter. The orders in [PRX] and [MnII] were unity and inverse fractional, respectively, in both low and high [H+] ranges. The dependence of reaction rate on temperature was studied and activation parameters were computed from Arrhenius
and Eyring plots. A mechanism consistent with the observed results is proposed and discussed. 相似文献
6.
Chromium(III)-lutidinato complexes of general formula [Cr(lutH)
n
(H2O)6−2n
]3−n (where lutH− is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)3]0 leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation
steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO4 and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were
characterized. The dependencies of pseudo-first-order rate constants on [H+] are as follows: k
obs1 = k
1 + k
−1/K
1[H+] and k
obs2 = k
2
K
2[H+]/(1 + K
2[H+]), where k
1 and k
2 are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k
−1 is the rate constant for the chelate-ring closure, and K
1 and K
2 are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate,
respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH−]: k
obs1 = k
OH(1) + k
O[OH−], where k
OH(1) and k
O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and
K
2 is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the
first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)4]3− were also studied and the values of the pseudo-first-order rate constants are [OH−] independent. 相似文献
7.
Murugesan Vairalakshmi Veerian Raj Ponnusamy Sami Kasi Rajasekaran 《Transition Metal Chemistry》2011,36(8):875-882
The kinetics of oxidation of phenol and a few ring-substituted phenols by heteropoly 11-tungstophosphovanadate(V), [PVVW11O40]4− (HPA) have been studied spectrophotometrically in aqueous acidic medium containing perchloric acid and also in acetate buffers
of several pH values at 25 °C. EPR and optical studies show that HPA is reduced to the one-electron reduced heteropoly blue
(HPB) [PVIVW11O40]5−. In acetate buffers, the build up and decay of the intermediate biphenoquinone show the generation of phenoxyl radical (ArO·) in the rate-determining step. At constant pH, the reaction shows simple second-order kinetics with first-order dependence
of rate on both [ArOH] and [HPA]. At constant [ArOH], the rate of the reaction increases with increase in pH. The plot of
apparent second-order rate constant, k
2, versus 1/[H+] is linear with finite intercept. This shows that both the undissociated phenol (ArOH) and the phenoxide ion (ArO−) are the reactive species. The ArO−–HPA reaction is the dominant pathway in acetate buffer and it proceeds through the OH− ion triggered sequential proton transfer followed by electron transfer (PT-ET) mechanism. The rate constant for ArO−–HPA reaction, calculated using Marcus theory, agrees fairly well with the experimental value. The reactivity of substituted
phenoxide ions correlates with the Hammett σ+ constants, and ρ value was found to be −4.8. In acidic medium, ArOH is the reactive species. Retardation of rate for the
oxidation of C6H5OD in D2O indicates breaking of the O–H bond in the rate-limiting step. The results of kinetic studies show that the HPA-ArOH reaction
proceeds through a concerted proton-coupled electron transfer mechanism in which water acts as proton acceptor (separated-CPET). 相似文献
8.
The complexation of As(V) in aqueous solutions in the presence of iron(III) was investigated spectrophotometrically with both
variable and constant ionic strengths. The determined thermodynamic and stoichiometric formation constants of the FeHAsO4+ species are log10∘β = 9.21± 0.01 and log10Iβ (1.0mol⋅dm−3 NaClO4) = 7.78 ± 0.01, respectively. The numerical treatment of the obtained spectral data was performed with the SPECA program. The analysis required the consideration
of the hydrolysis of Fe(III) and the protonation of As(V) in the pH range studied. No significant hydrolysis was observed
because of the low pH values (pH < 2.5) involved. The stabilities of the solid Fe(III) arsenates was established by solubility
experiments. All of the solubility experiments were performed in aqueous NaClO4 solutions at constant ionic strength (1.0mol⋅dm−3) and at 25∘C. The experimental data were consistent with FeAsO4⋅2H2O being the solid phase (log10 ∘ Kso = −24.30± 0.08). The corresponding thermodynamic constants were computed by means of the Modified Bromley's Methodology (MBM)
that describes the variation of the activity coefficients of all of the ions involved in the complexation and precipitation
equilibria with the medium and ionic strength. Finally, the solid phase obtained in this work was also characterized by FT-IR
and FT-Raman spectroscopies, and the hydration of the solid iron arsenate was confirmed by X-ray diffraction data. 相似文献
9.
S. I. Pechenyuk L. F. Kuz'mich E. V. Kalinkina S. I. Matveenko 《Russian Chemical Bulletin》1998,47(4):560-565
The influence of the pH of precipitation (pH1) and the ionic medium on the sorption properties of as-precipitated samarium(III) oxohydroxides,i.e., the pH of zero charge point and the rate of heterogeneous hydrolysis of the IrCl6
2−, RhCl6
3−, and PtCl4
2− complexes, was studied. The composition of precipitates was studied by the drop titration of solutions of samarium nitrate
and thermography. It was found that as-predipitated samarium oxohydroxides are amorphous and the substitution of NO3
− ions by OH− is not complete even at pH1 11. Heterogeneous hydrolysis occurs on the surface of samarium oxohydroxide, and its rate increases with increasing pH1. The as-precipitated samarium oxohydroxides have much higher sorption activities than crystalline Sm2O3, and their activities are similar to those of ferrogels.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 583–588, April, 1998. 相似文献
10.
Grace O. Ogunlusi Jide Ige Olayinka A. Oyetunji Jonathan F. Ojo 《Transition Metal Chemistry》2009,34(5):483-491
The kinetics of the reactions between azido-pentacyanocobaltate(III), Co(CN)5N3
3−, and iron(II) polypyridyl complexes, Fe(LL)3
2+ (LL = bipy, phen), have been studied in both neutral and acidic aqueous solutions at I = 0.1 mol dm−3 NaCl. The reactions were carried out under pseudo-first-order conditions in which the concentration of Fe(LL)3
2+ was kept constant, and the second-order rate constants obtained for the reactions at 35 °C were within the range of 0.156–0.219
dm3 mol−1 s−1 for LL = bipy and 0.090–0.118 dm3 mol−1 s−1 for LL = phen. Activation parameters were measured for these systems. The dependence of reaction rates on acid was studied
in the range [H+] = 0.001–0.008 mol dm−3. The reaction in acid medium shows interesting kinetics. Two reactive species were identified in acid medium, namely, the
protonated cobalt complex and the azido-bridged binuclear complex. The electron-transfer process is proposed to go by mixed
outer- and inner-sphere mechanisms in acid medium, in which electron transfer through the bridged inner-sphere complex (k
5) is slower than through the outer-sphere path (k
4).
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
11.
Fursemide is the chemical compound 4-chloro-2-(furan-2-ylmethylamino)-5-(aminosulfonyl) benzoic acid. It was oxidized by diperiodatocuprate(III)
in alkali solutions, and the oxidation products were identified as furfuraldehyde and 2-amino-4-chloro-5-(aminosulfonyl) benzoic
acid. The reaction kinetics were studied spectrophotometrically. The reaction was observed to be first order in [oxidant]
and fractional order each in [fursemide] and [periodate], whereas added alkali retarded the rate of reaction. The reactive
form of the oxidant was inferred to be [Cu(H3IO6)2]−. A mechanism consistent with the experimental results was proposed, in which oxidant interacts with the substrate to give
a complex as a pre-equilibrium state. This complex decomposed in a slow step to give a free radical that was further oxidized
by reaction with another molecule of DPC to yield 2-amino-4-chloro-5-(aminosulfonyl) benzoic acid and furfuraldehyde in a
fast step. This reaction was studied at 25, 30, 35, 40 and 45 °C, and the activation parameters E
a,ΔH
#,ΔS
# and ΔG
# were determined to be 51 kJ⋅mol−1,48.5 kJ⋅mol−1,−63.5 J⋅K−1⋅mol−1 and 67 kJ⋅mol−1, respectively. The value of log 10
A was calculated to be 6.8. 相似文献
12.
Sai Chodavarapu Seshatalpa Hela Pamidipati Gayatri Sridhar Yeleswarapu Anipindi Nageswara Rao 《Transition Metal Chemistry》1998,23(3):249-252
The reaction of the Cr(xx)2(H2O)2
− (xx = oxalate, malonate and methylmalonate) complexes with dissolved CO2 was studied by stopped-flow spectrophotometry in the 7 < pH < 9 range and between 20 to 30°C at an ionic strength of 0.5
mol dm−3 (NaCl). Under the experimental conditions the aqua complex ion consists of a pH-dependent mixture of Cr(xx)2(H2O)2
−, Cr(xx)2(OH) (H2O)2− and Cr(xx)2(OH)2
3−. The monohydroxo and dihydroxo species undergo CO2 uptake and subsequent intramolecular carbonate ligand chelation independently, at rates which are readily distinguishable
and are governed by the uptake rate constants k
1 and k
2 and chelation rate constants k
3 and k
4, respectively. Only the k
1 values for oxalato, malonato and methylmalonato complexes could be calculated; k
1 = 1084 and 1333 and 1650 mol−1 dm3 s−1, respectively. The results obtained were compared with those obtained from other systems that have either cobalt(III), iridium(III)
or rhodium(III) as central atoms.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
13.
Joanna Wiśniewska 《Transition Metal Chemistry》2007,32(1):107-111
The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of
the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([CoIII] = (0.6 − 2) × 10−3
M, [ptz] = 6 × 10−5
M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic
radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine
5-oxide. Linear dependences of the pseudo-first-order rate constants (k
1 and k
2) on [CoIII] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration
of the H+ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive
reducing species. The activation parameters for reactions studied were as follows: ΔH≠ = 44 ± 1 kJ mol−1, ΔS≠ = −100 ± 4 JK−1 mol−1 for the first step and ΔH≠ = 25 ± 1 kJ mol−1, ΔS≠ = −169 ± 4 J K−1 mol−1 for the second step, respectively. Mechanistic consequences of all the results are discussed. 相似文献
14.
Yasar Arafat Abbasi Akbar Ali Muhammad Haleem Khan Muhammad Mufazzal Saeed Kashif Naeem 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(1):277-283
The extraction behavior of nalidixic acid (HNA) in CH2Cl2 has been studied for various di- and trivalent metal ions such as Cu(II), Fe(II), Ni(II), Mn(II), Sb(II), Co(II), Sc(III),
Y(III), Nd(III) and Eu(III) from aqueous buffer solutions of pH 1–7 with 0.1 mol dm−3 nalidixic acid in dichloromethane. Separation factors of Sc(III) from these metals has shown that its clean separation is
possible at pH 3.4–4. The parameters affecting the extraction of Sc(III) were optimized. The composition of the extracted
adduct was determined by slope analysis method that came out to be Sc(NA)3. Extraction of Sc(III) was studied in the presence of various cations and anions. Among the anions studied only fluoride,
citrate and oxalate have significant interference whereas, Fe(III) has reduced the extraction to 53% that can be removed by
using ascorbic acid as reducing agent. The proposed extraction system proved good stability up to six extraction-stripping
stages for the extraction of Sc(III). 相似文献
15.
Formation of a singly bridged heterobimetallic CrIII–NC–FeII anation product of the cis − [Cr(cycb)(H2O)2]3+ and trans − [Cr(cyca)(H2O)2]3+ complexes, where cyca and cycb are meso- and rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane respectively, by [Fe(CN)6]4− ions is accompanied by an intensive absorbance increase within 390–470 nm due to an intermetal electron transition. A bell-shape
of the pseudo-first order rate constants/pH profile observed for the reactions which have been studied under a large excess
of the iron(II) complex is in accordance with the highest reactivity of the chromium(III) complexes in their monohydroxomonoaqua
forms. The reaction mechanism has been discussed based on the determined rate law. 相似文献
16.
G. J. De Jong U. A. Th. Brinkman 《Journal of Radioanalytical and Nuclear Chemistry》1977,35(1):223-232
For the system liquid anion-exchanger—Cr(III)−NCS−, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing
time of the Cr(III)−NCS− solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10−4 M Cr(III) by 0.1M Aliquat in CCl4 is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the
complex anion present in the organic phase is Cr(NCS)
6
3−
; when working with dilute metal ion solutions, the species extracted is Cr(NCS)4 (H2O)
2
−
. Separations of mixtures containing 10−2−10−4 M Co(II), Ni(II) and Cr(III) have successfully been accomplished. 相似文献
17.
The mixed valence Mn(III, IV) complexes, [Mn2O2L4]X3 with L=2,2-bipyridine or 1,10-phenanthroline and X=ClO
4
−
or PF
6
−
undergo partial ligand displacement reactions giving rise to the new compounds [Mn2O2L3A2]X3 with A=N, N-dimethylformamide or pyridine. The substitution is believed to take place at the labiled
4, Mn(III) centre. The substituted complexes have more deeply trapped valencies based on their electronic spectral characteristics.
The EPR spectra are found to be essentially unaffected by ligand substitutions. Computer simulations of frozen solutions as
well as polycrystalline spectra of the PF
6
−
salts showing hyperfine splittings are presented. All the complexes evolve oxygen from water when present as a solid phase
in contact with an aqueous solution containing Ce4+ions. The oxygen-evolving solution is found to contain MnO
4
−
ions. 相似文献
18.
Tatakuntla Satyanarayana Nageswara Rao Anipindi Veeraputhiran Subbiah Madhusudan Waman Pandit 《Transition Metal Chemistry》1992,17(4):325-327
The rapid oxidation ofbis(2,4,6-tripyridyl-1,3,5-triazine)-iron(II), [Fe(TPTZ)2]2+, bytrans-1,2-diaminocyclohexanetetraacetatomanganate(III), [MnIII(Y)]−, in acetate buffers was monitored using stopped-flow spectrophotometry. The reaction is first order in the substrate and
evidence was obtained for pre-complexation between the oxidant and the substrate. The reaction rate increases as the pH increases.
Characterisation of the products using the radiotracers54Mn and59Fe indicated that [MnII(Y)]2− and [Fe(TPTZ)2]3+ are the final products. The reaction obeys the rate law:
相似文献
19.
Hongmei Shi Shipeng Liu Shigang Shen Shuying Huo Weijun Kang 《Transition Metal Chemistry》2009,34(8):821-826
Kinetics of oxidation of dl-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO6)2]5−, has been studied in aqueous alkaline medium in the temperature range of 25–40 °C. The oxidation kinetics is first order
in the silver(III) and pipecolinate concentrations. The observed second-order rate constant, decreasing with increasing [periodate]
is virtually independent of [OH−]. α-Aminoadipate as the major oxidation product of pipecolinate has been identified by chromatographic analysis. A reaction
mechanism is proposed that involves a pre-equilibrium between [Ag(HIO6)2]5− and [Ag(HIO6)(H2O)(OH)]2−, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced in parallel by pipecolinate in rate-determining
steps (described by k
1 for the former Ag(III) species and k
2 for the latter). The determined rate constants and their associated activation parameters are k
1 (25 °C) = 0.40 ± 0.02 M−1 s−1, ∆H
1≠ = 53 ± 2 kJ mol−1, ∆S
1≠ = −74 ± 5 J K−1 mol−1 and k
2 (25 °C) = 0.64 ± 0.02 M−1 s−1, ∆H
2≠ = 41 ± 2 kJ mol−1, ∆S
2≠ = −110 ± 5 J K−1 mol−1. The time-resolved spectra, a positive dependence of the rate constants on ionic strength of the reaction medium, and the
consistency of pre-equilibrium constants derived from different reaction systems support the proposed reaction mechanism. 相似文献
20.
The interaction of (1,8)bis(2-hydroxybenzamido)3,6-diazaoctane (LH2) with iron(III) in acidic medium resulted in the formation of a mononuclear complex, Fe(LH3)4+ which further yielded, [Fe(LH2)]3+, [Fe(LH)]2+, and [FeL]+ due to protolytic equilibria. The formation of [Fe(LH3)]4+ was investigated under varying [H+]T (0.01–0.10 mol dm−3) and [Fe3+]T (1.00 × 10−3–1.70 × 10−2, [L]T = 1.0 × 10−4 mol dm−3) (I = 0.3 mol dm−3, 10% MeOH + H2O, 25.0 °C). The reaction was reversible and displayed monophasic kinetics; the dominant path involved Fe(OH)(OH2)
5
2+
and LH
4
2+
. The mechanism is essentially a dissociative interchange (I
d) and the dissociation of the aqua ligand from the encounter complex, [Fe(OH2)5OH2+, H4L2+] is rate limiting. The ligand binds iron(III) in a bidentate ([Fe(H3L)]4+), tetradentate ([Fe(H2L)]3+), pentadentate ([Fe(HL)]2+) and hexadentate fashion ([FeL]+) under varying pH conditions. Iron(III) promoted deprotonation of the amide and phenol moieties and chelation driven deprotonation
of the sec-NH
2
+
of the trien spacer unit are in tune with the above proposition. The mixed ligand complexes, [FeIII(LH)(X)] (X = N
3
−
, NCS−, ACO−) are also reversibly formed in solution thus indicating that there is a replaceable aqua ligand in the complex conforming
to its octahedral coordination, [Fe(LH)(OH2)]2+, the bound ligand is protonated at the sec-NH site. Despite the multidentate nature of the ligand the FeIII complexes are prone to reduction by sulfur(IV) and ascorbic acid. The redox reactions of different iron(III) species, FeIII(LHi) which involved ternary complex formation with the reductants have been investigated kinetically as a function of pH, [SIV]T and [ascorbic acid]T. The substantial pK perturbation of the bound ascorbate in [Fe(LH)(HAsc/Asc)]+/0 (ΔpK
{[Fe(LH)(HAsc)] − HAsc − } > 6) is considered to be compelling evidence for chelation of HAsc−/Asc2− leading to hepta coordination of iron(III) in the ascorbate complexes. A novel binuclear complex with composition, [FeIII
2C20N4H35O11 (NO3)] has been synthesized and characterized by i.r., u.v.–vis, e.s.r., e.s.i.-Mass, 57Fe Mossbauer spectroscopy and magnetic moment measurements. The complex was isolated as a mixture of two forms C
1 and C
2 with 75.3 and 24.7%, respectively as computed from Mossbauer data. The isomer shift (δ) (quadrupole splitting, ΔE
Q) are 0.32 mm s−1 (0.75 mm s−1) and 0.19 mm s−1 (0.68 mm s−1) for C
1 and C
2, respectively. The variable temperature magnetic moment measurements (10–300 K) of the sample showed that C
1 is an oxo dimer exhibiting antiferromagnetic interaction between the iron(III) atoms (S
1 = S
2 = 5/2, J = − 120 cm−1) while the dimer C
2 is a high spin species (S
1 = S
2 = 5/2) and exhibits normal paramagnetism obeying the Curie law. The cyclic voltametry response of the sample (DMF, [TEAP]
= 0.1 mol dm−3) displayed quasi-reversible responses at − 0.577 V and − 1.451 V (versus SCE). This is in tune with the fact that the C
2 species reverts rapidly in solution to the relatively more stable oxo-bridged dimer (C
1) which is reduced in two sequential steps: C1 + e− → [FeL]+ + FeII; [FeL]+ + e− → FeIIL, the high labilility of the FeII complex is attributed to the irreversibility. The X-band e.s.r. spectrum of the polycrystalline sample at room temperature
displayed a weak (unresolved) band at g = 4.2 and a strong band at g = 2.0 with hyperfine splitting due to the coordinated nitrogen (I = 1). At 77 K the band at g = 4.2 is intensified while that at g = 2 is broadened to the extent of near disappearance in agreement with the presence of the exchange coupled iron(III) centres.
Electronic supplementary material Electronic supplementary material is available for this article at
and accessible for authorised users.
An erratum to this article is available at . 相似文献
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