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1.
Leydi Erika Sarmiento Mildred Rodríguez Lorenzo Echevarria Vito Lubes 《Journal of solution chemistry》2010,39(10):1484-1491
The complex species formed between vanadium(III) and 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy), and 8-hydroxyquinoline
(8hq) were studied in aqueous solution by means of electromotive forces measurements, emf(H), at 25 °C with 3.0 mol⋅dm−3 KCl as the ionic medium. The potentiometric data were analyzed using the least-squares computational program LETAGROP, taking
into account the hydrolytic vanadium(III) species formed in solution. Analysis of the vanadium(III)–phen system data shows
the formation of [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes. In the vanadium(III)–bipy system the [VHL]4+, [V(OH)L]2+, [V2OL2]4+ and [V2OL4]4+ complexes were observed, and in the vanadium(III)–8hq system the complexes [V(OH)L]+, [V(OH)2L], [VL2]+ and [VL3] were detected. 相似文献
2.
The complex species formed in aqueous solution (25 ∘C, I = 3.0 mol-dm−3 KCl ionic medium) between V3+ cation and the ligands: picolinic acid (Hpic, HL) and dipicolinic acid (H2dipic, H2L), have been studied potentiometrically and by spectrophotometric measurements. The application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic species of V3+ ion, indicates that under the employed experimental conditions, the formation of the complexes [VL]2+, [V(OH)L]+, [VL2]+, [VL3], [V2OL4] with picolinic acid and the complexes [VL]+, [V(OH)L], [V(OH)2L]−, [V(HL)(L)], and [VL2]− with dipicolinic acid were observed. The stability constants of the complexes formed were determined by potentiometric measurements, and spectrophotometric measurements were done in order to perform a qualitative characterization of the complexes formed in aqueous solution. 相似文献
3.
Carmen Batista José Daniel Martínez Mary Lorena Araujo Felipe Brito Giuseppe Lubes Mildred Rodríguez Vito Lubes 《Journal of solution chemistry》2011,40(6):944-954
In this paper we present speciation results for the ternary vanadium(III)–dipicolinic acid (H2dipic) systems with the amino acids glycine (Hgly), proline (Hpro), α-alanine (Hα-ala), and β-alanine (Hβ-ala), obtained by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm−3 KCl as the ionic medium and a temperature of 25 °C. The experimental data were analyzed by means of the computational least-squares
program LETAGROP, taking into account hydrolysis of the vanadium(III) cation, the respective stability constants of the binary
complexes, and the acid base reactions of the ligands, which were kept fixed during the analysis. In the vanadium(III)–dipicolinic
acid–glycine system, formation of the ternary [V(Hdipic)(Hgly)]2+, [V(dipic)(Hgly)]+, [V(dipic)(gly)], [V(dipic)(gly)(OH)]− and [V(dipic)(gly)(OH)2]2− was observed; in the case of the vanadium(III)–dipicolinic acid–proline system the ternary complexes [V(Hdipic) (Hpro)]2+, [V(dipic)(Hpro)]+, [V(dipic)(pro)] and [V(dipic)(pro)(OH)]− were observed; in the vanadium(III)–picolinic acid–α-alanine were observed [V(Hdipic)(Hα-ala)]2+, [V(dipic) (Hα-ala)]+, [V(dipic)(αala)], [V(dipic)(α-ala)(OH)]− and [V(dipic)(α-ala)(OH)2]2−; and in the vanadium(III)–dipicolinic acid–β-ala system the complexes [V(dipic) (Hβ-ala)]+, [V(dipic)(β-ala)], [V(dipic)(β-ala)(OH)]− and [V(dipic)(β-ala)(OH)2]2− were observed. Their respective stability constants were determined, and we evaluated values of Δlog 10
K″ in order to understand the relative stability of the ternary complexes compared to the corresponding binary ones. The species
distribution diagrams are briefly discussed as a function of pH. 相似文献
4.
Freya Da Costa Giuseppe Lubes Mildred Rodríguez Vito Lubes 《Journal of solution chemistry》2011,40(1):106-117
Ternary complex formation reactions were studied between vanadium(III), dipicolinic acid and small molecular weight blood
serum components: lactic, oxalic, citric and ortophosphoric acids. The electromotive force measurement permitted us to determine
the chemical speciation of the complexes formed. In the vanadium(III)–dipicolinic acid–lactic acid system the complexes detected
were: V(dipic)(lac), V(dipic)(lac)(OH)− and V(dipic)(lac)(OH)22-(\mathrm{OH})_{2}^{2-}. In the vanadium(III)–dipicolinic acid–oxalic acid system the observed complexes were: V(dipic)(ox)−, V(dipic)(ox)(Hox)2− and V(dipic)(ox)23-(\mathrm{ox})_{2}^{3-}. In the vanadium(III)–dipicolinic acid–citric acid system the complexes V(dipic)(Hcit)−, V(dipic)(cit)2−, V(dipic)(cit)(OH)3−, V(dipic)(cit)(OH)24-(\mathrm{OH})_{2}^{4-} and V(dipic)(cit)(OH)35-(\mathrm{OH})_{3}^{5-} were detected. Finally in the vanadium(III)–dipicolinic acid–phosphoric acid system the complexes V(dipic)(H2PO4) and V(dipic)(HPO4)− were observed. The UV-vis spectra allowed us to perform a qualitative characterization of the complexes formed in aqueous
solution. 相似文献
5.
Isaida Shiozawa Giuseppe Lubes Mildred Rodríguez Vito Lubes 《Journal of solution chemistry》2011,40(1):17-25
In this work we present results for the speciation of the ternary complexes formed in the aqueous vanadium(III)–dipicolinic
acid and the amino acids cysteine (H2cys), histidine (Hhis), aspartic acid (H2asp) and glutamic acid (H2glu) systems (25 °C; 3.0 mol⋅dm−3 KCl as ionic medium), determined by means of potentiometric measurements. The potentiometric data were analyzed with the
least-squares program LETAGROP, taking into account the hydrolysis of vanadium(III), the acid-base reactions of the ligands,
and the binary complexes formed. Under the experimental conditions (vanadium(III) concentration = 2–3 mmol⋅dm−3 and vanadium(III): dipicolinic acid: amino acid molar ratio 1:1:1, 1:1:2 and 1:2:1), the following species [V(dipic)(H2asp)]+, [V(dipic)(Hasp)], [V(dipic)(asp)]−, [V(dipic)(asp)(OH)]2−, and [V(dipic)(asp)(OH)2]3− were found in the vanadium(III)–dipicolinic acid–aspartic acid system. In the vanadium(III)–dipicolinic acid–glutamic acid
system [V(Hdipic)(H2glu)]2+, [V(dipic)(H2glu)]+, [V(dipic)(Hglu)], [V(dipic)(Hglu)(OH)]−, and [V(dipic)(Hglu)(OH)2]2− were observed. In the vanadium(III)–dipicolinic acid–cysteine system the complexes [V(dipic)(H2cys)]+, [V(dipic)(Hcys)], [V(dipic)(cys)]−, and [V(dipic)(cys)(OH)]2− were present. And finally, in the vanadium(III)–dipicolinic acid–histidine system the complexes [V(Hdipic)(Hhis)]2+, [V(dipic) (Hhis)]+[\mathrm{V}(\mathrm{dipic}) (\mathrm{Hhis})]^{+}, [V(dipic)(his)], [V(dipic)(his)(OH)]−, and [V(dipic)(his)(OH)2]2− were observed. The stability constants of these complexes were determined. The species distribution diagrams as a function
of pH are briefly discussed. 相似文献
6.
Héctor Rosas Leydi Erika Sarmiento Mildred Rodríguez Vito Lubes 《Journal of solution chemistry》2010,39(7):1021-1029
The complex species formed between vanadium(III)-picolinic acid (HPic) and the amino acids: cysteine (H2Cys), histidine (HHis), aspartic acid (H2Asp) and glutamic acid (H2Glu) were studied in aqueous solution by means of electromotive forces measurements emf(H) at 25 °C and 3.0 mol⋅dm−3 KCl as ionic medium. Data analysis using the least-squares program LETAGROP indicates the formation of ternary complexes,
whose stoichiometric coefficients and stability constant were determined. In the vanadium(III)-picolinic acid-cysteine system
the model obtained was: [V(Pic)(H2Cys)]2+, [V(Pic)(HCys)]+, V(Pic)(Cys) and [V2O(Pic)(Cys)]+. The vanadium(III)-picolinic acid-histidine system contained the following complexes: [V(Pic)(HHis)]2+, [V(Pic)(His)]+, V(Pic)(His)(OH) and [V(Pic)2(HHis)]+. In the vanadium(III)-picolinic acid-aspartic acid system the model obtained was: V(Pic)(Asp), [V(Pic)(Asp)(OH)]− and [V2O(Pic)(Asp)]+ and finally, in the vanadium(III)-picolinic acid-glutamic acid system the complexes: V2O(Pic)2(HGlu)2, V(Pic)(HGlu)2 and V(Pic)2(HGlu) were observed. 相似文献
7.
Ternary complex species formed by the V3+ cation with the picolinic acid (Hpic, HL) and dipicolinic acid (H2dipic, H2L) ligands in aqueous solutions have been studied potentiometrically (25 °C, I=3.0 mol⋅dm−3 KCl ionic medium) and by spectrophotometric measurements. Application of the least-squares computer program LETAGROP to the
experimental emf (H) data, taking into account the hydrolytic V(III) species and the binary V3+–picolinic acid and V3+–dipicolinic acid complexes, shows that under the investigated conditions the following ternary complexes are formed: [V(dipic)(pic)],
[V(dipic)(pic)(OH)]− and [V(dipic)(pic)2]−. The stability constants of the ternary complexes were determined by potentiometric measurements whereas the spectrophotometric
measurements were done in order to obtain a qualitative characterization of the complexes formed in aqueous solution. 相似文献
8.
Joanna Wiśniewska 《Transition Metal Chemistry》2007,32(6):811-815
The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)2(H2O)2]3+ in CF3SO3H solution ([CoIII] = (2–6) × 10−3
m, [ptz] = 2.5 × 10−4
m, [H+] = 0.02 − 0.05 m, I = 0.1 m (H+, K+, CF3SO
3
−
), T = 288–308 K) and [Co(edta)]− in aqueous HCl ([CoIII] = (1 − 4) × 10−3
m, [ptz] = 1 × 10−4
m, [H+] = 0.1 − 0.5 m, I = 1.0 m (H+, Na+, Cl−), T = 313 − 333 K) were studied under the condition of excess CoIII using u.v.–vis. spectroscopy. The reactions produce a CoII species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k
obs) on [CoIII] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)2(H2O)2]3+ ion was found to be independent of [H+]. In the case of the [Co(edta)]− ion, the k
obs dependence on [H+] was linear and the increasing [H+] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows:
ΔH
≠ = 105 ± 4 kJ mol−1, ΔS
≠ = 93 ± 11 J K−1mol−1 for [Co(en)2(H2O)2]3+; ΔH
≠ = 67 ± 9 kJ mol−1, ΔS
≠ = − 54 ± 28 J K−1mol−1 for [Co(edta)]−. 相似文献
9.
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
10.
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
11.
The reaction of 3,6-di-(3-methyl-pyridin-2-yI)-s-tetrazine (DMPTZ, II) with CeIII salt [Ce(NO3)3 · 6H2O] generates a new ligand, N-(3-methyl-pyridin-2-yl)-formimidoyl-(3-methyl-pyridin-2-yl) hydrazone (L), and forms a new complex:
a mononuclear complex [Ce(L)(NO3)2 (H2O)3] · NO3 (III). Crystal data for III: space group P-1, with a = 0.7133(4) nm, b = 1.1139(2) nm, c = 1.4572(3) nm, α= 102.13(2)°, β=
99.81(3)°, γ= 91.10(3)°, Z = 2, V = 1113.6(7) nm3, μ = 2.123 mm−1 and F(000) = 630. L acts as a tri-dentate chelating ligand in III. There are 10 coordination sites around Ce3+ of III, which are respectively occupied by seven oxygen atoms (four from two nitrate anions and three from three H2O molecules) and three nitrogen atoms (all from L). The cerium atom and three chelating nitrogen atoms are coplanar. The mechanism
of the metal assisted decomposition is discussed briefly. 相似文献
12.
M. I. Hiremath S. T. Nandibewoor 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(7):1029-1033
The kinetics of ruthenium(III) catalyzed oxidation of L-proline by diperiodatocuprate(III) (DPC) in alkaline medium at constant
ionic strength (0.10 mol dm−3) has been studied spectrophotometrically using a rapid kinetic accessory. The reaction showed first order kinetics in [DPC]
and [RuIII] and apparently less than unit order dependence each in L-proline and alkali concentrations. A mechanism involving the formation
of a complex between the L-proline and the hydroxylated species of ruthenium (III) has been proposed. The active species of
oxidant and catalyst were [Cu(OH)2 (H3IO6)2 (H2IO6)2]4− and [Ru (H2O)5OH]2+ respectively. The reaction constants involved in the mechanism were evaluated. The activation parameters were computed with
respect to the slow step of the mechanism and discussed.
The text was submitted by the authors in English. 相似文献
13.
V. A. Afanasieva L. A. Glinskaya R. F. Klevtsova I. V. Mironov 《Journal of Structural Chemistry》2005,46(5):876-882
Protonation equilibrium has been studied for the acyclic gold(III) tetraaza metallocomplex [AuB]2+ [B = N, N′-bis(2-aminoethyl)-2,4-pentanediiminato(1−)] in aqueous solution. The synthetic procedure is described. The crystal
and molecular structure of the protonated form of the [AuHB](H5O2)(ClO4)4 complex has been determined. Monoclinic crystals with unit cell dimensions a = 11.964(2) Å, b = 13.789(3) Å, c = 15.496(3) Å, β = 109.00(3)°, V = 2417.1(8) Å3, Z = 4, ρcalc = 2.243 g/cm3, space group P21/n. The structure is built of nearly planar [Au(C9H20N4)]3+ complex cations, (H5O2)+ cations, and [ClO4]− anions. The gold atom coordinates four nitrogen atoms of the ligand, forming a square plane. The six-membered chelate ring
of the ligand is protonated at the central β-carbon atom and contains imine C=N bonds. The oxygen atoms of the perchlorate
ions are hydrogen bonded to the (H5O2)+ dihydroxonium ion and to the nitrogen atoms of the NH2 groups of the [AuHB]3+ cation.
Original Russian Text Copyright ? 2005 by V. A. Afanasieva, L. A. Glinskaya, R. F. Klevtsova, and I. V. Mironov
__________
Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 5, pp. 909–915, September–October, 2005. 相似文献
14.
V. Ciornea S. Shova Gh. Novitchi D. Ganzhu O. N. Kazheva A. Gulea Yu. A. Simonov 《Russian Journal of Coordination Chemistry》2009,35(11):817-823
Heterometallic compounds BaCr2(OH)(Ac)(Nta)2 · 4H2O (I) and [Fe(L)3][Cr2(OH)(Ac)(Nta)2] · nH2O (L is Bipy (II) and Phen (III); Bipy is, αα′-bipyridine, Phen is o,o′-phenanthroline, Ac− is acetate ion, Nta is nitrilotriacetate ion; n = 8 (II) and 6.25 (III)) are synthesized. According to the X-ray diffraction data, compounds II and III have ionic structures built of the isolated complex cations [Fe(L)3]2+, binuclear complex anions [Cr2(OH)(Ac)(Nta)2]2−, and crystallization water molecules. The magnetic properties of compounds II and III in the interval from 2 to 300 K confirm assumptions on the diamagnetic character of [Fe(L)3]2+ and indicate the antiferromagnetic interaction between the chromium atoms in the dimeric fragment [Cr2(OH)(Ac)(Nta)2]2−. 相似文献
15.
Kiran A. Thabaj Shivamurti A. Chimatadar Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2006,31(2):186-193
The kinetics of oxidation of PdII by CeIV have been studied spectrophotometrically in HClO4 media at 40 °C. The reaction is first order each in [CeIV] and [PdII] at constant [H+]. Increasing [H+] accelerates the reaction rate with fractional order in [H+]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At
constant acidity, increasing the added chloride concentration enhances the rate of reaction. H3Ce(SO4)4− and PdCl42− are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants
involved have been determined. 相似文献
16.
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
17.
The kinetics of the oxidation of promazine and chlorpromazine by hexaimidazolcobalt(III) were studied in the presence of a
large excess of cobalt(III) and H+ ions using u.v.–vis. spectroscopy ([CoIII] = (1–6) × 10−3 m, [ptz] = (2.5–10) × 10−5 m, [H+] = 0.05–0.8 m, I = 1.0 m (H+, Na+, Cl−), T = 333–353 K, l = 1 cm). In each case, the reversible reaction leads to formation of cobalt(II) species and a stable cationic radical. A
linear dependence of the pseudo-first-order rate constant (kobs) on [CoIII] with a non-zero intercept was established for both phenothiazine derivatives. A marked difference in the observed reaction
rate for promazine and chlorpromazine is associated with the difference in its ability to undergo oxidation and is consistent
with a trend in the redox potential changes for these reductants. The activation parameters for reactions studied were determined.
Mechanistic consequences of all the results are discussed. 相似文献
18.
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
19.
Rudragouda K. Patil Shivamurti A. Chimatadar Sharanappa T. Nandibewoor 《Transition Metal Chemistry》2008,33(5):625-633
The oxidation of antimony(III) by cerium(IV) has been studied spectrometrically (stopped flow technique) in aqueous sulphuric
acid medium. A minute amount of manganese(II) (10−5 mol dm−3) is sufficient to enhance the slow reaction between antimony(III) and cerium(IV). The stoichiometry is 1:2, i.e. one mole
of antimony(III) requires two moles of cerium(IV). The reaction is first order in both cerium(IV) and manganese(II) concentrations.
The order with respect to antimony(III) concentration is less than unity (ca 0.3). Increase in sulphuric acid concentration
decreases the reaction rate. The added sulphate and bisulphate decreases the rate of reaction. The added products cerium(III)
and antimony(V) did not have any significant effect on the reaction rate. The active species of oxidant, substrate and catalyst
are Ce(SO4)2, [Sb(OH)(HSO4)]+ and [Mn(H2O)4]2+, respectively. The activation parameters were determined with respect to the slow step. Possible mechanisms are proposed
and reaction constants involved have been determined. 相似文献
20.
Two solid complexes, fac–[Cr(gly)3] and [Cr(gly)2(OH)]2, (where gly is glycinato ligand) were prepared and their acid-catalysed aquation products were identified. The structure
of [Cr(gly)3] was solved by X-ray diffraction, revealing a cationic 3D sublattice with perchlorate anions inside its cavities. Acid-catalysed
aquation of [Cr(gly)3] and [Cr(gly)2(OH)]2 leads to the same inert product, [Cr(gly)2(H2O)2]+, in a two-stages process. At the first stage, intermediate complexes, [Cr(gly)2(O–glyH)(H2O)]+ and [Cr(gly)2(H2O)–OH–Cr(gly)2(H2O)]+, are formed respectively. Kinetics of the first aquation stage of [Cr(gly)3] were studied in HClO4 solutions. The dependencies of the pseudo first-order rate constants on [H+] are as follows: k
obs1H = k
0 + k
1
K
p1[H+], where k
0 and k
1 are rate constants for the chelate-ring opening via spontaneous and acid-catalysed reaction paths, respectively, and K
p1 is the protonation constant. The proposed mechanism assumes formation of the reactive intermediate as a result of proton
addition to the coordinated carboxylate group of the didentate ligand. Some kinetic studies on the second reaction stage,
the one-end bonded glycine liberation, were also done. The obtained results were analogous to those for stage I. In this case,
the proposed reactive species are intermediates, protonated at the carboxylate group of the monodentate glycine. Base hydrolysis
of two complexes, [Cr(gly)2(O–gly)(OH)]− and [Cr(gly)2(OH)2]−, was studied in 0.2–1.0 M NaOH. The pseudo first-order rate constants, k
obsOH, were [OH−] independent in the case of [Cr(gly)2(O–gly)(OH)]−, whereas those for [Cr(gly)2(OH)2]− linearly depended on [OH−]. The reaction mechanisms were proposed, where the OH− -catalysed reaction path was rationalized in terms of formation of the reactive conjugate base, [Cr(gly)2(OH)(O)]2−, as a result of OH− ligand deprotonation. Activation parameters were determined and discussed. 相似文献