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1.
Asim K. Das 《Transition Metal Chemistry》1989,14(5):390-392
Summary Stability constants (K
MAL
MA
) together with other thermodynamic parameters measuring the stabilities and the contribution of astatistical factors governing the stability of ternary complexes, MAL [M=CoII, NiII, CuII or ZnII; A=2, 2-dipyridylamine (A3), 5-nitro-o-phenanthroline (A5), 5-methyl-o-phenanthroline (A6); LH=benzohydroxamic acid] have been determined at 25°CC, at ionic strength 0.1 M KNO3. The results are compared with those for the complexes containing polyaminocarboxylic acids such as iminodiacetic acid (A1) and other heteroaromaticN-bases such as 2, 2-bipyridine (A2),o-phenanthroline (A4) and the stability constants are found in the sequence
K_{MA^4 L}^{MA^4 } > K_{MA^2 L}^{MA^3 } = ca.K_{MA^3 L}^{MA^3 } \gg K_{MA^1 L}^{MA^1 } .$$
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For all heteroaromaticN-bases, the sequence
K_{ML_2 }^{ML} $$
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has been found. The sequences are explained in terms of electrostatic interaction, change of electrophilicity of the bound metal and the -acidic character of the primary ligand. 相似文献
2.
Asim K. Das 《Transition Metal Chemistry》1989,14(3):200-202
Summary Stability constants (K
MAL
MA
) and other thermodynamic parameters of the MAL complexes (charges omitted) [M=CoII, NiII, CuII or ZnII; AH2=8-hydroxyquinoline-5-sulphonic acid; LH2=catechol (L1H2), 1,2-dihydroxybenzene-sulphonate (L2H2), 1,2-dihydroxybenzene-3, 5-disulphonate (L3H2), 4-nitro-1,2-dihydroxybenzene (L4H2)] have been determined at 25°C and at an 0.1 M KNO3 ionic strength by the extended Irying-Rossotti technique. The stability constants lie in the sequences:
K_{MAL}^{MA} ?K_{ML_2 }^{ML} ; K_{MAL}^{MA_1 } > K_{MAL}^{MA_2 } > K_{MAL}^{MA_3 } \gg K_{MAL}^{MA_4 } $$
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and all follow the Irving-Williams stability order. These observations can be explained in terms of electrostatic interaction, change of electrophilicity of the bound metal and -acidic character of the primary ligand. 相似文献
3.
Virender K. Sharma Fabien Casteran Frank J. Millero Concetta De Stefano 《Journal of solution chemistry》2002,31(10):783-792
The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [
CH(CH2SH)COOH; H3B+]. The values of dissociated constants, p
, for protonated cysteine species (H3B+ H+ + H2B, K
1; H2B H+ + HB–,K
2; HB– H+ + B2–,K
3) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH2O)–1 and between 5, and 45°C. The equations
were fitted to the results with a standard errors of the fits of 0.116, 0.057, and 0.093 for
,
, and
, respectively. The
results were used to determine new Pitzer parameters (0, 1, and C) for the interactions of Na+ and Cl– with cysteine species. These coefficients can be used to make reasonable estimates of the activity coefficients of the cysteine species and
for the dissociation of cysteine in physiological and natural waters containing mostly NaCl. 相似文献
4.
Summary The oxidation of H2O2 by [W(CN)8]3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law,
, strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k
s, given by
, involves the formation of [W(CN)8· H2O2]3–, [W(CN)8· H2O2·W(CN)8]6– and [W(CN)8· HO]3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)8·HO]3– (k
a) and its conjugate base [W(CN)8·O]4– (k
b). At 25 °C, I = 0.20 m (NaCl), the rate constant
with H
a
=40±6kJmol–1 and S
a
=–151±22JK–1mol–1; the rate constant
with H
b
=36±1kJmol–1 and S
b
=–136±2JK–1mol–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)8·HO]3–, K
5
=(5.9±1.7)×10–10
m, with
and
is the first acid dissociation constant of H2O2. The second pathway, with rate constant, k
f, involves the formation of [W(CN)8· HO2]4– and is followed by a formal two-electron redox process with [W(CN)8]3–. The pH-dependent rate constant, k
f, is given by
. The rate constant k
7
=23±6m
–1
s
–1 with
and
at 25°C, I = 0.20 m (NaCl). 相似文献
5.
K. P. Butin A. A. Moiseeva T. V. Magdesieva E. V. Sergeeva V. I. Rozenberg V. G. Kharitonov 《Russian Chemical Bulletin》1994,43(5):783-789
The potentials of electrochemical oxidation (
) and reduction (
) of monobromo- and isomeric di- and tribromo[2.2]paracyclophanes as well as
of mono-, di-, and tribromobenzenes were measured in acetonitrile. The similarity between the properties ofpseudo-para-disubstituted cyclophanes andmeta-disubstituted benzenes, on the one hand, andpseudo-meta-disubstituted cyclophanes andpara-disubstituted benzenes, on the other hand, was confirmed by the existence of a linear relationship between
of bromo-substituted [2.2]paracyclophanes and
of the corresponding bromo-substituted benzenes. The results were explained in terms of the qualitative theory of molecular orbitals, taking into account a through space interaction between the -systems of the benzene rings.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 839–845, May, 1994.The authors wish to express their gratitude to Professor R. Hoffmann (Cornell University, USA) for a useful discussion and criticisms of the text of this paper.This work was financially supported by the Russian Foundation for Basic Research (Project 93-03-5246). 相似文献
6.
Rajendiran Thekkel M. Mahalakshmy Rajaram Kannappan Ramu Rajeswari Janarthanam Venkatesan Rangarajan Rao Pillutla 《Transition Metal Chemistry》2003,28(3):280-287
Binuclear CuII complexes having new flexible heptadentate ligands 2,6-bis{[bis(3,3-N,N-dimethylaminopropyl)amino]methyl}-4-bromophenol [HL1], 2,6-bis(3,3-N,N-dimethylaminopropyl)amino]methyl}-4-methylphenol [HL2], and 2,6-bis{[bis(3,3-N,N-dimethylaminopropyl)amino]methyl}-4-methoxyphenol [HL3], capable of assembling two copper ions in close proximity have been synthesized. Comparisons of the charge-transfer (CT) features, observed in electronic spectra of these complexes, are correlated with the electronic effect on the aromatic ring of the ligand systems. Cyclic voltammetry has revealed the existence of two reduction couples,
The first is sensitive to the electronic effects of aromatic ring substituents of the ligand system, shifting to more positive potentials when more electrophilic groups replace the existing substituents. The conproportionation constants (k
con) for the mixed valent CuICuII complexes have been determined electrochemically. The magnetic susceptibilities of the complexes have been measured over the 70–300 K range and the exchange coupling parameter (–2J) determined by a least squares fit of the data which indicates an antiferromagnetic spin exchange (–2J = 94–172 cm–1) between the CuII ions with bridging units in the order: N3 NO2 > OAc > OH. 相似文献
7.
Ahmed A. Abdel-Khalek Mohamed M. Khalil Eman S. H. Khaled 《Transition Metal Chemistry》1993,18(2):153-157
The kinetics of the oxidation of [N-(2-hydroxyethyl)-ethylene-diamine-N,N,N-triacetato] cobalt(II), [CoII-(HEDTA)]–, by N-bromosuccinimide, NBS, have been studied in aqueous solutions and water-methanol solvent mixtures under various conditions. The reaction stoichiometry indicates that one mole of NBS reacts with one mole of [CoII(HEDTA)]–. In aqueous solutions the reaction obeys the following rate law:
相似文献
8.
The kinetics of the reaction of manganese(III) with oxalic acid (OA) has been studied in H2SO4 solutions. Under the experimental conditions of 6 × 10–3 <>0 < 0.4=" mol=">–3 and [H2SO4]0 0.2 mol dm–3 the observed pseudo-first order rate constant k
obs follows the expression
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