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1.
The kinetics of base hydrolysis ofcis-[RuCl2(en)2]+ (en=1,2-diaminoethane),cis-α-[RuCl2(trien)]+ andcis-α-[RuCl(OH)(trien)]2+ (trien=1,8-diamino-3,6-diazaoctane) have been studied. All the reactions are fast and obey the second-order rate law,-d[complex]/dt=k[OH−][complex], with complete retention of configuration. A conjugate base mechanism involving a squarepyramidal intermediate
is suggested. The Arrhenius parameters and rate constants found are respectively: ΔH≠ 14.2±0.5, 7.2±0.1, 10.9±0.1 M cal mol−1; ΔS≠ 1.3, 29, 22 cal deg−1 mol; log A 13.5, 6.9, 8.6 kOH 533 (27.2°C) 14.5 (24.4° C) 1.65 (25°C) M−1s−1. 相似文献
2.
Summary The kinetics of base hydrolysis of cis-[(salicylato)(RNH2) (en)2COIII]2+ (R = H, Me or Et) have been studied in MeOH-H2O medium at 35.0°C, I = 0.1 (ClO
4
–
) and 0.01 [OH-]Tmol dm-3 0.10. The phenoxide species [(RNH2)(en)2CoO2C6H4O]+, underwent both OH--independent (SNICB) and OH--catalysed (SN1CB) hydrolysis with K
obs=k
1+k
2[OH–]. Both k
1 and k
2 are appreciably enhanced by the medium for MeNH2 and EtNH2 complexes. In contrast, for the NH3 complex, k
1 decreases with increasing MeOH content and k
2 was non-existent beyond 60% (v/v) MeOH. These rate variations illustrate the importance of the solute-solvent interaction, presumably partly of hydrophobic origin, and solvent structure in existing stabilizing/destabilizing effects on the initial and transition states. 相似文献
3.
Guru C. Pradhan 《Transition Metal Chemistry》1992,17(2):104-108
The formation and dissociation of the binuclear complexes of FeIII withcis-[Co(en)2(RNH2)SalH]2+ [R=Me, Et and SalH=C6H4(OH)CO
2
−
] were studied by a stopped-flow technique at 20–35°C, and I=1.0 mol dm−3 (ClO
4
−
). The formation of the binuclear species, N5CoSalFe4+, involves reactions of the phenol form of the CoIII substrates with Fe(OH2)
6
3+
and Fe(OH2)5OH2+. The mechanism of reaction of Fe(OH2)5OH2+ is essentially Id, while that of Fe(OH2)
6
3+
appears to be Ia. The formation rate constant, k1, for Fe(OH2)
6
3+
/N5CoSalH2+ reaction decreases as the amine chain length increases, whereas the same (k2) for the Fe(OH2)5OH2+/N5CoSalH2+ reaction does not show any such trend. The binuclear species, N5CoSalFe4+, dissociates to yield a CoIII substrate and FeIII speciesvia a predominantly spontaneous dissociation path and a minor acid catalysed path which are relatively insensitive to the variation
in size of the non-labile amine chain length. 相似文献
4.
Summary The kinetics of the first step of base hydrolysis oftrans-bis(Hmalonato)bis(ethylenediamine)cobalt(III) [malH–=HO2CCH2CO
2
–
] has been investigated in the 15–35° C range, I=0.3 mol dm–3 (NaClO4) and [OH–]=0.015–0.29 mol dm–3. The rate law is given by –d In[complex]T/dt=k1[OH–] and at 30° C, k1=8.5×10–3 dm3 mol–1s–1, H=117.0±7.0 kJ mol–1 and S=99.0±24.0 JK–1mol–1. The activation parameters data are consistent with the SN1 cb mechanism. 相似文献
5.
The reductions of [Co(CN)5NO2]3−, [Co(NH3)5NO2]2+ and [Co(NH3)5ONO]2+, by TiIII in aqueous acidic solution have been studied spectrophotometrically. Kinetic studies were carried out using conventional
techniques at an ionic strength of 1.0 mol dm−3 (LiCl/HCl) at 25.0 ± 0.1 °C and acid concentrations between 0.015 and 0.100 mol dm−3. The second-order rate constant is inverse—acid dependent and is described by the limiting rate law:- k2 ≈ k0 + k[H+]−1,where k=k′Ka and Ka is the hydrolytic equilibrium constant for [Ti(H2O)6]3+. Values of k0 obtained for [Co(CN)5NO2]3−, [Co(NH3)5NO2]2+ and [Co(NH3)5ONO]2+ are (1.31 ± 0.05) × 10−2 dm3 mol−1 s−1, (4.53 ± 0.08) × 10−2 dm3 mol−1 s−1 and (1.7 ± 0.08) × 10−2 dm3 mol−1 s−1 respectively, while the corresponding k′ values from reductions by TiOH2+ are 10.27 ± 0.45 dm3 mol−1 s−1, 14.99 ± 0.70 dm3 mol−1 s−1 and 17.93 ± 0.78 dm3 mol−1 s−1 respectively. Values of K
a
obtained for the three complexes lie in the range (1–2) × 10−3 mol dm−3 which suggest an outer-sphere mechanism. 相似文献
6.
The base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ? t°C ? 35.0 and I = 0.10 mol dm?3 (ClO4?). The phenoxide species [(tetren)CoO2CC6H4O]+ undergoes both OH?-independent and OH?-catalyzed hydrolysis via SN1ICB and SN1CB mechanism, respectively. The OH?-independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH?-catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, ΔH≠ and ΔS≠, with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in ΔH≠ vs. ΔS≠ plot accomodating all data for k1 and k2 paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory. 相似文献
7.
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
8.
Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN5=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO4)2, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H2O)](ClO4)2 is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=kH[complex][H+]2 with kH =4.8 dm6 mol–2s–1 at 25 °C and I=1.0 mol dm–3 (NaClO4) with H=43 kJ mol–1 and S
298
=–89 JK–1 mol–1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN5 < [16]aneN5 < [17]aneN5. For the dissociation of the nickel(II) complex, rate=kH[Complex][H+] with kH=9.4×10–3 dm3mol–1 s–1 at 25 °C and I =1.0 mol dm–3 (NaClO4) with H=71 kJ mol–1 and S
298
=–47 JK–1mol–1.The cobalt(III) complexes, [CoLCl](ClO4)2, [CoL(H2O)]-(ClO4)3, [CoL(NO2)](ClO4)2, [CoL(DMF)](ClO4)3 (DMF=dimethylformamide) and [CoL(O2CH)](ClO4)2 have been characterised. The chloropentamine [CoCl([16]aneN5)]2+ undergoes rapid base hydrolysis with kOH=1.1× 105dm3 mol–1s–1 at 25°C and I=0.1 mol dm–3 (H=73 kJ mol–1 and S
298
=98 JK–1 mol–1). Rapid base hydrolysis of [CoL(NO2)]2+ is also observed and the origins of these effects are considered in detail. 相似文献
9.
Summary The hydrolysis ofcis-[CoCl(en)2(bzmH)]2+ (en=ethylenediamine, bzmH=benzimidazole) has been studied over the pH range 8.31–11.58 at I=0.1 mol dm–3 and 25°. Potentiometric titration of aqueous solutions of the [Co(en)2(bzmH)OH2]3+ complex obtained by silver(I) catalysed aquation of the chloro-complex give pK1=5.81 and pK2 = 8.84 for Equilibria (1) and (2) at 25° and I=0.1 mol dm–3. Spectrophotometric titration of the hydroxy complex also gives a value of pK2=8.88 for the ionisation of the coordinated benzimidazole. The kinetic data can be interpreted in terms of base hydrolysis ofcis-[CoCl(en)2(bzmH)]2+ (kOH=220 dm3 mol–1s–1) andcis-[CoCl(en)2(bzm)]+ (kOH=14.9 dm3 mol–1s–1). Comparisons with the corresponding imidazole and pyridine complexes are made. 相似文献
10.
Summary The kinetics of the acid-catalysed hydrolysis of the [(imidazole)4Co(CO3)]+ ion was found to follow the rate law -dln[complex]/dt = k
1
K[H+](1 + K[H
+]) in the 25–45 °C range, [H+] 0.05–1.0 m range and I = 1.0m. The reaction sequence consists of a rapid protonation equilibrium followed by the one-end dissociation of the coordinated
carbonato ligand (rate-determining step) and subsequent fast release of the monodentate carbonato ligand. The rate parameter
values, k
1 and ITK, at 25 °C are 6.48 × 10−3s−1 and 0.31m
−1, respectively, and activation parameters for k
1 are ΔH
1
≠ = 86.1 ± 1.2kJ mol−1 and ΔS
1
≠ = 2.1 ± 6.3 J mol−1K−1. The hydrolysis rate increases with increase in ionic strength. The different ways of dealing with the data fit are presented
and discussed. The kinetic results are compared with those for the similar cobalt(III) complexes. 相似文献
11.
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
12.
Summary The aquation ofcis-[Co(en)2(NH2Et)O2CR]2+ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05[OH–]T 0.35 mol dm–3 range (I=0.5 mol dm–3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co–O bond heterolysis. A substantially large positive value for the activation entropy supports SN1CB mechanism for base hydrolysis. 相似文献
13.
Summary Base hydrolysis of methyl ethylenediaminemonoacetate has been studied at I=0.1 mol dm–3 (NaClO4) over the pH range 7.4–8.8 at 25 °C. The proton equilibria of the ligand can be represented by the equations, where E is the free unprotonated ester species. Values of pK1 and pK2 are 4.69 andca. 7.5 at 25° (I=0.1 mol dm–3). For base hydrolysis of EH+, kOH=1.1×103 dm3 mol–1 s–1 at 25 °C. The species E is shown to undergo lactamisation to give 2-oxopiperazine (klact
ca. 1×10–3 s–1) at 25 °C. Formation of the lactam is indicated both by u.v. measurements and by isolation and characterisation of the compound.Base hydrolysis of the ester ligand in the complex [CuE]2+ has been studied over a range of pH and temperature, k
OH
25
=9.3×104 dm3 mol–1 s–1 with H=107 kJ mol–1 and S
298
=209 JK–1 mol–1. Base hydrolysis of [CuE]2+ is estimated to be some 1055 fold faster than that of the free ester ligand. The results suggest that base hydrolysis occursvia a chelate ester species in which the methoxycarbonyl group of the ligand is bonded to copper(II). 相似文献
14.
Ewa Kita Hasan Marai Lisiak Michał Miłosz Jasiński Tomasz Drewa 《Transition Metal Chemistry》2010,35(2):177-184
Base hydrolysis of [Cr(ox)2(pda)]3− (where pda is N,O-bonded 2,4- and 2,5- pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads
to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through
[Cr(ox)(pda)(OH)2]3− and [Cr(pda)(OH)4]3− complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d–d
band region, at 0.4–1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where
the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first
order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)3]3− were studied. The calculated rate constants were independent of [OH
−
]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox)2(pda)]3− and [Cr(2,4-pda)3]3− complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which
makes them promising candidates for dietary supplements. 相似文献
15.
B. Seshagiri Rao Rabindranath Nanda Kumuda Kanta Tripathy 《Transition Metal Chemistry》1981,6(2):97-100
Summary The kinetics of acid hydrolysis ofcis-[CoCl(btzH)(en)2]2+ andcis-[CoCl(btzMe)(en)2]2+ complexes (where btzH = benzotriazole, btzMe =N-methylbenzotriazole and en = ethylenediamine) have been investigated in HClO4 at ionic strength 1 = 0.25 mol dm–3 in the 30–40° range. In the 1.0 x 10–1 to 1.0 X 10–3 mol dm–3 acid strength range, the rate of aquation of the [CoCl(btzH)(en)2]2+ cation follows the relationship:-d ln[complex]/dt = k1 + k2KNH[H+]–1, where k1 and k2 are aquation rate constants of the acid independent and acid dependent steps respectively, and KNH is the acid dissociation constant of the coordinated benzotriazole.cis-[CoCl(btzMe)-(en)2]2+ undergoes acid independent hydrolysis presumably due to the absence of a labile N-H proton. The base hydrolysis could be followed for thecis-[CoCl(btzMe)(en)2]2+ complex only by measuring hydrolysis rates at 0°. 相似文献
16.
An O-bonded sulphito complex, Rh(OH2)5(OSO2H)2+, is reversibly formed in the stoppedflow time scale when Rh(OH2)
6
3+
and SO2/HSO
3
−
buffer (1 <pH< 3) are allowed to react. For Rh(OH2)5OH2++ SO2 □ Rh(OH2)5(OSO2H)2+ (k1/k-1), k1 = (2.2 ±0.2) × 103 dm3 mol−1 s−1, k−1 = 0.58 ±0.16 s−1 (25°C,I = 0.5 mol dm−3). The protonated O-sulphito complex is a moderate acid (K
d
= 3 × 10−4 mol dm−3, 25°C, I= 0.5 mol dm−3). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10−3 s−1 (31°C) to Rh(OH2)4(O2SO)+ and the chelated sulphito complex takes up another HSO
3
−
in a fast equilibrium step to yield Rh(OH2)3(O2SO)(OSO2H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH2)3(O2SO)(OSO2)- → Rh(OH2)3(O2SO)(SO3)− (k
iso
= 3 × 10−4 s−1, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na4[Rh2(μ-OH)2(OH)2(μ-OS(O)O)(O2SO)(SO3) (OH2)]5H2O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water
and most organic solvents and very stable to acid-catalysed decomposition 相似文献
17.
Parnajyoti Karmakar Subhasis Mallick Biplab K. Bera Arup Mandal Subala Mondal Sudip K. Mukhopadhyay Alak K. Ghosh 《Transition Metal Chemistry》2010,35(8):911-916
The kinetics of the interaction of glycine-l-leucine (Glyleu) with cis-[Pt(cis-dach)(OH2)2]2+ (dach = 1,2-diaminocyclohexane) has been studied spectrophotometrically as a function of [cis-[Pt(cis-dach)(OH2)2]2+], [Glyleu] and temperature at pH 4.0, where the complex exists predominantly as the diaqua species and Glyleu as a zwitterion.
The substitution reaction shows two consecutive steps: the first is the ligand-assisted anation and the second is the chelation
step. The activation parameters for both the steps were evaluated using Eyring’s equation. The low ∆H1≠ (51.9 ± 2.8 kJmol−1) and large negative value of ∆S1≠ (−152 ± 8 JK−1mol−1) as well as ∆H2≠ (54.4 ± 1.7 kJmol−1) and ∆S2≠ (−162 ± 5 JK−1mol−1) indicate an associative mode of activation for both the aqua ligand substitution processes. 相似文献
18.
Jonathan F. Ojo Jide Ige Grace O. Ogunlusi Olanrewaju Owoyomi Esan S. Olaseni 《Transition Metal Chemistry》2006,31(6):782-785
The kinetics of the reactions between Fe(phen)
3
2+
[phen = tris–(1,10) phenanthroline] and
Co(CN)5X3− (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm−3 (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H+] = 0.01 mol dm−3) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm3 mol−1 s−1. Ion-pair constants K
ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 104, 3.00 × 102 and 4.02 × 104 mol−1 dm−3 for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K−1 mol−1) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K−1) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E
a
(kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm3 mol−1 s−1) = (7.079 ± 0.035) × 1016, (1.413 ± 0.011) × 1017, and (9.772 ± 0.027) × 1020 for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions. 相似文献
19.
The kinetics of oxidation of phenyldiethanolamine (PEA) by a silver(III) complex anion, [Ag(HIO6)2]5−, has been studied in an aqueous alkaline medium by conventional spectrophotometry. The main oxidation product of PEA has
been identified as formaldehyde. In the temperature range 20.0–40.0 °C , through analyzing influences of [OH−] and [IO
4
−
]tot on the reaction, it is pseudo-first-order in Ag(III) disappearance with a rate expression: k
obsd = (k
1 + k
2[OH−]) K
1
K
2[PEA]/{f([OH−])[IO
4
−
]tot + K
1 + K
1
K
2 [PEA]}, where k
1 = (0.61 ± 0.02) × 10−2 s−1, k2 = (0.049 ± 0.002) M−1 s−1 at 25.0 °C and ionic strength of 0.30 M. Activation parameters associated with k
1 and k
2 have also been derived. A reaction mechanism is proposed involving two pre-equilibria, leading to formation of an Ag(III)-periodato-PEA
ternary complex. The ternary complex undergoes a two-electron transfer from the coordination PEA to the metal center via two
parallel pathways: one pathway is spontaneous and the other is assisted by a hydroxide ion. 相似文献
20.
Base hydrolysis of [Cr(ox)2(quin)]3− (where quin2− is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a
mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through [Cr(ox)(quin)(OH)2]3− and [Cr(quin)(OH)4]3− formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr–N bond. The kinetics
of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy
d–d band region at 0.4–1.0 M NaOH. The pseudo-first-order rate constants (k
obs0 and k
obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)(quin)(OH)2]3− and cis-[Cr(ox)2(OH)2]3− were studied. The determined pseudo-first-order rate constants were independent of [OH−]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, [Cr(ox)2(O-quin)(OH)]4−, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring
opening and the first oxalate dissociation were determined. 相似文献