共查询到20条相似文献,搜索用时 15 毫秒
1.
Abdel-Khalek Ahmed A. Ewais Hassan A. Khaled Eman S.H. Abdel-Hamied Anwar 《Transition Metal Chemistry》2004,29(1):7-11
The kinetics of oxidation of [CoIINM(H2O)]3– (N = nitrilotriacetate, M = malonate) by N-bromosuccinimide (NBS) in aqueous solution have been found to obey the equation: d[CoIII]/dt = k
1
K
2[NBS][CoII]T/{1 + K2[NBS] + (H+/K1)} where k
1 is the rate constant for the electron transfer process, K
1 the equilibrium constant for dissociation of [CoIINM(H2O)]3– to [CoIINM(OH)]4– + H+, and K
2 the pre-equilibrium formation constant. Values of k
1 = 1.07 × 10–3 s–1, K
1 = 4.74 × 10–8 mol dm–3 and K
2 = 472 dm3 mol–1 have been obtained at 30 °C and I = 0.2 mol dm–3. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [CoIINM(OH)]4– is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism. 相似文献
2.
Ahmed A. Abdel-Khalek El-Said M. Sayyah Eman S. H. Khalid 《Transition Metal Chemistry》1993,18(6):555-558
Summary The kinetics of oxidation of [CoII(EDTA)]2- (EDTA = ethylenediaminetetraacetate) by N-bromosuccinimide (NBS) in aqueous solution obey the equation: Rate = k
2
K
3[CoII]T[NBS]/{1 + [H+]/K
2 + K
3[NBS]} where k
2 is the rate constant for the electron-transfer process, K
2 the equilibrium constant for the dissociation of [CoII(EDTAH)(H2O)]– to [CoII(EDTA)(OH)]3– and K
3 the pre-equilibrium formation constant. The activation parameters are reported. It is proposed that electron transfer proceeds via an inner-sphere mechanism with the formation of an intermediate which slowly generates hexadentate[CoIII(EDTA)]–.Abstracted from the M.Sc. thesis of Eman S. H. Khaled. 相似文献
3.
Hassan A. Ewais 《Transition Metal Chemistry》2009,34(5):539-547
The oxidation of [CoII(nta)(ox)(H2O)2]3− and [CoII(nta)(ph)(H2O)2]3− (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous
solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [CoII(nta)(ox)(H2O)2]3− by periodate, obeys the following equation: d[CoIII]/dt = [CoII(nta)(ox)(H2O)23−][H5IO6] {k
4
K
5 + (k
5
K
6
K
2/[H+]} while the reaction of [CoII(nta)(ph)(H2O)2]3− with periodate in aqueous acidic medium obeys the following rate law: d[CoIII]/dt = k
6
K
8[CoII]T [IVII]T/{1 + [H+]/K
7 + K
8[IVII]
T
}. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic
activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes
by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions. 相似文献
4.
The kinetics of oxidation of the chromium(III)–dipicolinic acid complex [CrIII(DPA)2(H2O)2]– by N-bromosuccinimide (NBS) in aqueous solution to CrVI have been studied spectrophotometrically over the 20–40 °C range. The reaction is first order with respect to both [NBS] and [CrIII], and increases with pH over the 5.92–6.93 range. Thermodynamic activation parameters were calculated. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of [NBS] to chromium(III). 相似文献
5.
Hassan A. Ewais 《国际化学动力学杂志》2008,40(3):103-113
The mechanism of oxidation of ternary complexes, [CoII(nta)(S)(H2O)2]3? and [CoII(nta)(M)(H2O)]3? (nta = nitrilotriacetate acid, S = succinate dianion, and M = malonate dianion), by periodate in aqueous medium has been studied spectrophotometrically over the (20.0–40.0) ± 0.1°C range. The reaction is first order with respect to both [IO4?] and the complex, and the rate decreases over the [H+] range (2.69–56.20) × 10?6 mol dm?3 in both cases. The experimental rate law is consistent with a mechanism in which both the hydroxy complexes [CoII(nta)(S)(H2O)(OH)]4? and [CoII(nta)(M)(OH)]4? are significantly more reactive than their conjugate acids. The value of the intramolecular electron transfer rate constant for the oxidation of the [CoII(nta)(S)(H2O)2]3?, k1 (3.60 × 10?3 s?1), is greater than the value of k6 (1.54 × 10?3 s?1) for the oxidation of [CoII(nta)(M)(H2O)]3? at 30.0 ± 0.1°C and I = 0.20 mol dm?3. The thermodynamic activation parameters have been calculated. It is assumed that electron transfer takes place via an inner‐sphere mechanism. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 103–113, 2008 相似文献
6.
Chimatadar Shivamurti A. Koujalagi Sangappa B. Nandibewoor Sharanappa T. 《Transition Metal Chemistry》2001,26(6):662-667
The CrVI oxidation of HgI in an aqueous acid medium occurs to a modest extent only in presence of PdII and in H2SO4 above ca. 0.20 mol dm–3. The reaction is first order in [CrVI] in the presence of PdII catalyst. The order in [HgI] is less than unity, whereas that in [PdII] is unity. Increase in [H2SO4] accelerates the reaction rate. The added products, CrIII and HgII, do not significantly effect the reaction rate. A mechanism involving HCrO4
– and PdCl+ as the reactive species of oxidant and catalyst respectively, is proposed. The reaction constants involved in the mechanism have been evaluated. 相似文献
7.
R. M. Naik A. Srivastava A. K. Tiwari S. B. S. Yadav A. K. Verma 《Journal of the Iranian Chemical Society》2007,4(1):63-71
The kinetics and mechanism of interaction of periodate ion with [CoIIL(H2O)]2-n [L = trimethylenediaminetetraaceticacid (TMDTA)] and ethylene glycol bis(2-aminoethyl ether) N,N,N’,N’-tetraaceticacid (EGTA) have been studied spectrophotometrically by following an increase in absorbance at λmax = 550 nm in acetate buffer medium as a function of pH, ionic strength, temperature, various concentration of periodate and [CoIIL(H2O)]2-n under pseudo-first order conditions. The experimental observations have revealed that the intermediates having sufficiently high half life are produced during the course of both the reactions which finally get converted into a corresponding [CoIIIL(H2O)]3-n complexes as a final reaction product. The reaction is found to obey the general rate law Rate = (k2 [IO4 ?] + k3 [IO4 ?]2) [CoIIL(H2O)]2-n. This rate law is consistent with a four step mechanistic scheme (vide supra) where electron transfer proceeds through an inner sphere complex formation. The value of rate constant k2 is independent of pH over the entire pH range which suggest that unprotonated form of [CoIIL(H2O)]2-n is the only predominant species. The value of k2 is invariant to ionic strength variation in both the systems. The value of k3 is also found to be almost invariant to ionic strength in case of [CoIITMDTA(H2O)]2?-[IO4]? system but it decreases considerably in case of [CoIIEGTA(H2O)]2?-[IO4]? system with the corresponding decrease in ionic strength. The activation parameters have been computed and given in support of proposed mechanistic scheme. 相似文献
8.
Summary Peroxodisulfate ion readily oxidises CoII-YOH [YOH =N(2-hydroxyethyl)ethylenediaminetriacetate] with the formation of an intermediate complex. The kinetics of the electron-transfer step follow the rate law: Rate = 2kHKH[H+][S2O8]2-[CoII-YOH]/(1 + KH[H+]) where [S2O8]2– is the total peroxodisulfate concentration, kH is the rate constant for the electron-transfer process, and KH is the pre-equilibrium protonation constant. Activation parameters have been evaluated. The intermediate, which was identified spectrophotometrically, slowly rearranges to the quinquedentate species Co(YOH)(H2O). The rate of this rearangement has also been measured. 相似文献
9.
New mixed ligand complexes of benzoyldithiocarbazate (H2BDT) have been synthesized and characterized by elemental analyses, spectral studies (i.r., u.v.–vis., mass), thermal analysis and electrical conductivity measurements. The complexes have the general formulae: [M2(BDT)(OX)2] · xH2O; [Co2(BDT)(OX)2(H2O)4]; [M(HBDT)(OX)-(H2O)], [Ni(BDT)(py)2]
n
and [Ni(BDT)(L)]
n
where M = MnII, NiII and CuII; BDT = dithiocarbazate dianion; OX = 8-hydroxyquinolinate; x = 1 or 2; M = ZnII or CdII; HBDT = dithiocarbazate anion and L = 2,2-bipyridyl or 1,10-o-phenanthroline. For the [M2(BDT)(OX)2] · xH2O, [Co2(BDT)(OX)2(H2O)4], [Ni(BDT)(py)2]
n
and [Ni(BDT)(L)]
n
complexes, benzoyldithiocarbazate acts as a dibasic-tetradentate ligand in the enol form via the enolic oxygen, the hydrazide nitrogens and the thiolate sulphur, while it acts as a monobasic-tridentate ligand in the keto form in the [M(HBDT)(OX)(H2O)] complexes. The thermal behaviour of the complexes has been studied by t.g.–d.t.g. techniques. Kinetic parameters of the thermal decomposition process have been computed by Coats–Redfern and Horowitz–Metzger methods. It is obvious that the thermal decomposition in the complexes occurs directly at the metal–ligand bonds except for the ZnII and CdII complexes in which decomposition seems to be at a point in the benzoyldithiocarbazate moiety. From the calculated kinetic data it can be concluded that the dehydration processes in all complexes have been described as phase-boundary controlled reactions. The activation energy values reveal that the thermal stabilities of the homobimetallic complexes lie in the order: MnII < NiII < CoII, while the monomeric CdII complex has more enhanced thermal stability than the ZnII complex. 相似文献
10.
《Journal of Coordination Chemistry》2012,65(4):721-729
Four CuII and CoII complexes–[Cu(L1)Cl2(H2O)]3/2H2O · 1/2EtOH, [Cu(L1)2Cl2]6H2O, [Co(L1)Cl2]3H2O · EtOH, and [Co2(L1)(H2O)Cl4]1.5H2O · EtOH (L1 = 2,4,6-tri(2-pyridyl)-1,3,5-triazine; TPT)–were synthesized by conventional chemical method and used to synthesize another four metal complexes–[Cu(L1)I2(H2O)]6H2O, [Cu(L1)2I2]6H2O, [Co(L1)I(H2O)2]I · 2H2O, and [Co2(L1)I4(H2O)3]–using tribochemical reaction, by grinding it with KI. Substitution of chloride by iodide occurred, but no reduction for CuII or oxidation of CoII. Oxidation of CoII to CoIII complexes was only observed on the dissolution of CoII complexes in d6-DMSO in air while warming. The isolated solid complexes (CuII and CoII) have been characterized by elemental analyses, conductivities, spectral (IR, UV-Vis, 1H-NMR), thermal measurements (TGA), and magnetic measurements. The values of molar conductivities suggest non-electrolytes in DMF. The metal complexes are paramagnetic. IR spectra indicate that TPT is tridentate coordinating via the two pyridyl nitrogens and one triazine nitrogen forming two five-membered rings around the metal in M : L complexes and bidentate via one triazine nitrogen and one pyridyl nitrogen in ML2 complexes. In binuclear complexes, L is tridentate toward one CoII and bidentate toward the second CoII in [Co2(L1)Cl4]2.5H2O · EtOH and [Co2(L1)I4(H2O)3]. Electronic spectra and magnetic measurements suggest a distorted-octahedral around CuII and high-spin octahedral and square-pyramidal geometry around CoII. 相似文献
11.
Ahmed A. Abdel-Khalek Alaa E. D. M. Abdel-Hady Mohamed F. El-Shahat 《Transition Metal Chemistry》1995,20(5):430-434
Summary In aqueous solutions, [Cr(en)3]3+ aquates to [Cr(en)2-(H2O) 2]3+. A kinetic study of the oxidation of [Cr(en)3]3+ by N-bromosuccinimide (NBS) in aqueous solutions and water-alcohol solvent mixtures was performed. The reaction is first order with respect to both total [CrIII] and [NBS]. The rate is inversely dependent upon [H+] in the 7.0–7.9 pH range, and varies with the co-solvent according to the order: MeOH > EtOH > PrOH. An appropriate mechanism, in which the deprotonated [Cr(en)2(OH)(H2O)]2+ is the reactive species, is suggested. Thermodynamic activation parameters have been calculated.Abstracted from the PhD thesis (Ain Shams University) of A. E.- D. M. Abdel-Hady. 相似文献
12.
Summary The reaction between chromone-3-carboxaldehyde-4-phenylthiosemicarbazone (HCPT) and some hydrated metal salts of CoII, NiII and CuII give complexes of the type [Cu(HCPT)Cl2],[Cu(CPT)BrH2O],[Cu(CPT)2]·2H2O, [Ni(CPT)2(H2O)2]·2H2O, [Co(CPT)2(OAc)] and [Co(CPT)2(H2O)2]X·2H2O (where X=Cl or Br). The metal complexes were characterized by elemental analyses, molar conductivities, and spectal (i.r. and visible) and magnetic studies. I.r. spectra show that the HCPT coordinates in the thione or thiol form and behaves in a bidentate manner. Also, HCPT behaves as an oxidizing agent towards CoII forming diamagnetic CoIII complexes. An octahedral structure is proposed for both CoIII and NiII complexes, while a square-planar structure is proposed for CuII complexes on the basis of magnetic and spectral measurements. 相似文献
13.
The kinetics of oxidation of CoIIHEDTA {HEDTA = N-(2-hydroxyethyl)ethylenediamine-N,N,N-triacetic acid} by vanadate ion have been studied in aqueous acid in the pH range 0.75–5.4 at 43–57 °C. The reaction exhibits second-order kinetics; first-order in each of the reactants. The reaction rate is a maximum at pH = 2.1. A mechanism is proposed in which the species [CoIIHEDTA(H2O)]– and VO2
+ react to form an intermediate which decompose slowly to give pentadentate CoIIIHEDTA(H2O) and VIV as final products. The rate law was derived and the activation parameters calculated: H* = 26.96 kJ mol–1 and S* = –311.08 JK–1 mol–1. 相似文献
14.
The kinetics of the oxidation of the 2-aminomethylpyridineCoII complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H2O)2]2+[k2+k3/[H+]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied. 相似文献
15.
The structure of the title compound features mononuclear octahedral CoII cations, trans-[Co(H2O)2(MeCN)4]2+, and trinuclear anions, trans-[Co(H2O)2(MeCN)2(CoCl4)2]2–; the latter centrosymmetric units contain a central octahedral Co(H2O)2(MeCN)2 moiety with two tetrahedral [CoCl4]2– ligands. These two large ions are held in a network of intra- and inter-molecular hydrogen bonding. 相似文献
16.
Summary The reaction of warm alcoholic solutions of acetates of CoII, MnII, ZnII and NiII with 2, 6-diacetylpyridine andS-methylisothiosemicarbazide hydrogen iodide yielded the complexes: [Co(H2L)I2]·H2O, [Mn(H2L)(MeOH)2]I2, [Zn(H2L)(MeOH)I]I and [Ni(HL)]I, (H2L=the pentadentate pentaaza-ligand 2, 6-diacetylpyridine bis(S-methylisothiosemicarbazone)). The reaction of methanolic solutions of [Ni(HL)]I and NH4NCS or LiOAc.2H2O, give [Ni(HL)]NCS and NiL, respectively. For the complexes of CoII, MnII and ZnII, a pentagonal bipyramidal configuration is proposed, with H2L in the equatorial plane and two unidentate ligands (I and/or MeOH) in the axial positions. The complexes [Ni(HL)]X (X=I or NCS) and NiL probably have monomeric five- and dimeric six-coordinate structures, respectively, in which only the chelate ligand is involved in coordination. 相似文献
17.
Angelica M. Vecchio-Sadus 《Transition Metal Chemistry》1995,20(1):46-55
Summary The single-step electrochemical synthesis of neutral transition metal complexes of imidazole, pyrazole and their derivatives has been achieved at ambient temperature. The metal was oxidized in an Me2CO solution of the diazole to yield complexes of the general formula: [M(Iz)2] (where M = Co, Ni, Cu, Zn; Iz = imidazolate); [M(MeIz)2] (where M = Co, Ni, Cu, Zn; MeIz = 4-methylimidazolate); [M(PriIz)2] (where M = Co, Ni, Cu, Zn; PriIz = 2-isopropylimidazolate); [M(pyIz)n] (where M = CoIII, CuII, ZnII; pyIz = 2-(2-pyridyl)imidazolate); [M(Pz)n] (where M = CoIII, NiII, CuII, ZnII; Pz = pyrazolate); [M(ClPz)n] and [M(IPz)n] (where M = CoIII, NiII, CuII, ZnII; ClPz = 4-chloropyrazolate; IPz = 4-iodopyrazolate); [M(Me2Pz)n] (where M = CoII, CuI, ZnII; Me2Pz = 3,5-dimethylpyrazolate) and [M(BrMe2Pz)n] (where M = CoII, NiII, CuI, ZnII; BrMe2Pz = 3,5-dimethyl-4-bromopyrazolate). Vibrational spectra verified the presence of the anionic diazole and electronic spectra confirmed the stereochemistry about the metal centre. Variable temperature (360-90 K) magnetic measurements of the cobalt and copper chelates revealed strong antiferromagnetic interaction between the metal ions in the lattice. Data for the copper complexes were fitted to a Heisenberg (S=
) model for an infinite one-dimensional linear chain, yielding best fit values of J=–62––65cm–1 andg = 2.02–2.18. Data for the cobalt complexes were fitted to an Ising (S=
) model with J=–4.62––11.7cm–1 andg = 2.06–2.49. 相似文献
18.
Kandil Samir S. El-Hefnawy Gad B. Bakr Eman A. Abou El-Ezz Amro Z. 《Transition Metal Chemistry》2003,28(2):168-175
A new series of hexacoordinate cobalt(II), nickel(II) and copper(II) complexes of 5-(2-carboxyphenylazo)-2-thiohydantoin HL having formulae [LM(OAc)(H2O)2] · nH2O (M = CoII, CuII and NiII), [LMCl(H2O)2] · nH2O (M = CoII and NiII), [LCuCl(H2O)]2 · 2H2O, [LCu(H2O)3](ClO4) and [LCu(HSO4)(H2O)2] were isolated and characterized by elemental analyses, molar conductivities and magnetic susceptibilities, and by i.r., electronic and e.s.r. spectral measurements, as well as by thermal (t.g. and d.t.g.) analyses. The i.r. spectra indicate that the ligand HL behaves as a monobasic tridentate towards the three divalent metal ions via an azo-N, carboxylate-O and thiohydantoin-O atom. The magnetic moments and electronic spectral data suggest an octahedral geometry for CoII complexes, distorted octahedral geometry for both NiII and CuII complexes with a dimeric structure for [LCuCl(H2O)]2 · 2H2O through bridged chloro ligands. The X-band e.s.r. spectra reveal an axial symmetry for the copper(II) complexes with unsymmetrical Ms = ± 1 signal and G-parameter less than four for the dimeric [LCuCl(H2O)]2 · 2H2O. The thermogravimetry (t.g. and d.t.g.) of some complexes were studied; the order and kinetic parameters of their thermal degradation were determined by applying Coats–Redfern method and discussed. 相似文献
19.
The oxidation of CoIIW by bromine(V) is a complex process involving an induction period. The reaction was found to be first-order in both [CoIIW] and [Brv], and exhibits a complex dependence on [H+]. These observations were successfully explained by considering HBrO2, one of the intermediates formed in the direct but slow reaction between CoIIW and bromine(V), as the reacting species. The first-order limiting dependence in [H+] was due to the involvement of a protic equilibrium of HBrO2. The induction period appears due to the scavenging effect of Br– inadvertently present in the medium. It appears to be the first report where HBrO2 was found to be the reacting intermediate in the oxidation of metal ions and complexes by BrO–
3. 相似文献
20.
Summary The kinetics of oxidation of amines (EtNH2, Et2NH, Et3N) and aminoalcohols [H2NCH2CH2OH, H2N(CH2)3OH, (CH2CH2OH)2NH, (CH2CH2OH)3N] by N-bromosuccinimide (NBS) have been studied in aqueous HClO4 with PdCl2 as catalyst, and in the presence of Hg(OAc)2 to ensure oxidation by pure NBS. The order of reaction with respect to NBS was unity, however, an increase in [NBS]0 resulted in a decrease in the rate constant. The rate was directly proportional to [PdII] for the aminoalcohols while for EtNH2 the rate was proportional to k + k[PdII] (where k and k are rate constants for the uncatalysed and catalysed paths, respectively). Retarding effects for HClO4, succinimide, Cl– and AcOH on the rate of oxidation were observed. The kinetic data support the formation of [PdII-A] and [PdII-(A)2] complexes (where A represents amine or aminoalcohol). A mechanism, consistent with the observed kinetic data, is proposed. 相似文献