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  • 1
    Electronic Resource
    Electronic Resource
    Complex formation between nickel(II) and 2-(2-aminoethyl) benzimidazole: A kinetic and equilibrium study (1995)
    Springer
    Transition metal chemistry 20 (1995), S. 147-152 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The reversible complex formation between 2-(2-aminoethyl) benzimidazole (AEB) and nickel(II) was studied by stopped flow spectrophotometry at I = 0.30 mol dm−3. Both the neutral and monoprotonated form of AEB reacted to give the NiAEB2+ chelate. At 25 °C, the rates and activation parameters for the reactions NiII + AEB $$\xrightarrow{{k_f^L }}$$ NiAEB2+ and NiII + AEBH+ $$\xrightarrow{{k_f^{HL} }}$$ NiAEB2+ + H+ are k f L(dm−3 mol−1 s−1) = (2.17 ± 0.24) × 103, ΔH ≠ (kJ mol−1) = 40.0 ± 0.8, ΔS ≠ (JK−1 mol−1) = − 47 ± 3 and k inff pHL (dm3 mol−1 s−1) = 33 ± 10, ΔH ≠(kJ mol−1) = 42.0 ±2.7, ΔS ≠(JK−1 mol−1) = − 72 ± 9. The dissociation of NiAEB2+ was acid catalysed and k obs for this process increased linearly with [H+] in the 0.01–0.15 mol dm−3 (10–30 °C) range with k H(dm3 mol−1s−1) (25 °C) = 329 ± 6, ΔH ≠(kJ mol−1) = 40 ± 2 and ΔS ≠ (JK−1 mol−1) = − 61 ± 8. The results also indicated that the formation of NiAEB2+ involves a chelation-controlled, rate-limiting process. Analysis of the ΔS ° data for the acid ionisation of AEBH inf2 p2+ and the formation of NiAEB2+ showed that the bulky AEBH+ ion has a solvent structure breaking effect as compared to AEB [s aqS ° (AEBH+) − s aq ° (AEB) = 69 JK−1 mol−1], while AEBH inf2 p2+ is a solvent ordering ion relative to NiAEB2+ [s aq° (NiAEB2+) − ovS aq ° (AEBH inf2 p2+ ) = 11 JK−1 mol−1].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00167018
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  • 2
    Electronic Resource
    Electronic Resource
    Steric effects on complex formation between nickel(II) and (2-imidazoleazo) benzene, 2,2′-biimidazole and 2,2′-bibenzimidazole (1996)
    Springer
    Transition metal chemistry 21 (1996), S. 337-344 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The kinetics and mechanism of reversible complexation of NiII with (2-imidazoleazo)benzene (IAB), 2,2′-biimidazole (Biim) and 2,2′-bibenzimidazole (Bibzm) have been investigated at 15–35 °C, I = 0.30 mol dm−3. The stability constants, K M, of the [NiL]2+ species vary in the sequence: [Ni(IAB)]2+ 〈 [Ni(Bibzm)]2+ 〈 [Ni(Biim)]2+. The values of the spontaneous dissociation rate constant (k r) at 25 °C decrease in the sequence: [Ni(IAB)]+ 〉 [Ni(Biim)]2+ 〉 [Ni(Bibzm)]2+. The aquation of [Ni(IAB)]2+ is insensitive to acid catalysis, whilst [Ni(Biim)]2+ is relatively more susceptible towards acid-catalysed aquation than [Ni(Bibzm)]2+. The chelate ring in [NiL]2+ (L = IAB, Biim or Bibzm) is sterically strained. The formation of [Ni(IAB)]2+ and [Ni(Bibzm)]2+ may be chelation controlled while the normal I d mechanism is supported by our data for [Ni(Biim)]2+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00139030
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  • 3
    Electronic Resource
    Electronic Resource
    Ligand control on the reactions of oxygen- and sulphur-bonded (sulphito)pentaminecobalt(III) complexes in solution (1997)
    Springer
    Transition metal chemistry 23 (1997), S. 45-55 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of formation, acid-catalysed aquation, ligand isomerisation (CoIIIOSO2+→CoIIISO3+), intramolecular electron-transfer, and base-catalysed hydrolysis and isomerisation of O-bonded sulphito complexes, cis-[Co(en)2(B)(OSO2–O)]+[B=benzimidazole (bzimH), N-methylimidazole (N-meim)] and the anation of cis-[Co(en)2(B)OH)]2+ [B=bzimH, N-meim and imH (imidazole)] by oxSO2−3 are reported. Steric acceleration is observed in the formation and acid-catalysed aquation of the O-sulphito complexes. The ligand isomerisation leads to loss of the monodentate amine with the formation of trans-[Co(en)2(SO3–S)2]− (in an excess of sulphite). Steric acceleration is more pronounced in the isomerisation and base hydrolysis than in the redox process. The results indicate cis labilisation of the coordinated O-sulphite. The [(tetraethylenepentamine)Co(OSO2–O)]+ cation undergoes base hydrolysis 103 times faster than the corresponding (en)2(B) complexes; base-catalysed ligand isomerisation for the former is not observed unlike in the latter. The anation of cis-[Co(en)2(B)OH]2+ (B=imH, bzimH, N-meim) by SO2−3 in a mild alkali pH range (pH=7.9–9.6) and in an excess of SO2−3, yields exclusively trans-[Co(en)2(SO3–S)2]− with no evidence for the formation of the cis-[Co(en)2(B)(SO3–S)]+ or its O-sulphito analogue. The intramolecularly generated amido conjugate base of the sulphite ion-pair, {cis-[Co(en)2(B)OH]2+,SO32−}.41cm{cis-[Co(en)(en-H) (B)- OH2]2+,SO32−}, is believed to generate a five-coordinate intermediate (TBP) that captures the S-end of SO2−3 selectively from a site trans-to the amine B so that the amine is labilised by the trans effect of the sulphite. The NH-deprotonated coordinated imidazolate or benzimidazolate species, cis-[Co(en)2(bzm/im)OH]+, do not undergo anation by SO2−3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006901900302
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of complex formation between beryllium(II) and the 3-nitrosalicylatopentaamminecobalt(III) ion (1995)
    Springer
    Transition metal chemistry 20 (1995), S. 406-408 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The kinetics of formation and dissociation of the binuclear complex of Be2+ with 3-nitrosalicylatopentaamminecobalt(III) have been investigated in the 20–40 and 25–40 °C ranges (I = 0.3 mol dm −3), respectively. At 25 °C the rate and activation parameters for the formation of the binuclear species are: k f = 26.9 × 102 dm3mol−1s−1, ΔH ≠ = 104 ± 7kJ mol−1 ΔS ≠= 91 ± 22JK−1mor−1.The rate constant, activation enthalpy and activation entropy for the acid-catalysed dissociation of the binuclear species are: 1.25 ± 0.08dm3mol −1 at 25 °C, 53 ± 3kJ mol−1 and - 67 ± 9 J K −1 mol−1, respectively. The formation of the binuclear species is chelation controlled while the dechelation is acid catalysed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00139142
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  • 5
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of the interaction of pentaammine(pyridine-2-carboxylato)cobalt(III) ions with hexaaquanickel(II) and nickel(II) complexes: the role of chelating ligands (1998)
    Springer
    Transition metal chemistry 23 (1998), S. 175-181 
    Details
    ISSN: 1572-901X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reversible complexation of the pentaammine(pyridine-2-carboxylato)cobalt(III) ion [N5Co{O2C-(2)-C5H4 N}]2+ [N5=5HN3 and tetraethylenepentaammine (tetren)] with NiIIL(OH2)6-n [L=H2O (N5=tetren); L=bipy, ida2- (iminodiacetate) and nta3- (nitrilotriacetate), N5=5NH3 and tetren] has been investigated by the stopped-flow technique at 20-40 degC, and I= 0.3mol dm-3. At 25degC, the rate constants, kf(dm3 mol-1s-1), DeltaH(kJmol-1) and DeltaS(JK-1mol-1) for the formation of the ternary complexes [(tetren)-CoIII{O2C-(2)-C5H4N} NiIIL(OH2)6-n] are as follows: L=H2O, 530+9, 53+2, -15+7, respectively; L=bipy, 640+30, 37+3, -65+9; L=ida2-, 3900+100, 47+3, -18+11; L=nta3-, 10200+400, 49+1, −2+2. Nickel(II), in the ternary complexes, is chelated by the free pyridyl-N and the carboxylato moiety of the pyridine-2-carboxylate bound to the cobalt centre. The formation rate constant (kf) and the associated activation parameters are relatively insensitive to the N5 moieties for a given ligand L; kf increased in the order: Ni(OH2)62+Ni(bipy)(OH2)42+ Ni(ida)(OH2)3 (nta)(OH2)2-. Data analysis indicated that the mechanism shifted from the dissociative interchange (Id) to the chelation-controlled one, with the decrease of the available sites for coordination in NiIIL(OH2)6−n. The rate constants (kr) for the dissociation of [N5CoIII{O2C-(2)-C5 H4N}NiIIL(OH2) 6-(n+2)] to the parent reactants indicated steric acceleration [krL(5NH3) 〈krL(tetren)] and followed the trend: krNi(nta)-〉kr Ni(ida) 〉krNi(bipy)2+ for both pentaammine substrates. The chelate ring opening rate constants for the ternary complexes were estimated, from which it was apparent that the tetren envelope of cobalt(III) exerted relatively greater steric pressure as compared with 5NH3 in favouring opening up of the chelate ring.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006907428953
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  • 6
    Electronic Resource
    Electronic Resource
    Base hydrolysis of (αβ S)-(o-methoxy benzoato) (tetraethylenepentamine) cobalt(III) ion: A comparative study of the role of ion pairs and micelles (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 26 (1994), S. 681-692 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of base hydrolysis of (αβ S)-(o-methoxy benzoato) (tetraethylenepentamine)cobalt(III) obeyed the rate law: kobs = kOH[OH-], in the range 0.05 ≤ [OH-]T, mol dm-3 ≤ 1.0, I = 1.0 mol dm-3, and 20.0-40.0°C. At 25°C, kOH = 13.4 ± 0.4 dm3 mol-1 s-1, ΔH≠ = 93 ± 2 kJ mol-1 and ΔS≠ = 90 ± 5 JK-1 mol-1. Several anions of varying charge and basicity, CH3CO2-, SO32-, SO42-, CO32-, C2O42-, CH2(CO2)22-, PO43-, and citrate3- had no effect on the rate while phthalate2-, NTA3-, EDTA4-, and DTPA5- accelerated the process via formation of the reactive ion pairs. The anionic (SDS), cationic (CTAB), and neutral (Triton X-100) micelles, however, retarded the reaction, the effect being in the order SDS〉 CTAB 〉 Triton X-100. The importance of electrostatic and hydrophobic effects of the micelles on the selective partitioning of the reactants between the micellar and bulk aqueous pseudo-phases which control the rate are discussed. © 1994 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550260702
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetics and mechanism of reaction of trans-(diaqua)(N,N′-ethylene-bis-salicylidenimine) chromium(iii) with sulfur(iv): The labilizing effect of coordinated sulfite (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 30 (1998), S. 373-384 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of trans-[Cr(Salen)(OH2)2]+ with aqueous sulfite yields trans-[Cr(Salen)(OH2)(OSO2(SINGLEBOND)O)]- (O-bonded isomer). The rate and activation parameter data for the formation of the sulfito complex are consistent with a mechanism involving rate-limiting addition of SO2 to the CrIII(SINGLEBOND)OH bond. The complex ions, trans-[(OH2)Cr(Salen)(OSO2(SINGLEBOND)O)]-, and trans-[(OH)Cr(Salen)(OSO2(SINGLEBOND)O)]2-, undergo reversible anation by NCS-, N3-, imidazole, and pyridine resulting in the formation of trans-[XCr(Salen)(OSO2(SINGLEBOND)O)](N+1)-(n=1 for X=N3-,NCS-, and 0 for X=imidazole and pyridine) predominantly via dissociative interchange mechanism. The labilizing action of the coordinated sulfite on the trans-CrIII-X bond in trans-[XCr(Salen)(OSO2)](n+1)- follows the sequence: NCS-pyridine ca. N3- ca. imidazole. Data analysis indicated that the coordinated sulfite has little trans activating influence. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 373-384, 1998
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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