Showing papers on "Aquation published in 1977"

The comparative chemistry of ammine and methylamine complexes of rhodium(III) and cobalt(III)

Abstract: For the aquation of (CH3NH2)5RhCl2+, the first order rate coefficients are represented by ΔHaq* = 101.9 kJ mol−1 and ΔSaq* = −50.2 JK−1 mol−1 in 0.1 M HClO4, while for base hydrolysis the rate is first order in [(CH3NH2)5RhCl2+] and [OH−] at ionic strength 0.10 M and the rate coefficients (in M−1 s−1) are represented by ΔHOH*> = 108.6 kJ mol−1 and ΔSOH* = 74.1 J K−1 mol−1. Acid dissociation constants are reported for (RNH2)5MOH23+ (R = H or CH3; M = Rh or Co), and these, combined with spectral data, show CH3NH2 to be a poorer electron donor than NH3 in complexes of this type, contrary to expectations. The comparative kinetics of reactions of (RNH2)5MCl2+ support the assignment of an Ia mechanism to aquation when M = Rh or Cr, Id to aquation when M = Co, and Dcb for base hydrolysis in all these cases.

Stereospecific Formation of Pentaamine Complexes of Co(III) with Terdentate 2,6‐Bis(aminomethyl)pyridine

Abstract: Some pentaamine complexes of Co(III) with 2,6-bis(aminomethyl)pyridine (bamp), a diamine ligand (or two ammonia ligands) and one unidentate ligand have been prepared (Table 1). In all these species, bamp remains coordinated meridionally under a variety of conditions as shown by 1H- and 13C-NMR. spectroscopy and correlations by stereoretentive reaction cycles. The rates of amine proton exchange and of spontaneous aquation, Hg2+-induced aquation and base hydrolysis of some chloropentaamine complexes have been determined. They essentially follow the patterns observed for complexes with purely aliphatic amine ligands; the presence of a pyridine donor in these complexes does not suggest deviations from the mechanistic schemes usually proposed for the solvolytic reactions investigated.

Kinetics and mechanism of hydrolysis of cis-chlorobis(ethylenediamine)-(imidazole)cobalt(III) and cis-bromobis(ethylenediamine)(imidazole)cobalt(III) cations

Abstract: The kinetics of hydrolysis of cis-[CoX(imH)(en)2]2+(imH = imidazole; en = ethylenediamine; X = Cl or Br) cations have been investigated in perchlorate medium of I= 0.3 mol dm–3. In the range pH 0.5–5.7 the rate law for aquation takes the form –dln[CoIII]/dt=k1+k2KNH[H+]–1 where k1 and k2 are the aquation rate constants of [CoX(en)2(imH)]2+ and [CoX(im)(en)2]+ respectively and KNH is the acid dissociation constant of the co-ordinated imidazole. At 50 ° C the values of k1,k2KNH, ΔH‡, and ΔS‡ for the k1 path are (1.21 ± 0.02)× 10–5 s–1, (4.95 ± 0.11)× 10–11 mol dm–3 s–1, 92.3 ± 1.2 kJ mol–1, –54 ± 3 J K–1 mol–1 for the chloro-, and (5.52 ± 0.10)× 10–5 s–1, (33.4 ± 0.7)× 10–11 mol dm–3 s–1, 94.5 ± 0.3 kJ mol–1, and –34 ± 1 J K–1 mol–1 for the bromo-complex respectively. Values of k2 obtained from the base-hydrolysis studies are (1.28 ± 0.17)× 10–2 and (2.46 ± 0.22)× 10–2 s–1 at 31.8 °C for the chloro- and bromo-complexes respectively, and the imido-complex [CoCl(im)(en)2]+ also undergoes second-order base hydrolysis with a rate constant of 5.1 ± 1.0 dm3 mol–1 s–1 at the same temperature. The labilizing action of imidazole and its conjugate base on the Co–X bond appears to be comparable to that of pyridine and hydroxide respectively. Co-ordinated imidazole is 105 times stronger as an acid than free imidazole. The sulphate- and mercury(II)-catalysed aquations of both the substrates have also been studied. The value of kip/k1, where kip and k1 are the rate constants of aquation of [CoX(imH)(en)2]2+, [SO4]2– and [CoX(imH)(en)2]2+ species respectively, is 2.3 ± 0.2 at 60 °C for X = Cl and 4.6 ± 0.1 at 50 °C for X = Br. The mercury(II)-catalysed aquation follows second-order kinetics, –dln[CoIII]/dt=kHg[Hg2+] : at 30.5 °C the rate constant (kHg) and activation enthalpy and entropy are (3.48 ± 0.03)× 10–2 dm3 mol–1 s–1, 68.4 ± 0.7 kJ mol–1. and –48 ± 2 J K–1 mol–1 for the chtoro- and 12.4 ±0.5 dm3 mol–1 s–1, 53.4 ± 0.4 kJ mol–1, and –48 ± J K–1 mol–1 for the bromo-complex respectively.

Aquation of formato-, NN-dimethylformamide-, and fluoro-penta-amminechromium(III) complexes. Identification of reaction paths and kinetic studies

Abstract: The formato- and NN-dimethylformamide (DMF) complexes [Cr(NH3)5(O2CH)]2+ and [Cr(NH3)5(OCHNMe2)]3+ have been prepared and characterized. Ion-exchange separation of the aquation products in the case of the formato-complex indicates that ammonia loss features prominantly. With the DMF complex a single process corresponding to aquation of DMF is observed. Kinetic studies give k1= 1.79 × 10–4 s–1 at 50 °C. I = 1.00M(LiClO4),with activation parameters ΔH‡= 20.2 ± 0.5 kcal mol–1 and ΔS‡=–13.5 ± 1.7 cal K–1 mol–1. Aquation of [Cr(NH3)5F]2+ yields [Cr(NH3)5(H2O)]3+(k2) and [Cr(NH3)4(H2O)F]2+(k3) with the latter predominating over the conditions [H+]= 0.01–1.00M investigated. From product analyses and kinetic studies at different [H+] rate constants have been obtained at 50 °C. I = 1.00M(LiClO4). Aquation of fluoride is [H+]-dependent,k2=a+b[H+] with a= 2.1 × 10–6 s–1 and b= 2.9 × 10–6 l mol–1 s–1, while k3 for ammonia loss is independent of [H+], k3= 7.7 × 10–6 s–1.

Solute–water interactions in the aquation of isonicotinohydrazide and nicotinic acid complexes of pentacyanoferrate(II) at various pH

Abstract: Changes in the rate constants and activation parameters of the title reactions, as the state of protonation of the outgoing ligand and cyanides changes, seem to reflect solely changes due to the different charge type, i.e. the different contribution from water structuring around the activated complex. Rate constants for the title and related reactions are remarkably insensitive to changes in Fe–N bonding.

Kinetics and mechanism of hydrolysis of cis-benzimidazolechlorobis(ethylenediamine)cobalt(III) and cis-benzimidazolebromobis(ethylenediamine)cobalt(III) cations

Abstract: The kinetics of hydrolysis of cis-[CoX(bzmH)(en2)]2+(X = Cl or Br; bzmH = benzimidazole; en = ethylenediamine) cations have been investigated in perchlorate medium of I= 0.3 mol dm–3 and at 20–60 °C. In the range pH 6.8–8.5 and 20–40 °C the rate law for aquation takes the form –dln[CoIII]/dt=(k1, +k2KNH[H+]–1)/(1 +KNH[H+]–1) where k1 and k2 are the aquation rate constants of [CoX(bzmH)(en)2]2+ and [CoX(bzm)(en)2]+ respectively and KNH is the acid-dissociation constant of the co-ordinated benzimidazole. The pKNH of benzimidazole in [CoCl(bzmH)(en)2]2+ is 8.6 at 25 °C and I= 0.3 mol dm–3 from pH-titration and spectrophotometric measurements. Co-ordinated benzimidazole is 104 times stronger as an acid than free benzimidazole. The labilrzing action of benzimidazole on the Co–X bond is stronger than that of imidazole in the k1 path. This effect is, however, reversed in the k2 path [i.e. k2(im) > k2(bzm)]. The imido-base [CoX(bzm)(en)2]+ labilizes the Co–X bond ca. 700 times stronger than its conjugate-acid analogue.

Kinetics of aquation of Pentaammine(substituted salicylato)cobalt(III) complexes by ferric ion

Abstract: The aquation of pentaammine (substituted salicylato) cobalt(III) complexes [(NH3)5CoO2CC6H3(X)OH]2+,X = 5-SO3, 5-Br, 5-NO2, and 3-NO2 in the presence of ferric ion was studied spectrophotometrically in the 65°–80° range. Ferric ion catalyses the aquation of the substratesvia formation of a reactive binuclear species.

Kinetics of aquation of tris(5-nitro-1,10-phenanthroline)iron(II) in acetone–water and in t-butyl alcohol–water mixtures: endostatic analysis of activation parameters

Abstract: Rate constants and derived thermodynamic activation parameters are reported for the aquation of [Fe(5NO2-phen)3]2+ in acetone–water and in t-butyl alcohol–water mixtures. The data have been analysed to obtain kinetic activation parameters for reaction in corresponding mixtures where the ratio of activities of the two solvent components is constant, i.e. under endostatic conditions. A method is described for calculating endostatic activation parameters from kinetic data and molar thermodynamic excess functions for the binary mixture. The results of these calculations are discussed in the light of the known properties and structures of the solvent mixtures. The solvent dependence of the activation Gibbs function, ΔGα‡. calculated under endostatic conditions for the aquation of the iron complex, reflects changes in solvent structure more markedly than the conventional activation parameter ΔG‡ calculated directly from the rate constant using transition-state theory. This trend has been previously reported for the hydrolysis of 2-chloro-2-methylpropane, thereby indicating that the mechanisms of aquation for both reactants are similar, ie. dissociative.

Kinetics and mechanism of hydrolysis of cis-benzimidazolechlorobis(ethylenediamine)cobalt(iii) and cis-benzimidazolebromobis(ethylenediamine)cobalt(iii) cations

Abstract: The kinetics of hydrolysis of cis-[CoX(bzmH)(en2)]2+(X = Cl or Br; bzmH = benzimidazole; en = ethylenediamine) cations have been investigated in perchlorate medium of I= 0.3 mol dm–3 and at 20–60 °C. In the range pH 6.8–8.5 and 20–40 °C the rate law for aquation takes the form –dln[CoIII]/dt=(k1, +k2KNH[H+]–1)/(1 +KNH[H+]–1) where k1 and k2 are the aquation rate constants of [CoX(bzmH)(en)2]2+ and [CoX(bzm)(en)2]+ respectively and KNH is the acid-dissociation constant of the co-ordinated benzimidazole. The pKNH of benzimidazole in [CoCl(bzmH)(en)2]2+ is 8.6 at 25 °C and I= 0.3 mol dm–3 from pH-titration and spectrophotometric measurements. Co-ordinated benzimidazole is 104 times stronger as an acid than free benzimidazole. The labilrzing action of benzimidazole on the Co–X bond is stronger than that of imidazole in the k1 path. This effect is, however, reversed in the k2 path [i.e. k2(im) > k2(bzm)]. The imido-base [CoX(bzm)(en)2]+ labilizes the Co–X bond ca. 700 times stronger than its conjugate-acid analogue.