Aquation

About: Aquation is a research topic. Over the lifetime, 1443 publications have been published within this topic receiving 17507 citations.

Effect of Dipolar Aprotic Solvents on the Aquation of cis- and trans-Chloronitrobis(ethylenediamine)-cobalt(III)

Abstract: The kinetics of aquation of cis- and trans-[Co(en)2(NO2)Cl]+ were studied in aqueous mixtures of dipolar aprotic solvents over a range of temperatures.

Kinetics and mechanism of the base hydrolysis of cis-eq-[Cr(NCS)(S-pdtra)]−, trans-eq-[Cr(NCS)(edtrp)]− and trans-eq-[Cr(NCS)(R-pdtrp)]− complexes. Strong rate enhancement for NCS− ligand release with an increase of [OH−] only for the trans-equatorial isomers

Abstract: The [Cr(NCS)(edtrp)]−, [Cr(NCS)(R-pdtrp)]− and [Cr(NCS)(S-pdtra)]− complexes, that are derivatives of the trans-equatorial isomers of [Cr(edtrp)(H2O)]° and [Cr(R-pdtrp)(H2O)]° and the cis-equatorial isomer of [Cr(S-pdtra)-(H2O)]° (edtrp = ethylenediamine-N,N,N′-tripropionate, R-pdtrp = R-propane-1,2-diamine-N,N,N′-tripropionate, S-pdtra = S-propane-1,2-diamine-N,N,N′-triacetate) undergo aquation in alkaline media with a strong dependence of the rate on [OH−] for the trans-equatorial isomers and a very weak dependence for the cis-equatorial isomer. The thiocyanate ligand release follows a stereoretentive course for all reactants. Based on kinetic data the reaction mechanism has been discussed. Rate differences between the isomers are interpreted in terms of an interchange via a conjugate base (I c.b.) mechanism, assuming an equilibrium between the cis-equatorial-CrIII-S-pdtra complexes with penta- and tetradentate coordination of the edta-like ligand.

Kinetics of aquation and base hydrolysis of the macrocyclic complex trans-Bromo(N-meso-5,12-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene)nitro-cobalt(III) perchlorate

Abstract: The macrocyclic complex trans-[Co(dtcd)(NO2)Br] [ClO4] (dtcd = 5,12-dimethyl-l,4,8,1l-tetraaza-cyclotetradeca-4,ll-diene) has been prepared and its hydrolysis kinetics investigated. At 25oC and 0.1 M HN03 the aquation occurs with kaq = 6.2 x 10-3 s-1 to give the trans-Co(dtcd)(NO2)- (OH2)]2+ cation. The activation parameters at 298 K are ΔH? = 75.0 kJ mol-1 and ΔS? = -35.6 J K-1 mol-1. Hydrolysis of the bromide in the pH range 7.5-8.8 follows the rate expression kobs = kaq + kOH[OH-]. At 25oC (I = 0.1 M, NaClO4) kOH = 1.21 x 103 1. mol-1 s-1 with the activation parameters for base hydrolysis being ΔH? = 74.2 kJ mol-1 and ΔS? = +63.2 J K-1 mol-1 at 298 K. Aquation and base hydrolysis of the bromo complex at 25oC occur at rates 14 and 5 times faster respectively than those previously reported for the analogous trans-[Co(dtcd)(NO2)Cl]+ complex, the acceleration being due to a more favourable entropy of activation in each case.