Aquation

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

Supramolecular adducts between the hexacyanocobaltate(III) anion and poly(ethyleneimines): influence on the photoaquation efficiency of the complex

Abstract: Addition of open-chain branched poly(ethyleneimines) (PEIs) to aqueous solutions of Co(CN) 6 3- causes a decrease of the quantum yield for the photoaquation reaction of the complex. This quenching effect is analogous to that caused by cyclic poly(ethyleneimines), and it is attributed to the formation of adducts between the complex ion and the polymer, in which some CN - ligands are hydrogen-bound to protonated N atoms of the PEI and thus are prevented from definitely leaving the first coordination sphere of the metal ion

Kinetic, solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Abstract: Complexes of FeII with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H2O and in MeOH–H2O mixtures. Kinetics of acid catalysed aquation of FeII–monoxime complexes follow a rate law with kobs = k2[H+] + k3[H+]2, while kinetics of acid dissociation and base hydrolysis of the FeII–dioxime complex follow rate laws with kobs = k2[H+] and kobs = k2[OH−]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of FeII–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace FeII in acidic and neutral media, in water and in aqueous alcohols.

Kinetics and Mechanism of Ligand Substitution in Some Chromium(III) Tetraaza Macrocyclic Complexes in Acidic Media: Differences in Reactivity Between cis and trans Isomers

Abstract: Thiocyanate anation of the macrocyclic complexes cis-[Cr(cycb)(OH2)2]3+ and trans-[Cr(cyca)(OH2)2]3+ (cycb and cyca are rac- and meso-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, respectively), and mercury(II)-induced aquation of the product thiocyanato-N complexes, has been studied in acidic solution. The rate retardation with an increase of the acid concentration for both types of reactions follows the rate expression kobs = (k1 + k2Ka/[H+(aq)])/(1 + Ka/[H+(aq)]), corresponding to parallel reaction paths through aqua and hydroxo complexes. Some general trends in the differences in reactivity between the two geometrical isomers have been observed and are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Thermo- and photoaquation of trans dicyanobis(1,3-diaminopropane)chromium(1+) perchlorate. Quenching of photochemistry by photoproducts

Abstract: The compound trans-[Cr(tn) 2 (CN) 2 ]ClO 4 , where tn=1,3-diaminopropane, has been prepared and characterized. It undergoes an acid-catalyzed thermal aquation of the cyanide ligand to yield trans-Cr(tn) 2 (H 2 O)(CN) 2+ with a pseudo-first-order rate ccmstant of 8×10 -6 s -1 at 5×10 -4 H + and 15 o C

Phosphato complexes of cobalt(III). IV. Hydrolysis in basic solution

Abstract: The rates of hydrolysis of phosphato complexes of cobalt(111) in sodium hydroxide concentrations ranging from 0.02M to 0.37M, and at several ionic strengths, have been measured with a tracer technique. Bidentate phosphato complexes exhibit the same rates of hydrolysis as the corresponding monodentate complexes, due to a rapid conversion of the bidentate into the monodentate form. The general rate law for base hydrolysis of all the phosphato complexes is: d[PO34]/dt = {kH2O + kOH[OH-]}[complex] At 60o and at unit ionic strength, the rate constants for the complexes cis-[Co(NH3)4OH.PO4]-, cis-[Co en2OH.PO4]-, and [Co(NH3)5PO4] respectively are: 103kH2O (min-l) 85.0, 2.0, <1; and 103kOH (1. mole-1 min-l) 42.7, 12.0, 69.5. Mechanistic conclusions have been based on the measured enthalpies and entropies of activation and deuterium solvent isotope effects. For all complexes, kH2O is identified with an aquation mechanism involving synchronous interchange of the phosphate and solvent water between the first and second coordination spheres of the complexes. In the case of the tetrammine and bis(ethylenediamine) complexes, kOH is identified with a process involving synchronous interchange of phosphate and hydroxide ion between the first and second coordination spheres of the complexes. In the case of the pentammine complex, an SN2CB mechanism is considered to be more probable. A comparison with the base hydrolysis of halogen complexes of cobalt(111) is presented.