Aquation

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

Substitution of coordinated chlorides in cis-α and cis-β dichloro (triethylene tetramine) cobalt(III) chloride [Co(trien)Cl2]Cl by thiocyanate in aqueous medium

Abstract: Substitution of coordinated chlorides in cis-α, and cis-β dichloro (triethylene tetramine) cobalt(III) chloride by thiocyanate was studied in aqueous medium in the pH range 3.8 to 4.0 at 25–26° C. Substitution, as in aquation, took place in two steps corresponding to the two chlorides, one step being faster than the other. Mechanisms have been discussed in the paper.

Effect of Triton‐X‐100 Solvent in the Micellar Catalysis of the Aquation of Tris(2‐nitroso‐1‐naphtholate) Ferrate (II)

Abstract: The effect of triton‐X‐100 micelles on the aquation of Fe(C10H6N2O)3 2+ has been investigated with triton‐X‐100 as solvent. In liquid triton‐X‐100, over a range of [H2O] T (0.0–3 M), significant rate enhancement factors of 50–150 are observe. Acid inhibits the rate of aquation at fixed [H2O] T . A mechanism based on effective solvent participation in a chemical environment similar to that in reversed micelles is proposed in liquid triton‐X‐100 with dispersed water pockets. This mechanism predicts direct H2O substitution into the coordination sphere of Fe(C10H6N2O)3 2+ in the highly polar water pockets or cavities where the Fe (II) complex molecules are solubilized. Changes in the tumbling rate, structure, and activity of water are suggested to account for the observed changes in the rate of aquation as a function OH [H2O] T . All k ψ–[H2O] T profiles are structured and exhibit maxima with k ψ(max) shifted to progressively higher [H2O] T as the fixed concentration [H+] T is increased.

Quantitative Estimates of Steric Effects: Intramolecular Strain Energy Effects on the Activation Energy for Aquation of Some trans-Dichlorotetraaminecobalt(III) Complexes

Abstract: In an effort to quantitatively estimate steric contributions to the aquation rates of a series of structurally related cobalt(III) tetraamine complexes, strain energy minimization calculations have been performed on the reactant and some plausible transition state structures. Free energies of activation Δ G * obs , are factored as: Δ G * obs , = Δ G * bb + Δ G * strain + Δ G * CF + Δ G * solvation + … where Δ G * bb is the free energy change associated with bond breaking, Δ G * solvation is the solvation free energy difference between the reactant and a proposed transition stare, Δ G * CF is the difference in crystal field stabilization between the reactant and a proposed transition state, and Δ G * strain is the strain energy difference between the reactant complex and a proposed transition state. The activation energy for the aquation of a hypothetical ‘strain free’ complex is defined as Δ G * int and reflects the energy required for the bond breaking step with all other terms. For the cations trans -( RR,SS )-dichloro-1,8- diamino-3,6-diazaoctanecobalt(III)( trans [Co(2,2,2- tet)Cl 2 ] + ), trans -(RR,SS)- or trans -( RS )-dichloro-1.9- diamino-3,7-diazanonanecobalt(III)(trans [Co(2,3,2- tet)Cl 2 ] + and trans -( RS )-dichloro-1,10-diamino-4,7- diazadecanecobalt(III)( trans [Co(3,2,3-tet)Cl 2 ] + ) Δ G * int is found to be a constant 123 kJ/mol. For the trans -dichlorocobalt(III) complexes with the ligands 1,4,7,10-tetraazacyclotridecane([13]-ane-N 4 ), 1,4,8, 11-tetraazacyclotetradecane([14]-ane-N 4 ), 1,4,8,12- tetraazacyclopentadecane([15]-ane-N 4 ) and 1,5,9,13- tetraazacyclohexadecane([16]-ane-N 4 ), Δ G * int lies in the range 133–139 kJ/mol.

Secondary deuterium kinetic isotope effect for aquation, solvolysis, and isomerization reactions of trans-[Co(en)2(OSMe2)N3]2+, and the resolution of a mechanistic anomaly.

Abstract: The two closely spaced NH signals in the 1H NMR spectrum of trans-[Co(en)2(OSMe2)(N3)]2+ have been reassigned using 2D NMR and other techniques. Thus, the unusual syn to anti (to Co−N3) NH rearrangement on base catalyzed substitution of the selectively deuterated complex in ND3(l) has been reinterpreted as “normal”, with inversion of the effective deprotonation site accompanying the act of substitution. The re-examination of this system required a repeat study of the secondary isotope effect for the acid hydrolysis reaction, previously used to assign syn and anti amine sites, and this has been extended to other solvents (Me2SO, MeCN). The relative NH proton exchange rates are also reconsidered. A systematic rate reduction for Me2SO substitution is observed for deuterium incorporation into the cis-NH centers, irrespective of whether these are syn or anti, and the effect is much greater in Me2SO than in water. The results are interpreted in terms of zero point energy effects and coupled vibrations.