Aquation

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

Kinetics and mechanisms of substitution of aqua-ligands in cis -diaqua- bis (bipyridyl)ruthenium(ll) ion by L-cysteine in aqueous medium

Abstract: The title reaction has been studied spectrophotometrically and a rate-law established within the pH range 5.0 to 6.5, $$ {⤪ [Ru(bipy)_{2}(cys)_{2}]/dt={k_{1}k_{2}[Ru(bipy)_{2}(H_{2}O)_{2}^{2+}][cysH]⩈er k_{-1}+k_{2}[cysH]}} $$ (where k1 is the water dissociation rate constant of the substrate complex, k−1 is the aquation and k2 is the ligand capturing rate constant of the penta co-ordinate intermediate [Ru(bipy)2(H2O)]2+). The reaction rate was found to be pH-dependent. Activation parameters have been calculated and compared with other anionic ligands such as $ {⤪ N}_{3}^{−} $, SCN− and neutral ligands e.g. o-phen-anthroline, 2,2′-bipyridine etc. A mechanism involving dissociative interchange is proposed.

Kinetik und Mechanismus der Substitutionsreaktionen von Komplexverbindungen, 47. Mitt.: Aquationskinetik descis-[Co(en)2Cl (m-Toluidin)]2+ in sauren Lösungen

Abstract: The complex salt [Co(en)2Cl(m-toluidine)](NO3)2 has been synthesized and itscis configuration has been proved on the basis of i.r. spectra. The aquation kinetics of the complex ion has been studied at 4 temperatures in the presence of various amounts of perchloric acid. Experimental data are explained by assuming the following reaction scheme: the amino complex (I) is in equilibrium with its conjugated base, i.e. with the amido-complex (II). The equilibrium constant seems to be of the order of magnitude of 10−3. Both forms of the complex ion participate to aquation reactions. For the amino-form an activation energy of ΔH=25.6 kcal/mole and for the amido-form ΔH=20.4 kcal/mole have been found. These data are compared to the kinetic parameters of the aquation reaction of analogous complexes, and they are discussed, by presuming a dissociation mechanism.

Chromium(III) Complexes with 1,5,9-Triazanonane (3,3-tri) - CrX3(3,3-tri)n+ and CrCl(diamine)(3,3-tri)2+.

Abstract: The reaction of CrCl3 · 6H2O (dehydrated in DMSO) with 1,5,9-triazanonane (3,3-tri) gives mer- CrCl3(3,3-tri), the configuration being established by isomorphism with the corresponding Co(III) complex. This non-electrolyte is hydrolyzed in aqueous acidic solution and mer-[CrCl2(3,3-tri)- (OH2)]ClO4 can be isolated by anation with HCl in the presence of HClO4. Reaction of mer-CrCl3- (3,3-tri) in DMF with diamines produces complexes of the type [CrCl(diamine)(3,3-tri)] Cl2 [diamine= 1,2-diaminoethane (en), 1.2-diaminopropane (pn), 1,3-diaminopropane (tn), 2,2-dimethyl-1,3-diaminopropane (Me2tn) and cyclohexanediamine (chxn, cis plus trans mixture; two isomers A and B)] and these have been characterized as the ZnCl42− salts. The configuration of the triamine ligand in these complexes has been established as mer-(H↓)- by a single crystal X-ray analysis of [CrCl(en)(3,3-tri)]- ZnCl4, monoclinic, P21, a=7.932, b= 14.711, c= 8.312 A, β=104.6° and Z=2, refined to a conventional R factor of 0.034. The kinetics of the Hg2+- assisted chloride release from [CrCl(diamine)(3,3- tri)]ZnCl4 salts were measured spectrophotometrically (μ=1.0 M HClO4 or HNO3) over 15 K temperature ranges to give, in order, 104kHg (298.2 K) (M−1 s−1), Ea(kJ mol−1), ΔS# (J K−1 mol−1): en- (HClO4): 5.95, 78.1, -53; pn(HClO4); 5.24, 81.2; -44; tn(HClO4): 26.7, 85.6, -15; Me2tn(HClO4): 21.8, 78.6, -40; A-chxn(HNO3): 7.60, 81.0,-41; B-chxn(HNO3): 18.3, 56.8, -115. A ‘non-replaced ligand effect’ on the rate is observed for the first time in this series of homologous Cr(III) complexes. The kinetics of the thermal aquation (kH, 0.1 M HClO4) were measured titrimetrically for CrCl(diamine) (3,3-tri)2+ to give the following kinetic parameters: diamine=en: 107 kH (298.2)=5.34 s−1, Ea=99.2 kJ mol−1, ΔS#=-40 J K−1 mol-1; diamine =tn: 107 kH (298.2)=5.04 s−1, Ea= 82.8, ΔS#= -96.

Formation and kinetics of decomposition of monoaquobis(ethylenediamine)(pyridylmethyl)chromium(III) complexes

Abstract: Monoaquobis(ethylenediamine)(pyridylmethyl)chromium(III) complexes, 2-NC5H4CH2Cr(en)2(H2O)2+ and 3-NC5H4CH2Cr(en)2(H2O)2+, are prepared by the reduction of the corresponding picolyl chlorides by the CrII(en)22+ ion. The decomposition of these ions is studied in 0·01–1·0M-perchloric acid and in acetate buffers of pH 1–7. Spectral changes show that these complexes undergo aquation before carbon–chromium bond cleavage. Product studies as well as kinetic data and activation parameters obtained indicate that the 2- and 3-ions decompose via the penta-aquo-derivative, 2-NC5H4CH2Cr(H2O)52+, and the trisaquo-derivative, 3-NC5H4CH2Cr(en)(H2O)32+ respectively. Acetate-ion catalysis is also observed for the decomposition of these ions.

The solvolytic aquation and base hydrolysis of cis- and trans-fluorohydroxobis(ethylenediamine)cobalt(III) cations

Abstract: The first-order rate constants for the solvolytic aquation of cis- and trans-fluorohydroxobis(ethylenediamine)-cobalt(III) cations have been determined over a range of temperatures and the Arrhenius parameters calculated. The product isomerises immediately to an equilibrium mixture, so that it is not possible to determine its initial configuration. The kinetics for the replacement, by hydroxide ion, of co-ordinated fluorine in these cations have been studied and the Arrhenius parameters calculated. Here, unlike the case of solvolytic aquations, isomerisation is negligible under the experimental conditions and the stereochemical consequences of the reaction can be determined spectrophotometrically. Both the cis and the trans isomer of the reactant yield approximately 90%cis and 10%trans products directly.