Showing papers on "Aquation published in 1972"

Mechanistic Information on the Aquations of Complexes of the Pentaamminecobalt(III) Series from Kinetic Studies at High Pressures

Abstract: The logarithm of the pseudo-first-order rate coefficient k for the aquation of Co(NH3)5X(3–n)+ can be represented by a quadratic equation in the pressure P, or, better, bywhere P is in kbar, is the...

Steric course and kinetics of aquation of some haloaquotetraamminechromium(III) complexes

Abstract: The aquation stoioheiometry of cis. and trans-Cr(NH3),(OH2)Br2+ and cis- and trans-Cr(NH3)4(OH2)I2+ ions when either spontaneous, Hg2+ promoted, or carried out via the hydroxo forms generated in basic solution has been examined. The two latter treatments have been conducted on cis-Cr(NH3)4(OH2)C12+ ion. Spectrophotometric methods show all lose halide with retention of configuration. The rates of aquation in acid media of the Cr(NH3)4(OH2)Br2+ and Cr(NH3),(OH2)I2+ ions have been investigated and comparisons are made with related tetraammine and bis(ethylenediamine) oomplexes. Evidence has accumulated to show almost complete stereoretentivity in the aquation reactions of chromium(111) amine complexes.

Kinetics of the cis-dichlorodiammineplatinum(ii)-oxalate reaction in aqueous solution

Abstract: The substitution of the chloride ligands in cis-Pt(NH3)2Cl2 by oxalate has been studied in neutral and slightly acidic aqueous solutions. At 50°, the reaction is first-order with respect to complex concentration. The estimated first-order rate constant (3.9 × 10−4sec−1 at 50°) and the activation energy (17 kcals/mole) are similar to the corresponding values reported for the aquation of the complex ion. The reaction rate is only slightly pH dependent in the pH range 3–7 indicating that C2O4 −2 and HC2O4 − have similar reactivities. The rate of the reaction is inhibited by the presence of excess free chloride. These data have been interpreted in terms of a mechanism involving the rate-determining aquation of the complex. By comparison with previous studies in which amine molecules were employed as substituting groups oxalate is a very weak nucleophile. It is suggested that the known biological activity of dichloro complexes of platinum(II) involves reaction at nitrogen-containing rather than oxygen...

Optically active co-ordination compounds. Part XXX. Mono-dipeptide complexes of cobalt(III)

Abstract: Chloride and perchlorate salts of the cations [Co(NH3)3(α1α2)]+ and [Co(dien)(α1α2)]+, where α1α2H2 is a dipeptide, and dien = diethylenetriamine, have been prepared and characterised. A general structure for these complexes is proposed, in which the dipeptide ligand is terdentate and planar, having lost the amide proton. The protonation of [Co(dien)(glygly)]+ and [Co(NH3)3(glygly)]+ has been studied in detail by electronic absorption and 1H n.m.r. spectroscopy; complexes in which the oxygen atom of the amide group is protonated have been isolated from solutions in concentrated perchloric acid. In hot concentrated hydrochloric or hydrobromic acid [Co(NH3)3(glygly)] ClO4 gives crystalline [Co(NH3)3(glyglyH2)X]X2(X = halide) containing a bidentate peptide ligand. Concentrated aqueous solutions of this product deposit crystalline [Co(NH3)3(glyglyH)X]X, in which the peptide remains bidentate. Dilute aqueous solutions of [Co(NH3)3(glyglyH2)Cl] Cl2 undergo aquation as well as deprotonation; on the addition of base ring closure occurs to give [Co(NH3)3(glygly)]+. [Co(NH3)3(glygly)]-ClO4 can be recovered from dilute aqueous solutions of [Co(NH3)3(glyglyH2)Cl]Cl2 after ageing and addition of sodium perchlorate. The disproportionation of [Co(dien)(α1α2)]+ and [Co(NH3)3(α1α2)]+ in alkaline solution and the base-catalysed exchange at the methylene group of the C-terminal amino-acid are reported, together with some preliminary observations on the activation of the peptide towards condensation with aldehydes at the C-terminal residue.

Single-crystal Raman study of some aquo-pentachloro-salts [MCl5-(H2O)]2–(M = In or Fe)

Abstract: Raman single-crystal spectra are reported for eight hydrates and deuteriates [MCl5(H2O)]2–(M = In or Fe). Many fewer lattice modes were found than predicted, but for the anion internal modes factor-group predictions accord well with observation. A complete assignment in terms of anion C4v symmetry is deduced. Deuteriation enabled identification of all skeletal modes associated with oxygen-atom motions. The most unusual feature of the assignments is that π(MCl4) modes come above δ(MCl4) modes. Comparison with single-crystal assignments for [InCl5]2– show that the largest change is in the A1π(InCl4) mode which is raised upon aquation of the complex.

Influence of electrolyte dissociation upon rates of reactions. Part VII. Effects of sulphate and some dicarboxylate media upon rates of aquation of halogenopenta-amminecobalt(II) complexes and the rate of base hydrolysis of the acetatopenta-amminecobalt(II) complex

Abstract: Accelarations to the rates of aquation of chloropenta-amminecobalt(III)(at 35 °C) and bromopenta-amminecobalt-(III)(at 25 °C) complexes caused by some ion-pairing dicarboxylates and sulphate have been studied by spectrophotometry. Similar work with iodopenta-amminecobalt(III) has been carried out at 25 °C by means of 125I release. The results are analysed in terms of ion-pair rate constants of aquation. The ratios of these rate constants to those of the free cobalt(III) ions are in the range 2—3·1 : 1, being mainly independent of the halide component and only slightly related to the ion-pair dissociation constants. The rate of base hydrolysis of the acetatopenta-ammine-cobalt(III) complex at 25 °C, obtained by following the rate of release of [1-14C]acetate, is retarded in dicarboxylate and sulphate media. There is a distinct proportionality between corresponding ion-pair rate and dissociation constants. The latter have been calculated from e.m.f. measurements on a glass electrode–calomel electrode cell (for dicarboxylate media) and from solubility measurements (for sulphate media).

Octahedral cobalt(III) complexes of the chloropentammine type. XXVII. Effects of Methyl Substituents on reactivities of the cis-chloro-n-propylaminebis(ethylenediamine)-cobalt(III) cation

Abstract: Salts of one isomeric form of the chloro-n-butylamine-, chloro-iso-butyl-amine- and chloro-sec-butylamine-bis(ethylenediamine)cobalt(III) cations have been prepared and characterised to have a cis-configuration (IR and VIS spectroscopy). Rate constants for their spontaneous aquation, mercury(II)-induced aquation and base hydrolysis have been determined and the activation parameters calculated. The results are compared with data obtained for the n-propylamine complex with a view to investigate the effects of methyl (α, β, γ) substituents on reactivities. The rate-determining dissociation of the outgoing group (Cl− or HgCl+) takes place via either a square-pyramidal or a trigonal-bipyramidal intermediate, depending on whether the activation entropy is negative or positive. Salze einer isomeren Form des Chloro-n-butylamin-, Chloro-iso-butylamin- und Chloro-sec-butylamin-bis(atylendiamin)-kobalt(III)-Kations wurden dargestellt und spektroskopisch als Komplexe mit cis-Konfiguration charakterisiert. Die Geschwindigkeitskonstanten des spontanen bzw. durch HgII induzierten Ligandenaustausches mit H2O und des hydrolytischen OH-Eintausches wurden bestimmt und die Aktivierungsparameter berechnet. Die Ergebnisse werden mit den an den n-Propylaminkomplexen erhaltenen verglichen, besonders in Hinsicht auf den Einflus der (α, β, γ) Methylgruppen auf die Reaktivitaten. Die geschwindigkeitsbestimmende Abdissoziation von Cl-oder HgCl+ verlauft entweder uber einen quadratisch-pyramidalen oder einen trigonal-bi-pyramidalen Zwischenzustand, je nachdem, ob die Aktivierungsentropie negativ oder positiv ist.

Structural and mechanistic studies of co-ordination compounds. Part V. The preparation, aquation, and base hydrolysis of octahedral cobalt(III)–amine complexes containing isothiocyanate as an orienting ligand

Abstract: The prepration and characterization of trans-[Co(NH3)4(NCS)Cl]+ cation is described The kinetics of the aquation and base hydrolysis of this complex cation and those of trans-[Co(cyclam)(NCS)Cl]+ have been studied over a range of temperature These results are discussed in terms of the influence of nephelaxetic effects of these amine ligands on the central cobalt(III) ion

The vanadium(II) reduction of tris(2,2′-bipyridine)cobalt(III) and the dissociation of the tris(2,2′-bipyridine)cobalt(II) product

Abstract: The rate law for the vanadium(II) reduction of Co(bipy)33+(bipy = 2,2′-bipyridine), is independent of hydrogen-ion concentration and of the form, rate =k[V2+][Co(bipy)33+]. At 25 °C and µ= 2·0M(LiClO4), k= 1110 l mol–1 s–1ΔH‡= 3·6 ± 0·1 kcal mol–1, and ΔS‡=–32·6 ± 0·4 e.u. The reaction is of the outer-sphere type. The subsequent dissociation (by aquation) of the product Co(bipy)32+ has also been studied and the mechanism is discussed. At 25° the rate constant k1 for cleavage of the first chelate ring is 36·0 s–1, ΔH‡1= 12·4 ± 0·4 kcal mol–1, and ΔS‡1=–10·0 ± 1·6 e.u., µ= 2·0M(LiClO4). Activation parameters are compared with those for the corresponding dissociations of Fe(bipy)32+ and Ni(bipy)32+.

Aquation of tris-(1,10-phenanthroline) iron(II) in acid solution. A kinetics experiment

Abstract: The aquation of tris-(1,10-phenanthroline) iron(II) in acid solution is a reaction for which reliable kinetic data are available and it has an easily measured rate at accessible temperatures

Structural and mechanistic studies of co-ordination compounds. Part IV. The preparation, aquation, and base hydrolysis of trans-chloronitro- and trans-bromonitro-(1,4,8,11-tetra-azacyclotetradecane)cobalt-(III) cations

Abstract: The preparation and characterization of trans-[Co(cyclam)NO2Br]+ cation is described. The kinetics of the aquation and base hydrolysis of this complex cation and those of the base hydrolysis of trans-[Co(cyclam)NO2Cl]+ have been studied over a range of temperature. The first-order aquation rate constants are slower than those of the corresponding bis(ethylenediamine) and tetra-ammine analogues, whereas the second-order base hydrolysis rate constants are faster. These results support the earlier prediction made on the basis of the kinetic nephelauxetic effect of these amine ligands on the central cobalt(III) ion. Unimolecular mechanisms are assigned to these reactions.