Showing papers on "Aquation published in 1979"

Kinetische Untersuchungen von Aquotisierung und Halogenid-Anation an gemischten Hexahalogenoosmaten(IV)

Abstract: Fur 13 System vom Typ [OsL4IX]2− + H2O ⇄ [OsL4I(H2O)]− + X− (X = F, Cl, Br, I; L4 = aquatoriale Gruppe von 4 Liganden Cl und I) werden die Geschwindigkeitskonstanten der Aquotisierung bzw. Anation durch spektrophotometrische Messungen in wasrig sauren Losungen bestimmt. Bei Ersatz jedes Cl-Liganden durch I in L4 beobachtet man einen labilisierenden cis-Effekt von etwa 1 kcal/mol. Die trans-Lockerung an der Achse ClOsI betragt demgegenuber 5–6 kcal/mol. Fur die Austauschreaktionen wird ein assoziativer Mechanismus angenommen. Die thermodynamische Stabilitat der Monaquokomplexe ist bei den chloridreichen Verbindungen um etwa 1 kcal/mol, bei den iodidreichen bis zu 2 kcal/mol geringer als fur die entsprechenden Hexahalogenokomplexe. Kinetic Studies on Aquation and Halide Anation of Mixed Hexahalo Osmates(IV) Rate constants of 13 aquation resp. anation reactions of type [OsL4IX]2− + H2O ⇄ [OsL4I(H2O)]− + X− (X = F, Cl, Br, I; L4 = 4 ligands Cl and I in the equatorial plain) are determined spectrophotometrically in acidic aqueous solutions. The replacement of each Cl ligand by I in L4 gives a labilization of about 1 kcal/mol by cis-effect. Against this the trans-labilization on the axis ClOsI is 5–6 kcal/mol. For the exchange reactions an associative mechanism is assumed. The thermodynamic stability of the monaquo complexes compaired to the corresponding hexahalo complexes is less by 1 kcal/mol for the compounds containing many Cl and by 2 kcal/mol for those containing many I ligands.

Volumes of Activation for the Base Hydrolysis of [Rh(NH3)5X]2+ Complex Ions

Abstract: The pressure dependencies of the rates of base hydrolysis of [Rh(NH3)5X]2+ were measured at 313.2 K and μ1M, where X = Cl-, Br-, I- and NO3-, in the range 1-1500 bar. The respective Δν‡exp values are 19.3 ± 0.9, 20.2 ± 0.5, 20.4 ± 0.5 and 22.3 ± 0.9cm3 mol-1. The partial molar volumes of these complexes, as well as those of other relevant pentaamminerhodium(III) complexes, were also determined. The volume data are discussed in terms of the conventional dissociative conjugate base mechanism. The Δν‡exp for the aquation of [Rh(NH3)5NO3]2+ was found to be -6.9 ± 0.4cm3 mol-1 at 313.2K, [H+] 0.005M and μ0.1 M. An I mechanism is favoured for this process.

Effects of added potassium bromide and tetra-n-butylammonium bromide on the kinetics of aquation of tris(5-nitro-1,10-phenanthroline)iron(II) in various binary aqueous mixtures

Abstract: Rate constants are reported for the aquation of the title complex [Fe(5NO2-phen)3]2+ in a series of binary aqueous mixtures at 298.1 K as a function of the concentration of added KBr or [NBu4]Br. The co-solvents are acetone, dimethyl sulphoxide, acetonitrile, and t-butyl alcohol. In each system the first-order rate constant increases when [NBu4] Br is added but decreases when KBr is added. The results are used to show that salt effects on this reaction are determined to a large extent by the size of the ion, although certain changes in the pattern of kinetic data particularly for t-butyl alcohol mixtures show that hydration and solvation interactions play some part in determining the overall trend.

Kinetic and spectroscopic studies with a rapid-scanning spectrometer. Part 1. Transient intermediates in the dissociation of nickel(II) polyamine complexes

Abstract: Successive stages in the acid-catalysed aquation of several polyamine chelates of NiII have been characterised both optically and kinetically by means of a rapid-scanning spectrometer. Complete spectra of several new transient intermediates are reported and assigned. When two terdentate ligands, viz. diethylenetriamine (dien), are involved it is established that one is completely removed in two stages before the second starts to disengage. The stepwise acid dissociation of the [Ni(trien)(OH2)2]2+ ion (trien = triethylenetetramine) is shown to be much more complex than had previously been indicated.

Amino-acid complexes of cobalt(III). Preparation and hydrolysis reactions of trans-bis(1,2-diaminoethane)(amino-carboxylato)halogeno-cobalt(III) complexes containing the carboxylato-bonded amino-acids glycine, DL-alanine, and DL-aminobutyric acid

Abstract: A series of complexes of the type trans-[Co(en)2X{–O2C–CH(R)–NH3+}][ClO4]2(X = Cl– or Br–), containing the monodentate carboxylato-bonded amino-acids, glycine (R = H), DL-alanine (R = Me), and DL-aminobutyric acid (R = Et) have been prepared and characterised. All the complexes behave as monobasic acids and pKa values for the equilibrium (1) have been determined potentiometrically at 25 ± 0.1 °C. The kinetics and steric course of trans-[Co(en)2X{–O2C–CH(R)–NH3+}]2+ [graphic omitted] trans-[Co(en)2X{–O2C–CH(R)–NH2}]++ H+(1) base hydrolysis (X– displacement) of the species trans-[Co(en)2X{–O2C–CH(R)–NH2}]+ have been examined. Values of ΔH‡(298.15) lie between 92.9 and 96.6 kJ mol–1 for all the complexes studied. Values of ΔS‡(298.15) for the chloro-complexes lie in the region 76–87 J K–1 mol–1 and for the bromo-complexes in the region 92–101 J K–1 mol–1. Base hydrolysis of the DL-alanine and DL-aminobutyric complexes give 65 ± 5%trans- and 35 ± 5%cis-[Co(en)2OH{–O2C–CH(R)–NH2}]+. The products of base hydrolysis of the glycine complexes contain in addition minor quantities of the N-bonded complex [Co(en)2OH(NH2CH2CO2–)]+. The kinetics and steric course of the Hg (II)-assisted aquation of the complexes trans-[Co(en)2X{–O2C–CH(R)–NH3+}]2+ have also been studied. For the chloro-complexes ΔH‡(298.15) values of 80.9–82.2 kJ mol–1 and ΔS‡(298.15) values of 0.96–4.8 J K–1 mol–1 have been obtained, while for the bromo-complexes ΔH‡(298.15) values lie in the range 74.6–75.4 kJ mol–1 with ΔS‡(298.15) values in the range 28–35 J K–1 mol–1. The products of this reaction are 85 ± 5%cis-, 15 ± 5%trans-[Co(en)2OH2{–O2C–CH(R)–NH3+}]3+.

Die Quecksilber(II)-Ionen induzierte Hydrolyse gemischter Hexahalogenoosmate(IV)†

Abstract: Die besonders starke hydrolytische Wirksamkeit der Hg2+-Ionen gegenuber den Komplexen [OsXnI6−n]2−, X = Cl oder Br; n = 1 – 5, beruht auf dem elektrophilen Angriff an den I-Liganden. Durch kleine Mengen Hg2+ wird nur ein I abgespalten. Es bilden sich sehr stabiles [HgI]+ bzw. [HgI2] und die entsprechenden Pentahalogenomonaquoosmate(IV). Cis-[OsCl4I2]2− und fac-[OsCl3I3]2− lagern sich wahrend der Hydrolyse so um, das die thermodynamisch begunstigte Achse IOsH2O entsteht. Andere ein- oder zweiwertige Kationen zeigen bei der Aquotisierung nur eine geringe katalytische Wirkung, die mit der Ionengrose von Mg2+ zu Ba2+ zunimmt. Mercury(II)-Induced Hydrolysis of Mixed Hexahalo-Osmates(IV) The strong hydrolytic activity of Hg2+ ions on complexes [OsXnI6−n]2−, X = Cl or Br; n = 1 – 5, is due to electrophilic attack at the I ligands. Small amounts of Hg2+ remove only one I. The very stable [HgI]+ and [HgI2] are formed along with the corresponding pentahalo-monaquo-osmates(IV). In cis-[OsCl4I2]2− and fac-[OsCl3I3]2− ligands rearrange during hydrolysis giving the thermodynamically favoured IOsH2O axis. Other mono- and bivalent cations have only a slight catalytic effect on the aquation, increasing with the size from Mg2+ to Ba2+.

Kinetics of solvolysis and of formation of tetrachloroplatinate(II) in alcohol: Water mixtures

Abstract: Rate constants are reported for the reaction of [PtCl4]2− with hydrochloric-perchloric acid mixtures, in aqueous methanol and aqueous t-butanol at 308.2 K. The observed first-order rate constants are, from their dependence on chloride concentration, divisible into forward and reverse rate constants for the equilibrium: [PtCl14]2−+H2O⇌[PtCl3(OH2)]−+Cl−. The solvent dependence of aquation rates for [PtCl4]2− is compared with those for other chlorotransition metal complexes, and discussed in terms of the Grunwald-Winstein method of mechanism diagnosis in organic systems. The solvent dependence of rates of [PtCl4]2− formation is compared with the rates of formation of other metal complexes; differences between this platinum reaction and, for example, nickel(II) formation, are rationalised in terms of the reactant charge product difference and consequent solvent permittivity effects on rate trends.

Kinetics of substitution reactions of transition metal complexes in 1,3-dioxolan-2-one + water and 4-methyl-1,3-dioxolan-2-one + water solvent mixtures

Abstract: Rate constants are reported and discussed for several substitutions of inorganic complexes in ethylene carbonate (1,3-dioxolan-2-one) + water and in propylene carbonate (4-methyl-1,3-dioxolan-2-one) + water solvent mixtures. The reactions include aquation ofcis- and oftrans-[Co(en)2Cl2]+, aquation oftrans-[Cr(OH2)4Cl2]+, bromide substitution at [Pd(Et4dien)Cl]+, thiourea substitution atcis-[Pt(4-NCpy)2Cl2], and aquation and cyanide attack at [Fe(X-phen)3]2+ cations.

The Halomercury(II)-assisted Aquation of the Bromopenta-cyanocobaltate(III) Anions

Abstract: The aquation of the bromopentacyanocobaltate(III) ion was carried out in the presence of several kinds of hard acids or halomercury(II) complexes. The hard acids(H+, Na+, and Mg2+) had small effects, while the addition of mercury(II) halides significantly accelerated the aquation. The effect of mercury(II) halides was attributed to the monohalomercury(II) cations, which were formed in a small amount by the dissociation of the dihalomercury(II) complexes. The effect of the dihalomercury(II) complexes was also studied in the presence of an excess of sodium halide. The rate constant for halomercury(II)-assisted aquation was expressed by:kobsd=k0+k1[HgX+]+k2[HgX2], X−=Cl−,Br−.The values of k1 and k2 obtained (k1=1.6×104 mol−1 dm3 s−1, k2=1.0 mol−1 dm3 s−1, for X−=Cl−; k1=2.0×104 mol−1 dm3 s−1, k2=1.6×10−1 mol−1 dm3 s−1, for X−=Br−) were compared with the stability constants for the mercury(II) complexes formed by the combination with Br−.

Solvent-interchange reactions of the penta-amminecobalt(III) ions [Co(NH3)5(OH2)]3+ and [Co(NH3)5(dmf)]3+ in dimethylformamide (dmf)–water media

Abstract: The rate law for aquation of [Co(NH3)5(dmf)][ClO4]3 is first order with respect to the concentration of the cobalt(III) complex and independent of aluminium(III) or perchloric acid concentration, contrary to a previous report. Tracer experiments have shown more than 95% cobalt(III)–oxygen bond fission, and chromatographic analyses for the formato-complex indicated less than 1% carbon–nitrogen bond fission. It is concluded that aquation proceeds by water molecules replacing intact dimethylformamide (dmf) molecules. Solvent interchange between the aqua- and dimethylformamide complexes has been studied in dmf–water mixtures at 25, 45, and 65 °C. The activation enthalpy for aquation of the dmf complex is independent of the composition of the solvation shell of the complex. The dependence of rate and equilibrium constants on dmf concentration is interpreted in terms of a free dmf-co-ordinated dmf interaction at small dmf contents which decreased the aquation rate constants at a more rapid rate at small dmf contents than at larger dmf contents at all temperatures. This same interaction increased the equilibrium concentration of the dmf complex more rapidly at small dmf than at larger dmf contents at 65 and probably at 45 °C also. Other explanations for preferential solvation of the complexes are considered and rejected. The rate law for aquation is Raq=Kaq′[Co(NH3)5(dmf)3+]xH2O. The activation parameters for kaq′ are satisfactorily constant over the range 0–0.7 mol fraction dmf, viz.ΔH‡= 105 ± 2 kJ mol–1 and ΔS‡=–3 ± 7 J K–1 mol–1. The rate law for ligation is expressed as Rlig=klig′[Co(NH3)5(OH2)3+]xdmf. The activation parameters for klig′ are not constant; ΔH‡lig and ΔS‡lig both decrease with increasing dmf content (xdmf).