Showing papers on "Aquation published in 1983"

Photochemical, photophysical, and thermal behavior of the tris(1,10-phenanthroline)chromium(III) ion in aqueous solution

Abstract: The rate constant of the thermal aquation of chromium complex (Cr(phen)/sub 3//sup 3 +/(phen = 1,10-phenanthroline)) has been determined as a function of pH and temperature; the quantum yield of the photoaquation has been evaluated as a function of excitation wavelength, as a function of pH in the presence of excited-state quenchers iodide, oxygen (I/sup -/, O/sub 2/), and as a function of substrate concentration. The luminescence lifetime and intensity from the /sup 2/T/sub 1///sup 2/E excited states have been measured as a function of pH, (O/sub 2/), (I/sup -/), and (Cr(phen)/sub 3//sup 3 +/). The absorption spectrum of the /sup 2/T/sub 1///sup 2/E excited states has been obtained; the decay of the absorption has been monitored as a function of temperature and solution medium. The thermal, photochemical, and photophysical behavior of Cr(phen)/sub 3//sup 3 +/ in aqueous solution is very similar to that exhibited by Cr(bpy)/sub 3//sup 3 +/ (bpy = 2,2'-bipyridine) and is interpreted in terms of analogous mechanistic steps. It is believed that excitation into spin-allowed states yields /sup 4/T/sub 2/, which undergoes very efficient intersystem crossing to /sup 2/T/sub 1///sup 2/E: these latter states can depopulate via nonradiative decay (including ground-state quenching) or interact with H/submore » 2/O and hydroxyl radicals (OH/sup -/) to yield a Cr(phen)/sub 3/(H/sub 2/O)/sup 3 +/ intermediate, which is the direct precursor of the aquation products. Back intersystem crossing is not regarded as an important process. The thermal aquation of the ground state is visualized as occurring via the same intermediate. The relationship of the results reported here to photoracemization and thermal racemization observatons in the literature is made. 11 figures.« less

Reduction potentials of pentaammine complexes of cobalt(III), rhodium(III) and iridium(III): physical correlations

Abstract: The reduction potentials of a large range of [M(NH3)5L]π+ complexes (M = CoIII, RhIII, IrIII) have been determined in aqueous solution (μ 0.1 M, NaClO4). Irreversible reductions span the range from + 0.22 to -0.47 V for cobalt(III) complexes and from -0.86 to -1.45 V for rhodium(III),and occur near -1.7 V for iridium(III), determined against the standard (KCl) calomel electrode. Despite several reports to the contrary in the literature, no correlations exist of E½ with absorption spectra (Co and Rh), nuclear magnetic resonance spectra [δ(1HN), Co, Rh, Ir, and δ (59Co)], vibrational spectra [v(Co-N)], or rates of aquation and base hydrolysis (Co, Rh, Ir). Complexes which undergo outer-sphere [e.g., with Ru(NH3)62+] and predominantly inner-sphere (e.g., with VZ+aq) homogeneous electron transfer can be distinguished by the presence or absence of a correlation of In kex with E½ respectively, consistent with the expectations of the Marcus-Hush theory of outer-sphere electron transfer.

Enhancement of rates of reaction using neutral water/organic microemulsions as solvent media

Abstract: Relative to the rate constants for reactions in aqueous solutions the rate constants for reactions involving (i) Fe(phen)32+(phen = 1,10-phenanthroline), (ii) Fe(5-NO2phen)32+, (iii) 2,4-dinitrochlorobenzene, and (iv) crystal violet with either hydroxide or cyanide ions are increased markedly when two water/organic microemulsions formed from liquid components are used as reaction media; a similar though less significant change is observed in the related rates of aquation (hydrolysis).

Proton-promoted chelate ring opening in copper(II) polyamine complexes

Abstract: Etude cinetique de l'aquation acide des complexes de Cu(II) d'une serie de polyamines, en fonction de [H 3 O] + , temperature. Parametres d'activation

Photoreactions of rhodium(III) complexes: the cyanoammines Rh(NH3)5CN2+ and trans-Rh(NH3)4(H2O)CN2+

Abstract: Excitation par champ de coordinat des complexes cites. Produit de reaction, dans chaque cas, en solution aqueuse cis-Rh(NH 3 ) 4 H 2 OCN 2+ . Rendements quantiques de photo-aquation de NH 3 de Rh(NH 3 ) 5 CN 2+ (0,09) et de photo-isomerisation de trans-Rh(NH 3 ) 4 (H 2 O)CN 2+ (0,52). Etude theorique des mecanismes. Spectres electroniques UV

Photochemistry of iodopentaamminerhodium(III) in zeolite Y

Abstract: Etude de la photochimie des complexes de metaux de transition sur zeolites par la photoaquation du complexe de Rh III sur zeolite Y completement ou partiellement hydratee. Spectres IR de l'ion NH 4 + . Par irradiation a 436 nm, rendements quantiques: 0,18±0,03 (zeolite hydratee) et 0,13±0,03 (zeolite partiellement deshydratee)

Photochemistry of bromopentaamminecobalt(2+) ([Co(NH3)5Br]2+): wavelength, pressure, and medium dependence of redox and aquation

Abstract: Effets de la longueur d'onde, de la pression et du milieu sur le rapport de l'oxydoreduction a l'aquation du complexe cite. Rapport ∼2 a 254, 275, 313 et 365 nm tombant a ∼0 a 514,5 nm. Effet du melange glycerol/eau

Photostereochemistry of the cis-dicyanotetraamminechromium(III) ion

Abstract: Excitation par champ de coordinat de solutions aqueuses acides de cis-Cr (NH 3 ) 4 (CN) 2 + . Formation de Cr(NH 3 ) 3 (H 2 O)(CN) 2 + et CN − . Rendements quantiques dependant de la longueur d'onde. Mecanismes. Etude theorique

Double potential step chronoamperometry for reversible follow-up chemical reactions. Application to the aquation kinetics of bis(ethylenediaminemonoacetato)cobalt(II).

Abstract: A theory of double potential step chronoamperometry (DPSCA) is developed for the reversible follow-up reactions represented as Ox+ne\ightleftarrowsRed, Red\oversetk\undersetkK\ightleftarrowsZ, where k and K are the rate and the equilibrium constants of the follow-up chemical reaction, respectively. DPSCA is applied to investigate the kinetics of aquation reaction of [Co(edma)2]0 (edma: ethylenediamine-N-acetate), which is produced by electrolytic reduction of [Co(edma)2]+ in the range of pH 1.5 to 10.5. At pH 4.5,on the other hand, the hydrogen ions do not substantially contribute to the aquation and thus the rate approaches a lower limiting value (4.7×102s−1), which is in good agreement with that obtained in neutral region (4.5

Anation of the cis -Diaquabis(oxalato)chromate(III) Complex Ion by Oxalate Species

Abstract: in the absence of catalysis. In the presence of the nitrate ion, direct chelation of the binoxalato-0 ligand of trans-Cr(C204)2(0COC02H)(H20)2- (k3l’) competes favorably with aquation (kZl’) to fully activate this anation pathway. At 50.0 OC and an ionic strength of 1.20 M, kl = (4.02 f 0.06) X lo-) s-I, kll/kz = 0.50 i 0.04 M-l, kll‘/k2 = 0.26 f 0.04 M-I, k12/k2 = 1.56 i 0.10 M-I, and k3l’/k21’ = 3.0 * 0.5 M-I. The activation parameters of kl were found to be AH* = 18.0 EL: 0.2 kcal mol-l and AS* = -14.0 f 0.5 cal mol-l K-I at an ionic strength of 1.20 M. The reaction mechanism has been extended to include data previously reported near pH 1. The combined data show that nitrate-catalyzed anation proceeding through trans-Cr(C204)2(0COC02H)(H20)2- is a process of high activation enthalpy and positive activation entropy. In contrast, substitution proceeding through cis intermediates has a low activation enthalpy and a negative activation entropy.

Metal Catalyzed Aquation of Tris(malonato)chromate(III)ion. Kinetics and Mechanistic Study

Abstract: Metal ion catalyzed aquation of tris(malonato)chromate(III) ion has been followed spectrophotometrically in perchloric acid solution ([H+]=0.05 M) over a temperature range at an ionic strength of 2.0 M. Under these conditions kobsd=kH[H+]+kM[M2+] where kobsd is the observed first order rate constants for the protons and the metal ion catalyzed pathways. Metal ions exert appreciable catalytic effect on the aquation of the complex with kM following the sequence Cu(II)>Ni(II)>Co(II)>Zn(II)>Mn(II), which runs parallel to the metal monomalonato complex formation constants. A plausible mechanism for the metal promoted reactions is proposed.

Specific equatorial photolabilization of ammonium in cyanopentaamminerhodium (III)

Abstract: Fraction de NH 3 degage au cours de la photoaquation de [Rh(NH 3 ) 5 (CH)] 2+ en solution aqueuse, calculee a partir de l'analyse isotopique de NH 3 degage du complexe trans-[Rh(NH 3 ) 5 (CN)] 2+ enrichi en 15 N(2,69%). Mecanisme

Effects of electrolytic dissociation upon rates of reactions. Part 11. Metal ion catalysed rates of aquation of penta-ammineoxalatocobalt(III)

Abstract: Association constants (KML) of ion pairs formed between a series of divalent metal ions [including magnesium, and also lanthanum(III) ions](Mn+) and the divalent anion (L2–) of the complex penta-ammineoxalatocobalt(III) have been calculated from spectrophotometric u.v. absorbance measurements under virtually static conditions at 50 and 60 °C with ionic strength I= 0.5 mol dm–3. Some of these constants have also been estimated from e.m.f. measurements of a glass electrode/calomel electrode cell under the same conditions. Rate coefficients of aquation (kobs.) of the cobalt(III) species in the metal salt solutions at 60 °C and I= 0.5 mol dm–3 were determined from timed u.v. absorbance changes. From the kobs. and KML data, rate coefficients (k3) of the metal-oxalato ion pairs were estimated. The figures for the transition metals of the first series (manganese, cobalt, nickel, copper, and zinc) and for magnesium indicate an approximate linear relationship between the KML and k3 values; in terms of this, the k3 values for cadmium, lead, and lanthanum are of a lower order. There is a broad similarity between these features and those reported by others for various metal ion catalysed reactions, such as the rates of decarboxylation of 3-oxoglutaric acid.

Initial state and transition state contributions to solvent effects on activation enthalpies for substitution reactions of tris(1,10-phenanthroline)iron(II) in aqueous methanol

Abstract: Activation enthalpies have been determined for aquation of thetris(1,10-phenanthroline)iron(II) cation and for its reaction with hydroxide in 20, 40, and 80% (by volume) methanol, and for its reaction with cyanide in 20 and 40% methanol. Enthalpies of solution of the chloride salt of this cation, and of potassium cyanide, have been determined in the water-methanol mixtures. From these results and ancillary thermodynamic data we have dissected the variations of activation enthalpies for these three substitution reactions with solvent composition into their initial state and transition state components. In the water-rich mixtures (0 to 40% methanol) initial and transition state solvation effects are similar and dominated by the ligands, but in the reaction with hydroxide in 80% methanol there is a striking difference between initial and transition state behaviour.

Thorium(IV) and uranium(VI) complexes with some heterocyclic azo dyes in absolute ethanol

Abstract: Thorium(IV) and uranium(VI) chelate complexes with PAN, PAR, TAN and TAR have been studied in absolute ethanol. The uranyl ion forms complexes with PAN, PAR, TAN and TAR in the metal to ligand molar ratio of 1:1. Thorium(IV) forms complexes with PAR, TAR and TAN in the molar ratio of 1:2. In case of Th(IV)-PAN complexes the molar ratio is 1:2.4. The stability constants for all the above complexes have been worked out using the mole ratio method. The kinetics of aquation of Th(IV)-PAN complexes indicate that PAN acts as a tridentate ligand.

Synthesis, kinetics, and photochemistry of the chromium(III) dicyanoaquaethylenediaminetetraacetate complex

Abstract: Preparation d'un complexe Na 3 [Cr(Y)(CN) 2 (H 2 O)]•4H 2 O ou Y=EDTA qui est tridente (3 des groupes carboxyle etant non coordines). Aquation des groupes CN; parametres d'activation

Kinetics of reactions of bis(isothiocyanato)bis(dimethylglyoximato)cobaltate(III) in presence and absence of Hg2+ ion in acid perchlorate media

Abstract: At elevated temperatures (⩾ 70 °C) the title complex aquates significantly in aqueous acid media, releasing one thiocyanate in the first step, which exhibits no acid dependence. For this spontaneous aquation, the rate constant (kspont.) at 25 °C, ΔH≠ and ΔS≠ are 1.2×10−8s−1, 132 kJ mol−1 and 59 JK−1mol−1, respectively. This first step is followed by a slower second step in which, the second thiocyanate is released as the Co(dmgH)2 moiety is cleaved. The rate of release of thiocyanate is enhanced considerably by addition of Hg2+ and the complex changes smoothly into the corresponding di(aqua) product, [Co(dmgH)2(OH2)2+, without any complicating side reactions. Both the steps of the process are linearly dependent on [Hg2+]. For the catalysed reaction, the second-order rate constant at 25 °C, ΔH≠ and ΔS≠ for the first and second steps are 2.85 M−1s−1, 89 kJ mol−1, 60 JK−1mol−1; and 1.48 M−1s−1, 63 kJ mol−1, −30 JK−1mol−1, respectively. The observed linearity of the kobsvs [Hg2+] plots over a wide range of [Hg2+] concentration suggests a direct electrophilic (SE2) attack of the Hg2+ on the leaving thiocyanate ligand of the substrate complex; there is CoIII-NCS bond fission without the involvement of any long-lived binuclear intermediate of the type CoIII-NCS-HgII.

Effect of pressure on the aquation reactions of a series of bidentate carbonato-complexes of CoIII in aqueous solution

Abstract: The pressure dependencies of spontaneous and acid-catalyzed ring-opening, and subsequent decarboxylation reactions were studied for the complexes Co(en)2CO3+, α- and β-Co-(edda)CO3− and Co(nta)CO32−. The volumes of activation for the spontaneous ring-opening process of the anionic carbonato complexes areca. 10 cm3 mol−1 more negative than those for the corresponding acid-catalyzed process, and are ascribed to the increase in electrostriction around the free end of the carbonate ligand produced during the dissociative ring-opening step. The absence of such a difference for the Co(en)2CO3+ species and the magnitude of the volumes of activation suggest a ring-opening mechanism of the Ia type. No significant pressure effects were observed for the decarboxylation reactions. A plausible explanation is offered.

Influence of electrolytic dissociation upon rates of reactions. Part 10. Acid-catalysed aquations of some penta-ammine(carboxylato)cobalt(III) ions in aqueous solutions

Abstract: Rate coefficients of aquation at constant ionic strength in lithium perchlorate–perchloric acid media of a series of penta-ammine(carboxylato)cobalt(III) complexes [Co(NH3)5L]n+ have been calculated from u.v. absorbance measurements. With most of these, increases in the observed rate coefficients are not proportional to increases in the acid concentrations. The data have been used to calculate association constants of protonated forms of the complexes and the corresponding rate coefficients of aquation. The obtained association constants are 0.64 (L = acetate; I= 2.0, 40 °C), 0.1 (L =o-methoxybenzoate; I= 2.0, 40 °C), 116 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.24 (L = malonate; second association constant, I= 2.0, 40 °C), 0.69 (L = succinate; second association constant, I= 2.0, 40 °C), 0.02 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). With the tartrato-complex the observed rate coefficients increased linearly with increasing [HClO4] and this is also so with the oxalato-complex for I > 0.5 mol dm–3 but such increases are small when compared with those of the other d ica rboxylato-complexes of the present studies. U.v. spectral decreases at constant wavelength with increasing [HClO4] under virtually static conditions have also been used to estimate the association constants of the protonated complexes. The exceptions, since no spectral decreases were found, are the o-methoxybenzoato-complex, the oxalato-form at [HClO4] > 0.5 mol dm–3, and the doubly protonated tartrato-complex. The values obtained are 0.68 (L = acetate; I= 2.0, 30 °C), 125 (L = oxalate; first association constant, I= 0.5, 60 °C), 0.37 (L = malonate; second association constant, I= 2.0, 40 °C), 0.67 (L = succinate; second association constant, I= 2.0, 40 °C), 0.1 dm3 mol–1(L =o-phthalate; second association constant, I= 2.0 mol dm–3, 40 °C). These are in reasonable agreement with the above values derived from the kinetic data and from the latter the rate coefficients of aquation of the protonated species have been estimated. There appear to be broad relationships between the rate coefficients of the protonated forms and the association constants (comparing acetate with o-methoxybenzoate and succinate with malonate). This can perhaps account for the oxalate, tartrate, and o-phthalate complexes showing little evidence of double protonation. This feature is also discussed in terms of ligand chain lengths and it is also noted that in contrast to the first association constants of the protonated dicarboxylate complexes which are large but have relatively little catalytic effect, the second association constants are small but have strong influences upon the rates of aquation.