Showing papers on "Aquation published in 1989"

Photolytic and radiolytic study of platinum(III) complex ions containing aquo and chloro ligands

Abstract: The formations and characterizations of short-lived, monomeric platinum(III) complex ions containing aquo and chloro ligands have been studied by using pulse radiolysis and laser photolysis techniques coupled with uv-visible absorption and conductivity detection methods. Five different chemical routes have been used to generate in aqueous media the same or similar platinum(III) species: reaction of tetrachloroplatinum(II), (PtCl{sub 4}){sup 2{minus}}, with the hydroxyl radical, interactions of hexachloroplatinum(IV), (PtCl{sub 6}){sup 2{minus}}, with the hydrated electron, hydrogen atom, and tert-butyl alcohol radical, and the 265-nm photolysis of (PtCl{sub 6}){sup 2{minus}} with the latter giving rise to both oxidation-reduction and ligand-substitution processes. The platinum(III) Intermediates can be classified into two categories. The nascent or shorter lived species exhibit intense charge-transfer bands with peak maxima near 450 nm or at wavelengths below 300 nm, and they are proposed to be of a distorted-octahedral type with compositions of the form (Pt{sup III}-(Cl){sub 6-m}(X){sub m}) (m = 0-2; X = OH, H{sub 2}O). The longer lived Pt(III) complexes are characterized by a single charge-transfer band having a peak between 410 and 420 nm and by compositions of the type (PtP{sup III}(Cl){sub 4-n}(X){sub n}) (n = 1-3; X = OH, H{sub 2}O) having limiting square-planar structures. The mechanisms formore » the formations of the platinum(III) complex ions and for their interrelationships are discussed, and evidence is presented to indicate that these species act as catalytic agents in the thermal aquation of (PtCl{sub 6}){sup 2{minus}}. 43 refs., 7 figs., 3 tabs.« less

Activation volumes for aquation of chromium(III) pentaammine complexes with neutral leaving groups: comparison with and mechanistic differentiation from cobalt(III) analogues

Abstract: Influence de la temperature et de la pression sur l'Aquation d'une serie de complexes avec des coordinats: carboxamides, DMSO et trimethylphosphate. Comparaison de profil de volume avec une serie de complexes du cobalt(III), suggestion d'un mecanisme reactionnel

Binding Kinetics of Tetrachloro-1,2-diaminocyclohexaneplatinum(IV) (Tetraplatin) and cis-Diamminedichloroplatinum(II) at 37 °C With Human Plasma Proteins and With Bovine Serum Albumin. Does Aquation Precede Protein Binding?

Abstract: Experiments were conducted at 37 degrees C to study the kinetics of (a) binding of cis-diamminedichloroplatinum (II) (CDDP) and of a racemic mixture of d- and l-isomers of trans-tetrachloro-1,2-diaminocyclohexaneplatinum (IV) [or tetraplatin (TP)] to protein [human plasma proteins or bovine serum albumin (BSA)]; (b) aquation (acid hydrolysis) of CDDP and of TP; and (c) binding of charged (aquated) CDDP species to BSA. The experiments were performed at clinically relevant concentrations for CDDP, so that the proportional concentrations of platinum complexes relative to the concentrations of other chemical species in blood plasma were similar to those obtaining in the clinical use of the drug. "Free" (unbound) platinum complexes were separated from the protein-bound complexes were separated from the protein-bound complexes by gel filtration chromatography. By use of ion-exchange chromatography, charged platinum species were separated from the uncharged species and free charged platinum species of CDDP were separated from those bound to BSA. Platinum in various fractions was quantitated by atomic absorption spectrophotometry with electrothermal atomization; proteins were quantitated by te Bradford method with Coomassie blue dye. The kinetic data obtained by the application of these methods for CDDP are in good agreement with those obtained by other methods, e.g., binding rates based on separations by centrigugal ultrafiltration. The overall protein-binding reaction of CDDP was consistent with a binding process comprising two consecutive first-order reaction steps: the rate-controlling aquation reaction [half-life (t 1/2), approximately 2 hr] followed by a more rapid binding reaction of the charged (aquated) CDDP species to the protein (t 1/2, approximately 23 min). However, the results for TP indicated that prior aquation was not required for protein binding, and we could surmise that binding of TP to protein proceeds via a direct nucleophilic attack. An unexpected finding was the marked, reproducible difference in rates of aquation between the two lots of TP that we used; this finding suggests the need for cautions evaluation of pharmacokinetic data describing the behavior of TP.

Base-catalysed aquation of αβ-syn- and αβ-anti-chloro- and bromo-[1,9-bis(2′-pyridyl)-2,5,8-triazanonane]- and -[1,11-bis(2′-pyridyl)-2,6,10-triazaundecane]-cobalt(III) cations. An unusually base-sensitive halogenopentamine cobalt(III) system

Abstract: Complexes of the type [Co(picdien)X][ClO4]2 and [Co(picditn)X][ClO4]2[picdien = 1,9-bis(2′-pyridyl)-2,5,8-triazanonane, picditn = 1,11-bis(2′-pyridyl)-2,6,10-triazaundecane; X = Cl, Br, NO2, NCS, N3, MeCO2, or H2O] have been prepared. All complexes have the αβ configuration, those of picdien existing in either or both syn and anti forms, while only the anti forms of the picditn complexes have been isolated. Structures have been established by single-crystal X-ray diffraction and 1H n.m.r. spectroscopy in dimethyl sulphoxide and D2O. All complexes are unusually sensitive to base-catalysed hydrolysis over very wide ranges of pH. The pH-independent contribution to the solvolysis of the chloro- and bromo-picdien complexes is observed only at high temperatures and at high [H+] but there is a very important pH-independent contribution to the solvolysis of the corresponding picditn species, which are also somewhat more sensitive to base catalysis. Proton-exchange studies show that proton transfer is faster than substitution in even the most labile systems. The mechanism is discussed.

Cobalt-induced facile degradation of phenylurea to ammonia, carbon dioxide, and anilinium ion and other reactions of linkage isomeric cobalt(III) complexes of phenylurea

Abstract: A search for metal ion promoted hydrolysis of urea and the factors influencing linkage isomerization on a metal has led us to prepare and examine reactivities of N- and O-bound phenylurea complexes of pentaamminecobalt(III). The N-bonded isomer reacts in aqueous acid to yield principally [Co(NH3)6]3+, CO2, and anilinium ion (ca. 70%) but also via parallel paths leading to [(NH3)5CoOC(NH2)NHC6H5]3+ (linkage isomerization) and [(NH3)5CoOH2]3+ (aquation). The major path involves an elimination reaction of [(NH3)5CoNH2CONHC6H5]3+ to give anilinium ion and [(NH3)5CoNCO]2+. The latter complex, which has been isolated and characterized, is known to undergo rapid hydration (pH l 2) to [(NH3)5CoNH2CO2H]3+, which subsequently decomposes along three parallel paths to [Co(NH3)6]3+ and traces of [(NH3)5CoOH2]3+ and [(NH3)5CoOCONH2]3+. Kinetic data for the three parallel reactions of [(NH3)5CoNH2CONHC6H5]3+ in aqueous HCIO4 (1.0 M, 25.0 dC) are kelim= 1.04 X 10-2 s-1 (elimination), kNo = 2.39 X 10-3 s-1 (isomerization), and kaq = 1.13 X 10-3 s-1 (aquation). A single-crystal structure reveals that the urea exo C-N bond is 0.11 A longer than the endo C-N bond and, as in uncoordinated phenylurea, the electron-with-drawing phenyl ring is neither planar with nor conjugated to the urea moiety. These features are likely retained in the protonated form and account for the facility of the elimination path. By contrast, neither elimination nor hydrolysis of the O-bonded phenylurea complex was detected; instead it slowly undergoes parallel aquation and O- to N-linkage isomerization. Both processes are base-catalyzed, and each obeys a rate law of the form k(obsd) = ks + Koh[Oh-]. The equilibrium constant (K'No= Kno/Kon= 166) reflects the strong thermodynamic preference for the O rather than the N terminus of the neutral phenylurea molecule. However, the observed equilibrium is pH-dependent (K'(obsd) = K'NO[H+]/(Ka + [H+])); for pH g 3, the N-bonded isomer is more stable due to its selective deprotonation (K'NO(obsd) a 10n5, pH 6.2). The single-crystal structure determination of [(NH3)5CoNHCONHC6H5](C104)2-H20 shows the cobalt in an approximately octahedral environment with phenylurea bonded as its anion through the indicated nitrogen center. As observed for the free ligand, the phenyl substituent is twisted (37d) with respect to the approximately planar urea moiety. The compound crystallizes in the monoclinic system (b = 91.64d), with V = 1887.0 A3, space group C2/c, Z = 8, a = 15.751 (6) A, b = 12.277 (5) A, c = 9.762 A, and R = 0.046 and RW = 0.043 for 1381 diffractometer data (244 variables) with 1 g 3s(I), m = 105.47 cm-1, and F(000) = 1023.96.

Effect of solvent on the reactions of coordination complexes part VII: Kinetics of solvolysis of cis‐(bromo) (imidazole) bis‐(ethylenediamine)cobalt (III) and cis‐(bromo) (N‐methyl imidazole)bis‐(ethylenediamine) cobalt(III) in methanol‐water media

Abstract: The kinetics of the solvolytic aquation of cis-(Bromo) (imidazole) bis(ethylenediamine) cobalt (III) and cis-(Bromo) (N-methylimidazole) bis(ethylenediamine) cobalt(III) have been investigated in aqueous methanol media with methanol content 0-80% by weight and at temperatures 40-55°C. The pseudo-first order rate constant decreases with increasing methanol content. Plots of log k s aq vs. D s -1 (where D s is the bulk-dielectric constant of the solvent mixture) and log k s aq vs. the Grunwald-Winstein Y-solvent parameter are nonlinear, the curvature of the plots is relatively more significant for the imidazole complex. The plots of log k s aq vs. molfraction of methanol (X MeOH ) for both the substrates also deviate from linearity, the deviation being less and less marked, particularly for the N-methyl imidazole complex, as the temperature is increased. Hence preferential solvation phenomenon appears to be less significant when the N-H proton of imidazole is replaced by -CH 3 group. The plots of calculated values of the transfer free energy of the dissociative transition state, cis-{[(en) 2 Co(B)] 3+ }* (B = imidazole, N-methylimidazole), relative to that of the initial state, cis-[Co(en) 2 (B)Br] 2+ , for the transfer of the ions from water to the mixed solvent, against X MeOH exhibit maxima at X MeOH = 0.06, 0.27, and 0.12, 0.36 and minima at X MeOH = 0.12 and 0.19 for cis-[(en) 2 Co(imH)Br] 2+ and its N-methylimidazole analogue respectively which are in keeping with the solvent structural changes around the initial state and transition state of these substrates as the solvent composition is varied. Plots of activation enthalpy and entropy against molfraction of the solvent mixtures exhibit maxima and minima. This type of variations of the activation parameters, ΔH ≠ and ΔS ≠ , with X MeOH speaks of the enthalpy and entropy changes associated with the solvent-shell reorganization of the complex ions both in the initial and in the transition states which contribute appreciably to the overall activation enthalpy and entropy of the aquation reaction.

Effect of solvent on the reactions of coordination complexes. Part 9.—Kinetics of solvolysis of cis-(chloro)(cyclohexylamine) bis(ethylenediamine)cobalt(III) in methanol–water, propan-2-ol–water, ethylene glycol–water and t-butyl alcohol–water media

Abstract: The kinetics of the solvolytic aquation of cis-(chloro)(cyclohexylamine)-bis(ethylenediamine)cobalt(III) ion were investigated in water–methanol, water–propan-2-ol, water–ethylene-glycol (0–80 wt % alcohol) and water-t-butyl alcohol (0–50 wt % alcohol) media at 35–60 °C. Plots of log ksobsvs. D–1s(where Ds is the bulk dielectric constant of the solvent mixture), log ksobsvs. the Grunwald–Winstein solvent parameter, YButCl, and log ksobsvs. Xorg(= mole fraction of cosolvent) tended to be curved. Under isodielectric conditions (Ds≈ 50) at 50 °C, the plot of log ksobsvs. Xorg for methanol–water, ethanol–water, propan-2-ol–water, t-butyl alcohol–water, acetone–water, ethylene glycol–water also did not yield a satisfactory straight line. The observed dependence of solvolysis rate on Xorg has been interpreted in terms of preferential solvation of the initial and transition states which is believed to be at least partly controlled by the overall acidity and basicity of the mixed solvent media as well as the hydrophobic interaction effect. Variation of enthalpies and entropies of activation with solvent composition was correlated with changes in the physical properties of the solvent mixtures. The solvent isotope effect (kH2O/kD2O= 1.38 ± 0.16 at 50 °C) was, however, normal as observed for several other cis-[Co(en)2(primary amine)Cl]2+ complex ions.

Kinetics of aquation of [Fe(5-Br-phen)3]2+ ions in aqueous solutions as a function of temperature and pressure

Abstract: Rate constants are reported for the aquation of [Fe(5-Br-phen)3]2+ ions in aqueous solutions as a function of temperature, T, and pressure, p, yielding volumes and enthalpies of activation for the rate-determining loss of the first 5-Br-phen ligand. Data describing the dependence of molar volume of water on T and p are analysed to obtain T–p pairs at which the molar volume of water, V*(H2O;1) equals the molar volume at 298.15 K and 101 325 N m–2; i.e. under an isochoric condition which is extrinsic to the aqueous solution containing the iron(II) complex. Kinetic data for the aquation reaction are analysed to obtain rate constants, k, and related activation parameters under corresponding extrinsic isochoric conditions. This quantitative approach is applied to data describing the dependences of equilibrium constants characterising the acid dissociation of ethanoic acid(aq), the first ionization constant for orthophosphoric acid, and self-dissociation of water. The treatment is also applied to kinetic data describing the solvolysis in aqueous solution of benzyl chloride. For the three chemical equilibria the dependences are calculated of In K#, enthalpy ΔrH∞ and volume of reaction ΔrV∞ on T at fixed p, on p at fixed T, on T with p changing to keep V*(H2O; l) constant, and on p with t again changing to hold V*(H2O;l) constant. Similar treatements are applied to In k, enthalpies and volumes of activation. The procedures show how the suggestion made by Evans and Polanyi in 1935 can be acted on, at the same time retaining thermodynamic consistency with respect to standard and reference states for solutes in solution. Differences between isochoric [V*(H2O;l)] and both isobaric and isothermally derived parameters are discussed in terms of the role of solvent structure in controlling reaction and activation. The isochoric [V*(H2O)] dependence of rate constants on temperature for aquation of the above iron(II) complex differs from the corresponding isobaric dependence. The pattern for the solvolysis in aqueous solutions of benzyl chloride differs from that for the iron(II) complex. The differences are consistent with the changes in hydrophilic–hydrophobic character for a given substrate on going from initial to transition state.

The preparation and characterisation of chromium(III) complexes of C-meso-5, 12-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane (LM). Aquation and base hydrolysis kinetics ofcis- andtrans-[CrLMCl2]+

Abstract: The reaction of [CrCl3(DMF)3] with C-meso-5, 12-dimethyl-1, 4, 8, 11-tetra-azacyclotetradecane(LM) in DMF gives a mixture ofcis-[CrLMCl2]Cl (ca. 90%) andtrans-[CrLMCl2]Cl (ca. 10%). These complexes are readily separated, as thecis-isomer is insoluble in warm methanol while thetrans-isomer is soluble. Using the dichlorocomplexes as precursors it has been possible to prepare a range ofcis-[CrLMX2]+ complexes (X=Br−, NO3−, N3−, NCS− and X2=bidentate oxalate) and alsotrans-[CrLMX2]+ complexes (X=Br−, H2O or NCS−). The spectroscopic properties and detailed stereochemistry of the complexes are discussed.

Kinetics of aquation and base hydrolysis of some trans-[Co(tn)2(B)Cl]n+(tn = 1,3-diaminopropane; B = OH, NCS, N3, NO2, NH3, or CN) complexes. The effect of ring size on reactivity

Abstract: The rate constants for the displacement of Cl– from trans-[Co(tn)2(B)Cl]n+(tn = 1,3-diaminopropane; B = OH, NCS, N3, NO2, NH3, or CN) have been measured in water over a range of temperature and pH and the behaviour is compared to that of the analogous 1,2-diaminoethane complexes. For B = NCS, OH (and Cl), where substitution is accompanied by stereochemical change and a large positive ΔS‡, the rate of uncatalysed aquation is very much enhanced. For B = CN, NO2, NH3(and SO3), where the entropies of activation for uncatalysed aquation are smaller (even negative) and where substitution occurs with retention of configuration, the increase in reactivity is not much more than ten-fold. In the case of B = N3, where the diaminoethane complex aquates with steric change but with a negative ΔS‡ value, the reactivity increase is between the two limits and ΔS‡=+39 J K–1 mol–1. The base hydrolysis of all complexes studied is only increased by a factor of 10–20 in spite of the common occurrence of stereochemical change.

Linkage isomer ratios in thermal and photochemical anation of acidopentacyanocobaltate(III) anions

Abstract: Photolysis of [Co(CN) 5 X] n− ions, where X=CN − , N 3 − , Cl − , Br − , I − , OH − , and H 2 O, in slightly acidic aqueous thiocyanate solution has been found to give the linkage isomers of [Co(CN) 5 (CNS)] 3− , together with larger amounts of [Co(CN) 5 (H 2 O)] 2− . Photolyses at pH 13 and room temperature, and in acidic medium at −4 o C, demonstrate that direct photoanation occurs in competition with the more efficient aquation reaction

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

Abstract: The aquation ofcis-[Co(en)2(NH2Et)O2CR]2+ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.

UV photochemistry of trans-cyanothiocyanatotetraamminechromium(III). Communication between charge-transfer and ligand-field states

Abstract: Irradiation (at 295 and 250 nm) of the charge-transfer (CT) bands of trans-Cr(NH 3 ) 4 (CN) (NCS) + is 1×10 −3 M HClO 4 /010 M NaClO 4 solution results in aquation of all three types of ligands The predominance of NCS − loss is consistent with the NCS-to-Cr CT transition, and primary photoredox activity is demonstrated by Cr(II) scavenging

Kinetics of aquation of κ-chloro(diethylenetrianine)-(ethylenediamine)cobalt(III) ion in methanol-water medium

Abstract: Le complexe K-Co(dien)(en)Cl(ClO 4 ) 2 ,1/2H 2 O a ete prepare et caracterise. La cinetique d'hydratation de l'ion Co(dien)(en)Cl 2+ a ete etudiee sur un large intervalle de composition du solvant et de temperature. La temperature iso-cinetique obtenue indique que la reaction est entropiquement controlee et que l'interaction solute-solvant joue un role important. Les resultats sont en accord avec un mecanisme dissociatif

Pressure Effect on the Aquation of $trans-[Cr(tmd)_2F_2]^+\;and\;trans-[Cr(tmd)_2FCl]^+$ Ions

Abstract: The rate for the aquation of ion in aqueous acidic solution has been measured by spectrophotometric method at various temperatures and pressures. The rate constants are increased with increasing temperatures and pressures. The values of activation entropy are 5.2 eu for and -16.62 eu for ions. Activation volumes have all negative values and lie in the limited range for and $-8∼-7\;cm^3mol^{-1} for ion. From the above results, we may deduce that the mechanism for the aquation of and ions is interchange-associative mechanism and dissociative mechanism respectively.

Influence of changes in the ionic background on the aquation of chloride complexes of chromium(III) and their absorption spectra

Abstract: 1. The influence of changes in the ionic composition of the medium on the rate constants of the aquation of chloro complexes of chromium(III) CrCl j 3−j (j=1, 2, 3) has been studied, and the significant role of the ionic strength has been demonstrated. 2. Changes in the ionic medium have an appreciable influence on the absorption spectra, especially in the UV region, but the changes in the spectra are not necessarily associated with the formation of new complex species.

Substitution Kinetics of Palladium(II)diethylenetriamine Complexes in Basic Medium.

Abstract: Substitution reactions of the type Pd(R5dien)- H2O2+ + I−→ Pd(R5dien)I+ + H2O (R = H, Me and Et) were studied as a function of steric hindrance in the range 7⩽pH⩽12 in order to solve problems related to the nature of such reactions in basic medium. All the kinetic data can be interpreted in terms of an anation model in which the aqua complex is the only reactive species in this pH range. No evidence for conjugate base formation or for the participation of hydroxy bridged species was found. Deviations in the kinetic data at pH > 9 can be accounted for in terms of an increase in the fraction of the aqua complex resulting from a reverse aquation contribution of the iodo complex under such conditions.

Kinetics of Aquation and Base Hydrolysis of Some trans-(Co(tn)2(B)Cl)n+ (tn: 1,3-diaminopropane; B: OH, NCS, N3, NO2, NH3, or CN) Complexes. The Effect of Ring Size on Reactivity.

Abstract: The rate constants for the displacement of Cl– from trans-[Co(tn)2(B)Cl]n+(tn = 1,3-diaminopropane; B = OH, NCS, N3, NO2, NH3, or CN) have been measured in water over a range of temperature and pH and the behaviour is compared to that of the analogous 1,2-diaminoethane complexes. For B = NCS, OH (and Cl), where substitution is accompanied by stereochemical change and a large positive ΔS‡, the rate of uncatalysed aquation is very much enhanced. For B = CN, NO2, NH3(and SO3), where the entropies of activation for uncatalysed aquation are smaller (even negative) and where substitution occurs with retention of configuration, the increase in reactivity is not much more than ten-fold. In the case of B = N3, where the diaminoethane complex aquates with steric change but with a negative ΔS‡ value, the reactivity increase is between the two limits and ΔS‡=+39 J K–1 mol–1. The base hydrolysis of all complexes studied is only increased by a factor of 10–20 in spite of the common occurrence of stereochemical change.

Mechanism for Formation and Aquation of Palladium(II) Acetonitrile Complexes in Aqueous Solution. Variable‐Temperature and Variable‐Pressure Study of Stabilities and Kinetics

Abstract: Mechanism for Formation and Aquation of Palladium(II) Acetonitrile Complexes in Aqueous Solution : Variable-Temperature and Variable-Pressure Study of Stabilities and Kinetics

Effect of ion-pairing on the solvolytic aquation of bromopentaamminecobalt(III) ion in the presence of maleate and phthalate anions

Abstract: The rate of solvolytic aquation of bromopentaamminecobalt(III) ion has been measured in aqueous medium in the presence of maleate and phthalate anions at 40°, 45° and 50°C. The rate accelerating influence of maleate and phthalate is attributed to the formation of more labile ion-pairs. The rate and association constants of the ion-pairs have been calculated. Product analysis has been carried out in order to evaluate the participation of the associating anions in the act of substitution. Activation parameters for the aquation of the ion-pairs and of the other reaction pathways have been determined. Enthalpy, entropy and free-energy changes of the association equilibria have also been calculated.

Kinetics of aquation of [fe(5-br-phen)3]2+ ions in aqueous-solutions as a function of temperature and pressure - the isochoric controversy and analysis of equilibrium and kinetic data

Abstract: Rate constants are reported for the aquation of [Fe(5-Br-phen) 3 ] 2+ ions in aqueous solutions as a function of temperature and pressure, yielding volumes and enthalpies of activation for the rate-determining loss of the first 5-Br-phen ligand