Showing papers on "Aquation published in 1991"

Photoaquation of cis-bis(azine)tetraammineruthenium(ii) complexes, cis-ru(nh3)4(l)(l')n+1

Abstract: Near uV-visible range photolysis of cis-Ru{sup II}(NH{sub 3}){sub 4}(L){sub 2} (: = pyridine (py), 4-picoline (4-pic), isonicotinamide (isn), or 4-acetylpyridine (4-acpy)) and cis-Ru{sup II}(NH{sub 3}){sub 4}(isn)(L) (L = py, 4-pic, pyrazine, or 4-acpy) lead to isn, L, and ammonia aquation. The complexes were irradiated at 313, 365, 405, 436, 480, and 519 nm, in acidic (pH 3.5-4.0) aqueous solution and with {approximately} 10{sup {minus}3} M Ru complex concentration. The cis complexes have ligand field (LF) and metal-to-ligand charge-transfer (MLCT) states as the lowest energy excited states. The relative yields of the photoreactions of the cis complexes show patterns consistent with the excited-state tuning model proposed to explain photochemical properties of the pentaammine analogues, Ru{sup II}(NH{sub 3}){sub 5}(L), which undergo photosubstitution when LF is the lowest energy excited state, as is also the case for the trans complexes. For each cis complex, a fixed ratio of released ligands is observed at all irradiation wavelengths studied, this being a strong evidence that the observed photoreactions occur from one single LF excited state, or an ensemble of equilibrated LF excited states of the same electronic configuration. Ligands are more easily labilized along the axis with the weaker {pi}-acceptor ability. For a particular axis,more » the ligand with lower {pi}-acceptor ability is more easily labilized. 18 refs., 3 figs., 5 tabs.« less

Concerning the dependence of the volume of activation for a limiting D substitution mechanism on the size of the leaving group. The aquation of pentacyano(amine)ferrate(II) complexes

Abstract: A series of limiting dissociative substitution reactions of complexes of the type Fe(CN) 5 (NH 2 R) 3− (R=H, CH 3 , C 2 H 5 , i-C 3 H 7 , and CH 2 Ph) were studied as a function of pressure in order to investigate the dependence of the associated volume of activation on the size of the leaving group (NH 2 R). The results are compared to data available in the literature for other limiting dissociative substitution reactions of octahedral complexes, and a similar conclusion is reached. Possible reasons for this observation are presented

Oxidation of nickel(II) ethylenediaminetetraacetate by carbonate radical

Abstract: Reactions of the carbonate radical (CO3•–), generated by photolysis or by radiolysis of a carbonate solution, with nickel(II) ethylenediaminetetraacetate [NiII(edta)]2– were studied at pH 11.4 and ionic strength (I)= 0.2 mol dm–3. Time-resolved spectroscopy and kinetics for the transients were studied using flash photolysis whereas the stable products arising from ligand degradation of the complex were ascertained by steady-state radiolysis experiments. From the kinetic data it is suggested that CO3•– reacts initially with [NiII(edta)]2– to form a five-co-ordinated NiIII species [k=(4.5 ± 0.4)× 107 dm3 mol–1 s–1] which undergoes aquation with a first-order rate constant of (1.1 ± 0.3)× 103 s–1 to give [NiIII(edta)(H2O)]–. The latter reacts with iodide with a rate constant of (5.5 ± 0.4)× 105 dm3 mol–1 s–1. At the alkaline pH used [NiIII(edta)(H2O)]– undergoes transformation to give a radical intermediate which reacts with [NiII(edta)]2– to give ligand degradation products of which glyoxylic acid and formaldehyde were detected.

Nitrosyl–nitrite interconversion in pentacyanoruthenate(II) complexes

Abstract: The nucleophilic addition of OH– to [Ru(CN)5(NO)]2– leads to the N-bonded pentacyanonitroruthenate(II) ion (λmax= 320 nm, Iµ= 3850 dm3 mol–1 cm–1). The stoichiometry is 2:1 ([OH–]:[Ru]) and the equilibrium formation constant is 4.4 × 106 dm6 mol–2(25 °C, I= 1 mol dm–3). A kinetic study of the forward reaction showed that it is first order in the concentration of each reactant, with k= 0.95 dm3 mol–1 s–1(25 °C, I= 1 mol dm–3), ΔH‡= 57.3 ± 3.3 kJ mol–1 and ΔS‡=–54.0 ± 4.5 J K–1 mol–1. The mechanism involves two consecutive attacks by OH–, the first being rate determining. The reaction product decays by an aquation process, leading to [Ru(CN)5(H2O)]3– and free NO2–. The rate constant for the dissociation reaction of [Ru(CN)5(NO2)]4– is k–N= 2.00 × 10–4 s–1(25 °C, I= 1 mol dm–3). In the formation reaction, both nitrite (O-bound) and nitro (N-bound) linkage isomers are formed, with ko and kN being 0.23 and 0.15 dm3 mol–1 s–1 respectively (25 °C, I= 1 mol dm–3). The O-bound isomer isomerizes slowly to the thermodynamically more stable N-bound isomer. The kinetic and thermodynamic parameters have been analysed by comparison with the chemistry of the complexes [Fe(CN)5(NO)]2– and [Fe(CN)5(NO2)]4–.

Substitution of aqua ligands fromcis-diaqua-bis(bipyridyl) ruthenium(II) by 1, 10-phenanthroline in aqueous medium

Abstract: The kinetics of aqua ligand substitution fromcis-[Ru(bipy)2(H2O)2]2+ by 1, 10-phenanthroline (phen) have been studied spectrophotometrically in the 35 to 50°C temperature range. We propose the following rate law for the reaction within the 3.65 to 5.5 pH range: $$\begin{gathered} \frac{{d[Ru(bipy)_2 (phen)^{2 + } ]}}{{dt}} \hfill \\ = \frac{{k_1 k_2 [Ru(bipy)_2 (H_2 O)_2^{2 + } ][phenH^ + ]}}{{k_{ - 1} + k_2 [phenH^ + ]}} \hfill \\ \end{gathered}$$ where k1 is the water dissociation rate constant of the substrate complex; k−1 is the aquation and k2 is the ligand capturing rate of the pentacoordinate intermediate [Ru(bipy)2H2O]2+. Kinetics of the aqua ligand substitution by 2,2′-bipyridine have also been studied at 40°C for comparison. The substitution reactions were found to be pH dependent. Ionic strength has little effect on the rate constants. ΔH‡ and ΔS‡ were determined and compared with anation by other anionic ligands, e.g. N3−. SCN−etc. The results are consistent with a dissociative mechanism.

Photochemistry of macromolecular metal complexes. II. Synthesis, thermal, and photochemistry of some polypyridyl complexes of chromium (III) bound to macromolecules

Abstract: Polymer coordinated chromium(III) complexes [Cr(bpy)2(PAA)2]+, 1, [Cr(bpy)2-(PMA)2]+, 2, [Cr(phen)2(PAA)2]+, 3, and [Cr(phen)2(PMA)2]+, 4, [where bpy, phen, PAA and PMA are, respectively, 2,2′-bipyridine, 1,10-phenanthroline, poly(acrylic acid), and poly(methacrylic acid)] were synthesized. The polymer–chromium(III) complexes were characterized by elemental and spectroscopic analyses. Thermal substitution reactions of these macromolecular chromium(III) complexes in basic solutions lead to the replacement of the polypyridyl ligand by hydroxide ion while in strong acidic solutions the polymer complexes precipitate out. The photochemical reactions are qualitatively similar to that of the thermal reactions and the quantum yields are dependant on the pH of the medium. Further, lower quantum yields were observed for the aquation of the polymer complexes in comparison with the monomeric chromium(III) complexes and the results are discussed in terms of the effect of the polymer environment. Flash photolysis of 1 and 3 results in the formation of transients with maxima at 480 nm for 1 and 470 nm, 580 nm for 3. The decay of the transients were found to obey first order kinetics and the rate constants were determined. The transients were suggested to be the alkyl-chromium complexes. Flash photolysis of 2 and 4 does not produce transients which is interpreted to be due to the presence of a methyl group in the ligand which hinders the formation of the carbonchromium bond.

Effect of solvent on reactions of coordination complexes. Part 12. Kinetics and mechanism of chloride substitution reactions ofcis-(chloro)(2-aminoethanol)bis(ethylenediamine) cobalt(III) andcis-(chloro)(1-aminopropan-2-ol)-bis(ethylenediamine) cobalt(III) ions in acidic and basic ethylene glycol-water media

Abstract: The loss of chloride ion from the title complexes resulted in the predominant formation of the chelated amino-alcohol productscis-[Co(en)2(NH2CH2CH(X)O/H)]2+/3+ (X=H or Me). The kinetics of chloride release were investigated in aqueous ethylene glycol (EG) media (0 to 80% by wt of EG) at 40°–65°C in acidic media and at 20°–35°C in basic media. The rate constants decreased linearly with increasing mol fraction of the cosolvent. The plots of log kversus D s −1 (Ss=bulk dielectric constant, k=first order or second order rate constants) were essentially linear with negative slopes for the reactions in an acidic medium, and tended to be curved for the base catalysed reactions. The activation enthalpies and entropiesversus XEG (XEG=mol fraction of EG) plots indicated extrema which might be associated with the effects of the solvent structural changes on these thermodynamic parameters. The observed solvent isotope effect $$(k_{H_2 O} /k_{D_2 O} ) = 1.12$$ at 50°C, [HClO4]=0.010 mol dm−3 for Cl− release was lower than the value for the aquation ofcis-[Co(en)2(alkylamine)Cl]2+ complexes $$(k_{H_2 O} /k_{D_2 O} = 1.38 - 1.44)$$ reported in the literature. This is consistent with the lack of direct solvent molecule participation in the actual act of substitution at the cobalt(III) centre, as expected for a true intramolecular reaction.

Solvent effects on the aquation of chloropentammine-cobalt(III) perchlorate in ethanol-water

Abstract: The aquation kinetics of the chloropenta-aminecobalt(III) ion in H2O−EtOH mixtures have been determined. A new correlation is described for calculating the chemical potential from kinetic data and molar thermodynamic excess functions for binary mixtures. The rate constants correlate well with Grunwald-Winstein solvating power Y parameter and with the dielectric constant of the medium. The data supports the D mechanism.

Thermodynamic and kinetic studies on the complexation reactions of aqua(rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) copper (II)(blue) with neutral monodentate ligands

Abstract: In order to study the charge effects of the entering and leaving groups in substitution reactions of five-co-ordinate complexes, the equilibrium constants (K) of the complexation reactions of a trigonal-bipyramidal complex, aqua(rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)-copper(II), [CuL(H2O)]2+(blue isomer), with eight neutral monodentate ligands (L′), ammonia, methyl-, dimethyl-, trimethyl- and ethyl-amine, aniline, pyridine and piperidine, as well as the rate constants for the formation (kf) and the aquation (kaq) of [CuL(L′)]2+ have been determined in 0.20 mol dm–3 NaClO4 at 25.0°C. The formation rate constants are discussed in relation to a combination of the basicity, the softness and the size of the entering group. A plot of log kf against log K gives a straight line with a slope of 0.98. The kinetic results are consistent with an associative-interchange, Ia, mechanism.

Effect of hypoxia and acidosis on the cytotoxicity of six metal(ligand)4(rhodamine-123)2 complexes at normal and hyperthermic temperatures.

Abstract: Several analogues of PtCl4(Rh-123)2 in which the metal may be Pt or Pd and the coordinated ligand may be -Cl, -CN or -NO2 were prepared and tested in cell culture with EMT-6 cells at normal (37 degrees C) and hyperthermic (42 degrees C and 43 degrees C) temperatures and various environmental conditions (normally oxygenated vs. hypoxic and pH 7.40 vs. pH 6.45). Pd is a much more reactive metal than Pt, while -CN and -NO2 are more tightly bound ligands than is -Cl. The goal of these studies was to define the complex with the least cytotoxicity at 37 degrees C and the greatest enhancement in cytotoxicity under hyperthermic conditions. The Pt complexes Pt(CN)4(Rh-123)2 and Pt(NO2)4(Rh-123)2 were much less cytotoxic than PtCl4(Rh-123)2 under both normothermic and hyperthermic conditions. The Pd complexes were, in general, more cytotoxic than the corresponding Pt complexes. The level of metal (Pt or Pd) in the cells did not appear to be a major factor in the level of cytotoxicity obtained. Complexes which were not cytotoxic at 37 degrees C regardless of oxygenation level or pH did not become cytotoxic at hyperthermic temperatures. In conclusion, the optimal members of this series were the complexes with chloro ligands, indicating that aquation is probably a necessary step in the cytotoxic mechanism and cytotoxicity at 37 degrees C was necessary to obtain cytotoxicity at higher temperatures.

[Fe(phen)3]2+ aquation in aqueous polyacrylamide solution

Abstract: The aquation of tris(1, 10-phenanthroline) iron(II) has been studied in aqueous polyacrylamide solutions. The rate increases up to 2.8 times at low polymer concentrations, and subsequently decreases. These effects are attributed to changes in the local water activity in the region of the complex.

Formation of linkage isomers via the substitution of halides by selenocyanate in ruthenium(III) complexes

Abstract: Substitution of the halide ion of [Ru(NH3)5X]2+ (X=Cl− or Br−) by SeCN− was monitored spectrophotometrically between 45 and 60° C in aqueous medium. The pseudo-first order rate constants were evaluated by Guggenheim's procedure, which shows linearity for 2–3 half-lives. The rate increases linearly with [SeCN−] and all the plots have a positive intercept on the rate axis. The SeCN−-independent path represents aquation and the SeCN−-dependent path represents anation of the aqua complex with simultaneous formation of two isomeric (the N bonded and the Se bonded) products. The formation of the isomeric products is entropy controlled.

Synthesis, thermal, and photochemistry of some polypyridyl complexes of chromium (III) bound to macromolecules

Abstract: Polymer coordinated chromium(III) complexes [Cr(bpy) 2 (PAA) 2 ]+, 1, [Cr(bpy) 2 -(PMA) 2 ] + , 2, [Cr(phen) 2 (PAA) 2 ] + , 3, and [Cr(phen) 2 (PMA) 2 ] + , 4, [where bpy, phen, PAA and PMA are, respectively, 2,2'-bipyridine, 1,10-phenanthroline, poly(acrylic acid), and poly(methacrylic acid)] were synthesized. The polymer-chromium(III) complexes were characterized by elemental and spectroscopic analyses. Thermal substitution reactions of these macromolecular chromium(III) complexes in basic solutions lead to the replacement of the polypyridyl ligand by hydroxide ion while in strong acidic solutions the polymer complexes precipitate out. The photochemical reactions are qualitatively similar to that of the thermal reactions and the quantum yields are dependant on the pH of the medium. Further, lower quantum yields were observed for the aquation of the polymer complexes in comparison with the monomeric chromium(III) complexes and the results are discussed in terms of the effect of the polymer environment. Flash photolysis of 1 and 3 results in the formation of transients with maxima at 480 nm for 1 and 470 nm, 580 nm for 3. The decay of the transients were found to obey first order kinetics and the rate constants were determined. The transients were suggested to be the alkyl-chromium complexes. Flash photolysis of 2 and 4 does not produce transients which is interpreted to be due to the presence of a methyl group in the ligand which hinders the formation of the carbonchromium bond.

Thermal and photoreactivities of oxalatobis(polypyridyl)chromium(III) complexes in aqueous media

Abstract: The thermal and photochemistry of oxalatobis(polypyridyl)chromium(III) complexes have been studied. The rate constants for the thermal aquation reactions have been determined and the quantum yield for the photoaquation has been estimated as a function of excitation wavelength and pH of the solution. The quantum yield for photoaquation varies from 7×10−2 to 10−3 depending upon the pH of the solution and wavelength of excitation. The activation parameters for the thermal reactions have been estimated for the systems investigated.

Thermodynamic Parameters of Ionization of Kojic Acid and Its Coordinating Behaviour Towards Transition Metals.

Abstract: The thermodynamic parameters of ionization (pK, ΔG, ΔH and ΔS) of Kojic acid have been evaluated potentiometrically. The pK value decreases with increase in temperature and has a linear relationship with the concentration of dioxane. The process of solvation and aquation is discussed. The mechanism of complexation between Kojic acid and some transition metals is discussed and the log β value is calculated.