Showing papers on "Aquation published in 1968"

Acid-catalyzed aquation of hexaammineruthenium(II) and pentaaminepyridineruthenium(II) complex ions

Abstract: JOHN R. KUERZPEL, AND HENRY 'rAUBE 1976 PETER C. FORD, seems to be negative, though still small) and the rates are limited by the entropy of activation. The facile re- duction of [ ( N H I ) ~ C O O ] compared to [ ( N H 3 ) 4 C ~ - OHIz4+ is not surprising. When the superoxo ion is oxidant, the electron is absorbed into an orbital centered largely on the oxygenj3 and the bond rearrangement ac- companying electron transfer is small-thus note that the molecular framework remains intact on elec- tron transfer. However, when the dihydroxo-bridged species is the oxidant, the electron absorbed enters an orbital centered largely on Co, which is antibonding with respect to Co and one or more ligands. Rather drastic rearrangement of the molecular structure pre- ceding electron transfer is called for, and the rate of re- duction is correspondingly less. Our kinetic results differ from those of Sykesl in that we have observed only a single path for the reductions, whereas he reports three parallel paths for the reduction by Fez+. These paths differ in the way they depend on (H+). The rate law reported by him has the form -dln ([(;\'H,),C~o],~+)/dt = (Fe )[(kA/(H+)) f kB f hc(H+)] His value of k~ = 4.73 X lo-' ibT-' sec-I a t 25' (EB = 9.6 kcal/mol) is directly comparable to the specific rates we have recorded. The importance of the term first Inorgnizic Chenzistry order in (H+) when Fez+ is the reducing agent is not unexpected. We have concluded that the dominant form of the intermediate in acidic solution contains one proton more than the reactants, and the kinetic assistance by the proton in forming the intermediate is not unexpected when a weak reducing agent is used. The term inverse in (H+) may reflect the fact that OH- stabilizes Fe(II1) over Fe(II), and some kinetic assis- tance from the stabilization can be expected. All of the reactions are probably of the outer-sphere type. Direct attack on oxygen may be prevented bv the steric requirements of the 3 ligands on the coba!t centers. The operation of an outer-sphere mechanism can explain why Cr2+ reacts less rapidly than do2s V 2 + . The changes in dimension required when Cr?' is oxi- dized more than compensate for the greater driving force for the Crz+ compared to the V+ reaction. Acknowledgments.-Financial support by the Atomic Energy Commission, Grant No. At-04- 3-326, and by the National Science Foundation Fellow- ship held by A. B. M. in 1963-1966 is gratefully ac- knowledged. We Tvish also to acknowledge the above foundation for use of the spectrophotometer, purchased by them under Grant G-22611. COXTRIBUTION FROM THE CHEMICAL LABORATORIES OF STASFORD UKIVERSITY, STASFORD, CALIFORNIA, AND THE USIVERSITP OF CALIFORNIA AT SAXTA BARBARA, SANTA BARBARA, CALIFORSIA The Acid-Catalyzed Aquation of Hexaamminesuthenium(I1) and Pentaamminepyridineruthenium(I1) Complex Ions By P E T E R C. FORD, JOHX R . KUEMPEL, AND HENRY TAUBE Received April 10, 1968 The aquation rates of R u ( N H ~ ) and ~ ~ Ru(NH8):pyZf have been measured in acidic aqueous solutions. It is found that the rate of loss of coordinated ammonia or pyridine from these increases with increasing hydrogen ion concentration, the dif- ~ ~ + -d[Ru(NH3)e2+C] /dt = kl[H+] [Ru(SH3)eZ'], where ferential rate law for the loss of the first SH3 from R U ( S H ~ ) being: sec-l a t 25'. The pentaamminepyridine complex ion aquates a t a somewhat slower rate. kl = (1.24 zt 0.03) X Electron-withdrawing substituents on the pyridine ring stabilize the complex, resulting in even slower aquation rates. The stoichiometries and rate laws are described. T o explain the results, a mechanism is proposed in which an interaction of a proton with ruthenium 7r d electrons labilizes the metal-nitrogen bonds. Experimental Section Introduction Materials.-Water, which had been passed through a n iou- Recent experiments in this laboratory have been exchange column and then distilled, was redistilled in an all- concerned with the preparation and characterization of glass apparatus from basic potassium permanganate before being ruthenium complex ions of the type R U ( N H ~ ) ~ ~ ~ used X ~ + to , prepare the solutions. RulNHa)sCls, obtained from where X is a variable group attached to the pyridine Johnson Matthey and Co., London, was purified by double re- ring.l In the course of this research it was noticed crystallization from 1 M HCI and from mater. Ru(SHa)iCla was prepared from R U ( S H ~ ) as ~ C described in the literature.' that these complexes undergo slow aquation reactions in The syntheses of Ru(NHs)spy(C104)s and Ru(SH3)jpyX(C104)2, acidic solutions a t rates which increase with increasing H ~ also , reported where X = m-CHa, m-C1, p-CHa, and V Z - C O ~ C are hydrogen ion concentration. This interesting observa- elsewhere.' tion led us to investigate these reactions more carefully All kinetic experiments involving R ~ ( h - H 3 ) ~ ~ + w run e r in e 1 .o ?Vf and to extend the experiments to include the simpler ionic strength mixtures of p-toluenesulfonic acid (C7H:SOaH) and lithium p-toluenesulfonate (C7H7S03Li). These mixtures ion Ru(NH3)e2+. (1) P. Ford, D. P. Rudd, R. Gaunder, and H. Taube, J . Ain. CIZPVZ. SOC., (2) K. Gleu and K. Rehm, Z. Ailovp. Allgem. Chein., 927, 237 (1936).

The preparation of hydridopentammine- and hydridoaquotetramminerhodium(III) sulphates and other salts; the formation of alkyl and fluoroalkyl derivatives

Abstract: The action of metallic zinc on ammoniacal solutions of chloropentamminerhodium chloride in presence of sulphate ion leads to the formation of hydridopentamminerhodium(III) sulphate Several other salts of the cation have been preparedThe pentammine undergoes an aquation reaction to form the aquo-ion [Rh(NH3)4(H2O)H]2+ in which the water is trans to the hydrido-groupThe interaction of the hydrido-species with ethylene, propene, and but-I-ene and with tetrafluoroethylene and other fluoro-olefins has been studied and crystalline salts have been isolated The ir and nmr spectra of certain of these species are given, and the electronic spectra discussed

Mechanism and steric course of octahedral aquation. Part X. The preparation, properties, aquation, and anation of some cis-bisunidentato-(1,4,8,11-tetra-azacyclotetradecane)cobalt(III) cations

Abstract: The preparation and characterisation of a series of complexes of the type, cis-[Co cyclam X2]Y (X =½CO3, Cl, Y = Cl; X = NO2, N3, NCS, Y = NO3 and ½[PtCl6]; cyclam = 1,4,8,11-tetra-azacyclotetradecane) and cis- and trans-[Co cyclam(H2O)2](ClO4)3 are reported. In all the preparative experiments, substitution takes place with complete retention of configuration although a slow subsequent isomerisation to the more stable trans isomer can be observed. The kinetics of the aquation of the cis-dichloro-cation have been studied over a range of temperature. This complex is some 15,000 times more labile than its trans isomer at 25°, the effect arising from a much lower activation energy. The anation of cis-[Co cyclam Cl H2O]2+ by thiocyanate has also been investigated. The reactions of the cis isomer are compared with those of the trans isomers and also with those of the corresponding bis(ethylenediamine)complexes.

A kinetic study of the aquation of fluoropentamminechromium(III) cation in aqueous solution

Abstract: The rate constants for the aquation of [Cr(NH3)5F]2+ have been measured by polarography over wide ranges of pH and temperature. In the pH range 1 to 10·5 the rate of aquation is independent of pH. The Arrhenius parameters for the aquation of [Cr(NH3)5F]2+ are compared with previously obtained data for the corresponding chloro-, bromo-, and iodo-complexes. These values are in general agreement with a bi-molecular SN2 mechanism for aquation of the fluoro-complex and a solvent assisted SN1 mechanism for the aquation of the other three halogeno-complexes.The effect of added anions such as sulphate and pyrophosphate on the rate of aquation, is discussed in terms of ion-pair formation, which for the fluoro-complex produces very little increase in rate, while for the chloro-, bromo-, and iodo-complexes, appreciable catalysis is observed. This is found to be in agreement with the proposed mechanisms.

Kinetics of the Aquation of Pentammine Amino Acid Cobalt(III) Complexes

Abstract: The rate of aquation of pentamminecobalt(III) complexes of the general formula [Co(NH3)5amH]3+ (amH stands for an amino acid molecule with proton on the nitrogen atom), containing unidentate glycine, β-alanine, sarcosine and betaine, has been measured at 55°C, and ionic strength 0.1 and 1.0 in the acid concentration range up to 0.5 M. The kinetic term is expressed byRate=[complex](k_H_2O+k_H^+[H^+]) The kH2O and kH+ values for glycine, β-alanine, sarcosine and betaine complex are respectively as follows (at μ=1.0): kH2O, 0.40×10−6, \lesssim0.2×10−6, 0.25×10−6, and 0.44×10−6 sec−1; kH+, 2.0×10−6, 26×10−6, 1.8×10−5, and 1.0×10−6 M−1 sec−1. The kH+ alues increase with increase in pKa values of the amino acids, but are smaller than those for the aquation of carboxyl-atopentamminecobalt(III) complexes. This difference seems to be due to the electrostatic shielding of the car boxy late group by the protonated amino group.

The kinetics of the reaction of aquomanganese(III) ions with hydrazoic acid in perchlorate media

Abstract: The reaction of aquomanganese(III) ions with hydrazoic acid in perchlorate media is of the first order in total [MnIII] and second order in [HN3], and one MnIII ion is consumed for every HN3 molecule which disappears. The observed third-order rate constant increases with increasing acidity. This is interpreted by the reaction of a hydrazidopentaquomanganese(III) ion, Mn(H2O)5HN33+, with HN3 to produce an azide radical H2N6+·, which then reacts rapidly with another MnIII ion to produce molecular nitrogen. The energy and entropy of activation are determined. The significance of hydrazido-complexes in the aquation of azido-complexes is discussed.

Rate constants for the reduction of monohalogenochromium(III) complexes with europium(II)

Abstract: The reactions of europium(II) with monohalogenochromium(III) complexes, EuII+ CrX2+→ EuIII+ CrII+ X–, have been studied in aqueous perchloric acid solutions, µ= 1·0M. In all but the reaction of monofluorochromium(III) allowances were made for the uncatalysed and chromium(II)-catalysed aquation of CrX2+. Contributions from these reactions are of decreasing importance in going from Crl2+ to CrF2+, and can be ignored for the latter. At 25° rate constants are Crl2+(4·1 × 10–2 sec.–1) > CrBr2+(3·4 × 10–3 sec.–1) > CrCl2+(1·4 × 10–3 sec.–1) > CrF2+(6·0 × 10–4 sec.–1). Although there is no proof, the reactions are discussed in terms of an inner-sphere mechanism. The effect which bridging halide ions have on electron-transfer reactions is considered.

Aquation of tris-[1,10-phenanthroline]iron(II) complexes in t-butyl alcohol–water mixtures

Abstract: Rates of acid aquation of several substituted tris-(1,10-phenanthroline)iron(II) complexes have been determined in aqueous t-butyl alcohol. Variation of rate constant with solvent composition and with nature of the ligand substituent and of the anion has been investigated. Activation parameters for aquation of the 5-nitro-complex have been obtained over a range of aqueous t-butyl alcohol solvent compositions. Results are discussed in terms of the effect of t-butyl alcohol on the structure of the water in aqueous t-butyl alcohol, and the consequent effects on rates and mechanism of aquation.

Kinetics of peroxodisulphate oxidations in t-butyl alcohol–water solvent mixtures

Abstract: Kinetics of reaction between peroxodisulphate and iodide, hexacyanoferrate(II), and a series of substituted tris-(1,10-phenanthroline)- and tris-(2,2′-bipyridyl)-iron(II) complexes have been investigated in aqueous t-butyl alcohol. The iron(II) complexes react by parallel oxidation and aquation, the relative importance of these two paths depending on solvent composition and ligand substituent. The variation of rates of oxidation with solvent composition does not reflect the effect of the t-butyl alcohol on the structure of the water in the way that has been observed for aquation of several complexes.

Kinetic studies on 4d and 5d transition-metal complexes. Part IV. Kinetic studies on the chloropenta-amminerhodium(III)–aquopentaamminerhodium(III) system

Abstract: The kinetics of the forward and reverse reactions in the system [Rh(NH3)5Cl]2++ H2O [graphic omitted] [Rh(NH3)5H2O]3++ Cl– in aqueous solution have been studied in the temperature range 77–97·5° at a number of ionic strengths in the range 0·01–0·07 M. The aquation rate constant is independent of ionic strength and is summarised by the equation k1(sec.–1)= 2·838 × 1010 exp (–24,419 ± 220)/RT The anation rate constant exhibits the primary salt effect. The rate constant at zero ionic strength is summarized by the equation k–2°(mole 1.–1sec.–1)= 1·584 × 1017 exp (–28,244 ± 200)/RT

The reactivity of co-ordinated oxalate. Part VI. Acid-catalysed aquation of the trisoxalatocobaltate(III) anion

Abstract: The stoicheiometry of the acid-catalysed aquation of the trisoxalatocobaltate(III) anion is represented by 10H++ 2Co(C2O4)33–⇌ 2Co2++ 5H2C2O4+ 2CO2. The rate of aquation is repressed by addition of oxalate ions and therefore a reversible dissociation yielding oxalate ions precedes the electron-transfer step.

A study of the co-ordination behaviour of various 2-pyridylketones. Part II. Rhodium(III) complexes of 2-benzoylpyridine

Abstract: Reaction of rhodium trichloride and 2-benzoylpyridine (PhCOpy) in ethanol affords the complex Rh(PhCOpy)2Cl2,Rh(PhCOpy)Cl4. The cation has been obtained as perchlorate in yellow and orange isomeric forms. Both isomers have trans chloride ligands. Reaction of any of these compounds with boliing water gives Rh(PhCOpy)2Cl2,OH, a neutral six-co-ordinate rhodium(III) complex containing one unidentate 2-benzoyl-pyridine molecule co-ordinated via oxygen. Reflexing the last compound in aqueous ethanol gives a further neutral complex, Rh(PhCOpy)2Cl3 containing one molecule of benzoylpyridine co-ordinated through nitrogen only Another neutral complex [Rh(PhCOpy)Cl2,H2O],H2O is considered to arise from the aquation of the Rh(PhCOpy)Cl4– anion.Corresponding bromo-complexes have been prepared and spectroscopic data, including assignments of rhodium–halogen stretching frequencies, are presented.

Phosphato complexes of cobalt(III). IV. Hydrolysis in basic solution

Abstract: The rates of hydrolysis of phosphato complexes of cobalt(111) in sodium hydroxide concentrations ranging from 0.02M to 0.37M, and at several ionic strengths, have been measured with a tracer technique. Bidentate phosphato complexes exhibit the same rates of hydrolysis as the corresponding monodentate complexes, due to a rapid conversion of the bidentate into the monodentate form. The general rate law for base hydrolysis of all the phosphato complexes is: d[PO34]/dt = {kH2O + kOH[OH-]}[complex] At 60o and at unit ionic strength, the rate constants for the complexes cis-[Co(NH3)4OH.PO4]-, cis-[Co en2OH.PO4]-, and [Co(NH3)5PO4] respectively are: 103kH2O (min-l) 85.0, 2.0, <1; and 103kOH (1. mole-1 min-l) 42.7, 12.0, 69.5. Mechanistic conclusions have been based on the measured enthalpies and entropies of activation and deuterium solvent isotope effects. For all complexes, kH2O is identified with an aquation mechanism involving synchronous interchange of the phosphate and solvent water between the first and second coordination spheres of the complexes. In the case of the tetrammine and bis(ethylenediamine) complexes, kOH is identified with a process involving synchronous interchange of phosphate and hydroxide ion between the first and second coordination spheres of the complexes. In the case of the pentammine complex, an SN2CB mechanism is considered to be more probable. A comparison with the base hydrolysis of halogen complexes of cobalt(111) is presented.

A study of some redox reactions of the chromium(II)–ethylenediamine-tetra-acetate complex. Evidence for outer-sphere mechanisms

Abstract: Reactions of the chromium(II)–EDTA complex with CrF2+, CrCl2+, CrBr2+, Co(NH3)5Cl2+, Cl2, Br2, I2, and IrCl62– have been studied in perchlorate reaction media pH 2·7–5·0, and at temperatures in the range 0–20°. The reactions are all rapid and final spectra were recorded within 3 min. of mixing. The products are [CrIIIYH(H2O)] and the related conjugate-base form [CrIIIY(H2O)]–(ethylenediaminetetra-acetate, EDTA = Y4–). Complexes of the type [CrIIIYH(X)]–, where X– is a halide ion, have not as yet been prepared. If it is assumed that the aquation of such complexes is slow then the chromium(II)–EDTA reactions are probably of the outer-sphere type. Other possible mechanisms are considered. Reactions with H2O2, O2, and (H2O)4Cr(OH)2Cr(H2O)44+ are also rapid, the same products are obtained, and there is no evidence for the formation of binuclear chromium(III)–EDTA complexes. Again outer-sphere mechanisms are a strong possibility.

The kinetics of some isotopic exchange reactions of anionic ruthenium-(II), -(III), and -(IV) chloro-complexes in concentrated aqueous H36Cl solutions

Abstract: The kinetics of the apparent isotopic exchange reaction RuCl63–+36Cl–⇆ RuCl536Cl3–+ Cl– have been studied and rate parameters obtained. Increase of the total hydrochloric acid concentration from 6·0 to 11·75 M causes a decrease in the rate of exchange which, in this acid concentration range, is considerably less then the known rate of aquation of RuCl63– in more dilute acid. The activation enthalpy of the exchange in both 6·0 and 11·3M-hydrochloric acid is ca. 25 kcal. mole–1, which indicates that the overall exchange of chloride ions is controlled by the aquation of RuCl63–. The low exchange rates are correlated with the considerable reduction in water activity at high acid concentrations, and this is taken as evidence for the operation of a genuine SN2 type mechanism in the acid hydrolysis of RuCl63–. The effect of producing small amounts of lower oxidation states of ruthenium in RuCl63––36Cl– exchange solutions was investigated. The results indicated that, whereas ruthenium(II) does not cause noticeable catalysis, ruthenium(I) may be extremely active. Irradiations with 2537 and 3660 A light showed that the RuCl63––36Cl– exchange system is not strongly photosensitized by these wavelengths. The small acceleration observed with 3660 A light may arise from photoaquation of RuCl63–.Isotopic chloride-ion exchange experiments were carried out on 0·025M-ruthenium(II) and mononuclear ruthenium(IV) solutions in ca. 11M-hydrochloric acid at 25°. Infinite-time activity distributions indicated that the principal chlororuthenium species undergoing exchange in these solutions were RuCl42–, for ruthenium(II), and a RuCl62––RuOHCl52– equilibrium mixture, for ruthenium(IV). The rates of exchange revealed that the order of ligand lability in the higher (anionic) chloro-complexes of ruthenium is Ru(II) > Ru(III) > Ru(IV). The most important factors which contribute to (i) the variation in rates of solvolytic aquation of Group VIII transition-metal hexachloro-complexes, (ii) the occurrence of depressed rates of aquation at high acid concentrations, and (iii) direct chloride–chloride substitution paths in metal chloro-complexes, are also discussed.