Outer-sphere Ion Pairs Research Articles

Metachors and dissociation of salts of oxo acids of group VI heavy metals in aqueous solutions

The backround of the previously introduced concept of the metachor is outlined. This concept is applied to aqueous solutions of Se, Te, Mo, and W oxo acids and their sodium and potassium salts for which the metachors, calculated from the experimental surface tension values, are used to gain insight into their dissociation state in solution. The normal salts with mononuclear and binuclear anions (Me2XO3, Me2XO4, and Me2X2O7 types) in aqueous solutions at concentrations of 0.1-0.5 mol dm-3 are completely dissociated in the 2nd step and their metachors are about 10 cm3 mol-1, whereas KHSeO4 and Na2W3O10 with its bulky trinuclear anion are dissociated in the 1st step only and their metachors at the above concentrations lie in the 4.5 to 5.5 cm3 mol-1 range (at concentrations as low as 0.025 mol dm-3 for the latter). The metachor of the free acid H2SeO4 is as low as 2.5-1.5 cm3 mol-1, corresponding to an appreciable association in the 1st dissociation step. The metachor only reflects the "chemical" association due to short-range forces, whereas it is indifferent to physical outer-sphere ion pairing.

Kinetic Studies of the Electron Transfer Reactions in Iron(II) and Iron(III) Systems. XI. Electron Transfer Reaction between Aquairon(II) and Tris(1,10-phenanthroline)iron(III) in Water Mixed with Methanol, Ethanol, 1-Propanol, and Ethylene Glycol

Abstract The electron transfer reaction Fe2+aq+Fe(phen)33+→Fe3+aq+Fe(phen)32+ has been investigated in order to find out the influence of the dielectric nature of media on the reaction rates, by the method of stopped-flow spectrophotometry. As the reaction media, were used aqueous mixtures with various alcohols, such as methanol, ethanol, 1-propanol, and ethylene glycol at their various mole fractions x. The second-order rate constant k grows larger approximately linearly with the increase in x, in a sequence: methanol<ethylene glycol<ethanol<1-propanol. When In k is plotted against D−1 (the reciprocal dielectric constant), all points come together on a single straight line with a positive slope, indifferent to the kinds of the alcohols used. This fact suggests that the reaction proceeds through three successive elementary processes, Fe2+aq+Fe(phen)33+\overseti→[Fe(H2O)62+·Fe(phen)33+]\oversetii→[Fe(H2O)63+·Fe(phen)32+]\oversetiii→Fe3+aq+Fe(phen)32+, in which Process i is the formation of an outer-sphere ion-pair between two reacting ions, Process ii the intramolecular electron transfer in the intermediate complex, and Process iii the separation of the ion-pair into the product ions, the last being the rate-determining step. The reaction scheme is compared with that of the reaction Fe2+aq+Fe(OH)2+→Fe(OH)2++Fe2+aq, where the first step of the ion-pair formation is rate-determining.

Ion Association of Some 2:2 Electrolytes in Water at 25 °C. III. A New Interpretation of Experimental Results and the Determination of Formation Constants of Inner-sphere Ion-pairs

Abstract The results of previous studies on ion association were re-examined. The formation constants of inner-sphere ion-pairs were obtained for several bivalent-metal sulfates by estimating the formation constants of outer-sphere ion-pairs with the help of the ion-association theory. The interactions between metal and sulfate ions were discussed by comparing these results.

Desolvation processes in the association of peroxodisulfate and sulfate with bivalent metals in aqueous solution: A calorimetric study

ΔH° and ΔS° have been determined, by direct calorimetry and by using published stability constants, for the association of Co(II) and Cu(II) with sulfate and peroxodisulfate anions. The results refer to an aqueous medium at T = 25°C and I = 0.5 M. Their examination seems to indicate, for the associations of sulfate, an outer-sphere ion pair formation in the case of cobalt, and an inner-sphere in the case of copper. This is in agreement with previous results for bivalent anions with a tetrahedral structure. By contrast, the desolvating ability of peroxodisulfate seems to be different from that of sulphate.

Ionization equilibria in solutions of nickel(II) chloride in dimethyl-sulphoxide

Visible absorption spectra and the molar conductance curve of NiCl 2 dissolved in dimethyl-sulphoxide (DMSO) have been determined at 25°C. The results indicate the formation of the [NiCl(DMSO) 5] + inner-sphere complex followed by the formation of the {NiCl(DMSO) 5] +Cl −} outersphere ion-pair as the concentration of NiCl 2 increases. The [NiCl 2(DMSO) 4] inner-sphere complex in pure dimethyl sulphoxide at 25°C is formed to but a small extent, but its relative content increases upon addition of the non-coordinating diluent, chlorobenzene. Dilutions with chlorobenzene also enhance coordination disproportionation producing the [NiCl 3 DMSO] − tetrahedral complex. The stability constant of the monochloro complex derived from the conductometric data has the value of 297 ( ±10)M −2 at 25°C, and the estimated value of the association constant of the [NiCl (DMSO) 5] +Cl − complex electrolyte, dominating in moderately concentrated solutions at room temperature, is 7(±3)M −1.

Appearance of sulphatoferric complexes in the oxidation of ferrous sulphate solutions. A study by pulse radiolysis

The rate of the reaction between perhydroxyl radicals and ferrous ions, like that between hydroxyl radicals and ferrous ions, is little affected when the ferrous ions are associated with sulphate. However, sulphate ions displace HO–2 from the ferric hydroperoxide complex by an outer-sphere ion-pair formation mechanism (Id): SO2–4+ Fe3+(H2O)6,HO–2⇌ Fe3+(H2O)6,HO–2SO2–4, Fe3+(H2O)6,HO–2SO2–4→ Fe3+(H2O)5SO2–4+ HO–2+ H2O. The equilibrium constant for the first of these reactions is 90 ± 20 M–1, and the rate constant for the second is approximately 104 s–1. Sulphate reacts with the ferric-hydroperoxide-ferrous bridge compound similarly, with an equilibrium constant of 100 ± 20 M–1 and a rate constant of the same order of magnitude as for the ferric hydroperoxide complex. Additional reactions take place when the concentration of sulphate ions is high enough.New determinations have been made of the rate constants and activation parameters for the reaction of hydrated ferric ions with sulphate. A detailed mechanism is given for reactions occurring during irradiation of the Fricke dosimeter in the absence of sodium chloride.

Formation of scandium(III) chlorate and scandium(III) bromate complexes in aqueous solution

Stoichometric stability constants for the formation of scandium(III) chlorate and scandium(III) bromate complexes have been measured at several temperatures by using a liquid cation exchanger. Relations between ligational enthalpy and entropy changes are discussed in connexion with the formation of outer-sphere ion pairs and inner-sphere complexes.

Oxidation of iodide ion by iron(III) ion in aqueous solution

The kinetics of the redox reaction between Fe3+ and I– ion have been reinvestigated over a wide range of reactant concentrations using the method of initial rates. The first-order dependence on Fe3+ and second-order dependence on I– have been confirmed, the third-order rate constant being 16·0 ± 1·0 I2 mol–2 s–1 at 25°C and ionic strength of 1·0M. In the presence of added ferrous ion, however, the previously derived rate laws do not adequately describe the reaction under all conditions. It is believed that the inner-sphere complex Fel2+ does not form to a significant extent, but that an outer-sphere ion-pair between Fe3+ and I– is a likely intermediate. A di-iodo-species may also be involved, and stationary-state assumptions, leading to relatively simple rate expressions, are not valid under all conditions.

The thermodynamics of lanthanide hexacyanoferrate(III) complexation

The thermodynamic parameters of the formation of LnFe(CN) 6 at zero ionic strength have been determined by the entropy titration technique. The stability is due to the relatively large and positive entropies of formation since the enthalpies are small and endothermic. The thermodynamic data is interpreted as supporting a model of outer sphere ion-pairing in LnFe(CN) 6.

Thermodynamic parameters of the alkaline earth monofluorides

Potentiometry and calorimetry have been used to determine stability constants and heats of formation of the alkaline earth monofluoride complexes in aqueous solution at an ionic strength of 1·00 M (NaClO 4). Enthalpies have been determined by calorimetry and by the temperature differential technique. The enthalpies of complexation were all found to be endothermic while the entropies are large and positive. Comparison with the acetate complexes indicates similarities in the trends of ΔH and ΔS from magnesium to barium. The larger entropy changes for the monofluoride complexes can be accounted for by the greater decrease in the overall water structure when the fluoride ion is complexed. The values for formation of MgF + do not fall in line with those of the other alkaline earths and are interpreted as indicating that MgF + exists as an outer sphere ion pair.

Magnetic resonance studies of outer-sphere ion-pair formation in N,N-dimethylformamide solutions of aluminum(III) halides

Magnetic resonance studies of outer-sphere ion-pair formation in N,N-dimethylformamide solutions of aluminum(III) halides

Rates of substitution of the hydrated beryllium cation by hydrogen fluoride and fluoride ion

The rate of formation of the monofluoroberyllium species Be(OH2)3F+ was measured by a conductimetric stopped-flow technique. At acid concentrations exceeding 0.01M two parallel reaction paths were identified: Be(OH2)42+ +F- ↔ Be(OH2)3F+ (k1,k-1) Be(OH2)42+ +HF- ↔ Be(OH2)3F+H+(k2,k-2) At 25� and an ionic strength of O.2M, k1 = 724 � 95 l. mole-l sec-1 and k2 = 73 � 3 l. mole-1 sec-1. Both substitution paths exhibit activation energies of 8.9 � 0.8 kcal/mole. The data are interpreted in terms of an SN11P mechanism which is also proposed for the analogous Be2+ + SO42- reaction. Outer-sphere ion pairs of Be(OH2)42+ with respectively F-, HF, and SO42- undergo substitution with the same activation energy. A linear free energy relation exists between the rate of formation of the inner-sphere complexes from the outer-sphere ion pairs and the accompanying free energy changes.

Lanthanide and actinide sulfate complexes—II: Determination of thermodynamic parameters

A calorimetric titration technique has been used to obtain the enthalpies of formation in solutions of 2·00 M ionic strength of LnSO 4 + and Ln(SO 4) 2 − (Ln = lanthanide ions). Using the temperature coefficient technique for solvent extraction data, the enthalpies of formation were calculated for the sulfate complexes of Ce, Pm, Eu, Am, Cm and Cf. The entropies were evaluated using ΔG data reported previously. The ΔH 1 values were endothermic and ranged from 3·7 (La) to 4·4 (Dy) kcal. The ΔS 1 values varied from 18·4 (La) to 20·4 (Dy) cal/deg. From these thermodynamic parameters, it is concluded that the extent of inner sphere complexation is equal to or greater than that of outer sphere ion pairing.

Complexes of Trivalent Lanthanide and Actinide Ions. I. Outer-Sphere Ion Pairs

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComplexes of Trivalent Lanthanide and Actinide Ions. I. Outer-Sphere Ion PairsGregory R. Choppin and William F. StrazikCite this: Inorg. Chem. 1965, 4, 9, 1250–1254Publication Date (Print):September 1, 1965Publication History Published online1 May 2002Published inissue 1 September 1965https://doi.org/10.1021/ic50031a003RIGHTS & PERMISSIONSArticle Views524Altmetric-Citations137LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (566 KB) Get e-Alerts Get e-Alerts

Thiocyanate complexes of some trivalent lanthanide and actinide elements

The stability constants for the formation of MSCN 2+ and M(SCN) 2 + where MNd(III), Eu(III), Pu(III), Am(III), Cm(III) and Cf(III) have been determined using the solvent extraction method and an ionic strength of 1·00 M. The enthalphy and entropy values for the formation of NdSCN 2+ and AmSCN 2+ indicate that these complexes are outer sphere ion pairs.

Basicity of Nitrate Ion in Nonaqueous Solvents

In aqueous media nitrate ion, like the perchlorate and sulfate ions, is a sufiiciently weak base that its character as an electron pair donor (or proton acceptor) in dilute solutions of electrolytes usually can be ignored. Hence, its function is adequately described by its contribution to the total ionic strength. Unequivocal quantitative evidence for nitrate complexes with simple metal ions in solution has been difficult to obtain. However, very recently reported stability constants for mono-nitrate complexes with trivalent aquo lanthanide ions have a range from 0.6 to 2.9, placing these in a position of intermediate stability between the corresponding monochloro and mono-thiocyanatol complexes of the same metals (5). Also, standard entropy and enthalpy changes fot formation of the mono-nitrate complexes are consistent with an outer sphere ion pair model for their structure.