Reactivity and solvatochromism of pentacyanoferrate(II) complexes in diol–water mixtures

Rate constants are reported for substitution at the pentacyanoferrate(II) ions [Fe(CN)5L]3−, where L=3,5-dimethylpyridine or 3-cyanopyridine, in binary aqueous mixed solvents containing up to 60vol% 1,2-ethanediol, 1,2-butanediol, methanol or ethanol. Trends for diol-containing mixtures are compared with those for monohydroxylic alcohols, and the reactivity pattern for these complexes is compared with those established earlier for base hydrolysis of tris(1,10-phenanthroline)iron(II) and for the aquation of cis-dichloro-bis- (1,2-ethanediamine)cobalt(III). The solvatochromic behaviour of several pentacyanoferrate(II) ions has been established in binary aqueous mixtures containing 1,2-ethanediol, 1,2-butanediol, 1,4-butanediol and 1,2-pentanediol. A correlation between reactivity and solvatochromism is presented. This revised version was published online in June 2006 with corrections to the Cover Date.     

Initial state and transition state contributions to solvent effects on rate constants for racemisation and dissociation of the [Fe(phen)3]2+ cation in DMSO-water mixtures

Summary Rate constants for racemisation and dissociation of the tris(1,10-phenanthroline)iron(II) cation, and solubilities of its picrate, are reported for dimethyl sulphoxide-water mixtures (0 to 40% by vol DMSO) at 298.2 K. The observed solvent effects on reactivity are analysed in terms of initial state and transition state contributions, and the pattern established compared with patterns for methanol- and acetone-water mixtures. In all cases the hydrophobic periphery of the ligand is dominant. Rate constants are also reported for racemisation and dissociation of the analogous complex [Fe(sb)₃]²⁺, where sb = the Schiff base from 2-benzoylpyridine andp-toluidine, in aqueous methanol.     

In Situ FT-IR Studies of the Zirconium (IV) Acetylacetonate Catalyzed Urethane Reaction of Butanediols

A comparative kinetic study of the urethane reactions of phenyl isocyanate and 1,2-, 1,3-, and 1,4-butanediol was carried out in dichloromethane solution with zirconium (IV) acetylacetonate as catalyst. In situ FT-IR was used to follow the kinetics of the reactions at a constant temperature of 15°–30°C. The rate constants for the reaction of the primary hydroxyl group and the secondary hydroxyl group were calculated as k _prim and k _sec, respectively. Analysis of the second-order rate constants of these systems indicated that k _prim follows 1,2-butanediol >1,3-butanediol >1,4-butanediol. The ratio of k _prim/k _sec in 1,2-butanediol was the highest and the order followed was the same as with the reaction rate. Activation energies and Eyring parameters were also determined for the urethane reaction of butanediols.     

Ionic strength effects in binary aqueous mixtures: Study of the reaction between Co(en)2(2-pzCO2)2+ and Fe(CN)5H2O3−

The reaction between Co(en)₂(2?pzCO₂)²⁺ (bis-ethylenediamine (2-pyrazinecarboxylato)cobalt(III)) and Fe(CN)₅H₂O^3? (aquopentacyanoferrate(II)) to form the binuclear complex [(en)₂Co( μ-pzCO₂)Fe(CN)₅]^? has been studied in several isodielectric binary mixtures at 298.2 K (cosolvents: methanol, ethanol, tertbutyl alcohol, ethyleneglycol, and glycerol). Results were rationalized by using a free energy relationship. The importance of correcting the rate constants obtained in the different mixtures from the ionic strength influence has been shown. © 1995 John Wiley & Sons, Inc.     

Solvation of inorganic complexes: transfer chemical potentials for mono- and bi-nuclear cobalt(III) complexes to methanol + water mixtures

Solubilities in MeOH--H₂O mixtures at 298.2 K are reported for a number of salts of mono- and bi-nuclear cobalt(III) complexes. From these solubilities and published single ion transfer chemical potentials, on the TPTB (Ph₄P⁺ = BPh^– ₄ ) assumption, transfer chemical potentials have been derived for these mono- and bi-nuclear cobalt(III) complexes. The results and trends are discussed in relation to those for other complexes and ions in these binary aqueous solvent mixtures.     

Dielectric properties of binary mixtures of three butanediols with 1,4-dioxane and 2-ethyl-1-hexanol at T = 298.2 K

Experimental results of dielectric investigations for solutions of the three butanediols {2,3-butanediol (2,3BD), 1,3-butanediol (1,3BD), and 1,4-butanediol (1,4BD)}, in 1,4-dioxane (1,4DX) are reported for various mole fractions at T = 298.2 K. Values of relative permittivity were measured at 100 kHz. The molecular dipole moments were determined using Guggenheim method. The variations of effective dipole moment and correlation factor, g, with mole fraction in these materials were investigated using Kirkwood–Frohlich equation. Dielectric measurements were also carried out on binary polar mixtures of the butanediols with 2-ethyl-1-hexanol (2EH) for various concentrations at T = 298.2 K. The Kirkwood correlation factor, the Bruggeman factor, and the excess permittivity were determined.     

Experimental Study of the Excess Molar Enthalpy of Ternary Mixtures Containing Water + (1,2-Propanediol, or 1,3-Propanediol, or 1,2-Butanediol, or 1,3-Butanediol, or 1,4-Butanediol, or 2,3-Butanediol)+Electrolytes at 298.15 K and Atmospheric Pressure

Excess molar enthalpies (H _m ^E) of ternary mixtures containing water+(1,2-propanediol or 1,3-propanediol or 1,2-butanediol or 1,3-butanediol or 1,4-butanediol or 2,3-butanediol)+(sodium bromide, or ammonium bromide, or tetraethyl ammonium bromide, or 1-n-butyl-3-methylimidazolium bromide at 0.1 mol⋅dm⁻³) at 298.15 K and atmospheric pressure have been determined as a function of composition using a modified 1455 Parr mixture calorimeter. The H _m ^E values are negative for all mixtures over the whole composition range. The influence of the electrolyte on the hydrophobic and hydrophilic effects as well as on the behavior of H _m ^E is discussed.     

Redox reactions of cobalt(III) complexes in aqueous organic mixtures effects: of single ion assumptions on initial state-transition state solvation analysis

Summary Solvent effects on the kinetics of redox reactions of cobalt(III) complexes were assessed in aqueous mixtures containing methanol,t-butanol, and acetone according to three different extra-thermodynamic assumptions —Wells, TATB, and TPTB^** — at 298.2 K. The calculated values of transfer functions of individual ions and initial and transition states were often markedly different. In some cases these differences led to different conclusions in the evaluation of the role of solvation in the reactions investigated.     

Experimental Study of the Excess Molar Volumes of Binary and Ternary Mixtures Containing Water + (1,2-Ethanediol,or 1,2-Propanediol,or 1,3-Propanediol,or 1,2-Butanediol) + (1-<Emphasis Type="Italic">n</Emphasis>-Butyl-3-methylimidazolium Bromide) at 298.15 K and Atmospheric Pressure

Densities of binary and ternary mixtures containing water + (1,2-ethanediol or 1,2-propanediol or 1,3-propanediol or 1,2-butanediol) + (1-n-butyl-3-methylimidazolium bromide at 0.01 mole fraction) at 298.15 K and atmospheric pressure have been determined as a function of composition using an Anton Paar densimeter (Model DMA 55). Excess molar volumes (V_m^EV_{\mathrm{m}}^{\mathrm{E}}) were calculated. The values are negative for all mixtures over the whole composition range.     

Solvation of iron and chromium complexes in alcohol–water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H₂O and one in MeOH–H₂O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H₂O and t-BuOH–H₂O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H₂O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H₂O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H₂O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H₂O-rich aqueous-alcohol mixtures. Some spectroscopic (¹H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.     

Octahedral cobalt(III) complexes of the chloropentammine type. XXVII. Effects of Methyl Substituents on reactivities of the cis-chloro-n-propylaminebis(ethylenediamine)-cobalt(III) cation

Salts of one isomeric form of the chloro-n-butylamine-, chloro-iso-butyl-amine- and chloro-sec-butylamine-bis(ethylenediamine)cobalt(III) cations have been prepared and characterised to have a cis-configuration (IR and VIS spectroscopy). Rate constants for their spontaneous aquation, mercury(II)-induced aquation and base hydrolysis have been determined and the activation parameters calculated. The results are compared with data obtained for the n-propylamine complex with a view to investigate the effects of methyl (α, β, γ) substituents on reactivities. The rate-determining dissociation of the outgoing group (Cl^? or HgCl⁺) takes place via either a square-pyramidal or a trigonal-bipyramidal intermediate, depending on whether the activation entropy is negative or positive.     

Synthesis,characterization and thermodynamics of some novel tertiary phosphine cobalt(III) unsymmetrical tetradentate Schiff Base complexes

The [Co(salpyren)PBu₃]ClO₄ · H₂O, [(N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III)perchlorate · monohydrate; [Co(Mesalpyren)PBu₃]ClO₄ · H₂O, [(7-methyl-N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III)perchlorate · monohydrate; [Co(Phsalpyren)PBu₃]ClO₄ · H₂O [(7-phenyl-N-salicylidene-N′-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III) perchlorate · monohydrate, were synthesized and characterized. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically for the 1:1 adduct formation of [Co(chel)PBu₃]ClO₄ · H₂O, where (chel = salpyren, Mesalpyren, Phsalpyren) as acceptors with phosphites [P(OR)₃ (R = Me, Et and i-Pr)] as donors, in acetonitrile (CH₃CN) and dimethylformamide (DMF) solvents, in constant ionic strength (I = 0.1 m NaClO₄) and at various temperatures T = 283 to 313 K. The trend of the equilibrium constants of the donors (phosphites) toward a given cobalt(III) Schiff base complex is as follows: P(OEt)₃ > P(Oi-Pr)₃ > P(OMe)₃. The trend of the equilibrium constants of the cobalt(III) Schiff base complexes toward a given phosphite is as follows: 7-Mesalpyren > salpyren > 7-Phsalpyren. The trend of the equilibrium constants with a given donor toward a given acceptor with respect to the solvent is as follows: CH₃CN > DMF.     

Determination of dissociation constants for coordination compounds of Cr(III) and Co(III) using potentiometric and spectrophotometric methods

The acid–base properties of analogous complex ions of chromium(III) and cobalt(III) in aqueous solution have been studied. The equilibrium constants for all metal complexes were determined by using potentiometric and spectrophotometric titration methods. First, dissociation constants for the studied complexes of Cr(III) and Co(III) were determined by means of the potentiometric titration method and using the STOICHIO computer programme. Then, pH-spectrophotometric titrations were performed and the OriginPro 7.5 computer programme was used to calculate the same constants. The measurements using both methods were carried out under the same conditions of temperature, T = 298.15 K, and over the same pH range 2.00–10.00, respectively. It turned out that the two methods used enabled us to obtain acidity constants in very good agreement.     

Solubilities and Transfer Chemical Potentials for Cobalt(III) Complexes in <Emphasis Type="BoldItalic">t</Emphasis>-butanol– <Emphasis Type="BoldItalic">i</Emphasis>-propanol–, and ethanol–water Mixtures

Solubilities in t-BuOH–, i-PrOH–, and EtOH–H₂O mixtures at 298.2 K are reported for a number of salts of mono- and bi-nuclear cobalt(III) complexes. From these solubilities and published single ion transfer chemical potentials, on the TATB (Ph₄As ⁺≡ BPh₄^-) assumption, transfer chemical potentials have been derived for most of these cobalt(III) complexes. The results and trends are discussed in relation to those for other ions and complexes. Effects of ligand nature for transfer to t-BuOH–H₂O mixtures are detailed and, for a selection of complexes, trends for transfer of a given complex to t-BuOH–, i-PrOH–, EtOH– , and MeOH– H₂O mixtures are compared.     

Ionization constants for water and for very weak organic acids in aqueous organic mixtures

A potentiometric method using a glass electrode has been applied to the determination of apparent ionization constants for water in binary mixtures of water with 11 organic solvents at 25°C. Further calculations with these apparent ionization constants permit evaluation of the acid ionization constant for some of the organic solvents as solutes in purely aqueous solvent by two different methods. Resulting values of pK _a derived from this work are: 1,2-propanediol (14.8 and 14.8), 2,3-butanediol (15.0 and 14.7), 1,3-butanediol (15.5 and 14.8), 1,4-butanediol (14.5 and 14.4), 2-butene-1,4-diol (14.0 and 13.9), 2-butyne-1,4-diol (12.1 and 12.4), 2-methoxyethanol (15.2 and 14.8), 2-ethoxyethanol (15.0 and 14.5), and triethylene glycol (14.6 and 14.3). None of the 11 solvents shows appreciable basicity.     

Solubilities of salts of cobalt(III), chromium(III), and iron(II) complexes in aqueous methanol; transfer chemical potentials of anions

Summary We report solubilities of a variety of salts of cobalt(III), chromium(III), and iron(II) complexes in methanol-water mixtures at 298.2K. From these solubilities and published transfer chemical potentials for the complex cations we are able to derive transfer chemical potentials for such anions as nitrate, thiosulphate, peroxodisulphate, dithionate, thiocyanate, and antimonyl tartrate. Transfer chemical potentials for several hexahalogenometallate anions, and tetrachloroplatinate(II), are derived from published solubilities. A comparative picture of transfer chemical potentials for anions is thus available, with the transition metal complex anions in the overall context of anions and their solvation characteristics in methanol-water mixtures.On leave from the Faculty of Science, Sohag, Egypt.     

Thermodynamics of Cobalt(III) Schiff base complexes in various solvents

The electronic and steric effects of some Schiff bases and the solvent on the thermodynamic parameters of the pentacoordinate Co(III) Schiff base complexes were studied. The formation constants and the thermodynamic parameters were measured spectrophotometrically for 1:1 adduct formation of the complexes as acceptors with tributylphosphine (PBu₃) as donor, in some solvents (acetonitrile, tetrahydrofuran, butanol, ethanol and N,N-dimethylformamide) in constant ionic strength (I = 0.01 M, sodium perchlorate) and at various temperatures. The trend of the reactivity of the pentacoordinate cobalt(III) Schiff base complexes toward tributylphosphine according to the solvent is as follows: acetonitrile > tetrahydrofuran > butanol > ethanol > N,N-dimethylformamide. The trend of the reactivity of pentacoordinate cobalt(III) Schiff base complexes toward the donor in a given solvent according to the equatorial Schiff base is as follows: BBE > BAE > Salen.     

Attenuation of substituent effects on reactivities of low-spin iron(II) complexes of Schiff base ligands

Substituent effects on reactivity are compared for base hydrolysis of tris-ligand-iron(II) complexes of Schiff base ligands derived from 2–acetylpyridine and substituted benzylamines and their aniline analogues. The methylene spacer in the former effectively isolates the iron from substituent effects in the phenyl ring, as indicated by the almost equal rate constants for base hydrolysis of the complexes derived from benzylamine and its 4–methyl, 4–fluoro, and 4– trifluoromethyl derivatives. Rate constants for base hydrolysis of the (substituted) benzylamine derivatives are also reported for some Me2CO-H2O and DMSO-H2O solvent mixtures. Reaction is faster in all these binary aqueous mixtures, mainly due to the higher chemical potentials of hydroxide ion.     

Kinetics of base hydrolysis of novel low spin Fe(II) amino acid Schiff base chelates—hydrophobic structural effects

The reactivity against OH^? ion of some novel Fe(II) complexes of Schiff base ligands derived from salicylaldehyde or o‐hydroxynaphth‐aldehyde and some variety of amino acids has been examined in aqueous and aqua‐ethanol mixtures. The rate law and relevant mechanism were assumed. Base hydrolysis kinetics measurements revealed pseudo‐first‐order doubly stage rates because of the presence of mer‐ and fac‐isomers. The evaluated rate constants and activation parameters are consistent with the stability constants of the investigated complexes. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 595–602, 2002     

Preparation and reactions of some 1,2,3,4-Tetrahydro-2,3-disubstituted 7(or 8)hydroxy-1,4-dioxopyrazino[1,2-a] indoles

1,2,3,4-Tetrahydro-2,3-disubstituted 7(or 8) hydroxy-1,4-dioxopyrazino[1,2-a]indoles have been prepared by the condensation of 6(or 5)benzyloxyindole-2-carbonyl chloride with d1-N- alkylamino acid ethyl esters in the presence of triethyl amine followed by the hydrogenolysis over palladium-carbon. Methylation and alkaline hydrolysis of 1,2,3,4-tetrahydro-2-benzy1-1,4-dioxopyrazino[1,2-a]indole are discussed.