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.     

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.     

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.     

Transfer chemical potentials for cobalt(III) and chromium(III) complexes from water into aqueous methanol; their relevance to reactivity trends for cobalt(III)-chloride aquation

Summary We report solubilities of a number of cobalt(III) and chromium(III) complex salts in methanol-water mixtures. From these, and published solubilities of salts of other complexes of these metals, we have calculated transfer chemical potentials from water into aqueous methanol for a variety of cationic and anionic complexes of cobalt(III) and chromium(III), using the assumption _m(Ph₄As⁺) + _m(BPh ₄ ^– ). The established trends are discussed in terms of electrostatic factors and of the hydrophilicity or hydrophobicity of the ligands present. The effects of single ion assumptions on conclusions of initial state-transition state analyses of solvent effects on reactivity are assessed with particular reference to aquation of thetrans-[Co(en)₂Cl₂]⁺ andtrans-[Co(py)₄Cl₂]⁺ cations.On leave from the Faculty of Science, Sohag, Egypt.     

Solvatochromism and solvation of ternary iron-diimine-cyanide complexes

Summary The solvatochromic behaviour of several complexes [Fe(LL)₂(CN)₂] with LL=Schiff base diimine has been established in a series of non-aqueous solvents, as has that of two analogues containing diazabutadiene ligands. Transfer chemical potentials have been derived from appropriate solubility measurements for several iron(II)-and iron(III)-diimine-cyanide complexes into aqueous methanol, and for [Fe(bipy)₂(CN)₂] into several binary aqueous solvent series. The usefulness of solvatochromic shifts and transfer chemical potentials as indicators of selective solvation is discussed. Kinetics of oxidation of catechol and of 4-t-butyl catechol by [Fe(bipy)(CN)₄]^– in aqueous solution are described.     

Regiospecific carboncarbon bond formation by oxidative coupling of η1-allyl or η1-propargyl ligands of organoiron complexes

Novel and regiospecific coupling reactions of η⁵-C₅H₅(CO)₂Fe(η¹-allyl) and (η⁵-C₅H₅(CO)₂Fe(η¹-propargyl) complexes due to oxidation by silver hexafluorophosphate are reported. The mono- and bi-nuclear products contain (substituted) hexadiene and hexatetraene ligands while variable amounts of protonation products are also formed.     

Cationic complexes of Eu(III) and Sr(II) with diphosphine dioxides in organic extracts

IR spectroscopy was used to study the structure and composition of Eu(III) and Sr(II) complexes formed by cation-exchange extraction of these metals from their aqueous nitrate solutions with dichlorethane solutions of mixtures of chlorinated cobalt(III) dicarbollide (CCD) as a superacid with diphenyldiphosphine dioxides containing a methyl (Me-DPDO), ethyl (Et-DPDO), or polyoxyethylene bridge between two phosphorus atoms of phosphine oxide groups. At molar ratios DPDO/CCD ≤ 1, [Eu(H₂O)_nL₄]³⁺ complexes are formed in organic phases, whereas with an excess of DPDO relative to CCD, Eu(NO₃)L ₄ ²⁺ complexes are formed, where L = Me-or Et-DPDO. Polyoxyethylenediphosphine dioxide forms anhydrous complexes of composition Eu:L = 1:1 and 1:2 with Eu(III) and outer-spheric complexes of composition Sr:L = 1:1 and 1:2 with Sr(II), where the organic ligand molecules envelop the hydrated Sr(H₂O) _n ²⁺ cation. The peculiarities of extraction of the complexes are explained based on data about their composition and structure.     

Reactivity trends of cobalt(III) complexes towards various amino acids based on the properties of the amino acid alkyl chains

The reactivity of the cobalt(III) complexes dichlorido[tris(2‐aminoethyl)amine]cobalt(III) chloride, [CoCl₂(tren)]Cl, and dichlorido(triethylenetetramine)cobalt(III) chloride, [CoCl₂(trien)]Cl, towards different amino acids (l ‐proline, l ‐asparagine, l ‐histidine and l ‐aspartic acid) was explored in detail. This study presents the crystal structures of three amino acidate cobalt(III) complexes, namely, (l ‐prolinato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) diiodide monohydrate, [Co(C₅H₈NO₂)(C₆H₁₈N₄)]I₂·H₂O, I , (l ‐asparaginato‐κ²N,O)[tris(2‐aminoethyl)amine‐κ⁴N,N′,N′′,N′′′]cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), II , and (l ‐prolinato‐κ²N,O)(triethylenetetramine‐κ⁴N,N′,N′′,N′′′)cobalt(III) chloride perchlorate, [Co(C₄H₇N₂O₃)(C₆H₁₈N₄)](Cl)(ClO₄), V . The syntheses of the complexes were followed by characterization using UV–Vis spectroscopy of the reaction mixtures and the initial rates of reaction were obtained by calculating the slopes of absorbance versus time plots. The initial rates suggest a stronger reactivity and hence greater affinity of the cobalt(III) complexes towards basic amino acids. The biocompatibility of the complexes was also assessed by evaluating the cytotoxicity of the complexes on cultured normal human fibroblast cells (WS1) in vitro. The compounds were found to be nontoxic after 24 h of incubation at concentrations up to 25 mM.     

Structure,solvatochromism, and solvation of trans-[CoIII(cyclam)(NCS)2](NCS) and the structure of [CoII(Me4cyclam) (NCS)]2[Co(NCS)4]MeOH

The structures of trans-[CoIII(cyclam)(NCS)2](NCS) and of [CoII(Me4cyclam)(NCS)]2[Co(NCS)4]·MeOH have been established by X-ray diffraction methods. The solvatochromic behavior of the trans-[Co(cyclam)(NCS)2]+ cation in several binary aqueous solvent mixtures is reported. Transfer chemical potentials for this complex from H2O into MeOH-H2O mixtures have been established from solubility measurements on its thiocyanate salt. The solvatochromic behavior of this cation is discussed in the context of other solvatochromic inorganic complexes; its transfer chemical potentials are discussed in relation to those of other cobalt(III) complexes.     

Direct 1H, 13C, and 15N NMR Study of Lanthanum(III), Thulium(III), and Ytterbium(III) Complex Formation with Nitrate and Isothiocyanate

An ¹H, ¹³C, and ¹⁵N NMR study has been completed for the complexes of La(III), Tm(III), and Yb(III) with nitrate and isothiocyanate in aqueous solvent mixtures. Signals for four complexes are observed for both the Tm³⁺–NO₃ ^– and Yb³⁺–NO₃ ^– solutions, with the species identified as the mono-, di-, tetra-, and either the penta - or hexanitrato. These results are consistent with those determined for the nitrate complexes of the Ce(III)–Eu(III) metal ions. The chemical shifts for the Tm(III) and Yb(III) nitrate complexes indicate a pseudocontact binding mechanism prevails. The complexes of diamagnetic La(III) with NO₃ ^– produce three signals in the ¹⁵NO₃ ^– spectra, with assignments paralleling those observed with the paramagnetic lanthanides. Three complexes are formed in the La³⁺–NCS^– solutions, with signals assigned to the mono-, di-, and triisothiocyanato species.     

Uncharged encapsulated iron(II) complexes: transfer chemical potentials and solvation in water-methanol and water-t-butanol mixtures

Summary Transfer chemical potentials have been determined from measured solubilities for four uncharged encapsulated iron(II) complexes containing three diimine ligating moieties and O₃BOBu-n and O₃BF capping groups, in H₂O–MeOH andt-BuOH–H₂O solvent mixtures, The trends in transfer chemical potentials are discussed in terms of the natures of the encapsulating ligands, and are compared with those for a selection of other iron(II)-diimine complexes.     

Electrochemical reduction of cobalt and nickel complexes with ligands stabilizing metal in low oxidation state

Electrochemical reduction of cobalt(ii) complexes containing -acceptor ligands (L = bpy, Ph₂Ppy) proceeds through three consecutive reversible steps: one-electron transfer to form a more stable Co^IL complex, transfer of two electrons at more negative potentials to form an anionic [NiL]^– complex, and reduction of the ligand to the radical anion. The stability of the cobalt complexes with different ligands decreases in the series Ph₂Ppy > Ph₃P > bpy.     

Synthesis and Mossbauer Spectra Studies of Mono-Binuclear Iron(III) Complexes with a Quinquedentate Ligand Derived from Saucylaldehyeds and Diethylenetriamine

Mono- and bi-nuclear iron(III) complexes of general formula [FeXL] and [LFe-Y-FeL](Bph₄)₂ have been prepared, and their spin state of iron atom in the complexes has been studied by means of the temperature dependence of the Mössbauer spectra, electronic spectra and magnetic measurement, where X is a mono- dentate ligand such as Cl-, NCS-, NCO-, N3-, pyridine and L denotes a quinquedentate Schiff base derived from salicylaldehyde and diethylenetriamine, and Y denotes bridged ligand such as pyrazine(pyr), 4,4′-bipyridine(bpy) and 4,4′-vinylenebipyridine(vibpy). On the basis of the Mössbauer and magnetic data, it was concluded that these complexes were all the high-spin (S = 5/2) slate. The effect of gamma ray irradiation for these complexes has been discussed.     

Uncharged Co(lll) Complexes: Transfer Chemical Potentials and Base Hydrolysis in Water-Methanol Mixtures

Solubilities are reported for three Co(III) complexes of 2-aminophenol, 2-amino-4-nitrophenol and 6-amino-2,4-dimethylphenol. Transfer chemical potentials have been derived from appropriate solubility measurements in aqueous methanol. The trends in transfer chemical potentials are discussed in terms of the nature of the coordinated ligands and are compared with those for selected of other inorganic Co(III) complex ions. The kinetics of base hydrolysis of Co(III) complexes in aqueous methanol solutions are described and the change in the activation barrier δ_mΔG^≠ is determined. Solvent effects on reactivity trends are analysed into initial state and transition state components. The small decrease in the rate constant, with increasing proportion of methanol, is ascribed to a greater effect of solvent on the initial state.     

Kinetics of Reduction of Some Surfactant-Cobalt(III) Complexes by Iron(II)

The electron transfer kinetics of the reaction between the surfactant-cobalt(III) complex ions, cis-[Co(en)₂(C₁₂H₂₅NH₂)₂]³⁺, cis-α-[Co(trien)(C₁₂H₂₅NH₂)₂]³⁺(en:ethylenediamine, trien:triethylenetetramine, C₁₂H₂₅NH₂ : dodecylamine) by iron(II) in aqueous solution was studied at 298, 303, 308 K by spectrophotometry method under pseudo-first-order conditions using an excess of the reductant in self-micelles formed by the oxidant, cobalt(III) complex molecules, themselves. The rate constant of the electron transfer reaction depends on the initial concentration of the surfactant cobalt(III) complexes. ΔS^# also varies with initial concentration of the surfactant cobalt(III) complexes. By assuming outer-sphere mechanism, the results have been explained based on the presence of aggregated structures containing cobalt(III) complexes at the surface of the self-micelles formed by the surfactant cobalt(III) complexes in the reaction medium. The rate constant of each complex increases with initial concentration of one of the reactants surfactant-cobalt(III) complex, which shows that self micelles formed by surfactant-cobalt(III) complex itself has much influence on these reactions. The electron transfer reaction of the surfactant-cobalt(III) complexes was also carried out in a medium of various concentrations of β-cyclodextrin. β-cyclodextrin retarded the rate of the reaction.     

Mixed-ligand cyanide cobalt(III) complexes with 1,2-cyclohexanediaminetetraacetic acid: Synthesis and photochemical properties

[Co(CN)₂(H₃Cdta)] · 2H₂O (I) and Na₂[Co(CN)(Cdta)] · 3H₂O (II) (Cdta⁴⁻ is the 1,2-cyclohexanediaminetetraacetate) were synthesized. In I, the two cyanide ions and the Cdta nitrogen atoms are located in the equatorial plane, the carboxyl groups connected to different N atoms are in axial positions; in addition one of them, like two other uncoordinated carboxyl groups, is protonated. In II, Cdta is a pentadentate ligand coordinated in the cis-equatorial mode. UV excitation of the dicyano complexes at the ligand-to-metal charge transfer band gives organic derivatives of cobalt(III) stable enough for chromatographic isolation. Photolysis of II in neutral medium gives aqua(cyclohexanediaminetriacetato)cobalt (III) complexes as the final products.     

Synthesis of Co(III) molybdoheteropolyanions using carbonato-ammine Co(III) complexes as starting materials

The preparation of two cobalt(III) molybdoheteropolyanions, [CoMo₆O₂₄H₆]³⁻ and [Co₂Mo₁₀O₃₈H₄]⁶⁻, was systematically studied using some carbonato-ammine cobalt(III) complexes as starting materials. The selectivity and yields of products were significantly influenced by the number of ammine ligands and the charge on the complexes.     

A new binucleating ligand incorporating four oxime groups and its copper(II), manganese(II) and cobalt(III) complexes

A new binucleating ligand incorporating four oxime groups, butane-2,3-dione O-[4-aminooxy-2,3-bis-(2-hydroxyimino-1-methyl-propylideneaminooxymethyl)-but-2-enyl]-dioxime, (H₄mto), has been synthesized and its dinuclear cobalt(III), copper(II), and homo- and hetero-tetranuclear copper(II)–manganese(II) complexes have been prepared and characterized by ¹H- and ¹³C-n.m.r., i.r., magnetic moments and mass spectral studies. Elemental analyses, stoichiometric and spectroscopic data indicate that the metal ions in the complexes are coordinated to the oxime nitrogen atoms (C=N) and the data support the proposed structure for H₄mto and its complexes. Moreover, dinuclear cobalt(III) and copper(II) complexes of H₄mto have a 2:1 metal:ligand ratio.     

Kinetic,solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Complexes of Fe^II with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H₂O and in MeOH–H₂O mixtures. Kinetics of acid catalysed aquation of Fe^II–monoxime complexes follow a rate law with k_obs = k₂[H⁺] + k₃[H⁺]², while kinetics of acid dissociation and base hydrolysis of the Fe^II–dioxime complex follow rate laws with k_obs = k₂[H⁺] and k_obs = k₂[OH⁻]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of Fe^II–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace Fe^II in acidic and neutral media, in water and in aqueous alcohols.     

Sedimentation potential of complexes of nitroamminecobalt(III) in aqueous solution at 25°C

Sedimentation potentials (SP) were measured for a series of nitroamminecobalt(III) chlorides in aqueous solution. The magnitudes of the sedimentation potentials varied with the number of NO ₂ ^– ligands in the complexes and a definite positive signal was observed for a neutral complex [Co(NO₂)₃(NH₃)₃]⁰. The division of the partial molar volumes of nitroamminecobalt(III) complexes based on the observed SP values resulted in comparable values of the partial molar volume for the Cl^– ion, suggesting no appreciable hydrolysis nor ionic association occur for these nitroammine-cobalt(III) complexes.