Inner-sphere oxidation of ternary nitrilotriacetatocobalt(II) complexes involving oxalate and phthalate by periodate

The oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ and [Co^II(nta)(ph)(H₂O)₂]³⁻ (nta = nitrilotriacetate, ox = oxalic acid and ph = phthalic acid) by periodate have been studied kinetically in aqueous solution over 20–40 °C and a variety of pH ranges. The rate of oxidation of [Co^II(nta)(ox)(H₂O)₂]³⁻ by periodate, obeys the following equation: d[Co^III]/dt = [Co^II(nta)(ox)(H₂O)₂³⁻][H₅IO₆] {k ₄ K ₅ + (k ₅ K ₆ K ₂/[H⁺]} while the reaction of [Co^II(nta)(ph)(H₂O)₂]³⁻ with periodate in aqueous acidic medium obeys the following rate law: d[Co^III]/dt = k ₆ K ₈[Co^II]_T [I^VII]_T/{1 + [H⁺]/K ₇ + K ₈[I^VII] _T }. Initial cobalt(III) products were formed and slowly converted to final products, fitting an inner-sphere mechanism. Thermodynamic activation parameters have been calculated. A common mechanism for the oxidation of ternary nitrilotriacetatocobalt(II) complexes by periodate is proposed and supported by an excellent isokinetic relationship between ΔH* and ΔS* values for these reactions.     

Kinetics and Mechanism of Oxidation of Chromium(III)‐guanosine 5‐Monophosphate Complex by Periodate

The kinetics of oxidation of the chromium(III)‐guanosine 5‐monophosphate complex, [Cr^III(L)(H₂O)₄]³⁺(L = guanosine 5‐monophosphate) by periodate in aqueous solution to Cr^VI have been studied spectrophotometrically over the 25–45 °C range. The reaction is first order with respect to both [IO₄^?] and [Cr^III], and increases with pH over the 2.38–3.68 range. Thermodynamic activation parameters have been calculated. It is proposed that electron transfer proceeds through an inner‐sphere mechanism via coordination of IO₄^? to chromium(III).     

Kinetic studies on the oxidation of [N-phenylethylethylenediaminetriacetate]chromium(III) by periodate

Summary Kinetic studies of the oxidation of [Cr^IIIZ(H₂O)](Z=N-phenylethylethylenediaminetriacetate) by periodate ion, to produce chromium(VI), were carried out in aqueous solutions. The reaction is first order with respect to both total chromium(III) and total periodate, and the rate is inversely dependent upon H⁺ in the 5.43–7.02 pH range. The reaction may follow a two-step inner-sphere electron transfer mechanism. The activated parameters are reported. Steric effects of the phenyl ring account for the smaller electron-transfer rate constants for [Cr^IIIZ(H₂O)] compared to [Cr^III(TOH)(H₂O)], (TOH=N-(2-hydroxyethyl)ethylenediaminetriacetate).     

Kinetics and mechanism of the oxidation of nitrilotris(methylenephosphonato)chromium(III) by periodate

The kinetics of oxidation of nitrilotris(methylenephosphonato)chromium(III), Cr^IIINTMP, by periodate to yield Cr^VI have been studied spectrophotometrically over the 5.80–6.85 pH range at 22–33 °C. The reaction rate, which is first-order with respect to [Cr^IIINTMP] and [IO^– ₄] and inversely dependent on [H⁺], obeys the rate law:-d[Cr^IIINTMP/dt=kKK_h[IO^- ₄] [Cr^III]_T/K_h+ [H⁺] +KK_h[IO^- ₄] The values of the intramolecular electron transfer, k, and the formation constant of the intermediate complex, K, were determined at various temperatures. The hydrolysis constant for Cr^IIINTMP, K _h , was determined spectrophotometrically and is in agreement with the value estimated from the kinetic data. The activation parameters were calculated from the temperature dependence of the specific rate constants. A mechanism is proposed in which the hydroxo complex, [CrHNTMP(OH)]^3–, is the reactive species. The results support a mechanism where intramolecular electron transfer is the rate-determining step.     

Inner-sphere oxidation of ternary iminodiacetatochromium(III) complexes involving DL-valine and L-arginine as secondary ligands. Isokinetic relationship for the oxidation of ternary iminodiacetato-chromium(III) complexes by periodate

Background  

In this paper, the kinetics of oxidation of [Cr^III(HIDA)(Val)(H₂O)₂]⁺ and [Cr^III(HIDA)(Arg)(H₂O)₂]⁺ (HIDA = iminodiacetic acid, Val = DL-valine and Arg = L-arginine) were studied. The choice of ternary complexes was attributed to two considerations. Firstly, in order to study the effect of the secondary ligands DL-valine and L-arginine on the stability of binary complex [Cr^III(HIDA)(IDA)(H₂O)] towards oxidation. Secondly, transition metal ternary complexes have received particular focus and have been employed in mapping protein surfaces as probes for biological redox centers and in protein capture for both purification and study.     

A kinetic investigation of the oxidation of <Emphasis Type="SmallCaps">dl</Emphasis>-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion

Kinetics of oxidation of dl-pipecolinate by bis(hydrogenperiodato)argentate(III) complex anion, [Ag(HIO₆)₂]⁵⁻, has been studied in aqueous alkaline medium in the temperature range of 25–40 °C. The oxidation kinetics is first order in the silver(III) and pipecolinate concentrations. The observed second-order rate constant, decreasing with increasing [periodate] is virtually independent of [OH⁻]. α-Aminoadipate as the major oxidation product of pipecolinate has been identified by chromatographic analysis. A reaction mechanism is proposed that involves a pre-equilibrium between [Ag(HIO₆)₂]⁵⁻ and [Ag(HIO₆)(H₂O)(OH)]²⁻, a mono-periodate coordinated silver(III) complex. Both Ag(III) complexes are reduced in parallel by pipecolinate in rate-determining steps (described by k ₁ for the former Ag(III) species and k ₂ for the latter). The determined rate constants and their associated activation parameters are k ₁ (25 °C) = 0.40 ± 0.02 M⁻¹ s⁻¹, ∆H ₁^≠ = 53 ± 2 kJ mol⁻¹, ∆S ₁^≠ = −74 ± 5 J K⁻¹ mol⁻¹ and k ₂ (25 °C) = 0.64 ± 0.02 M⁻¹ s⁻¹, ∆H ₂^≠ = 41 ± 2 kJ mol⁻¹, ∆S ₂^≠ = −110 ± 5 J K⁻¹ mol⁻¹. The time-resolved spectra, a positive dependence of the rate constants on ionic strength of the reaction medium, and the consistency of pre-equilibrium constants derived from different reaction systems support the proposed reaction mechanism.     

Kinetics of oxidation of a 2-aminomethylpyridinechromium(III) complex by periodate

The oxidation kinetics of the 2-aminomethylpyridineCr^III complex with periodate in aqueous solution were studied and found to obey the rate law:Rate = [Cr^III]_T [IO₄ ^-]{k¹K² + k₂ K₁ K₃/[H⁺]}/{1+K₁/[H⁺] + k₂[IO₄ ^-]+K₁K₃/[H⁺][IO₄ ^-]} where K ₁, K ₂ and K ₃ are the deprotonation of [Cr(L)₂(H₂O)]³⁺ and pre-equilibrium formation constants for [(L)₂—Cr—OIO₃]²⁺ and [(L)₂—Cr—OH—OIO₃]⁺ precursor complexes respectively. An inner-sphere mechanism was proposed. The effect of Cu²⁺ on the oxidation rate was studied over the (1.0–9.0) × 10⁻⁵ mol dm⁻³ range. The reaction rate was found to be inversely proportional to the Cu²⁺ concentration over the range studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

Mixed-ligand chromium(III)-oxalate-pirydinedicarboxylate complexes: potential biochromium sources: kinetic studies in NaOH solutions and effect on 3T3 fibroblasts proliferation

Base hydrolysis of [Cr(ox)₂(pda)]³⁻ (where pda is N,O-bonded 2,4- and 2,5- pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The main reaction path proceeds through [Cr(ox)(pda)(OH)₂]³⁻ and [Cr(pda)(OH)₄]³⁻ complexes. The kinetics of the first oxalate dissociation was studied spectrophotometrically, within the lower energy d–d band region, at 0.4–1.0 M NaOH. The character of spectroscopic changes was consistent with a consecutive reaction model, where the chelate-ring opening and the one-end bonded oxalato liberation are the first and the second reaction stages. The pseudo-first order rate constants (k _obs0 and k _obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)₃]³⁻ were studied. The calculated rate constants were independent of [OH ⁻ ]. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined. Effect of the [Cr(ox)₂(pda)]³⁻ and [Cr(2,4-pda)₃]³⁻ complexes on 3T3 fibroblasts proliferation was studied. The results manifested low cytotoxicity of these complexes, which makes them promising candidates for dietary supplements.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid with the Amino Acids Glycine,Proline, <Emphasis Type="Italic">α</Emphasis>-Alanine and <Emphasis Type="Italic">β</Emphasis>-Alanine Studied in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this paper we present speciation results for the ternary vanadium(III)–dipicolinic acid (H₂dipic) systems with the amino acids glycine (Hgly), proline (Hpro), α-alanine (Hα-ala), and β-alanine (Hβ-ala), obtained by means of electromotive forces measurements emf(H) using 3.0 mol⋅dm⁻³ KCl as the ionic medium and a temperature of 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid base reactions of the ligands, which were kept fixed during the analysis. In the vanadium(III)–dipicolinic acid–glycine system, formation of the ternary [V(Hdipic)(Hgly)]²⁺, [V(dipic)(Hgly)]⁺, [V(dipic)(gly)], [V(dipic)(gly)(OH)]⁻ and [V(dipic)(gly)(OH)₂]²⁻ was observed; in the case of the vanadium(III)–dipicolinic acid–proline system the ternary complexes [V(Hdipic) (Hpro)]²⁺, [V(dipic)(Hpro)]⁺, [V(dipic)(pro)] and [V(dipic)(pro)(OH)]⁻ were observed; in the vanadium(III)–picolinic acid–α-alanine were observed [V(Hdipic)(Hα-ala)]²⁺, [V(dipic) (Hα-ala)]⁺, [V(dipic)(αala)], [V(dipic)(α-ala)(OH)]⁻ and [V(dipic)(α-ala)(OH)₂]²⁻; and in the vanadium(III)–dipicolinic acid–β-ala system the complexes [V(dipic) (Hβ-ala)]⁺, [V(dipic)(β-ala)], [V(dipic)(β-ala)(OH)]⁻ and [V(dipic)(β-ala)(OH)₂]²⁻ were observed. Their respective stability constants were determined, and we evaluated values of Δlog ₁₀ K″ in order to understand the relative stability of the ternary complexes compared to the corresponding binary ones. The species distribution diagrams are briefly discussed as a function of pH.     

Speciation of the Ternary Complexes of Vanadium(III)–Dipicolinic Acid and the Amino Acids Cysteine,Histidine, Aspartic and Glutamic Acids in 3.0 mol⋅dm<Superscript>−3</Superscript> KCl at 25 °C

In this work we present results for the speciation of the ternary complexes formed in the aqueous vanadium(III)–dipicolinic acid and the amino acids cysteine (H₂cys), histidine (Hhis), aspartic acid (H₂asp) and glutamic acid (H₂glu) systems (25 °C; 3.0 mol⋅dm⁻³ KCl as ionic medium), determined by means of potentiometric measurements. The potentiometric data were analyzed with the least-squares program LETAGROP, taking into account the hydrolysis of vanadium(III), the acid-base reactions of the ligands, and the binary complexes formed. Under the experimental conditions (vanadium(III) concentration = 2–3 mmol⋅dm⁻³ and vanadium(III): dipicolinic acid: amino acid molar ratio 1:1:1, 1:1:2 and 1:2:1), the following species [V(dipic)(H₂asp)]⁺, [V(dipic)(Hasp)], [V(dipic)(asp)]⁻, [V(dipic)(asp)(OH)]²⁻, and [V(dipic)(asp)(OH)₂]³⁻ were found in the vanadium(III)–dipicolinic acid–aspartic acid system. In the vanadium(III)–dipicolinic acid–glutamic acid system [V(Hdipic)(H₂glu)]²⁺, [V(dipic)(H₂glu)]⁺, [V(dipic)(Hglu)], [V(dipic)(Hglu)(OH)]⁻, and [V(dipic)(Hglu)(OH)₂]²⁻ were observed. In the vanadium(III)–dipicolinic acid–cysteine system the complexes [V(dipic)(H₂cys)]⁺, [V(dipic)(Hcys)], [V(dipic)(cys)]⁻, and [V(dipic)(cys)(OH)]²⁻ were present. And finally, in the vanadium(III)–dipicolinic acid–histidine system the complexes [V(Hdipic)(Hhis)]²⁺, [V(dipic) (Hhis)]⁺[\mathrm{V}(\mathrm{dipic}) (\mathrm{Hhis})]^{+}, [V(dipic)(his)], [V(dipic)(his)(OH)]⁻, and [V(dipic)(his)(OH)₂]²⁻ were observed. The stability constants of these complexes were determined. The species distribution diagrams as a function of pH are briefly discussed.     

Kinetics and mechanism of oxidation of <Emphasis Type="Italic">N</Emphasis>-methylethylamine by bis(hydrogenperiodato)argentate(III) complex anion

Oxidation of N-methylethylamine by bis(hydrogenperiodato)argentate(III) ([Ag(HIO₆)₂]⁵⁻) in alkaline medium results in demethylation, giving rise to formaldehyde and ethylamine as the oxidation products. The oxidation kinetics has been followed spectrophotometrically in the temperature range of 20.0–35.0 °C, and shows an overall second-order character: being first-order with respect to both Ag(III) and N-methylethylamine. The observed second-order rate constants k′ increase with increasing [OH⁻] of the reaction medium, but decrease with increasing the total concentration of periodate. An empirical rate expression for k′ has been derived as: k′ = (k _a + k _b[OH⁻])K ₁/{f([OH⁻])[IO₄ ⁻]_tot + K ₁}, where k _a and k _b are rate parameters, and K ₁ is an equilibrium constant. These parameters have been evaluated at all the temperatures studied, enabling calculation of activation parameters. A reaction mechanism is suggested to involve two pre-equilibria, leading to formation of an intermediate Ag(III) complex, namely [Ag(HIO₆)(OH)(MeNHEt)]²⁻. In the subsequent rate-determining steps, this intermediate undergoes inner-sphere electron transfer from the coordinated amine to the metal center via two distinct routes, one of which is spontaneous while the other is mediated by a hydroxide ion.     

Kinetic study of the promazine oxidation to promazine 5-oxide by trisoxalatocobaltate(III) in basic aqueous media

The kinetics of the oxidation of promazine by trisoxalatocobaltate(III) were studied in the presence of a large excess of the cobalt(III) in tris buffer solution using u.v.–vis spectroscopy ([Co^III] = (0.6 − 2) × 10⁻³ M, [ptz] = 6 × 10⁻⁵ M, pH = 6.6–7.8, I = 0.1 M (NaCl), T = 288−308 K, l = 1 cm). The reaction proceeds via two consecutive reversible steps. In the first step, the reaction leads to formation of cobalt(II) species and a stable cationic radical. In the second step, cobalt(III) is reduced to cobalt(II) ion and a promazine radical is oxidized to the promazine 5-oxide. Linear dependences of the pseudo-first-order rate constants (k ₁ and k ₂) on [Co^III] with a non-zero intercept were established for both redox processes. Rates of reactions decreased with increasing concentration of the H⁺ ion indicating that the promazine and its radical exist in equilibrium with their deprotonated forms, which are reactive reducing species. The activation parameters for reactions studied were as follows: ΔH^≠ = 44 ± 1 kJ mol⁻¹, ΔS^≠ = −100 ± 4 JK⁻¹ mol⁻¹ for the first step and ΔH^≠ = 25 ± 1 kJ mol⁻¹, ΔS^≠ = −169 ± 4 J K⁻¹ mol⁻¹ for the second step, respectively. Mechanistic consequences of all the results are discussed.     

Kinetic studies on H+-catalysed aquation of some chromium(III)-oxalato-amino acid complexes

The following chromium(III) complexes with serine (Ser) and aspartic acid (Asp) were obtained and characterized in solution: [Cr(ox)₂(Aa)]²⁻ (where Aa = Ser or Asp), [Cr(AspH₋₁)₂]⁻ and [Cr(ox)(Ser)₂]⁻. In acidic solutions, [Cr(ox)₂(Aa)]²⁻ undergoes acid-catalysed aquation to cis-[Cr(ox)₂(H₂O)₂]⁻ and the appropriate amino acid. [Cr(ox)(Ser)₂]⁻ undergoes consecutive acid-catalysed Ser liberation to give [Cr(ox)(H₂O)₄]⁺, and the [Cr(Asp)₂]⁻ ion is converted into [Cr(Asp)(H₂O)₄]²⁺. Kinetics of these reactions were studied under isolation conditions. The determined rate expressions for all the reactions are of the form: k _obs = a + b[H⁺]. Reaction mechanisms are proposed, and the meaning of the determined parameters has been established. Evidence for the formation of an intermediate with O-monodentate amino acid is given. The effect of the R-substituent at the α-carbon atom of the amino acid on the complex reactivity is discussed.     

Manganese(II) catalyzed periodate oxidation of a ternary dipicolinatochromium(III) complex with iminodiacetate as co-ligand: mechanistic and kinetic study

The kinetics and mechanism of the oxidation of [Cr^III(DPA)(IDA)(H₂O)]^? (DPA = dipicolinate and IDA = iminodiacetate) by periodate in the presence of Mn(II) as a catalyst have been investigated. The rate of the reaction increases with increasing pH, due to the deprotonation equilibria of the complex. Addition of Mn(II) in the concentration range of (2.5–10) × 10^?6 mol dm^?3 enhanced the reaction rate; the reaction is first order with respect to both [IO₄ ^?] and the Cr complex, and obeys the following rate law: \( {\text{Rate}} = [ {\text{Cr}}^{\text{III}} ({\text{DPA}})({\text{IDA}})({\text{H}}_{2} {\text{O}})^{ - } ][{\text{Mn}}^{\text{III}} ]\{ (k_{7} + K_{1} k_{8} /[{\text{H}}^{ + } ]) + [{\text{I}}^{\text{VII}} ]((k_{9} k_{11} /k_{ - 9} + k_{11} ) + (K_{1} k_{10} k_{12} )/(k_{ - 10} + k_{12} )[{\text{H}}^{ + } ])\} . \) Catalysis by Mn(II) is believed to be due to initial oxidation of Mn(II) to Mn(III), which acts as the oxidizing agent. It is proposed that electron transfer proceeds through an inner-sphere mechanism via coordination of IO₄ ^? to Cr(III). Thermodynamic activation parameters were calculated using the transition state theory equation.     

Self-assembly of metal(II) tetraaza macrocyclic complexes with cyclobutane-1-carboxylic acid-1-carboxylate ligand linked by hydrogen bond

The reaction of [M(L)]Cl₂ · 2H₂O (M = Ni²⁺ and Cu²⁺, L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^1.18,0^7.12]docosane) with 1,1-cyclobutanedicarboxylic acid (H₂-cbdc) generates 1D and 2D hydrogen-bonded infinite chains [Ni(L)(H-cbdc⁻)₂] (1) and [Cu(L)(H-cbdc⁻)₂] (2). (H-cbdc⁻ = cyclobutane-1-carboxylic acid-1-carboxylate). These complexes have been characterized by X-ray crystallography, spectroscopy, and cyclic voltammetry. The crystal structure of 1 shows a distorted octahedral coordination geometry around the nickel(II) ion, with four secondary amines and two oxygen atoms of the H-cbdc⁻ ligand at the trans position. In 2, the coordination environment around the central copper(II) ion shows a Jahn–Teller distorted octahedron with four Cu–N bonds and two long Cu–O distances. The cyclic voltammogram of the complexes undergoes two one-electron waves corresponding to M^II/M^III and M^II/M^I processes. The electronic spectra and electrochemical behavior of the complexes are significantly affected by the nature of the axial H-cbdc⁻ ligand.     

Heterometallic compounds with the binuclear complex anion [Cr<Subscript>2</Subscript>(OH)(Ac)(Nta)<Subscript>2</Subscript>]<Superscript>2−</Superscript>: Synthesis and structure

Heterometallic compounds BaCr₂(OH)(Ac)(Nta)₂ · 4H₂O (I) and [Fe(L)₃][Cr₂(OH)(Ac)(Nta)₂] · nH₂O (L is Bipy (II) and Phen (III); Bipy is, αα′-bipyridine, Phen is o,o′-phenanthroline, Ac⁻ is acetate ion, Nta is nitrilotriacetate ion; n = 8 (II) and 6.25 (III)) are synthesized. According to the X-ray diffraction data, compounds II and III have ionic structures built of the isolated complex cations [Fe(L)₃]²⁺, binuclear complex anions [Cr₂(OH)(Ac)(Nta)₂]²⁻, and crystallization water molecules. The magnetic properties of compounds II and III in the interval from 2 to 300 K confirm assumptions on the diamagnetic character of [Fe(L)₃]²⁺ and indicate the antiferromagnetic interaction between the chromium atoms in the dimeric fragment [Cr₂(OH)(Ac)(Nta)₂]²⁻.     

N,N′-Bis(aryl)pyridine-2,6-dicarboxamide complexes of ruthenium: Synthesis,structure and redox properties

Reaction of five N,N′-bis(aryl)pyridine-2,6-dicarboxamides (H₂L-R, where H₂ denotes the two acidic protons and R (R = OCH₃, CH₃, H, Cl and NO₂) the para substituent in the aryl fragment) with [Ru(trpy)Cl₃](trpy = 2,2′,2″-terpyridine) in refluxing ethanol in the presence of a base (NEt₃) affords a group of complexes of the type [Ru^II(trpy)(L-R)], each of which contains an amide ligand coordinated to the metal center as a dianionic tridentate N,N,N-donor along with a terpyridine ligand. Structure of the [Ru^II(trpy)(L-Cl)] complex has been determined by X-ray crystallography. All the Ru(II) complexes are diamagnetic, and show characteristic ¹H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on the [Ru^II(trpy)(L-R)] complexes shows a Ru(II)–Ru(III) oxidation within 0.16–0.33 V versus SCE. An oxidation of the coordinated amide ligand is also observed within 0.94–1.33 V versus SCE and a reduction of coordinated terpyridine ligand within −1.10 to −1.15 V versus SCE. Constant potential coulometric oxidation of the [Ru^II(trpy)(L-R)] complexes produces the corresponding [Ru^III(trpy)(L-R)]⁺ complexes, which have been isolated as the perchlorate salts. Structure of the [Ru^III(trpy)(L-CH₃)]ClO₄ complex has been determined by X-ray crystallography. All the Ru(III) complexes are one-electron paramagnetic, and show anisotropic ESR spectra at 77 K and intense LMCT transitions in the visible region. A weak ligand-field band has also been shown by all the [Ru^III(trpy)(L-R)]ClO₄ complexes near 1600 nm.     

Metallosurfactants of Chromium(III) Coordination Complexes. Synthesis, Characterization and Determination of CMC Values

A number of mixed ligand chromium(III)–surfactant coordination complexes, of the type cis-[Cr(en)₂(A)X]²⁺ and cis-α-[Cr(trien)(A)X]²⁺ (A = Dodecyl or Cetylamine; X = F⁻, Cl⁻, Br⁻) were synthesized from the corresponding dihalogeno complexes by ligand substitution. These compounds form foam in aqueous solution when shaken. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for evaluation of the temperature-dependent critical micelle concentration (cmc) and the thermodynamics of micellization (Δ G_m⁰, Δ H_m⁰ and Δ S_m⁰).     

Kinetics and mechanism of base hydrolysis of chromium(III) complexes with oxalates and quinolinic acid

Base hydrolysis of [Cr(ox)₂(quin)]³⁻ (where quin²⁻ is N,O-bonded 2,3-pyridinedicarboxylic acid dianion) causes successive ligand dissociation and leads to a formation of a mixture of oligomeric chromium(III) species, known as chromates(III). The reaction proceeds through [Cr(ox)(quin)(OH)₂]³⁻ and [Cr(quin)(OH)₄]³⁻ formation. Dissociation of oxalato ligands is preceded by the opening of the Cr-quin chelate-ring at the Cr–N bond. The kinetics of the chelate-ring opening and the first oxalate dissociation were studied spectrophotometrically, within the lower energy d–d band region at 0.4–1.0 M NaOH. The pseudo-first-order rate constants (k _obs0 and k _obs1) were calculated using SPECFIT software for an A → B → C reaction pattern. Additionally, kinetics of base hydrolysis of [Cr(ox)(quin)(OH)₂]³⁻ and cis-[Cr(ox)₂(OH)₂]³⁻ were studied. The determined pseudo-first-order rate constants were independent of [OH⁻]. A mechanism is postulated that the reactive intermediate with the one-end bonded quin ligand, [Cr(ox)₂(O-quin)(OH)]⁴⁻, formed in the first reaction stage, subsequently undergoes oxalates substitution. Kinetic parameters for the chelate-ring opening and the first oxalate dissociation were determined.