Influence of solvent structure on the aquation of K‐chloro(diethylenetriamine)(ethylenediamine) cobalt(III) ion in water and mixed aqueous solvents

The aquation of K‐[Co(dien)(en)Cl]²⁺ was followed spectrophotometrically within the temperature range (40–60°C) in water, water–isopropyl alcohol, and water–tert‐butyl alcohol media of varying solvent composition up to 50 and 60 vol% of the organic solvent component respectively. The nonlinear plot of log k vs. D^?1_s was attributed to the differential solvation of the initial and transition states. The variation of ΔH^≠, ΔS^≠, and ΔG^≠ with the mole fraction of the organic component was analyzed and discussed. The isokinetic temperatures were found to be 330 and 317 K for water–isopropyl alcohol and water–tert‐butly alcohol mixtures respectively, indicating that the aquation reaction is entropy controlled. The application of free energy cycle at 25°C for the aquation reaction in both co‐solvents suggests that the transition state is more stable than the initial one. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 1–6, 2002     

Effects of solvent on the reactions of coordination complexes: Part 17. Kinetics and mechanism of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt (III) in methanol + water and dimethylsulphoxide + water media

The base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ? t°C ? 35.0 and I = 0.10 mol dm^?3 (ClO₄^?). The phenoxide species [(tetren)CoO₂CC₆H₄O]⁺ undergoes both OH^?-independent and OH^?-catalyzed hydrolysis via SN₁ICB and SN₁CB mechanism, respectively. The OH^?-independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH^?-catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, ΔH^≠ and ΔS^≠, with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in ΔH^≠ vs. ΔS^≠ plot accomodating all data for k₁ and k₂ paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory.     

Effects of solvents on the reactions of coordination complexes: Part 20. Kinetics and mechanism of base hydrolysis of (αβS) (Salicylato) (Tetraethylenepentamine) Cobalt(III) in aquo-organic solvent media

The kinetics of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine) cobalt(III) have been investigated in aquo-organic solvent media at 15.0 < t, °C < 40.0, and I = 0.10 mol dm (ClO₄^?) using propane-2-ol (?70% v/v), t-butanol (?60% v/v), acetone (?70% v/v), acetonitrile (?50% v/v), and ethylene glycol (?70% v/v) as cosolvents. Both the spontaneous and base-catalyzed hydrolysis of the phenoxide species [(tetren)CoO₂CC₆H₄O]⁺ were appreciably accelerated by the cosolvents PrⁱOH, Bu^tOH, Me₂CO, and MeCN. On the contrary the base hydroylsis (k₂) was retarded while spontaneous aquation (k₁) was accelerated to a small extent with increased EG content. Variation of log k₁ and log k (k = k₂ at I = 0) with mole fraction (_X0.S) or reciprocal of the relative permitivity (D_s^?1) of the media were nonlinear. The transfer free energy of the transition state relative to that of the initial state of the substrate for transfer of species from water to mixed solvents also varied nonlinearly with _X0.S, or D_s^?1 indicating solvent specificity. The activation parameters, ΔH^≠ and ΔS^≠ varied nonlinearly with solvent composition exhibiting extrema. The preferential solvation and solvent structural effects mediated the kinetics and energetics of the reaction. © 1995 John Wiley & Sons, Inc.     

Kinetics of the mercury(II)‐catalyzed substitution of coordinated cyanide ion in hexacyanoruthenate(II) by nitroso‐R‐salt

The kinetics and mechanism of Hg²⁺‐catalyzed substitution of cyanide ion in an octahedral hexacyanoruthenate(II) complex by nitroso‐R‐salt have been studied spectrophotometrically at 525 nm (λ_max of the purple‐red–colored complex). The reaction conditions were: temperature = 45.0 ± 0.1°C, pH = 7.00 ± 0.02, and ionic strength (I) = 0.1 M (KCl). The reaction exhibited a first‐order dependence on [nitroso‐R‐salt] and a variable order dependence on [Ru(CN)₆^4?]. The initial rates were obtained from slopes of absorbance versus time plots. The rate of reaction was found to initially increase linearly with [nitroso‐R‐salt], and finally decrease at [nitroso‐R‐salt] = 3.50 × 10^?4 M. The effects of variation of pH, ionic strength, concentration of catalyst, and temperature on the reaction rate were also studied and explained in detail. The values of k₂ and activation parameters for catalyzed reaction were found to be 7.68 × 10^?4 s^?1 and E_a = 49.56 ± 0.091 kJ mol^?1, ΔH^≠ = 46.91 ± 0.036 kJ mol^?1, ΔS^≠ = ?234.13 ± 1.12 J K^?1 mol^?1, respectively. These activation parameters along with other experimental observations supported the solvent assisted interchange dissociative (I_d) mechanism for the reaction. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 215–226, 2009     

Effects of solvent on the reactions of coordination complexes. part 24. kinetics of base hydrolysis of some (aminomonocarboxylato)(tetraethylene‐pentamine)cobalt(III) complexes in methanol+water media: The role of substrate hydrophobicity and solvent structure

The kinetics of base hydrolysis of some (aminomonocarboxylato)(tetraethylenepentamine)cobalt(III) complexes, [(tetren)CoO₂CR]²⁺ (R= NH₂CH₂, pyridine‐2 ,  NH₂CH₂CH₂,  NH₂CH(CH₃) (αβS isomer); R= NH₂CH(CH₃) (αβR isomer)), have been investigated in methanol–water media (0–80 vol % MeOH) at 15.0≤t°C≤40.0 (0.02 mol dm⁻³ NaOH). The second‐order rate constant at zero ionic strength, k₂°, increases nonlinearly with X_MeOH. The transfer free energy of the initial state and the transition state of the amido conjugate base ([Δ_tG (i)]_(s←w)) for the glycinato‐ and pyridine‐2–carboxylato complexes have been calculated using the solubility data of their picrate salts, pK _NH date of their N‐protonated forms, and the k₂° values in mixed solvent media. The kinetic solvent effects have been interpreted in terms of preferential solvation of the initial state, transition state, and the solvent structure. The activation enthalpies and entropies varied nonlinearly with X_MeOH displaying extrema, which is attributable to the solvent structural effects on these thermodynamic parameters. It is also evident that the mutation process, αβR→αβS isomer for the α‐alaninato complex, where this isomerisation refers to the arrangement of the tetren skeleton around the planar secondary NH is sensitive to the nature of the cosolvent molecules and solvent structure. The mutation process is generally more favorable for the five coordinate amido conjugate bases than the initial state. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 55–64, 1999     

ACE applied to the quantitative characterization of benzo‐18‐crown‐6‐ether binding with alkali metal ions in a methanol–water solvent system

ACE was applied to the quantitative evaluation of noncovalent binding interactions between benzo‐18‐crown‐6‐ether (B18C6) and several alkali metal ions, Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺, in a mixed binary solvent system, methanol–water (50/50 v/v). The apparent binding (stability) constants (K_b) of B18C6–alkali metal ion complexes in the hydro‐organic medium above were determined from the dependence of the effective electrophoretic mobility of B18C6 on the concentration of alkali metal ions in the BGE using a nonlinear regression analysis. Before regression analysis, the mobilities measured by ACE at ambient temperature and variable ionic strength of the BGE were corrected by a new procedure to the reference temperature, 25°C, and the constant ionic strength, 10 mM . In the 50% v/v methanol–water solvent system, like in pure methanol, B18C6 formed the strongest complex with potassium ion (log K_b=2.89±0.17), the weakest complex with cesium ion (log K_b=2.04±0.20), and no complexation was observed between B18C6 and the lithium ion. In the mixed methanol–water solvent system, the binding constants of the complexes above were found to be about two orders lower than in methanol and about one order higher than in water.     

Structures and Dynamic Solution Behavior of Cationic,Two‐Coordinate Gold(I)–π‐Allene Complexes

A family of seven cationic gold complexes that contain both an alkyl substituted π‐allene ligand and an electron‐rich, sterically hindered supporting ligand was isolated in >90 % yield and characterized by spectroscopy and, in three cases, by X‐ray crystallography. Solution‐phase and solid‐state analysis of these complexes established preferential binding of gold to the less substituted C?C bond of the allene and to the allene π face trans to the substituent on the uncomplexed allenyl C?C bond. Kinetic analysis of intermolecular allene exchange established two‐term rate laws of the form rate=k₁[complex]+k₂[complex][allene] consistent with allene‐independent and allene‐dependent exchange pathways with energy barriers of ΔG^≠₁=17.4–18.8 and ΔG^≠₂=15.2–17.6 kcal mol^?1, respectively. Variable temperature (VT) NMR analysis revealed fluxional behavior consistent with facile (ΔG^≠=8.9–11.4 kcal mol^?1) intramolecular exchange of the allene π faces through η¹‐allene transition states and/or intermediates that retain a staggered arrangement of the allene substituents. VT NMR/spin saturation transfer analysis of [{P(tBu)₂o‐binaphthyl}Au(η²‐4,5‐nonadiene) ]⁺SbF₆^? ( 5 ), which contains elements of chirality in both the phosphine and allene ligands, revealed no epimerization of the allene ligand below the threshold for intermolecular allene exchange (ΔG^≠_298K=17.4 kcal mol^?1), which ruled out the participation of a η¹‐allylic cation species in the low‐energy π‐face exchange process for this complex.     

Effect of the ionic strength on the redox reaction of dicyanobis(bipyridine)iron(III)‐iodide in binary and ternary solvent systems

The redox reaction between dicyanobis(bipyridine)iron(III) and iodide ion follows first‐order kinetics in 10% (v/v) tertiary butyl alcohol‐water. The reaction was found first and zero order in iodide and dicyanobis(bipyridine)iron(III), respectively, at 0.06 M ionic strength and 293 ± 1 K. The thermodynamic parameters of activation such as E_A (16.07 kJ mol^?1), A (1 × 10^?4 M s^?1), ΔH^# (13.6 kJ mol^?1), ΔS^# (?329.81 J K^?1 mol^?1), and ΔG^# (90.1 kJ mol^?1) were determined. The effect of the ionic strength on the rate constant leads to recognizing the stabilization or destabilization of the transition state complex that forms during the rate‐determining step of the reaction. The value of the zero‐order rate constant was decreased with increasing ionic strength that yielded a negative value of the slope in each binary and ternary solvent systems. This negative sign refers to the electron transfer between opposite charge carriers such as [Fe^III(bpy)₂(CN)₂]⁺ and I^? during the rate‐determining step. The destabilization of the transition state complex is surfaced by the increasing slope, that is, 5 < 10 < 15% (v/v) tertiary butyl alcohol‐water with a gradual decrease in the rate constant. However, its stability emerges by relatively small values of the slope in 17.5 < 25 ≤ 30% (v/v) tertiary butyl alcohol‐water and 8:2:90 < 6:4:90% (v/v) dioxane: tertiary butyl alcohol: water with reasonably fast rate of reaction.     

Kinetics of the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione with β‐pinene and 2‐carene: Temperature,high pressure,and solvent effects

The data on temperature, solvent, and high hydrostatic pressure influence on the rate of the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 1 ) with 2‐carene ( 2 ), and β‐pinene ( 4 ) have been obtained. Ene reactions 1 + 2 and 1 + 4 have high heat effects: ∆H_r‐n ( 1 + 2 ) −158.4, ∆H_r‐n( 1 + 4 ) −159.2 kJ mol⁻¹, 25°C, 1,2‐dichloroethane. The comparison of the activation volume (∆V^≠( 1 + 2 ) −29.9 cm³ mol⁻¹, toluene; ∆V^≠( 1 + 4 ) −36.0 cm³ mol⁻¹, ethyl acetate) and reaction volume values (∆V_r‐n( 1 + 2 ) −24.0 cm³ mol⁻¹, toluene; ∆V_r‐n( 1 + 4 ) −30.4 cm³ mol⁻¹, ethyl acetate) reveals more compact cyclic transition states in comparison with the acyclic reaction products 3 and 5 . In the series of nine solvents, the reaction rate of 1+2 increases 260‐fold and 1+4 increases 200‐fold, respectively, but not due to the solvent polarity.     

Poly(styrene‐b‐isobutylene) multiarm star‐block copolymers

Multiarm star‐branched polymers based on poly(styrene‐b‐isobutylene) (PS‐PIB) block copolymer arms were synthesized under controlled/living cationic polymerization conditions using the 2‐chloro‐2‐propylbenzene (CCl)/TiCl₄/pyridine (Py) initiating system and divinylbenzene (DVB) as gel‐core‐forming comonomer. To optimize the timing of isobutylene (IB) addition to living PS⊕, the kinetics of styrene (St) polymerization at −80°C were measured in both 60 : 40 (v : v) methyl cyclohexane (MCHx) : MeCl and 60 : 40 hexane : MeCl cosolvents. For either cosolvent system, it was found that the polymerizations followed first‐order kinetics with respect to the monomer and the number of actively growing chains remained invariant. The rate of polymerization was slower in MCHx : MeCl (k_app = 2.5 × 10⁻³ s⁻¹) compared with hexane : MeCl (k_app = 5.6 × 10⁻³ s⁻¹) ([CCl]_o = [TiCl₄]/15 = 3.64 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M). Intermolecular alkylation reactions were observed at [St]_o = 0.93M but could be suppressed by avoiding very high St conversion and by setting [St]_o ≤ 0.35M. For St polymerization, k_app = 1.1 × 10⁻³ s⁻¹ ([CCl]_o = [TiCl₄]/15 = 1.82 × 10⁻³M; [Py] = 4 × 10⁻³M; [St]_o = 0.35M); this was significantly higher than that observed for IB polymerization (k_app = 3.0 × 10⁻⁴ s⁻¹; [CCl]_o = [Py] = [TiCl₄]/15 = 1.86 × 10⁻³M; [IB]_o = 1.0M). Blocking efficiencies were higher in hexane : MeCl compared with MCHx : MeCl cosolvent system. Star formation was faster with PS‐PIB arms compared with PIB homopolymer arms under similar conditions. Using [DVB] = 5.6 × 10⁻²M = 10 times chain end concentration, 92% of PS‐PIB arms (M_n,PS = 2600 and M_n,PIB = 13,400 g/mol) were linked within 1 h at −80°C with negligible star–star coupling. It was difficult to achieve complete linking of all the arms prior to the onset of star–star coupling. Apparently, the presence of the St block allows the PS‐PIB block copolymer arms to be incorporated into growing star polymers by an additional mechanism, namely, electrophilic aromatic substitution (EAS), which leads to increased rates of star formation and greater tendency toward star–star coupling. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1629–1641, 1999     

Effect of solvent and structure on the kinetics and mechanism of the aquation of bromopentaamine cobalt(III) complex in binary aqueous mixtures

The kinetics of aquation of bromopentaamine cobalt(III) complex have been investigated spectrophotometrically in aqueous‐organic solvent media using acetonitrile, urea, and dimethyl sulfoxide as co‐solvents at 45 ≤ T (°C) ≤ 65. The logarithms of rate constant of the aquation reaction vary nonlinearly with the reciprocal of the dielectric constant for all cosolvent mixtures, indicating a specific solute–solvent interaction. Also, the rate constants are correlated with the total number of moles of water and the organic solvents. However, the solvent effects on the solvation components of the enthalpy of activation, ΔH^?, and the entropy of activation, ΔS^?, have been studied. Analysis of the solvent effect confirmed a common I_d mechanism for the aquation of the cobalt(III) complex. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36:494–499, 2004     

Evidence for a Rapid Degenerate Hetero‐Cope‐Type Rearrangement in [Cp*W(S)2S‐CH2‐CHCH2]

Treatment of the salt [PPh₄]⁺[Cp*W(S)₃]^? ( 6 ) with allyl bromide gave the neutral complex [Cp*W(S)₂S‐CH₂‐CH?CH₂] ( 7 ). The product 7 was characterized by an X‐ray crystal structure analysis. Complex 7 features dynamic NMR spectra that indicate a rapid allyl automerization process. From the analysis of the temperature‐dependent NMR spectra a Gibbs activation energy of ΔG^≠ (278 K)≈13.7±0.1 kcal mol^?1 was obtained [ΔH^≠≈10.4±0.1 kcal mol^?1; ΔS^≠≈?11.4 cal mol^?1 K^?1]. The DFT calculation identified an energetically unfavorable four‐membered transition state of the “forbidden” reaction and a favorable six‐membered transition state of the “Cope‐type” allyl rearrangement process at this transition‐metal complex core.     

Ultrafast Photoinduced Charge Separation Leading to High‐Energy Radical Ion‐Pairs in Directly Linked Corrole–C60 and Triphenylamine–Corrole‐C60 Donor–Acceptor Conjugates

Closely positioned donor–acceptor pairs facilitate electron‐ and energy‐transfer events, relevant to light energy conversion. Here, a triad system TPACor‐C₆₀ , possessing a free‐base corrole as central unit that linked the energy donor triphenylamine ( TPA ) at the meso position and an electron acceptor fullerene (C₆₀) at the β‐pyrrole position was newly synthesized, as were the component dyads TPA‐Cor and Cor‐C₆₀ . Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady‐state fluorescence studies showed efficient energy transfer from ¹ TPA* to the corrole and subsequent electron transfer from ¹corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron‐transfer products, the corrole radical cation ( Cor^?+ in Cor‐C₆₀ and TPA‐Cor^?+ in TPACor‐C₆₀ ) and fullerene radical anion (C₆₀^??), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, k_CS, was found to be about 10¹¹ s^?1, suggesting the occurrence of an ultrafast charge‐separation process. Interestingly, although an order of magnitude slower than k_CS, the rate of charge recombination, k_CR, was also found to be rapid (k_CR≈10¹⁰ s^?1), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge‐separated species relaxed directly to the ground state in polar solvents while in toluene, formation of ³corrole* was observed, thus implying that the energy of the charge‐separated state in a nonpolar solvent is higher than the energy of ³corrole* being about 1.52 eV. That is, ultrafast formation of a high‐energy charge‐separated state in toluene has been achieved in these closely spaced corrole–fullerene donor–acceptor conjugates.     

Ruthenium(III)-catalyzed mechanistic studies of oxidation of benzhydrols by sodium N-chloro-p-toluenesulfonamide in HCl medium

The kinetics of oxidation of benzhydrol and its p-substituted derivatives (YBH, where Y=H, Cl, Br, NO₂, CH₃, and OCH₃) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT), catalyzed by ruthenium(III) chloride, in the presence of hydrochloric acid in 30% (v/v) MeOH medium has been studied at 35°C. The reaction rate shows a first-order dependence on [CAT]_O and a fractional-order each on [ YBH]_O, [Ru(III)], and [H⁺]. The reaction also has a negative fractional-order (−0.35) behavior in the reduction product of CAT, p-toluenesulfonamide (PTS). The increase in MeOH content of the solvent medium retards the rate. The variation of ionic strength of the medium has negligible effect on the rate. Rate studies in D₂O medium show that the solvent isotope effect, k′H₂O/k′D₂O, is equal to 0.60. Proton inventory studies have been made in H₂O(SINGLEBOND)D₂O mixtures. The rates correlate satisfactorily with Hammett σ relationship. The LFE relationship plot is biphasic and the reaction constant ρ=−2.3 for electron donating groups and ρ=−0.32 for electron withdrawing groups at 35°C. Activation parameters ΔH^≠, ΔS^≠, and ΔG^≠ have been calculated. The parameters, ΔH^≠ and ΔS^≠, are linearly related with an isokinetic temperature β=334 K indicating enthalpy as a controlling factor. A mechanism consistent with the observed kinetics has been proposed. © 1997 John Wiley & Sons, Inc.     

Kinetics of Oxygen Exchange in the System BrO - H2O (D2O)

The kinetics of oxygen exchange between water (H₂O, D₂O) and ¹⁸O-labelled bromate ion has been investigated over the range of 1.7 ≤ pH ≤ 14.3 and 20 ≤ °C ≤ 95. At 60° and ionic strength I ? 1.0M (NaNO₃), the experimental results were consistent with the rate laws (R in moll^?1 s^?1): From the temperature dependence of the rate constants the activation parameters ΔH^≠, ΔS^≠ and ΔC^≠ were derived. In the acid-catalysed region the form of the rate law and the direction of the solvent isotope effect were the same as previously found, but the numerical values of ΔH^≠ and k_2H/k_2D differ considerably. For the spontaneous and the OH^?-catalysed exchange reactions bimolecular displacement mechanisms are proposed.     

Mechanistic Aspects of Ligand Substitution on the Hydroxopentaaquarhodium(III) Ion in Aqueous Solution by Sulfur‐Containing Bioactive Ligands

The kinetics of the interactions between three sulfur‐containing ligands, thioglycolic acid, 2‐thiouracil, glutathione, and the title complex, have been studied spectrophotometrically in aqueous medium as a function of the concentrations of the ligands, temperature, and pH at constant ionic strength. The reactions follow a two‐step process in which the first step is ligand‐dependent and the second step is ligand‐independent chelation. Rate constants (k₁ ～10^?3 s^?1 and k₂ ～10^?5 s^?1) and activation parameters (for thioglycolic acid: ΔH₁^≠ = 22.4 ± 3.0 kJ mol^?1, ΔS₁^≠ = ?220 ± 11 J K^?1 mol^?1, ΔH₂^≠ = 38.5 ± 1.3 kJ mol^?1, ΔS₂^≠ = ?204 ± 4 J K^?1 mol^?1; for 2‐thiouracil: ΔH₁^≠ = 42.2 ± 2.0 kJ mol^?1, ΔS₁^≠ = ?169 ± 6 J K^?1 mol^?1, ΔH₂^≠ = 66.1 ± 0.5 kJ mol^?1, ΔS₂^≠ = ?124 ± 2 J K^?1 mol^?1; for glutathione: ΔH₁^≠ = 47.2 ± 1.7 kJ mol^?1, ΔS₁^≠ = ?155 ± 5 J K^?1mol^?1, ΔH₂^≠ = 73.5 ± 1.1 kJ mol^?1, ΔS₂^≠ = ?105 ± 3 J K^?1 mol^?1) were calculated. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes. The products of the reactions have been characterized from IR and ESI mass spectroscopic analysis. A rate law involving the outer sphere association complex formation has been established as      

Non-isothermal Kinetics of the First-stage Decomposition Reaction of the Complex of Terbium p-Methylbenzoate with 1,10-Phenanthroline

The thermal behavior of Tb₂ (p‐MBA)₆(phen)₂ (p‐MBA=p‐methylbenzoate; phen=1,10‐phenanthroline) in a static air atmosphere was investigated by TG‐DTG, SEM and IR techniques. The thermal decomposition of the Tb₂(p‐MBA)₆(phen)₂ occurred in three consecutive stages at T_P of 354, 457 and 595 °C. By Malek method, RO (n<1) was defined as kinetic model for the first‐step thermal decomposition. The activation energy (E) of this step is 170.21 kJ·mol^‐1, the enthalpy of activation (ΔH^≠) 164.98 kJ·mol^‐1, the Gibbs free energy of activation (ΔG^≠) 145.04 kJ·mol^‐1, the entropy of activation (ΔS^≠) 31.77 J·mol^‐1·K^‐1, and the pre‐exponential factor (A) 10^15.21 s^‐1.     

Donor property of cobalt(II) Schiff base complexes toward triphenyltin(IV)‐chloride: A kinetic study

In this study, some cobalt(II)tetraaza Schiff base complexes were used as donors in coordinating to triphenyltin(IV)chloride as acceptors; the kinetics and mechanism of the adduct formation were studied spectrophotometrically. Co(II)tetraaza Schiff base complexes used were [Co(amaen)][N,N′‐ethylene‐bis‐(o‐amino‐α‐methylbenzylideneiminato)cobalt(II)] ( 1 ), [Co(appn)] [N,N′‐1,2‐propylene‐bis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)] ( 2 ), [Co(ampen)] [N,N′‐ethylene‐bis‐(o‐amino‐α‐phenylbenzylideneiminato)cobalt‐(II)] ( 3 ), [Co(cappn)][N,N′‐1,2‐proylene‐bis‐(5‐chloro‐o‐amino‐α‐phenylbenzylideneiminato)cobalt(II)] ( 4 ), and [Co(campen)] [N,N′‐ethylene‐bis‐(5‐chloro‐o‐amino‐α‐phenylbenzylid‐eneiminato)cobalt(II)] ( 5 ). The reactivity trend of the complexes in interaction with triphenyltin(IV)chloride was Co(amaen) > Co(appn) > Co(ampen) > Co(cappn) > Co(campen). The linear plots of k_obs versus the molar concentration of the triphenyltin(IV)chloride, a high span of the second‐order rate constant k₂ values, and large negative values of ΔS^≠ and low ΔH^≠ values suggest an associative (A) mechanism for the acceptor–donor adduct formation. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 635–640, 2012     

Synthesis,kinetics and mechanism of the reaction of a quasi‐aromatic copper(II) complex, [Cu(PnAO)‐6H]0, with aromatic aldehydes

The quasi‐aromatic metal complex (1,1,2,8,9,9‐hexamethyl‐4,6‐dioxa‐5‐hydro‐3,7,10,14‐tetraazacyclotetradecane‐2,7,10,12‐tetraene)copper(II), [Cu(PnAO)‐6H]⁰ (AH), was synthesized. Reactions of AH were studied spectrophotometrically in acidic media (pH = 1 ∼ 2, EtOH:H₂O = 1:4 v/v) with para‐substituted benzaldehydes (ald). The Cu,2N,3C quasi‐aromatic heterocyclic ring in AH is highly reactive at the central‐aromatic‐carbon atom, C12, to most aldehydes. A novel parallel, competitive and consecutive second‐order reaction mechanism is proposed. To obtain the rate constants following this mechanism, the Gauss‐Newton‐Marquardt and Runge‐Kutta methods were employed. Consistent results were obtained. Effects of acidity, solvent, temperature and substituent R (RH, CH₃, OCH₃, Cl) of the aromatic aldehydes on the reaction rate constants were studied. The results support the proposed SN2 mechanism. A linear free energy relationship between the rate constant k₁ and the Hammett parameters for the substituted benzaldehydes as well the activation parameters are presented. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 1–8, 2001     

Study of solvent effects on the stability constant and ionic mobility of the dibenzo‐18‐crown‐6 complex with potassium ion by affinity capillary electrophoresis

The effect of solvent on the strength of noncovalent interactions and ionic mobility of the dibenzo‐18‐crown‐6 complex with K⁺ in water/organic solvents was investigated by using affinity capillary electrophoresis. The proportion of organic solvent (methanol, ethanol, propan‐2‐ol, and acetonitrile) in the mixtures ranged from 0 to 100 vol.%. The stability constant, K_KL, and actual ionic mobility of the dibenzo‐18‐crown‐6‐K⁺ complex were determined by the nonlinear regression analysis of the dependence of the effective electrophoretic mobility of dibenzo‐18‐crown‐6 on the concentration of K⁺ (added as KCl) in the background electrolyte (25 mM lithium acetate, pH 5.5, in the above mixed hydro–organic solvents). Competitive interaction of the dibenzo‐18‐crown‐6 with Li⁺ was observed and quantified in mixtures containing more than 60 vol.% of the organic solvent. However, the stability constant of the dibenzo‐18‐crown‐6‐Li⁺ complex was in all cases lower than 0.5 % of K_KL. The log K_KL increased approximately linearly in the range 1.62–4.98 with the increasing molar fraction of organic solvent in the above mixed solvents and with similar slopes for all four organic solvents used in this study. The ionic mobilities of the dibenzo‐18‐crown‐6‐K⁺ complex were in the range (6.1–43.4) × 10^?9 m² V^?1 s^?1.