Inner-sphere oxidation of a ternary dipicolinatochromium(III) complex involving a malonic acid co-ligand

The oxidation of a ternary complex of chromium(III), [Cr^III(DPA)(Mal)(H₂O)₂]^?, involving dipicolinic acid (DPA) as primary ligand and malonic acid (Mal) as co-ligand, was investigated in aqueous acidic medium. The periodate oxidation kinetics of [Cr^III(DPA)(Mal)(H₂O)₂]^? to give Cr(VI) under pseudo-first-order conditions were studied at various pH, ionic strength and temperature values. The kinetic equation was found to be as follows: \( {\text{Rate}} = {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} \mathord{\left/ {\vphantom {{\left[ {{\text{IO}}_{4}^{ - } } \right]\left[ {{\text{Cr}}^{\text{III}} } \right]_{\text{T}} \left( {{{k_{5} K_{5} + k_{6} K_{4} K_{6} } \mathord{\left/ {\vphantom {{k_{5} K_{5} + k_{6} K_{4} K_{6} } {\left[ {{\text{H}}^{ + } } \right]}}} \right. \kern-0pt} {\left[ {{\text{H}}^{ + } } \right]}}} \right)} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}}} \right. \kern-0pt} {\left\{ {\left( {\left[ {{\text{H}}^{ + } } \right] + K_{4} } \right) + \left( {K_{5} \left[ {{\text{H}}^{ + } } \right] + K_{6} K_{4} } \right)\left[ {{\text{IO}}_{4}^{ - } } \right]} \right\}}} \) where k ₆ (3.65 × 10^?3 s^?1) represents the electron transfer reaction rate constant and K ₄ (4.60 × 10^?4 mol dm^?3) represents the dissociation constant for the reaction \( \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)_{2} } \right]^{ - } \rightleftharpoons \left[ {{\text{Cr}}^{\text{III}} \left( {\text{DPA}} \right)\left( {\text{Mal}} \right)\left( {{\text{H}}_{2} {\text{O}}} \right)\left( {\text{OH}} \right)} \right]^{2 - } + {\text{H}}^{ + } \) and K ₅ (1.87 mol^?1 dm³) and K ₆ (22.83 mol^?1 dm³) represent the pre-equilibrium formation constants at 30 °C and I = 0.2 mol dm^?3. Hexadecyltrimethylammonium bromide (CTAB) was found to enhance the reaction rate, whereas sodium dodecyl sulfate (SDS) had no effect. The thermodynamic activation parameters were estimated, and the oxidation is proposed to proceed via an inner-sphere mechanism involving the coordination of IO₄ ^? to Cr(III).     

Kinetics and mechanism of oxidation of the chromium(III)-DL-aspartic acid complex/periodate reaction. Evidence for iron(II) catalysis

The kinetics of oxidation of the chromium(III)-DL- aspartic acid complex, [CrIIIHL]+ by periodate have been investigated in aqueous medium. In the presence of Fe^II as a catalyst, the following rate law is obeyed:

Inner sphere oxidation of N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) by N-bromosuccinimide in aqueous weakly acidic solutions

The kinetics of oxidation of N,N′-ethylenebis(isonitrosoacetyleacetoneimine)copper(II) complex, Cu^IIL, by N-bromosuccinimide (SBr) in weakly aqueous acidic solutions was studied under pseudo-first-order conditions. Plots of ln(A _∞  ? A _t ) versus time where A _t and A _∞ are absorbance values of the Cu(III) product at time t and infinity, respectively, showed marked deviations from linearity. The curves showed an acceleration of reaction rate consistent with an autocatalytic behavior. In the presence of Hg(II) ions, plots of ln(A _∞  ? A _t ) versus time are linear up to >85 % of reaction. The value of the observed rate constant, k _obs, increases with decreasing pH. At constant reaction conditions, the dependence of the observed rate constants, k _obs, is described by Eq. (1). 1 $$ k_{\text{obs}} = k_{\text{o}} + k_{1} \left[ {{\text{H}}^{ + } } \right] $$ The dependence of both k _o and k ₁ on [SBr] is not linear. The mechanism of the title reaction is consistent with an inner sphere mechanism in which a pre-equilibrium step precedes the electron transfer step. The overall rate law is represented by Eq. (2) where [Cu^IIL]_t and K ₁ represent the total copper(II) complex concentration and the pre-equilibrium formation constant, respectively. 2 $$ d\left[ {{\text{Cu}}^{\text{III}} {\text{L}}^{ + } } \right]/dt = \left\{ {\left( {k_{\text{o}} + k_{1} \left[ {{\text{H}}^{ + } } \right]} \right)\left[ {\text{SBr}} \right]\left[ {{\text{Cu}}^{\text{II}} {\text{L}}} \right]_{t} } \right\}/\left( {1 + K_{1} \left[ {\text{SBr}} \right]} \right) $$ .     

Kinetics and mechanism of oxidation of cis-diaquabis(glycinato)chromium(III) by periodate ion in aqueous solutions

The kinetics of oxidation of cis-[Cr^III(gly)₂(H₂O)₂]⁺ (gly = glycinate) by $ {\text{IO}}_{ 4}^{ - } $ has been studied in aqueous solutions. The reaction is first order in the chromium(III) complex concentration. The pseudo-first-order rate constant, k _obs, showed a small change with increasing $ \left[ {{\text{IO}}_{ 4}^{ - } } \right] $ . The pseudo-first-order rate constant, k _obs, increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the reactive species. The reaction has been found to obey the following rate law: $ {\text{Rate}} = 2k^{\text{et}} K_{ 3} K_{ 4} \left[ {{\text{Cr}}\left( {\text{III}} \right)} \right]_{t} \left[ {{\text{IO}}_{ 4}^{ - } } \right]/\left\{ {\left[ {{\text{H}}^{ + } } \right] + K_{ 3} + K_{ 3} K_{ 4} \left[ {{\text{IO}}_{ 4}^{ - } } \right]} \right\} $ . Values of the intramolecular electron transfer constant, k ^et, the first deprotonation constant of cis-[Cr^III(gly)₂(H₂O)₂]⁺, K ₃ and the equilibrium formation constant between cis-[Cr^III(gly)₂(H₂O)(OH)] and $ {\text{IO}}_{ 4}^{ - } $ , K ₄, have been determined. An inner-sphere mechanism has been proposed for the oxidation process. The thermodynamic activation parameters of the processes involved are reported.     

Effect of size of tetraalkylammonium counterions on the temperature dependent micellization of AOT in aqueous medium

Different tetraalkylammonium, viz. N⁺(CH₃)₄, N⁺(C₂H₅)₄, N⁺(C₃H₇)₄, N⁺(C₄H₉)₄ along with simple ammonium salts of bis (2-ethylhexyl) sulfosuccinic acid have been prepared by ion-exchange technique. The critical micelle concentration of surfactants with varied counterions have been determined by measuring surface tension and conductivity within the temperature range 283–313 K. Counterion ionization constant, α, and thermodynamic parameters for micellization process viz., $\Delta G_m^{\text{0}} $ , $\Delta H_m^{\text{0}} $ , and $\Delta S_m^{\text{0}} $ and also the surface parameters, Γ_max and A_min, in aqueous solution have been determined. Large negative $\Delta G_m^{\text{0}} $ of micellization for all the above counterions supports the spontaneity of micellization. The value of standard free energy, $\Delta G_m^{\text{0}} $ , for different counterions followed the order $${\text{N}}^{\text{ + }} \left( {{\text{CH}}_{\text{3}} } \right)_4 >{\text{NH}}_{\text{4}}^{\text{ + }} >{\text{Na}}^{\text{ + }} >{\text{N}}^{\text{ + }} \left( {{\text{C}}_{\text{2}} {\text{H}}_5 } \right)_{\text{4}} {\text{ $>$ N}}^{\text{ + }} \left( {{\text{C}}_{\text{3}} {\text{H}}_{\text{7}} } \right)_4 >{\text{N}}^{\text{ + }} \left( {{\text{C}}_{\text{4}} {\text{H}}_{\text{9}} } \right)_4 $$ , at a given temperature. This result can be well explained in terms of bulkiness and nature of hydration of the counterion together with hydrophobic and electrostatic interactions.     

Synthesis and structural characterization of three dinuclear Copper(II) complexes incorporating pyrazolyl-derived ligands

Three new binuclear copper complexes of formulae $ \left[ {{\text{Cu}}_{2}^{\text{II}} {\text{Pz}}_{2}^{\text{Me3}} {\text{Br}}_{ 2} \left( {{\text{PPh}}_{ 3} } \right)_{ 2} } \right] $ (1), $ \left[ {{\text{Cu}}_{ 2}^{\text{II}} {\text{Pz}}_{2}^{\text{Ph2Me}} {\text{Cl}}_{ 2} \left( {{\text{PPh}}_{ 3} } \right)_{ 2} } \right] $ (2) and $ \left[ {{\text{Cu}}_{2}^{\text{II}} \left( {{\text{Pz}}^{\text{PhMe}} } \right)_{ 4} {\text{Cl}}_{ 4} } \right] $ (3) (Pz^Me3?=?3,4,5-trimethylpyrazole, Pz^Ph2Me?=?4-methyl-3,5-diphenylpyrazole and Pz^PhMe?=?3-methyl-5-phenylpyrazole) have been synthesized and characterized by chemical analysis, FTIR and ³¹P NMR spectroscopy and single-crystal X-ray diffraction. Complex 1 is a doubly bromo-bridged dimer, while complexes 2 and 3 are chloro-bridged dimers. The Cu(II) centers are in a distorted tetrahedral geometry for 1 and 2 and a distorted square pyramidal N₂Cl₃ environment for 3.     

Thermochemical properties of the coordination complex of 8-hydroxyquinolinato-bis-(salicylato) praseodymium (III)

The product, [Pr(C₇H₅O₃)₂(C₉H₆NO)], which was formed by praseodymium nitrate hexahydrate, salicylic acid (C₇H₆O₃), and 8-hydroxyquinoline (C₉H₇NO), was synthesized and characterized by elemental analysis, UV spectra, IR spectra, molar conductance, and thermogravimetric analysis. In an optimalizing calorimetric solvent, the dissolution enthalpies of [Pr(NO₃)₃·6H₂O(s)], [2 C₇H₆O₃(s) + C₉H₇NO(s)], [Pr(C₇H₅O₃)₂(C₉H₆NO)(s)], and [solution D (aq)] were measured to be, by means of a solution-reaction isoperibol microcalorimeter, $ \begin{gathered}\Updelta_{\text{s}} H_{\text{m}}^{\theta}\left[ {{ \Pr }\left( {{\text{NO}}_{ 3} } \right)_{ 3} \cdot 6{\text{H}}_{ 2} {\text{O}}\left( {\text{s}} \right), 2 9 8. 1 5{\text{ K}}} \right] \, = - ( 20. 6 6 { } \pm \, 0. 29)\,{\text{kJ}}\,{\text{mol}}^{ - 1} , \\\Updelta_{\text{s}} H_{\text{m}}^{\theta } \left[ { 2 {\text{C}}_{7} {\text{H}}_{ 6} {\text{O}}_{ 3} \left( {\text{s}} \right) +{\text{ C}}_{ 9} {\text{H}}_{ 7} {\text{NO}}\left( {\text{s}}\right),{ 298}. 1 5 {\text{ K}}} \right] \, = \, ( 4 2. 2 7 { }\pm \, 0. 3 1)\,{\text{kJ}}\,{\text{mol}}^{ - 1} , \\\Updelta_{\text{s}} H_{\text{m}}^{\theta } \left[ {{\text{solutionD }}\left( {\text{aq}} \right), 2 9 8. 1 5 {\text{ K}}} \right] \,= - \left( { 8 9. 1 5 { } \pm \, 0. 4 3}\right)\,{\text{kJ}}\,{\text{mol}}^{ - 1} , \\\end{gathered} $ Δ s H m θ [ Pr ( NO 3 ) 3 · 6 H 2 O ( s ) , 2 9 8.1 5 K ] = ? ( 20.6 6 ± 0.2 9 ) kJ mol ? 1 , Δ s H m θ [ 2 C 7 H 6 O 3 ( s ) + C 9 H 7 NO ( s ) , 298.1 5 K ] = ( 4 2.2 7 ± 0.3 1 ) kJ mol ? 1 , Δ s H m θ [ solution D ( aq ) , 2 9 8.1 5 K ] = ? ( 8 9.1 5 ± 0.4 3 ) kJ mol ? 1 , and $ \Updelta_{\text{s}} H_{\text{m}}^{\theta } \left\{ {\left[ {{\Pr }\left( {{\text{C}}_{ 7} {\text{H}}_{ 5} {\text{O}}_{ 3} }\right)_{ 2} \left( {{\text{C}}_{ 9} {\text{H}}_{ 6} {\text{NO}}}\right)} \right]\left( {\text{s}} \right),{ 298}. 1 5 {\text{ K}}}\right\} \, = - \left( { 4 1.0 4 { } \pm \, 0. 3 3}\right)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ Δ s H m θ { [ Pr ( C 7 H 5 O 3 ) 2 ( C 9 H 6 NO ) ] ( s ) , 298.1 5 K } = ? ( 4 1.0 4 ± 0.3 3 ) kJ mol ? 1 , respectively. Through an improved thermochemical cycle, the enthalpy change of the designed coordination reaction was calculated to be $\Updelta_{\text{r}} H_{\text{m}}^{\theta} = \, ( 2 1 3. 1 8\pm0. 6 9)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ Δ r H m θ = ( 2 1 3.1 8 ± 0.6 9 ) kJ mol ? 1 , the standard molar enthalpy of the formation was determined as $ \Updelta_{\text{f}} H_{\text{m}}^{\theta} \left\{ {\left[ {{\Pr }\left( {{\text{C}}_{ 7} {\text{H}}_{ 5} {\text{O}}_{ 3} }\right)_{ 2} \left( {{\text{C}}_{ 9} {\text{H}}_{ 6} {\text{NO}}}\right)} \right]\left( {\text{s}} \right), 2 9 8. 1 5 {\text{K}}}\right\} \, = \, - \, ( 1 8 7 5. 4\pm 3.1)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ Δ f H m θ { [ Pr ( C 7 H 5 O 3 ) 2 ( C 9 H 6 NO ) ] ( s ) , 2 9 8.1 5 K } = ? ( 1 8 7 5.4 ± 3.1 ) kJ mol ? 1 .     

The role of the heteroatom (X?=?SiIV, PV, and SVI) on the reactivity of {��-[(H2O)RuIII(��-OH)2RuIII(H2O)][X n+W10O36]}(8?n)? with the O2 molecule

The mechanism of reaction of the di-Ru-substituted polyoxometalate, {??-[(H₂O)Ru^III(??-OH)₂Ru^III(H₂O)][X ⁿ⁺W₁₀O₃₆]}^(8?n)?, I_X, with O₂, i.e. I_X?+?O₂????{??-[(^·O)Ru^IV(??-OH)₂Ru^IV(O^·)][X ⁿ⁺W₁₀O₃₆]}^(8?n)??+?2H₂O, (1), was studied at the B3LYP density functional and self-consistent reaction field IEF-PCM (in aqueous solution) levels of theory. The effect of the nature of heteroatom X (where X?=?Si, P and, S) on the calculated energies and mechanism of the reaction (1) was elucidated. It was shown that the nature of X only slightly affects the reactivity of I_X with O₂, which is a 4-electron oxidation process. The overall reaction (1): (a) proceeds with moderate energy barriers for all studied X??s [the calculated rate-determining barriers are X?=?Si (18.7?kcal/mol)?<?S (20.6?kcal/mol)?<?P (27.2?kcal/mol) in water, and X?=?S (18.7?kcal/mol)?<?P (21.4?kcal/mol)?<?Si (23.1?kcal/mol) in the gas phase] and (b) is exothermic [by X?=?Si [28.7 (22.1) kcal/mol]?>?P [21.4 (9.8) kcal/mol]?>?S [12.3 (5.0) kcal/mol]. The resulting $ \left\{ {\gamma - \left[ {\left( {^{ \cdot } {\text{O}}} \right) {\text{Ru}}^{\text{IV}} \left( {\mu - {\text{OH}}} \right)_{2} {\text{Ru}}^{\text{IV}} \left( {{\text{O}}^{ \cdot } } \right)} \right]\left[ {{\text{X}}^{{{\text{n}} + }} {\text{W}}_{10} {\text{O}}_{36} } \right]} \right\}^{{\left( {8 - {\text{n}}} \right) - }} $ , VI_X, complex was found to have two Ru^IV?=?O^· units, rather than Ru^V?=?O units. The ??reverse?? reaction, i.e., water oxidation by VI_X is an endothermic process and unlikely to occur for X?=?Si and P, while it could occur for X?=?S under specific conditions. The lack of reactivity of VI_X biradical toward the water molecule leads to the formation of the stable [{Ru ₄ ^IV O₄(OH)₂(H₂O)₄}[(??-XW₁₀O₃₆]₂}^m? dimer. This conclusion is consistent with our experimental findings; previously we prepared the $ \left[ {\left\{ {{\text{Ru}}_{4}^{\text{IV}} {\text{O}}_{4} ({\text{OH}})_{2} \left( {{\text{H}}_{ 2} {\text{O}}} \right)_{4} } \right\}} \right[\left( {\gamma - {\text{XW}}_{10} {\text{O}}_{36} } \right]_{2} \}^{{{\text{m}} - }} $ dimers for X?=?Si (m?=?10) [Geletii et al. in Angew Chem Int Ed 47:3896?C3899, 2008 and J Am Chem Soc 131:17360?C17370, 2009] and P (m?=?8) [Besson et al. in Chem Comm 46:2784?C2786, 2010] and showed them to be very stable and efficient catalysts for the oxidation of water to O₂.     

Thermodynamic studies on Pr2TeO6

The standard Gibbs energy of formation of Pr₂TeO₆ $ (\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)) $ was derived from its vapour pressure in the temperature range of 1,400–1,480 K. The vapour pressure of TeO₂ (g) was measured by employing a thermogravimetry-based transpiration method. The temperature dependence of the vapour pressure of TeO₂ over the mixture Pr₂TeO₆ (s) + Pr₂O₃ (s) generated by the incongruent vapourization reaction, Pr₂TeO₆ (s) = Pr₂O₃ (s) + TeO₂ (g) + ½ O₂ (g) could be represented as: $ { \log }\left\{ {{{p\left( {{\text{TeO}}_{ 2} ,\;{\text{g}}} \right)} \mathord{\left/ {\vphantom {{p\left( {{\text{TeO}}_{ 2} ,\;{\text{g}}} \right)} {{\text{Pa}} \pm 0.0 4}}} \right. \kern-0em} {{\text{Pa}} \pm 0.0 4}}} \right\} = 19. 12- 27132\; \left({\rm{{{\text{K}}}}/T} \right) $ . The $ \Updelta_{\text{f}} G^{^\circ } \;\left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} } \right) $ could be represented by the relation $ \left\{ {{{\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)} \mathord{\left/ {\vphantom {{\Updelta_{\text{f}} G^{^\circ } \left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} ,\;{\text{s}}} \right)} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}}} \right. \kern-0em} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}} \pm 5.0} \right\} = - 2 4 1 5. 1+ 0. 5 7 9 3\;\left(T/{\text{K}}\right) .$ Enthalpy increments of Pr₂TeO₆ were measured by drop calorimetry in the temperature range of 573–1,273 K and heat capacity, entropy and Gibbs energy functions were derived. The $ \Updelta_{\text{f}} H_{{298\;{\text{K}}}}^{^\circ } \;\left( {{ \Pr }_{ 2} {\text{TeO}}_{ 6} } \right) $ was found to be $ {{ - 2, 40 7. 8 \pm 2.0} \mathord{\left/ {\vphantom {{ - 2, 40 7. 8 \pm 2.0} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}}} \right. \kern-0em} {\left( {{\text{kJ}}\,{\text{mol}}^{ - 1} } \right)}} $ .     

Extraction kinetics of Uranium(VI) and Thorium(IV) with Tri-iso-amyl phosphate from nitric acid using a Lewis Cell

The extraction kinetics of uranium(VI) and thorium(IV) with Tri-iso-amyl phosphate (TiAP) from nitric acid medium has been investigated using a Lewis Cell. Especially, dependences of the extraction rate on stirring speed, temperature, interfacial area were firstly measured to elucidate the extraction kinetics regimes. The experimental results demonstrated that extraction kinetic of U(VI) is governed by chemical reactions at interface with an activation energy, E_a, of 43.41 kJ/mol, while the rate of Th(IV) extraction is proved to be intermediate controlled, of which the E_a is 23.20 kJ/mol. Reaction orders with respect to the influencing parameters of the extraction rate are determined, and the rate equations of U(VI) and Th(IV) at 293 K have been proposed as $$ {\text{r}} = - {\text{dcUO}}_{ 2} \left( {{\text{NO}}_{ 3} } \right)_{ 2} /{\text{dt}} = 1. 80 \times 10^{ - 3} \left[ {{\text{UO}}_{ 2} \left( {{\text{NO}}_{ 3} } \right)_{ 2} } \right]^{ 1.0 1} \left[ {\text{TiAP}} \right]^{0. 5 5} , $$ $$ {\text{r}} = - {\text{dcTh }}\left( {{\text{NO}}_{ 3} } \right)_{ 4} /{\text{dt}} = 1. 8 8\times 10^{ - 3} \left[ {{\text{Th }}\left( {{\text{NO}}_{ 3} } \right)_{ 4} } \right]^{ 1.0 4} \left[ {\text{TiAP}} \right]^{ 1. 7 7} \left[ {{\text{HNO}}_{ 3} } \right]^{0. 3 8} , $$ respectively.     

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol by bis(hydrogen periodato)argentate(III) complex anion: a kinetic study

Oxidation of 3-(4-methoxyphenoxy)-1,2-propanediol (MPPD) by bis(hydrogenperiodato) argentate(III) complex anion, [Ag(HIO₆)₂]⁵⁻ has been studied in aqueous alkaline medium by use of conventional spectrophotometry. The major oxidation product of MPPD has been identified as 3-(4-methoxyphenoxy)-2-ketone-1-propanol by mass spectrometry. The reaction shows overall second-order kinetics, being first-order in both [Ag(III)] and [MPPD]. The effects of [OH⁻] and periodate concentration on the observed second-order rate constants k′ have been analyzed, and accordingly an empirical expression has been deduced:

Kinetics and mechanism of oxidation of hydroxylamine by tetrachloroaurate(III) ion

The oxidation of H₂NOH is first-order both in [NH₃OH⁺] and [AuCl₄ ^–]. The rate is increased by the increase in [Cl^–] and decreased with increase in [H⁺]. The stoichiometry ratio, [NH₃OH⁺]/[AuCl₄ ^–], is 1. The mechanism consists of the following reactions.

Vibratio nal assig nme nts,co nformatio nal a nalysis,a nd molecular structures of $$\left[ {\text{C}_{\text{ n}} \text{mim}} \right]\left[ {\text{NTF}_{\text{2}} } \right]$$C nmimNTF2 ( n = 2, 4, 6, a nd 8) imidazolium-based io nic liquids: a combi ned experime ntal a nd qua ntum chemical approach

This work is aimed at providing physical insights about the interactions of cations, anion, and ion pairs of four imidazolium-based ionic liquids of \(\left[ {{\text{C}}_{\text{n}} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\) with varying alkyl chain lengths (n = 2, 4, 6, and 8) using both DFT calculations and vibrational spectroscopic measurements (IR absorption and Raman scattering) in the mid- and far regions. The calculated Mulliken charge distributions of \(\left[ {{\text{C}}_{\text{n}} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\) ion pairs indicate that hydrogen-bonding interactions between oxygen and nitrogen atoms (more negative charge) on \(\left[ {{\text{NTF}}_{2} } \right]^{ - }\) anion and the hydrogen atoms (more positive charge) on the imidazolium ring play a dominating role in the formation of ion pair. Thirteen stable conformers of \(\left[ {{\text{C}}_{2} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\) were optimized. According to our results, the strongest and weakest hydrogen bonds were existing in \(\left[ {{\text{C}}_{2} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\) and \(\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\), respectively. A redshift of 290, 262, 258, and 257 cm^?1 has been observed for cations involving \(\left[ {{\text{C}}_{2} {\text{mim}}} \right]^{ + }\), \(\left[ {{\text{C}}_{4} {\text{mim}}} \right]^{ + }\),\(\left[ {{\text{C}}_{6} {\text{mim}}} \right]^{ + }\), and stretching vibrations of \({\text{C}}12{-}{\text{H}}3\), respectively. By increasing the chain length, the strength of hydrogen bonds decreases as a result of \({\text{C}}12{-}{\text{H}}3\) bond elongation and less changes are observed in stretching vibrations of \({\text{C}}12{-}{\text{H}}3\) compared to the free cations. To the best of our knowledge, this research is the first work which reports the far-IR of \(\left[ {{\text{C}}_{4} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\), \(\left[ {{\text{C}}_{6} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\), and \(\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\) and the mid-IR of \(\left[ {{\text{C}}_{8} {\text{mim}}} \right]\left[ {{\text{NTF}}_{2} } \right]\).     

Kinetics and mechanism of the oxidation of diaquabis(1,10-phenanthroline) iron(II) by periodate in aqueous and micellar media

The kinetics of oxidation of [Fe^II(phen)₂(H₂O)₂]²⁺ (phen = 1,10-phenanthroline) by periodate were investigated in aqueous acidic medium at different [H⁺] over a temperature range of 20–40 °C. The reaction was studied under pseudo-first-order conditions by taking [IO ₄ ^? ] > tenfold over [Fe^II(phen)₂(H₂O) ₂ ²⁺ ]. The reaction rate increases with increasing [H⁺], and the kinetics of oxidation obeyed the following rate law:

$$ {\text{Rate}} = \left[ {{\text{Fe}}^{\text{II}} ({\text{phen}})_2({\text{H}}_{2} {\text{O}})_{2}^{2 + } } \right]\left[ {{\text{IO}}_{4}^{ - } } \right]\left\{ {k_{4} K_{2} + k_{5} K_{1} K_{3} [{\text{H}}^{ + } ]} \right\} $$

The surfactant sodium dodecyl sulfate was found to enhance the rate, whereas cetyltrimethylammonium bromide had little effect. Activation parameters associated with k ₂ and k ₃ were calculated. An electron transfer from Fe(II) to I(VII) is identified as the rate-determining step. The I(VI) species thus generated reacts in a fast step with another Fe(II) complex.

     

Preparation and electrochemical properties of nano-sized cryptomelane particles for the formation of potentiometric potassium ion sensors

The potentiometric response of 100-nm spherical K_1.3Mn₈O₁₆ particles versus K⁺ ions has been studied in aqueous media using a polymeric technology. The stoichiometry of this material evolves in potassium nitrate solution towards K_1.08Mn₈O₁₆. A stable and reversible response has been obtained with a sensitivity of 47 mV dec^?1 in the range from 8?×?10^?5 to 1 mol·L^?1, and a rather good selectivity towards Li⁺, Na⁺, Mg²⁺ and Ca²⁺ $\left( {{\text{log K}}_{{{{\text{K}}^{\text{ + }} } \mathord{\left/ {\vphantom {{{\text{K}}^{\text{ + }} } {{\text{X}}^{n + } }}} \right. \kern-0em} {{\text{X}}^{n + } }}} \approx - {\text{3}}} \right)$ . We assume that this potentiometric response is the result of the ability of K_1.08Mn₈O₁₆ to specifically adsorb K⁺ ions.     

Assessment of the global and range-separated hybrids for computing the dynamic second-order hyperpolarizability of solution-phase organic molecules

A comparison is presented of uncontracted multireference singles and doubles configuration interaction (MRCI) and internally contracted MRCI potential energy surfaces for the reaction ${\text{H}}\left( {^{2} {\text{S}}} \right) + {\text{O}}_{2} \left( {^{3} \sum\nolimits_{g}^{ - } {} } \right) \to {\text{HO}}_{2} \left( {^{2} {\text{A}}^{{\prime \prime }} } \right)$ . It is found that internal contraction leads to significant differences in the reaction kinetics relative to the uncontracted calculations.     

Synergistic extraction of some univalent cations into nitrobenzene by using sodium dicarbollylcobaltate and nonactin

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium $ {\text{M}}^{ + } \left( {\text{aq}} \right) \, + {\mathbf{1}}\cdot{\text{Na}}^{ + } \left( {\text{nb}} \right) \Leftrightarrow {\mathbf{1}}\cdot{\text{M}}^{ + } \left( {\text{nb}} \right) \, + {\text{Na}}^{ + } \left( {\text{aq}} \right) $ taking place in the two-phase water–nitrobenzene system $ \begin{gathered} ({\text{M}}^{ + } = {\text{ Li}}^{ + } ,{\text{ K}}^{ + } ,{\text{ Rb}}^{ + } ,{\text{ Cs}}^{ + } ,{\text{ H}}_{ 3} {\text{O}}^{ + } ,{\text{NH}}_{4}^{ + }, {\text{ Ag}}^{ + } ,{\text{ Tl}}^{ + } ;{\mathbf{1}} \\ = {\text{ nonactin}};{\text{ aq }} = {\text{ aqueous phase}},{\text{ nb }} = {\text{nitrobenzene phase}}) \\ \end{gathered} $ were determined. Moreover, the stability constants of the 1·M⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the series of $ {\text{Cs}}^{ + } < {\text{ Rb}}^{ + } < {\text{ H}}_{ 3} {\text{O}}^{ + } ,{\text{ Ag}}^{ + } < {\text{ Tl}}^{ + } < {\text{ Li}}^{ + } < {\text{ K}}^{ + } < {\text{NH}}_{4}^{ + } $ .     

Thermal investigations of SmFeTeO6 and SmCrTeO6 compounds

SmFeTeO₆ and SmCrTeO₆ were synthesized by heating the respective oxides in molar quantities and characterized by X-ray technique. Thermogravimetric studies suggested that SmFeTeO₆ and SmCrTeO₆ vapourize incongruently according to the reactions: $$ \begin{aligned} {\text{SmFeTeO}}_{ 6}{({\text{s}})} & \to {\text{SmFeO}}_{ 3} {( {\text{s}})} + {\text{TeO}}_{ 2} {( {\text{g}})} + \left( { 1/ 2} \right){\text{O}}_{ 2}{( {\text{g}})} \\ {\text{SmCrTeO}}_{ 6} {( {\text{s}})} & \to {\text{SmCrO}}_{ 3} {( {\text{s}})} + {\text{TeO}}_{ 2}{( {\text{g}})} + \left( { 1/ 2} \right){\text{O}}_{ 2}{( {\text{g}})}. \\ \end{aligned} $$ X-ray diffraction data of both the compounds have been indexed on the hexagonal system. Partial pressures of TeO₂(g) were measured over SmFeO₃(s) and SmCrO₃(s) by employing the Knudsen effusion mass loss technique. The standard Gibbs free energy of formation of (Δ_f G°) SmFeTeO₆(s) and SmCrTeO₆(s) were obtained from partial pressures and represented by the following relations: $$\Updelta_{\text{f}} G^{\circ} \left( {{\text{SmFeTeO}}_{6}{( {{\text{s}},\,T})}} \right) \pm 2 5\,{\text{kJ}}\,{\text{mol}}^{ - 1} = - 1 5 1. 6 5+ 0. 1 5\left(T \right)\quad \left( 1 ,0 90{-} 1,1 80\,{\text{K}} \right) \\ \Updelta_{\text{f}} G^{\circ } \left( {{\text{SmCrTeO}}_{ 6} {( {{\text{s}},\,T})}} \right) \pm 2 5\,{\text{kJ}}\,{\text{mole}}^{ - 1} = - 2 5 2. 8 6+ 0. 1 2(T)\quad \left( { 1,100 {-} 1 , 1 7 5\,{\text{K}}} \right).$$      

Kinetics and mechanism of oxidation of aquaethylenediaminetetraacetatocobaltate(II) by <Emphasis Type="Italic">N</Emphasis>-bromosuccinimide in aqueous acidic solution

The oxidation of aquaethylenediaminetetraacetatocobaltate(II) [Co(EDTA)(H₂O)]⁻² by N-bromosuccinimide (NBS) in aqueous solution has been studied spectrophotometrically over the pH 6.10–7.02 range at 25 °C. The reaction is first-order with respect to complex and the oxidant, and it obeys the following rate law:

Thermochemical properties of hydrazinium dipicrylamine in N-methyl pyrrolidone and dimethyl sulfoxide

The enthalpies of dissolution for Hydrazinium Dipicrylamine (HDPA) in N-methyl pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) were measured using a RD496-2000 Calvet microcalorimeter at 298.15 K. Empirical formulae for the calculation of the enthalpies of dissolution (Δ_diss H) were obtained from the experimental data of the dissolution processes of HDPA in NMP and DMSO. The linear relationships between the rate (k) and the amount of substance (a) were found. The corresponding kinetic equations describing the two dissolution processes were $ {{\text{d}\alpha } \mathord{\left/ {\vphantom {{\text{d}\alpha} {\text{d}t}}} \right. \kern-0pt} {\text{d}t}} = 10^{ - 2.71}\left( {1 - \alpha } \right)^{1.23} $ d α / d t = 10 ? 2.71 ( 1 ? α ) 1.23 for the dissolution of HDPA in NMP, and $ {{\text{d}\alpha } \mathord{\left/ {\vphantom {{\text{d}\alpha} {\text{d}t}}} \right. \kern-0pt} {\text{d}t}} = 10^{ - 2.58}\left( {1 - \alpha } \right)^{0.81} $ d α / d t = 10 ? 2.58 ( 1 ? α ) 0.81 for the dissolution of HDPA in DMSO, respectively.