溶剂萃取动力学的研究 II: 三辛基氧化膦从盐酸体系中萃取铀(IV)的速率

The kinetics of the oxtraction of U(IV) chloride in the TOPO-HCl system has been studied using the single drop technique, The effects of the concentrations of U(IV, TOPO and HCl on the extraction rate for U(IV) have been examined. The extraction rate measured were found to be of first order with respect to (U(IV)) and (TOPO) (0). Moreover, the rate varied with (HCl)^3^/^2 between 2-7M hydrochloric acid. The extraction rate equation can be written as R=K(U(IV))(TOPO)(0) The rate constant K was evaluated to be 3.7X10^-^5 at 3M HCl and 15`C. The extraction rate was increased with increasing temperature. The apparent activation energy was found to be 10.8 kcal/mol between 15 to 45`C. It is suggested that the rate-controlling step may be the chemical reaction of UCl4 with TOPO at the interface and the formation of the interfacial complex UCL4.TOPO.     

A reinterpretation of the magnetic properties of the mixed-valence (Nb(V)/Nb(IV)) Zintl phase, Cs(9)Nb(2)As(6)

A new mixed-valent (Nb(V)/Nb(IV)) Zintl phase, Cs(9)Nb(2)As(6), has been prepared and characterized, recently (Gascoin, F.; Sevov, S. C. Inorg. Chem. 2002, 41, 5920). Niobium is present in the form of isolated, edge-sharing tetrahedral, Nb(2)As(6)(9)(-) dimers. The reported magnetic susceptibility features a broad maximum at approximately 36 K which has been interpreted as the onset of long-range antiferromagnetic order. Such a high transition temperature is difficult to understand as the compound is insulating and the interdimer Nb-Nb distance is 7.2 A. It is shown here that the observed magnetic properties follow straightforwardly from a statistical occupation of the equivalent intradimer Nb sites by equal concentrations of Nb(IV)(4d(1), S = (1)/(2)) and Nb(V)(4d(0)). From this analysis the broad maximum arises from intradimer antiferromagnetic exchange with an exchange constant, J/k = -40 K, and there is no long-range magnetic order except, possibly, below 5 K.     

Molecular paramagnetic semiconductor: crystal structures and magnetic and conducting properties of the Ni(dmit)(2) salts of 6-oxoverdazyl radical cations (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation ([1](+)) and its mono- and dimethyl derivatives ([2](+) and [3](+)) with Ni(dmit)(2) anions (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([1](+)[Ni(dmit)(2)](-) (4), [2](+)[Ni(dmit)(2)](-) (5), [3](+)[Ni(dmit)(2)](-) (6), and [1](+)[Ni(dmit)(2)](3)(-) (7)) have been prepared, and the magnetic susceptibilities (chi(M)) have been measured between 1.8 and 300 K. The chi(M) values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i). a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (THETAV;) of -0.4 and -1.7 K and (ii). a dimer system with strong negative exchange interactions of 2J/k(B) = -354 and -258 K, respectively. The dimer formations in Ni(dmit)(2) anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)(2) dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -600 K and a central interaction of 2J(2)/k(B) = -280 K for 4 and 2J(1)/k(B) = -30 K and 2J(2)/k(B) = -580 K for 6, respectively. The results of the temperature dependence of the g(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 degrees C was sigma = 0.10 S cm(-)(1) with an activation energy E(A) = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.     

Substituent effects on core structures and heterogeneous catalytic activities of Mn(III)(μ-O)2Mn(IV) dimers with 2,2':6',2″-terpyridine derivative ligands for water oxidation

[(OH(2))(R-terpy)Mn(μ-O)(2)Mn(R-terpy)(OH(2)) ](3+) (R-terpy = 4'-substituted 2,2':6',2″-terpyridine, R = butoxy (BuO), propoxy (PrO), ethoxy (EtO), methoxy (MeO), methyl (Me), methylthio (MeS), chloro (Cl)) have been synthesized as a functional oxygen-evolving complex (OEC) model and characterized by UV-vis and IR spectroscopic, X-ray crystallographic, magnetometric, and electrochemical techniques. The UV-vis spectra of derivatives in water were hardly influenced by the 4'-substituent variation. X-ray crystallographic data showed that Mn centers in the Mn(III)(μ-O)(2)Mn(IV) cores for derivatives with R = H, MeS, Me, EtO, and BuO are crystallographically indistinguishable, whereas the derivatives with R = MeO and PrO gave the significantly distinguishable Mn centers in the cores. The indistinguishable Mn centers could be caused by rapid electron exchange between the Mn centers to result in the delocalized Mn(μ-O)(2)Mn core. The exchange integral values (J = -196 to -178 cm(-1)) for delocalized cores were lower than that (J = -163 to -161 cm(-1)) for localized cores, though the Mn···Mn distances are nearly the same (2.707-2.750 ?). The half wave potential (E(1/2)) of a Mn(III)-Mn(IV)/Mn(IV)-Mn(IV) pair of the derivatives decreased with an increase of the electron-donating ability of the substituted groups for the delocalized core, but it deviated from the correlation for the localized cores. The catalytic activities of the derivatives on mica for heterogeneous water oxidation were remarkably changed by the substituted groups. The second order rate constant (k(2)/mol(-1) s(-1)) for O(2) evolution was indicated to be correlated to E(1/2) of a Mn(III)-Mn(IV)/Mn(IV)-Mn(IV) pair; k(2) increased by a factor of 29 as E(1/2) increased by 28 mV.     

Rigid MIIL2Gd2III (M = Fe, Ru) complexes of a terpyridine-based heteroditopic chelate: a class of candidates for MRI contrast agents

Rigid chelates of high-molecular weight, [M(tpy-DTTA)2]6- (M = Fe, Ru), are obtained upon self-assembly around one M(II) ion of two terpyridine-based molecules substituted in the 4'-position with the polyaminocarboxylate diethylenetriamine-N,N,N',N'-tetraacetate, tpy-DTTA4-. The protonation constants of tpy-DTTA4- (log K1 = 8.65(4), log K2 = 7.63(4), log K3 = 5.25(6), log K4 = 3.30(7)) and [Fe(tpy-DTTA)2]6- (log K1 = 8.40(4), log K2 = 7.26(4)) have been determined by potentiometry, 1H NMR and UV-vis titrations. The thermodynamic stability constant log K(GdL) of [Fe(tpy-DTTA)2Gd2(H2O)4] measured at 25 degrees C by potentiometry is 10.87. This relatively low value is due to the direct linkage of the polyaminocarboxylate part to the electron-withdrawing terpyridine. UV-vis absorbance spectra of [M(tpy-DTTA)2Gd2(H2O)4] and 1H NMR spectra of [M(tpy-DTTA)2Eu2(H2O)4] revealed similar solution behavior of the Fe and Ru complexes. An I(d) water-exchange mechanism (DeltaV++ = +6.8 +/- 1 cm3 mol(-1)) with a rate constant of k(ex)298 = (5.1 +/- 0.3) x 10(6) s(-1) has been found for [Fe(tpy-DTTA)2Gd2(H2O)4] by 17O NMR. A slow rotational correlation time (tau(RO) = 410 +/- 10 ps) and the presence of two water molecules (q = 2) in the coordination inner-sphere of each Gd(III) ion have also been determined for this complex. A remarkably high relaxivity has been observed for both [M(tpy-DTTA)2Gd2(H2O)4] complexes (at 20 MHz and 37 degrees C, r(1) = 15.7 mM(-1) s(-1) for the Fe complex, and r(1) = 15.6 mM(-1) s(-1) for the Ru complex).     

Extraction of ternary complexes of thorium(IV) with 3-phenyl-4-benzoyl-5-isoxazolone and neutral donors from nitric acid medium

The extraction behaviour of thorium(IV) from aqueous nitric acid employing 3-phenyl-4-benzoyl-5-isoxazolone (HPBI) in the presence of tri-n-octyl phosphine oxide (TOPO) as well as tri-n-butyl phosphate (TBP) in xylene medium was investigated. The extraction constant (log k(ex)) for the binary organic phase species Th(PBI)(4) was determined to be 8.26 which is by far the largest amongst the corresponding values known for other beta-diketones. The overall extraction constant (log K) for the ternary species Th(PBI)(4) TBP and Th(PBI)(4).2TOPO were estimated to be 14.96 and 20.96 respectively. An inverse correlation of the adduct formation constant (log K(s)) with the pK(a) of the beta-diketones, 2-thenoyltrifluoroacetone, 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and HPBI, was observed. The steric as well as the electronic effects of adduct formation have been discussed. Analytical application of HPBI for the separation of (234)Th radiotracer from natural uranium (99.3% (238)U) has been suggested.     

Evaluation of the Hydrophilic Property of Sodium Ion-pair Complexes with 3m-Crown-m Ethers (m = 5, 6) and Their Benzo-derivatives by Solvent Extraction

The ion-pair formation constants {K(j)(0): j = MA (metal salt), MLA} of NaO(2)CCF(3) (Na(+)tfa(-)) and its ion-pair complexes (MLA) in water (w) were determined potentiometrically at 25 degrees C and an ionic strength (I) of zero. 15-Crown-5 (15C5), 18-crown-6 ethers (18C6), and their mono-benzo derivatives were used as crown ethers (L). The extraction of Natfa by these four L from w into 1,2-dichloroethane was done at 25 degrees C, and then the extraction constants (K(ex)) for NaLtfa were calculated by using the K(j) values, which were estimated from the corresponding K(j)(0) ones at I of the w-phases, and other equilibrium constants. Also, the distribution constants (K(D,MLA)) of NaLtfa between the two phases were obtained from a thermodynamic cycle expressing K(ex). An interaction of w-molecules with NaLA was considered using a relation of log K(D,MLA) with log K(D,L), derived from the Scatchard-Hildebrand equation, where K(D,L) denotes the distribution constant of L between the two phases. The interaction increased in the order of NaL (picrate) < free L 相似文献   

A rapid extractive spectrophotometric method for the determination of tin in canned foods with 5,7-dichloro-8-quinolinol

A rapid method for the spectrophotometric determination of tin in canned foods, based on formation of the binary Sn(IV)-5,7-dichloro-8-quinolinol complex and extraction into chloroform has been developed. The absorption maximum at 390nm ( = 1.26 x 10(4) l.mole(-1).cm(-1)) is used for the determination. Beer's law is obeyed up to 6mug of tin per ml. Organic matter is destroyed by digestion with acid. Potential interferences have been studied. The detection limit for tin is 2.5mg kg .     

A mechanistic approach to the kinetics of oxidation of uranium(IV) by hexachloroplatinate(IV) in aqueous perchlorate solutions. Evidence of the formation of a binuclear intermediate complex

The kinetics of hexachloroplatinate(IV) oxidation of uranium(IV) ion in aqueous perchloric acid solutions at a constant ionic strength of 1.0 mol dm(-3) has been investigated using the stopped-flow and conventional spectrophotometric techniques. The oxidation reaction was found to proceed through two distinct stages. The initial stage was found to be relatively fast corresponding to the formation of [(H(2)O)(n)U(IV)·Cl(6)Pt(IV)](2+) binuclear intermediate complex (with the rate constant k(1) = 1.75 × 10(4) dm(3) mol(-1)s(-1), k(-1) = 6.8 s(-1), and the formation constant K = 2.6 × 10(3) dm(3) mol(-1) at [H(+)] = 1.0 mol dm(-3) and 25 °C for binuclear formation). This stage was followed by a much slower stage corresponding to the transfer of two electrons from U(IV) to Pt(IV) in the rate-determining step (with the rate constant k = 5.32 × 10(-5) s(-1) at [H(+)] = 1.0 mol dm(-3) and 25 °C). The reaction stoichiometry was found to depend on the molar ratio of the reactants concentration. The experimental results indicated the decrease of the observed first-order rate constants with increasing the [H(+)] for the decomposition of the binuclear intermediate complex through the slow-second stage, whereas no change was observed with respect to the rate of formation of the binuclear complex at the initial rapid part. A tentative reaction mechanism consistent with the kinetic results is discussed.     

Spectrophotometric studies on ion-pair extraction equilibria of the iron(ii) and iron(III) complexes with 4-(2-pyridylazo)resorcinol

The ion-pair extraction equilibria of the iron(II) and iron(III) chelates of 4-(2-pyridylazo)resorcinol (PAR, H(2)L) are described. The anionic chelates were extracted into chloroform with benzyldimethyltetradecylammonium chloride (QC1) as counter-ion. The extraction constants were estimated to be K(ex1)(Fe(II)) = [Q{Fe(II)(HL)L}](0)/[Q(+)][{Fe(II)(HL)L}(-)] = 10(8.59 +/- 0.11), K(ex2)(Fe(II)) = [Q(2){Fe(II)L(2)}](o)/ [Q(+)](2)[{Fe(II)L(2)}(2-)] = 10(12.17 +/- 0.10) and K(ex1)(Fe(III)) = [Q{Fe((III))L(2)}](o)/(Q(+)][{Fe(III)L(2)}(-)] = 10(6.78 +/- 0.15) at I = 0.10 and 20 degrees , where [ ](o) is concentration in the chloroform phase. Aggregation of Q{Fe(III)L(2)} in chloroform was observed and the dimerization constant (K(d) = [Q(2){Fe(III)L(2)}(2)](o)/[Q{Fe(III)L(2)}](o)(2)) was evaluated as log K(d) = 4.3 +/- 0.3 at 20 degrees . The neutral chelates of {Fe(II)(HL)(2)} and {Fe(III)(HL)L}, and the ion-pair of the cationic chelate, {Fe(III)(HL)(2)}ClO(4), were also extracted into chloroform or nitrobenzene. The relationship between the forms and extraction properties of the iron(II) and iron(III) PAR chelates are discussed in connection with those of the nickel(II) and cobalt(III) complexes. Correlation between the extraction equilibrium data and the elution behaviour of some PAR chelates in ion-pair reversed-phase partition chromatography is also discussed.     

The antimony(III)-bridged heteropolyanion sandwich dimers [Sb(II3(A-α-XW9O34)2]11- (X = SiIV, GeIV and C-shaped double-sandwich [SbIII6O2(PW6O26)(A-α-PW9O34)2]15-

Interaction of potassium antimony(iii) tartrate hydrate K(2)(SbC(4)H(2)O(6))(2)·3H(2)O with the trilacunary Keggin derivatives [A-α-XW(9)O(34)](10-) (X = Si(IV), Ge(IV)) and [A-α-PW(9)O(34)](9-) in aqueous acidic medium (pH 4.8) resulted in three novel polyanions, [Sb(3)(A-α-XW(9)O(34))(2)](11-) (X = Si(IV) (1), Ge(IV) (2)) and [Sb(6)O(2)(A-PW(6)O(26))(A-α-PW(9)O(34))(2)](15-) (3), which were isolated as the hydrated potassium salts K(11)[Sb(3)(A-α-XW(9)O(34))(2)]·31H(2)O (X = Si(IV) (K-1), Ge(IV) (K-2)) and the mixed potassium-sodium salt K(14)Na[Sb(6)O(2)(A-PW(6)O(26))(A-α-PW(9)O(34))(2)]·61H(2)O (KNa-3) salts, respectively, and characterized by single-crystal X-ray diffraction, IR spectroscopy, as well as elemental and thermogravimetric analyses. The Sb(III)-containing polyanions 1-3 possess unique structural features, as they represent the first examples of sandwich-type POMs with trigonal-pyramidal Sb(III)O(3) linkers. The stability of 1-3 in aqueous media was investigated by multinuclear ((183)W, (31)P) NMR and UV-Vis spectroscopy.     

Mixed-valent [FeIV(mu-O)(mu-carboxylato)2FeIII]3+ core

The symmetrically ligated complexes 1, 2, and 3 with a (mu-oxo)bis(mu-acetato)diferric core can be one-electron oxidized electrochemically or chemically with aminyl radical cations [*NR3][SbCl6] in acetonitrile yielding complexes which contain the mixed-valent [(mu-oxo)bis(mu-acetato)iron(IV)iron(III)]3+ core: [([9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](ClO4)2 (1(ClO4)2), [(Me3[9]aneN3)(2FeIII2)(mu-O)(mu-CH3CO2)2](PF6)2 (2(PF6)(2)), and [(tpb)(2FeIII2)(mu-O)(mu-CH3CO2)2] (3) where ([9]aneN3) is the neutral triamine 1,4,7-triazacyclononane and (Me3[9]aneN3) is its tris-N-methylated derivative, and (tpb)(-) is the monoanion trispyrazolylborate. The asymmetrically ligated complex [(Me3[9]aneN3)FeIII(mu-O)(mu-CH3CO2)2FeIII(tpb)](PF6) (4(PF6)) and its one-electron oxidized form [4ox]2+ have also been prepared. Finally, the known heterodinuclear species [(Me3[9]aneN3)CrIII(mu-O)(mu-CH3CO2)2Fe([9]aneN3)](PF6)2 (5(PF6)(2)) can also be one-electron oxidized yielding [5ox]3+ containing an iron(IV) ion. The structure of 4(PF6).0.5CH3CN.0.25(C2H5)2O has been determined by X-ray crystallography and that of [5ox]2+ by Fe K-edge EXAFS-spectroscopy (Fe(IV)-O(oxo): 1.69(1) A; Fe(IV)-O(carboxylato) 1.93(3) A, Fe(IV)-N 2.00(2) A) contrasting the data for 5 (Fe(III)-O(oxo) 1.80 A; Fe(III)-O(carboxylato) 2.05 A, Fe-N 2.20 A). [5ox]2+ has an St = 1/2 ground state whereas all complexes containing the mixed-valent [FeIV(mu-O)(mu-CH3CO2)2FeIII]3+ core have an St = 3/2 ground state. M?ssbauer spectra of the oxidized forms of complexes clearly show the presence of low spin FeIV ions (isomer shift approximately 0.02 mm s(-1), quadrupole splitting approximately 1.4 mm s(-1) at 80 K), whereas the high spin FeIII ion exhibits delta approximately 0.46 mm s(-1) and DeltaE(Q) approximately 0.5 mm s(-1). M?ssbauer, EPR spectral and structural parameters have been calculated by density functional theoretical methods at the BP86 and B3LYP levels. The exchange coupling constant, J, for diiron complexes with the mixed-valent FeIV-FeIII core (H = -2J S1.S2; S(1) = 5/2; S2 = 1) has been calculated to be -88 cm(-1) (intramolecular antiferromagnetic coupling) and for the reduced diferric form of -75 cm(-1) in reasonable agreement with experiment (J = -120 cm(-1)).     

Ab initio study of the ClO + NH2 reaction: prediction of the total rate constant and product branching ratios

The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + 3NH (X(3)Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + 3NH (X(3)Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k1(HCl + HNO) = 4.7 x 10(-8)(T(-1.08)) exp(-129/T), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T(-0.62)) exp(-24/T), k3(HOCl + NH) = 4.8 x 10(-29)(T5.11) exp(-1035/T), and k(total) = 5.0 x 10(-9)(T(-0.67)) exp(-1.2/T), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.     

Comparative kinetics and mechanism of oxygen and sulfur atom transfer reactions mediated by bis(dithiolene) complexes of molybdenum and tungsten

Although the kinetics and mechanism of metal-mediated oxygen atom (oxo) transfer reactions have been examined in some detail, sulfur atom (sulfido) transfer reactions have not been similarly scrutinized. The reactions [M(IV)(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-) + Ph(3)AsQ --> [M(VI)Q(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-) + Ph(3)As (M = Mo, W; Q = O, S) with variable substituent X' have been investigated in acetonitrile in order to determine the relative rates of oxo versus sulfido transfer at constant structure (square pyramidal) of the atom acceptor and of atom transfer at constant structure of the atom donor and metal variability of the atom acceptor. All reactions exhibit second-order kinetics and entropies of activation (-25 to -45 eu) consistent with an associative transition state. At parity of atom acceptor, k(2)(S) (0.25-0.75 M(-1)s(-1)) > k(2)(O) (0.023-0.060 M(-1)s(-1)) with M = Mo and k(2)(S) (4.1-66.7 M(-1)s(-1)) > k(2)(O) (1.8-9.8 M(-1)s(-1)) with M = W. At constant atom donor and X', k(2)(W) > k(2)(Mo) with reactivity ratios k(2)(W)/k(2)(Mo) = 78-184 (Q = O) and 16-89 (Q = S). Rate constants refer to 298 K. At constant M and Q, rates increase in the order X' = Me less, similar OMe < H < Br < COMe < CN; increasing electron-withdrawing propensity accelerates reaction rates. The probable transition state involves significant Ph(3)AsQ...M bond-making (X' rate trend) and concomitant As-Q bond weakening (bond energy order As-O > As-S). Orders of oxo and sulfido donor ability of substrates and complexes are deduced on the basis of qualitative reactivity properties determined here and elsewhere. This work complements previous studies of the reaction systems [M(IV)(O-p-C(6)H(4)X')(S(2)C(2)Me(2))(2)](1-)/XO where the substrates are N-oxides and S-oxides and k(2)(W) > k(2)(Mo) at constant substrate also applies. The reaction order of substrates is Me(3)NO > (CH(2))(4)SO > Ph(3)AsS > Ph(3)AsO. This research provides the first quantitative information of metal-mediated sulfido transfer.     

Cation-independent electron transfer between ferricyanide and ferrocyanide ions in aqueous solution

Electron transfer between Fe(CN)(6)(3-) and Fe(CN)(6)(4-) in homogeneous aqueous solution with K(+) as the counterion normally proceeds almost exclusively by a K(+)-catalyzed pathway, but this can be suppressed, and the direct Fe(CN)(6)(3)(-)-Fe(CN)(6)(4-) electron transfer path exposed, by complexing the K(+) with crypt-2.2.2 or 18-crown-6. Fe((13)CN)(6)(4-)-NMR line broadening measurements using either crypt-2.2.2 or (with extrapolation to zero uncomplexed [K(+)]) 18-crown-6 gave consistent values for the rate constant and activation volume (k(0) = (2.4 +/- 0.1) x 10(2) L mol(-1) s(-1) and Delta V(0) = -11.3 +/- 0.3 cm(3) mol(-1), respectively, at 25 degrees C and ionic strength I = 0.2 mol L(-1)) for the uncatalyzed electron transfer path. These values conform well to predictions based on Marcus theory. When [K(+)] was controlled with 18-crown-6, the observed rate constant k(ex) was a linear function of uncomplexed [K(+)], giving k(K) = (4.3 +/- 0.1) x 10(4) L(2) mol(-2) s(-1) at 25 degrees C and I = 0.26 mol L(-1) for the K(+)-catalyzed pathway. When no complexing agent was present, k(ex) was roughly proportional to [K(+)](total), but the corresponding rate constant k(K)' (=k(ex)/[K(+)](total)) was about 60% larger than k(K), evidently because ion pairing by hydrated K(+) lowered the anion-anion repulsions. Ionic strength as such had only a small effect on k(0), k(K), and k(K)'. The rate constants commonly cited in the literature for the Fe(CN)(6)(3-/4-) self-exchange reaction are in fact k(K)'[K(+)](total) values for typical experimental [K(+)](total) levels.     

Overoxidation of phenol by hexachloroiridate(IV)

It has been previously established that the aqueous oxidation of phenol by a deficiency of [IrCl(6)](2-) proceeds through the production of [IrCl(6)](3-) and phenoxyl radicals. Coupling of the phenoxyl radicals leads primarily to 4,4'-biphenol, 2,2'-biphenol, 2,4'-biphenol, and 4-phenoxyphenol. Overoxidation occurs through the further oxidation of these coupling products, leading to a rather complex mixture of final products. The rate laws for oxidation of the four coupling products by [IrCl(6)](2-) have the same form as those for the oxidation of phenol itself: -d[Ir(IV)]/dt = {(k(ArOH) + k(ArO(-))K(a)/[H(+)])/(1 + K(a)/[H(+)])}[ArOH](tot)[Ir(IV)]. Values for k(ArOH) and k(ArO(-)) have been determined for the four substrates at 25 °C and are assigned to H(2)O-PCET and electron-transfer mechanisms, respectively. Kinetic simulations of a combined mechanism that includes the rate of oxidation of phenol as well as the rates of these overoxidation steps show that the degree of overoxidation is rather limited at high pH but quite extensive at low pH. This pH-dependent overoxidation leads to a pH-dependent stoichiometric factor in the rate law for oxidation of phenol and causes some minor deviations in the rate law for oxidation of phenol. Empirically, these minor deviations can be accommodated by the introduction of a third term in the rate law that includes a "pH-dependent rate constant", but this approach masks the mechanistic origins of the effect.     

Polarographic behaviour and determination of acrivastine in capsules and human urine

Dibenzo-18-crown-6 (DB18C6) is used for the liquid-liquid extraction, and recovery of titanium from paints, pigment, paper and pulp industries. The extraction mechanism of titanium(IV) from pH 4 medium with DB18C6 in dichloromethane was investigated. The DB18C6 concentration in organic phase, the concentration of titanium, the effect of pH and interference ions such as Mo(6+), V(5+), Nb(5+), Ta(5+), Zr(4+), Fe(3+), etc. in the aqueous phase and the temperature on the distribution coefficient for the Ti(IV) have been examined. The titanium was determined by spectrophotometric and inductively coupled plasma atomic emission spectroscopic (ICP-AES) method. Titanium forms a colourless complex with DB18C6 at pH 4.0 which is extracted with dichloromethane having molar absorptivity 1.53x10(4) lmol(-1)cm(-1) at 285 nm. It obeys Beer's law in the range of 0.16-3.84 ppm of titanium. The colour was developed with thiocyanate which has molar absorptivity 1.50x10(3) lmol(-1)cm(-1) at 425 nm. The extract is directly inserted in the plasma for ICP-AES measurement, which enhance the sensitivity several folds and the limits for estimation are 0.5-30 ngml(-1). The overall formation (logbeta(2)K'e) and extraction (K(ex)) constants calculated are 18.61+/-0.02 and 1.03+/-0.03x10(-10), respectively. The transportation of titanium has been discussed. The titanium is preconcentrated and determined in standard and environmental samples.     

Magnetic semiconductor: structural,magnetic, and conducting properties of the salts of the 6-oxoverdazyl radical cation with M(dmit)(2) anions (M = Ni,Zn, Pd,and Pt,dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Five kinds of (1:1), (1:3), and (2:1) salts of 3-[4-(diethylmethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation [V](+) with M(dmit)(2) anions (M = Ni, Zn, Pd, and Pt, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([V](+)[Ni(dmit)(2)](-) (1), [V](+)[Ni(dmit)(2)](3)(-) (2), [V](+)(2)[Zn(dmit)(2)](2-) (3), [V](+)(2)[Pd(dmit)(2)](2-) (4), and [V](+)(2)[Pt(dmit)(2)](2-) (5)) and an iodide salt of [V](+) ([V](+)[I](-) (6)) have been prepared, and the magnetic susceptibilities (chi(M) values) have been measured between 1.8 and 300 K. The chi(M) of the (1:1) Ni salt (1) can be well reproduced by the sum of the contributions from (i) a Curie-Weiss system with a Curie constant (C) of 0.376 K emu/mol and a negative Weiss constant (theta) of -1.5 K and (ii) the one-dimensional Heisenberg antiferromagnetic alternating chain system with 2J(A-B)/k(B) = -274 K (alternation parameter alpha = J(A-C)/J(A-B) = 0.2). The chi(M) of the (1:3) Ni salt (2) can be well explained by the two-term contributions from (i) the Curie-Weiss system with C = 0.376 K emu/mol and theta = -5.0 K and (ii) the dimer system with 2J/k(B) = -258 K. The magnetic properties of 1 and 2 were discussed based on the results obtained by crystal structure analysis and ESR measurements of 1 and 2. The chi(M) values of the (2:1) Zn, Pd, Pt salts 3, 4, and 5 and [V](+)[I](-) salt 6 follow the Curie-Weiss law with C = 0.723, 0.713, 0.712, and 0.342 K emu/mol and theta = -2.8, -3.1, -2.6, and +0.02 K, respectively, indicating that only the spins of the verdazyl radical cation contribute to the magnetic property of these salts. The salts 1, 3, and 5 are insulators. On the other hand, the conductivity (sigma) of the Ni salt 2 and Pd salt 4 at 20 degrees C was sigma = 8.9 x 10(-2) and 1.3 x 10(-4) S cm(-)(1) with an activation energy E(A) = 0.11 and 0.40 eV, respectively. The salts 2 and 4 are new molecular magnetic semiconductors.     

Magnetic studies on hexaiodorhenate(IV) salts of univalent cations. Spin canting and magnetic ordering in K2[ReI6] with Tc = 24 K

The ionic salts of rhenium(IV) of formula (Cat)(2)[ReI(6)] with Cat = Li(+) (1), Na(+) (2), K(+) (3), Rb(+) (4), Cs(+) (5), NH(4)(+) (6), and AsPh(4)(+) (7) [AsPh(4)(+) = tetraphenylarsonium cation] have been synthesized, and the structures of two of them (namely, 3 and 6) were determined by single-crystal X-ray diffraction. 3 crystallizes in the monoclinic system, space group Pn, with a = 7.815(1) A, b = 7.874(1) A, c = 11.335(1) A, beta = 90.38(1) degrees, and Z = 2 whereas 6 crystallizes in the tetragonal system, space group P4/mnc, with a = 7.881(1) A, b = 7.881(1) A, c = 11.474(2) A, and Z = 2. The structures of 3 and 6 are made up of discrete [ReI(6)](2)(-) anions and K(+) (3) or NH(4)(+) (6) cations held together by electrostatic forces (3 and 6) and N-H.I hydrogen bonds (6). The rhenium(IV) cation in 3 and 6 is surrounded by six iodide ligands in an octahedral environment with the Re-I bond lengths varying in a very narrow range [2.704(3)-2.738(3) and 2.716(1)-2.722(2) A for 3 and 6, respectively]. The [ReI(6)](2)(-) anions in 6 describe a tetragonally distorted body-centered cubic structure. In 3, the arrangement of these units is similar but more distorted. The different arrangement of the anions in 3 and 6 accounts for the centrosymmetric (6) and non-centrosymmetric (3) structures observed. The magnetic properties of 1-7 were investigated in the temperature range 2.0-300 K. The magnetic behavior of 7 is that of a magnetically diluted Re(IV) complex with a large value of the zero-field splitting of the ground level (|2D| = 49.8 cm(-)(1)) whereas those of 1, 2, and 4-6 are typical of antiferromagnetically coupled systems with susceptibility maxima at 28 (1), 27 (2), 21 (4), 16 (5), and 20 K (6). In the case of compound 3, its magnetic behavior in the high-temperature range is parallel to that observed in the parent salts but below 24 K it is a weak ferromagnet with a canting angle of ca. 1.2 degrees.     

A highly efficient solvent system containing functionalized diglycolamides and an ionic liquid for americium recovery from radioactive wastes

Three room temperature ionic liquids (RTILs), viz. C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), were evaluated as diluents for the extraction of Am(III) by N,N,N',N'-tetraoctyl diglycolamide (TODGA). At 3 M HNO(3), the D(Am)-values by 0.01 M TODGA were found to be 102, 34 and 74 for C(4)mim(+)·PF(6)(-), C(6)mim(+)·PF(6)(-) and C(8)mim(+)·PF(6)(-), respectively. The extraction of Am(III) decreased with increasing feed acidity for all three diluents, indicating an ion exchange mechanism for the extraction. The stoichiometry of the extracted species suggested that two TODGA molecules were associated with Am(III) during the extraction for all three RTILs and the conditional extraction constants have been determined. The D(M)-values for different metal ions followed the order: 75 (Am(III)) > 30.7 (Pu(IV)) > 3.9 (Np(IV)) > 1.19 (Pu(VI)) > 0.52 (U(VI)) > 0.12 (Cs(I)) > 0.024 (Sr(II)). The distribution behaviour of Am(III) was also studied with a recently synthesized calix[4]arene-4DGA (C4DGA) extractant dissolved in C(8)mim(+)·PF(6)(-). Using this extractant diluent combination, the D(Am)-value was 194 at 3 M HNO(3) using 5 × 10(-5) M C4DGA, suggesting a very high distribution coefficient at very low extractant concentrations. The stoichiometry of the extracted species containing Am was found to be 1:2 (M:L) in C(8)mim(+)·PF(6)(-). The thermodynamics of the extraction was also studied for both extractants in C(8)mim(+)·PF(6)(-). The use of RTILs gives rise to significantly improved extraction properties than the commonly used n-dodecane and an unusual increase in separation factor values was seen for the first time which can lead to selective separation of Am from wastes containing a mixture of U, Pu and Am.