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1.
The formation constants of dioxouranium(VI)—1,2,3,4,5,6-benzenehexacarboxy- late [mellitate(6?)] complexes were determined in NaCl aqueous solutions at 0.1 ≤ I ≤ 1.0 mol·L?1 and t = 25 °C by ISE-[H+] glass-electrode potentiometry. The speciation model obtained at each ionic strength includes the following species: ML4?, MLH3?, MLH2 2 ?, MLH3 ?, M2L2?, MLOH5? and ML(OH)2 6? (M = UO2 2 + and L6? = mellitate). The ionic strength dependence of the protonation constants of mellitate and of the metal-ligand complexes was investigated using the SIT (Specific Ion Interaction Theory) approach. Formation constants at infinite dilution are [for the generic equilibrium $p{\rm UO}_{\rm 2}^{{\rm 2 + }} + q({\rm L}^{{\rm 6} - }) + r{\rm H}^{\rm + }\rightleftharpoons({\rm UO}_{\rm 2}^{{\rm 2 +}})_p({\rm L})_q {\rm H}_r^{(2p - 6q + r)};\,\beta _{pqr}$ ]: log10 β 110 = 10.155, log10 β 111 = 16.084, log10 β 112 = 20.749, log10 β 113 = 24.038, log10 β 210 = 17.936, log10 β 11?1 = 2.327 and log10 β 11?2 = ?6.804. Simple linear relationships between the formation constants and the stoichiometric coefficients of reactants are reported. The sequestering capacity of mellitate towards UO2 2+ was quantified using a sigmoid Boltzman-type equation.  相似文献   

2.

Abstract  

The results of an investigation on the interactions between phytate ion (myo-inositol hexaphosphate, Phy) and some lanthanoid cations (La3+, Nd3+, Sm3+, Dy3+, and Yb3+) are reported. The stability constants of various LnH j Phy species (Ln = generic lanthanoid) were determined by potentiometry (ISE-H+ glass electrode) in NaClaq at I = 0.15 mol dm−3 and t = 25 °C, and the corresponding formation enthalpies by calorimetric titration. The thermodynamic data obtained were used to provide a speciation scheme for the lanthanoid(III)–phytate systems at different temperatures. The sequestering ability of this ligand toward Ln3+ was also evaluated by calculation of pL50 values (the total concentration of ligand necessary to bind 50% of a cation present in trace amounts) under different conditions, and equations were formulated to model their dependence on temperature and pH.  相似文献   

3.
The reagent 2-pyridyl thiourea produces a reddish brown complex with rhenium in hydrochloric acid medium in the presence of tin(II) chloride. The complex shows absorption maxima at 405 nm, obeys Beer's law for a range of 1–16 ppm of rhenium. The sensitivity and molar absorptivity is found to be 0.0115g cm–2 and 1.603×104 1 mol–1 cm–1 respectively showing an improvement over other sulphur-nitrogen bearing ligands. Composition found by Job's and mole ratio method, indicates that the complex contains metal and reagent in the ratio 12. Stability constant and stepwise formation constants of the complex have been evaluated by Harvey-Manning's method (logK overall=8.825), Leden's method (logK overall=8.3096), Rossotti-Rossotti's method (logK overall=8.653) and Yatsimirskii's method (logK overall=8.740). The relative error per 1% absolute photometric error is found to be 2.7%.  相似文献   

4.
Solution equilibrium studies on the Cu(II)-polyamine-(aminomethyl)phosphonic acid (glycinephosphonic acid) ternary systems (polyamine: ethylenediamine (en), diethylenetriamine (dien), N,N,N′,N′,N″-pentamethyldiethylenetriamine (Me5dien)) have been performed by pH-potentiometry, UV–vis spectrophotometry and EPR methods. The obtained results suggest the formation of the heteroligand complexes with [Cu(A)(Gly(P))] stoichiometry in all studied systems. Additionally, in the systems with dien the protonated [Cu(dien)(H–Gly(P))]+ species also exists in acid solution and in the system with en the [Cu(en)(Gly(P))H-1] species is formed in the basic solution. Our spectroscopic results indicate the tetragonal geometry for the [Cu(en)(Gly(P))] species, the geometry slightly deviated from square pyramidal for the [Cu(dien)(Gly(P))] complex and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me5dien)(Gly(P))] species. The coordination modes in these heteroligand complexes are discussed.  相似文献   

5.
Three rare earth compounds, KEu[AsS4] (1), K3Dy[AsS4]2 (2), and Rb4Nd0.67[AsS4]2 (3) have been synthesized employing the molten flux method. The reactions of A2S3 (A = K, Rb), Ln (Ln = Eu, Dy, Nd), As2S3, S were accomplished at 600 °C for 96 h in evacuated fused silica ampoules. Crystal data for these compounds are: 1, monoclinic, space group P21/m (no. 11), a = 6.7276(7) Å, b = 6.7190(5) Å, c = 8.6947(9) Å, β = 107.287(12)°, Z = 2; 2, monoclinic, space group C2/c (no. 15), a = 10.3381(7) Å, b = 18.7439(12) Å, c = 8.8185(6) Å, β = 117.060(7)°, Z = 4; 3, orthorhombic, space group Ibam (no. 72), a = 18.7333(15) Å, b = 9.1461(5) Å, c = 10.2060(6) Å, Z = 4. 1 is a two-dimensional structure with 2[Eu(AsS4)] layers separated by potassium cations. Within each layer, distorted bicapped trigonal [EuS8] prisms are linked through distorted [AsS4]3− tetrahedra. Each Eu2+ cation is coordinated by two [AsS4]3− units by edge-sharing and bonded to further two [AsS4]3− units by corner-sharing. Compound 2 contains a one-dimensional structure with 1[Dy(AsS4)2]3− chains separated by potassium cations. Within each chain, distorted bicapped trigonal prisms of [DyS8] are linked by slightly distorted [AsS4]3− tetrahedra. Each Dy3+ ion is surrounded by four [AsS4]3− moieties in an edge-sharing fashion. For compound 3 also a one-dimensional structure with 1[Nd0.67(AsS4)2]4− chains is observed. But the Nd position is only partially occupied and overall every third Nd atom is missing along the chain. This cuts the infinite chains into short dimers containing two bridging [As4]3− units and four terminal [AsS4]3− groups. 1 is characterized with UV/vis diffuse reflectance spectroscopy, IR, and Raman spectra.  相似文献   

6.
The molecular structures, vibrational frequencies, and electron affinities of the SF5On/SF5On (n = 1–3) species have been examined with four hybrid density functional theory (DFT) methods. The basis set used in this work is of double-ζ plus polarization quality with additional diffuse s- and p-type functions, denoted DZP++. The geometries are fully optimized with each DFT method independently. The SF5On (n = 1–3) species should be potential greenhouse gases. The anion SF5O2 with Cs symmetry has a 3A″ electronic state, and the neutral SF5O3 with 2A″ electronic state has Cs symmetry. The anions SF5O2 and SF5O3 should be regarded as SF5·O2 and SF5O·O2 complexes, respectively. Three different types of the neutral–anion energy separation presented in this work are the adiabatic electron affinity (EAad), the vertical electron affinity (EAvert), and the vertical detachment energy (VDE). The EAad values predicted by the B3PW91 method are 5.22 (SF5O), 4.38 (SF5O2), and 3.61 eV (SF5O3). Compared with the experimental vibrational frequencies, the BHLYP method overestimates the frequencies, and the other three methods underestimate the frequencies. The bond dissociation energies De (SF5On → SF5Onm + Om) for the neutrals SF5On and De (SF5On → SF5Onm + Om and SF5On → SF5Onm + Om) for the anions SF5On are reported.  相似文献   

7.
The CH radical production induced by 193 nm two-photon photolysis of CHCl3 has been measured for the first time via the cavity ring-down absorption spectroscopy of its A–X bands, using a commercial nanosecond pulsed dye laser. The range of pressure and laser intensity, as well as the time window detection, have been carefully chosen to ensure a constant CH number density during the measurement and to avoid post-photolysis reactivity. Internal energy distribution of the CH(X2II) fragment has been derived from population distribution simulations, leading to an average vibrational temperature Tvib = 1900 ± 50 K and rotational temperature Trot = 300 ± 20 K. Two competing mechanisms can be invoked for the CH production channel: either two-photon absorption via resonant excited states of CHCl3 leading to dissociation of excited CHCl3, or two-photon sequential dissociation via the formation of the vibrationally excited CHCl2 fragment. The latter mechanism is proposed to be the prominent process for CH formation.  相似文献   

8.
Single bubble evolution on a micro-electrode (Pt, φ = 0.2 mm) was observed in 0.36 M KOH solution under terrestrial (1-G) and microgravity (μ-G) environments. The bubble size during galvanostatic electrolysis (j = −2.6 × 103 A m−2) was measured by CCD images, which allowed us to calculate the gas evolution efficiency, fG, by comparison with the consumed charge. The efficiency under μ-G increased until 1 s after starting electrolysis and then reached constant value (fG = 0.85), while, under 1-G, it showed a lower value and remarkably decreased 2 s after the beginning of the measurement. Such differences between μ-G and 1-G were explained by the mass transfer rate of the dissolved gas. Bubble-induced microconvection dominated the mass transfer under μ-G without any buoyancy force, on the other hand, the single-phase free convection (microscopic natural convection) influenced the bubble growth under 1-G.  相似文献   

9.
[cis-Co(en)2(N3)2]C7H3ClNO4·1.25H2O (Cocnb) was synthesised and detailed packing analyses were undertaken to delineate the topological complementarity of [cis-Co(en)2(N3)2]+ and a 2-chloro-4-nitro benzoate anion (cnb) for second sphere coordination in the crystal lattice. The complex was completely characterised by elemental analyses, spectroscopic studies (IR, UV/visible, 1H and 13C NMR). The compound crystallizes in the monoclinic (space group C2/c) with a = 21.9843(18), b = 8.7959(7), c = 23.0121(18) Å, β = 116.426(1)°, V = 3984.9(6) Å3, and Z = 8. In the crystal lattice, discrete ions of [cis-Co(en)2(N3)2]+ and cnb are arranged in A–B–A–B pattern (in both a and c directions of the lattice) forming columns of anions and cations. The anionic columns are π stacked and are involved in extensive hydrogen bonding interaction. It appears that the topological feature of [cis-Co(en)2(N3)2]+ is conducive for generating second sphere interactions with aromatic carboxylates. This strategy may be used as a viable method for the capture of aromatic carboxylate anions.  相似文献   

10.
Oxygen/sulfur-bridged incomplete cubane-type molybdenum aqua clusters [Mo3( 3-S)(-X)(-S)2(H2O)9]4+ (X=O, S) in hydrochloric acid react with dien (diethylenetriamine) to give [Mo3( 3-S)(-X)(-S)2(dien)(dien)2]Cl3·nH2O [1, X=O, n=3; 2, X=S, n=4; dien=NH2(CH2)2NH(CH2)2NH], respectively, where each cluster has a deprotonated dien. The X-ray structural analysis of 1 revealed proton dissociation from an amino group of one of the three dien ligands: one Mo–N distance [1.987(4) Å] is clearly shorter than the other eight Mo–N distances [2.229(3)–2.276(3) Å]. The 1H NMR spectra of the Mo–dien clusters 1 and 2 in D2O show two well-resolved methylene proton signals in the 2.8- to 3.0-ppm region, which indicates that both deprotonated amines in 1 and 2 receive D+ ions from solvent D2O. The factors for the proton dissociation are discussed.  相似文献   

11.
The aqueous protonation and anion-binding SeO 2 –/4 SO 2– 4 , and NO 3 ) constants of the macrocyclic polyamine ligand, dipyridino-hexaaza-28-crown-8(L), were measured in 0.1M KCl using a potentiometric titration technique. The protonation sequence of the aza groups of L was studied in D2O from the chemical shifts of the nonlabile protons so as to find the charge distribution geometry as a function of pD. The study indicates that in 0.1M KC1 fully protonated L forms stable l: 1 complexes with SeO 2– 4 (logK=3.68) and SO 2– 4 (logK=3.55), but not with NO 3 (logK < l.5). All of the amine pK values were above 6.3, thus allowing the use of the protonated form of this ligand over a wide pH range.  相似文献   

12.
A novel effective method for preparing polyaluminum chloride (PAC) with high content of Al13 polymer through conventional electrolysis coupled with rare earth Nd-Fe-B magnetic field was introduced. The content of Al13 polymer in PAC synthesized by this method was highly influenced by the electrobath voltage (E), the magnetic flux density (B), the current density (i) and the distance between the two adjacent electrodes (dadj). A total aluminum concentration (AlT) in the PAC solution of 0.8 mol l−1 was obtained when the E, B and i was 2.2 V, 0.4 T and 3.2 A dm−2, respectively. The optimum dadj and circulating flow (Qf) were 20 mm and 23.7 l h−1. With accelerated mass transfer rate by external magnetic field and high Qf, this process had the advantages of forming more Al(OH)4 as the precursor of Al13 polymer and inhibiting the concentration polarization more obviously than conventional electrolysis process. Under the optimum conditions, the amount of Al13 polymer in PAC accounted for 82.3% of the AlT (AlT = 0.8 M, basicity = 2.2), which was higher than that of PAC prepared by other methods.  相似文献   

13.
In this communication, an amperometric glucose biosensor based on MnO2/MWNTs electrode was reported. MnO2 was homogeneously coated on vertically aligned MWNTs by electrodeposition. The MnO2/MWNTs electrode displayed high electrocatalytic activity towards the oxidation of glucose in alkaline solution, showing about 0.30 V negative shift in peak potential with oxidation starting at ca. −0.20 V (vs. 3 M KCl–Ag/AgCl) as compared with bare MWNTs electrode. At an applied potential of +0.30 V, the MnO2/MWNTs electrode gives a linear dependence (R = 0.995) in the glucose concentration up to 28 mM with a sensitivity of 33.19 μA mM−1. Meanwhile, the MnO2/MWNTs electrode is also highly resistant toward poisoning by chloride ions. In addition, interference from the oxidation of common interfering species such as ascorbic acid, dopamine, and uric acid is effectively avoided. The MnO2/MWNTs electrode allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensor.  相似文献   

14.
Using investigations of the copper(I)–1,10-phenanthroline system as an example, it is shown that thermal lensing can be used for determining stability constants at a level of concentrations one–two orders of magnitude lower compared to conventional spectrophotometry, with better precision of measurements. The values of stability constants are log2= 11.7 ± 0.7 without regard for stepwise chelation, and logK 1= 5.9 ± 0.3, logK 2= 5.4 ± 0.3, and log2= 11.3 ± 0.6 taking into account stepwise chelation. It is shown that, when shifting from microgram to nanogram amounts of reactants in the determination of stability constants by thermal lensing, changes in the kinetic parameters of the reaction studied should be taken into account. The thermal-lens limit of detection of copper(I) is 2 × 10–8M; the linear calibration range is 4 × 10–8–2 × 10–5M (488.0 nm, pump power 120 mW). The data obtained were used for determining copper(I) in the hydrogen sulfide layer of the Baltic Sea.  相似文献   

15.
The kinetics of phenylalanine (phe) oxidation by permanganate has been investigated in absence and presence of cetlytrimethylammonium bromide (CTAB) using conventional spectrophotometric technique. The rate shows first- and fractional-order dependence on [MnO4] and [phe] in presence of CTAB. At lower values of [CTAB] (≤10.0 × 10−4 mol dm−3), the catalytic ability of CTAB aggregates are strong. In contrast, at higher values of [CTAB] (≥10.0 × 10−4 mol dm−3), the inhibitory effect was observed in absence of H2SO4. We find that anions (Br, Cl and NO3) in the form of sodium salts are strong inhibitors for the CTAB catalyzed oxidation. Kinetic and spectrophotometric evidences for the formation of an intermediate complex and an ion-pair complex between phe and MnO4, CTAB and MnO4, respectively, are presented. A mechanism consistent with kinetic results has been discussed. Complex formation constant (Kc) and micellar binding constant (Ks) were calculated at 30 °C and found to be Kc = 319 mol−1 dm−3 and Ks = 1127 mol−1 dm−3, respectively.  相似文献   

16.
A quasi-classical trajectory method (QCT) running on the 1A′ and 1A″ potential energy surfaces (PESs) given by Dobbyn and Knowles [A.J. Dobbyn, P.J. Knowles, Mol. Phys. 91 (1997) 1107] has been employed to study the dynamical stereochemistry of the chemical reaction O(1D) + D2 → OD + D, especially the vector correlations between products and reagents. The results indicate that product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane on both PESs, with different rotational polarization behaviors of product OD for the two PESs and for different collision energies. Calculations show that the alignment effect of products become weaker with an increase of the collision energy on the 1A′ PES but is not sensitive to the collision energy on the 1A″ PES. When the collision energy increases, the product OD mainly tends to the forward scattering on the 1A′ PES and displays a switch from the backward scattering to the forward one on the 1A″ PES. These differences are probably attributed to the different characteristics of the two PESs.  相似文献   

17.
Solution equilibrium studies on Cu2+–L1–L2 ternary systems have been performed by pH-potentiometry, UV–Vis spectrophotometry and EPR methods (L1 corresponds to polyamines such as ethylenediamine (en), diethylenetriamine (dien), or N,N,N′,N′,N″-pentamethyldiethylenetriamine (Me5dien) and L2 represents 1-aminoethylphosphonic acid (α-alaninephosphonic acid)). The obtained results suggest the formation of heteroligand complexes with [Cu(L1)(α-Ala(P))] stoichiometry in all studied systems. Additionally, in the system with en the [Cu(en)(α-Ala(P))H−1] species is formed in basic solution. Our spectroscopic results indicate tetragonal geometry for the [Cu(en)(α-Ala(P))] species, geometry slightly deviated from square pyramidal for the [Cu(dien)(α-Ala(P))] complex and strongly deviated from square pyramidal towards trigonal bipyramidal for the [Cu(Me5dien)(α-Ala(P))] species. The coordination modes in these heteroligand complexes are discussed.  相似文献   

18.
Mesoporous MnO2 (mesoMnO2) is synthesized facilely through sol–gel process using nonionic surfactant polyxyethylene fatty alcohol (AEO9) as template. Transmission electron microscopy (TEM) image and N2 adsorption/desorption isotherm show that the obtained mesoMnO2 material presents disordered porous structure and appropriate pore size suitable for the immobilization of glucose oxidase (GOx). An amperometric glucose biosensor based on GOx entrapped in mesoMnO2 is fabricated, in which mesoMnO2 also acts as a catalyst for the electrochemical oxidation of H2O2 produced by enzyme reaction. The biosensor shows fast and sensitive current response to glucose in the linear range of 0.0009–2.73 mM. The response time (t95%) is less than 7 s. The sensitivity and detection limit are 24.2 μA cm−2 mM−1 and 1.8 × 10−7 M (S/N = 3), respectively. This indicates that mesoMnO2 has promising application in enzyme immobilization and biosensor construction.  相似文献   

19.
Catalytic activity of Ru(acac)3 in the presence of different phosphorus compounds (P(OMe)3, P(OPh)3, PPh3 and dppe) was investigated for the first time in the hydrolysis of NaBH4. Phosphorus compound, usually known as poison in catalysis, is involved in the formation of a species which has higher catalytic activity in comparison with Ru(acac)3 alone. Varying the phosphorus compound affects the catalytic activity and lifetime of the catalyst as well as the kinetics and the activation parameters of the hydrolysis of NaBH4. For all of the phosphorus compounds, the hydrogen generation was found to be zero-order with respect to the substrate concentration and first-order regarding the catalyst concentration. The catalyst system with P(OMe)3 shows the highest catalytic activity and provides the largest total turnover number (TTON = 20,700 over 72 h) in the hydrolysis of NaBH4. The highest activation energy and enthalpy values were obtained for the catalyst with dppe (Ea = 59 ± 2, ΔH# = 60 ± 2 kJ/mol) while the lowest values were found for the catalyst system with PPh3 (Ea = 46 ± 2, ΔH# = 43 ± 1 kJ/mol).  相似文献   

20.
From conductometric and UV-VIS spectrophotometric studies of the reaction between 18-crown-6 (L) and dichloropicric acid (HA) in dry and water saturated 1,2-dichloroethane, it has been concluded that formation of a 1:1 homoconjugate HA 2 accompanies the simple protonation of L, viz, L+HALH+A and L+2HALH+HA 2 . The electrolytes LH+A and LH+HA 2 are extensively, or practically completely dissociated in both solvents under the experimental conditions. The specie LH+A appears to be a contact ion pair in DCE. The stability constant of HA 2 in the dry solvent, 5.7×103 mol–1-cm3, is some 102.4 times that in propylene carbonate reflecting the difference in H-bond accepting capacity of the two solvents. Hydration of HA, A and HA 2 in wet dichloroethane is negligible or slight. As expected, LH+ is rather strongly hydrated, the ratio of the hydration constants of LH+ and L being about 1×101.  相似文献   

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