摘要:

Conditions for the determination of trace Co in seawater are described. The method involves formation of the dimethylglyoxime complex and adsorptive accumulation onto a hanging mercury drop electrode at an applied potential of −0.70 or −0.96 V vs. SCE. The adsorbed complex is then reduced by scanning the electrode potential to −1.20 V; the reduction peak potential (Ep) is −1.12 V. Nickel behaves in a similar manner withEpof −0.99 V but the Co complex appears to be preferentially adsorbed, making analysis for Co possible even in the presence of a large excess of Ni. Adsorption of organic matter also occurs; this does not affect analytical sensitivity but limits the maximum deposition time allowed in the analysis.Determination of Co in six seawater samples yielded results ranging from 4 to 114 ng L−1. Good agreement was obtained with the one reference sample (NASS-1) for which there was a certificate value.Keywords: cobalt, dimethylglyoxime, stripping voltammetry, adsorption, seawater.

ISSN:0008-4042    

DOI:10.1139/v90-027

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The cations [Hg(E′PR′3)n]2+(E′ = S or Se; R′ = c-C6H11,n = 2–4; R′ = Ph,n = 3 or 4) are obtained in solution from the new salts [Hg(E′PR′3)n](ClO4)2(E′ = S or Se;n = 2, R′ = c-C6H11;n = 3, R′ = Ph) and their stoichiometric mixtures with E′PR′3. They have been characterized at reduced temperature using multinuclear (13C,31P,77Se (where appropriate), and199Hg) NMR. Cations of the type [(μ-ER)6(HgE′PR′3)4]2+(ER = S alkyl, SePh, or TePh, but not SPh), prepared cleanly in solution from Hg (ER)2, [Hg(E′PR′3n](ClO4)2, and E′PR′3in the correct stoichiometric ratio, have been characterized in the same manner, and shown to possess an adamantanoid structure. The product with ER = TePh, E′PR′3 = SPPh3has been isolated analytically pure. These tetranuclear cations are the first discrete species containing the adamantanoid skeleton (μ-ER)6(HgE′)4(E, E′ = chalcogen). At reduced temperature, inversion at E is slow on the NMR time scale for ER = TePh. Under these conditions, the TePh-bridged cations occur predominantly as an isomer ofC1symmetry for E′PR′3 = SPPh3, SPCy3, SePPh3. However, the SePCy3analogue appears to exist as an equilibrium mixture of an isomer ofC1symmetry and an isomer ofC3symmetry. Ligand redistribution occurs in the binary system [(μ-SePh)6(HgE′P(C6H11)3)4]2+(E′ = S or Se):[(μ-SePh)6(HgPPh3)4]2+, giving equilibrium mixtures of [(μ-SePh)6(HgPPh3)4–n(HgE′P(C6H11)3)n]2+for which the individual components have been fully characterized using NMR.Keywords: adamantanoid clusters, benzene chalcogenate, mercury(II), NMR, phosphine chalcogenide.

ISSN:0008-4042    

DOI:10.1139/v90-028

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The binuclear compoundtrans,trans-bis(ferrocenylidene)acetone [(C5H5)Fe(C5H4CHCH)]2CO (dFca) has been synthesized in quantitative yield and characterized by FT-IR,1H and13C NMR, and mass spectroscopy. Cyclic voltammetry and coulometry measurements suggest that a reversible two-electron oxidative process takes place at 0.68 V vs. SSCE. FT-IR and UV–VIS spectroelectrochemical analyses show that this oxidative process occurs at the ferrocenyl centers. The compound is also found to be emissive in the solid state (λmax = 780 nm), and charge transfer assignments for the lowest singlet and triplet excited states are made.Keywords: ferrocenyl, spectroelectrochemistry, electronic charge transfer, emission spectroscopy.

ISSN:0008-4042    

DOI:10.1139/v90-029

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A wide study was carried out of the acid–base behaviour of ferricyanide ions in aqueous perchloric acid media in the range 0.1–11.5 M. This study shows that protonation and decomposition of the ferricyanide ions occur simultaneously. The three successive protonation equilibria were found in the acidity ranges 0.1–4.0, 3.5–8.5, and 7.0–11.5 M HClO4, respectively. A kinetic study was also made of the decomposition reaction at 60 °C. The kinetic data are explained by considering a reaction mechanism involving homolytic and heterolytic dissociation steps. The homolytic and heterolytic rate constants corresponding to each of the four protonated species were determined, along with the acid–base protonation constants, pK1 = −6.25 ± 0.10; pK2 = −3.23 ± 0.03; and pK3 = −0.60 ± 0.02.Keywords: acid–base behaviour, protonated species, decomposition, homolytic dissociation, heterolytic dissociation.

ISSN:0008-4042    

DOI:10.1139/v90-030

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Partial molar and integral molar properties of mixing for PbO–PbCl2melts have been investigated by using solid electrolyte galvanic cells of the type: Ni–NiO | CaO–ZrO2 | PbO–PbCl2 | Pb. Thermodynamic properties, such as activities and partial molar enthalpies of mixing, calculated from the measured cell potentials show pronounced negative deviations from ideality. To explain this behaviour and to predict the concentration dependence of the thermodynamic properties of these solutions, a theoretical model based on a number of possible reaction mechanisms has been developed. It is shown that in a non-ideal solution, the activity of any component A+X−is given asequilibriumwhereandare respectively the cation and anion fractions in a solution that has reached the ionic composition representing a specific reaction mechanism at equilibrium. From the activity data, the limiting experimental conditions for removing the oxygen impurity from PbCl2melts and for recovery of Pb and O2by fused salt electrolysis have been established.Keywords: oxychlorides, activities, solution properties, PbO–PbCl2, EMF.

ISSN:0008-4042    

DOI:10.1139/v90-031

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Setschenow coefficients have been derived from solubility measurements on cyclohexane, benzene, naphthalene, 1-naphthol, 1,5-dihydroxynaphthalene, and anthracene in alkali halide, tetraalkylammonium bromide, and tetraphenylarsonium chloride aqueous solutions at 298.2 K. Single ion Setschenow coefficients have thence been obtained by an assumption involving extrapolation of the tetraalkylammonium bromide results to zero cation volume. Setschenow coefficients for the tetraalkylammonium cations correlate well with a hydrophobicity parameter based on their transfer chemical potentials from water into 1,2-dichloroethane.Keywords: solubilities, aqueous salt solutions, Setschenow coefficients.

ISSN:0008-4042    

DOI:10.1139/v90-032

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Activity coefficients for sodium metal in the equimolar CuTe alloy were measured up to 54 at. % sodium at 913 K. The experimental technique consisted of an alloy concentration cell with a solid alumina electrolyte. The results indicated that the solutions were Henrian up to 1 at. % sodium. In addition, for dilute sodium concentrations, there is an exosolution effect. However, for the more concentrated solutions, there is some ionicity.Keywords: tellurides, thermodynamics, alkali metals.

ISSN:0008-4042    

DOI:10.1139/v90-033

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Densities and viscosities have been determined for six binary mixtures of bromoform, aniline,n-hexane, benzonitrile, butyronitrile, and benzylnitrile at different mole fractions and temperatures. The excess volumesVE, apparent excess values of viscosity δη, excess Gibbs energy of activation of flow ΔG*E, and partial molar volumesVihave been calculated from the experimental data. Furthermore, attempts were made to calculate theoretically the excess isobaric thermal expansion coefficient δα, of the mixtures using the refractive index mixture rules. These results are in good agreement with the experimental data obtained from densities. Various excess functions and thermodynamic parameters have been used in the discussion of results to understand the nature and type of interactions in binary mixtures.Keywords: excess volume, refractive index mixture rules, interactions, bromoform, density, viscosity.

ISSN:0008-4042    

DOI:10.1139/v90-034

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

We have implemented at theabinitiolevel the vibronic coupling formalism for infrared and vibrational circular dichroism (VCD) intensities of Nafie and Freedman. We report here the results of a series of calculations on model systems. Hydrazine and hydrogen peroxide exist in chiral conformations. Although low barriers to racemization preclude the possibility of optical resolution of the parent compounds, the localgaucheconfiguration at the heteroatom bond is preserved in substituted hydrazines and peroxides and these chiral fragments may contribute significantly to the vibrational chiroptical properties of the molecules in which they appear. The calculated VCD rotational strengths for the chiralgaucheforms of both molecules suggest that the torsional mode is very intense in the VCD spectrum. Ingauchehydrazine of P chirality, the in- and out-of-phase umbrella motions of the nitrogen atoms, ν6 and ν12, respectively, give rise to an intense CD couplet with negative rotational strength to the long wave length side. In hydrazine, all combinations of NH stretches are relatively weak in the IR but the highest frequency mode of b symmetry, ν8, has moderate positive strength. The in- and out-of-phase OOH bends of HOOH behave as a coupled oscillator system, exhibiting a strong bisignate CD pattern. The signals calculated for the OH stretches are not consistent with a coupled oscillator model. The nearly degenerate stretches result in a single band arising from the more intense negative rotational strength of the antisymmetric mode ν5, in HOOH ofPchirality. An alternative model, based on induced charge flow along the chirally disposed skeleton (i.e., Nafie and Freedman's 3-bond electronic current model), explains the calculated sign of the antisymmetric mode, ν5. Significant changes in the VCD patterns due to deuterium substitution in both chiral molecules are discussed.Keywords: vibrational circular dichroism (VCD),abinitio, infrared intensities, molecular orbital, vibronic coupling theory, methanol, methanamine, hydrazine, hydroxylamine, hydrogen peroxide.

ISSN:0008-4042    

DOI:10.1139/v90-035

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The structure of 8-oxabicyclo[3.2.1]octane was calculated byabinitiomeans at the STO-3G level, and the structural data used to assign the microwave spectrum of the title compound in the range of 26.5 to 40 GHz fitting 144 lines up toJ = 48 by adjusting the rotational and three centrifugal distortion constants in the WatsonAreduction. Structural parameters were deduced from the rotational constants by allowing all bond lengths and angles to vary in a least-squares manner. These parameters were in good agreement with those calculated at the STO-3G and 3-21G levels. Of many satellite lines observed, only the most intense could be utilized for locating the two lowest fundamental vibrations, estimated to occur at 190 and 240 cm−1. The far-infrared spectrum is reported in the region of 80 to 300 cm−1, exhibiting only one distinct sequence of Q branches at 264 cm−1. On the basis of unsealedabinitioforce fields at both levels of the theory the corresponding fundamentals are assigned, respectively, to a twisting (A″) and a bending (A′) of the cycloheptane ring.Keywords: 8-oxabicyclo[3.2.1]octane, microwave and far-infrared spectra,abinitioSTO-3G and 3-21G geometries.

ISSN:0008-4042    

DOI:10.1139/v90-036

出版商:NRC Research Press    

年代:1990

数据来源: NRC