Spectrophotometric determination of palladium by solvent extraction as the Pd(II)-biacetylmonoxime 2-pyridylhydrazone complex

Determination of trace levels of palladium(II) is described. The method relies upon the extraction of palladium(II)-biacetylmonoxime 2-pyridylhydrazone (BMPH) from aqueous acidic solution into chloroform to form a purple-reddish complex. The molar absorptivity of the Pd-BMPH complex is about 7500 liters mol^?1 cm^?1 at 560 nm in the chloroform extract. The highly colored chloroform extract is suitable for spectrophotometric determination. The method devised has been applied to the determination of palladium in $\text{Pd}\text{CaCO}{}_3$ catalyst with good results.     

X-ray study of Hg2Cl2Br2 and HgCl2HgBr2 reactions in solid state

The reactions (I) Hg₂Cl₂(s) + Br₂(g) and (II) HgCl₂(s) + HgBr₂(s) have been investigated by an X-ray method. Both the reactions yield two forms of the mixed halide HgClBr, designated as α-HgClBr and β-HgClBr. The cell parameters of the two are as follows:α-HgClBr: $\text{a = 6.196}\text{A}\text{?}$, $\text{b = 13.12}\text{A}\text{?}$, $\text{c = 4.37}\text{A}\text{?}$, z = 4, ? = 5.91 g/cm³. The powder pattern and cell parameters are similar to that of HgCl₂. Therefore it is probable that the chlorine atoms, in the linear halogenHghalogen molecules of HgCl₂ structure have been replaced by bromines, and since the radius of the bromine atom is larger than that of chlorine, the lattice is larger in this case.β-HgClBr: $\text{a = 6.78}\text{A}\text{?}$, $\text{b = 13.175}\text{A}\text{?}$, $\text{c = 4.17}\text{A}\text{?}$, z = 4, ? = 5.40. These parameters are the same as those reported in the literature for β-Hg(ClBr)₂, and its X-ray powder pattern is similar to HgCl₂. Therefore this phase also has linear halogenHghalogen molecules but the distribution of Cl and Br atoms is perhaps random.Heating the products (I) and (II) up to the melting point increases the amount of α phase and decreases the β phase, whereas crystallization increases the β phase. DTA study has supported the X-ray findings.     

Anodic stripping determination of mercury in air with a glassy carbon electrode

A technique for stripping determination of mercury traces in air employing a glassy carbon electrode is described. The sample is passed at 2 liters min^?1 for 2 hr through an absorber containing 0.2 M potassium permanganate and 10% $\text{w}\text{v}$ sulfuric acid (1:1). After reduction with hydroxylamine hydrochloride, the determination is carried out in 0.12 M potassium thiocyanate at pH 2.0 ± 0.2 in the presence of 0.2 ppm of cupric ions. Calibration curves were found to be linear in the range 20 ppb-1 ppm Hg(II) in the cell. The accuracy of the method was tested over simulated samples and it was found to be better than 95%; the relative standard deviation was 5% or less. The limit of detection of mercury in air was approximately 10 μg m^?3.     

Model predictions of mean librational frequencies for rigid molecules in dilute decalin solution

The product of the reduced inertia J_r of a dipolar molecule and the square of the far infrared absorption maximum wave-number $\text{ν}$_max that it displays in dilute solution is shown, using a three-parameter Mori/itinerant oscillator model, to be related to the mean-square action on the molecule and hence by a simple argument to the solute volume of rotation V. Estimates of V have been made for seventeen rigid molecules (mainly substituted phenyls) and their $\text{ν}$_max values have been measured in decalin solution at 293 and 110 K. Provided allowance is made for translation—rotation coupling in four cases, the derived relation I_r$\text{ν}$²_max = (8a_a²c²kT)^?1V²P(0) is found to be approximately obeyed at both temperatures with P(0) (the solute-independent mean-square torque acting on a molecule of unit V) having a value of 4.0 × 10¹⁷ (N m^?2)² at both temperatures. It should now be possible to predict $\text{μ}$_max for other solutes in decalin if their structures are known.     

The influence of water-soluble alcohols on the Hg(II) and xylenol orange complexing reaction

The Hg(II)/xylenol orange (XO) complex has been studied in the presence of the watersoluble alcohols methanol, ethanol, propanol, iso-propanol, ethylene glycol, and glycerol. Only one binary complex Hg(II)/XO = 1:2 is formed in a HCit-Na₂HPO₄ pH 6.6–6.8 buffer in a 25% EtOH medium. Hg(II) can be determined (0.16–3.0 ppm) with a molar absorptivity of 3.2 × 10⁴ liter mol⁻¹ cm⁻¹.A reaction mechanism of chelation is suggested according to the experimental results. The proposed model is based on the assumption of a 1:11 intramolecular sigmatropics process allowed by the orbital symmetry, followed by an ion association with the cationic species of the solution. The constants of the reaction have been calculated and the study of the interferences and the role of strong electrolytes carried out.     

Spectrophotometric and polarographic study of pyridine-2-aldehyde guanylhydrazone-Cu(II) complex

The reaction between Cu(II) and pyridine-2-aldehyde guanylhydrazone nitrate (PAG) was investigated by using the techniques of spectrophotometry and polarography.A spectrophotometric determination of Cu(II) with PAG can be performed in a concentration range varying from 0.39–5.50 ppm of copper; the molar absorptivity is 1.2 × 10⁴ liters mole^?1 cm^?1 at 380 nm and the relative error is ±0.6%.The complex gave rise to a single well defined cathodic wave ($\text{E}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= ?0.34 V}\text{for pH}\text{= 8.1}$). The reduction process is diffusion controlled, involves two electrons, and is irreversible.The stoichiometry 1:1 of the complex was established by different methods and by both techniques. The apparent stability constants were computed as log K = 4.4 ± 0.1 and 4.7 from spectrophotometric and polarographic techniques, respectively.     

Molecular structure of liquid alcohols

A new thermodynamic treatment of continuous association is presented, where the various equilibria between i-mers are replaced by a single equilibrium between an OH groups in the bonded and the non-bonded states, linked in both cases to an indefinite ensemble of molecules. The treatment leads to an association constant K which differs from those considered in the theories of Kretschmer and Wiebe and of Wiehe and Bagley. For pure alcohols the association constant can be estimated from the vapor pressure of the alcohol and that of the homomorphous hydrocarbon. The fraction γ of free OH groups determined in this way is markedly smaller than those calculated from the other theories. For the normal alcohols the product $\text{K}\text{V}{}_{\mathrm{<mtext>A</mtext>}}$ is approximately constant at a given temperature, $\text{V}{}_{\mathrm{<mtext>A</mtext>}}$ being the molar volume. This can be expected from the increasing of the standard entropy of the non-bonded molecules when the molecular volume increases. For secondary and tertiary alcohols the product K$\text{V}{}_{\mathrm{<mtext>A</mtext>}}$ is significantly lower due to steric hindrances. However for all the alcohols considered here the enthalpy of the hydrogen bond remains nearly constant — δH being equal to 24.8 ± 2 kJ mol^?1.     

High frequency titrations: The mercury(ii)-thiocyanate reaction

Soluble complex-formation of mercury(II) thiocyanate has been studied oscillometrically. The titration of mercury(II) nitrate with thiocyanate gives one inflection corresponding to the formation of Hg(SCN)₂, while in the reverse titration the formation of Hg(SCN)⁺ is also indecated. The method is useful for a rapid determination of very small quantities of mercury or thiocyanate in highly dilute solutions. The titrations can be effected in presence of nitric acid provided its total acidity in the system does not exceed about $\text{1}\text{300}$N. Further Work on the mercury(II) -halide and mercury(II)-cyanide reactions is in progress.     

The rate constants of the gas-phase reactions K + Cl ⇆ K+ + Cl− and KCl + M ⇆ K+ + Cl− + M from measurements in atmospheric pressure flames

Mass spectrometric studies of the ions present in H₂/O₂/N₂ flames with potassium and chlorine added have demonstrated that ionization can occur in the forward steps of K + Cl ? K⁺ + Cl^? (II), KCl + M ? K⁺ + Cl^? + M (IV), where M is any third body. Variations of [K⁺] with time in these systems have been measured and establish that the rate coefficients (in ml molecule^?1 s^?1) of the ion-producing steps are k₂ = 5 × 10^?10T^{?$\text{1}\text{2}$} exp(?10 500/T) and k₄ = 2.2 × 10⁷T^?3.5 × exp(?60 800/T). Coefficients for ion-ion recombination have been obtained from k₂ and k₄ using the equilibrium constants of (II) and (IV) and are k_?2 = 1.7 × 10^?9T^{?$\text{1}\text{2}$} and k_?4 = 1.1 × 10^?17T^?3, with each one in the ml molecule^?1 s^?1 system of units. Replacement of the N₂ in one of these flames with sufficient Ar to maintain the temperature constant leaves the measured k₂ and k_?2 unchanged, but lowers the observed k₄ and k_?4. This confirms that ion-recombination in the backward step in (II) is a two-body process, whereas in (IV) it is termolecular.     

Thermal investigation of diamine complexes of Zn(II) in the solid state

The complexes [Zn(en)₃]X2·n H₂O, where en = ethylenediamine, X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 1 or 0.5, and [Zn(tn)₂]X₂·n H₂O, where tn=1,3-diaminopropane, X=Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 0 or 0.25, have been synthesized and their thermal investigations carried out. The complexes were characterized by elemental analysis and IR spectral data. These complexes have been observed to decompose through several isolable as well as non-isolable complex species as intermediates during heating. [Zn(tn)₂]SO₄ undergoes solid-state phase transition in the temperature range 126–145°C. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) have been synthesized pyrolytically in the solid state from their corresponding mother diamine complexes. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) complexes decompose through non-isolable hemidiamine species. ZnX₂ (X = Cl^? or Br^?) complexes of tn undergo melting after formation of the monodiamine species. In contrast, the corresponding en complexes undergo melting at non-stoichiometric composition. Diamine (en or tn) is found to be bridging in all monodiamine (en or tn) complexes; whilst their mother complexes possess chelated en or tn. The thermal stability sequence of en and tn complexes of Zn(II) is ZnCl₂ < ZnBr₂ < ZnSO₄. ΔH values are reported for some steps of decomposition. Possible mechanistic paths have been reported for each step of decomposition.     

Phase diagram and some physical properties of V2O3+x1 (0 ? x ? 0.080)

The magnetic and electric properties of V₂O_3+x were investigated by measurements of magnetic susceptibility, electrical resistivity, magnetotorque, Mössbauer of doped ⁵⁷Fe, and NMR of ⁵¹V, and the results were compared with those of the (V_1?xTi_x)₂O₃ system or highly pressured V₂O₃. The results obtained are as follows: (1) The metallic state shows an antiferromagnetic ordering at T_N (x). The value of T_N for metallic V₂O₃, obtained by interpolation to x = 0, shows the coincidence between V₂O_3+x and the (V_1?xTi_x)₂O₃ system. (2) Magnetic susceptibility of V₂O_3+x is expressed as χ_M(V₂O_3+x) = (1?x)χ_M(V³⁺) + xχ_M(V⁴⁺). χ_M(V⁴⁺) obeys the Curie-Weiss law $\text{(χ}{}_{\mathrm{<mtext>M</mtext>}}\text{(}\text{V}{}^{\mathrm{4+}}\text{) =}\text{0.77}\text{T}\text{+ 17)}$. (3) In the insulating phase, the electrical resistivity ? is expressed as a common equation: $\text{? = 10}{}^{\mathrm{?1.8}}\text{exp}\text{(}\text{E}\text{kT}\text{)}$. This implies that the substitution of Ti or nonstoichiometry (V⁺⁴ + metal vacancies) has little influence on the carrier mobility (or bandwidth). (4) There is a critical length in the c-axis (? 14.01 Å) where the metal-insulator transition takes place. This suggests that the length of the c-axis plays an important role in the metal-insulator transition of V₂O₃-related compounds.     

Phase equilibria in the system V2O3Ti2O3TiO2 at 1473°K

The phase equilibria in the V₂O₃Ti₂O₃TiO₂ system have been determined at 1473°K by the quench method, using both sealed tubes and controlled gaseous buffers. For the latter, $\text{CO}{}_2\text{H}{}_2$ mixtures were used to vary the oxygen fugacity between 10^?10.50 and 10^?16.73 atm. Under these conditions the equilibrium phases are: a sesquioxide solid solution between V₂O₃ and Ti₂O₃ with complete solid solubility and an upper stoichiometry limit of (V, Ti)₂O_3.02; an M₃O₅ series which has the V₃O₅ type structure between V₂TiO₅ and V_0.69Ti_2.31O₅ and the monoclinic pseudobrookite structure between V_0.42Ti_2.58O₅ and Ti₃O₅; series of Magneli phases, V₂Ti_n?2O_2n?1Ti_nO_2n?1, n = 4–8; and reduced rutile phases (V, Ti)O_2?x, where the lower limit for x is a function of the $\text{V}\text{(V + Ti)}$ ratio. The extent of the different solid solution areas and the location of the oxygen isobars have been determined.     

The tris(picolinate)vanadate(II) ion: Redox properties and electron transfer kinetics with cobalt(III) amines

Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 10³ M^?1) cm^?1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E_{$\text{1}\text{2}$} = ?0.448 V vs NHE, and ΔS_rc^θ = ?6 cal · mol^?1 · deg^?1. Electron transfer kinetics with [CO(en)₃]³⁺ led to k₁₂ = 3100 M^?1 s^?, ΔH^≠ = 12.4 kcal · mol^?1 and ΔS^≠ = ?0.9 cal · mol^?1 · deg^?1 (I = 0.10 M). For the related [Co(NH₃)₆]³⁺ complex, k₁₃ = 1.9 × 10⁴ M^?1 s^?1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.     

Kinetics of the reaction of aluminum EDTA and cobalt(II) EDTA with calmagite

The reaction of aluminum EDTA with calmagite was found to be first-order in calmagite, half-order in aluminum EDTA, and zero-order in excess EDTA. The three-halves-order apparent rate constant at pH 9.48 and 20°C with ionic strength 0.30 was 0.232 ± 0.0141^{$\text{1}\text{2}$} · mol^{$\text{1}\text{2}$} · s^?1. The activation energy was 3.2 ± 0.3 kcal/mol. The pH dependence was complex between 8 and 10. The mechanism proposed is a rapid dissociation of a dimer of aluminum EDTA to a monomer followed by a rate-determining displacement of the EDTA by calmagite. The reaction of Co(II) EDTA with calmagite was confirmed to be first-order in Co(II) EDTA and first-order in calmagite with an activation energy of 7.5 ± 0.6 kcal/mol.     

Gas phase oxidative-addition reactions of alkyl radicals at complexed cobalt(II) centres

Negative chemical ionisation mass spectrometry is used as a probe to identify reactions between hydrocarbon radicals and cornplexed cobalt(II) centres in the gas phase. Methane NCI mass spectra of a series of cobalt(II) complexes containing O₄, O₂N₂ and N₄ donor atom sets are characterised by adduct ions of the form [M + C_nH_2n+1]^? at m/z values above the molecular ion, [M]^?. Formation of such ionic species has been rationalised in terms of a one-electron oxidative-addition mechanism involving attack by hydrocarbon plasma-derived alkyl radicals at the metal centre prior to electron capture: Co^IIL_n + R^? → RCo^IIIL_n$\text{e}{}^{\mathrm{?}}$ [Co^IL_n]^?. The competing resonance electron attachment reaction: Co^IIL_n$\text{e}{}^{\mathrm{?}}$ also occurs within the ion source.     

The mechanism of ascorbic acid oxidation by Cu(II)-poly-4-vinylpyridine complexes

The mechanism of ascorbic acid (DH₂) oxidation with molecular oxygen catalysed by the polynuclear complex of Cu²⁺ with poly-4-vinylpyridine (PVP), partially quaternized by dimethylsulphate, has been studied. The half-conversion time of the reaction of DH₂ with Cu(II) PVP under anaerobic conditions is independent of [Cu²⁺]. At pH 3.5, t_0.5 (sec) = 0.8 + 5 × 10^?4 [DH₂]. The formation of an intermediate cupric-ascorbate complex is suggested (K_c ≈ 10⁴ M^?1). Free radicals of ascorbic acid are detected by the ESR-method combined with a flow technique. The small steady-state concentration of radicals indicates that their decay occurs inside the macromolecular complex. The rate constant of the PVP Cu(II) DH^? ternary complex dissociation is ≈0.4 sec^?1 (pH 3.5). The reaction of Cu(I) PVP with O₂ is not accompanied by formation of O₂^? outside the macromolecule bulk. The rate constant of this reaction is 1.3 ± 0.15) × 10² M^?1 sec^?1 (pH 3.5). The cyclic mechanism of the catalytic reaction is suggested to include interchange of the redox state of copper-ions. About $\text{2}\text{3}$ of the total copper ion exists in the form Cu(I) PVP during the reaction at pH 3.5. The rate of DH₂ oxidation under these conditions is limited by the rate of Cu(I) PVP reaction with O₂. At pH 4.5 the overall reaction rate is limited by the rate of interaction of Cu(II) PVP with DH^?.     

Preparation and properties of PdPSe single crystals

Single crystals of PdPSe were shown to be n-type semiconductors. Weak Pauli paramagnetic behavior was observed, which is consistent with the presence of delocalized electrons. Electrical measurements showed a room-temperature resistivity ? = 70 ohm-cm, activation energy of resistivity E_a = 0.32 eV, and Hall mobility μ = 34 cm² V^?1 sec^?1. Photoelectronic measurements in aqueous solutions of $\text{I}{}^{\mathrm{?}}\text{I}{}^{\mathrm{?}}{}_3$ indicate that PdPSe has high quantum efficiencies below 800 nm. The indirect optical band gap is 1.28(2) eV.     

The behaviour of copper and thallium hexafluoromolybdates(V) in acetonitrile

Copper(I), copper(II), and thallium(III) hexafluoromolybdates(V), prepared by the oxidation of the metals in acetonitrile with molybdenum hexafluoride (A. Prescott, D.W.A.Sharp, and J.M. Winfield, $\text{J. Chem. Soc., Dalton Trans.}$, 1975, 963) have been investigated by cyclic voltametry. Half wave potentials, E_{$\text{1}\text{2}$} V vs. Ag^p+/Ag were obtained using a evacuable cell equipped with anexternal Ag^p+/Ag electrode, enabling strict anerobic conditions to be maintained. A number of reversible or quasi-reversible electron transfer processes have been observed, enabling comparison with synthetic work to be made. Results for Cu^I and Cu^II hexafluoromolybdates(V) are in accord with preparative experience. MoF₆. Mo^VI/Mo^VE_{$\text{1}\text{2}$} +1.600V, oxidises Cu metal to Cu^II in MeCN, and Cu^II is reduced by Cu^O to Cu^I , Cu^lI/Cu^IE_{$\text{1}\text{2}$} = +0.750 or +0.710V for Cu^I and Cu^II solutes respectively, Cu^I/Cu^OE$\text{1}\text{2}$ = ?0.720V not reversible. A wave at E_{$\text{1}\text{2}$} = ?0.350V is assigned to Mo^V/Mo^IV by analogy with Ag^I hexafluoromolybdate (D.W.A. Sharp, unpublished work). E_{$\text{1}\text{2}$} data for I₂ in MeCN, I₂/I₃^- = 0.280, I₃^?/I^? = -0.116V, suggest that reduction of MoF₆^? by I is not likely, in contrast to the situation in SO₂ (A.J. Edwards and R.D. Peacock, $\text{Chem. Ind.}$, 1960, 1441). Reduction of MoF₆^? by Cu^o in MeCN should be feasible, but appears to be very slow. Pure Tλ^III hexafluoromolybdate(V) is obtained from Tλ^o and MoF₆ only when the mole ratio MoF₆:Tλ>5:1. Smaller ratios produce yellow solids in which Mo:Tλ is $\text{ca}$. 2:1. Tλ^III is a stronger oxidising agent than Cu^II in MeCN, as oxidation of Cu^I by Tλ^III is rapid and quantitative. However a reversible electron transfer wave assignable to Tλ^III/Tλ^I is not observed in the expected fange +1.600 to +0.710V possibly because of solute-electrode interactions.     

Synthèse et structure cristalline d'un nouvel oxyde mixte FeV2O6H0.5 relation avec la structure type diaspore

Single crystals of a new compound, FeV₂O₆H_0.5, have been obtained by hydrothermal synthesis at 650°C and 2 kbar. An electron microprobe analysis indicated that the chemical formula is FeV₂O₆. This compound has an orthorhombic symmetry, space group P2₁2₁2₁ with Z = 4. The unit cell dimensions are

$\text{a = 4.891}\text{A}\text{?}\text{, b = 9.553}\text{A}\text{?}\text{, c = 8.786}\text{A}\text{?}$

These parameters are related to a′, b′, c′ of the diaspore-type VO₂ by the relations: $\text{a ? a′, b ? b′, c ? 3c′}$. The structure, based on single crystal data, has been determined from Patterson and Fourier syntheses. A structural refinement gave a final R-factor of 2.4%. The new structure can be deduced from that of the diaspore-type VO₂, by displacement of one third of the cations from an octahedral site to an adjacent unoccupied tetrahedral site, which is located in a channel parallel to the c axis. The calculation of the cation and oxygen valences indicated that some O^2? were in fact OH^?. This conjecture was supported by thermogravimetric analysis. The chemical formula was indeed Fe³⁺₂V³⁺V⁴⁺V⁵⁺₂O₁₁(OH). Some intensities of the powder diffraction lines changed strongly when the preparation temperature was reduced from 650°C to 300°C. This was explained by an increase of the hydrogen ratio in the formula FeV₂O₆H_x, which implies a structural change. The different phases FeV₂O₆H_x can be considered as solid solutions between two extreme phases with different structure: one with the present one and the other with a diaspore-type structure.