Stable free-radical complexing reagents in applications of electron spin resonance to the determination of metals: Part 2. Spin-labelled iminooxime [1]

Possibilities for the determination of metals by means of the intensity of the e.s.r. signal of the chelate-fonning reagent, spin-labelled iminomonoxime — 4-oximinomethyl-2,2,5,5-tetramethyl-3-imidazoline-1-oxyl, have been studied. The dissociation constant of the oxime group (pK^T_a = 9.36 ± 0.08) and the reagent partition constant in the chloroform—water system (log K_D = 0.80 ± 0.11) are reported. The reagent extracts copper, cobalt and nickel into chloroform. Copper is extracted as its CuA₂, chelate (log K_D = 0.91 ± 0.03; log K_ex = -3.35 ± 0.09; log β₂, = 15.8 ± 0.2). Several properties of the spin-labelled and conventional oximes are compared. It is confirmed that a radical-containing substituent produces a strong electron-acceptor effect. Unusual extractive and e.s.r.- spectroscopic behaviour of cobalt is indicated; an adduct of the spin-labelled chelate with atmospheric oxygen seems to be formed. Methods for the determination of cobalt and nickel based on the extraction with spin-labelled oxime into chloroform and subsequent separation of the excess of reagent on a chromatographic column are described. The detection limits are 3 × 10^-7 M for cobalt and 10^-6 M for nickel.     

Effect of solvents and substituents on the distribution coefficients of alkyl-substituted β-diketones and their copper chelates

The distribution ratios of alkyl-substituted β-diketone derivatives and their copper(II) chelates between water and a number of common water-immiscible solvents were investigated, in order to establish the effect of substituents and solvents on the extraction. A plot of the logarithms of the distribution coefficients of the β-diketones and of their copper chelates as a function of the number of carbon atoms in the molecule, gave a linear relationship. The relationship between the distribution coefficients of the copper chelate (P_CuA2) and those of β-diketone (P_HA) was shown to be log P_CuA2=2 log P_HA +const.     

Extraction—spectrophotometric determination of traces of cadmium with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 10⁴ l mol^-1 cm^-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml^-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR₂-2CDBA. The conditional extraction constant is log K'_ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β₂ = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.     

Complexation equilibria and spectrophotometric determination of zinc (II) with 2-(4′-methyl-2′-thiazolylazo)-4,6-dimethylphenol

2-(4′-methyl-2′-thiazolylazo)-4,6-dimethylphenol has been synthesized and its acid—base behaviour (pK_a1=0.03 ± 0.01, pK_a2=9.70±0.09) and complexation equilibria with zinc (logβ₁₀₁=6.70±0.04, logβ₁₀₂ = 13.70±0.02) studied in a 40% (v / v) ethanol—water medium at I=0.25 M NaClO₄. A spectrophotometric method for the determination of 0.2–1.5 ppm of zinc has been developed (ε=1.83 × 10⁴ 1. mol⁻¹ cm⁻¹ at 590 nm) and applied to its determination in lubricating oils.     

Acidobasic properties of molten potassium tetrahalogenogallates (X=Cl,I)

Molten potassium tetrachlorogallate and potassium tetraiodogallate were studied in terms of halogenoacidity, based on X^? ion-exchange. Titration of KX solution with GaX₃ were achieved and characterized by the shift of cathodic voltammetric curves. Autodissociation constants K_i,X/mol² kg^?1 were determined: ?log K_i,Cl=4.25±0.05 and ?log K_i,I=2.6±0.05, as well as the solubility values of KX: 0.41±0.02 and 0.80±0.02 mol kg^?1 for KCl and KI respectively.     

Analytical applications of azoisoxazoles. III. Complexes of cobalt,copper, and cadmium with 2-(5′-methyl-2′-isoxazolylazo)-4-methoxyphenol

2-(5′-methyl-2′-isoxazolylazo)-4-Methoxyphenol has been synthesized and its ionization constant (pK_a = 7.98 ± 0.08) spectrophotometrically determined in a 4% ($\text{v}\text{v}$) ethanol-water medium at μ = 0.25 M (NaClO₄). The reagent originates water soluble complexes with cobalt (log β₂ = 11.45 ± 0.16), copper (log β₁ = 7.15 ± 0.10), and cadmium (log β₁ = 3.96 ± 0.12), and can be used for the spectrophotometric determination of cobalt and copper as well as metallochromic indicator for copper.     

Cation-Induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates

Cation-induced dimerization of nickel(II), platinum(II), and palladium(II) meso-tetra(benzo-15-crown-5)porphyrinates (Ni(II)TCP, Pd(II)TCP, and Pt(II)TCP) on treatment with potassium thiocyanate in a chloroform-methanol solution has been studied by electronic absorption spectroscopy. The formation of [{MTCP}₂(K⁺)₄](SCN^?)₄ in solution induces a hypsochromic shift of the Soret band and a bathochromic shift of the β-band with respect to their positions in the spectrum of MTCP. The equilibrium constants (K) for the 2MTCP + 4K⁺ = [{MTCP}₂(K⁺)₄] processes at 20°C are determined to be as follows: log K _Ni(II)TCP = 27.31 ± 1.67, logK _Pd(II)TCP = 27.16 ± 1.43, and logK _Pt(II)TCP = 26.15 ± 1.56.     

Complexation of silver(I) with benzylpenicilline and oxacilline

The complexation of Ag⁺ ions with anions of β-lactam antibiotics, such as benzylpenicilline (Bzp^?) and oxacilline (Oxa^?), in aqueous solution at 25°C and an ionic strength of 0.1 (KNO₃) was studied potentiometrically using a silver indicator electrode. The formation constants of the complexes AgBzp (logβ = 2.21 ± 0.01), AgBzp ₂ ^? (logβ = 3.91 ± 0.02), Ag₂Oxa⁺ (logβ = 4.89 ± 0.01), AgOxa (logβ = 2.88 ± 0.01), (logβ = 5.43 ± 0.01) were determined.     

Spektrophotometrische Untersuchung der Eisen(III)-Komplexe mit o-Methylbenzamidoxim

The complex formation of Fe³⁺ with o-methyl benzamide oxime was studied spectrophotometrically in methanol solution. The stepwise process gives complexes 1∶1, 1∶2 and 1∶3. The formation constants are lgK ₁ = lg β₁ = 1,88 ± 0,12, lgK ₂ = 3,53 ± 0,2, lgK ₃ = 4,96 ± 0,2, lg β₂ = 1,65 ± 0,32 and lg β₃ = 1,43 ± 0,4, whereK ₃ = β₁ · β₂ · β₃. All measurements were carried out at 25°C and an ionic strength μ=1.     

Stability of diammine and chloroammine gold(I) complexes in aqueous solution

The substitution equilibria AuCl ₂ ^? + iNH ₄ ⁺ = Au(NH₃)_iCl_{2 ? i} + iCl^? + iH⁺, β _i ^* . were studied pH-metrically at 25°C and I = 1 mol/L (NaCl) in aqueous solution. It was found that logβ ₁ ^* = ?5.10±0.15 and logβ ₂ ^* = ?10.25±0.10. For equilibrium AuNH₃Cl_solid = AuNH₃Cl, log K _s = ?3.1±0.3. Taking into account the protonation constants of ammonia (log K _H = 9.40), the obtained results show that for equilibria AuCl ₂ ^? + iNH₃ = Au(NH₃)_iCl_{2 ? i} + iCl^?, logβ₁ = 4.3±0.2, and logβ₂ = 8.55±0.15. The standard potentials E ₀ ^1/0 of AuNH₃Cl⁰ and Au(NH₃) ₂ ⁺ species are equal to 0.90±0.02 and 0.64±0.01 V, respectively.     

Stability constants for aqueous silver/bromide/thiocyanate complexes

Stability constants for aqueous Ag⁺/Br^?, Ag⁺/SCN^?, and mixed Ag⁺/Br^?/SCN^? complexes are determined at 25° C by using data generated potentiometrically in solutions having ionic strengths of 0.4, 1.0, and 2.0 m. Monte Carlo numerical methods which yield apparent stability constants for these complexes as well as confidence limits are described in detail. Explicit consideration of speciation shows that under useful precipitation conditions (high bromide and low thiocyanate), a significant fraction of soluble silver is present as AgBr_n (SCN)^1?n?m_m complexes. The most prevalent mixed complexes under these conditions are AgBr (SCN)^? (log β₁₁=8.0 ± 0.5) and AgBr₂(SCN)^2? (log β₂₁=9.2 ± 0.3). The free energies of formation of the other tri- and tetra-coordinate mixed complexes are nearly indistinguishable (log β₁₂=9.3 ± 0.5; log β₃₁=9.0 ± 0.6; log β₂₂=9.6 ± 0.9; log β₁₃=10.3 ±0.5).     

Spectrofluorimetric determination of niobium with morin enhanced by cetyltrimethylammonium bromide micelles

The effect of surfactants on the fluorescence of the niobium—morin system is described. Cationic surfactants strongly enhanced the intensity (e.g., cetyltrimethylammonium bromide (CTAB) gives an 80-fold increase), while anionic and non-ionic surfactants are without effect. The formation of 1:1 and 1:3 (Nb:morin) complexes is demonstrated spectrophotometrically. The conditional stability constants for these complexes in CTAB micelles are β₁ = (1.14 ± 0.01) × 10⁴ l mol^?1 amd β₃ = (5.66 ± 0.02 × 10¹⁰ l³ mol^?3. The micellar-enhanced fluorimetric method has a 1 μg l^?1 detection limit, and is highly selective. The r.s.d. for the determination of 50 μg l^?1 Nb is 3.5%.     

4-carboxy-1,2-cyclohexanedionedioxime complexes of nickel(ii) in alkaline media

The reactions of 4-carboxy-1,2-cyclohexanedionedioxime and nickel(II) were studied in alkaline media. Spectrophotometric studies indicate the presence of a 1:1 complex ion, NiD^-. Magnetic susceptibility measurements on a series of solutions of varying ratios of vic-dioxime and nickel(II) showed that the 1:1 complex ion was diamagnetic and that two paramagnetic complexes, probably NiD₂^4- and NiD₃^7-, are present in solution. The stability constants for the three complexes were calculated from spectrophotometric and magnetic susceptibility data. The log K values were found to be log K₁ = 28.74 ± 0.60, log K₂ = 0.76 ± 0.15, and log K₃ = 3.67 ± 0.73, respectively.     

The triplet state of photosynthetic pigments. I. Pheophytins

ZFS constants (in cm^?1) and decay rate constants for the lowest triplet state of pheophytins have been determined by ESR: pheophytin a: D = 341 ± 3,E = 33 ± 3, K_T = 1050 s^?1; pheophytin b: D = 358 ± 8, E = 46 ± 5, K_T = 630 s^?1; bacteriopheophytin: D = 256 ± 4, E = 54 ± 5/37 ± 5, K_T ≈ 4000 s^?1. In addition values for the decay rate constants and relative populating rates of the individual spin levels have been obtained; these numbers turn out to be appreciably different from those for the corresponding chlorophylls. For the series pheophytin a, b and bacteriopheophytin we find parallel behaviour with the corresponding chlorophylls. The effects of side group substitution and pyrrole ring reduction on the ZFS constant D can be understood by including configuration interaction between the excited states using the 4-orbital model. The change of the mean triplet decay constant K_T upon side group substitution and pyrrole ring reduction follows an energy gap law. Substitution of the central Mg-ion by two protons, however, causes K_T to increase; this is attributed to the introduction of an extra promoting mode - of the NH-group - and/or to the presence of low lying nπ^* states in pheophytins.     

Dimerization of copper(II) decanoate in 1,4-dioxane-water mixed solvents

Complex formation of copper(II) with decanoic acid (HA) has been studied by potentiometric measurement in 1,4-dioxane-water mixtures at a constant ionic concentration of 0.1 mol dm^?3 (Na, H)ClO₄ and at 25°C. The experimental data can be interpreted with the formation of CuA⁺, CuA₂ and Cu₂A₄. The dimerization constant formulated as:

was found to be log K_dim = 3.75, 4.02 and 4.26 for 0.3, 0.4 and 0.5 mole fractions of dioxane, respectively. Absorbances at 373 and 670 nm are interpreted with the aid of the formation constants determined by potentiometry. Solvent effect on the dimerization of the monomeric copper(II) decanoate is discussed on the basis of selective solvation of CuA₂ and Cu₂A₄ with water molecules.     

The titrimetric determination of beryllium(II) with 1,2-phenylenediamine-N,N,N′,N′-tetraacetic acid

Beryllium (ca. 10^?2?10^?4 M) is determined by adding excess of 1,2-phenylenediamine-N,N,N′, N′-tetraacetic acid (PhDTA, H₄L) and back-titrating with copper(II); arsenazo-I serves as indicator. Formation constants of BeL and BeHL were determined by potentiometry: log K_BeL=6.48±0.02 and log K^H_BeHL=3.48±0.03 (25°C, I=1 M in NaClO₄). Expressions for the titration curve are given together with theoretical errors.     

Extraction—spectrophotometric determination of copper(II) with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of copper (II) is described. The ion-associate formed between the copper(II)—4-(2-pyridylazo)-resorcinol (PAR) anion and tetradecyldimethylbenzylammonium chloride (TDBA) is extracted with chloroform at pH 9.7. The absorption maximum of the extracted species occurs at 510 nm, the molar absorptivity being 8.05 (± 0.07) × 10⁴ l mol^-1 cm^-1. Beer's Law is obeyed in the concentration range 0.1–0.5 μg Cu ml^-1. The composition of the ion-associate is estimated to be [Cu(PAR)₂(TDBA)₂]. The conditional extraction constant is log K'_ex ≈ 8. The interference of some cations and anions is studied. The method is suitable for analysis of waters.     

Renium(V) complexation with <Emphasis Type="Italic">N</Emphasis>-ethylthiourea

The stepwise complexation of rhenium(V) with N-ethylthiourea has been studied by the potentiometric method in 6 mol/L HCI at 298 K. It has been found that rhenium(V) forms five complex species with this ligand of the following compositions: [ReOLCl₄]^?, [ReOL₂Cl₃], [ReOL₃Cl₂]⁺, [ReOL₄Cl]²⁺, and [ReOL₅]³⁺. The calculated logarithms of stepwise formation constants of the complexes are the following: logK₁ = 4.10 ± 0.05, logK₂ = 3.16 ± 0.02, logK₃ = 2.61 ± 0.02, logK₄ = 2.26 ± 0.02, and logK₅ = 1.80 ± 0.02. It has been shown that the introduction of the ethyl radical into the thiourea molecule leads to an increase in the stability of rhenium(V) complexes.     

Polyhydroxysäuren als Komplexbildner

The reaction of mucic acid (H₆ Mu) with Cobalt(II) and Nickel(II) ions has been studied in 1.0M-Na⁺(NO ₃ ^? ) ionic medium at 25° C using a glass electrode. The e.m.f. data in the range 8≦?log [H⁺]≦10 are explained by assuming $$\begin{gathered} Me^{2 + } + H_4 Mu^{2 - } \rightleftharpoons MeH_3 Mu^ - + H^ + \beta ''_1 \hfill \\ Me^{2 + } + H_4 Mu^{2 - } \rightleftharpoons MeH_2 Mu^{2 - } + 2 H^ + \beta ''_2 \hfill \\ \end{gathered}$$ with equilibrium constants log β′₁ = — 9.36; — 9.34; log β′₂ = — 18.11; — 18.08 for Co(II) and Ni(II) resp.     

Extraction of Ni(II) from nitrate media by Di-n-octylphosphinic acid dissolved in toluene

The extraction of Ni(II) from nitrate media of ionic strength 1.0 mol dm⁻³ by di-n-octylphosphinic acid (HR) in toluene solution has been studied over a range of pH and reagent concentrations. The data have been analysed both graphically and numerically to determine the stoichiometry of the extracted complexes and their extraction constants. Evidence was found for the formation of both NiR₂(HR)₄ (log K₂₄ = −9.14±0.06) and NiR₂(HR)₂ (logK₂₂ = −7.35±0.10), the former being the predominant species although the latter is important at low reagent concentrations and high pH values.