A. Corsini

Aggregation of meso-tetra-(p-sulphonatophenyl)porphine and its cu(II) and zn(II) complexes in aqueous solution.

The aggregation of meso-tetra(p-sulphonatophenyl)porphine, an analytical reagent for the determination of metals at low concentration, has been studied over a wide concentration range by both spectrophotometric and (1)H NMR methods. Up to a concentration of about 3 x 10(-4)M, the experimental data were satisfactorily accounted for by a monomer-dimer equilibrium. At higher concentrations, the best fit of the chemical shift data required postulation of a tetramer. Analysis of the experimental data for the Zn(II) complex indicated the occurrence of dimerization at higher concentrations.

Stability of metal oxinates — I Effect of ligand basicity

Abstract A linear correlation between the (solution) stability of metal oxinates and (d. log cKNH+e. log cKOH) has been developed where d and e are parameters that relate the sensitivity of the metal-ion to the nitrogen and oxygen donor-atom basicities, respectively. Both parameters are proportional to the ionic charge, Z/r, of the metal. Solution for the proportionality constants results in a correlation for which the predicted slope is Z/r, and good agreement is obtained for those metal oxinates in which significant ionic character is presumed. For appreciably covalent complexes, Z/r is not an appropriate parameter and poor agreement is obtained. Application to stability data in the literature is successful, except for data for halo-substituted oximates, and the correlation presents an alternative to arguments based on metal-to-ligand π-bonding. The failure of the equation to correlate data for the halo-substituted oxinates is explained in terms of the anomalous electronic properties of the halogen substituents.

U(VI) COMPLEXES OF OXINE AND DERIVATIVES.

Infrared bands due to the hydrogen-bonded (+)N-H cdots, three dots, centered O system in the oxine adduct of U(VI) have been identified and found to occur in the spectra of several newly prepared U(VI) adducts of oxine derivatives. Interligand steric effects in the U(VI) complexes of most 7-substituted oxines prevent the formation of the 1:3 adduct. Complexes of the type ML(2)X, where X is a small co-ordinating species present in solution, are formed instead. With 2-substituted oxines, steric interactions between the 2-substituent and co-ordinated water result in destabilization of the complex and subsequent hydrolysis as the pH of the solution is raised. Experiments involving the use of [(14)C]-oxine were found to distinguish between co-ordinated and lattice-held oxine and are potentially valuable in studies of oxine adducts formed by other metal ions.

The 1:3 uranium(VI)-8-hydroxyquinoline compound: its composition and thermal conversion into bis(8-hydroxyquinolinato)dioxouranium(VI).

Evidence is provided to show that in the red compound formed between uranium(VI) and 8-hydroxyquinoline, the ligand-to-uranium ratio is slightly lower than 3:1, at least when the compound is prepared by a widely accepted procedure. Competition between 8-hydroxyquinoline and other ligands such as water or ammonia is probably responsible for the non-stoichiometry. Further, it is shown that a procedure frequently used for the thermal conversion of the red compound into bis(8-hydroxyquinolmato)dioxouranium(VI) yields a compound in which the ligand-to-uranium ratio is less than 2:1. Conditions which lead to the thermal preparation of the stoichiometric bis compound are described.

Multielement preconcentration of trace metals from natural waters by solvent extraction with an alkylated oxine derivative

Kelex 100, a commercially available alkylated oxine derivative, is shown to be effective, in purified form, for the simultaneous extraction of trace levels of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Pb(II), and Zn(II) from natural waters into toluene. The high lipophilicity of the extractant and its chelates affords large preconcentration factors in a single batch-extraction. Back-extraction with a small volume of nitric acid provides additional enrichment for subsequent determination of total (soluble) metal by graphite-furnace atomic-absorption spectrometry (GFAAS). Calibration with standard solutions can be used, which has advantages over the method of standard additions.

Stability of metal oxinates — II Effect of the solvent composition

Abstract The protonation constants and the stability of metal complexes of several 5-substituted derivatives of oxine have been measured in 40, 60, and 75% vol/vol dioxane. The change in metal-complex stability with increasing dioxane content follows in large measure the stability change in the OH proton complexes, and is opposite to the change in stability of the (NH)+ complexes. It appears that the effect of solvent composition on metal-complex stability yields only gross information on the relative importance of the OM and NM bonds in bidentate complexes of the type studied. Some data on SH and SM complexes is also presented.

Preconcentration of cadmium, chromium, copper and lead in drinking water on the polyacrylic ester resin, XAD-7.

The conditions (e.g. pH, resin, particle size, foreign ions) affecting the uptake of Cd(II), Cr(III), Cu(II) and Pb(II) from aqueous solution by the SM-7 (also called XAD-7) resin, were studied. Based on these studies, a two-column method was developed to overcome the effect of complexation by humic substances. The method was successfully tested with the NBS multielement water standard, SRM 1643a, and was subsequently applied to enrich Cd(II), Cr(III), Cu(II) and Pb(II) in 15 drinking water samples from Hamilton, Ontario. The metals were determined using graphite furnace atomic absorption spectrometry. The results for the drinking water samples showed that leaching of copper and lead occurred from the distribution system.

Composition of the thorium(IV)-8-hydroxyquinoline adduct compound

The orange compound formed between thorium(IV) and 8-hydroxyquinoline by conventional precipitation is non-stoichiometric. The composition is very sensitive to experimental conditions; the average ratio of bound 8-hydroxyquinoline to thorium was found to be 4.9:1. The deficiency of 8-hydroxyquinoline is due either to partial hydrolysis of thorium, or to the presence of co-ordinated water. A simple procedure for the preparation of the pure tetrakis compound is described.

Substituted acridines as potential terdentate ligands—II: Metal chelate formation

Abstract The stability of metal chelates of the rigid ligands 4-amino-5-hydroxyacridine and 4,5-dihydroxyacridine have been studied. The results have been compared with existing data for several 2-substituted 8-hydroxyquinolines, and the stability effects have been explained in terms of ring strain and substituent steric hindrance.

Substituted acridines as potential terdentate ligands—I: Synthesis and protonation constants

Abstract Some potentially terdentate acridine ligands have been synthesized and their protonation constants determined in 50 per cent v/v dioxane-water by potentiometric and spectrophotometric methods. The order of protonation of the donor sites has been determined and the effect of steric hindrance on protonation behaviour assessed.