L.Strinna Erre

Metal complex formation on the surface of amorphous aluminium hydroxide part I. Copper (II) complexes of glutamic and aspartic acids

Abstract The role of glutamic and aspartic acids in affecting the adsorption of copper (II) onto aluminium hydroxide from aqueous solution has been studied by means of analytical and spectroscopic (ESR and reflectance absorption) measurements. It has been found that the sorption behavior may be accounted for by the interaction of surface-adsorbed ligands with copper (II) in solution to yield complexes, having 1:1 and 1:2 metal to ligand ratios, where the ligands coordinate through the amino and α-carboxyl groups. At low pH values, the presence of adsorbed ligands significantly enhances the metal sorption over that for the “uncomplexed” ion. However, at high pH values, the ligand excess in solution competes with surface for the metal ion and inhibits Cu (II) uptake.

Anion-induced metal binding in amorphous aluminium hydroxide

Abstract The adsorption of VO 1+ and Cu 2+ ions on freshly-prepared aluminium hydroxide gels was studied using analytical and spectroscopic techniques. The cation adsorption is shown to involve hydrolytic complexes of metal ions. In addition, a correlation is found between the adsorption capacity of the gels and the nature of the anions present in the exchange solution, sulphate enhancing the copper uptake with respect to chloride. These findings are explained in terms of negative charges arising on the surfaces upon selective binding of sulphate, which promote the metal adsorption. Desorption experiments reveal that the adsorbed ions are quantitatively removed only by strong chelating agents. The role of such interactions in determining the soil nutrient status is discussed.

Interaction of metal ions with humic-like models. Part VII. Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 2,5-dihydroxybenzoic acid

Abstract Complexes of formula M(2,5-DHB) 2 4H 2 O (M = Mn, Co, Ni, Zn, Cu and Cd; 2,5-DHB = 2,5-dihydroxybenzoate) were prepared and characterized by means of infrared and electronic spectroscopy, and by electron spin resonance. For the Zn complex the crystal and molecular structure was also determined by single-crystal X-ray diffraction analysis. The crystal is orthorhombic, space group Pbca (No. 61), with a = 18.503(4), b = 13.536(3), c = 6.900(2) A, and Z = 4. The final refinement used 877 reflections and gave a residual R value of 0.041. The complex has slightly compressed octahedral coordination, with the zinc atom bound to two monodentate carboxylate groups lying in trans positions and four water molecules. X-ray data and infrared spectra show the Mn, Co, Ni, Zn and Cd complexes to be isostructural with the Zn compound. The electronic, infrared and ESR spectra of the copper(II) complex are consistent with a CuO 4− based chromophore involving two water molecules and two monodentate carboxylate groups in the metal plane, and long axial contacts.

Interaction of metal ions with humic-like models. Part 5. The crystal and molecular structure of diaquabis(2,6-dihydroxybenzoato)-dioxouranium(VI) octahydrate ☆

Abstract The crystal and molecular structure of the complex [UO 2 (DHB) 2 (H 2 O) 2 ]·8H 2 O (DHB = 2,6-di- hydroxybenzoato) has been determined from single- crystal X-ray analysis and refined to a final R value of 0.033 for 3620 observed reflections. The complex crystallizes in the monoclinic system, space group C 2/ m , with a = 6.704(3), b = 20.171(6), c = 9.454(4) A and Z = 2. The coordination about the uranyl group, which is linear, involves two bidentate carboxylate groups and two water molecules in trans positions giving rise to an irregular hexagonal bipyramid. Intra- molecular hydrogen bonds between phenolic and carboxylate groups forming six-membered rings allow the molecule to be nearly planar. Spectroscopic (IR, NMR and electronic absorption) data and thermal properties of the compound are also reported.

COORDINATION OF METAL IONS BY INDOLIC ACIDS. COMPLEXES OF INDOLE-2-CARBOXYLIC, -3-ACETIC, -3-PROPANOIC AND -3-BUTANOIC ACIDS WITH SOME DIVALENT METAL IONS

Abstract Metal complexes of indole-2-carboxylic (ICH), -3-acetic (IAH), -3-propanoic (IPH) and -3-butanoic (IBH) acids, were prepared and characterized by means of thermal analysis, magnetic measurements. ESR. IR and electronic spectroscopy. While Cu(IA)2 · H2O, Cu(IP)2 · H2O, Cu(IP)2 and Cu(IB)2 are tetracarboxylatebridged dimers of the copper(II) acetate monohydrate-type, Cu(IC)2 · 2H2O appears to be monomeric with the copper atom in square planar coordination involving two carboxylate groups and two water molecules. Six-coordination at the metal ions, most likely involving bjdentate carboxylate groups and water molecules, is suggested for the complexes M(IC)2 · 2 H2O (M=Co, Ni, Mn and Zn). All the ligands appear to behave as simple carboxylic acids, being able to coordinate metal ions through the carboxylic groups alone.

Interaction of metal ions with humic-like models. Part 6. Molecular structure, spectral and thermal properties of diaquabis(2,6-dimethoxybenzoato)dioxouranium(VI) monohydrate

The crystal and molecular structure of [UO 2 (DMB) 2 (H 2 O) 2 ]·H 2 O (DMB = 2,6-dimethoxybenzoate), complex I , has been detcrmined by X-ray diffraction and refined to a final R value of 0.0411. The compound belongs to the space group P 2 1 / a with cell constants a = 12.649(4), b = 14.418(5), c = 13.460(4) A and Z = 4. As in the analogous complex [UO 2 (DHB) 2 (H 2 O) 2 ]·8H 2 O (DHB = 2,6- dihydroxybenzoate), compound II , the uranyl ion is bound to two bidentate carboxylate groups and two water molecules, but the point-symmetry is lower because the carboxylates, and the water molecules, are in vicinal positions. The lack of hydrogen- bonds between carboxylate groups and ortho -methoxy substituents and, possibly, steric factors account for the rotation of the phenyl rings with respect to the equatorial plane of the metal, the dihedral angle between the ‘best planes’ being about 77°. Detectable changes in the bond distances and angles within the carboxylate groups are produced by the non-planarity of the ligand. Spectroscopic and thermal properties of complexes I and II are also compared.

Copper(II) complexes of 4-aminobenzoic and 4-aminosalicylic acids

Copper(II) complexes of 4-aminobenzoic (HAB) and 4-aminosalicylic (HAS) acids were prepared and characterized by means of thermal analysis, magnetic measurements, ESR, IR and electronic spectroscopy. Both ligands behave as monodentate (carboxylate bonded) or bridging bidentate (amino and carboxylate bonded) donors yielding two types of complexes having essentially planar CuO4 and CuN2O2 chromophores, respectively.

Interaction of metal ions with humic-like models. Part 3. Thermal behaviour of aquo-bridged polymeric complexes of 2,6-dimethoxybenzoic acid with divalent metal ions

Abstract The thermal behaviour of some metal complexes of 2,6-dimethoxybenzoic acid has been investigated by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). The intermediates formed at various stages have been studied using a variety of analytical and spectroscopic methods. A mechanism of decomposition leading to 1:1 metal/ligand complexes of 2-hydroxy- o -anisic acid plus methyl 2,6-dihydroxybenzoate in the first stage and to binary oxides as final products is demonstrated.

Metal complex formation on the surface of amorphous aluminium hydroxide. part II. Copper (II) complexes with pyridinedicarboxylic acids

Abstract The formation of complexes of copper (II) with pyridinedicarboxylic acids (PDC) on the surface of aluminium hydroxide, upon adsorption of metal ion and ligands from aqueous solution, has been studied by means of analytical and spectroscopic (ESR, IR and reflectance absorption) measurements. It has been found that, depending on the ligand structure, different complex species may be formed. Particularly, 2, x −PDC ( x = 3, 4 or 5) ligands yield complexes, with 1:1 or 1:2 metal-to-ligand ratios, where the ligand binds to the surface through the x -carboxylate group and chelates the metal via the pyridine nitrogen and the 2-carboxylate group. With the 2,6-PDC ligand only one type of surface complex is formed, where the metal ion is in a compressed octahedral environment, being bound to two tridentate ligands, which interact also with the surface through the uncoordinate oxygens. With 3, y -PDC ( y = 4 or 5) surface complexes are observed only at high surface ligand concentrations. They are most likely formed by monodentate (N- or O-) coordination of a surface-adsorbed PDC molecule to a metal ion that is also bound to surface groups. As a consequence of the different structures of the surface complexes, the metal adsorption behaviour is strongly ligand dependent.

Metal complex formation on the surface of amorphous aluminium hydroxide. Part III. Copper(II) complexes of O-phospho-L-serine and O-phospho-L-tyrosine

Abstract Electron spin resonance (ESR) and electronic spectra of gels of amorphous aluminium hydroxide after adsorption of copper(II), in the presence of O -phospho-L-serine or O -phospho-L-tyrosine, from aqeous solutions over the pH range 4–8, indicated the formation of complexes having 1:1 or 1:2 metal-to-ligand ratios. In these gels, the ligands bind to the surface through the phosphate groups and chelate the metal via the amino and carboxylate groups. The adsorption behaviour of copper(II) and ligands was compared to that observed previously for the analogous copper(II)—glutamic, aspartic or pyridinedicarboxylic acids—aluminium hydroxide systems.