Potentiometric studies in aqueous solution at 25 °C and ionic strength 0.5 mol dm-3 in NaCICL show that beryllium(II) with different polyamino carboxylic acids forms the following complexes: EDTA (ethylenediaminetetraacetic), 1,2-PDTA (1,2-propylenediamine-VA',V',V,-tetraacetic), and CDTA (iraní-1,2-cyclohexanediamine-Vyy.A'./V'-tetraacetic) (ligands, H4L), [BeHL]-, [BeL]2-, and [Be3(OH)3(HL)]; EDDADP (ethylenediamine-

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media.

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N‘,N‘-tetraacetic (3,4-TDTA), ortho-phenylenediamine-N,N,N‘,N‘-tetraacetic (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N‘,N‘-tetraacetic (4-Cl-o-PhDTA) acids, H4L, with Cu(II) and Fe(III) is described. The stability constants and the partial molar enthalpies of the complexes formed (25 °C, I = 0.5 mol dm-3 in KNO3) were respectively determined by means of emf and calorimetry measurements. For the system 3,4-TDTA−Fe(III) (25 °C, I = 0.5 mol dm-3 in NaClO4), the stability constants of the complexes FeL- and [FeL(OH)]2- were also determined spectrophotometrically. The calorimetric measurements show that the complex formation is entropy driven, exothermic for Cu(II) and endothermic for Fe(III). The partial molar entropy of complexation (ΔS°) is much the same as that of the EDTA complexes. X-ray diffraction structural analysis of Na[Fe(4-Cl-o-PhDTA)(H2O)]·1.5H2O revealed that, in [FeL(OH2)]- (monoclinic C2/c, a = 10.693(3) Å, b = 13.931(3) Å, c = 24.686(6) Å, β = 94.21(2)°, V= 3667(2) Å3, Z = 8), the iron(III) is seven coordinated, with one water molecule filling the seventh position, similar to the iron(III) anionic chelates of 3,4-TDTA, o-PhDTA, and EDTA. The presence of the Cl atom in the aromatic ring produces an asymmetry in the Fe−N bond distances.