Equilibria in aqueous solutions at ionic strength I = 1.00 (NaCICL or NaNCb) and 25 °C between the 1:1 thallium-(III) complexes [T1(L)] (L are diaminotetraacetate ligands edta and cdta and the hexaamine tpen {tetrakis(2pyridylmethyl)ethylenediamine}) and different coligands A (A are OH-, Cl-, Br-, I-, SCN-, N3-, py, en, Hen+, phen, bpy, gly-, Hgly, ox2-, and ida2-) have been investigated by means of potentiometric pH titrations and l3C and 'H NMR, Raman, and IR spectroscopy. Each ligand gives rise to the following equilibria, allowing the determination of the corresponding equilibrium constants by pH measurements: (1) [T1(L)(H20)]" -[Tl(L)(OH)]"-1 + H+; (2) [T1(L)(H20)]" + A -[T1(L)(A)]" + H2O. The presence of [T1(L)(A)] in solution and the corresponding data have been confirmed by NMR for [Tl(edta)(A)] and [Tl(cdta)(A)]: Although the l3C coordination chemical shifts are small, heteronuclear coupling constants 7(205/203Tl, 13C) and, in particular, those involving the carboxylate function can be employed for monitoring structural changes and the determination of equilibrium constants. The cdta complexes, having a rigid stereochemistry imposed by the cyclohexyl ring, in solution exhibit conformations for the glycine-type chelate rings which are close to those found in the solid for analoguous edta complexes. The parameter *123 457(T1,H) for the acetate groups of the cdta ligand established conformational similarities for all the complexes with monodentate coligands A, different from those coordinating in a bidentate fashion, suggesting that also the complex [T1(L)(H20)"]-exists as a monoaquo species, i.e., n = 1. Two-dimensional NMR for [Tl(cdta)(phenH)] and [Tl(cdta)(phen)]provides simple and direct evidence for the formation of stable mixedligand complexes with CN = 7 and 8 in aqueous solution. Raman spectra of solutions with equilibria of types (1) and ( 2) for L = edta allow the assignment of bands to the mixed-ligand complexes present in agreement with the equilibrium constants obtained. The X-ray crystal structures of two complexes which were isolated in crystalline form, i.e., Ca[Tl(edta)(0H)]*3H20 (monoclinic, space group P2\/c, a = 13.744(8) A, b = 9.141(2) A, c = 13.752(0) A, 13= 100.71(0)°, Z = 4) and [Tl(tpen)(N0s)](C104)2 (monoclinic, space group P2\lc, a = 12.718(6)A, b = 13.640(7) A, c = 18.883(9) A, f3 = 108.84(4)°, Z = 4) showed a CNs of 7 for the former and 8 for the latter Tl(III) complex salt.

Complex formation between N,N,N',N'-tetrakis(2-aminoethyl)ethane-1,2-diamine (penten) and the metal ions Mn 2 , Co 2 , Cu 2 , Zn 2 , Cd 2 , Hg 2 , Ag , Pb 2 , and Tl 3 (in 1.00m NaNO 3 and 258) was investigated by potentiometry and spectrophotometry. These are the first reported values of the stability constants for this ligand with Ag , Pb 2 , and Tl 3 . The X-ray crystal structure of [Tl(NO 3 )(penten)](NO 3 ) 2 was determined. In this structure, Tl 3 shows a coordination number of seven made up of the six N-donors and one O-atom of NO À 3 .

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