Equilibria and dynamics of thallium-EDTA (Tl(edta)X2-) complexes (X = halide, pseudohalide) studied by multinuclear NMR

Abstract

Equilibria and dynamics in aqueous solutions of mixed complexes Tl(edta)X[sup 2[minus]] containing ionic medium (1 M NaClO[sub 4]) have been studied by means of [sup 205]Tl-, [sup 15]N-, [sup 13]C-, and [sup 1]H-NMR and potentiometry. Individual [sup 205]Tl chemical shifts have been determined for all the investigated complexes (X = H[sub 2]O, OH, Cl, Br, CN, SCN). For the pseudohalide complexes the [sup 15]N- and [sup 13]C-NMR shifts as well as the spin-spin coupling constants J([sup 205]Tl-[sup 15]N) and J([sup 205]Tl-[sup 13]C) have also been determined. The coupling constant [sup 1]J([sup 205]Tl-[sup 13]C) for the complex Tl(edta)CN[sup 2[minus]] is remarkably large, 10 479 Hz, indicating a very strong thallium-carbon bond. The stability constants, K[sub x] = [Tl(edta)X[sup 2[minus]]]/([Tl(edta)[sup [minus]]][X[sup [minus]]]), determined by a combination of [sup 205]Tl- and [sup 13]C-NMR and potentiometry, for X = Cl, CN, and SCN are, respectively: log K[sub x] = 2.6 ([+-] = [sigma]), 8.72 ([+-] 0.03) and 2.70 ([+-] 0.03). In order to facilitate the discussion of reaction mechanisms, the crystal and molecular structure of the compound Na[sub 2][Tl(edta)CN]-3H[sub 2]O has been determined using single-crystal x-ray diffraction. This compound crystallizes in the monoclinic space group P2[sub 1]/c (no. 14) with a = 7.769 (2)more » [angstrom], b = 14.130 (6) [angstrom], c = 17.069 (5) [angstrom], [beta] = 101.44(2)[degree], and Z = 4.« less