Equilibrium and structure of thallium(III)-ethylenediamine complexes in pyridine solution and in solid

The formation of three [TI(en)(n)](3+) complexes (n = 1-3) in a pyridine so lvent has been established by means of Tl-205 and H-1 NMR. Their stepwise s tability constants based on concentrations, K-n = [Tl(en)(n)(3+)]/{[Tl(en)( n-1)(3+)](.)[en]}, at 298 K in 0.5 M NaClO4 ionic medium in pyridine, were calculated from Tl-205 NMR integrals: log K-1 = 7.6 +/- 0.7; log K-2 = 5.2 +/- 0.5 and log K-3 = 2.64 +/- 0.05. Linear correlation between both the Tl -205 NMR shifts and spin-spin coupling Tl-205-H-1 versus the stability cons tants has been found and discussed. A single crystal with the composition [ Tl(en)(3)](ClO4)(3) was synthesized and its structure determined by X-ray d iffraction. The Tl3+ ion is coordinated by three ethylenediamine ligands vi a six N-donor atoms in a distorted octahedral fashion. (C) 2001 Elsevier Sc ience BN. All rights reserved.