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

Abstract

The formation of three [Tl(en) n ] 3+ complexes ( n=1–3) in a pyridine solvent has been established by means of 205Tl and 1H NMR. Their stepwise stability constants based on concentrations, K n =[Tl(en) n 3+ ]/{[Tl(en) n−1 3+ ]·[en]}, at 298 K in 0.5 M NaClO 4 ionic medium in pyridine, were calculated from 205Tl 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 205Tl NMR shifts and spin–spin coupling 205Tl– 1H versus the stability constants has been found and discussed. A single crystal with the composition [Tl(en) 3](ClO 4) 3 was synthesized and its structure determined by X-ray diffraction. The Tl 3+ ion is coordinated by three ethylenediamine ligands via six N-donor atoms in a distorted octahedral fashion.