The X-ray structure of {C(NH2)(3)}[Tl(dota)]center dot H2O shows that the Tl3+ ion is deeply buried in the macrocyclic cavity of the dota4 ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) with average TlN and TlO distances of 2.464 and 2.365 angstrom, respectively. The metal ion is directly coordinated to the eight donor atoms of the ligand, which results in a twisted square antiprismatic (TSAP') coordination around Tl3+. A multinuclear H-1, C-13, and Tl-205 NMR study combined with DFT calculations confirmed the TSAP' structure of the complex in aqueous solution, which exists as the Lambda(lambda lambda lambda lambda)/Delta(delta delta delta delta) enantiomeric pair. 205Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl(dota)](-) + H+ reversible arrow [Tl(Hdota)] to be determined, which turned out to be pKH(Tl(dota)) = 1.4 +/- 0.1. [Tl(dota)]- does not react with Br, even when using an excess of the anion, but it forms a weak mixed complex with cyanide, [Tl(dota)](-) + CN reversible arrow [Tl(dota)(CN)](2), with an equilibrium constant of K-mix = 6.0 +/- 0.8. The dissociation of the [Tl(dota)](-) complex was determined by UVvis spectrophotometry under acidic conditions using a large excess of Br, and it was found to follow proton-assisted kinetics and to take place very slowly (similar to 10 days), even in 1 M HClO4, with the estimated half-life of the process being in the 10(9) h range at neutral pH. The solution dynamics of [Tl(dota)](-) were investigated using C-13 NMR spectroscopy and DFT calculations. The C-13 NMR spectra recorded at low temperature (272 K) point to C-4 symmetry of the complex in solution, which averages to C-4v as the temperature increases. This dynamic behavior was attributed to the Lambda(lambda lambda lambda lambda) <-> Delta(delta delta delta delta) enantiomerization process, which involves both the inversion of the macrocyclic unit and the rotation of the pendant arms. According to our calculations, the arm-rotation process limits the Lambda(lambda lambda lambda lambda) <-> Delta(delta delta delta delta) interconversion.