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The X-ray structure of {C(NH2)3}[Tl(dota)]·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 Tl-N and Tl-O distances of 2.464 and 2.365 Å, 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 ¹H, 13C, and 205Tl NMR study combined with DFT calculations confirmed the TSAP' structure of the complex in aqueous solution, which exists as the Λ(λλλλ)/Δ(δδδδ) enantiomeric pair. 205Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl(dota)]- + H+ ⇆ [Tl(Hdota)] to be determined, which turned out to be pKHTl(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- ⇆ [Tl(dota)(CN)]2-, with an equilibrium constant of Kmix = 6.0 ± 0.8. The dissociation of the [Tl(dota)]- complex was determined by UV-vis 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 (~10 days), even in 1 M HClO4, with the estimated half-life of the process being in the 109 h range at neutral pH. The solution dynamics of [Tl(dota)]- were investigated using 13C NMR spectroscopy and DFT calculations. The 13C NMR spectra recorded at low temperature (272 K) point to C4 symmetry of the complex in solution, which averages to C4v as the temperature increases. This dynamic behavior was attributed to the Λ(λλλλ) ↔ Δ(δδδδ) 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 Λ(λλλλ) ↔ Δ(δδδδ) interconversion. [ABSTRACT FROM AUTHOR]

Here we report on the synthesis and structural characterization of the dithallium(III)-containing 30-tungsto -4-phosphate [Tl 2 Na 2 (H 2 O) 2 {P 2 W 15 O 56 } 2 ] 16- (1) by a multitude of solid-state and solution techniques. Polyanion 1 comprises two octahedrally coordinated Tl 3+ ions sandwiched between two trilacunary {P 2 W 15 } Wells-Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by 31 P and 203/205 Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei ( 203 Tl, 205 Tl, 31 P, 183 W). 23 Na NMR showed a time-averaged signal of the Na + counter cations and the structurally bonded Na + ions. 203/205 Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl 3 Na(H 2 O) 2 (P 2 W 15 O 56 ) 2 ] 14- , which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion 1 was also tested against bacteria and Leishmania.

We have synthesized and structurally characterized the first discrete thallium-containing polyoxometalate, [Tl 2 {B-β-SiW 8 O 30 (OH)} 2 ] 12- (1). Polyanion 1 was characterized in the solid-state and shown to be solution-stable by 203/205 Tl NMR, electrospray ionization mass spectrometry, and electrochemical studies. The antibacterial activity of 1 was also investigated.