Summary. The speciation of Tc(VII) in 12 M sulfuric acid was studied by NMR, UVvisible and XAFS spectroscopy, experimental results were supported by DFT calculation and were in agreement with the formation of TcO 3 OH(H 2 O) 2 .Heptavalent transition metal complexes of group VII with the d 0 electronic configuration are often used in catalysis and biomedical applications. [1,2,3] For manganese, the high electron affinity and oxidation potential of its heptavalent complexes make these species the catalysts of choice for oxidation of organic compounds.[4] The chemistry of Re(VII) complexes has been extensively studied, and species with the ReO 3 + core (e.g., CH 3 ReO 3 ) have been reported to be efficient catalysts. [3] Concerning technetium, its coordination chemistry has mainly been driven by radiopharmaceutical applications. Pentavalent and trivalent Tc complexes have been the most studied while heptavalent coordination complexes are still rare. [5] Permetallates with the tetrahedral geometry are the most common heptavalent species and are stable in aqueous media over a large range of pH and electrochemical potential. [6] In concentrated acid, permetallates are generally unstable and reduction, dimerisation, dehydration or complexation can occur. [7,8,9,10] The reaction of pertechnetate in water with strong acid leads to dehydration and various complexes with TcO 3 + core have been synthesized. [11] In theses synthetic reactions, it is assumed that the anhydrous Tc 2 O 7 is formed as an intermediate product. [11] Sulfuric acid is widely used in industrial applications; it is also a solvent of choice for dehydration process. [12-13] Speciation of Mn(VII) in H 2 SO 4 has been documented; manganese heptoxide is formed after dissolution of KMnO 4 and the MnO 3 + cation has been reported. [14,15,16]. For technetium and rhenium, speciation data are still sparse, the HReO 2 (SO 4 ) 2 .3H 2 O complex has been mentioned while technetium heptoxide has been proposed but no structural nor speciation data were provided. [17][18] In the present work, the speciation of technetium complexes after dissolution of KTcO 4 in sulfuric acid has been performed. The molecular structure and spectroscopic properties of the complexes were studied by UV-visible, X-ray absorption fine structure (XAFS) and NMR spectroscopy and density functional theory (DFT) techniques.Potassium pertechnetate (~ 30 mg) was placed in glass vials, and 1 M, 6 M, 12 M sulfuric acid (5 mL) was added with a glass pipette. After dissolution of the salt, a yellow color is observed in 12 M while for 1 M and 6 M, the solution remains clear. UV-visible spectroscopy measurements in 1 M and 6 M show the presence of TcO 4 -while in 12 M, the spectrum of the yellow solution differs from that of the pertechenate (vide supra). The conditions of formation of the yellow species were investigated by NMR spectroscopy. Technetium samples were prepared in H 2 SO 4 (from 3 M to 18 M) and 99 The 99 Tc NMR data were fit by allowing the pK a s and the chemical shifts of the unprot...
