Investigation of Astatine Cation Electromigration

Abstract

Electromigration of astatine ( 210 ' 2 " At) has been investigated in aqueous solutions of 0.25 mole I" 1 H(Na)C10"+5 • 10" 3 mole Γ 1 K 2 Cr 2 0, orNa 2 S 2 0, at 25°C, 0.7 < pH < 10.4. Like K 2 Cr 2 0,, Na 2 S 2 0" seems to oxidize astatine only to At(0) + , i. e. to an univalent cation, probably being protonized hypoastatine acid (H 2 0) n At + . The literature data on oxidation of astatine by Na, S 2 0 8 to At 3+ (AtO + ) were not confirmed. The mean mobility of the At(©) + cation is well described by the empiric equation _ = "At(Q) + (1 + *" dp ·«"'+)-(1+6 pH) where = 7.6(3.0)· 10" 5 molel" 1 is the deprotonation constant of (H 2 0) n At + , δ =0.18; "ΑΙ(Θ) + =+3.80(5) Χ ΙΟ" 4 cm 2 V"' s" 1 . In solutions of K 2 Cr 2 0 7 with pH > 1.7 and in solutions without oxidation agents At(0) + is unstable and is converted to a neutral form, probably, At 0 .

Astatine Standard Redox Potentials and Speciation in Acidic Medium

“…[52][53][54][55] The nature of species III remains, however, unknown, and several forms are proposed: At + , AtO + , and At 3+ . [5][6][7][8][9] Some authors have attempted to identify the nature of the cationic form by comparing its behavior with inorganic sorbents with that of model cations. For example, Rössler et al 5 proposed At + considering the difference in retention volumes obtained by HPLC on Aminex A7 cation-exchange resin between species III and Tl + .…”

“…In accordance with the literature, species I was prepared in 0.1 mol/L Na 2 S 2 O 3 and HClO 4 (E ∼ 0.2 V vs NHE), 5 species II in 0.1 mol/L HClO 4 concentration (E ∼ 0.5 V vs NHE) 6 and species III with a mixture of 5 10 -3 mol/L K 2 Cr 2 O 7 and 0.1 mol/L HClO 4 (E ∼ 1 V vs NHE). 7,14 The oxidation of species I was studied in the biphasic water/toluene system and the potential of the solution was varied using the SO 3 2-/SO 4 2-redox couple ([SO x 2-] total ) 0.1 mol/L) in 0.1 mol/L HClO 4 . 3 In the case of the oxidation of species II, the ion exchanger resin Dowex-50WX8 was used and the E variation was realized using the Fe 3+ /Fe 2+ redox couple ([Fe n+ ] total ) 0.1 mol/L) 15 at different HClO 4 concentrations (from 10 -2 to 0.3 mol/L).…”

“…6,7 These three species, referred to as species I, II, and III, respectively, correspond to three different oxidation states. Whereas the oxidation states -I, 0, and +I were considered by Appelman, 8 Visser et al 9 argued that At(0) could not exist in aqueous solution.…”

Assessment of an effective quasirelativistic methodology designed to study astatine chemistry in aqueous solution

“…At + was prepared in 0.1 mol L À1 HClO 4 and NaClO 4 solution (pH = 1 and E E 0.6 V vs. NHE) and AtO + with a mixture of 5 Â 10 À3 mol L À1 K 2 Cr 2 O 7 , 0.1 mol L À1 HClO 4 and 0.1 mol L À1 NaClO 4 (pH = 1 and E E 1 V vs. NHE). [45][46][47] The stability constants between inorganic ligands (Cl À , Br À ) and cationic species of astatine (At(x) + ) were determined using a competition method proposed by Champion et al 41 and previously used with the SCN À anion. The method consists in studying the distribution of astatine between the aqueous phase and toluene as a function of ligand concentration.…”

Questioning the Affinity of Electrophilic Astatine for Sulfur-containing Compounds: Unexpected Bindings Revealed

“…7,8 This cationic charge was evidenced as well by electromigration experiments. 9,10 It was generally represented as At(Ø) + , with some authors proposing At + or AtO + . 9−11 While investigating experimentally the effects of pH and potential, in combination with theoretical studies, we have recently established the formation of AtO + .…”