Structure and Solubility of Tetrapropylammonium Pertechnetate and Perrhenate

The crystal structure was determined and the physicochemical properties were studied for tetrapropylammonium pertechnetate and perrhenate. Pr4NMO4 (M = Tc, Re) are isostructural and crystallize as colorless prismatic crystals in the orthorhombic system, space group Pna21, Z = 4. For M = Tc at 25°C, a = 13.22(4) A, b = 12.35(3) A, c = 10.13(4) A; for M = Re at −120°C, a = 13.169(2) A, b = 12.311(2) A, c = 10.107(1) A. The Re-O distances are 1.677(12), 1.704(5), 1.719(4), and 1.739(11) A. Each anion in this structure has four neighboring cations with Re…N distances of 5.06–5.34 A. The solubility product of Pr4NTCO4 is (6.19 ± 0.50) × 10−5 mol2/L2. The Gibbs energy of dissolution of [(C3H7)4N]TcO4 in dilute aqueous solutions is 24.0 ± 0.5 kJ/mol. The association constant K 1 for (Pr4N+)…(TcO 4 − ) in water and aqueous solutions is 10.8 ± 0.7 L/mol. The solubility of Pr4NTcO4 increases with the solution acidity, similarly to the solubility of Bu4NTcO4. Upon precipitation of Pr4NTcO4 from model solutions containing (2.0–7.5) × 10−2 mol/L Tc in 3–4 M HNO3, (2.0–7.5) × 10−8 mol/L 239PuO2(NO3)2, and 5.7 mCi/L 106Ru(NO)(NO3)3, the technetium decontamination factors from 239Pu and 106Ru were (0.5–1.5) × 102 and (6.0–7.5) × 102, respectively.