Struktur und eigenschaften von UO₂(H₂AsO₄)₂ · H₂O

UO₂(H₂AsO₄)₂ · H₂O was synthesized by dissolving elemental uranium in arsenic acid (80.5%) for twelve weeks at room temperature. The resulting small crystals were transparent and of yellow-green color. The crystal structure was refined from single-crystal X-ray data: C2/c, a = 1316.4(3) pm, b = 886.2(2) pm, c = 905.0(3) pm, β= 124.41(3)°, R1 = 0.023, wR2 = 0.060, 981 structure factors, and 65 variable parameters. The uranium atoms of this new structure type are coordinated by two very close oxygen atoms in linear arrangement. Four further oxygen atoms which belong to four different AsO₄ tetrahedra and the oxygen atom of the water molecule complete the 7-fold coordination of the uranium atoms. [UO₂(H₂O)]²⁺ and two H₂AsO₄^- units form infinite electroneutral chains which are the main building units of the structure and which are interconnected by hydrogen bridging bonds. IR heating experiments show that dehydration around 500 K leads to a complete decomposition of the structure. Magnetic measurement gave a diamagnetic behavior with a susceptibility of χ = -8.68 10^-9 m³/mol in good agreement with the diamagnetic increment of the compound (χ = -8.20 10^-9 m³/mol) calculations with U⁶⁺.