Ionothermal synthesis of uranyl compounds that incorporate imidazole derivatives

Abstract

Ionothermal reactions of uranyl nitrate with various salts in methylimidazolium-based ionic liquids have produced single crystals of three uranyl compounds that incorporate imidazole derivatives as charge-balancing cations. (C4H7N2)[(UO2)(PO3F)(F)] (1) crystallizes in space group C2, a=17.952(1)Å, b=6.9646(6)Å, c=8.5062(7)Å, β=112.301(1)°, (C6H11N2)2[(UO2)(SO4)2] (2) crystallizes in space group C2/c, a=31.90(1)Å, b=9.383(5)Å, c=13.770(7)Å, β=93.999(7)° and (C6H11N2)[(UO2)2(PO4)(HPO4) (3) crystallizes in space group P21/n, a=9.307(2), b=18.067(4), c=9.765(2), β=93.171(2). The U6+ cations are present as (UO2)2+ uranyl ions coordinated by three O atoms and two F atoms in 1 and five O atoms in 2 and 3 to give pentagonal bipyramids. The structural unit in 1 is composed of F-sharing dimers of uranyl pentagonal bipyramids linked into sheets through corner-sharing fluorophosphate tetrahedra. The structural unit in 2 is composed of uranyl pentagonal bipyramids with one chelating sulfate tetrahedron linked into chains by three other corner-sharing sulfate tetrahedra. In 3, the structural unit is composed of chains of uranyl pentagonal bipyramids linked into sheets through edge- and corner-sharing phosphate and hydrogen phosphate tetrahedra. N-methylimidazolium cations occupy the interstitial space between the uranyl fluorophosphate sheets in 1, whereas 1-ethyl-3-methylimidazolium cations link the uranyl sulfate and phosphate units in 2 and 3 into extended structures.