Aquatetrakis(dimethyl sulfoxide)dioxoneptunium(VI) silicotungstate [NpO2(DMSO)(4)(H2O)](2)(SiW12O40): Synthesis and crystal structure

Single crystals of [NpO2(DMSO)(4)(H2O)](2)(SiW12O40) were prepared and the structure was solved (Siemens P3/PC MoKalpha radiation, triclinic, R = 0.07 16 for 4320 observed reflections). The structure consists of [NpO2(DMSO)(4) H2O](2+) complex cations and (SiW12O40)(4-) heteropoly anions (HPAs). The a nions and cations are linked to form chains by hydrogen bonds (O . . .O 2.8 2(3) and 2.67(3) Angstrom). Each water molecule of the [NpO2(DMSO)(4)H2O](2 +) cation is a proton donor for the oxygen atoms of two neighboring HPAs. T he coordination polyhedron of Np(VI) is a pentagonal bipyramid (C.N. 7). Th e NpO2 group is nearly linear and almost symmetrical; the O=Np=O angle is 1 79(1)degrees, the Np=O bond lengths are 1.73(2) and 1.74(2) Angstrom. The e quatorial plane about the NpO22+ cation is formed by the oxygen atoms of th e four DMSO molecules and one water molecule (Np-O-eq. 2.33(1)-2.48(1) Angs trom). The SiO44- tetrahedra in the HPA have two equally probable statistic al orientations.