Structures and syntheses of four Np5+ sulfate chain structures: Divergence from U6+ crystal chemistry

Four Np5+ sulfates, X4[(NpO2)(SO4)2]Cl (X=K, Rb) (KS1, RbS1), Na3[(NpO2)(SO4)2](H2O)2.5 (NaS1), and CaZn2[(NpO2)2(SO4)4](H2O)10 (CaZnS1) were synthesized by evaporation of solutions derived from hydrothermal treatment. Their structures were solved by direct methods and refined on the basis of F2 for all unique data collected with MoKα radiation and a CCD-based detector to agreement indices (KS1, RbS1, NaS1, CaZnS  1) R1=0.0237R1=0.0237, 0.0593, 0.0363, 0.0265 calculated for 2617, 2944, 2635, 2572 unique observed reflections, respectively. KS1 crystallizes in space group P2/n  , a=10.0873(4)a=10.0873(4), b=4.5354(2)b=4.5354(2), c=14.3518(6)c=14.3518(6), β=103.383(1)°β=103.383(1)°, V=638.76(5)Å3, Z=2Z=2. RbS1 is also monoclinic, P2/n  , with a=10.5375(8)a=10.5375(8), b=4.6151(3)b=4.6151(3), c=16.0680(12)c=16.0680(12), β=103.184(1)°β=103.184(1)°, V=699.33(9)Å3, Z=2Z=2. NaS1 is monoclinic, P21/m  , with a=7.6615(5)a=7.6615(5), b=7.0184(4)b=7.0184(4), c=11.0070(7)c=11.0070(7), β=90.787(1)°β=90.787(1)°, V=591.81(6)Å3, Z=4Z=4. CaZnS1 is monoclinic, P21/m,   with a=8.321(2)a=8.321(2), b=7.0520(2)b=7.0520(2), c=10.743(3)c=10.743(3), β=91.758(5)°β=91.758(5)°, V=630.1(3)Å3, Z=2Z=2. The structures of KS1 and RbS1 contain chains of edge-sharing neptunyl hexagonal bipyramids, with sulfate tetrahedra attached to either side of the chain by sharing edges with the bipyramids. NaS1 and CaZnS1 both contain chains of neptunyl pentagonal bipyramids and sulfate tetrahedra in which each bipyramid is linked to four tetrahedra, three by sharing vertices and one by sharing an edge. Bipyramids are bridged by sharing vertices with sulfate tetrahedra. Each of these structures exhibits significant departures from those of uranyl sulfates.

The structures of four Np5+ sulfates, X4[(NpO2)(SO4)2]Cl (X=K, Rb), Na3[(NpO2)(SO4)2](H2O)2.5, and CaZn2[(NpO2)2(SO4)4](H2O)10 contain chains formed by the sharing of edges and vertices between neptunyl polyhedra and sulfate tetrahedra. These structures exhibit significant departures from those of uranyl sulfates.Figure optionsDownload as PowerPoint slide