CRYSTAL STRUCTURES OF SIX NEW URANYL SELENATE AND SELENITE COMPOUNDS AND THEIR RELATIONSHIP WITH URANYL MINERAL STRUCTURES

摘要

Three uranyl selenates, one mixed uranyl selenate-selenite, and two uranyl selenite compounds have been synthesized using mild hydrothermal techniques. The structure of each has been determined using single-crystal diffraction data collected with MoKα X-ray radiation and an APEX CCD-based detector. The isotypic compounds (1) Cs_2Ni_3(H_2O)_4[(UO_2)_8(SeO_4)_4O_8] and (2) Cs_2Co_3(H_2O)_4[(UO_2)_8(SeO_4)_4O_8] are monoclinic, space group C2/c, with cell parameters of a 8.755(3), b 14.228(5), c 17.927(8) A, β 103.739(3)° and a 8.744(2), b 14.380(4), c 17.901(5) A, β 103.654(3)°, respectively. The structure of (3) Cs_2(H_2O)_4[(UO_2)_4(SeO_4)_2O_2(OH)_2] is triclinic, space group P1 with cell parameters a 8.6877(4), b 8.7164(4), c 8.9589(8) A, α 95.964(10), β 99.155(10), and γ 117.318(10)°. The mixed selenate-selenite phase (4) Cs_2(H_2O)_5[(UO_2)_7(SeO_4)_2(SeO_3)_2O_4].H_2O is monoclinic, space group P2_1/m, with cell parameters a 9.1381(3), b 15.0098(5), c 15.1732(5) A, β 91.171(10)°. The compound (5) Li_2(H_2O)_6[(UO_2)_3(SeO_3)_2O_2] is monoclinic, with cell parameters P2_1/c, a 7.5213(9), b 7.0071(9), c 17.3282(19) A, β 98.834(2)°. (6) Cs_2(H_2O)_2[(UO_2)_4(SeO_3)_5] is monoclinic, P2_1, with cell parameters a 10.913(3), b 12.427(3), c 18.448(4) ?, β 90.393(3)°. Compounds 1, 2, and 3 contain sheets of uranyl pentagonal bipyramids and selenate tetrahedra with the zippeite-type topology. Compound 4 is a unique mixed selenate-selenite compound that contains sheets that are topologically intermediate between the zippeite-type and phosphuranylite-type topologies. Compound 5 contains a uranyl selenite sheet based on the phosphuranylite anion-topology, as found in the minerals marthozite and guilleminite. Compound 6 contains a novel sheet consisting of uranyl pentagonal and hexagonal bipyramids, as well as SeO_3 pyramids.