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

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 Mo K αX-ray radiation and an APEX CCD-based detector. The isotypic compounds ( 1 ) Cs 2 Ni 3 (H 2 O) 4 [(UO 2 ) 8 (SeO 4 ) 4 O 8 ] and ( 2 ) Cs 2 Co 3 (H 2 O) 4 [(UO 2 ) 8 (SeO 4 ) 4 O 8 ] are monoclinic, space group C 2/ c , with cell parameters of a 8.755(3), b 14.228(5), c 17.927(8) A, β103.739(3)° and a 8.744(2), b 14.380(4), c 17.901(5) A, β103.654(3)°, respectively. The structure of ( 3 ) Cs 2 (H 2 O) 4 [(UO 2 ) 4 (SeO 4 ) 2 O 2 (OH) 2 ] is triclinic, space group P 1 with cell parameters a 8.6877(4), b 8.7164(4), c 8.9589(8) A, α95.964(10), β99.155(10), and γ117.318(10)°. The mixed selenate-selenite phase ( 4 ) Cs 2 (H 2 O) 5 [(UO 2 ) 7 (SeO 4 ) 2 (SeO 3 ) 2 O 4 ]. H 2 O is monoclinic, space group P 2 1 /m, with cell parameters a 9.1381(3), b 15.0098(5), c 15.1732(5) A, β91.171(10)°. The compound ( 5 ) Li 2 (H 2 O) 6 [(UO 2 ) 3 (SeO 3 ) 2 O 2 ] is monoclinic, with cell parameters P 2 1 / c , a 7.5213(9), b 7.0071(9), c 17.3282(19) A, β98.834(2)°. ( 6 ) Cs 2 (H 2 O) 2 [(UO 2 ) 4 (SeO 3 ) 5 ] is monoclinic, P 2 1 / n , with cell parameters a 10.913(3), b 12.427(3), c 18.448(4) A, β90.393(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.