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Crystals of four potassium uranyl chromates, K 8 [(UO 2 )(CrO 4 ) 4 ](NO 3 ) 2  ( 1 ), K 5 [(UO 2 )(CrO 4 ) 3 ](NO 3 )·(H 2 O) 3  ( 2 ), K 4 [(UO 2 ) 3 (CrO 4 ) 5 ](H 2 O) 8  ( 3 ) and K 2 [(UO 2 ) 2 ·(CrO 4 ) 3 (H 2 O) 2 ](H 2 O) 4  ( 4 ), have been synthesized by evaporation of aqueous solutions of (UO 2 )(NO 3 ) 2 (H 2 O) 6  and K 2 CrO 4 . The structure of ( 1 ) (triclinic,  P 1̅,  a  = 7.0397(6),  b  = 9.7341(9),  c  = 9.7568(9) Å,  α  = 105.846(2),  β  = 97.992(2),  γ  = 93.271(2)°,  V  = 633.8(1) Å 3 ,  Z  = 1) was solved by direct methods and refined to  R 1 = 0.044 ( wR 2 = 0.098). It is based upon clusters of composition [(UO 2 )(CrO 4 ) 4 ] that consist of  Ur O 4  square bipyramids ( Ur : UO 2  2+  uranyl ion) that share corners with four different CrO 4  tetrahedra. The clusters are arranged in layers parallel to the (100) plane. K +  cations and NO 3  -  groups are located between the clusters. The crystal structure of ( 2 ) (orthorhombic,  P 2 1 2 1 2 1 ,  a  = 6.1112(11),  b  = 12.136(2),  c  = 27.464(4) Å,  V  = 2036.9(6) Å 3 ,  Z  = 4) was solved by direct methods and refined to  R 1 = 0.047 ( wR 2 = 0.071). it contains chains of composition [(UO 2 )(CrO 4 ) 3 ] that are parallel to the  b  axis. The chains consist of  Ur O 5  pentagonal bipyramids that share all equatorial corners with different CrO 4  tetrahedra. Planes containing the equatorial ligands of the  Ur O 5  pentagonal bipyramids are approximately parallel to the (100) plane. K +  cations, NO 3  groups and H 2 O groups are between the chains. The crystal structure of ( 3 ) (monoclinic,  P 2 1 / c ,  a  = 8.2336(7),  b  = 18.8042(17),  c  = 21.2413(18) Å,  β  = 89.979(2)°,  V  = 3288.7(5) Å 3 ,  Z  = 4) has been solved by direct methods from a crystal twinned on the (001) plane and refined to  R 1 = 0.060 ( wR 2 = 0.125). The structure is based upon topologically complex sheets of composition [(UO 2 ) 3 (CrO 4 ) 5 ] with  Ur O 5  pentagonal bipyramids that share their corners with CrO 4  tetrahedra. The sheets are parallel to the (010) plane. K +  cations and H 2 O groups are located in the interlayer between the sheets. The crystal structure of ( 4 ) (monoclinic,  P 2 1 / c ,  a  = 10.7417(5),  b  = 14.5290(7),  c  = 14.1387(6) Å,  β  = 108.135(1)°,  V  = 2097.0(2) Å 3 ,  Z  = 4) was solved by direct methods and refined to  R 1 = 0.036 ( wR 2 = 0.067). It is based upon sheets of composition [(UO 2 ) 2 (CrO 4 ) 3 (H 2 O) 2 ] that are parallel to the (010) plane. K +  cations and additional H 2 O groups are in the interlayer. Nodal representations of uranyl chromate structural units are developed, and a comparison with related structures are presented.

zeitschrift für kristallographie - crystalline materials

Structural topology of potassium uranyl chromates: crystal structures of K 8 [(UO 2 )(CrO 4 ) 4 ](NO 3 ) 2 , K 5 [(UO 2 )(CrO 4 ) 3 ](NO 3 )(H 2 O) 3 , K 4 [(UO 2 ) 3 (CrO 4 ) 5 ](H 2 O) 8  and K 2 [(UO 2 ) 2 (CrO 4 ) 3 (H 2 O) 2 ](H 2 O) 4