Crystal Chemistry of Rubidium Uranyl Molybdates: Crystal Structures of Rb6[(UO2)(MoO4)4], Rb6[(UO2)2O(MoO4)4], Rb2[(UO2)(MoO4)2], Rb2[(UO2)2(MoO4)3] and Rb2[(UO2)6(MoO4)7(H2O)2]

Abstract Five Rb uranyl molybdates have been prepared by solid-state reactions and hydrothermal syntheses. The structure of each compound has been investigated using single-crystal X-ray diffraction data collected using Mo K α radiation and a Charge-Coupled-device-based area detector. The structure of Rb 6 [(UO 2 )(MoO 4 ) 4 ] (monoclinic, C 2/ c , Z =4, a =17.312(1) A, b =11.5285(8) A, c =13.916(1) A, β =127.634(1)°, V =2199.4(3) A 3 , R 1 =0.029) is based on finite clusters of composition [(UO 2 )(MoO 4 ) 4 ] 6− composed of a Ur O 4 ( Ur : UO 2 2+ uranyl ion) tetragonal bipyramid that shares each equatorial vertex with an adjacent MoO 4 tetrahedron. The structure of Rb 6 [(UO 2 ) 2 O(MoO 4 ) 4 ] (triclinic, P -1, Z =2, a =10.1567(5) A, b =10.1816(5) A, c =13.1129(6) A, α =76.921(1)°, β =76.553(1)°, γ =65.243(1)°, V =1184.8(1) A 3 , R 1 =0.047) is based upon chains of composition [(UO 2 ) 2 O(MoO 4 ) 4 ] 6− containing Ur O 5 pentagonal bipyramids and MoO 4 tetrahedra. The structure of Rb 2 [(UO 2 )(MoO 4 ) 2 ] (monoclinic, P 2 1 / c , Z =8, a =12.302(1) A, b =13.638(1) A, c =13.508(1) A, β =94.975(2)°, V =2257.8(4) A 3 , R 1 =0.059) contains sheets of composition [(UO 2 )(MoO 4 ) 2 ] 2− involving corner-sharing Ur O 5 pentagonal bipyramids and MoO 4 tetrahedra. The structure of Rb 2 [(UO 2 ) 2 (MoO 4 ) 3 ] (orthorhombic, Pna 2 1 , Z =4, a =20.214(1) A, b =8.3744(4) A, c =9.7464(5) A, V =1649.9(1) A 3 , R 1 =0.027) consists of a framework with composition [(UO 2 ) 2 (MoO 4 ) 3 ] 2− that involves corner-sharing Ur O 5 pentagonal bipyramids and MoO 4 tetrahedra. The structure of Rb 2 [(UO 2 ) 6 (MoO 4 ) 7 (H 2 O) 2 ] (orthorhombic, Pbcm , Z =4, a =13.961(2) A, b =10.7515(16) A, c =25.579(4) A, V =3839(1) A 3 , R 1 =0.037) consists of a framework of corner-sharing Ur O 5 pentagonal bipyramids, Ur O 4 (H 2 O) pentagonal bipyramids and MoO 4 tetrahedra. These structures are compared to those of other uranyl molybdates. The structural diversity and variability of uranyl molybdates is related to the high degree of flexibility of the U–O–Mo linkages.

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