Crystal Chemistry of Uranyl Halides Containing Mixed (UO₂)(X_mO_n)₅ Bipyramids (X = Cl, Br): Synthesis and Crystal Structure of Cs₂(UO₂)(NO₃)Cl₃

Abstract

Single crystals of Cs 2 (UO 2 )(NO 3 )Cl 3 were prepared by a hydrothermal method at 205 • C. The crystal structure has been solved by Direct Methods: monoclinic, P2 1 /n, a = 10.3748(13), b = 9.4683(13), c = 12.5535 (16)Å, β = 110.280(2) • , V = 1156.7(3)Å 3 , R 1 = 0.029. In the structure, strongly bonded linear uranyl cations UO 2 2+ are equatorially coordinated by two O and three Cl atoms to form (UO 2 )Cl 3 O 2 pentagonal bipyramids. Each bipyramid shares its O-O edge with an adjacent (NO 3 ) − anion to form finite clusters with the chemical composition [(UO 2 )(NO 3 )Cl 3 ] 2− . The Cs + cations provide three-dimensional connectivity of the structure by forming Cs-O and Cs-Cl contacts to the uranyl nitrate chloride complexes. Related structures of mixed-ligand uranyl halides are compared.

Uranyl Nitrates: By-Products of the Synthetic Experiments or Key Indicators of the Reaction Progress?

“…Two crystallographically nonequivalent Cs + ions are arranged in between the [(UO 2 )(NO 3 )Cl 3 ] 2− complexes, forming 5O + 4Cl and 3O + 6Cl coordination geometries with average bond lengths of 3.358 and 3.492 Å, respectively. The crystal structure of 3 is a polymorph modification of the Cs 2 [(UO 2 )(NO 3 )Cl 3 ] phase recently reported in [15], and which was obtained following 4 days of hydrothermal synthesis at 205 • C. Thus, compound 3 should be regarded as α-modification since it was obtained at room temperature conditions. The crystal structure of β-Cs 2 [(UO 2 )(NO 3 )Cl 3 ] modification [15] differs from the structure of 3 by the Ur polyhedra arrangement: in the first structure, equatorial planes are arranged approximately parallel to (011) or (01-1) (Figure 3d), while in the structure of 1 equatorial planes of Ur are coplanar.…”

“…5.8 Å, while in other directions such spacing is significantly larger (7.8-8.2 Å). The crystal structure of 3 is a polymorph modification of the Cs2[(UO2)(NO3)Cl3] phase recently reported in [15], and which was obtained following 4 days of hydrothermal synthesis at 205 °C. Thus, compound 3 should be regarded as α-modification since it was obtained at room temperature conditions.…”

“…Thus, compound 3 should be regarded as α-modification since it was obtained at room temperature conditions. The crystal structure of β-Cs2[(UO2)(NO3)Cl3] modification [15] differs from the structure of 3 by the Ur polyhedra arrangement: in the first structure, equatorial planes are arranged approximately parallel to (011) or (01-1) (Figure 3d), while in the structure of 1 equatorial planes of Ur are coplanar. The crystal structure of 4 contains one symmetrically nonequivalent U 6+ atom forming Ur (U-OUr = 1.771(2) Å), equatorial plane of which is built by four O atoms from two trans-arranged edge-shared NO3 groups (<U-NOeq> = 2.514 Å), and another two O atoms that belong to H2O molecules (U-H2Oeq = 2.397(2) Å) and separate nitrate groups, thus resulting in the formation of hexagonal bipyramids as coordination polyhedra for the U 6+ atoms (Figure 2b).…”

“…The topology of the uranyl-nitrate-chloride cluster in the structures of 1-3 (Figure 2a) is one of the simplest, being formed only by two coordination polyhedra that share a common edge and belong to the cc0-1:1-5 type [19]. But never the less, this type of topology is rather rare, it has been previously observed in six crystal structures only, five of which are organically templated uranyl compounds [20][21][22] and the one pure inorganic β-Cs 2 [(UO 2 )(NO 3 )Cl 3 ] [15]. It is of special interest that this topological type has been found exclusively in the structures with three halogen ions arranged in the equatorial plane of Ur pentagonal bipyramid.…”