Crystal Structure of [UO2SO4{(CH3)HNCONH(CH3)}2]

Abstract

Within the framework of our research into the complexation in the UO 2 XO 4 -L -H 2 O system at 25°ë (X = S, Se; L are dimethylcarbamide isomers), we found that the composition and structure of the uranyl compounds formed depend appreciably, along with the nature of the tetrahedral oxo anion, on the structure of molecules L, in particular, on their ability to be involved in hydrogen bonds. In all four systems, new uranyl complexes have been obtained. In the case of symmetric amide structure (L = N , N '-dimethylcarbamide, s -Dmur ), anhydrous complexes UO 2 SO 4 ( s -Dmur ) 2 ( I ) and UO 2 SeO 4 ( sDmur ) 2 ( II ) crystallized [1], while in the case of the asymmetric structure (L = N , N -dimethylcarbamide, a -Dmur ), the anhydrous complex UO 2 SO 4 ( a -Dmur ) 2 ( III ) [2] and the aqua complex [ UO 2 SeO 4 ( aDmur ) 2 (H 2 O )] · H 2 O ( IV ) [3] were formed. Since the structures of compounds II -IV are known, we aimed at a single-crystal X-ray diffraction study of I . EXPERIMENTALThe experimental data were collected on a CAD4 Enraf-Nonius four-circle automated diffractometer. The structure was solved by the heavy atom method and refined by least-squares calculations in the fullmatrix anisotropic approximation for all non-hydrogen atoms. The hydrogen atoms of the s -Dmur molecules were determined geometrically and refined in the riding model with fixed isotropic thermal parameters. All calculations were carried out using SHELX97 software.The crystal data and structure refinement parameters for I are presented in Table 1, the atomic coordinates and thermal parameters are given in Table 2, and selected geometric characteristics are listed in Table 3. RESULTS AND DISCUSSIONThe uranium coordination polyhedron is the UO 2 O 5 pentagonal bipyramid whose axial positions are occupied by the uranyl oxygen atoms and the equatorial plane is formed by three oxygen atoms of three sulfate ions and two oxygen atoms of two s -Dmur molecules. The volume of the Voronoi-Dirichlet polyhedron (VDP) of uranium, which is shaped like a pentagonal prism ( 9.0 Å 3 ), is in good agreement with the average value for uranium(VI) atoms surrounded by oxygen (9.2(3) Å 3 ) [4]. The solid angles ( W ) corresponding to the VDP faces common to uranium and coordinated oxygen atoms are indicated in Table 3. The sulfur coordination polyhedron is the SO 4 tetrahedron, which acts as a tridentate bridging ligand with respect to uranyl (T 3 type of coordination [5]). The volume of sulfur VDP ( 5.5 Å 3 ) coincides with the average value (5.5(1) Å 3 ) known for S(VI) atoms surrounded by oxygen [6]. The s -Dmur molecules located in the cis -position with respect to each other are monodentate terminal ligands (M 1 type).The main structural unit of the crystal of I is the (Fig. 1) having the crystal chemical formula AT 3 (A = ) and stretched along [100]. The [ UO 2 SO 4 { sDmur )} 2 ] ∞ ribbons are combined into a three-dimensional framework through a system of N -H···O hydrogen bonds (Table 3). Compound I is isostructural to the selenate-containing complex...