The first sodium uranyl chromate, Na4[(UO2)(CrO4)3]:: Synthesis and crystal structure determination

The first sodium uranyl chromate, Na-4[(UO2)(CrO4)(3)], has been obtained by high-temperature solid-state reaction. The structure (triclinic, P (1) over bar, Z = 2, a = 7.1548(3), b 8.4420(3), c = 11.5102(5) Angstrom, alpha = 80.203(1)degrees, beta = 79.310(1)degrees, gamma = 70.415(1)degrees V = 639.24(4) Angstrom(3)) has been solved by direct methods and refined on the basis of F-2 for all unique reflections to R1 = 0.024 [calculated on the basis of 4374 unique observed reflections (\F-o\ greater than or equal to 4sigma(F))]. The structure is based on chains of composition [(UO2)(CrO4)(3)] that are parallel to [(1) over bar 01]. The chains contain UrO(5) pentagonal bipyramids (Ur = Uranyl) that share all equatorial corners with CrO4 tetrahedra. Cr(1)O-4 and Cr(3)O-4 tetrahedra bridge between two adjacent UrO(5) bipyramids, whereas Cr(2)O-4 tetrahedra share one corner with one UrO(5) bipyramid each. The [(UO2)(CrO4)(3)] chains are planar and oriented parallel to (313). The Na+ cations provide linkage of the chains in the structure.