The crystal structure of silver chromate

Abstract

Single crystals of silver chromate were prepared by slow diffusion of potassium chromate and silver nitrate solutions in a gel-filled U-tube. The thin tabular crystals belong to the orthorhombic space group Pnma with a = 10.063(11), b = 7.029(4), c = 5.540(2)Å, and Z = 4. Intensity data were measured with a ϑ – 2ϑ step-scan technique using an automated diffractometer and Mo K α radiation. The structure was solved by heavy atom methods and refined by full matrix least-squares techniques with anisotropic thermal parameters used only for the heavy atoms to a final residual of R = 0.064 for the 325 observed reflections used in the analysis. The silver atoms are coordinated to the oxygen atoms of the chromate to generate an interlocking network that propagates throughout the crystal. The two crystallographically independent silver atoms have coordinations best described as tetragonal bipyramidal and distorted tetrahedral, respectively. The shortest AgO distance is 2.34 Å. The silver-oxygen interactions perturb the tetrahedron of the chromate group with CrO distances of 1.69, 1.67, and 1.63(1) Å and angles varying from 106.1 to 111.6(8)°. The metal atom coordination in silver chromate is compared to that of potassium chromate.