Preparation and Crystal Structure of Hg9As4O16, a Mercury Arsenate(V) with Triangular Hg3 4+ Cations

Abstract

Abstract The new compound Hg9As4O16 has been prepared by thermal decomposition o f the mercury(I) arsenate(V) (Hg2)3(AsO4)2 in the presence of HgO in an evacuated, sealed silica tube. It crystallizes with a rhombohedral structure (R3c, Z = 6), which has been determined from two single-crystal diffractometer data sets collected at 295 K (a = 1665.3(1) pm, c = 1083.8(1) pm, R = 0.051 for 2353 structure factors and 62 variable parameters) and 170 K (a = 1660.3(2) pm, c = 1083.0(1) pm, R = 0.037 for 1681 F-values). It corresponds to the formula (Hg3 4+)3(AsO4 3-)4 with almost equilateral mercury triangles and nearly perfect ASO4 tetrahedra. The average Hg-Hg bond distance of 267.5 pm is considerably greater than the average Hg-Hg distance of 251.3 pm round in mercury(I) compounds, reflecting the atoms.