Crystal structure of kuznetsovite Hg3(AsO4)Cl

The crystal structure of a rare supergene mineral kuznetsovite Hg-3(AsO4)Cl, previously determined from powder data, is refined (space group P2(1)3, a = 8.379(3) Angstrom, V = 588.3(4) Angstrom(3), Z = 4, d(calc) = 8.763 g/cm(3), 3.44 < theta < 24.96 degrees, 563 I-hkl(msd)/211 I-hkl(indep), R-1 = 0.0997, wR(2) = 02515). It is formed from the Cl- and (AsO4)(3-) anions (As-O...1.74(3) and 1.79(1) Angstrom) and the trigonal cations Hg-3(4+) (Hg-Hg 2675(5) Angstrom, angle HgHgHg 60 degrees). The coordination polyhedron around each mercury atom involves two mercury atoms, two oxygen atoms at short Hg-O distances (2.17(3) and 2.28(3) Angstrom, angle OHgO 94.3(13)degrees), and more remote oxygen and chlorine atoms (Hg-O 2.601(6) Angstrom: Hg-Cl 2.838(9) Angstrom). The polyhedron is irregular and close to a trigonal antiprism. The Hg-3 triangles alternate with AsO4 tetrahedra along each coordinate axis. Taking into consideration only short Hg-O bonds (2.17(3) and 2.28(3) Angstrom), one can isolate a framework with chlorine ions lying in the cavities.