Preparation and crystal structures of (Hg3)(PO4)Cl, (Hg3)(AsO4)Cl and (Hg3)(AsO4)Br -: Mercury compounds with the triangular Hg34+ cluster

The compounds (Hg-3)(PO4)Cl, (Hg-3)(AsO4)Cl and (Hg-3)(AsO4)Br have been prepared under hydrothermal conditions at 200 degreesC, starting from stoichiometric mixtures of the corresponding mercury halides and mercury phosphates or arsenates, respectively. The formula (Hg-3)(AsO4)Cl is identical with that of the mineral kuznetsovite. All compounds are isotypic and crystallize with four formula units in the space group P2(1)3 [(Hg-3)(PO4)Cl: a = 8.2912(5) Angstrom; (Hg-3)(AsO4)Cl: a = 8.3983(6) Angstrom; (Hg-3)(AsO4)Br: a = 8.4611(5) Angstrom]. All crystal structures have been refined from single crystal diffractometer data sets under consideration of merohedral twinning according to a diagonal mirror plane as twin element. The structures comprise of equilateral mercury triangles with mean distances (d) over bar (Hg-Hg) = 2.659 Angstrom, which are bonded to halogen and oxygen atoms of nearly perfect PO4 or AsO4 tetrahedra, respectively.