Preparation and Crystal Structures of (Hg3 )(P0 4 )Cl, (Hg3)(As04)Cl and (Hg3)(As04)Br - Mercury Compounds with the Triangular Hg34+ Cluster

Z. Naturforsch. 56 b, 753-758 (2001); received March 12, 2001 Kuznetsovite, Mercury Cluster Hg34+, Merohedral Twinning The compounds (Hg3)(PC>4)Cl, (Hg3)(AsC>4)Cl and (Hg3)(As0 4 )Br have been prepared under hydrothermal conditions at 200 °C, starting from stoichiometric mixtures of the corresponding mercury halides and mercury phosphates or arsenates, respectively. The formula (Hg3)( As0 4 )Cl is identical with that of the mineral kuznetsovite. All compounds are isotypic and crystallize with four formula units in the space group P2\ 3 [(Hg3)(P0 4 )Cl: a = 8.2912(5) A; (Hg3)(As0 4 )Cl: a = 8.3983(6) A; (Hg3)(As0 4 )Br: a = 8.4611(5) A]. 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(Hg-Hg) = 2.659 A, which are bonded to halogen and oxygen atoms of nearly perfect PO4 or ASO4 tetrahedra, respectively.