Na2Hg3S4: a thiomercurate with layered anions

Dark red crystals of Na2Hg3S4 were obtained by reacting a stoichiometric mixture of Na2S and HgS at 870 K. Na2Hg3S4 is orthorhombic, oP36, space group Pbca with a=7.308(5)Ä, b=14.011(8)Ä, c=8.231(3)Ä and Z=4. The crystal structure was determined from four-circle diffractometer data and refined to a conventional R of 0.056 for 718 reflections with Fo(2)>3sigma(Fo(2)) and 43 variables (Rw=0.065). Na2Hg3S4 crystallizes with a new structure type whose outstanding feature is the formation of strongly corrugated anionic layers, 2-oo-[Hg3S4](2-), running parallel to (010). These layers are based on a network of 16-membered rings formed by alternating mercury and sulphur atoms. Two thirds of the mercury atoms are in a trigonal planar co-ordination by suphur (d(Hg-S)=2.49Ä) while the remaining atoms are linearly coordinated (d(Hg-S)=2.344Ä). The Na(+) ions are coordinated by five sulphur atoms in a distorted square pyramidal configuration. The structure of Na2Hg3S4 can formally be derived from a distorted close-packed array of chalcogen atoms (stacking sequence, (hc)2; stacking direction, [010]).