P. K. Ummat

Preparation, structure, and properties of mercury layer and chain compounds

In this paper is reviewed the preparation, structure, and electrical properties of salts of the polyatomic mercury cations Hg32+ and Hg42+, the infinite chain compounds Hg3−δMF6 (M=As, Sb, Nb, and Ta), and the layer compounds Hg3NbF6 and Hg3TaF6.

The preparation and structure of chain and sheet mercury compounds

This paper is a review of the preparation and structures of the polymercury cations Hg32+ and Hg32+, the mercury chain compounds, Hg3-δAsF6, Hg3-δSbF6, Hg3-δ NbF6 and Hg3_δTaF6, and the mercury layer compounds Hg3NbF6 and Hg3TaF6. The chain compounds Hg3-δMF6 are hard, golden yellow insoluble crystals with a shiny metallic appearance that have linear chains of mercury atoms parallel to the a and b axes of a tetragonal cell. They are non-stoichiometric because the Hg-Hg distance is not com mensurate with the tetragonal lattice of AsF6− octahedra. The layer compounds have a silver colour with a distinct metallic lustre, but they are quite soft. They have sheets of hexagonally close-packed mercury atoms separated by a layer of NbF6− or TaF6− octahedra. In contrast to the chain compounds the layer compounds are stoichiometric. The interconversion of the chain and layer compounds is described and discussed.

Electrical properties of chain and sheet mercury compounds

The electrical resistivity of the chain compounds Hg3-δAsF6 and Hg3-δSbF6 decreases with decreasing temperature. It is shown that the temperature dependence of the resistivity of Hg3-δSbF6 depends on the rate that a sample is cooled from room temperature to liquid helium temperature. The electrical resistivity of the layered compounds Hg3TaF6 and Hg3NbF6is metallic from 300 to 1.4 K. The induced torque, de Haas-van Alphen effect and resistivity of the chain compounds are related to the cylindrical Fermi surface model. Superconductivity of the compounds is discussed.

Superconducting effects of Hg3-δSbF6

The resistivity and AC susceptibility of Hg3- delta SbF6 cooled at different rates were measured between 1.4 and 4.2K. There is a superconducting transition at 4.1K in slowly cooled samples with no anisotropy in the superconducting transition temperature for current directions parallel and perpendicular to the c axis. Superconductivity of fast cooled samples occurs below 3.9K and susceptibility changes over a range of temperature. The superconductivity which depends on cooling rate is attributed to mercury trapped in isolated regions, with the size of the regions depending on the rate of cooling.