CRYSTAL CHEMISTRY OF MERCUROUS INORGANIC COMPOUNDS AND MINERALS. N.A.Pal'chik, S.A.Magarill, L.M.Volkova. Institute of Geology Sib. Branch RAS, Novosibirsk, Russia; Institute of Inorganic Chemistry Sib. Branch RAS, Novosibirsk, Russia; Institute of Chemistry FE Branch RAS, Vladivostok, Russia

An unique property of mercury, due to its electron shell structure, is the capacity for forming linear Hg_n (n=2,3,4,() systems with the Hg-Hg distance of 2.46-2.64 Å. The Hg-Hg bond lengths were found to be dependent on n: in Hg₂ dumbbell 2.46-2.54, in Hg₃ chain 2.55, for Hg₄ 2.58-2.62, and in Hg( infinite chain 2.64 Å. In these systems, Hg has the formal valency from +1 to +0.3. In terlinguaite and kusnetsovite minerals, mercury atoms form planar triangles with the Hg-Hg distances of 2.71 and 2.64 Å, respectively. In the triangles, the formal valency of Hg is +1.33, suggesting that this structural fragment involves a mixed-valent mercury atom. In terlinguaite, however, the Hg²⁺ is coordinated two oxygen atoms and the Hg-Hg distance to the nearest mercury atom of the triangle is more then 3 Å. Similarly, in the structure of wattersite, Hg²⁺ polyhedra and (Hg₂)²⁺ dumbbells are at a distance of >3 Å. The Hg₄(AsF₆)₂ structure is also of interest in that a linear (Hg₄)²⁺ tetrad (with the distances 2.58-2.62 Å) is bonded to the other tetrad at the Hg-Hg distance of 2.98 Å to form an infinite polymer with the chain charge +0.5.

A relation between conducting and other physical properties and structural peculiarities of these compounds is discussed in this report. As an example, in the Hg₃AsF₆ structure, infinite Hg-Hg chains (2.64 Å), running in two mutually perpendicular nonintersecting directions, are responsible for anisotropic superconductivity. Crystal chemical properties of these minerals and inorganic compounds will allow an understanding and an explanation for their physical properties, crystallization conditions, as well as modelling the basic skeleton of new minerals and compounds and predicting their physical properties.