Two new cubic structures of mercury arsenidehalidesстатья
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Аннотация:Crystal structures of Hg4As2Br3 (I) and Hg7.4As4Cl6 (II), which was prepared for the first time, have been refined based on the X-ray single crystal experiments, Both phases crystallize in the cubic space group Pa3. Crystal data: I, a = 12.610(1), Z = 8, R(1) = 0.0602; II, a = 12.178(1), Z = 4, R(1) = 0.0584. Characteristic of both structures are the As2Hg6 octahedra having an As-As separation of ca, 2.38 Angstrom. Such octahedra share vertices with AsHg4 tetrahedra in I, while in II they compose a perovskite-like three-dimensional network by sharing all vertices, Part of the mercury atoms in II have no neighbors up to 3.53 Angstrom and are considered to possess a zero oxidation state, An idealized path for the I to II structure transformation, which is based on the difference of halogen radii, is suggested. (C) 1996 Academic Press, Inc.