On crystal chemistry of mercury chromates. Details of fragmentation and packing in crystal structures

In the crystal structures of the minerals edoylerite, deanesmithite, and wattersite and in the structures of the compounds HgCrO₄, Hg₃O₂CrO₄ (analog of the mineral schuetteite), and Pb₂HgO₂CrO₄, there are atomic groups or fragments linked by relatively strong (covalent) bonds. The anion fragments represented by CrO₄ tetrahedra are condensed into pairs and chains, in which adjacent tetrahedra are related by symmetry centers. The cation fragments form various patterns from zigzag ribbons of Hg₄S₄] rings to ribbons and frameworks with Hg₆O₂] r-octahedra, Hg₂CrO] and Pb₂HgO] triangles, and Hg₆Cr₂O₄] (stella quadrangula) groups. The symmetry of the fragments and their assemblies is analyzed. Analysis of the reference crystal-forming planes has revealed cation sublattices (close to the F-cubic sublattice in two cases), determining the typical features of the structures.Original Russian Text Copyright © 2004 by S. V. Borisov, S. A. Magarill, and N. V. PervukhinaTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 3, pp. 471–479, May–June, 2004.