Crystallographic isomorphism in the structural type of alpha-HgI2 by example of KHgI3 center dot H2O, beta-Ag2HgI4, and beta-Cu2HgI4

摘要

The structure of KHgI3 center dot H2O is assigned to the family of crystal structures having the three-layer cubic packing of iodine anions with cations in the tetrahedral voids (the structures of alpha-HgI2, beta-Ag2HgI4, and beta-Cu2HgI4 among them). Crystallographic analysis shows that the nodes of the three-layer close packing are populated by iodine anions and K cations in the ratio 3/4: 1/4. Transformation of the structure of alpha-HgI2 into the structure of KHgI3 center dot H2O can be formally represented as the replacement of (HgI)(n)(+) fragments by (KH2O)(n)(+) fragments: (Hg2I4)-(HgI)(+) + (KH2O)(n)(+) = KHgI3 center dot H2O. Perforated layers of vertex-sharing HgI4 tetrahedra break down into parallel isolated chains. Channels formed in place of I-Hg-I-Hg-fragments are occupied by-H2O-K-H2O-chains weakly bound to neighbors.