Structure maps of close-packed layered compounds and DNA

Close-packed layered compounds such as FexGa2S3+x and NxC3Al4+x (x = 0-4) a re analyzed as chains of covalent-bonded S = Ga(-S-Fe)(x)-S-Ga=S or Al=C(-A l=N)(x)-Al=C=Al (-N=Al)(x)-C with delocalized bonds. The rules for valence compounds allow RM, R(MR)(n) (n = 1, 2, 3), RMMR, and different combination s and substitutions. The conformation of the chains is characterized by the Jagodzinski-Wyckoff symbols c and h and a similar notation s and t at the occupation of tetrahedral sites, The interactions between the different ato ms are analyzed by structure maps with the self-coordination numbers of nea rest and next-nearest neighbors as parameters. A similar analysis of 18 dif ferent DNA or RNA reveals four different groups within different fields of the structure map similar to solid solutions or nonperiodic polytypes of la yered compounds. (C) 1999 Academic Press.