Polytypism in columnar group 14 halide salts: structures of (Et2NH2)3Pb3X9 x nH2O (X = Cl,Br) and (beta-alaninium)2SnI4

The crystal structures of three hybrid organoammonium metal halide salts composed of edge-sharing MX(6) octahedra have been determined. The genesis of these structures can be traced to the parent hexagonal MX(2) structure via dimensional reduction and recombination arguments. The structures of (Et(2)NH(2))(3)Pb(3)X(9) x nH(2)O (X = Br, I) contain unique columnar (Pb(3)X(9))(n)(3)(n)(-) structures, built up of edge-shared PbX(6) octahedra. The interaction of the Et(2)NH(2)(+) cations with the parent PbX(2) structures leads to a rearrangement of the lattice into the observed columnar structure. Groups of six Et(2)NH(2)(+) cations are hydrogen bonded to these columns, girdling them at their narrowest points. These hydrogen bonds contribute to the formation of the zigzag nature of the columnar inorganic framework. The resultant structures are recombinate analogues (polytypes) of the (Pb(3)X(9))(n)(3)(n)(-) stacks that would be obtained by the dimensional reduction process of the parent layer PbX(2) structure into simple edge-shared ribbons of PbX(6) octahedra. These structures can be described in terms of the stacking of planar bibridged Pb(3)X(8)(2-) units decorated with a single halide ion at a terminal lead ion site. In a similar fashion, (beta-alaH)(2)Sn(2)I(6) contains corrugated (Sn(2)I(6))(n)(2)(n)(-) columns (beta-ala = beta-alanine), with the cations sitting in the clefts of the columns.