Inorganic Chemistry, Vol.41, No.26, 7024-7030, 2002
Polytypism in columnar group 14 halide salts: Structures of (Et2NH2)(3)Pb3X9 center dot nH(2)O (X =Cl, Br) and (beta-alaninium)(2)SnI4
The crystal structures of three hybrid organoammonium metal halide salts composed of edge-sharing MX6 octahedra have been determined. The genesis of these structures can be traced to the parent hexagonal MX2 structure via dimensional reduction and recombination arguments. The structures of (Et2NH2)(3)Pb3X9.nH(2)O (X = Br, I) contain unique columnar (Pb3X9)(n)(3n-) structures, built up of edge-shared PbX6 octahedra. The interaction of the Et2NH2+ cations with the parent PbX2 structures leads to a rearrangement of the lattice into the observed columnar structure. Groups of six Et2NH2+ 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 (Pb3X9)(n)(3n-) stacks that would be obtained by the dimensional reduction process of the parent layer PbX2 structure into simple edge-shared ribbons of PbX6 octahedra. These structures can be described in terms of the stacking of planar bibridged Pb3X82- units decorated with a single halide ion at a terminal lead ion site. In a similar fashion, (beta-alaH)(2)Sn2I6 contains corrugated (Sn2I6)(n)(2n-) columns (beta-ala = beta-alanine), with the cations sitting in the clefts of the columns.