Hierarchical structures in tin(II) oxalates

Abstract

Six new Sn^II oxalates exhibiting a hierarchy of structures have been prepared employing hydrothermal methods. The compounds I [C₁₀N₂H₁₀] [Sn(C₂O₄)₂], II [C₁₀N₂H₁₀][Sn₂(C₂O₄)₃], and III [C₈N₄H₂₆] [Sn(C₂O₄)₂]₂·2H₂O possess zero-dimensional molecular structures; IV [C₁₀N₂H₈] ₂[Sn(C₂O₄)]₂ and V [C₁₂N₂H₈][SnC₂O₄] have one-dimensional chain structures; and compound VI [C₅N₂H₁₄] ₂[Sn₄(C₂O₄)₆]·7H₂O has a two-dimensional layer structure. The Sn^II ions have 4- and 6-coordination with square-pyramidal or pentagonal-bipyramidal geometry, in which the lone pair of electrons also occupies one of the vertices. Weak intermolecular forces such as hydrogen-bond interactions, π···π interactions, and lone-pair-π interactions have been observed and appear to lendstructural stability. Theoretical studies indicate that the π···π interaction energy between the bound 1,10-phenanthroline molecules is of the order of 5-6 kcal mol^-1 in V. Natural bond orbital (NBO) analysis on two model compounds, II and IV, indicates reasonable lone-pair-π interactions. The close structural relationship between all the compounds indicates that a building-up process from the zero-dimensional monomer can be considered. The present structures provide opportunities for evaluating the structure-directing role of the lone pair of electrons of Sn^II.