Hierarchical structures in tin(II) oxalates

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][Sn-2-(C2O4)(3)], and III [C8N4H26][Sn(C2O4)(2)](2)-2H(2)O 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)[Sn-4(C2O4)(6)]center dot 7H(2)O 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, pi center dot center dot center dot pi interactions, and lone-pair-pi interactions have been observed and appear to lend structural stability. Theoretical studies indicate that the pi center dot center dot center dot pi interaction energy between the bound 1,10-phenanthroline molecules is of the order of 5-6 kcalmol(-1) in V. Natural bond orbital (NBO) analysis on two model compounds, II and IV, indicates reasonable lone-pair-pi 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. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).