Self-assembled organoplatinum(II) supermolecules as crystalline, SO2 gas-triggered switches

Square-planar platinum(II) complexes containing N,C,N terdentate coordinating, anionic 'pincer' ligands reversibly bind gaseous SO2 in the solid state by Pt-S bond formation and cleavage giving five-coordinate adducts. When the starting material is crystalline, exposure to this gas leads to quantitative adduct formation with the unique feature that the product is also crystalline, although the crystal structures of the adduct and the SO2 free complex are significantly different from each other and are both non-porous. Remarkably, the reverse reaction, i.e. the release of SO2 gas, modifies but does not destroy the crystalline ordering in the arylplatinum assemblies. These processes include repetitive expansion and reduction of the crystal lattice without any loss of crystallinity of the material. Variation of the ligand framework revealed that the presence of intermolecular interactions such as alpha- or beta -type networks is not an essential prerequisite for these crystalline transformations. Consequently, this class of supermolecules provides access to sensitive crystalline switches with 'on' and 'off' positions which are a direct response to the gaseous environment.