Two sandwich-type compounds from Keggin polyoxometalate, d10 metals and the product of in situ catalyzed decarboxylation of pyrazine-2,3-dicarboxylic acid

Two supramolecular Keggin polyoxometalate compounds with sandwich-type structure, [Cu4(pz)6][SiW12O40]∙2H2O (1) and [Ag2(pz)2][Ag2(pz)(H2O)2(SiW12O40)] (2)(pz = pyrazine), have been synthesized by in situ generation of pyrazine ligand from pyrazine-2,3-dicarboxylic acid (H2pzdc) under hydrothermal conditions and characterized by IR spectroscopy and TGA. In 1 the combination of CuI ions and pz creates a honeycomb 2-D layer, these layers sandwich [SiW12O40]4 − anions, constructing a multi-sandwich supramolecular compound. In 2 a 2-D layer is formed from [Ag2(pyrazine)2∙(H2O)2]n2n + and [SiW12O40]n4n− and the layers sandwich 1-D [Ag2-(pyrazine)2]n2n + linear chains to construct another multi-sandwich supramolecular compound. The pyrazine molecules in 1 and 2 are the product of decarboxylation reaction of pyrazine-2,3-dicarboxylic acid catalyzed by Keggin polyoxometalates. Two compounds show the similar intense fluorescent emissions in the solid state.