Honeycomb-like layers constructed by hydrogen bonds. Synthesis, structure, and property of two new supramolecular compounds based on polyoxotungstate

Two new compounds based on polyoxotungstate [Co-2(PCA)(4)(H2O)(6)][SiW12O40]center dot 8H(2)O (1), [Cd-2(PCA)(4)(H2O)(6)][SiW12O40]center dot 8H(2)O (2) (PCA = pyridine-4-carboxylic acid) are prepared and characterized by single crystal X-ray diffraction, elemental analysis, IR spectroscopy, and thermal analysis. The results of the single crystal X-ray diffraction analysis reveal that 1 and 2 are isomorphic and two water molecules in the compounds act as the bridging groups of two cobalt or cadmium atoms, forming dinuclear coordination cations. The ligand PCA adopts a monodentate coordination mode and its uncoordinated carboxyl oxygen atom and the protonized nitrogen atom form hydrogen bonds with other ligands, by which the cations are linked into a supramolecular 2D network with hexagonal grids. The polyoxotungstate anions are arranged above and below the cationic grids. A strong emission peak at 420 nm of 2 is attributed to a ligand-metal transition.