HONEYCOMB-LIKE LAYERS CONSTRUCTED BY HYDROGEN BONDS. SYNTHESIS, STRUCTURE, AND PROPERTY OF TWO NEW SUPRAMOLECULAR COMPOUNDS BASED ON POLYOXOTUNGSTATE

摘要

Two new compounds based on polyoxotungstate [Co2(PCA)4(H2O)6][SiW_(12)O_(40)]·8H2O (I), [Cd2(PCA)4(H2O)6][SiW_(12)O_(40)]·8H2O (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 pro-tonized 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.