A Novel Uranyl Complex with Dimeric Lacunary Polyoxoanion: [(A-α-SiW9O33)2K{UO2(H2O)}2]11−.

A novel uranyl complex with dimeric lacunary polyoxoanion like open-mouthed clam, Na5[A-α-SiW9O33H3)2K{UO2(H2O)}2], was prepared and characterized by elemental analysis, infrared and ultraviolet-visible spectroscopy and single crystal X-ray diffraction. In the anion, two A-α-SiW9O3310- groups share two terminal oxygen atoms Od' derived from removal of three corner-shared W atoms from saturated α-Keggin anion, forming a dimeric anion with an open mouth in which potassium ion and uranyl ions are coordinated. Uranium atom adopts a pentagonal bipyramidal geometry. The coordinating anions are linked by sodium ions via coordination of terminal or bridging oxygen atoms, forming two-dimensional layer arrangement. Between the layers are the hydrogen bonds from which a supramolecular architecture is created. UV-VIS spectrum gives W-O and U-O charge transfer transitions at 230-265 and 432 nm, showing the change of geometry of the polyanion and weakening of the U-O bonds of the uranyl cation. [ABSTRACT FROM AUTHOR]