Sandwich-type polyoxometalates of the later lanthanide ions. Syntheses and structures of [(AXW9O34)2(H2OM)3CO3]11- (X = P5+, As5+) (M = Tb3+, Dy3+, Er3+)

Six new complexes were synthesized in a 0.1M aqueous carbonate solution and characterized by elemental analyses, thermogravimetric analyses, infrared spectroscopy and X-ray single crystal structure analyses. The single-crystal structure analysis was on K11[(A-AsW9O34)2(H2ODy)3- CO3]·22H2O. The results revealed that the complexes are isomorphic and their structures consist of wo lacunary [A-XW9O34]9 Keggin moieties linked by a (OMOH2)3C belt, forming an A-type sandwich structure. The CO2þ 3 is tridentate and fixes three M3+ centers together by its oxygens. Each M3+ cation is mono-capped trigonal-prismatic coordination, achieved by two terminal oxygens of an edge-shared pair of WO6 octahedra to each [A-XW9O34]9 and two oxygens from the belt, and the cap by one water