Two organic-inorganic hybrids based on polyoxometalates: synthesis, crystal structure, and characterization

Two new Keggin-and Wells-Dawson-type polyoxometalate-based organic-inorganic hybrid copper-organonitrogen complexes have been synthesized under hydrothermal conditions: [Cu-I(4,4'-bpy)](2)[H2SiW12O40]center dot 2H(2)O (4,4'-bpy 4,4'-bipyridine) (1) and {[Cu-I(4,4'-bpy](3)[Cu-II(en)(2)](2)[(As2W3W15O62)-W-V-O-VI]}(2) [Cu-3(I)(4,4'-bpy)(3)(H2O)(2)](H3O)center dot 4H(2)O (2) (en = ethylenediamine), and characterized by elemental analysis, IR spectra, TGA, XRD, and single crystal X-ray diffraction. In 1, [Cu(4,4'-bpy)](+) cations form polymeric chains [Cu(4,4'-bpy)](n)(n+) and a weak Cu-O linkage makes the anions situate between two chains, forming an infinite 1-D ladder-chain structure. Such 1-D ladder-chains are further interconnected via hydrogen bonding into a 3-D supramolecular framework. Compound 2 with covalently bonded 3-D structure consists of saturated Wells-Dawson tungstoarsenate polyoxoanions and copper complexes with two types (rigid and flexible) of ligands. The polyoxoanion has the highest connectivity for Wells-Dawson tungstoarsenate polyoxoanion coordination polymers to date. XPS spectra indicate that three W atoms in the Dawson unit were reduced and that there coexist Cu-I and Cu-II in 2.