Influence of different site symmetries of Eu3+ centers on the luminescence properties of Anderson-based compounds

Two compounds, [Eu(H2O)7][Al(OH)6Mo6O18] · 4H2O (1) and {(C2H5NO2)2[Eu(H2O)5]}[Al(OH)6Mo6O18] · 10H2O (2), have been synthesized by conventional solution method and determined by single-crystal X-ray diffraction. Compound 1 shows a 1D chain structure built up of alternating Anderson-type polyanions [Al(OH)6Mo6O18]3− and hydrated rare-earth ions Eu3+. Compound 2 displays a 3D supramolecular network structure containing 1D sandglass-like channels along c axis, which were occupied by repetitive array of (H2O)8 clusters. Extensive hydrogen bonds play an important role in the formation of the 3D structures of 1 and 2. Luminescence measurements reveal that 1 and 2 exhibit intense red and orange fluorescent emission at room temperature, respectively. Origin of the distinct emission can be assigned to the different site symmetries of Eu3+ centers in the two compounds. These results are consistent with the crystal structures of the two compounds.