CRYSTAL-STRUCTURE AND LUMINESCENCE SITE OF NA9[EUW10O36].32H2O

Na9[EuW10O36].32H2O, obtained from aqueous solutions, crystallizes in space group Cc with a=11.484(5), b=23.020(7), c=23.581(6) angstrom, beta=91.71(3)-degrees, V=6231(3) angstrom , M(r)=3349.4, D(x)=3.57 Mg m-3, and Z = 4. A full-matrix least-squares refinement finally yields R=0.070 and R(w)=0.086 for 6473 independent reflections. The local symmetry around Eu3+ for the [EuW10O36]9- anion is approximately square antiprismatic. Photoexcitation into the oxygen-to-tungsten charge transfer bands of a solid sample leads to red emission due to f-f transitions within Eu3+, as a result of an intramolecular energy transfer from the W5O18 group to the Eu atom. The spectral transitions of photoluminescence recorded at 4.2 K can be interpreted based on the assumption of a C4v point group for Eu3+, which is consistent with the co-ordination geometry for the Eu atom.