Synthesis, Crystal Structures, and Photophysical Properties of Homodinuclear Lanthanide Xanthene-9-carboxylates

Three new homodinuclear lanthanide(III) complexes of xanthene-9-carboxylic acid, [Ln2(XA)6(DMSO)2(H2O)2](Ln = Eu (1), Tb (2) and Gd (3); HXA = xanthene-9-carboxylic acid; DMSO = dimethylsulfoxide), have been synthesized, of which 1 and 2 were structurally characterized by single-crystal X-ray diffraction. These compounds crystallize in the monoclinic space group P21/n with a =17.849(4) A, b = 9.6537(19) A, c = 23.127(5) A, beta = 109.06(3) degrees , and V = 3766.5(13) A3 for 1 and a =17.809(4) A, b = 9.6548(19) A, c = 23.075(5) A, beta = 108.97(3) degrees , and V = 3752.1(13) A3 for 2. The crystal structures of 1 and 2 consist of homodinuclear species that are bridged by two oxygen atoms from two carboxylate ligands. The two lanthanide ions are related by a center of inversion. Each lanthanide ion is coordinated by eight oxygen atoms in an overall distorted square-prismatic geometry. Six of the oxygen atoms are furnished by the carboxylate moieties, and the remaining two oxygen atoms are provided by water and DMSO molecules. The photophysical properties of these complexes in the solid state at room temperature have been investigated. The quantum yields were found to be 0.06 +/- 0.01 and 7.30 +/- 0.73% for 1 and 2, respectively.