Synthesis, crystal structures, and photophysical properties of homodinuclear lanthanide xanthene-9-carboxylates

Three new homodinuclear lanthanide(III) complexes of xanthene-9-carboxylic acid, [Ln 2 (XA) 6 (DMSO) 2 (H 2 O) 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 P2 1 /n with a =17.849(4) Å, b = 9.6537(19) Å, c = 23.127(5) Å, β= 109.06(3)°, and V = 3766.5(13) Å 3 for 1 and a =17.809(4) Å, b = 9.6548(19) Å, c = 23.075(5) Å, β = 108.97(3)°, and V = 3752.1(13) Å 3 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 pr