Crystal Structure and Spectroscopic Study of Novel Two- and Three-Dimensional Photoluminescent Eu(III)−Adipate Compounds

Two new photoluminescent compounds with the formulas of [Eu2(adipate)3(H2O)]·H2O (1) and [Eu2(adipate)3(4H2O)] (2) were synthesized by using Eu(III) chloride and adipic acid under hydrothermal reaction conditions in aqueous solution. Compound 1, a 3-D layered framework, possesses infinite Eu−O−Eu polyhedral chains and self-assembled adipate ligands between Eu−O layers. Compound 2 has dimeric Eu2O16 units interconnected by adipate ligand, resulting in 2-D open frameworks with a cavity among the ligands. Crystal data 1: monoclinic space group C2/c, with a = 14.2486(12) Å, b = 8.2733(7) Å, c = 39.298(2) Å, β = 99.530(6) °, and Z = 8. 2: monoclinic space group P21/c, with a = 11.661(4) Å, b = 14.011(3) Å, c = 9.013(4) Å, β = 110.87(3) °, and Z = 2. The ligand conformations of two Eu(III)−adipate (1 and 2) compounds present anti/anti/anti, gauche/anti/gauche, and intermediate forms. Both compounds 1 and 2 showed strong red luminescence upon excitation, and their luminescence decay involves the multiphonon relaxation mechanism.