Europium and Terbium Coordination Polymers Assembled from Hexacarboxylate Ligands: Structures and Luminescent Properties

Six lanthanide coordination polymers of the formula [Ln(L-1)(0.5)(H2O)(2)]center dot 2H(2)O [where Ln(3+): Eu3+ (1), Tb3+ (2), and Gd3+(3)] and [Me2NH2][Ln(H2L2)(H2O)(4)]. 0.5DMF center dot xH(2)O [where Ln(3+): Eu3+ (4), Tb3+ (5), and Gd3+(6)], based on p-terphenyl-2,2 '',2''',5,5 '',5'''-hexacarboxylate acid (H6L1), and p-terphenyl-3,2''',3 '',5,5 '',5''',-hexacarboxylate acid (H6L2), have been solvothermally synthesized and structurally characterized. Complexes 1-3 are 3D frameworks exhibiting 6-connected pcu alpha-Po primitive cubic network with topology (4(12).6(3)), while complexes 4-6 show two-dimensional (2D) architectures showing simplified 3,4-connected binodal net and (4.6(2)) (4(2).6(2).8(2)) topology. Detailed photophysical behaviors have been explored on Eu3+, Tb3+, and Gd3+ complexes. The calculated triplet state energies of H6L1 and H6L2 lie above the emissive levels of Eu3+ or Tb3+ in an ideal range for sensitizing. Furthermore, it is demonstrated that the optimum energy gap between the triplet state of ligand H6L1 and the emissive level of Tb3+ ion makes the overall quantum yield of Tb3+ complex (2) larger than its corresponding Eu3+ complex (1). In addition, the coordinated water in the inner sphere has a significant negative influence on the overall quantum yield, especially for the Eu3+ complex (4) compared to the Tb3+ complex (5), due to the deactivation process caused by vibrational OH oscillators.