Photophysical Studies of Europium Coordination Polymers Based on a Tetracarboxylate Ligand

Reaction of europium sulfate octahydrate with p-terphenyl-3,3 '',5,5 ''-tetracarboxylic acid (H(4)ptptc) in a mixed solvent system has afforded three new coordination polymers formulated as {[Eu(ptptc)(0.75)(H2O)(2)]center dot 0.5DMF center dot 1.5H(2)O}(n) (1), {[Me2H2N](2) [Eu-2(ptptc)(2)(H2O)(DMF)]center dot 1.5DMF center dot 7H(2)O}(n) (2), and {[Eu(Hptptc)(H2O)(4)]center dot 0.5DMF center dot H2O}(n) (3). Complex 1 exhibits a three-dimensional (3D) metal-organic framework based on {Eu-2(mu(2)-COO)(2)(COO)(4)}(n) chains, complex 2 shows a 3D metal-organic framework constructed by [Eu-2(mu(2)-COO)(2)(COO)(6)](2-) dimetallic subunits, and complex 3 features a 2D layer architecture assembling to 3D framework through pi center dot center dot center dot pi interactions. All complexes exhibit the characteristic red luminescence of Eu(III) ion. The triplet state of ligand H(4)ptptc matches well with the emission level of Eu(III) ion, which allows the preparation of new optical materials with enhanced luminescence properties. The luminescence properties of these complexes are further studied in terms of their emission quantum yields, emission lifetimes, and the radiative/nonradiative rates.