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 (H4ptptc) in a mixed solvent system has afforded three
new coordination polymers formulated as {[Eu­(ptptc)0.75(H2O)2]·0.5DMF·1.5H2O}n (1), {[Me2H2N]2 [Eu2(ptptc)2(H2O)­(DMF)]·1.5DMF·7H2O}n (2), and {[Eu­(Hptptc)­(H2O)4]·0.5DMF·H2O}n (3). Complex 1 exhibits
a three-dimensional (3D) metal–organic framework based on {Eu2(μ2-COO)2(COO)4}n chains, complex 2 shows a 3D metal–organic
framework constructed by [Eu2(μ2-COO)2(COO)6]2– dimetallic subunits,
and complex 3 features a 2D layer architecture assembling
to 3D framework through π···π interactions.
All complexes exhibit the characteristic red luminescence of Eu­(III)
ion. The triplet state of ligand H4ptptc 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.