Syntheses, structures and fluorescence of three novel 3D coordination polymers [Cd3(TMA)2(H-PRZ)(H2O)3(OH)] · H2O, Cd2Na2(TMA)2(H2O)4 and [Cd2Co(TMA)2(H2O)4] · 2H2O (TMA=trimesic acid, PRZ=piperazine)

The hydrothermal reactions of H₃TMA (or Na₃TMA) with metal acetate yield three novel coordination polymers [Cd₃(TMA) ₂(H-PRZ)(H₂O)₃(OH)]·H₂O (1), Cd₂Na₂(TMA)₂(H₂O)₄ (2) and [Cd₂Co(TMA)₂(H₂O)₄] ·2H₂O (3) (TMA=trimesic acid, PRZ=piperazine). The three Cd(II) centers in 1 are bridged by TMA ligands and a μ₃-O atom of coordinated hydroxide to generate a sandwich-liked tri-layer motif. These motifs with a Cd₃O core are further interlinked by hydrogen bond interactions to stack in a 3D coordination framework with a porous dimension of ca. 7.5×5.5 Å. Complex 2 is a three-dimensional polymer based on tetranuclear heterometallic clusters. The centrosymmetric tetranuclear heterometallic cluster contains a Cd₂Na₂ parallelogram cluster core. These clusters are connected through the coordination of carboxylate oxygen atoms of TMA ligands to form a 3D coordination framework. Complex 3 represents the first structural characterization of a trimesate complex containing two different transitional metals. Each TMA^3- ligand in the Cd₂Co(C₉H₃O₆) ₂(H₂O)₄ structure unit of 3 binds to other three structure units, resulting in a 3D coordination polymer. The three complexes exhibit strong fluorescent emission bands at 420 nm (λ_ex=314 nm) for complex 1, 424 nm (λ_ex=314 nm) for complex 2, and 419 nm (λ_ex=308 nm) for complex 3 in the solid state at room temperature. The preliminary magnetic property of complex 3 has been investigated.