A series of 1D-to-3D coordination polymers from an unsymmetrical tetracarboxylic acid and various N-donor ligands: Syntheses, structures and photoluminescence properties

Five new coordination polymers (CPs) based on unsymmetrical tetracarboxylic acid and varied auxiliary N-donor ligands, [Ln(α-Hbptc)(H₂O)₄]·H₂O (Ln = Eu, 1; Tb, 2), [Cu₂(α-bptc)(bipy)(H₂O)₄]·H₂O (3), [Cd₂(α-bptc)(phen)₂(H₂O)₂]·H₂O (4), [Cd₂(α-bptc)(bpee)_0.5(H₂O)₄]·3H₂O (5), [α-H₄bptc = 2,3,3′,4′-biphenyl tetracarboxylic acid, bipy = 4,4′-bipyridine, bpee = 1,2-bis(4-pyridyl)ethylene, phen = 1,10-phenanthroline] have been hydrothermally synthesized. Compounds 1 and 2 are isomorphous and show a 2D 6³-hcb network in the absence of any N-donor ligand. Compound 3 is a 1D “loop” chain structure with alternating the 14- and 40-membered metallacycles in the presence of bipy. Compound 4 features 1D wavy chain by using phen instead of bipy. The coordination structures of 1–4 are further extended into 3D supramolecular frameworks through different hydrogen bonds. Compound 5 possesses a 3D pillar-layer framework built via the 2D layers with opposite handedness and bpee. The solid state photoluminescence properties of compounds 1, 2, 4, and 5 were investigated. Compounds 1 and 2 exhibit characteristic Eu(III) and Tb(III) emissions in the red and green light regions, respectively. Compounds 4 and 5 display strong fluorescent emissions at 404 and 380 nm in solid state at room temperature, respectively.