Synthesis, structural characterization, and luminescence properties of zinc(II) coordination polymers containing bis(4-pyridyl)benzylamine

Two new zinc(II) coordination polymers [Zn(bpba)₂(NO₃)₂]_n (1) and [Zn(bpba)(SO₄)]_n•2nH₂O•nDMF (2) were successfully synthesized by reacting zinc(II) ions with bis(4-pyridyl)benzylamine (bpba) containing different counter anions (NO₃⁻ and SO₄²⁻). The resulting polymers were fully characterized using various experimental techniques: single-crystal X-ray diffraction analysis, elemental analysis, infrared spectra, ultraviolet/visible spectra, and thermogravimetric analysis. Single-crystal X-ray analyses revealed that the zinc(II) ions in 1 and 2 are tetra-coordinated and adopt a distorted tetrahedral geometry. Polymer 1 exhibits a one-dimensional helical chain structure, which extends into two-dimensional supramolecular networks through hydrogen bonding and C-H•••π interactions. Polymer 2 adopts a three-dimensional network structure resulting from the coordination of zinc(II) and sulfate ions as well as bpba ligands. An investigation of the solid-state photoluminescence properties of the polymers at room temperature revealed that their emissions were redshifted compared with those of the free ligand, which is attributed to metal-perturbed intra-ligand charge transfer.