Synthesis, structure, and luminescence property of a series of Ag–Ln coordination polymers with the N-heterocyclic carboxylato ligand

Abstract Six Ln–Ag coordination polymers {[LnAg 2 (IN) 4 (H 2 O) 5 ]·NO 3 ·2H 2 O} n (Ln=Ho (1) and Tb (2), HIN=isonicotinic acid), {[PrAg 2 (IN) 4 (H 2 O) 2 ]·NO 3 ·H 2 O} n (3), [LnAg(pdc) 2 ] n (Ln=Eu(4) and Pr (5), H 2 pdc=3,4-pyridine-dicarboxylic acid) and [NdAg(bidc) 2 (H 2 O) 4 ] n (6) (H 2 bidc=benzimidazole-5,6-dicarboxylic acid) have been hydrothermally synthesized and characterized by single crystal X-ray diffraction, elemental analysis, IR, UV–vis-NIR absorption spectra, fluorescence spectra and thermogravimetric analysis. Structural analyses reveal that the six polymers exhibit 0D (polymer (1)), 1D (polymer (2)), 2D (polymers (3) and (5)) and 3D (polymers (4) and (6)) infinite structures, respectively. Polymers (1)–(6) exhibit the Ln(III) characteristic emission in the near-infrared (NIR) region or in the visible region. Especially, the NIR emission bands of polymers 1, 5 and 6 evidently present shift or splitting due to formation of the Ln–Ag coordination polymers. This can be attributed to the tune of inner levels in Ln–Ag system caused by the interact and influence between the 4d orbital of the Ag(I) ion and the 4f orbital of the Ln(III) ion, which can be confirmed by the UV–vis-NIR absorption spectra of the polymers. In addition, the distortion of coordination geometry as well as difference of the coordination number around the Ag(I) ion affect the structure framework.