Syntheses, structures and near-infrared luminescent properties of a series of Ln(III) coordination polymers

► Four polymers have been synthesized by hydrothermal methods. ► Polymers 1–4 possess 1D or 2D infinite structures. ► Polymers 1–4 show characteristic emission bands of Ln(III) ions in the NIR region. ► Their NIR emissions present shift and split relative to theoretical bands of Ln(III). ► Their NIR emissions and UV-Vis-NIR absorption spectra can evidence each other. Using aromatic carboxylic acids as main ligands, four Ln(III) coordination polymers, [Er(CH3C6H4COO)2(Ac)(H2O)]n (1), [Yb(β-C10H7COO)2(Ac)(H2O)]n (2), [Nd(C9H7O2)3]n (3) and [Ho(C9H7O2)3]n (4) (CH3C6H4COO=p-toluylate, Ac=acetate, β-C10H7COO=β-naphthoyloxy, C9H7O2=cinnamate), were synthesized by hydrothermal method and their structures were studied by single-crystal X-ray diffraction. Polymers 1 and 2 possess 2D layer structures, and polymers 3 and 4 possess 1D chain structures. At room temperature in the solid state, the IR, UV–Vis–NIR spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four polymers were determined. In the NIR region, polymers 1–4 show characteristic emission bands of the corresponding Ln(III) ions which exhibit shift, splitting or broadness in comparison with their theoretical emission bands. This can be confirmed by their UV–Vis–NIR spectra and discussed emphatically.