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

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.