Synthesis, structures and near-infrared luminescence properties of Ho3+ and Yb3+ coordination complexes Original Research Article

Four Ln3+ coordination complexes with the formulas [Ln(p-toluylate)2(Ac)(H2O)]n (Ln=Ho 1, Yb 2) and {[Ln2(OOCCH2CH2COO)3(H2O)4]·6H2O}n (Ln=Ho 3, Yb 4) were synthesized hydrothermally. Their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isomorphic and form infinite 2D network structures comprising p-toluylate and acetate (Ac–) moieties. Complexes 3 and 4 are also isomorphic and possess infinite 2D structures in which succinate acts as bridging ligands that are connected to a 3D hydrogen bonding network by O–H…O hydrogen bonds. Solid-state IR and UV-Vis-NIR spectra, excitation and emission spectra were determined for the four complexes at room temperature. Complexes 1 and 2 exhibit characteristic NIR emission bands of Ln3+ ions but these are shifted and split relative to the theoretical positions. This is also evident for their UV-Vis-NIR spectra. The influence of ligands on enhancing the NIR luminescence of Ln3+ ions in complexes is discussed.