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

Four Ln(3+) coordination complexes with the formulas [Ln(p-toluylate)(2)(Ac)(H2O)](n) (Ln=Ho 1, Yb 2) and {[Ln(2)(OOCCH2CH2COO)(3)(H2O)(4)]center dot 6H(2)O}(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 center dot center dot center dot 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 Ln(3+) 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 Ln(3+) ions in complexes is discussed. (C) 2013 Elsevier Ltd. All rights reserved.