Syntheses, structures and photophysical properties of heteronuclear Zn–Ln coordination complexes

Four heteronuclear Zn–Ln coordination complexes, [Nd2Zn2(p-toluylate)10(phen)2] (1), [Ln2Zn2(p-toluylate)10(phen)2]·2(HAc)1/2 (Ln=Tb 2, Ho 3) and [PrZn2(p-toluylate)5(Ac)2(phen)2] (4) (phen=1, 10-phenanthroline), are synthesized by the hydrothermal method and their structures are measured by single-crystal X-ray diffraction. The IR and UV–vis–NIR absorption spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four complexes are determined at room temperature. In the NIR region (or in the visible region), the complexes show the characteristic emission bands of Ln3+ ions, which may be attributed to sensitization from the ligands (the ligand directly-coordinated to Ln3+ ions and d-block) to Ln3+ ions after forming the Zn–Ln complexes. It is reported for the first time in this paper that the Zn–Pr complex 4 can exhibit the broad emission band in the NIR region. In addition, the shift, split or broadness of the ff emission bands in the NIR region of complexes 1, 3 and 4 are discussed.