Syntheses, structures, photoluminescence and semiconductor properties of two novel mercury-lanthanide complexes with a three-dimensional open framework

Two novel mercury-lanthanide complexes [Hg3Cl6(u-IA)3Ln(H2O)2]n (IA = isonicotinic acid anion; Ln = Pr (1) and Sm (2)) have been synthesized under hydrothermal conditions and structurally determined by single crystal X-ray diffraction. Complexes 1 and 2 are isostructure and feature a three-dimensional (3-D) open framework with two types of one-dimensional (1-D) chains. Based on the condensed 3-D open framework, there is a large void space being 1010.3 A3 and 1018.1 A3 which occupy 27.2% and 27.4% of the unit-cell volume for complexes 1 and 2, respectively. Solid-state UV/Vis diffuse reflectance spectroscopy reveals that there is a wide optical band gap of 3.51 eV and 3.54 eV for complexes 1 and 2, respectively. Photoluminescence measurements using solid-state samples discover that both complexes display red light emission. The emission bands can be ascribed to the characteristic emission of the 4f electron intrashell transitions of the Ln3+ ions, i.e. 1D2 → 3H4 and 3P0 → 3F3 transitions for complex 1, as well as 4G5/2 → 6H5/2, 4G5/2 → 6H7/2 and 4G5/2 → 6H9/2 transitions for complex 2.