A novel tetranuclear Pb2+ compound based on ethylenediaminetetraacetate and azide mixed-ligands: Synthesis, structure and properties

A novel tetranuclear lead-edta compound [Pb4(edta)(H2O)2(N3)4]n (1) (H4edta = ethylenediaminetetraacetic acid) has been synthesized by the reaction of PbF2 with H4edta and NaN3 mixed-ligands under hydrothermal conditions, and was characterized by elemental analysis, thermal analysis, luminescence, powder X-ray diffraction and single-crystal X-ray diffraction. The results of X-ray crystallographic analysis reveal that compound 1 is the first 3D Pb(II)-edta coordination polymer with a high ratio of lead. Remarkably, the edta4− ligand uses all its 10 donor atoms (8O ​+ ​2 ​N) coordinated to Pb(II) ions and formed a 2D layer. The 2D layers are further linked to a complex 3D coordination polymer by the inorganic chain [Pb5(N3)10]n. Time-dependent density functional theory (TDDFT) calculations reveal that the mechanism of the fluorescence emission is dominantly resulted from the ligand-to-metal charge transfer (LMCT) for 1, which is in good agreement with its fluorescence spectra and crystal structure. Optical absorption spectra indicate that 1 has wide optical band-gaps and can be probably used as wide optical band-gap semiconductor material.