Synthesis, structure and XPS of a novel two-dimensional CuII–EuIII heterometallic–organic framework

Hydrothermal reaction of Eu2O3, CuI, 2, 2′-bipyridine-5, 5′-dicarboxylic acid and 2, 2′-bipyridine in the presence of ethanol and water affords a new 4f–3d heterometallic coordination polymer {[EuCu(bpdc)2·(H2O)4 I)]·2H2O}n (1), (H2bpdc = 2, 2′-bipyridine-5, 5′-dicarboxylic acid). Compound 1 was structurally characterized by elemental analysis, FT-IR spectroscopy, single-crystal X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and luminescence measurement. Single-crystal X-ray diffraction analysis reveals that the heterometallic polymer is interconnected by Eu3+ through carboxylic groups to produce a linear 1D structure along a direction, then through Cu2+ chelating double nitrogen atoms of bpdc2− ligand along b direction to form a 2D (two-dimensional) CuII–EuIII heterometallic–organic framework. X-ray photoelectron spectroscopies (XPS) confirm that chemical valences of Eu and Cu are + 3 and + 2 respectively. The fluorescent intensity change between H2bpdc ligand and compound 1 reveals a radical static quenching effect from CuII ions.

Graphical AbstractSingle-crystal X-ray diffraction analysis reveals that the heterometallic polymer is interconnected by Eu3+ through carboxylic groups to produce a linear 1D structure along a direction, then through Cu2+ chelating double nitrogen atoms of bpdc2− ligand along b direction to form a 2D CuII–EuIII heterometallic–organic framework. X-ray photoelectron spectroscopies (XPS) confirm that chemical valences of Eu and Cu ions are + 3 and + 2 respectively.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► The structure of title compound is a novel two-dimensional CuII–EuIII heterometallic–organic framework. ► There is no EuIII–CuII heterometallic organic framework containing iodine ion which has been reported before. ► The oxidation state of Cu before and after reaction is + 1 and + 2 respectively indicating a redox reaction happened during this process. ► XPS (X-ray photoelectron spectroscopy) investigation of crystallizing samples was carried out to elucidate the electronic states for the title compound.