New EuIII pyromellitic metal-organic framework of intense red orange luminescence and high thermal stability for marking in gunshot residues

Full text: The preparation, general characterization, and experimental and theoretical photoluminescence investigations of a new europiumIII metal–organic framework [EuHbtec]n 1 supported by 1,2,4,5-benzenetetracarboxylic acid, H4btec (pyromellitic acid), are discussed in this work. The crystal structure was obtained from X-ray powder diffraction (XRPD), with the data collected at the MCX beamline of ELETTRA synchrotron. In this structure, the monoprotonated Hbtec3– ligands act in three different coordination modes to EuIII centers: μ2-η1:η2 chelating/bridging, η2 chelating, and η1 monodentate modes. The three-dimensional (3D) network is constructed by secondary building units (SBU) chains, connected through carboxylate groups of the Hbtec3– ligands. Using the Sparkle/RM1 model, the ground-state geometry of [EuHbtec]n 1 was calculated in the solid phase and then used to obtain the several investigative spectroscopic parameters. This study demonstrates that intense luminescence occurs through ligand sensitization. The exceptional thermal stability is proven by thermogravimetric analysis, with the network collapsing at 489 °C, the largest among the congener compounds. Thus, by combining its intense emission and high thermal stability, [EuHbtec]n 1 was utilized for marking of gunshot residues (GSRs), with its preliminary tests showing very promising results for applications in forensic contexts and public safety. (author)