Systematic Study of the Luminescent Europium-Based Nonanuclear Clusters with Modified 2‑Hydroxybenzophenone Ligands

The reaction of 2-hydroxybenzophenone derivatives with europium ions has afforded a new family of luminescent nonanuclear Eu­(III) clusters. Crystal structure analysis of the clusters reveals that the metal core comprises two vertex-sharing square pyramidal units. Most of these complexes show emissions typical of Eu3+ ion under visible light excitation (400–420 nm) at room temperature. Photophysical characterization and DFT study reveal a correlation between luminescent efficiencies of Eu­(III) complexes and the electronic features of the ligands, which can be tuned by the nature of substituents in the 4-position of the ligands. The ligands with a fluorine substituent possess more suitable triplet energy levels, resulting in more intensive luminescence.