Photophysical Processes in ‘Supramolecular Balls’ Formed by Lanthanide Chloride with 2,2′‐Bipyridine

The europium complex EuCl₂(bpy)₂(H₂O)₂]Cl?1.25 C₂H₆O?0.37 H₂O, where bpy is 2,2′‐bipyridine, was synthesized and investigated with the aim to relate its molecular geometry and crystal packing to the efficiency of energy‐transfer processes. The presence of H‐bonds between noncoordinated Cl^? ions and coordinated H₂O molecules leads to the formation of discrete trimers assembled by a number of C? H???Cl and stacking interactions into ‘supramolecular balls’ which contain Cl^? ions and solvate molecules (H₂O and EtOH). The additional stabilization of the complex is due to intramolecular N???C interactions between two bpy ligands that causes some shortening of the Eu? N bonds. Deciphering the luminescence properties of the Eu complex was performed under consideration of both the composition of the inner coordination sphere and the peculiarities of the crystal packing. The influence of the latter and the bpy orientation on the energy of the ligand→Eu charge‐transfer state (LMCT) was established, and an additional excited state induced by the π‐stacking interaction (SICT) was identified.