“…The lanthanide cations (Ln 3+ ) as hard Lewis acids exhibit a strong binding affinity for O -donor ligands such as β-diketone compounds (HL) [ 43 , 44 , 45 , 46 , 47 , 48 , 49 ]. Typically electrically neutral tris complexes, Ln(L) 3 are most likely to be formed [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ], but in some cases, the anionic tetrakis complexes, (Cat + )[Ln(L) 4 ] − are also formed [ 49 , 56 , 57 , 58 , 59 ]. The two categories of these compounds exhibit good luminescent properties [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ].…”