Seven-coordinate, pentagonal-bipyramidal (PBP) complexes [Ln(bbpen)Cl] and [Ln(bbppn)Cl], in which Ln = Tb 3+ (products I and II), Eu 3+ (III and IV), and Gd 3+ (V and VI), bbpen 2− = N,N'-bis(2-oxidobenzyl)-N,N'bis(pyridin-2-ylmethyl)ethylenediamine, and bbppn propanediamine, were synthesized and characterized by single-crystal X-ray diffraction analysis, alternating current magnetic susceptibility measurements, and photoluminescence (steady-state and time-resolved) spectroscopy. Under a

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... magnetic field of 0.1 T, the Tb 3+ complexes I and II revealed single-ion magnet (SIM) behavior. Also, upon excitation at 320 nm at 300 K, I and II presented very high absolute emission quantum yields (0.90 ± 0.09 and 0.92 ± 0.09 respectively), while the corresponding Eu 3+ complexes III and IV showed no photoluminescence. Detailed theoretical calculations on the intramolecular energy transfer (IET) rates for the Tb 3+ products indicated that both excited singlet and triplet ligand states contribute efficiently to the overall emission performance. The