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 bbppnpropanediamine, 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 static 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

Two discrete mononuclear complexes, [Tb(bbpen)(NO 3 )] (I) and [Tb(bbppn)(NO 3 )] (II), for which H 2 bbpen = N,N′-bis(2-hydroxybenzyl)-N,N′-bis(pyridin-2-ylmethyl)ethylenediamine and H 2 bbppn = N,N′-bis(2-hydroxylbenzyl)-N,N'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates II from I and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of H 2 bbppn is described here for the first time, while that of complex II has been redetermined in the monoclinic C2 space group in light of new diffraction data. In II, selective crystallization leads to spontaneous resolution of enantiomeric molecules in different crystals. Absolute emission quantum yields (ϕ) and luminescence excited-state lifetimes (at room temperature and 11 K) were measured for both complexes. Despite their similar molecular structures, I and II exhibit remarkably different ϕ values of 21 ± 2% and 67 ± 7%, respectively, under UV excitation at room temperature. Results of quantum-mechanical (DFT and TD-DFT) calculations and experimental PL measurements also performed for H 2 bbpen and H 2 bbppn confirmed that both ligands are suitable to work as "antennas" for Tb III . Considering the 5 D 4 lifetime profiles and the significantly higher absolute quantum yield of II, it appears that thermally active nonradiative pathways present in I are minimized in II due to differences in the conformation of the ethylenediamine bridge.