This would also explain why the λmax decreases down the groupa more ionic bond would lower the energy of the transition, hence a lower λmax. The two divalent lanthanide complexes (1-Eu, and 1-Yb) also showed the same transition at ca. 280 nm, and the LMCT bands in the visible region. However, no f→f or f→d transitions could be distinguished except in the case of 1-Yb. In this instance, a more concentrated sample (1.0 mM in toluene) revealed a weak (ϵ = 110 M -1 cm -1 ) absorption band at 600 nm which could be assigned as an f→d transition at the metal. UV-visible absorption spectra were also recorded for 2-Y, 2-La, 2-Pr and 2-Sm (Figure ). In all cases, the spectra were essentially featureless, with The electronic structures of compounds 1-Eu and 2-Sm were studied by means of complete active space self-consistent field spin-orbit-based (CASSCF-SO) calculations, as implemented in OpenMolcas, where the active spaces are defined by considering seven and five 4f electrons in seven orbitals, respectively (see SI for computational details).