Role of Triplet States of Two Different Ligands in the Sensitized Emission of Ln^III (Eu^III, Tb^III) in d–f Hybrid Tetranuclear Heterometal (Zn^II₂Ln^III₂, Cd^II₂Ln^III₂) Complexes

Abstract

Abstract The crystal structures of synthesized d–f hybrid tetranuclear heterometal Zn II 2 Eu III 2 and Cd II 2 Eu III 2 complexes, involving a pair of carboxylate ligands in a rare μ 4 ‐η 2 :η 2 bridging mode, reveal that the metal centers are arranged alternately in a rhombic plane within 4 Å from each other. The Zn II 2 Eu III 2 and Zn II 2 Tb III 2 complexes exhibit efficient sensitization compared with the Cd II ‐analogues. Under proper excitation, the lowest ππ* triplet states of both ligands N , N′ ‐dimethyl‐ N , N′ ‐bis(2‐hydroxy‐3,5‐dimethylbenzyl)ethylenediamine (H 2 L) and hexafluoroacetylacetone (Hhfac) act as donors, implying synergistic energy transfer (ET). The ratio of the sensitized efficiency for the heterocomplexes in different media at 298 K and 77 K, based on the observed transients, reveal the role of Zn II and Cd II in the ET process. The ratio of the ET rate constants obtained from the time‐resolved phosphorescence of the complexes at 77 K and time‐dependent DFT calculations on homocomplexes support this contention.