Odd-even effect on luminescence properties of europium aliphatic dicarboxylate complexes

Abstract

The odd–even effect in luminescent [Eu2(L)3(H2O)x]·y(H2O) complexes with aliphatic dicarboxylate ligands (L: OXA, MAL, SUC, GLU, ADP, PIM, SUB, AZL, SEB, UND, and DOD, where x=2–6 and y=0–4), prepared by the precipitation method, was observed for the first time in lanthanide compounds. The final dehydration temperatures of the Eu3+ complexes show a zigzag pattern as a function of the carbon chain length of the dicarboxylate ligands, leading to the so-called odd-even effect. The FTIR data confirm the ligand–metal coordination via the mixed mode of bridge–chelate coordination, except for the Eu3+-oxalate complex. XRD results indicate that the highly crystalline materials belong to the monoclinic system. The odd– even effect on the 4 f–4 f luminescence intensity parameters (Ω2 and Ω4) is explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom model. In this method, the long-range polarizabilities (a*) were simulated by a ghost atom located at the middle of each ligand chain. The values of a* were estimated using the localized molecular orbital approach. The emission intrinsic quantum yield (QLn Ln) of the Eu3+ complexes also presented an the odd-even effect, successfully explained in terms of the zigzag behavior shown by the Ω2 and Ω4 intensity parameters. Luminescence quenching due to water molecules in the first coordination sphere is also discussed and rationalized.