The influence of the odd-even effect of aliphatic dicarboxylate ligands on the photoluminescent properties of europium complexes

Abstract

Eleven [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) were synthesized and characterized by elemental and thermal analysis, FTIR spectroscopy and powder X-ray diffraction. The obtained data confirms the ligand to metal ratio, the hydration degree, the coordination mode and that the complexes are crystalline. The oddeven effect was observed for the final dehydration temperature of the Eu3+ complexes (Fig. 1). Moreover, the effect was also observed in the experimental and theoretical photoluminescent properties such as the intensity parameters, Ω2 and Ω4 (Fig. 2) and the emission intrinsic quantum yield, QLnLn (Fig. 3) of the Eu3+ complexes. The odd-even effect on the Ω2 and Ω4 values could be explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom (GA) model, in which the long-range polarizabilities (α*) were determined by simulating the presence of a ghost atom in the middle of each ligand carbon chain and the localized molecular orbital approach. The GA approach is an extension of the Bond Overlap Model (BOM) [1].