abstract
The odd-even effect in luminescent [Eu-2(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 (omega(2) and omega(4)) is explained by using an extension of the dynamic coupling mechanism, herein named the ghost-atom model. In this method, the long-range polarizabilities (alpha*) were simulated by a ghost atom located at the middle of each ligand chain. The values of alpha* were estimated using the localized molecular orbital approach. The emission intrinsic quantum yield (QLnLn) of the Eu3+ complexes also presented an the odd-even effect, successfully explained in terms of the zigzag behavior shown by the omega(2) and omega(4) intensity parameters. Luminescence quenching due to water molecules in the first coordination sphere is also discussed and rationalized.
keywords
METAL-ORGANIC FRAMEWORKS; INTRAMOLECULAR ENERGY-TRANSFER; SELF-ASSEMBLED MONOLAYERS; SPECTROSCOPIC PROPERTIES; INTENSITY PARAMETERS; 4F-4F TRANSITIONS; CHEMICAL-BOND; CARBOXYLATES; ALTERNATION; COVALENCY
subject category
Chemistry; Physics
authors
Assuncao, IP; Neto, ANC; Moura, RT; Pedroso, CCS; Silva, IGN; Felinto, MCFC; Teotonio, EES; Malta, OL; Brito, HF
our authors
Albano Neto Carneiro Neto
Junior ResearcherProjects
CICECO - Aveiro Institute of Materials (UID/CTM/50011/2019)
SusPhotoSolutions - Soluções Fotovoltaicas Sustentáveis (SUSPHOTOSOLUTIONS)
acknowledgements
The authors thank the funding agencies for financial support: Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP). This work was partially developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT (Portuguese agency) Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. A.N.C.N. also thanks SusPhotoSolutions - Solucoes Fotovoltaicas Sustentaveis, CENTRO-01-0145-FEDER-000005.