Modeling, Structural, and Spectroscopic Studies of Lanthanide-Organic Frameworks

resumo

In this paper, we report the hydrothermal synthesis of three lanthanide-organic framework materials using as primary building blocks the metallic centers Eu3+, Tb3+, and Gd3+ and residues of mellitic acid: [Ln(2)(MELL)(H2O)(6)] (where Ln(3+) = Eu3+, Tb3+, and Gd-3; hereafter designated as (1), (2) and (3)). Structural characterization encompasses single-crystal X-ray diffraction studies, thermal analysis, and vibrational spectroscopy, plus detailed investigations on the experimental and predicted (using the Sparkle/AM1 model) photophysical luminescent properties. Crystallographic investigations showed that the compounds are all isostructural, crystallizing in the orthorhombic space group Pnnm and structurally identical to the lanthanum 3D material reported by the group of Williams. (2) is highly photoluminescent, as confirmed by the measured quantum yield and lifetime (37% and 0.74 ms, respectively). The intensity parameters (Omega(2), Omega(4), and Omega(6)) of (1) were first calculated using the Sparkle/AM1 structures and then employed in the calculation of the rates of energy transfer (W-ET) and back-transfer (W-BT). Intensity Parameters were used to predict the radiative decay rate. The calculated quantum yield derived from the Sparkle/AM1 structures was approximately 16%, and the experimental value was 8%. We attribute the registered differences to the fact that the theoretical model does not consider the vibronic coupling with O-H oscillators from coordinated water molecules. These results clearly attest for the efficacy of the theoretical models employed in all calculations and open a new window of interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

palavras-chave

2D COORDINATION POLYMERS; LIGAND-FIELD PARAMETERS; EMISSION QUANTUM YIELD; RARE-EARTH IONS; SPARKLE MODEL; INTENSITY PARAMETERS; BENZENEHEXACARBOXYLIC ACID; EUROPIUM(III) COMPLEXES; HYDROTHERMAL SYNTHESIS; CRYSTAL-STRUCTURES

categoria

Chemistry

autores

Rodrigues, MO; Paz, FAA; Freire, RO; de Sa, GF; Galembeck, A; Montenegro, MCBSM; Araujo, AN; Alves, S

nossos autores

agradecimentos

The authors acknowledge the financial support from CAPES and CNPq (Brazilian agencies) through the PADCT, IMMC (Instituto do Milenio de Materiais Complexos), and from RENAMI (Rede de Nanotecnologia Molecular e de Interfaces, Brazil). We also wish to thank CENAPAD (Centro Nacional de Proccssamento de Alto Desempenho) at Campinas, Brazil, for providing access to their computational facilities and Fundacao para a Ciencia e a Tecnologia for financial support (PPCDT/QUI/58377/2004).

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