resumo
Phase-pure and highly crystalline [Ln(Hpmd)(H2O)] materials [where Ln(3)+ Eu-3+ (1), Gd-3+ (2) and Tb-3+ (3); H(4)pmd 1,4-phenylenebis(methylene) diphosphonic acid] were prepared by using three distinct approaches: (i) conventional hydrothermal synthesis (180 degrees C, 3 days); (ii) microwave-assisted heating (50 W irradiation power, 40 degrees C, 5 seconds; nano-sized aggregates with sizes ranging between 100 and 150 nm); and (iii) ultrasound-assisted synthesis which, for highly diluted reactive mixtures (Ln(3)+ : H4pmd : H2O of 1 : 1 : 7200), permitted the preparation of isolated nano-crystals at ambient temperature with 5 minutes of ultrasonic irradiation. Compounds were structurally characterized by powder X-ray diffraction (Rietveld refinement and variable-temperature studies), thermogravimetry, vibrational spectroscopy, elemental analysis and electron microscopy (SEM andEDS). The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K revealing that the Ln(3)+ cations act as isolated centers. A strategy to calculate the vibrational spectra of MOF structures and based on the known embedded-clusters approach is proposed and applied to [ Ln(Hpmd)(H2O)]. This allowed the identification, along with deuteration of the materials, of the vibrational modes of the confined water molecule in the structure. Compound 1 was tested in the methanolysis of styrene oxide at 55 degrees C: it is shown that microcrystalline 1 (1-m) does not possess significant catalytic activity; on the other hand, the nano-sized counterpart (1-n) exhibits relatively high catalytic activity and excellent selectivity to 2-methoxy-2-phenylethanol (100% yield within 48 h of reaction time). Photoluminescence studies both at ambient and low temperatures showed, on the one hand, that bulk materials are composed of a single lanthanide site and, on the other hand, that the organic linker is a suitable sensitizerof Tb-3+ (absolute quantum yield of ca. 14% for 3). It is further demonstrated that the coordinated water molecule has a pivotal role in the quenching of the photoluminescence of Eu-3+ in 1: deuteration of the material results in a ca. 3.4 times improvement of the decay time (e. g., at 300 K the lifetime improves from 0.58 +/- 0.01 ms to 1.98 +/-0.01 ms).
palavras-chave
METAL-ORGANIC FRAMEWORK; CAMBRIDGE STRUCTURAL DATABASE; CRYSTAL-STRUCTURE DETERMINATION; DENSITY-FUNCTIONAL THEORY; POWDER DIFFRACTION DATA; COORDINATION POLYMERS; ADSORPTION PROPERTIES; HYDROGEN STORAGE; HYBRID MATERIALS; WATER-MOLECULES
categoria
Materials Science; Physics
autores
Vilela, SMF; Ananias, D; Fernandes, JA; Silva, P; Gomes, AC; Silva, NJO; Rodrigues, MO; Tome, JPC; Valente, AA; Ribeiro-Claro, P; Carlos, LD; Rocha, J; Paz, FAA
nossos autores
Ana Catarina Costa Gomes Alves
Investigador Auxiliar
Anabela Tavares Aguiar Valente
Investigador Principal
Duarte Ananias
Investigador Auxiliar
Filipe Alexandre Almeida Paz
Investigador Principal
João Rocha
Prof. Catedrático
José Alberto Pires Fernandes
Bolseiro de pós-Doutoramento
Luís Carlos
Professor Catedrático
Nuno João Silva
Investigador Principal
Patrícia Rodrigues da Silva
Bolseiro de investigação
Paulo Ribeiro-Claro
Professor Associado com Agregação
Sérgio Manuel Felipe Vilela
Bolseiro de pós-DoutoramentoGrupos
G1 - Materiais Porosos e Nanossistemas
G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G4 - Materiais Renováveis e Economia Circular
G6 - Materiais Virtuais e Inteligência Artificial
agradecimentos
We would like to thank Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), the European Union, QREN, FEDER, COMPETE and Laboratorio Associado Centro de Investigacao em Materiais Ceramicos e Compositos, CICECO (Pest C-CTM/LA0011/2013), the research unit QOPNA (PEst-C/QUI/UI0062/2013) for their general funding scheme. We further wish to thank FCT for the R&D project PTDC/QUI-QUI/098098/2008 (FCOMP-01-0124FEDER-010785), for the doctoral research grant nos SFRH/BD/66371/2009 ( to SV) and SFRH/BD/46601/2008 ( to PS), for the post-doctoral research grant SFRH/BPD/63736/2009 (to JAF)and for the Ciencia2008 program (NJOS). Magnetic studies were performed with the support of research grants MAT2007-61621, MAT2009-13977-C03-01 and CONSOLIDER CSD2007-00010 from the Ministry of Education, Spain. We further wish to thank Dr Rosario Soares for assistance with the powder X-ray diffraction data measurements, and Prof. Veronica de Zea Bermudez (UTAD) for granting access to the TGA instrument.