resumo
Three-dimensional lanthanide-organic frameworks formulated as (CH(3))(2)NH(2)[Ln(pydc)(2)]center dot 1/2H(2)O [Ln(3+) = Eu(3+) (1a) or Er(3+) (1b); pydc(2-) corresponds to the diprotonated residue of 2,5-pyridinedicarboxylic acid (H(2)pydc)], [Er(4)(OH)(4)(pydc)(4)(H(2)O)(3)]center dot H(2)O (2), and [Pr(2)(III)Pr(1.25)(IV)O(OH)(3)(pydc)(3)] (3) have been isolated from typical solvothermal (1a and 1b in N,N-dimethylformamide - DMF) and hydrothermal (2 and 3) syntheses. Materials were characterized in the solid state using single-crystal X-ray diffraction, thermogravimetric analysis, vibrational spectroscopy (FF-IR and FT-Raman), electron microscopy, and CHN elemental analysis. While synthesis in DMF promotes the formation of centrosymmetric dimeric units, which act as building blocks in the construction of anionic infinity(3){[Ln(pydc)(2)](-)} frameworks having the channels filled by the charge-balancing (CH(3))(2)NH(2)(+) cations generated in situ by the solvolysis of DMF, the use of water as the solvent medium promotes clustering of the lanthanide centers: structures of 2 and 3 contain instead tetrameric [Er(4)(mu(3)-OH)(4)](8+) and hexameric vertical bar Pr(6)(mu(3)-O)(2)(mu(3)-OH)(6)vertical bar clusters which act as the building blocks of the networks, and are bridged by the H(2-x)pydc(x-) residues. It is demonstrated that this modular approach is reflected in the topological nature of the materials inducing 4-, 8-, and 14-connected uninodal networks (the nodes being the centers of gravity of the clusters) with topologies identical to those of diamond (family 1), and framework types bct (for 2) and bcu-x (for 3), respectively. The thermogravimetric studies of compound 3 further reveal a significant weight increase between ambient temperature and 450 degrees C with this being correlated with the uptake of oxygen from the surrounding environment by the praseodymium oxide inorganic core.
palavras-chave
SECONDARY BUILDING UNITS; CAMBRIDGE STRUCTURAL DATABASE; INORGANIC 3D NETWORKS; COORDINATION POLYMERS; CRYSTAL-STRUCTURE; HYDROTHERMAL SYNTHESIS; MAGNETIC-PROPERTIES; SUPRAMOLECULAR ISOMERISM; LUMINESCENT PROPERTIES; SOLVENT HYDROLYSIS
categoria
Chemistry; Crystallography; Materials Science
autores
Shi, FN; Cunha-Silva, L; Trindade, T; Paz, FAA; Rocha, J
nossos autores
Fa-Nian Shi
Investigador
Filipe Alexandre Almeida Paz
Investigador Principal
João Rocha
Prof. Catedrático
Tito Trindade
Professor CatedráticoProjectos
Nanogotas de Água em Materiais Microporosos e Híbridos Orgânicos-Inorgânicos (PTDC/QUI/65805/2006)
agradecimentos
We are grateful to Fundacao para a Ciencia e a Tecnologia (Portugal) for their general financial support (PPCDT/QUI/58377/2004 and PTDC/QUI/65805/2006 supported by FEDER), the postdoctoral scholarships Nos. SFRH/BPD/9309/2002 (to F.-N.S.) and SFRH/BPD/34895/2007 (to L.C.-S.), and for funding towards the purchase of the single-crystal diffractometer.