Multifunctional micro- and nanosized metal–organic frameworks assembled from bisphosphonates and lanthanides

Abstract

Phase-pure and highly crystalline [Ln(Hpmd)(H2O)] materials [where Ln3+ = Eu3+ (1), Gd3+ (2) and Tb3+ (3); H4pmd = 1,4-phenylenebis(methylene)diphosphonic acid] were prepared by using three distinct approaches: (i) conventional hydrothermal synthesis (180 °C, 3 days); (ii) microwave-assisted heating (50 W irradiation power, 40 °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 (Ln3+ : 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 and EDS). The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K revealing that the Ln3+ 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 °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 sensitizer of Tb3+ (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 Eu3+ 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).

S. M. F. Vilela, D. Ananias, J. A. Fernandes, P. Silva, A. C. Gomes, N. J. O. Silva, M. O. Rodrigues, J. P. C. Tomé, A. A. Valente, Paulo Ribeiro-Claro, L. D. Carlos, J. Rocha, F. A. A. Paz.


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Multifunctional micro-and nanosized metalorganic frameworks assembled from bisphosphonates and lanthanides.

Abstract

Phase-pure and highly crystalline [Ln(Hpmd)(H2O)] materials [where Ln3+ = Eu3+ (1), Gd3+ (2) and Tb3+ (3); H4pmd = 1,4-phenylenebis(methylene)diphosphonic acid] were prepared by using three distinct approaches: (i) conventional hydrothermal synthesis (180 °C, 3 days); (ii) microwave-assisted heating (50 W irradiation power, 40 °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 (Ln3+ : 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 and EDS). The magnetic behavior of 1 and 2 was investigated between ambient temperature and ca. 2 K revealing that the Ln3+ 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 °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 sensitizer of Tb3+ (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 Eu3+ 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).

Vilela, S. M. F.; Ananias, D.; Fernandes, J. A.; Silva, P.; Gomes, A. C.; Silva, N. J. O.; Rodrigues, M. O.; Tome, J. P. C.; Valente, A. A.; Ribeiro-Claro, P.; Carlos, L. D.; Rocha, J.; Paz, F. A. A.


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Transposition of chirality from diphosphonate metal–organic framework precursors onto porous lanthanide pyrophosphates

Abstract

Chiral porous inorganic materials, lanthanide pyrophosphates, were prepared from chiral porous metal–organic framework precursors, which upon thermal decomposition transpose their chirality and porosity onto the inorganic framework. It is argued that this synthesis concept may be extended to other chiral porous inorganic solids.

FN Shi,, F. A. A. Paz, Paulo Ribeiro-Claro, J. Rocha.


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Transposition of chirality from diphosphonate metal–organic framework precursors onto porous lanthanide pyrophosphates.

Abstract

Chiral porous inorganic materials, lanthanide pyrophosphates, were prepared from chiral porous metal-organic framework precursors, which upon thermal decomposition transpose their chirality and porosity onto the inorganic framework. It is argued that this synthesis concept may be extended to other chiral porous inorganic solids.

Shi, F. N.; Paz, F. A. A.; Ribeiro-Claro, P.; Rocha, J.


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Analysis of the microcrystalline inclusion compounds of triclosan with β-cyclodextrin and its tris-O-methylated derivative.

Abstract

Solid 1:1 inclusion compounds of triclosan with native and permethylated 6-cyclodextrin (beta-CD and TRIMEB) were prepared by co-crystallisation and co-evaporation, respectively, and studied by FT-IR and C-13{H-1} CP/MAS NMR spectroscopies, thermogravimetric analysis, X-ray diffraction and theoretical calculations. Results showed that triclosan inclusion into TRIMEB afforded an amorphous solid, whilst beta-CD triclosan is composed of microcrystals belonging to two different phases. In the phase featuring larger crystals, X-ray diffraction was carried out and the beta-CD host units, packing head-to-head in infinite channels, were refined; the geometry for the included but highly disordered triclosan molecules was assessed by theoretical calculations. The bacterial growth inhibitory action of the inclusion compounds was studied in comparison to that of pure triclosan on Gram-negative (Salmonella, Escherichia) and Gram-positive strains (Bacillus, Listeria, Enterococcus and Staphylococcus) typically associated with human pathologies, and also on environmental bacteria isolated from different soil and water sources. The antimicrobial activities obtained in the present work showed that, of the two CD hosts, TRIMEB brings the most favourable carrier effect: it reduced the toxicity of triclosan against some of the environmental strains and afforded slightly higher action against virulent strains. (C) 2013 Elsevier B.V. All rights reserved.

Ramos, A. I.; Braga, T. M.; Fernandes, J. A.; Silva, P.; Ribeiro-Claro, P. J.; Paz, F. A. A.; Lopes, M. F. S.; Braga, S. S.


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