Modelling the luminescence of extended solids: an example of a highly luminescent MCM-41 impregnated with a Eu3+ beta-diketonate complex.

Abstract

A regular MCM-41 type mesostructured silica was used as a support for the incorporation of the highly luminescent tris(β-diketonate) complex Eu(tta)3ephen yielding the hybrid MCM–Eu material. Suitable characterization by powder X-ray diffraction (XRD), thermogravimetric analyses (TGA), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), 13C and 21Si solid state NMR spectroscopy and photoluminescence was accomplished. The combination of ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence techniques shows that the complex incorporation seems to modify essentially the second Eu3+ coordination shell. For a material that has a simply impregnated lanthanide complex, the herein reported maximum 5D0 quantum yield value of 0.31 is a significantly high value, being almost in the same scale of the values obtained for the materials with covalently bonded complexes. A detailed theoretical photoluminescence study of the MCM–Eu with the recently developed Luminescence Package – LUMPAC is presented. The high accuracy of the theoretical calculations is achieved through the comparison with the experimental values. Aiming at a deeper understanding of the photoluminescence process, the ligand-to-Eu3+ intramolecular energy transfer and back-transfer rates were also predicted. The dominant pathway involves the energy transfer between the lowest energy ligand triplet and the 5D0 level (9.70 × 107 s−1).

Felicio, M. R.; Nunes, T. G.; Vaz, P. M.; Botas, A. M. P.; Ribeiro-Claro, P.; Ferreira, R. A. S.; Freire, R. O.; Vaz, P. D.; Carlos, L. D.; Nunes, C. D.; Nolasco, M. M.


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Effect of the Cation on the Interactions between Alkyl Methyl Imidazolium Chloride Ionic Liquids and Water.

Abstract

A systematic study of the interactions between water and alkyl methyl imidazolium chloride ionic liquids at 298.2 K, based on activity coefficients estimated from water activity measurements in the entire solubility range, is presented. The results show that the activity coefficients of water in the studied ILs are controlled by the hydrophilicity of the cation and the cation–anion interaction. To achieve a deeper understanding on the interactions between water and the ILs, COSMO-RS and FTIR spectroscopy were also applied. COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies, suggesting the formation of complexes between three molecules of water and one IL molecule. On the basis of quantum-chemical calculations, it is found that cation–anion interaction plays an important role upon the ability of the IL anion to interact with water. The changes in the peak positions/band areas of OH vibrational modes of water as a function of IL concentration were investigated, and the impact of the cation on the hydrogen-bonding network of water is identified and discussed.

Khan, I. ; Taha, M.; Ribeiro-Claro, P.; Pinho, S. P.; Coutinho, J. A. P.


Full Article

Synthesis, Structural Elucidation, and Catalytic Properties in Olefin Epoxidation of the Polymeric Hybrid Material [Mo3O9(2-[3(5)-Pyrazolyl]pyridine)](n)

Abstract

The reaction of [MoO2Cl2(pzpy)] (1) (pzpy = 2-[3(5)-pyrazolyl]pyridine) with water in an open reflux system (16 h), in a microwave synthesis system (120 °C, 2 h), or in a Teflon-lined stainless steel digestion bomb (100 °C, 19 h) gave the molybdenum oxide/pyrazolylpyridine polymeric hybrid material [Mo3O9(pzpy)]n (2) as a microcrystalline powder in yields of 72–79%. Compound 2 can also be obtained by the hydrothermal reaction of MoO3, pzpy, and H2O at 160 °C for 3 d. Secondary products isolated from the reaction solutions included the salt (pzpyH)2(MoCl4) (3) (pzpyH = 2-[3(5)-pyrazolyl]pyridinium), containing a very rare example of the tetrahedral MoCl42– anion, and the tetranuclear compound [Mo4O12(pzpy)4] (4). Reaction of 2 with excess tert-butylhydroperoxide (TBHP) led to the isolation of the oxodiperoxo complex [MoO(O2)2(pzpy)] (5). Single-crystal X-ray structures of 3 and 5 are described. Fourier transform (FT)-IR and FT Raman spectra for 1, 4, and 5 were assigned based on density functional theory calculations. The structure of 2 was determined from synchrotron powder X-ray diffraction data in combination with other physicochemical information. In 2, a hybrid organic–inorganic one-dimensional (1D) polymer, ∞1[Mo3O9(pzpy)], is formed by the connection of two very distinct components: a double ladder-type inorganic core reminiscent of the crystal structure of MoO3 and 1D chains of corner-sharing distorted {MoO4N2} octahedra. Compound 2 exhibits moderate activity and high selectivity when used as a (pre)catalyst for the epoxidation of cis-cyclooctene with TBHP. Under the reaction conditions used, 2 is poorly soluble and is gradually converted into 5, which is at least partly responsible for the catalytic reaction.

Amarante, T.R.; Neves, P.; Gomes, A. C.; Nolasco, M. M.; Ribeiro-Claro, P.; Coelho, A. C.; Valente, A. A.; Paz, F. A. A.; Smeets, S.; McCusker, L. B.; Pillinger, M.; Goncalves, I. S.


Full Article

Intermolecular C–H···O interactions in cyclopentanone: an inelastic neutron scattering study.

Abstract

The inelastic neutron scattering (INS) spectra of cyclopentanone were obtained for pure and 50% CCl4 solution forms. Spectra are compared with infrared and Raman data, and with DFT calculated eigenvectors. This exercise aims to find spectroscopic evidence in the neutron spectra for the presence of C–H⋯O hydrogen bonds. These are weak interactions with an energy of ca. −6 kJ mol−1 as predicted by DFT. The neutron spectra show narrow and sharp bands which allows for an assignment of the vibrational modes. The simulated neutron spectrum of C–H⋯O bonded cyclopentanone dimers matches the experimental spectrum of the pure compound, whereas the monomer simulation monomer matches the experimental spectrum of the diluted solution, meaning that such interaction can be probed by INS. Assignment of the 95 cm−1 band to the νH⋯O anti-translational mode, being supported by DFT results and in agreement with previous literature data, is considered and discussed.

Pedro D. Vaz, Mariela M. Nolasco, Paulo J.A. Ribeiro-Claro.


Full Article

Intermolecular C–H⋯O interactions in cyclopentanone: An inelastic neutron scattering study.

Abstract

The inelastic neutron scattering (INS) spectra of cyclopentanone were obtained for pure and 50% CCl4 solution forms. Spectra are compared with infrared and Raman data, and with DFT calculated eigenvectors. This exercise aims to find spectroscopic evidence in the neutron spectra for the presence of C-H center dot center dot center dot O hydrogen bonds. These are weak interactions with an energy of ca. -6 kJ mol(-1) as predicted by DFT. The neutron spectra show narrow and sharp bands which allows for an assignment of the vibrational modes. The simulated neutron spectrum of C-H center dot center dot center dot O bonded cyclopentanone dimers matches the experimental spectrum of the pure compound, whereas the monomer simulation monomer matches the experimental spectrum of the diluted solution, meaning that such interaction can be probed by INS. Assignment of the 95 cm(-1) band to the nu H center dot center dot center dot O anti-translational mode, being supported by DFT results and in agreement with previous literature data, is considered and discussed.

Vaz, P. D.; Nolasco, M. M.; Ribeiro-Claro, P. J. A.


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©Copyright 2024 - Computational Spectroscopy Lab - Department of Chemistry - University of Aveiro - 3810-193 Aveiro
©Copyright 2024 - Computational Spectroscopy Lab - Department of Chemistry - University of Aveiro - 3810-193 Aveiro

©Copyright 2024 - Computational Spectroscopy Lab - Department of Chemistry - University of Aveiro - 3810-193 Aveiro