Persona:
Gavira Vallejo, José María

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0000-0002-6037-5731
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Gavira Vallejo
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José María
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2018 - 20203
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Autor: Romero Muñiz, Carlos ×

Resultados de la búsqueda

Mostrando 1 - 3 de 3
  • Miniatura
    Publicación
    Impact of Small Adsorbates in the Vibrational Spectra of Mg- and Zn-MOF-74 Revealed by First-Principles Calculations
    (American Chemical Society, 2020) Romero Muñiz, Carlos; Merkling, Patrick; Calero, Sofía; Gavira Vallejo, José María
    In this work, we analyze the influence of small adsorbates on the vibrational spectra of Mg- and Zn-metal–organic framework MOF-74 by means of first-principles calculations. In particular, we consider the adsorption of four representative species of different interaction strengths: Ar, CO2, H2O, and NH3. Apart from a comprehensive characterization of the structural and energetic aspects of empty and loaded MOFs, we use a fully quantum ab initio approach to evaluate the Raman and IR activities of the normal modes, leading to the construction of the whole vibrational spectra. Under this approach, not only are we able to proceed with the complete assignment of the spectra in terms of the usual internal coordinates but also we can discern the most relevant vibrational fingerprints of the adsorbates and their impact on the whole MOF spectra. On the one hand, some of the typical vibrational modes of the small molecules are slightly shifted but still visible when adsorbed on the MOFs, especially those appearing at high wavenumbers where the empty MOFs lack IR/Raman signals. On the other hand, some bands arising from the organic ligands are affected by the presence of the absorbates, displaying non-negligible frequency shifts, in agreement with recent experiments. We find a strong correlation between all of these frequency shifts and the interaction strength of the adsorbate with the hosting framework. The findings presented in this work expand the capabilities of vibrational spectroscopy techniques to analyze porous materials and can be useful for the design of sensors and new devices based on MOF technology.
  • Miniatura
    Publicación
    A comprehensive study of the molecular vibrations in solid-state benzylic amide [2]catenane
    (Royal Society of Chemistry, 2019) Romero Muñiz, Carlos; Paredes Roibás, Denís; Hernanz, Antonio; Gavira Vallejo, José María
    The interpretation of vibrational spectra is often complex but a detailed knowledge of the normal modes responsible for the experimental bands provides valuable information about the molecular structure of the sample. In this work we record and assign in detail the infrared (IR) spectrum of the benzylic amide [2]catenane, a complex molecular solid displaying crimped mechanical bonds like the links of a chain. In spite of the large size of the unit cell, we calculate all the vibrational modes of the catenane crystal using quantum first-principles calculations. The activity of each mode is also evaluated using the Born effective charges approach and a theoretical spectrum is constructed for comparison purposes. We find a remarkable agreement between the calculations and the experimental results without the need to apply any further empirical correction or fitting to the eigenfrequencies. A detailed description in terms of the usual internal coordinates is provided for over 1000 normal modes. This thorough analysis allows us to perform the complete assignment of the spectrum, revealing the nature of the most active modes responsible for the IR features. Finally, we compare the obtained results with those of Raman spectroscopy, studying the effects of the rule of mutual exclusion in vibrational spectroscopy according to the different levels of molecular symmetry embedded in this mechanically interlocked molecular compound.
  • Miniatura
    Publicación
    Assignment of the Raman Spectrum of Benzylic Amide [2]Catenane: Raman Microscopy Experiments and First-Principles Calculations
    (American Chemical Society, 2018) Romero Muñiz, Carlos; Paredes Roibás, Denís; Hernanz, Antonio; López García, Concepción; Gavira Vallejo, José María
    In this work, we use Raman spectroscopy and quantum first-principles calculations to unveil the experimental spectrum of a complex molecular solid-like benzylic amide [2]catenane, a representative example of a mechanically interlocked molecular architecture. We use large-scale density functional theory calculations to obtain the complete set of vibrational normal modes of the catenane crystal, whose unit cell contains 544 atoms. Subsequently, we demonstrate that these calculations are able to accurately reproduce the experimental Raman spectrum of this molecular compound, without introducing any empirical corrections or fittings in the calculated eigenfrequencies. Thanks to the good agreement between the experimental and theoretical spectra, it is possible to carry out the complete assignment of the main vibrational modes responsible for the whole spectrum. A detailed description in terms of the usual internal coordinates is given for all of these representative modes. This description, rather difficult from the experimental point of view, provides valuable information about the molecular structure of this compound, compatible with experimental evidences reported in the literature.