Add time:09/03/2019         Source:sciencedirect.com

The building blocks of the Metal–Organic Frameworks (MOFs) may have different chemical groups or atoms, thus these solids have quite diversified properties. The understanding at the molecular level of the MOFs in possible applications may allow the design of new optimized materials with specific sites accordingly chosen, by means of the reticular chemistry. The MOFs M2DEBDC (M = Mg or Mn and E = O or S) are composed by divalent metallic cations connected by 2,5-dihydroxybenzene-1,4-dicarboxylate (DOBDC) or by 2,5-disulfhydrylbenzene-1,4-dicarboxilate (DSBDC). In this work, Density Functional Theory (DFT) calculations were performed to unveiling the strength of the possible acidic and basic sites of M2DEBDC. The analyses indicated that M2DSBDC may have more efficient basic sites than M2DOBDC with the first materials presenting less ionic character. The positive Bader charges over the metallic cations followed the increasing order Mn(II) < Mg(II), suggesting that Mg2DEBDC contains more efficient acidic Lewis sites than Mn2DEBDC. The flexibilities of the solid structures occurred in the crescent order: Mg2DOBDC < Mg2DSBDC < Mn2DOBDC ≃ Mn2DSBDC. Considering the experimental evidence that Mn2DOBDC is a better catalyst than Mg2DOBDC and the mechanistic results obtained through DFT calculations, the structural flexibility seems to be a more important factor than the electronic factor of the charge to explain the catalytic performance of the materials.

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