Acidic and basic sites of M2DEBDC (M = Mg or Mn and E = O or S) acting as catalysts for cyanosilylation of aldehydes

Abstract 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 M 2 DEBDC (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 M 2 DEBDC. The analyses indicated that M 2 DSBDC may have more efficient basic sites than M 2 DOBDC with the first materials presenting less ionic character. The positive Bader charges over the metallic cations followed the increasing order Mn(II)  2 DEBDC contains more efficient acidic Lewis sites than Mn 2 DEBDC. The flexibilities of the solid structures occurred in the crescent order: Mg 2 DOBDC  2 DSBDC  2 DOBDC ≃ Mn 2 DSBDC. Considering the experimental evidence that Mn 2 DOBDC is a better catalyst than Mg 2 DOBDC 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.