Supramolecular assembling of molecular ion-ligands on graphite-based solid materials directed to specific binding of metal ions

• Assembling of graphite arene-sites with e-defficient aromatic ligands is highly stable.
• Ligands-functionalized AC surfaces embody the metal-binding abilities of the ligands.
• Ligands/AC hybrid materials improve adsorptivity to metal ions of the parent AC.
• Pd(II)/ligands/AC materials exhibit catalytic activity on n-octene hydrogenation.
• Ligands attached to graphitic surfaces stabilize Pd(0) nanoparticles.

Molecular ligands with a particular topology, based on a polar heteroaromatic nucleus linked to hydrophilic (metal-complexing) substituents, form very stable assemblies with activated carbons (ACs) due to strong π–π interactions between the planar pyrimidine moiety and the arene centers of the AC surfaces. Heteroatomic functions at the edges of the AC graphitic sheets do not alter the interaction mode with the ligands nor the stability of the assemblies. That results in the formation of stable hybrids, AC/ligand, whose surface chemical properties, specially the acid base behavior and the affinity to metal ions, reflect those of the non-conjugated, hydrophilic moieties of the ligands. Consequently, such hybrid materials show metal ion adsorptivities that are superior to those of the parent AC and correlate with the metal-binding abilities of the non-conjugated substituents. Significant amounts of meso- and macropores are required in the parent AC to efficiently transfer the chemical properties of the ligand non-conjugated substituents to the hybrid AC/ligand. After adsorption of metal ions, new hybrids, AC/ligand/metal, emerge with interesting potential applications. Thus, an AC/triamine ligand/Pd(II) hybrid showed high catalytic activity in hydrogenation reactions due to the formation of highly stable Pd nanoparticles at the AC surface during the first reaction cycle.

This article describes the molecular basis that direct the formation of stable supramolecular assemblies between Lewis base-substitued pyrimidines and the Cπ centers of the graphitic surface of activated carbons. This process allows the formation of (solid) functionalized hybrid materials, whose surface express the properties of the Lewis base substituent of the pyrimidine molecule. On this background the metal ion sequestering properties of the above hybrid materials relate mainly to the metal ion-complexation properties of the Lewis base moiety of the anchored molecule. This method constitutes an interesting resource in the designing of heterogeneous catalysts based on solid-supported metal complexes.Figure optionsDownload as PowerPoint slide