Some Theoretical and Experimental Insights on the Mechanistic Routes Leading to the Spontaneous Grafting of Gold Surfaces by Diazonium Salts

Abstract

The spontaneous grafting of diazonium salts on gold may involve the carbocation obtained by heterolytic dediazonation and not necessarily the radical, as usually observed on reducing surfaces. The mechanism is addressed on the basis of DFT calculations and experiments carried out under conditions where the carbocation and the radical are produced selectively. The calculations indicate that the driving force of the reaction leading from a gold cluster, used as a gold model surface, and the carbocation to the modified cluster is higher than that of the analogous reaction starting from the radical. The experiments performed under conditions of heterolytic dediazonation show the formation of thin films on the surface of gold. The grafting of a carbocation is therefore possible, but a mechanism where the cleavage of the Ar-N bond is catalyzed by the surface of gold cannot be excluded.

Alkyl-Modified Gold Surfaces: Characterization of the Au–C Bond

“…The results of the above periodic calculations can be compared with that of nonperiodic DFT calculations on an Au20 cluster. As already observed in the grafting of aryl groups, 12 binding an alkyl group (valeric group) to the surface of Au20 changes its geometry ( Figure 5). The bond distances between neighboring gold atoms change after the grafting: in the bare cluster d(Au15−Au17) = d(Au15−Au14) = 2.90 Å, while after grafting to Au15 the gold atom distance changes: d(Au15− Au17)/d(Au15−Au14) = 3.03, indicating an effect similar to that observed in the case of thiols and aryl radicals.…”

“…In the literature, the binding energy of alkylthiols varies from −25 kcal/mol for conjugated molecules to −44 kcal/mol depending on the length and the chemical structure. 41,42 The above values can also be compared with that calculated (with two different methods) for Au− C(aryl) bonds obtained by grafting diazonium salts on gold: −34.4 kcal/mol (Au19−C 6 H 5 ) 12 and −24.0 kcal/mol [Au(111), TOP site]−C 6 H 5 . 23 These calculations indicate that the energy of Au(111)−C(alkyl) bond is equivalent to that of an Au−C(aryl) bond; the Au(111)−S−alkyl bond is more stable than the Au(111)−C(alkyl) one by −8.6 kcal/mol.…”

“…The bond distances between neighboring gold atoms change after the grafting: in the bare cluster d(Au15−Au17) = d(Au15−Au14) = 2.90 Å, while after grafting to Au15 the gold atom distance changes: d(Au15− Au17)/d(Au15−Au14) = 3.03, indicating an effect similar to that observed in the case of thiols and aryl radicals. 9,12 The dihedral angles are also modified: (Au17−Au15−Au11−Au14) is 3.6°for Au20 but 20.0°in Au20−(CH 2 ) 3 −COOH. After grafting, the gold atom is pulled out from the mean surface plane of the Au20 cluster by about 0.86 Å ( Figure 5).…”

Interactions between the Aryldiazonium Cations and Graphene Oxide: A DFT Study

“…e adsorption properties of aryldiazonium cations on graphene surfaces are investigated by the DFT method using the generalized gradient approximation (GGA) [11] or PBE [12][13][14][15]. e graphene oxide (GOx) model is approximated by using a 5 × 5 graphene model that contains epoxy, hydroxyl, and carboxy groups on its surface (Figure 1(a)).…”

Partitioning of aryl radicals in micellar systems

“…Moreover, metals in foods can induce production of radicals in the aqueous regions of the colloidal systems and antioxidants added to foods need to be designed (for example, by modulating their hydrophobicity) to achieve their maximum concentration at the site of production of radicals. Results may be also useful to improve the use of ArN 2 + as starting material to graft functionalities or change surface properties of carbon and various metals, because the grafting process rests on the production of highly reactive aryl radicals at the substrate‐solution interface …”