![]() ![]() Annealing at 460 K then leads to the removal of linking silver atoms and the formation of a covalently bonded structure. ![]() This creates an organometallic intermediate structure. Deposition of DITP onto silver substrates causes iodine to dissociate from the molecule, followed by the formation of C-Ag-C coordination bonds between molecules. The molecule consists of three phenylene rings, with the outer aryl groups bonded at the meta positions of the central ring and functionalised with iodine. This investigation used the molecule 4,4″-diiodo-m-terphenyl (DITP), shown in Fig. Here, we offer a comparison using a similar, iodine terminated molecule on silver substrates, investigating how the structure of the surface affects the formation of intermediate and final products with emphasis on the templating effect of the surface. These structures included zigzag chains and closed hexagonal rings, both before and after annealing. After heating the substrates, covalently bonded structures were observed. Recent studies of 4,4″-dibromo-m-terphenyl on Cu(111) 11, 12 or Cu(110) 13 have shown the formation of intermediate metal-organic structures at room temperature. The relationship between the alignment of the intermediate and final structures with the substrate is an additional influential factor to be explored and is investigated here. Several studies have attempted to address the problem, investigating the effects of both the bulk chemistry 26 and topology of the surface 27, as well as other factors such as the influence of halogens 28, 29 and reaction kinetics 30, on structure formation. However the mechanistic process by which the intermediate state is formed and converted to the covalent product is still debated. This reaction has the advantage of creating covalent bonds between constituent molecules, making structures formed in this way more thermally stable than those formed through hydrogen bonds or van der Waals interactions. The addition of thermal energy leads to the reductive elimination of the metal atoms, resulting in the formation of covalent bonds between molecular units, shown in Fig. The resulting surface-stabilised radicals are then joined via substrate metal adatoms, creating an intermediate metal-organic state. Aryl-halides deposited onto a metal surface undergo dissociation of their halide groups in a reaction catalysed by the metal substrate. Of particular interest is on-surface synthesis based on the Ullmann coupling reaction 25. Such systems are readily studied by scanning probe microscopies, such as scanning tunnelling microscopy (STM) and atomic force microscopy (AFM), providing real-space imaging with sub-molecular resolution. These have been created through a variety of different strategies 1, 2, 3, 4, 5, 6, 7 facilitating the synthesis of molecular chains, 8, 9, 10, 11, 12, 13, 14, 15, 16 graphene nanoribbons 17, 18, and 2D molecular frameworks 19, 20, 21, 22, 23, 24. Over the past decade, there has been great progress in the development of on-surface synthesis of 1D and 2D covalently bonded structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometallic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. ![]()
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