The Emergence of Multiple Coordination Numbers in Gold–Cyanoarene Complexes: A Study of the On-Surface Coordination Mechanism

Abstract

In coordination chemistry, knowledge on the oxidation state of the central metal is a significant basis for the design and synthesis of novel complexes. We examined the mechanism of on-surface coordination bonding to d-block metals by investigating the coordination of the newly designed and synthesized 4-(3,3-dimethyl-2,3-dihydro-1H-indol-1-yl)­benzonitrile (IBN) ligand with Au adatoms on a Au(111) surface. The formation of mono-, di-, tri-, and tetra-IBN complexes of gold [Au–(IBN) n (n = 1, 2, 3, and 4)] and metal-free hydrogen-bonded IBN complexes on the Au surface was examined by scanning tunneling microscopy. The nature of the coordinated Au adatom was clarified by density functional theory calculations. The 5d z 2 pseudospheroidal orbital of the Au adatom is the predominant contributor to the Au–N coordination bond, and the Au(111) surface maintains a zero oxidation state of the Au adatom for coordination numbers n = 1, 2, 3, and 4. This on-surface control of the oxidation state of the Au adatom explains the different coordination numbers that were observed when Au adatoms coordinate to IBN molecules, together with an absence of variability in the electronic structures of the Au complexes as a function of their coordination number.

Facet-Selective Dissociation and Radical-Mediated Reaction of Dibenzotetrathiafulvalene Molecules on Low-Index Copper Surfaces

“…Therefore, it is very challenging to identify individual atoms in STM images. As reported in the literature, in some cases, the adatoms in the coordinated complexes can be clearly identified in STM images, − however, there are also reports in which the feature for the involved adatoms is invisible. − It has been reported that Cu adatoms exist at room temperature, and the density of Cu adatoms on the surface enlarges with the increase of temperature, indicating that Cu adatoms are available for forming complexes in our experiment. In addition, coordination of S atoms to individual Cu is frequently reported, , which also supports our proposed hypothesis.…”

Formation of 2D Self-Assembled Layers of Allyl Cyanide on Pd(111)

“…On the other hand, the distances i 1 = 7.6 Å and i 2 = 10.5 Å between the closest CN and the CH 2 groups estimated for the (8 × 5)-M i 2D layer (230 K, Figures and ) are significantly larger than the typical hydrogen bond lengths reported in the literature. ,,− This observation suggests that the other type of surface interactionsthe long-range interactionsmust be responsible for self-assembling in this type of 2D layer.…”

“…The attractive interactions within a 2D layer of organic adsorbates are frequently attributed to hydrogen bonding between neighboring species, ,,,− which is related to so-called short-range interactions typically acting within 5 Å. The typical length of hydrogen bonds previously reported in the literature amounts to 2.5 ± 0.2 Å as derived from available computational results, − 2.9 ± 0.3 Å as directly estimated from the STM results for a variety of organic molecules, ,, and 2.5 ± 0.6 Å as estimated by us from the structural models provided by the authors for various molecules adsorbed on coinage metal surfaces. ,, These values are comparable with the distances between the adjacent CN and CH 2 groups derived from our experimental results for the low-temperature range (169 and 210 K). Specifically, the characterizing distances i 3 = 3.6 Å (cNGs, 210 K) and i 4 = 3.6 Å (hexagons, 160 K) between the CN group of one molecule and the nearest H atom of a neighboring molecule (involved in the terminal CH 2 group) are close to the previously reported typical lengths of hydrogen bonding.…”

“…Previously, the formation of 2D layers governed either by purely long-range interactions or by their combination with short-range forces was reported for a number of adsorbate systems. The authors attributed the driving force for the formation of 2D layers to the dipole–dipole, electrostatic, elastic stress field and surface-state mediated interactions. − Specifically, for cyano-containing compounds (mostly, higher mass organic molecules), a large body of experimental work was previously published, in which the combination of long- and short-range interactions was put forward to explain the experimental results. ,,− Thus, Gottardi et al observed a hexagonal closed-packed phase forming upon the adsorption of a triarylamine derivate 4,4,8,8,12,12-hexamethyl-4 H ,8 H ,12 H -benzo­[1,9]­quinolizino­[3,4,5,6,7- defg ]­acridine-2,6,10-tricarbonitrile on Au(111). The authors explained the experimentally observed patterns by a combination of (i) long-range attractive dipolar coupling of the terminal CN-groups of two adjacent molecules (CN···CN bond) and (ii) short-range hydrogen bonding between the nitrogen atom of the CN-group and an H atom of the phenyl ring in close proximity.…”

“…Thus, for organic compounds containing cyano groups, mainly two types of interactions were previously identified: short-range hydrogen bonding ,,,− and long-range dipolar interaction. ,,, In the latter case, both attractive ,, and repulsive interactions were discussed for different adsorption systems. To the best of our knowledge, no other types of long-range interactions were experimentally demonstrated for any type of cyano compound.…”