Epitaxy-Induced Assembly and Enantiomeric Switching of an On-Surface Formed Dinuclear Organocobalt Complex Raphael Hellwig, † Tobias Paintner, † Zhi Chen, ‡ Mario Ruben, ‡,¶ Ari Paavo Seitsonen, § Florian Klappenberger,* ,† Harald Brune, ∥,⊥ and Johannes V. Barth † † Physik Department E20, Technische Universitä t Mü nchen, Garching D-85748, Germany ‡ Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen D-76344, Germany ¶ Institute de Physique et Chimie de Mate ́ riaux de Strasbourg (IPCMS), CNRS-Universite ́ de Strasbourg, Strasbourg F-67034, France § De ́ partement de Chimie, Ecole Normale Supe ́ rieure (ENS), Paris Cedex 05 F-75230, France ∥ Institute of Physics, Ecole Polytechnique Fe ́ de ́ rale de Lausanne (EPFL), Station 3, Lausanne CH-1015, Switzerland ⊥ Institute for Advanced Study (TUM-IAS), Lichtenbergstr. 2a, Garching D-85748, Germany * S Supporting Information ABSTRACT: We report on the surface-guided synthesis of a dinuclear organocobalt complex, its self-assembly into a complex nanoarchitecture, and a single-molecule level investigation of its switching behavior. Initially, an organic layer is prepared by depositing hexakis((trimethylsilyl)ethynyl)-benzene under ultra- high-vacuum conditions onto Ag(111). After Co dosage at 200 K, low-temperature scanning tunneling microscopy (STM) reveals an epitaxy-mediated organization mechanism of molecules and on- surface formed organometallic complexes. The dinuclear complexes contain two bis(η 2 -alkynyl) π-tweezer motifs, each stabilizing a single Co atom and express two enantiomers due to a conformation twist. The chirality is transferred to the two-dimensional architecture, whereby its Co adatoms are located at the corners of a 3.4.6.4 rhombitrihexagonal tessellation due to the systematic arrangement and anchoring of the complexes. Extensive density functional theory simulations support our interpretation of an epitaxy-guided surface tessellation and its chiral character. Additionally, STM tip-assisted manipulation experiments on isolated dinuclear complexes reveal controlled and reversible switching between the enantiomeric states via inelastic electron processes. After activation by bias pulses, structurally modified complexes display a distinctive Kondo feature attributed to metastable Co configurations. KEYWORDS: cobalt alkynyl complex, surface tessellation, single-molecule switch, scanning tunneling microscopy T he rational design and synthesis of 2D-confined functional nanoarchitectures of well-defined optic, magnetic, and catalytic properties remain one of the key challenges toward the realization of future nanotechnol- ogy. 1−6 When targeting the controlled fabrication and embedding of magnetic nanoobjects, such as single atoms, 7 small clusters, 8 or single-molecule magnets, 9 stepwise bottom- up construction via templates under ultrahigh-vacuum (UHV) conditions provides a versatile route. One-atom thick sheets of graphene and boron nitride proved to be suitable templates for the trapping of metallic clusters 10−14 at specific sites of the substrate-related Moire ́ lattices. Open-porous metal−organic coordination networks 15 were employed for the selective decoration with transition-metal clusters 16 and the confinement of single atoms. 17 A self-assembled and highly ordered layer of diphenyl oxalic amide molecules was used to selectively bind monomeric cobalt on top of benzene rings, thereby establishing a well-ordered Co superlattice. 18 Metal alkynyl complexes 19 are attractive for various research fields, such as non-linear optics, 20 intramolecular charge transfer systems, 21 and photovoltaics. 22 Moreover, they constitute the key building block for metallopolymers, an emerging class of functional soft materials. 23 Despite their importance for functional materials, insight on interfacial alkynyl complexes is scarce, but a handful of first results demonstrate interesting prospects. Liu et al. reported the formation of surface-guided molecular wires stabilized by Ag- bisalkynyl coordination. 24 Polyyne-coupled dinuclear com- plexes proved that mixed valence state chemistry is operational Received: September 9, 2016 Accepted: January 18, 2017 Published: January 18, 2017 Article www.acsnano.org © 2017 American Chemical Society 1347 DOI: 10.1021/acsnano.6b06114 ACS Nano 2017, 11, 1347−1359