Robust Supramolecular Network on Ag(111): Hydrogen‐Bond Enhancement through Partial Alcohol Dehydrogenation

Alcohol oxidation and self‐assembly: the in situ oxidation of hydroxyl functional groups to quinone groups promotes the formation of enhanced hydrogen bonds and allows reorganization of the resulting supramolecular self‐assemblies, which evolve from a weakly bound dense phase to a strongly bound nanoporous open structure (see picture).

     

On-Surface Assembly of Au-Dicyanoanthracene Coordination Structures on Au(111)

On-surface metal-organic coordination provides a promising way for synthesizing different two-dimensional lattice structures that have been predicted to possess exotic electronic properties. Using scanning tunneling microscopy (STM) and spectroscopy (STS), we studied the supramolecular self-assembly of 9,10-dicyanoanthracene (DCA) molecules on the Au(111) surface. Close-packed islands of DCA molecules and Au-DCA metal-organic coordination structures coexist on the Au(111) surface. Ordered DCA₃Au₂ metal-organic networks have a structure combining a honeycomb lattice of Au atoms with a kagome lattice of DCA molecules. Low-temperature STS experiments demonstrate the presence of a delocalized electronic state containing contributions from both the gold atom states and the lowest unoccupied molecular orbital of the DCA molecules. These findings are important for the future search of topological phases in metal-organic networks combining honeycomb and kagome lattices with strong spin-orbit coupling in heavy metal atoms.     

Tailoring Large Pores of Porphyrin Networks on Ag(111) by Metal–Organic Coordination

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu‐mediated metal–organic coordination networks based on two pyridyl‐ and cyano‐bearing free‐base porphyrins on Ag(111) are elucidated by use of low‐temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano‐terminated module directly forms 2D porous networks featuring fourfold‐coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm² only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two‐ and fourfold monoatomic coordination nodes with monotopic nitrogen‐terminated linkers on the very same metal substrate—a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low‐dimensional structures on surfaces.     

Competitive Metal Coordination of Hexaaminotriphenylene on Cu(111) by Intrinsic Copper Versus Extrinsic Nickel Adatoms

The interplay between the self-assembly and surface chemistry of 2,3,6,7,10,11-hexaaminotriphenylene (HATP) on Cu(111) was complementarily studied by high-resolution scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) under ultra-high vacuum conditions. To shed light on the competitive metal coordination, comparative experiments were carried out on pristine and nickel-covered Cu(111). Directly after room-temperature deposition of HATP onto pristine Cu(111), self-assembled aggregates were observed by STM, and XPS results indicated still protonated amino groups. Annealing up to 200 °C activated the progressive single deprotonation of all amino groups as indicated by chemical shifts of both the N 1s and C 1s core levels in the XP spectra. This enabled the formation of topologically diverse π–d conjugated coordination networks with intrinsic copper adatoms. The basic motif of these networks was a metal–organic trimer, in which three HATP molecules were coordinated by Cu₃ clusters, as corroborated by the accompanying density functional theory (DFT) simulations. Additional deposition of more reactive nickel atoms resulted in both chemical and structural changes with deprotonation and formation of bis(diimino)–Ni bonded networks already at room temperature. Even though fused hexagonal metal-coordinated pores were observed, extended honeycomb networks remained elusive, as tentatively explained by the restricted reversibility of these metal–organic bonds.     

Structure and Conformation of Individual Molecules upon Adsorption of a Mixture of Benzoporphyrins on Ag(111), Cu(111), and Cu(110) Surfaces

The front cover artwork is provided by the groups of Prof. Dr. Hans-Peter Steinrück and Prof. Dr. Norbert Jux at the Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg. The image shows a mixture of six 2H-tetrakis-(3, 5-di-tert-butyl-phenyl)(x)benzoporphyrins (2H-diTTBP(x)BPs, x = 0, 1, 2-cis, 2-trans, 3, or 4) molecules forming a porous square structure on Ag(111) as observed in scanning tunneling microscopy (STM) at room temperature. Read the full text of the Research Article at 10.1002/cphc.202300355 .     

Fivefold Symmetry and 2D Crystallization: Self-Assembly of the Buckybowl Pentaindenocorannulene on a Cu(100) Surface

The modification of metal electrode surfaces with functional organic molecules is an important part of organic electronics. The interaction of the buckminsterfullerene fragment molecule pentaindenocorannulene with a Cu(100) surface is studied by scanning tunneling microscopy, dispersion-enabled density functional theory, and force field calculations. Experimental and theoretical methods suggest that two adjacent indeno groups become oriented parallel to the surface upon adsorption under mild distortion of the molecular frame. The binding mechanism between molecule and surface is dominated by strong electrostatic interaction owing to Pauli repulsion. Two-dimensional aggregation at room temperature leads to a single lattice structure in which all molecules are oriented unidirectionally. Their relative arrangement in the lattice suggests noncovalent intermolecular interaction through C−H⋅⋅⋅π bonding.     

An Electron‐Rich Cyclic (Alkyl)(Amino)Carbene on Au(111), Ag(111), and Cu(111) Surfaces

The structural properties and binding motif of a strongly σ‐electron‐donating N‐heterocyclic carbene have been investigated on different transition‐metal surfaces. The examined cyclic (alkyl)(amino)carbene (CAAC) was found to be mobile on surfaces, and molecular islands with short‐range order could be found at high coverage. A combination of scanning tunneling microscopy (STM), X‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations highlights how CAACs bind to the surface, which is of tremendous importance to gain an understanding of heterogeneous catalysts bearing CAACs as ligands.     

Conformation Diversity of a Fused‐Ring Pyrazine Derivative on Au(111) and Highly Ordered Pyrolytic Graphite

Heterocyclic aromatic compounds have attracted considerable attention because of their high carrier mobility that can be exploited in organic field‐effect transistors. This contribution presents a comparative study of the packing structure of 3,6‐didodecyl‐12‐(3,6‐didodecylphenanthro[9,10‐b]phenazin‐13‐yl)phenanthro[9,10‐b]phenazine (DP), an N‐heterocyclic aromatic compound, on Au(111) and highly ordered pyrolytic graphite (HOPG). High‐resolution scanning tunneling microscopy (STM) combined with atomistic simulations provide a picture of the interface of this organic semiconductor on an electrode that can have an impact on the field‐effect transistor (FET) performance. DP molecules adsorb with different conformational isomers (R/S: trans isomers; C: cis isomer) on HOPG and Au(111) substrates. All three isomers are found in the long‐range disordered lamella domains on Au(111). In contrast, only the R/S trans isomers self‐assemble into stable chiral domains on the HOPG surface. The substrate‐dependent adsorption configuration selectivity is supported by theoretical calculations. The van der Waals interaction between the molecules and the substrate dominates the adsorption binding energy of the DP molecules on the solid surface. The results provide molecular evidence of the interface structures of organic semiconductors on electrode surfaces.     

Supramolecular Assembly of a 2D Binary Network of Pentacene and Phthalocyanine on Cu(100)

A crystalline nanoporous molecular network was tailored by supramolecular assembly of pentacene and F₁₆CuPc on Cu(100). The structure and self‐assembly mechanisms of the pure and binary layers were analyzed by STM. F₁₆CuPc films and mixed layers of pentacene/F₁₆CuPc in a ratio of 2:1 show two enantiomorphic chiral domains with high structural order in contrast to pentacene which exhibits no long‐range order in pure films. A model of the epitaxial relationship on Cu(100) is given, which suggests C? F???H bonding as a possible driving force for the bimolecular self‐assembly in addition to the still strong interaction between the substrate and the organic bilayer.     

In-Situ Growth of Gadolinium Phthalocyaninato Sandwich Complexes on the Ag(111) Surface

We report a low-temperature scanning tunneling microscopy investigation of the in-situ growth of gadolinium phthalocyaninato complexes by combined deposition of free-base phthalocyanines and gadolinium atoms on a smooth Ag(111) substrate. A careful control of the stoichiometry allows the expression of a multilevel structurecomposed of irregularly distributed Gd_x-1(Pc)_x complexes, x=2–5, thus paving new avenues for surface-confined columnar growth.     

2H‐Tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin on a Cu(110) Surface: Room‐Temperature Self‐Metalation and Surface‐Reconstruction‐Facilitated Self‐Assembly

The adsorption behavior of 2H‐tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin (2HTTBPP) on Cu(110) and Cu(110)–(2×1)O surfaces have been investigated by using variable‐temperature scanning tunneling microscopy (STM) under ultrahigh vacuum conditions. On the bare Cu(110) surface, individual 2HTTBPP molecules are observed. These molecules are immobilized on the surface with a particular orientation with respect to the crystallographic directions of the Cu(110) surface and do not form supramolecular aggregates up to full monolayer coverage. In contrast, a chiral supramolecular structure is formed on the Cu(110)–(2×1)O surface, which is stabilized by van der Waals interactions between the tert‐butyl groups of neighboring molecules. These findings are explained by weakened molecule–substrate interactions on the Cu(110)–(2×1)O surface relative to the bare Cu(110) surface. By comparison with the corresponding results of Cu–tetrakis(3,5‐di‐tert‐butyl)phenylporphyrin (CuTTBPP) on Cu(110) and Cu(110)–(2×1)O surfaces, we find that the 2HTTBPP molecules can self‐metalate on both surfaces with copper atoms from the substrate at room temperature (RT). The possible origins of the self‐metalation reaction at RT are discussed. Finally, peculiar irreversible temperature‐dependent switching of the intramolecular conformations of the investigated molecules on the Cu(110) surface was observed and interpreted.     

Two‐Dimensional Ketone‐Driven Metal–Organic Coordination on Cu(111)

Two‐dimensional metal–organic nanostructures based on the binding of ketone groups and metal atoms were fabricated by depositing pyrene‐4,5,9,10‐tetraone (PTO) molecules on a Cu(111) surface. The strongly electronegative ketone moieties bind to either copper adatoms from the substrate or codeposited iron atoms. In the former case, scanning tunnelling microscopy images reveal the development of an extended metal–organic supramolecular structure. Each copper adatom coordinates to two ketone ligands of two neighbouring PTO molecules, forming chains that are linked together into large islands through secondary van der Waals interactions. Deposition of iron atoms leads to a transformation of this assembly resulting from the substitution of the metal centres. Density functional theory calculations reveal that the driving force for the metal substitution is primarily determined by the strength of the ketone–metal bond, which is higher for Fe than for Cu. This second class of nanostructures displays a structural dependence on the rate of iron deposition.     

Metalation of 2HTCNPP on Ag(111) with Zn: Evidence for the Sitting atop Complex at Room Temperature

We study the interaction and metalation reaction of a free base 5,10,15,20-terakis(4-cyanophenyl)porphyrin (2HTCNPP) with post-deposited Zn atoms and the targeted reaction product Zn-5,10,15,20-terakis(4-cyanophenyl)porphyrin (ZnTCNPP) on a Ag(111) surface. The investigations are performed with scanning tunneling microscopy at room temperature after Zn deposition and subsequent heating. The goal is to obtain further insights in the metalation reaction and the influence of the cyanogroups on this reaction. The interaction of 2HTCNPP with post-deposited Zn leads to the formation of three different 2D ordered island types that coexist on the surface. All contain a new species with a bright appearance, which increases with the amount of post-deposited Zn. We attribute this to metastable SAT (“sitting atop”) complexes formed by Zn and the macrocycle, that is, an intermediate in the metalation reaction to ZnTCNPP, which occurs upon heating to 500 K. Interestingly, the activation barrier for the successive reaction of the SAT complex to the metalated ZnTCNPP species can also be overcome by a voltage pulse applied to the STM tip.     

基于全氟酞菁铜和碗烯双分子体系在银和石墨表面自组装行为的低温扫描隧道显微镜研究

Corannulene (COR) is considered a promising molecular building block for organic electronics owing to its intriguing geometrical and electronic properties. Intensive research efforts have been devoted to understanding the assembly behavior and electronic structure of COR and its derivatives on various metal surfaces via low-temperature scanning tunneling microscopy (LT-STM). Here we report the formation of binary molecular networks of copper hexadecafluorophthalocyanine (F₁₆CuPc)-COR self-assembled on the highly oriented pyrolytic graphite (HOPG) and Ag (111) substrates. Intermolecular hydrogen bonding between F₁₆CuPc and COR facilitates the formation of binary molecular networks on HOPG and further induces a preference for bowl-down configured COR molecules. This observed configuration preference disappears on Ag (111) substrate, where COR molecules lie on the substrate with their bowl openings pointing up and down randomly. We propose that strong interfacial interactions between the molecule and Ag (111) surface constrain the bowl inversion of the COR molecule, which thus retains its initial configuration upon adsorption.     

The self-assembly of porphine molecules on NaCl pre-covered Cu(110) surface

The self-assembly of porphine molecules on NaCl pre-covered Cu(110) surface has been investigated at a single molecular level by scanning tunneling microscopy. The pre-grown NaCl stripe pattern has been partly interrupted due to the adsorption of porphine molecules at RT. Annealing the sample at 333 K and 423 K gradually promotes the formation of self-assembly network composed of porphine molecules and Cu atoms. Annealing at 473 K helps to convert this self-assembly structure into organometallic nanoribbon through C–Cu–C connecting.