Breaking Radial Dipole Symmetry in Planar Macrocycles Modulates Edge-to-Edge Packing and Disrupts Cofacial Stacking.

Dipolar interactions are ever-present in supramolecular architectures, though their impact is typically revealed by making dipoles stronger. While it is also possible to assess the role of dipoles by altering their orientations by using synthetic design, doing so without altering the molecular shape is not straightforward. We have now done this by flipping one triazole unit in a rigid macrocycle, tricarb.

Tuning Ligand-Coordinated Single Metal Atoms on TiO and their Dynamic Response during Hydrogenation Catalysis.

Invited for this month's cover is the group of Steven Tait at Indiana University. The image shows single metal atoms stabilized by small molecules on a titanium dioxide powder support that are active in catalyzing ethylene hydrogenation. The Full Paper itself is available at 10.

Variations in Complementary Hydrogen Bonds Direct Assembly Patterns of Isosteric Polyheteroaromatics at Surfaces.

Intermolecular interactions guide self-assembly on the surface. Precise control over these interactions by rational design of the molecule should allow fine control over the self-assembly patterns. Functional groups installed for electronic modulation often induce significant changes in the molecular dimensions, thereby disrupting the original assembly pattern.

Tuning Ligand-Coordinated Single Metal Atoms on TiO and their Dynamic Response during Hydrogenation Catalysis.

Ligand-coordinated supported catalysts (LCSCs) are of growing interest for heterogeneous single-atom catalysis. Here, the effect of the choice of organic ligand on the activity and stability of TiO -supported single-atom Pt-ligand catalysts was investigated for ethylene hydrogenation. The activity of these catalysts showed a significant dependence on the choice of ligand and also correlated with coordination number for Pt-ligand and Pt-Cl .

On-Surface Synthesis of a Five-Membered Carbon Ring from a Terminal Alkynyl Bromide: A [4 + 1] Annulation.

We report an on-surface synthesis of five-membered carbon ring via a [4 + 1] annulation reaction, starting from a simple terminal alkynyl bromide, 4-(bromoethynyl)biphenyl, on Ag(110). The combination of scanning tunneling microscopy (STM), synchrotron radiation photoemission spectroscopy (SRPES), and density functional theory (DFT) calculations unravel the reaction pathway and mechanism. Three basic reaction steps are involved, successively including the formation of alkynyl-Ag-alkynyl bridged organometallic dimer, the generation of alkylidene carbene intermediate, and the final [4 + 1] annulation involving a hydrogen transfer step.

In Situ Investigations of Al/Perovskite Interfacial Structures.

Interfacial properties of perovskite layers and metal electrodes play a crucial role in device performance and long-term stability of perovskite solar cells. In this work, we performed a comprehensive study of the interfacial structures and ion migration at the interface of a CHNHPbI perovskite layer and an Al electrode using in situ synchrotron radiation photoemission spectroscopy measurements. It was found that the Al electrode can react with the perovskite layers, leading to the formation of aluminum iodide species and the bonding between Al and N, as well as the reduction of Pb ions to metallic Pb species at the interface.

Reaction selectivity of homochiral versus heterochiral intermolecular reactions of prochiral terminal alkynes on surfaces.

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge. Here, competing reactions of a prochiral alkyne on Ag(111): two-dimensional (2D) homochiral Glaser coupling and heterochiral cross-coupling with a Bergman cyclization step have been examined. We demonstrate control strategies in steering the reactions between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters, as confirmed by high-resolution scanning probe microscopy (SPM).

Sequence-Defined Macrocycles for Understanding and Controlling the Build-up of Hierarchical Order in Self-Assembled 2D Arrays.

Anfinsen's dogma that sequence dictates structure is fundamental to understanding the activity and assembly of proteins. This idea has been applied to all manner of oligomers but not to the behavior of cyclic oligomers, aka macrocycles. We do this here by providing the first proofs that sequence controls the hierarchical assembly of nonbiological macrocycles, in this case, at graphite surfaces.

Supramolecular Tessellations at Surfaces by Vertex Design.

Assembly and tessellation of organic species at surfaces are important for the design of advanced materials, particularly for the development of spontaneous self-assemblies of supramolecular systems of increasing complexity. However, there are few examples where the ability to steer the system between supramolecular tessellations has been achieved. Here, we demonstrate a series of steps to reduce and then restore molecular symmetry; those variations impact vertex symmetry and thus generate a series of tessellations that reflect the molecular symmetry.

Surface Self-Assembly, Film Morphology, and Charge Transport Properties of Semiconducting Triazoloarenes.

Surface-assisted molecular self-assembly is a powerful strategy for forming molecular-scale architectures on surfaces. These molecular self-assemblies have potential applications in organic electronics, catalysis, photovoltaics, and many other technologies. Understanding the intermolecular interactions on a surface can help predict packing, stacking, and charge transport properties of films and allow for new molecular designs to be tailored for a required function.

Multi-electron Reduction Capacity and Multiple Binding Pockets in Metal-Organic Redox Assembly at Surfaces.

Metal-ligand complexation at surfaces utilizing redox-active ligands has been demonstrated to produce uniform single-site metals centers in regular coordination networks. Two key design considerations are the electron storage capacity of the ligand and the metal-coordinating pockets on the ligand. In an effort to move toward greater complexity in the systems, particularly dinuclear metal centers, we designed and synthesized tetraethyltetra-aza-anthraquinone, TAAQ, which has superior electron storage capabilities and four ligating pockets in a diverging geometry.

Kinetic Strategies for the Formation of Graphyne Nanowires via Sonogashira Coupling on Ag(111).

The selection of a reaction pathway with high energy barrier in a multipath on-surface reaction system has been challenging. Herein, we report the successful control of the reaction system of 1,1'-biphenyl-4-bromo-4'-ethynyl (BPBE) on Ag(111), in which three coupling reactions (Glaser, Ullman, Sonogashira) are involved. Either graphdiyne (GDY) or graphyne (GY) nanowires can be formed by distinct kinetic strategies.

Amphiphile self-assembly dynamics at the solution-solid interface reveal asymmetry in head/tail desorption.

Amphiphilic alkoxybenzonitriles (ABNs) of varying chain length are studied at the solution/graphite interface to analyze dynamics of assembly. Competitive self-assembly between ABNs and alkanoic acid solvent is shown by scanning tunneling microscopy (STM) to be controlled by concentration and molecular size. Molecular dynamics (MD) simulations reveal key roles of the sub-nanosecond fundamental steps of desorption, adsorption, and on-surface motion.

Redox Isomeric Surface Structures Are Preferred over Odd-Electron Pt.

The formation of metal-ligand coordination networks on surfaces that contain redox isomers is a topic of considerable interest and is important for bifunctional metallochemistry, including heterogeneous catalysis. Towards this end, a tetrazine with two electron withdrawing pyrimidinyl substituents was co-deposited with platinum metal on the Au(100) surface. In a 2:1 metal:ligand ratio, only half of the platinum is oxidized to the +2 oxidation state, with the remainder coordinating to the ligand without charge transfer, as Pt .

Supramolecular Assemblies on Surfaces: Nanopatterning, Functionality, and Reactivity.

Understanding how molecules interact to form large-scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those that are mediated by coordinated metal centers or substrates are discussed.

Redox-active ligand controlled selectivity of vanadium oxidation on Au(100).

Metal-organic coordination networks at surfaces, formed by on-surface redox assembly, are of interest for designing specific and selective chemical function at surfaces for heterogeneous catalysts and other applications. The chemical reactivity of single-site transition metals in on-surface coordination networks, which is essential to these applications, has not previously been fully characterized. Here, we demonstrate with a surface-supported, single-site V system that not only are these sites active toward dioxygen activation, but the products of that reaction show much higher selectivity than traditional vanadium nanoparticles, leading to only one V-oxo product.

From Foldable Open Chains to Shape-Persistent Macrocycles: Synthesis, Impact on 2D Ordering, and Stimulated Self-Assembly.

Small molecule self-assembly at surfaces offers an efficient route to highly ordered organic films that can be programmed for a variety of chemical and electronic applications. The success of these materials depends on the ability to program intermolecular interactions to guide precise structural ordering. Toward this objective, we have designed and synthesized a series of bis(triazolo)benzene-based π-conjugated molecules.

Complex molecular surfaces and interfaces: concluding remarks.

This paper is derived from our concluding remarks presentation and the ensuing conversations at the Faraday Discussions meeting on Complex Molecular Surfaces and Interfaces, Sheffield, UK, 24th-26th July 2017. This meeting was comprised of sessions on understanding the interaction of molecules with surfaces and their subsequent organisation, reactivity or properties from both experimental and theoretical perspectives. This paper attempts to put these presentations in the wider context and focuses on topics that were debated during the meeting and where we feel that opportunities lie for the future development of this interdisciplinary research area.

Physical and chemical model of ion stability and movement within the dynamic and voltage-gated STM tip-surface tunneling junction.

The interaction and mobility of ions in complex systems are fundamental to processes throughout chemistry, biology, and physics. However, nanoscale characterization of ion stability and migration remains poorly understood. Here, we examine ion movements to and from physisorbed molecular receptors at solution-graphite interfaces by developing a theoretical model alongside experimental scanning tunneling microscopy (STM) results.

Multifunctional Tricarbazolo Triazolophane Macrocycles: One-Pot Preparation, Anion Binding, and Hierarchical Self-Organization of Multilayers.

Programming the synthesis and self-assembly of molecules is a compelling strategy for the bottom-up fabrication of ordered materials. To this end, shape-persistent macrocycles were designed with alternating carbazoles and triazoles to program a one-pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF6 (-) , with surprisingly high affinities (β2 =10(11)  M(-2) in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K2 /K1 )=1200.

Two- and Three-Electron Oxidation of Single-Site Vanadium Centers at Surfaces by Ligand Design.

Rational, systematic tuning of single-site metal centers on surfaces offers a new approach to increase selectivity in heterogeneous catalysis reactions. Although such metal centers of uniform oxidation states have been achieved, the ability to control their oxidation states through the use of carefully designed ligands had not been shown. To this end, tetrazine ligands functionalized by two pyridinyl or pyrimidinyl substituents were deposited, along with vanadium metal, on the Au(100) surface.