Direct Observation of Chiral MetalOrganic Complexes Assembled on a Cu(100) Surface (original) (raw)
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Enantiopure Supramolecular Motifs of Self-Assembled Diamine-Based Chiral Molecules on Cu(100)
The Journal of Physical Chemistry C
The assembly of two Diphenylethylenediamine enantiomers, separately deposited on Cu(100), is investigated from the first stages of two-dimensional crystallization to the nucleation and growth of the second layer. By means of Scanning Tunneling Microscopy, we show that the chirality of the enantiomers is expressed at different levels of molecular organization. Below the monolayer completion, a disordered phase coexists with domains of a square lattice aligned with the principal crystallographic directions of the substrate. The intrinsic chirality of the molecules is only manifested through specific features contained within the corresponding unit cell. For increasing coverage, this arrangement is accompanied by a second square structure, which appears to be clockwise or counterclockwise rotated with respect to the Cu(100) directions depending on the enantiomer. The nucleation of molecular chains on top of the aligned square structure gives rise to a second layer exhibiting a striped-like configuration with remarkable left-or right-handed helicity that mirrors that of the particular enantiomer. The nearly flat configuration of the first layer molecules is confirmed by angular dependent X-ray absorption experiments and supported by molecular dynamics simulations.
Nano Letters, 2005
We report a comparative study on the 2D self-assembly of two related ditopic benzoic acid species, which have similar shape and endgroups but different backbone symmetry. High-resolution scanning tunneling microscopy data reveal how the symmetry information of molecular building blocks is readily expressed in the resulting chiral or nonchiral supramolecular networks. The underlying square Cu(100) surface steers network orientation and accounts for carboxylate formation, resulting in an unusual intermolecular hydrogen bond motif. Our results demonstrate that symmetry and chiral resolution in 2D supramolecular assembly can be controlled via the design of functional molecules and choice of substrate.
Surface-assisted coordination chemistry and self-assembly
Dalton Trans., 2006
This article discusses different approaches to build up supramolecular nanoarchitectures on surfaces, which were simultaneously investigated by scanning tunneling microscopy (STM) on the single-molecule level. Following this general road map, first, the hydrogen-bonding guided self-assembly of two different, structural-equivalent molecular building blocks, azobenzene dicarboxylic acid and stilbene dicarboxylic acid, was studied. Secondly, the coordination chemistry of the same building blocks, now acting as ligands in metal coordination reactions, towards co-sublimed Fe atoms was studied under near surface-conditions. Extended two-dimensional tetragonal network formation with unusual Fe 2 L 4/2-dimers at the crossing points was observed on copper surfaces. Complementary to the first two experiments, a two-step approach based on the solution-based self-assembly of square-like tetranuclear complexes of the M 4 L 4-type with subsequent deposition on graphite surfaces was investigated. One-and two-dimensional arrangements as well as single molecules of the M 4 L 4-complexes could be observed. Moreover, the local electronic properties of a single M 4 L 4-complexes could be probed with submolecular resolution by means of scanning tunnelling spectroscopy (STS).
Langmuir, 2004
The bonding and self-assembly of a chirally organized monolayer of alanine on the Cu(110) surface has been investigated using reflection-absorption infrared spectroscopy, low-energy electron diffraction (LEED), and scanning tunneling microscopy (STM). This multitechnique approach has enabled an in-depth understanding of the hierarchy of chirality transfer: from a single adsorbed molecule, to size-defined chiral clusters, and then to an overall chiral assembly. The data have indicated that the alanine is in its anionic form, bound to the copper surface through the oxygens of the ionized carboxylate group and the nitrogen of the neutral amino group. Importantly, the methyl group is held away from the surface, resulting in direct chirality transfer into the footprint of the adsorbed alanine molecules, with the local adsorption motif for S-alanine being the mirror image of that created for R-alanine. STM has shown that S-alanine molecules self-organize to form size-defined chiral clusters of six or eight molecules at the surface, interspersed with chiral channels of bare metal. Together, these clusters and channels further self-assemble into a chiral array with one unique chiral domain sustained across the entire surface. A similar chiral assembly, but with the mirror organization, has been observed for R-alanine. Structural models for the individual clusters are proposed, and in conjunction with LEED data, overall models for these chiral phases of both Sand R-alanine have been constructed. Overall, this adsorption system has been found to be both strongly chemisorbed and capable of extensive intermolecular H-bonding, causing stresses that lead not only to the chiral self-organization of molecules but also to a specific self-organization of the empty chiral channels and spaces that intersperse the structure which, in turn, chirally assemble across macroscopic length scales to give a surface with global organizational chirality.
Adsorption structure and bonding of trimesic acid on Cu(100)
Surface Science, 2011
Combining scanning tunneling microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy using synchrotron radiation, we have studied the adsorption and growth of trimesic acid (TMA, 1,3,5-benzenetricarboxylic acid, C 6 H 3 (COOH) 3 ) on Cu(100) in a wide range of coverages (from submonolayer to multilayer ones) at room temperature and after subsequent annealing. A series of coveragedependent TMA structures, transitions between these structures, and their properties are characterized, demonstrating the interplay between the bonding, orientation, and deprotonation reaction of adsorbed species. In particular, it is shown that the degree of deprotonation in TMA overlayers depends on the amount of deposited molecules non-monotonously, and that such behavior is well consistent with the formation mechanism proposed for the TMA/Cu(100) system. The results provide a good platform for further understanding of non-covalent interactions and self-assembly phenomena underlying the growth of supramolecular nanoassemblies of aromatic carboxylic (benzenecarboxylic) acids on metallic substrates.
The Journal of Physical Chemistry C, 2009
The self-assembly of the amino acid L-methionine on Cu(111) was investigated under ultrahigh vacuum (UHV) conditions by scanning tunneling microscopy (STM), helium atom scattering (HAS) and X-ray photoelectron spectroscopy (XPS). The system is strongly influenced by the substrate reactivity and the deposition temperature. The STM and HAS structural analysis yields that, for temperatures below 273 K, the biomolecules assemble in strings oriented with an angle of -10°with respect to the 〈110〉 axes of the substrate. For temperatures above 283 K, a regular and ordered one-dimensional (1D) phase arises following an angle of +10°with respect to the same directions. High resolution STM data of this ordered 1D arrangement evidence molecular dimerization and dimer alignment into ordered chains which are commensurate with the Cu(111) atomic lattice. XPS measurements reveal that the high temperature ordered phase consists of an exclusively anionic ensemble with a deprotonated carboxylic group and a neutral amino group, while the low temperature phase is heterogeneously composed of both zwitterionic and anionic species, depending on whether the molecules are immobilized in clusters of dimers on the free terraces or at the low-coordinated adsorption sites of the substrate step-edges. These combined results evidence a structural transformation of the supramolecular assembly which is triggered by a thermally activated process involving the underlying Cu(111) substrate and which carries the intrinsic chiral signature of the adsorbed molecular units.