Covalent assembly of a two-dimensional molecular ‘‘sponge’’ on a Cu(111) surface:Confined electronic surface states in open and closed pores

We present a new class of on-surface covalent reactions, formed between diborylene-3,4,9,10-tetraaminoperylene and trimesic acid on Cu(111), which gives rise to a porous 2D-'sponge'. This aperiodic network allowed the investigation of the dependence of electron confinement effects upon pore size, shape and even in partial confinement

Magnetic exchange coupling of a synthetic Co(II)-complex to a ferromagnetic Ni substrate

On-surface assembly of a spin-bearing and non-aromatic porphyrin-related synthetic Co(II)-complex on a ferromagnetic Ni thin film substrate and subsequent magnetic exchange interaction across the interface were studied by scanning tunnelling microscopy (STM), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and density functional theory +U (DFT + U) calculations

Physics and chemistry at surfaces : exploring molecular architectures and their properties

In this thesis we combine surface chemistry and surface physics to architecture molecular layers in a bottom-up approach. The formation of self-assembled molecular structures at surfaces on the basis of dipole-dipole interactions, H-bonding, metal coordination and covalent bonding is studied. The molecules of different structure and with specific functional groups are investigated on selected substrates, namely Au(111), Ag(111), Cu(111), Cu(100) or Bi reconstructed Cu(100). A number of model cases for controlling on-surface architectures and their properties has been found and is reported about in this thesis: 1) Architecture control of a coordination polymer, comprised from chiral and flexible molecular building blocks, by tuning of the intermolecular bonding motif; 2) Chirality transfer in a 1D coordination polymer formed from chiral molecules; 3) Dimensionality (0D, 1D, 2D) control via selection of the transition metal adatom, which modifies a ligand and participates in an on-surface coordination complex; 4) Demonstration of a 2D molecular ‘sponge’, created on the basis of a borylene derived covalent link with angular flexibility; 5) Investigation of confined 2D electron states in quantum boxes of different size and shape; 6) Self -sorting of bi-molecular system in a 2D array by the coulomb interaction of the surface dipole which depends on band-alignment, charge transfer and the screening in the substrate. Specifically, we show that chiral and flexible [7]helicene molecules with cyano-groups, covalently attached in symmetric positions, give rise to a 1D arrangement. The intrinsically chiral species imprints its chirality onto the weakly H-bonded assembly, which occurs if molecules are deposited on samples held at low (~90 K) temperatures. This imprint vanishes under the influence of stronger metal-coordination bonds formed after providing metal coordination centers to the H-bonded assembly. The flexibility of the helicene as well as the competition between intermolecular and molecule-surface interactions allow the coordinated chains to assemble in structures with the mirror symmetry apparently being reduced. The next important issue, addressed in this thesis, is the on-surface modification of the ligand as an approach to control the dimensionality of the resulting on-surface polymer. We present a novel metal-specific reaction of amino- /imino- functionalized perylene derivatives. This precursor is modified upon addition of Co, Fe or Ni at room-temperature into an endo-ligand. In contrast, the presence of Cu adatoms in conjunction with thermal activation leads to the formation of an exo-ligand. Thus the type of metal ligand defines whether a 1D or 2D coordinated polymer can be formed. We show that borylene-functionalized molecules react upon thermal activation with trimesic acid in a novel on-surface reaction. Moreover, the covalent connection, formed in this reaction, exhibits a high degree of flexibility and allows for the formation of the differently sized pores. The resulting molecular ‘sponge’, created this way, serves as a template confining the surface state electrons. We investigate the effect of size and shape of the pores on this quantum phenomenon. Furthermore, we present a new way of creating highly-ordered bimolecular self-sorted chessboard arrays. The bi-component mixture of Mn-phthalocyanine (MnPc) and Cu-phthalocyanine (CuPc) on Bi/Cu(100) self-assembles without participation of any chemical bonding or molecular functionalization but only on the basis of the lateral 2D Coulomb interactions. We resolve charge-transfer channels of two types, directing the supramolecular self-assembly: one oriented perpendicular to the substrate surface, the other oriented in-plane. These investigations are performed in ultra-high vacuum conditions (UHV) with the use of variable temperature Scanning Tunneling Microscopy / Spectroscopy (STM/STS), X-Ray Photoelectron Spectroscopy (XPS) and synchrotron-based Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The experimental results are supported by Density Functional Theory (DFT) calculations, performed by research partners

Probing the spatial and momentum distribution of confined surface states in a metal coordination network

The Shockley surface state on Cu(111) reacts sensitively to the perturbation by molecular adsorbates on the surface. In the porous structure of a metal-coordinated molecular network on Cu(111), the surface state is confined to a series of discrete states. Energy and momentum of eigenstates in the pores are related to both the energy dispersion of the free surface state and the geometric and energetic details of the confining barrier formed by the molecular network. The penetration of the confined state into the barrier is found to be sensitive to the constituting architectural elements

CCDC 988044: Experimental Crystal Structure Determination

Related Article: Aneliia Shchyrba, Susanne C. Martens, Christian Wäckerlin, Manfred Matena, Toni Ivas, Hubert Wadepohl, Meike Stöhr, Thomas A. Jung, Lutz H. Gade|2014|Chem.Commun.|50|7628|doi:10.1039/C4CC02463J,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Controlling the Dimensionality of On-Surface Coordination Polymers via Endo- or Exoligation

The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the predetermined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo- or heterometal adatoms, which may also play a role in the molecular transformation. The amino-functionalized perylene derivative, 4,9-diaminoperylene quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (-1 H2 or -3 H2) depending on the nature of the present adatoms (Fe, Co, Ni or Cu). In this way, the molecule is converted to an endo- or an exoligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either 1D or 2D coordination polymers

Chirality Transfer in 1D Self-Assemblies:Influence of H-Bonding vs Metal Coordination between Dicyano[7]helicene Enantiomers

<p>Chiral recognition as well as chirality transfer in supramolecular self-assembly and on-surface coordination is studied for the enantiopure 6,13-dicyano[7]helicene building block. It is remarkable that, with this helical molecule, both H-bonded chains and metal-coordinated chains can be formed on the same substrate, thereby allowing for a direct comparison of the chain bonding motifs and their effects on the self-assembly in experiment and theory. Conformational flexure and both adsorbate/adsorbent and intermolecular interactions can be identified as factors influencing the chiral recognition at the binding site. The observed H-bonded chains are chiral, however, the overall appearance of Cu-coordinated chains is no longer chiral. The study was performed via scanning tunneling microscopy, X-ray-photoelectron spectroscopy and density functional theory calculations. We show a significant influence of the molecular flexibility and the type of bonding motif on the chirality transfer in the ID self-assembly.</p>

Controlling the Dimensionality of On-Surface Coordination Polymers via Endo- or Exoligation

The formation of on-surface coordination polymers is controlled by the interplay of chemical reactivity and structure of the building blocks, as well as by the orientating role of the substrate registry. Beyond the predetermined patterns of structural assembly, the chemical reactivity of the reactants involved may provide alternative pathways in their aggregation. Organic molecules, which are transformed in a surface reaction, may be subsequently trapped via coordination of homo- or hetero­metal adatoms, which may also play a role in the molecular transformation. The amino-functionalized perylene derivative, 4,9-diamino­perylene quinone-3,10-diimine (DPDI), undergoes specific levels of dehydrogenation (−1 H₂ or −3 H₂) depending on the nature of the present adatoms (Fe, Co, Ni or Cu). In this way, the molecule is converted to an endo- or an exoligand, possessing a concave or convex arrangement of ligating atoms, which is decisive for the formation of either 1D or 2D coordination polymers