Minna T. Räisänen

Functionalizing hydrogen-bonded surface networks with self-assembled monolayers

One of the central challenges in nanotechnology is the development of flexible and efficient methods for creating ordered structures with nanometre precision over an extended length scale. Supramolecular self-assembly on surfaces offers attractive features in this regard: it is a ‘bottom-up’ approach and thus allows the simple and rapid creation of surface assemblies, which are readily tuned through the choice of molecular building blocks used and stabilized by hydrogen bonding, van der Waals interactions, π–π bonding or metal coordination between the blocks. Assemblies in the form of two-dimensional open networks are of particular interest for possible applications because well-defined pores can be used for the precise localization and confinement of guest entities such as molecules or clusters, which can add functionality to the supramolecular network. Another widely used method for producing surface structures involves self-assembled monolayers (SAMs), which have introduced unprecedented flexibility in our ability to tailor interfaces and generate patterned surfaces. But SAMs are part of a top-down technology that is limited in terms of the spatial resolution that can be achieved. We therefore rationalized that a particularly powerful fabrication platform might be realized by combining non-covalent self-assembly of porous networks and SAMs, with the former providing nanometre-scale precision and the latter allowing versatile functionalization. Here we show that the two strategies can indeed be combined to create integrated network–SAM hybrid systems that are sufficiently robust for further processing. We show that the supramolecular network and the SAM can both be deposited from solution, which should enable the widespread and flexible use of this combined fabrication method.

Effects of pore modification on the templating of guest molecules in a 2D honeycomb network

1,7-Diadamantanethioperylene-3,4:9,10-tetracarboxylic diimide, (Ad-S)2–PTCDI, adsorbed on Au(111) from solution was investigated by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). (Ad-S)2–PTCDI forms a well-ordered monolayer whose structure is described by a (2√63 × √19)R19.1° chiral unit cell containing four molecules. Codeposition of (Ad-S)2–PTCDI with 1,3,5-triazine-2,4,6-triamine (melamine) yields a honeycomb network whose (7√3 × 7√3)R30° unit cell is identical to the unsubstituted PTCDI/melamine analogue. The effect of the adamantyl thioether moieties on the adsorption of guest molecules is investigated using adamantane thiol and C60. While the thioether units do not affect the packing of adamantane thiol molecules a pronounced influence is seen in the case of fullerene. Pore modification involving different combinations of enantiomers of (Ad-S)2–PTCDI give rise to distinctly different arrangements of C60 molecules. The diversity of patterns is further increased by the presence of unsubstituted PTCDI molecules.

A Supramolecular Network as Sacrificial Mask for the Generation of a Nanopatterned Binary Self-Assembled Monolayer**

Supramolecular self-assembly on surfaces has become a straightforward and flexible route for the generation of extended nanoscale structures, with porous networks serving as templates to control the arrangement of metal clusters or guest molecules. The latter includes thiols, which are particularly interesting as they afford an enormous flexibility in surface functionalization. Recently we have shown that a supramolecular network of perylene-tetracarboxylic di-imide (PTCDI) and 1,3,5-triazine-2,4,6-triamine (melamine), which involves a triple hydrogen bonding motif (Figure 1a), can be used as a template for an all-solution-based generation of periodic patterns of thiol self-assembled monolayer (SAM) nanoislands on Au(111) (Figure 1b). These network–SAM hybrid structures can be further processed in an electrochemical environment, as demonstrated by underpotential deposition (UPD) of Cu, where one atomic layer of the metal intercalates at the SAM–substrate interface but not between network and substrate (Figure 1c). While formation and modification of network–SAMhybrids demonstrate the robustness of the PTCDI–melamine network, it is nevertheless of limited stability as evidenced by its displacement upon prolonged exposure to a thiol solution. Since the formation of hybrid structures is a kinetically controlled process, substitution of the network by thiols different to those in the network pores is a potential way to produce binary SAMs (Figure 1d) over extended areas with resolution and pattern definition unmatched by other approaches such as random insertion,mixing, or lithographic techniques.However, the feasibility of this approach critically depends on the properties of the thiol islands filling the nanopores. One evident issue is their stability against replacement by the second thiol species that depends on a number of mutually dependent factors such as molecule–substrate bond strength, intermolecular interactions,

A supramolecular hydrogen-bonded network as a diffusion barrier for metal adatoms.

Confined in a molecular corral: A supramolecular network changes the mechanism by which underpotential deposition (UPD) of copper proceeds on a gold electrode modified by a self-assembled monolayer (SAM). Lateral diffusion of Cu adatoms is suppressed between adjacent cells of a network/SAM hybrid structure. Instead, UPD occurs by direct deposition into the SAM filled pores of the network, where the Cu adatoms are confined.

Mn(II) acetate: an efficient and versatile oxidation catalyst for alcohols

A homogeneous catalytic system consisting of Mn(II) acetate (18 μmol), tert-butylhydroperoxide (2.5 mmol), acetonitrile (1.5 mL) and trifluoroacetic acid (91 μmol) was developed for efficient and selective oxidation of various alcohols (1 mmol). The system yielded good to quantitative conversions (42–100%) of various secondary alcohols, such as 2-octanol, fenchyl alcohol and borneol, to their corresponding ketones. Primary alcohols, for example 1-octanol and differently substituted benzyl alcohols, were mainly converted to their corresponding carboxylic acids. Studies with a selection of hydrocarbons, tertiary amines and a cyclic ether isochroman showed that besides alcohols, other substrates can be oxidised as well.

Binding of deposited gold clusters to thiol self-assembled monolayers on Au(111) surfaces

We study the mechanisms involved in Au nanocluster deposition on thiol self-assembled monolayer modified Au(111) surfaces. Molecular dynamics simulations reveal a wide range of cluster-surface binding configurations within a very narrow deposition energy range (0.2–0.6 eV/atom for ∼2.5 nm diameter clusters). These go from noncovalent to full contact and include surprising intermediate cases in which the clusters are bound to the underlying Au(111) surface via molecular links and nanowires. Experiments show that, subsequently, the clusters are covered by thiols and slightly flattened.

Two- and three-dimensional packing diagrams of M(salophen) complexes

For better understanding of two- (2D) and three-dimensional (3D) crystal engineering of metal complexes, the 2D and 3D packing diagrams of metal salophen (=N,N′-o-phenylene-bis(salicylideneimine)) complexes are compared in detail. According to the 3D structures, determined by X-ray crystallography, N,N′-(o-phenylene)bis(4-hexyloxysalicylideneiminato)Cu(II) (1) and N,N′-(o-phenylene)bis(4-decyloxysalicylidene-iminato)Ni(II) (2) have a square-planar coordination geometry. 1 forms a host–guest complex with CH2Cl2 solvent molecule via intermolecular hydrogen bonds. In 2 the interdigitating alkyl chains allow the molecules to be packed in parallel sheets with a zigzag-type pattern while in 1 the molecules are packed in coplanar layers. In both structures the layers are connected by short {M}⋯H contacts (3.07 A in 1, 3.15 A in 2). The molecular packings in planes of the 3D structures are compared with previously determined 2D surface patterns of five equivalent Cu(II), Ni(II) and Co(II) complexes formed at the liquid–solid interface. The structures were studied at the interface by means of scanning tunneling microscopy. It is shown that in the case of 2 the 2D structures observed in the plane of a bulk crystal and at the liquid–solid interface are not comparable. As shown, even the metal ion and the alkyl chain length affect differently on the 2D and 3D packing. The role of molecular planarity on the packing diagrams is addressed by comparing the nearly planar single crystal structures of salophen complexes 1 and 2 to the structure of N,N′-ethylene-bis(4-octyloxysalicylideneiminato)Cu(II) which has a twisted salen moiety.

A One-Pot Synthesis of N-Aryl-2-Oxazolidinones and Cyclic Urethanes by the Lewis Base Catalyzed Fixation of Carbon Dioxide into Anilines and Bromoalkanes

The multicomponent assembly of pharmaceutically relevant N-aryl-oxazolidinones through the direct insertion of carbon dioxide into readily available anilines and dibromoalkanes is described. The addition of catalytic amounts of an organosuperbase such as Bartons base enables this transformation to proceed with high yields and exquisite substrate functional-group tolerance under ambient CO2 pressure and mild temperature. This report also provides the first proof-of-principle for the single-operation synthesis of elusive seven-membered ring cyclic urethanes.

Practical Method for 2‐Hydroxyphenylketimine Synthesis

Abstract A series of hydroxyphenylketimines, of which 15 are new, was synthesized in methanol at high temperature (200°C) using a sealed steel reactor. This reaction setup especially enhances the synthesis of 2‐hydroxyphenylketimines, with yields up to six times higher than those obtained with the conventional acid‐catalyzed method under refluxing conditions. In fact, some imines were achievable only by the autoclave method.

Structural and spectroscopic characterization of Cu(salen) complexes bearing long alkoxy chains

Cu(II) salen (salen = N,N′-ethylene-bis(salicylideneimine)) complexes bearing alkoxy chains of C12 (1) and C10 (2) in the salicylidene moieties were synthesized and subsequently characterized by several independent methods: single crystal X-ray diffraction, infrared spectroscopy, mass spectrometry, and UV-Vis spectroscopy. The solid state structures show that the spatial orientation and packing of the complexes are not affected by the alkyl chain length but by a coordinated solvent molecule, as demonstrated by the structure of 1 having methanol in an axial position.