Extremely Strong Self-Assembly of a Bimetallic Salen Complex Visualized at the Single-Molecule Level

A bis-Zn­(salphen) structure shows extremely strong self-assembly both in solution as well as at the solid–liquid interface as evidenced by scanning tunneling microscopy, competitive UV–vis and fluorescence titrations, dynamic light scattering, and transmission electron microscopy. Density functional theory analysis on the Zn₂ complex rationalizes the very high stability of the self-assembled structures provoked by unusual oligomeric (Zn–O)_<i>n</i> coordination motifs within the assembly. This coordination mode is strikingly different when compared with mononuclear Zn­(salphen) analogues that form dimeric structures having a typical Zn₂O₂ central unit. The high stability of the multinuclear structure therefore holds great promise for the development of stable self-assembled monolayers with potential for new opto-electronic materials

Tip-Induced Chemical Manipulation of Metal Porphyrins at a Liquid/Solid Interface

Changing abruptly the potential between a scanning tunneling microscope tip and a graphite substrate induces “high-conductance” spots at the molecular level in a monolayer formed by a manganese chloride–porphyrin molecule. These events are attributed to the pulse-induced formation of μ-oxo-porphyrin dimers. The pulse voltage must pass a certain threshold for dimer formation, and pulse polarity determines the yield

Dibenzo Crown Ether Layer Formation on Muscovite Mica

Stable layers of crown ethers were grown on muscovite mica using the potassium–crown ether interaction. The multilayers were grown from solution and from the vapor phase and were analyzed with atomic force microscopy (AFM), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and surface X-ray diffraction (SXRD). The results show that the first molecular layer of the three investigated dibenzo crown ethers is more rigid than the second because of the strong interaction of the first molecular layer with the potassium ions on the surface of muscovite mica. SXRD measurements revealed that for all of the investigated dibenzo crown ethers the first molecule lies relatively flat whereas the second lies more upright. The SXRD measurements further revealed that the molecules of the first layer of dibenzo-15-crown-5 are on top of a potassium atom, showing that the binding mechanism of this layer is indeed of the coordination complex form. The AFM and SXRD data are in good agreement, and the combination of these techniques is therefore a powerful way to determine the molecular orientation at surfaces