Iron(II) pyridine-2-carbaldehyde-2-pyridylhydrazone complexes modified with Fréchet type dendritic wedges for scanning tunneling microscopy

Iron(II) pyridine-2-carbaldehyde-2-pyridylhydrazone complexes modified with Fréchet type dendritic wedges for scanning tunneling microscopy
Marc Häusler
Scanning tunneling microscopy (STM) is a technique of big importance in studying nanoscopic phenomena. While the behaviour of organic molecules on highly ordered pyrolitic graphite (HOPG) is well examined, not many complexes have been examined and studied.
Pyridine-2-carbaldehyde-2-pyridylhydrazone (Hpaphy) was selected for its possibilities for modification. To generate a favourable interaction between Hpaphy and the HOPG substrate Fréchet type dendritc wedges were coupled to Hpaphy. For the dendritic wedges several modifications were synthesized. Of three dendritic wedges crystal structures could be obtained showing the high purity and homogeneity of the compounds.
The iron(II) Hpaphy complexes show an interesting acid-base behaviour. The acidity of the amine proton on the Hpaphy backbone is strongly enhanced in the complex allowing for easy deprotonation. The deprotonation is accompanied by strong changes in solubity behaviour and UV-vis spectra.
While the dendritic wedges and the free ligand with the dendritic wedge gave monolayers that could be examined by STM the standard methods for monolayer formation, solution casting and liquid-slid interface, did not give observable monolayers of the complex compounds on HOPG. To overcome this problem Langmuir-Blodgett experiments were conducted. One compound was then selected for a deposition experiment and examined with STM.