Bead-like structures and self-assembled monolayers from 2,6-dipyrazolylpyridines and their iron(II) complexes

Drop-casting acetone solutions of [Fe(bpp)(2])[BF4](2) (bpp = 2,6-di[pyrazol-1-yl] pyridine) onto a HOPG surface affords unusual chain-of-beads nanostructures. The beads in each chain are similar in size, with diameters in the range of 2-6 nm and heights of up to 10 angstrom, which is consistent with them containing between 10-50 molecules of the compound. The beads can be classified into two types, which exhibit different conduction regimes by current-imaging tunnelling spectroscopy (CITS) which appear to correlate with their positions in the chains, and may correspond to molecules containing high-spin and low-spin iron centres. Similarly drop-cast films of the complex on a gold surface contain the intact [Fe(bpp) 2][BF4] 2 compound by XPS. 4-Mercapto-2,6-di[pyrazol-1-yl] pyridine undergoes substantial decomposition when deposited on gold, forming elemental sulfur, but 4-(N-thiomorpholinyl)-2,6-di[pyrazol-1-yl] pyridine successfully forms SAMs on a gold surface by XPS and ellipsometry.