Metal–Organic Coordination Networks of Ferric Wheels, their Surface-supported Supramolecular Architectures and STM/STS Imaging

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Abstract
Six-membered ferric wheels [Fe6Cl6(L2)6] were generated from the corresponding N-alkylsubstituted diethanolamines (H2L2) {L2 = [®-N(CH2CH2O)2]2−; ® = Me-[CH2-]17 (3d); Me-[CH2-]19 (3e)}, calcium hydride and iron(III) chloride. Compound 3d was characterized by X-ray crystal structure analysis. The lipophilic tails of 3d interdigitate to create strands that, by lateral van der Waals interactions, pack to form 2D layers. The stacking of these sheets creates the final 3D architecture of the crystal. An elementary structure formation process of complex molecule 3d on highly oriented pyrolytic graphite (HOPG) was studied. Using scanning tunneling microscopy (STM) under ambient conditions, we succeeded in combining high-resolution topography mapping with simultaneous current–voltage characteristics (scanning tunneling spectroscopy, STS) measurements on single molecules deposited on HOPG surfaces. One of the most interesting results is that the location of the individual metal ions in their organic matrix is directly addressable by STS.