Synthesis of chiral self-assembling rhombs and their characterization in solution, in the gas phase, and at the liquid-solid interface

Chiral, enantiopure metallo-supramolecular rhombs self-assemble in solution through coordination of bis-pyridyl-substituted ligands with (en)M(NO ₃)₂ (en = ethylenediamine, M = Pd^II, Pt ^II). Characterization by NMR and CD spectroscopy in solution and by ESI-FT-ICR mass spectrometry in the gas phase suggests that an equilibrium exists in water/methanol of a major 2:2 complex and a minor 3:3 complex of ligands and metal corners. In the gas phase, doubly charged 2:2 complexes fragment into two identical singly charged halves followed by metal-mediated C-H and C-C bond activation reactions within the ethylenediamine ligands. Electrochemical scanning tunneling microscopy (EC-STM) provides in situ imaging of the complexes even with submolecular resolution. Flat-lying rhombs are deposited under potential control from an aqueous electrolyte on a Cu(100) electrode surface precovered by a tetragonal pattern of chloride anions from the supporting electrolyte. Chirality induces the formation of only one domain orientation. Density functional calculations help to interpret the STM images.