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Dimerization and Self-Assembly of Aromatic C-Nitroso Compounds

Aromatic C-nitroso compounds can appear as nitroso monomers, and Z- and E-azodioxy dimers. In solution, there is an equilibrium between monomers and dimers which is usually shifted towards the monomers at ambient conditions. However, lowering of solution temperature or crystallization favor dimerization. We studied possible dimerization and/or oligomerization of several new aromatic dinitroso derivatives differing in the spacer group between the aromatic rings. Compounds with multiple aromatic nitroso groups are interesting because thay can form oligomeric and polymeric azodioxides. Solution-state structures and nitroso monomer-azodioxide equilibria of aromatic dinitroso compounds were investigated by one- and two-dimensional variable temperature 1H NMR spectroscopy and quantum chemical calculations.1 Inspection of NMR spectra revealed that aromatic dinitroso compounds dimerize at low temperatures yielding the mixture of monomers and Z- and/or E- azodioxides. The proton chemical shifts of nitroso monomer-azodioxide mixtures were assigned and validated by DFT calculations. In most cases, a preference towards the formation of Z-dimer was observed. The ability of aromatic C-nitroso compounds to dimerize could be used for design of self-assembled bilayers on metal surfaces (Figure 1). Our studies suggested that adsorption of nitrosobenzene derivatives, functionalized with sulfur headgroups, on an Au(111) surface results with the formation of ordered self-assembled monolayers and bilayers with molecules arranged into hexagonal structures.2 More recently, we investigated the possibility of self-assembly and dimerization of sulfur-containing aromatic dinitroso compounds, with nitroso groups in mutual meta-position, on gold surface.3 The results demonstrated that aromatic dinitroso compounds dimerize on an Au(111) surface by forming bilayers through E-azodioxide bonds. However, adlayers of dinitroso compounds are less ordered when compared to those of mononitroso compounds probably due to the steric hindrance of meta-situated nitroso groups.

Aromatic C-nitroso compounds, Dimerization, Self-assembly

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