Alkyl chain length defines 2D architecture of salophen complexes on liquid-graphite interface

A series of Cu^II, Ni^II and Co^II salophen [salophen = N,N′-(o-phenylene)bis(salicylideneimine)] complexes were prepared, and their two-dimensional (2D) assemblies on a liquid-graphite interface were studied by scanning tunnelling microscopy (STM). Depending on their varying alkyl chain lengths (C₈, C₁₀ or C ₁₂), two different new adlayers, parallelogram and honeycomb, were recorded. According to STM data, the driving force for these assemblies is a subtle interplay between a maximum amount of attractive van der Waals interaction of the alkyl chains and weak hydrogen bonding of the phenoxy moieties. Thus, the alkyl chain length defines the favoured 2D structure for each metal complex. As shown here, the self-assembled monolayers of the salophen complexes studied provide an attractive approach to varying the surface architecture.