Coordination Amphiphile: Design of Planar-Coordinated Platinum Complexes for Monolayer Formation at an Air-Water Interface Based on Ligand Characteristics and Molecular Topology

We aim to establish the importance of molecular design for the formation of monolayers at an air-water interface within the concept "coordination amphiphile", which is based on ligand characteristics and molecular topology. For this purpose, five types of platinum complexes containing a coordination plane, including salicylaldiminato (SA) and beta-(iminomethyl)azolato (IA) complexes, were prepared where the ligand characteristics were controlled. Polymethylene-vaulted and non-vaulted complexes were then examined to assess the effects of molecular topology on interfacial activity. SA complexes tend to undergo random aggregation at an air-water interface, while the weak hydrophilicity of SA can assist in the formation of a stable monolayer if hydrophobic and hydrophilic chains are introduced to the structure. In contrast, IA complexes exhibit topological specificity; imidazolato and pyrazolato complexes form monolayers only for non-vaulted and vaulted complex, respectively. Molecular modelling and association constants of the compounds suggest that an appropriate hydrophilicity of the coordination plane and intermolecular interactions involving hydrogen bonding are important factors for monolayer formation.