Monolayers of novel calix[4]arene derivative and its palladium(II) complexes formed at the air-water interface

5,11,17,23-Tetra-tert-butyl-25,27-di{[(2′-amino-4′- methylthio)butyryl]aminoethoxy}- 26,28-dihydroxycalix[4]-arene (L) and its mono- and binuclear palladium(II) complexes (PdLCl₂ and Pd₂LCl₄) were synthesized. Their monolayers at the air-water interface were investigated by film balance measurements (compression/expansion experiments, area relaxation experiments, viscosity measurements) and Brewster angle microscopy. The monolayer of L is inclined to form domains and multilayers, while the monolayer of PdLCl₂ demonstrates good reversibility and high collapse pressure. The monolayer formed by Pd₂LCl₄ exhibits extraordinary cohesiveness, stability, and robustness. Its extraordinary properties are likely due to the intermolecular cross-linkage of precursor complex of Pd₂LCl₄ via strong chloride bridges. This provides an example of improving mechanical properties of film through intermolecular metal complexing.