Stereochemical Effects on Monolayer Formation of a Chiral Amphiphilic Ruthenium(III) Complex

A chiral amphiphilic ruthenium(III) complex, [Ru(acac) 2 (C12-acac)] (acac = 2,4-pentanedionato, C12-acac = 3-dodecyl-2,4-pentanedionato), has been synthesized. The complex was resolved into pure optical isomers by being eluted with methanol on a column packed with an ion-exchange adduct of Δ-[Ru(phen) 3 ] 2+ (phen = 1,10-phenanthroline) and a synthetic hectorite clay. The surface pressure−molecular area (π− A ) curves of the pure enantiomer and the racemic mixture were obtained in the temperature range 10−30 °C. The π−A curve of the pure enantiomer was little affected by the change of temperature, while that of the racemic mixture was displaced toward the larger molecular area with the increase of temperature. The pure enantiomer was concluded to form a more packed monolayer than the racemic mixture. When the monolayer of either the Δ- or Λ-enantiomer was formed on a subphase containing Δ-[Ru(phen) 3 ]Cl 2, the molecular area of the monolayer was expanded due to the binding of Δ-[Ru(phen) 3 ] 2+ in a stereoselective way. The AFM images of the chiral and racemic monolayers deposited on mica at 20 mN m - 1 showed that the chiral molecules formed an oblique lattice ( a = 0.59 nm, b = 0.55 nm, and φ = 63 °C), while the racemic mixture exhibited no two-dimensional surface order.