Resolution of optically active tris- and bis(diketonato)metal(III) complexes and their monolayer properties at an air–water interface

Abstract

The monolayer properties of tris- and bis(diketonato)metal(iii) complexes were investigated at the air–water interface. The following eight complexes were synthesized: [Cr(acacNO₂)₃ ] (acacNO₂=3-nitropentane-2,4-dionato), [Co(acacNO₂)₃ ], [Ru(PHE)₃ ] (PHE=1,3-diphenylpropane-1,3-dionato), [Ru(HPD)₃ ] (HPD=heptane-3,5-dionato), [Ru(NND)₃ ] (NND=nonane-4,6-dionato), [Ru(DMH)₃ ] (DMH=2,6-dimethylheptane-3,5-dionato), fac-[Ru(acacF₃)₃ ] (acacF₃=1-1,3-bis(trifluoromethyl)propane-1,3-dionato) and [Ru(acac)₂(PHE)]. When these complexes were eluted with a methanol–chloroform mixture on a column packed with Δ-[Ru(phen)₃ ]²⁺ /laponite, resolution was achieved for [Cr(acacNO₂)₃ ], [Co(acacNO₂)₃ ], [Ru(HPD)₃ ], [Ru(NND)₃ ] and [Ru(acac)₂(PHE)]. To study the monolayer behavior, a chloroform solution of a ruthenium(iii) complex was spread onto a water surface and a surface pressure–molecular area (π–A) curve was measured. The π–A curves for [Ru(DMH)₃ ], fac-[Ru(acacF₃)₃ ] and [Ru(NND)₃ ] were reversible. The π–A curves for other compounds displaced irreversibly towards smaller molecular areas on the second compression, indicating that the compounds formed microcrystallites under high surface pressure. In the case of [Ru(NND)₃ ], the stereochemical effects on monolayer formation were studied by comparing the π–A curves between a racemic mixture and an enantiomer. As a result, the racemic mixture of the complex was found to form a more compact monolayer than the pure enantiomer.