Aggregation behavior of alkylethylenediamine palladium(II) complexes in water and in water/organic solvent mixtures

Bis(N-hexylethylenediamine)palladium(II) chloride (abbreviated as [Pd(hex-en)2]Cl2) and (ethylenediamine) (N,N′-dialkylethylenediamine)palladium(II) chloride (alkyl = hexyl or octyl, i.e., [Pd(en)(dihex-en)]Cl2 or [Pd(en)(dioct-en)]Cl2), were newly prepared and their aggregation behavior was studied in water and in water/organic solvent mixtures using mainly NMR spectroscopy. The [Pd(hex-en)2]Cl2 complex is highly soluble in water and the solution shows a clear critical point of aggregation at 0.4 mol kg−1. The physical properties in solutions were compared between complexes having the same chemical formulas but different geometrical structures. The [Pd(en)(dihex-en)]Cl2 and [Pd(en)(dioct-en)]Cl2 complexes are more hydrophobic than [Pd(hex-en)2]Cl2 and [Pd(oct-en)2]Cl2, and tend to aggregate in the presence of small amounts of water in chloroform. It is characteristic that the solubility and aggregation behavior depend on the geometrical structure around the headgroup rather than the rational formula in a series of these metallosurfactants.