Synthesis and spectroscopic studies of cobalt(III) complexes of the chiral pendant-arm macrocycle N,N′,N″-tris[(2S)-2-hydroxypropyl]-1,4,7-triazacyclononane (H3L); crystal structure of the hydrogen-bridged dimer [CoLH3LCo][PF6]3

Abstract

The preparation of the chiral macrocyclic ligand N,N′,N″-tris[(2S)-2-hydroxypropyl]-1,4,7-triazacyclononane (H₃L) by reaction of (S)-propylene oxide with 1,4,7-triazacyclononane is described. The ligand forms a complex with Co^III whose spectroscopic properties are markedly pH dependent. The crystal structure of the [PF₆]^– salt of the principal basic form of the complex has been determined and shows that the compound is a dimer, [CoLH₃LCo][PF₆]₃. The spectroscopic properties, including the circular dichroism, of the complex in neutral, acidic and basic non-aqueous media are discussed.