Synthesis, geometrical and absolute configuration of the tris(S-arginine)cobalt(III) trinitrate isomers and synthesis and molecular structure of (-)589-anti(N)-Δ-cis(N),cis(O)-Λ-cis(N),cis(O)-di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) tetranitrate tetrahydrate

In a direct synthesis reaction of the tris(aminocarboxylato)cobalt(III) complexes with S-arginine all four theoretically possible tris(S-arginine)cobalt(III) diastereomers were obtained as tripositive complex ions. Besides, one out of 24 theoretically possible isomers of di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) tetrapositive ion was obtained. Geometrical and absolute configurations of the tris(S-arginine)cobalt(III) isomers were determined by electronic and CD spectroscopy. The molecular structure of the (-)₅₈₉-anti(N)-Δ-cis(N),cis(O)-Λ-cis(N),cis(O)-di-μ-hydroxo-tetrakis(S-arginine)dicobalt(III) ion was solved by X-ray crystal structure analysis. The complexes obtained represent the first examples of cationic aminocarboxylato complexes of this type. For the first time the formation of the di-μ-hydroxo-tetrakis(aminocarboxylato)dicobalt(III) complex has been observed as a reaction concurrent to the formation of tris(aminocarboxylato)cobalt(III) complexes. Finally, the stereoselectivity of S-arginine in the tris(S-arginine)cobalt(III) isomers synthesis was discussed.