Structures of three cis-β1 and three cis-β2 isomers of [Co(trien)(aminoacidato)]2+ complexes

Abstract

The crystal structures and absolute configurations of three cis-β1 and three cis-β2 isomers of [Co(trien)(L-aminoacidato)]2+, namely β1-Λ(SSS)(λλδ)/(λδδ)-[Co(trien)(L-isoleucinato)](ClO4)2, L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate (1), β1-Λ(SRS)(λδλ)-[Co(trien)(L-valinato)](ClO4)2, L-valinato(triethylenetetramine)cobalt(III) diperchlorate (2), β1-Δ(RSS)(δλδ)-[Co(trien)(L-pyroglutamato)]ClO4, L-pyroglutamato(triethylenetetramine)cobalt(III) perchlorate (3), β2-Δ(RRS)(δδλ)-[Co(trien)(L-isoleucinato)]I2·H2O, L-isoleucinato(triethylenetetramine)cobalt(III) diiodide monohydrate (4), β2-Δ(RRS)(δδλ)-[Co(trien)(L-isoleucinato)](ClO4)2·2H2O, L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (5), and β2-Λ(SSS)(δλλ)[Co(trien)(L-leucinato)](ClO4)2·2H2O, L-leucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (6), have been determined. Both β1 and β2 isomers form inter-cation hydrogen-bonding interactions through double or triple hydrogen bonds which link the cations into helices. However, the motifs of the interactions are different in β1 and β2 isomers, resulting in different packing structures. A localized hydrophobic area is observed in the packing structure of (1), a unique feature amongst these six structures. This work describes the first synthesis of the β1 isomer by direct reaction between amino acids and cis-α-[Co(trien)Cl2]Cl in mildly basic solution.