Structures of three cis-beta1 and three cis-beta2 isomers of [Co(trien)(aminoacidato)]2+ complexes

The crystal structures and absolute configurations of three cis-beta(1) and three cis-beta(2) isomers of [Co(trien)(L-aminoacidato)](2+), namely beta(1)-Lambda(SSS)(lambdalambdadelta)/(lambdadeltadelta)-[Co(trien)(L-isoleucinato)](ClO(4))(2), L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate (1), beta(1)-Lambda(SRS)(lambdadeltalambda)-[Co(trien)(L-valinato)](ClO(4))(2), L-valinato(triethylenetetramine)cobalt(III) diperchlorate (2), beta(1)-Delta(RSS)(deltalambdadelta)-[Co(trien)(L-pyroglutamato)]ClO(4), L-pyroglutamato(triethylenetetramine)cobalt(III) perchlorate (3), beta(2)-Delta(RRS)(deltadeltalambda)-[Co(trien)(L-isoleucinato)]I(2).H(2)O, L-isoleucinato(triethylenetetramine)cobalt(III) diiodide monohydrate (4), beta(2)-Delta(RRS)(deltadeltalambda)-[Co(trien)(L-isoleucinato)](ClO(4))(2).2H(2)O, L-isoleucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (5), and beta(2)-Lambda(SSS)(deltalambdalambda)[Co(trien)(L-leucinato)](ClO(4))(2).2H(2)O, L-leucinato(triethylenetetramine)cobalt(III) diperchlorate dihydrate (6), have been determined. Both beta(1) and beta(2) 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 beta(1) and beta(2) 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 beta(1) isomer by direct reaction between amino acids and cis-alpha-[Co(trien)Cl(2)]Cl in mildly basic solution.