The absolute configuration of Λ-[Co(sen)] [(R,R)(+)tart] C1.6H₂O and of Δ-[Co(sen)] [(R,R)(+)tart] C1.4. 5H₂O (sen is 5-Methyl-5-(4-amino-2-azabutyl)-3,7-diazanonane-1,9-diamine): A comment on the mode of chiral resolutions by (R,R)(+)Tartrate on the antipodal cations of cobalt(III) salts

Abstract

The X-ray crystal structures of the Λ and ∆ diastereoisomeric pair of [Co(sen)] [(R,R)(+)tart] ClnH₂O (sen is 5-methyl-5-(4-amino-2-azabutyl)-3,7-diazanonane-1,9-diamine, tart is tartrate) have been determined. Crystals of the less soluble Λ isomer, (Λ-(1); n = 6), are othorhombic, space group P2₁2₁2₁, with a 10.817(8), b 13.626(8), c 17.724(6) Å, while those of the non-preferred Λ isomer, (Λ-(1); n = 4.5), are monoclinic, space group P2₁, with a 9,469(8), b 12.116(9), c 12.132(7) Å, β 95.94(6)º. Both structures were solved by the Patterson method, and refined to R 3.8% (Λ-(1)) and 10.8% (Λ-(1)). In ∆-(1) the waters of hydration are partly disordered in the unit cell. Both crystal structures exhibit extensive hydrogen bonding; however, the mode of contact between the cation and the tartrate dianion in the two compounds is slightly different. In Λ-(1) the three amino hydrogens involved each have only one close contact to a tartrate oxygen, whereas in ∆-(1) each hydrogen has two close contacts. The mode of chiral resolution thus seems to depend on the strength of the hydrogen bonding found in this 'local block', and not simply on its ability to form such a block, since both enantiomers do so.