The crystal structure of potassium ΛΔ-rac-2,3-butanediamine-N,N,N',N'-tetraacetatecobaltate hemihydrate

Abstract

The crystal structure of ΛΔ-K [Co(rac-bdta)] . 1/2 H2O was solved by the X-ray diffraction method and refined by the least squares method to R = 0.047 on the basis of 3 847 diffraction values. The substance crystallizes in a space group with symmetry P 1 with the following lattice parameters: a = 0.9412(5), b = 1.2166(6), c = l.5370(9)nm, α = 70.68(4), β = 73.45(4), γ = 83.24(4)°. The crystal structure consists of two symmetrically independent enantiomer pairs Δ-[Co(R,R)-bdta] and Λ-[Co(S,S)-bdta]- K+ ions and molecules of water of crystallization. The Co(III) atom is octahedrally coordinated by rac(bdta)4- forming four glycine and one ethylenediamine chelate ring. The stereospecific coordination of rac(bdta)4- is based on an energy preference for equatorially located methyl groups on the central ethylenediamine ring. Two types of strain in the [Co(rac-bdta)]- complex are derived from the three five-membered rings in the equatorial plane of the complex and repulsion between the methyl and methylene hydrogen atoms.