Conformations of malonate chelate rings: the crystal and molecular structure of sodium (+)546ethylenediaminebis(malonato)cobaltate(III) dihydrate

Abstract

The crystal structure of Na(+)₅₄₆[Co(mal)₂(en)],2H₂O has been determined by the heavy-atom method from photographic data. Crystals are orthorhombic, space group P2₁2₁2₁, with a= 13.46(2), b= 14.24(2)c= 7.344(10)Å, and Z= 4. Refinement by full-matrix least-squares gave R 0.05 for 838 observed reflections. The absolute configuration of the complex ion is Δ, in agreement with correlations from c.d. spectra. The tris-bidentate complex has an approximate two-fold axis with the two malonate ligands adopting boat conformations and folding towards each other while the ethylenediamine ligand is skewed oblique rather than parallel to the pseudo-three-fold axis of the anion. This result confirms the prediction that chair conformations are energetically unfavoured for malonate complexes and suggests the nature of the conformation interconversions shown by solution n.m.r. studies.