Structural aspects of the synthetic oxygen-carrier NN′-ethylenebis-(salicylideneiminato)cobalt(II): structure of the addition compound with oxygen containing dimethylformamide

Abstract

The crystal structure of the oxygen addition compound of NN′-ethylenebis(salicylideneiminato)cobalt(II), [Co(salen)], of formula [Co(salen)]₂(O₂)(dmf)₂(dmf = dimethylformamide) has been determined by the three-dimensional X-ray analysis. The crystals are monoclinic with a= 28·85, b= 12·94, c= 11·31 Å, β= 118·7°, Z = 4, space group C2/c. The structure was solved by Patterson and Fourier syntheses and refined by least-squares method to R 0·075, using 1440 independent reflexions. A crystallographic two-fold axis refers the two halves [Co(salen)O(dmf)] of the molecule. Two cobalt atoms are joined by an O–O bridge. The co-ordination poly hedron of the cobalt atoms is a distorted octahedron. The tetradentate salen ligand occupies the equatorial positions with Co–N distances of 1·894 and 1·872 ± 0·006 Å and Co–O distances of 1·900 and 1·903 ± 0·006 Å. The axial positions are occupied by the oxygen atom of the dimethylformamide molecule (Co–O distance of 2·150 ± 0·007 Å) and by an oxygen atom of the O–O bridge. The Co–O (bridge) bond length is 1·910 ± 0·006 Å. The O–O bond length and the Co–O–O angle are 1·339 ± 0·006 Å and 120·3°± 0·2° respectively. The torsional angle around the O–O bond is 110·1°. The geometry of the Co–O₂–Co group suggests that the electronic structure of the O₂ bridge is different from that expected for a superoxo- or a peroxo-group.