Steric effects in the reversible oxygenation of cobalt–Schiff-base complexes. Part II. Crystal and molecular structure of [NN′-butylenebis-(salicylideneiminato)]pyridinecobalt( II )

The crystal structure of the title compound has been determined from three-dimensional X-ray data by Fourier methods and refined by anisotropic block-diagonal least squares to R 0·058 for 3230 independent reflections. Crystals are monoclinic, space group P21, with cell parameters a= 18·128, b= 10·597, c= 11·381 Å, and β= 100·6°, Z= 4. The two crystallographically independent molecules (A) and (B) are stereochemically non-equivalent : in (A) the cobalt atom geometry is a square pyramid with the metal atom displaced 0·21 Å towards the apical pyridine, whereas in (B) it is largely distorted towards a trigonal bipyramid. There are significant differences in the co-ordination bond lengths involving the quadridentate ligand: mean Co–O 1·905(8) in (A) and 1·939(7)Å in (B), Co–N 2·140(7) and 2·056(8)(B), and 1·887(9)Å(A). However in both molecules the butylene-bridge methyl groups are found in the bis-axial conformation, in spite of steric hindrance due to pyridine. The behaviour towards oxygenation is discussed on the basis of the structural results.