Sterically hindered co-ordination sites in metal complexes. Part 2. Structural characterisation of two ligand conformations in the nickel(II) complex of the ‘fly-over’ ligand 2,2′-tetramethylenedioxydi(8-N-salicylideneiminonaphthalene)

Abstract

The crystal and molecular structure of the title complex has been determined at 295 K from three-dimensional X-ray diffraction data measured by counter techniques. The complex crystallises in the monoclinic space group P2₁/c with a= 18.631(1), b= 35.524(2), c= 9.756(1)Å, β= 111.21(1)°, U= 6 019.6 ų, and Z= 8. The structure has been solved by conventional Patterson and Fourier techniques and refined by block-diagonal least squares to final residuals of R= 0.043, R′= 0.058 for 7 179 independent reflections with I/σ(I) 3.0. The trans-planar ‘capped’ structure proposed in Part 1 is confirmed (Ni–O, mean 1.820 Å; Ni–N, mean 1.910 Å) although it emerges that the dimensions and shape of the cavity are markedly sensitive to which of two conformations is adopted by the polymethylene bridging group. The details of the structures of the two independent molecules are discussed with respect to the potential of Schiff-base compounds of this type to serve as possible models for oxygen carriers in biological systems.