Ab-initio X-ray powder diffraction structural characterization of co-ordination compounds: polymeric [{MX2(bipy)}n] complexes (M = Ni or Cu; X = Cl or Br; bipy = 4,4′-bipyridyl)

Abstract

In the absence of crystals of suitable quality, the crystal structures of five [MX₂(bipy)](M = Ni or Cu; X = Cl or Br; bipy = 4,4′-bipyridyl) phases were determined, ab initio, from powder diffraction data. The nickel compounds contain symmetrically bridging halides and trans-D_4h octahedrally co-ordinated metal atoms; on the contrary, the co-ordination about the copper atoms in [CuBr₂(bipy)] is square planar, with long Cu ⋯ Br contacts in the axial direction, due to Jahn–Teller distortion. Interestingly, [CuCl₂(bipy)] is dimorphic; both in the orthorhombic and in the monoclinic phases, the copper co-ordination is substantially square planar as in the bromide analogue, but none of the two phases is isomorphous to it.