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)

In the absence of crystals of suitable quality, the crystal structures of five [MX(2)(bipy)] (M = Ni or Cu; X = Cl or Br; bipy = 4,4'-bipyridyl) phases were determined, nb 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.