The synthesis of five-coordinated bis(trihalophenolato)tri (pyridine)nickel (II) and four-coordinated his (trihalophenolato)di(pyridine) nickel(II) complexes from an aqueous solution and their characterisation by FT-IR, X-ray, DSC and elemental analysis is described. The thermal polymerisation of these complexes was carried out in the solid state and in the melt. Structural analyses were performed using H-1 NMRI C-13 NMR and FT-IR spectroscopic analyses. T(g)s were determined by differential thermal analysis and the molecular weights by viscometric method. (C) 2000 Elsevier Science Ltd. All rights reserved.