A series of 1,2-bis(arylimino)acenaphthylidenes (L1–L5) and their corresponding 4,4′-methylenebis(1-(2,6-diisopropylphenylimino)-2-(arylimino)acenaphthylene) derivatives (L6–L10) were synthesized and used to form mono-nuclear nickel bromides LnNiBr₂ (n = 1–5, Ni1–Ni5) and bi-nuclear nickel halides LnNi₂X₄ (n = 6–10: X = Br, Ni2-1–Ni2-5; n = 4, X = Cl, Ni2-6). All the organic compounds were fully characterized by FT-IR spectra, NMR measurements and elemental analysis. The nickel complexes were characterized by FT-IR spectra and elemental analysis and the molecular structures of the representative complexes Ni1, Ni2-1 and Ni2-3 were confirmed by single-crystal X-ray diffraction. Upon activation with either Et₂AlCl or MAO, all the nickel complex pre-catalysts exhibited high activity toward ethylene polymerization over the temperature range from ambient to 50 °C. In general, the bi-nuclear complexes showed a positive synergetic effect with higher activity than their mono nuclear analogs. The resultant polyethylene possessed higher molecular weight and a high degree of branching.