A new family of nickel halides (bromides Ni1-Ni5 and chlorides Ni6-Ni10) ligated by 1-(2,6-dibenzhydryl-4-nitrophenylimino)-2-(arylimino)acenaphthylene (Aryl = 2,6-Me2C6H3L1, 2,6-Et2C6H3L2, 2,6-iPr2C6H3L3, 2,4,6-Me3C6H2L4, and 2,6-Et2-4-MeC6H2L5) have been prepared and well characterized, and the scope of their catalytic properties toward the polymerization of ethylene has been investigated. Upon activation with either Et2AlCl or EASC, the nickel bromide complexes displayed better activities than their nickel chloride counterparts and produced higher-molecular-weight polyethylene in the range of 106 g mol-1 with a very narrow range of molecular weight distributions. In comparison with reference precatalysts with non-nitro substituents (CH3, F or Cl), the title complexes experienced a modest negative effect on catalytic activity upon replacement with a NO2 moiety (activity up to 4.61 × 106 g PE (mol Ni)-1 h-1 at 20 °C). Conversely, the NO2 moiety exerted a positive effect to increase the molecular weight of the resulting polyethylene, and Ni4/Et2AlCl gave polyethylene with a maximum molecular weight of as high as 32.8 × 105 g mol-1, which is not only the highest among the title complexes but also higher than any literature values reported with 1,2-diiminoacenaphthylnickel halides.