Two crystal forms (alpha and beta) of a novel halogen bridged one-dimensional Ni-III-Br-Ni-III compound, {[Ni(en)(2)Br](ClO4)(2)}infinity (en=C2H8N2), have been prepared by electrochemical oxidation. X-ray crystal structure analysis of the or form revealed that a bridging Br ion is located on the midpoint between two Ni atoms and the Ni-Br distance of 2.640(1) Angstrom is significantly elongated by introducing a bulky ClO4- ion as a counter anion. An average Ni-Br distance of 2.693(2) Angstrom for the beta form can be estimated from the lattice parameter along the chain. X-ray photoelectron spectra indicate that both forms have the Ni-III-X-Ni-III structure. Magnetic susceptibility data for both forms show strong antiferromagnetic coupling (J=-1700) between electronic spins (S=1/2) localized on the Ni-III on the linear chain.