Nickel superoxide dismutase (NiSOD) is a metalloenzyme that converts O-2(center dot-) into H2O2 and O-2 by cycling between Ni-II and Ni-III oxidation states. Reduced NiSOD contains Ni-II in a square-planar N2S2 coordination environment formed by two cysteinate S atoms, an amide N, and an amine N to Ni-II. [Me4N](Ni-II(BEAAM)) represents the first NiN2S2 complex containing Ni in a mixed amine/ amide environment. [ Me4N]( NiII( BEAAM)) contains Ni - S bonds at 2.177(2) and 2.137(2) angstrom and Ni-N bonds at 1.989(7) and 1.858(6) angstrom, which compare well with the metalloenzyme. Orange solutions of [Me4N](Ni-II(BEAAM)) in MeCN are diamagnetic and stable toward O-2 for weeks. A quasireversible Ni-II/III redox couple is observed for [Ni-II(BEAAM)](NMe4) at 0.12(1) V vs Ag/AgCl. These data suggest that NiSOD utilizes the mixed amine/amide ligands to modulate the Ni-II/III redox couple to best match the O-2(center dot-) reduction/oxidation couples while maintaining O-2 stability.