Divalent and trivalent nickel complexes of 1,4,8,11-tetraazacyclotetradecane, denoted as cyclam hereafter, coordinated by methyl coenzyme M (MeSCoM-) and coenzyme M (HSCoM-) have been synthesized in the course our model studies of methyl coenzyme M reductase (MCR). The divalent nickel complexes Ni(cyclam)(RSCoM)(2) (R = Me, H) have two trans-disposed RSCoM- ligands at the nickel(II) center as sulfonates, and thus, the nickels have an octahedral coordination. The SCoM2- adduct Ni(cyclam)(SCoM) was also synthesized, in which the SCoM2- ligand chelates the nickel via the thiolate sulfur and a sulfonate oxygen. The trivalent MeSCoM adduct [Ni(cyclam)(MeSCoM)(2)](OTf) was synthesized by treatment of [Ni(cyclam)(NCCH3)(2)](OTf)(3) with ((Bu4N)-Bu-n)[MeSCoM]. A similar reaction with ((Bu4N)-Bu-n)[HSCoM] did not afford the corresponding trivalent HSCoM- adduct, but rather the divalent nickel complex polymer [-Ni-II(cyclam)(CoMSSCoM)-](n) was obtained, in which the terminal thiol of HSCoM- was oxidized to the disulfide (CoMSSCoM)(2-) by the Ni(III) center.