There is an extensive reactivity chemistry between trans-[Os-VI(tpy)(Cl)(2)(N)](+) (1) (tpy = 2,2':6',2"-terpyridine) and N-3(-) Reaction of 1 with N-3(-) in CH2Cl2 or acetone occurs by electron transfer to give trans,trans-(tpy)(Cl)(2)Os-II(N-2)Os-II(Cl)(2)(tpy). In CH3N, trans-Os-II(tpy)(Cl)(2)(N-2) forms but undergoes solvolysis to give trans-Os-II(tpy)(Cl)(2)(CH3CN). 1 reacts with excess N-3(-) in CH3CN to give Os-II(tpy)(Cl)(2)(5-CH3-tetrazolate), which has been characterized by X-ray crystallography. This is the first known Os-tetrazolato complex. 1 reacts with N-3(-) in the presence of CS2 to give trans-[Os-II(tpy)(Cl)(2)(NS)](+), SCN-, and N-2.