Multiple mixed-valence behavior in trans,trans-[(tpy)(Cl)2Os(III)(mu-1,3-N3)Os(III)(Cl)2(tpy)]+. An azido bridge from the reaction between trans-[Os(VI)(tpy)(Cl)2(N)]+ and NH3

Reaction between the Os(VI)-nitrido complex, trans-OsVI(tpy)(Cl)2(N)]PF6 (tpy = 2,2':6',2' '-terpyridine), and ammonia (NH3) under N2 in dry CH3CN gives the mu-1,3-azido bridged OsII-N3-OsII]- dimer, trans,trans-NH4(tpy)(Cl)2OsII(N3)OsII(Cl)2(tpy)]. It undergoes air oxidation to give the OsIII-N3-OsIII]+ analogue, trans,trans-(tpy)(Cl)2OsIII(N3)OsIII(Cl)2(tpy)]PF6 (OsIII-N3-OsIII]PF6), which has been isolated and characterized. The structural formulation as a mu-1,3-N3 bridged complex has been established by infrared and 15N NMR measurements on the 15N-labeled forms, OsIII-14N=15N=14N-OsIII]+, OsIII-15N=14N=15N-OsIII]+, and OsIII-15N=15N=15N-OsIII]+. Cyclic voltammetric measurements in 0.2 M Bu4NPF6/CH3CN reveal the existence of five chemically reversible waves from 1.40 to -0.12 V for couples ranging from OsV-OsIV/OsIV-OsIV to OsIII-OsII/OsII-OsII. DeltaE1/2 values for couples adjacent to the three mixed-valence forms are 0.19 V for OsIII-OsII, 0.52 V for OsIV-OsIII, and >0.71 V for OsV-OsIV. In CH3CN at 60 degrees C, OsIII-N3-OsIII]+ undergoes a 2 + 3] cycloaddition with CH3CN at the mu-N3- bridge followed by a solvolysis to give trans-OsIII(tpy)(Cl)2(5-MeCN4)] and trans-OsIII(tpy)(Cl)2(NCCH3)]PF6.