Crystallographic data are presented for a series of Os(TV-Vr) hydrazido complexes. The structural changes with electron content including a shortening of the Os-N bond and an increase in the Os-N-N angle from Os(IV) to Os(VI) can be rationalized by an electronic structural model. This model predicts an increase in electron donor character of the hydrazido ligand from four to six electrons from Os(IV) to Os(VI). The structures of trans-[Os-VI(tpy)(Cl)(2)(NN(CH2)(4)O)](2+) and cis-[Os-IV(tpy)(Cl)(NCCH3)(NN(CH2)(4)O)](+) are illustrated.