The synthesis, UV-vis spectra, and electrochemical behavior of the nitrile-bonded trans-[(RuCl)-Cl-II(cyclam)(4-NCpyH(+))](BF4)(2) (4-Ncpy = 4-cyanopyridine; cyclam = 1,4,8,11-tetraazacyclotetradecane) and of trans-[Ru-III-Cl(cyclam)(NHC(O)-4-pyH(+))](2+) are described. The UV-vis spectrum of the Ru(H) nitrile complex shows a MLCT band at 549 mn at pH 1, which is shifted to 440 mn at pH similar to6, for the unprotonated species. trans-[Ru-II- CI(cyclam)(4-NCpyH(+))](2+) was electrolytically oxidized (+600 mV vs Ag/AgCl) at pH I to Ru(III), followed by hydrolysis (k = 0.25 s(-1)) of the coordinated nitrile to give trans-[(RuCl)-Cl-III(cyclam)(NEC(O)-4-pyH(+))](2+), in which the an-tide is deprotonated and coordinated through nitrogen. The identity of the species is pH dependent, the nitrogen-bonded amide prevailing at low pH (<7), but the oxygen-bonded amide is formed through linkage isomerization at higher pH (>8). Reduction of trans-[(RuCl)-Cl-III(cyclam)(NHC(O)-4-pyH)](2+) in acidic media does not result in fast aquation (k = similar to2.4 x 10(-5) s(-1)) as for other amides on ruthenium(H) pentaammine, but instead linkage isomerization occurs, resulting in the oxygen-bonded species, with an estimated rate constant of similar to2 x 10(-2) s(-1), smaller than in the pentaammine analogues.