The mpz+/mpz.bul. pair as organic analog of the NO+/NO.bul. ligand redox system (mpz = N-methylpyrazinium). A combined electrochemical and spectroscopic study (UV/Vis/NIR, IR, EPR) of complexes (mpz)M(CN)52-/3- (M = Fe, Ru, Os). Inorganic Chemistry, (36)14:2969--2974, 1997. [PUMA: complex;visible cyano pentacyano methylpyrazinium IR electrochem complex metal redn complex;IR spectra complex;iron spectroscopy;UV complex;osmium nitrosyl spectroscopy;electrochem spectroscopy;ruthenium complex;EPR spectroscopy;methylpyrazinium analog;near]