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)
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Inorganic Chemistry 36 (14): 2969--2974 (1997)

The oxidn. and redn. behavior of (mpz)M(CN)52- between the group 8 pentacyanometalates(II) and the N-methylpyrazinium ion mpz+ was studied using spectroelectrochem. techniques (UV/visible/NIR, IR, EPR) in nonaq. and, in part, aq. media. As a further source of information on the electronic structure, the authors studied the variable solvatochromism of MLCT absorption bands in the precursor ions (mpz)M(CN)52-. The mpz-centered 1-electron redn. showed a tendency for concomitant loss of cyanide (EC process) to yield (mpz)M(CN)42-, the lability increasing in the order M = Os \textless\textless Ru \textless Fe. In contrast to the EPR spectra obtained from redn. with S2O42- in aq. media, which showed no evidence for close mpz.bul./metal assocn., the intra muros electrolysis expts. in DMSO or acetonitrile yielded the following results: The EPR spectrum that was previously assigned to (mpz)Fe(CN)53- is now ascribed to (mpz)Fe(CN)42-. Whereas the dissociatively inert osmium radical complex (mpz)Os(CN)53- is distinguished by a broad EPR signal with a rather large value giso = 2.0157, the EPR spectrum of (mpz)Ru(CN)43- reveals well-resolved sep. coupling with the 99Ru and 101Ru isotopes in natural abundance. Spectroelectrochem. and reactivity patterns of (mpz)M(CN)52- are reminiscent of results for corresponding nitrosyl complexes (NO)M(CN)52-, which suggests that the mpz+/mpz.bul. ligand redox pair can function as an org. analog of the NO+/NO.bul. redox system. on SciFinder(R)
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