Multistep redox sequences of azopyridyl (L) bridged reaction centers in stable radical complex ions (μ-L)MCl(η5-C5Me5)2$\surd$+, M = Rh or Ir: Spectroelectrochemistry and high-frequency EPR spectroscopy

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Dalton Transactions, (2003)
DOI: 10.1039/B305311C


The dinuclear complex cations (μ-L)MCl(η5-C5Me5)2n, M = Rh or Ir and L = abpy (= 2,2'-azobispyridine) or abcp (= 2,2'-azobis(5-chloropyrimidine)), could be isolated as paramagnetic hexafluorophosphates (n = 1+) or, for M = Ir, as diamagnetic bis-hexafluorophosphates (n = 2+). In addn. to the reversible one-electron process as indicated by this convertibility there are two successive chloride-releasing redn. steps, sepd. by unusually large potential differences DEEC between 0.75 V (Rh2/abpy) and 1.14 V (Ir2/abcp), leading to the spectroelectrochem. characterized complexes (η5-Me5C5)M(μ-L)MCl(η5-C5Me5)+ and (m-L)M(h5-C5Me5)2. This large splitting of DEEC establishes the capability of azopyridyl bridges for mediating efficient metal-metal communication beyond mere electron transfer. The neutral complexes (m-L)M(h5-C5Me5)2 are distinguished by a series of intense absorption bands in the near IR, the lowest absorption energies being displayed by the Ir2/abcp combination. The stable electron reservoir intermediates (μ-L)MCl(η5-C5Me5)2+ were identified as complexes of L.- anion radicals via their small g anisotropy as measured through high-frequency (\textgreater200 GHz) EPR spectroscopy. on SciFinder(R)



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