The pyrazine-bridged diosmium(II) complex (μ-C4H4N2)Os(CN)526- was synthesized as the hexapotassium salt and was converted to the Bu4N+ salt compd. by ion exchange. Its stepwise oxidn. to the OsIII2OsII and OsIII2OsIII states was monitored spectroelectrochem. in MeCN/0.1 M Bu4NPF6 in the UV-visible-NIR and IR regions and by EPR. The OsII2 species exhibits long-wavelength solvatochromic MLCT bands at 14,800 and 18,480 cm-1. The pentaanionic mixed-valent ion has a comproportionation const. Kc of 105.8 and is distinguished by several electronic absorptions in the IR region. The bands at 1970, 2480, 4000, 5000, 7170, and 11,900 cm-1 are similar but appreciably lower in energy than those reported for the analogous complex (μ-C4H4N2)Os(NH3)525+. In addn. to CN vibrational stretching features shifted on electron transfer there is an addnl. sharp band only for the 5- ion at 1582 cm-1 which is attributed to a pyrazine ring vibration. The intensity of this band suggests an unsym. situation and thus valence localization on the vibrational time scale. The EPR signals at g$\bot$ = 2.0563 and g‖ = 1.761 point toward excited states lying close to the doublet ground state and to significant metal/cyanide interaction. Compared to the Creutz-Taube ion (μ-C4H4N2)Ru(NH3)525+ and its Os homolog, the 5- ion described here exhibits a lower degree of metal-metal coupling. on SciFinder(R)
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