The dinuclear radical anion complexes [(mu-L)[Re(CO)(3)Cl](2)](*)(-), L = 2,2'-azobispyridine (abpy) and 2,2'-azobis(5-chloropyrimidine) (abcp), were investigated by EPR at 9.5, 94, 230, and 285 GHz (abpy complex) and at 9.5 and 285 GHz (abcp complex). Whereas the X-band measurements yielded only the isotropic metal hyperfine coupling of the (185,187)Re isotopes, the high-frequency EPR experiments in glassy frozen CH(2)Cl(2)/toluene solution revealed the g components. Both the a((185,187)Re) value and the g anisotropy, g(1) - g(3), are larger for the abcp complex, which contains the better pi-accepting bridging ligand. Confirmation for this comes also from IR and UV/vis spectroscopy of the new [(mu-abcp)[Re(CO)(3)Cl](2)](o/)(*)(-)(/2)(-) redox system. The g values are reproduced reasonably well by density functional calculations which confirm higher metal participation at the singly occupied MO and therefore larger contributions from the metal atoms to the g anisotropy in abcp systems compared to abpy complexes. Additional calculations for a series of systems [(mu-abcp)[M(CO)(3)X](2)](*)(-) (M = Tc or Re and X = Cl, and X = F, Cl, or Br with M = Re) provided further insight into the relationship between spin density distribution and g anisotropy.
Stabilisiert durch zweifache Chelatkoordination von {Cu(Ph3P)2}+ ist das Radikalanion von 2,2′‐Azobis(5‐chlorpyrimidin), das im Komplex (siehe Bild) eine N‐N‐Bindungslänge von 1.345(7) Å aufweist – in Übereinstimmung mit einer einfach reduzierten Azofunktion.
Double chelate coordination of [Cu(Ph P) ] stabilizes the radical anion of 2,2'-azobis(5-chloropyrimidine), which exhibits a N-N bond length of 1.345(7) Å in the complex (see picture). This is consistent with a one-electron reduced azo functionality.
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