| Abstract
| - The oxidative electron-transfer properties of several superphane complexes consisting of cyclopentadienylcobalt cyclobutadiene moieties linked by either three (compounds 1 and 4) or five (compounds 2 and5) bridging methylene groups have been studied by experimental and theoretical methods. In both cases twoseparate one-electron oxidations are found. The mixed-valent monocations of the (−CH2−)5-bridged complexesare valence-trapped with very weak interactions between metal centers. The (−CH2−)3 complexes, however,have strong interactions between the two molecular halves. The intervalence transfer (IT) band of 1+ hascharacteristics of both class II (localized) and class III (delocalized) behavior, but the IR spectra of carboxy-labeled 4+ clearly establish trapped valence for the monocations of the propano-bridged systems. Photoelectronspectra and ab initio calculations at the UHF level show that, in the ground electronic state, 1+ has a half-filled orbital (i.e., electron spin) that is essentially localized in one Co dxy, orbital, but that the charges on thetwo metals are unequal owing to inductive electronic effects which give unequal electron flow from the ligandsto the two metal centers. Calculations and IR (carbonyl) spectral shifts suggest about a 70:30 charge ratiobetween the two metal centers in 1+ and 4+, whereas both spin and charge localization is virtually completein the pentano-bridged complexes 2+ and 5+. The intervalence transition in 1+ is proposed to proceed througha “hole”-transfer process mediated by a π-cyclobutadiene MO, ultimately involving a through-bond transannularmechanism.
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