| Sumario: | A series of isostructural dimeric manganese complexes of the type [(Medtne)Mn(u-O)(μ- R)](X) have been prepared and characterized. The dimanganese cores of these complexes are rigidly held together by the hexadentate ligand Medtne (Medtne = 1 ,2-bis(4,7-dimethyl-1 ,4,7-triazacyclonon-1- yl)ethane). Molecular structures for the entire series have been obtained by X-ray diffraction measurements, of which complexes 2 (R = OBPh), 3 (R = OC-PROXVL), 4 (B = OC-TEMPO), and 5 (R = OBPhNIT) are reported here (HOC-PROXYL = 3-carboxy-2,2,5,5-tetramethylpyrrolidin-1 -yloxy; HOC-TEMPO = 4-carboxy-2,2,6,6-tetramethylpiperidin-1-yloxy; and HOBPhNIT = 2-(4-(dihydroxyboranyl)- phenyl)-4,4,5,5-tetramethyl-3-oxyimidazolidin-1-oxide). The structures of 1 (R = OAc) and 6 (R = OCPhNIT) have been reported previously (HOCPhNIT = 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-3- oxyimidazolidin-1-oxide). All complexes exhibit several redox states, which have been investigated by electrochemistry. Complexes 1, 3, 4, and 6 contain a mixed-valent MnMn core with an isolated magnetic ground state of S = 1/2. The exchange coupling between the manganese ions is strong throughout the series (J ≈ -130 ± 10 cm, H= -2JSS). The radical complexes 3,4, and 6 exhibit, in addition, long- range exchange interaction (6.9, 7.7, and 8.8 Å, respectively) between the organic radical and the dimanganese core. The intramolecular anisotropic coupling was determined from cw-EPR line shape analyses at S-, X-, and Q-band frequencies and from the intensity of half-field signals detected in normal- and parallel-mode (J= -120 × 10, -105 × 10, and -140 × 10 cm, for 3,4, and 6 respectively). Distance information was obtained for the dimanganese core and the organic radicals from these values by using a three-spin dipole model and local spin contributions for the manganese ions.
|
|---|