Mixed valence interactions in di-. mu. -oxo bridged manganese complexes
The complexes ((L)/sub 2/MnO/sub 2/Mn(L)/sub 2/)/sup 3 +/ where L = 2,2'-bipyridine or 1,10-phenanthroline, have been examined, in addition to the corresponding (IV, IV) complex of phenanthroline. The crystal structure of the mixed valence (III, IV) compound with L = 2,2'-bipyridine demonstrated that this complex has deeply trapped valences, corresponding to class II in the classification of Robin and Day since the bond lengths differ considerably about the manganese ions. We have examined the electronic spectrum of the (III, IV) complexes and observed broad bands in the near infrared which we have assigned to the mixed valence band expected for a class II system. No comparable band is observed for the phenanthroline (IV, IV) complex. Lowering the pH of (III, IV) dimer solutions reversibly cleaves the antiferromagnetically coupled (III, IV) dimers as determined by the increase in solution magnetic susceptibility; loss of the near infrared band occurs with dimer cleavage, although the remainder of the visible spectrum is substantially unaltered. Both absorbance and solution magnetic susceptibility changes with pH are reversible. The solvent dependence of the near infrared band is small but apparently opposite to that predicted by Hush's theory. However, the bandwidths agree well with those predicted from Hush's treatment (e.g., 0.53 ..mu..m/sup -1/ predicted, 0.46 ..mu..m/sup -1/ observed). A band at 688 cm/sup -1/ in the infrared spectrum of the bipyridyl (III, IV) dimer is shifted by isotopic substitution with /sup 18/O, and has been assigned to one of the stretching modes of the Mn/sub 2/O/sub 2/ bridge; analogous bands are found for the phenanthroline (III, IV) and -(IV, IV) complexes. Pertinent aspects of the electrochemistry are also discussed.
- Research Organization:
- Univ. of California, Berkeley, CA (United States)
- OSTI ID:
- 7288242
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 99:20
- Country of Publication:
- United States
- Language:
- English
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