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11 M. A. S. Aquino, J.-S. Lim and G. Sykes, J. Chem. Soc., Dalton
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Fig. 6 Cyclic voltammogram of complex 1 in CH3OH [0.1 mol dmϪ3
TBAPF6 as supporting electrolyte, glassy carbon working elec-
trode (diameter 3 mm), ferrocene as internal standard, scan rate of
50 mV sϪ1].
12 R. Than, A. A. Feldmann and B. Krebs, Coord. Chem. Rev., 1999,
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13 T. Klabunde, N. Sträter, R. Fröhlich, H. Witzel and B. Krebs, J. Mol.
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Crystal Structures, University of Göttingen, Germany, 1997.
26 L. Zsolnai, H. Pritzkow and G. Hutter, ZORTEP, University of
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27 K. Nakamoto, in Infrared and Raman Spectra of Inorganic and
Coordination Compounds, 3rd edn., John Wiley & Sons, NY, 1977,
part III, pp. 231, 232, 242.
In view of this, the redox properties of complex 1 were
investigated by cyclic voltammetry in methanolic solution
(Fig. 6). One quasi-reversible wave was observed at Ϫ0.41 V vs.
NHE (Ϫ0.81 V vs. Fcϩ/Fc), which could be attributed to an
III
Fe2 to FeIIIFeII redox process. Unfortunately, this value may
not be compared to the di(µ-methoxo) complexes listed in
Table 2, since no electrochemical data have been reported for
these species. On the other hand, this E1/2 value compares very
well with the corresponding Fe2III/FeIIIFeII redox couple in the
[Fe2(BIOMP)(OAc)2]ϩ complex (E1/2 = Ϫ0.355 V vs. NHE)34
which contains one phenolate and one 1-methylimidazole
group terminally bonded to the FeIII centres. However, these
E1/2 values are cathodically shifted when compared to the
reported value of ϩ0.367 vs. NHE at pH 5.0 for uteroferrin,4
which has only one terminal phenolate coordinated to the non-
reducible FeIII centre, while in the complexes there is one terminal
phenolate ligand on each FeIII centre. In summary, we have
synthesized and fully characterized a dinuclear FeIII complex
with the new tridentate HBHA ligand, which contains phen-
olate and imidazole donor groups. The complex [Fe2III(BHA)2-
(µ-OCH3)2(µ-OAc)](ClO4) (1), represents a rare example of
a diiron() complex triply bridged by two methoxo and one
acetate exogenous groups,29 which parallels closely the (µ-OH)2-
(µ-carboxylato) structural core and the FeIII ؒ ؒ ؒ FeIII distance of
the hydroxylase component of MMOH.18,19 Moreover, the
coordination environment of the FeIII centres and the magnetic
and spectroscopic properties indicate that 1 can be considered
as a potential structural model for the oxidized form of purple
acid phosphatases.
28 L. Yin, P. Cheng, X. Yao and H. Wang, J. Chem. Soc., Dalton Trans.,
1997, 2109.
29 C. M. Grant, M. J. Knapp, W. E. Streib, J. C. Huffman,
D. N. Hendrickson and G. Christou, Inorg. Chem., 1998, 37,
6065.
30 R. Viswanathan, M. Palaniandavar, P. Prabakaran and P. T.
Muthiah, Inorg. Chem., 1998, 37, 3881.
Acknowledgements
This work was supported by grants from Capes, CNPq and
PRONEX.
31 F. Le Gall, F. F. Biani, A. Caneschi, P. Cinelli, A. Cornia,
A. C. Fabretti and D. Gatteschi, Inorg. Chim. Acta, 1997, 262, 123.
32 (a) B. Chiari, O. Piovesana, T. Tarantelli and P. F. Zanazzi, Inorg.
Chem., 1982, 21, 1396; (b) B. Chiari, O. Piovesana, T. Tarantelli
and P. F. Zanazzi, Inorg. Chem., 1984, 23, 3398; (c) S. J. Barclay,
P. E. Riley and K. N. Raymond, Inorg. Chem., 1984, 23, 2005;
(d ) J. D. Walker and R. Poli, Inorg. Chem., 1990, 29, 756;
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J. Chem. Soc., Chem. Commun., 1991, 198; ( f ) A. S. Attia,
B. J. Conklin, C. W. Lange and C. G. Pierpont, Inorg. Chem., 1996,
35, 1033; (g) A. J. Blake, C. M. Grant, S. Parsons, G. A. Solan and
R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1996, 321.
33 L. Dongwhan and S. J. Lippard, J. Am. Chem. Soc., 1998, 120,
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