Model Compounds for Iron Proteins. Structures and Magnetic, Spectroscopic, and Redox Properties of Fe III M II and [Co III Fe III ] 2 O Complexes with (μ-Carboxylato)bis(μ-phenoxo)dimetalate and (μ-Oxo)diiron(III) Cores Sujit K. Dutta, ² Ru 1 diger Werner, ‡ Ulrich Flo 1 rke, § Sasankasekhar Mohanta, ² Kausik K. Nanda, ² Wolfgang Haase, ‡ and Kamalaksha Nag* ,² Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India, Institut fu ¨r Physikalische Chemie der Technischen Hochschule, D-64287 Darmstadt, Germany, and Anorganische und Analytische Chemie der Universita ¨t Gesamthochschule Paderborn, D-33098 Paderborn, Germany ReceiVed July 7, 1995 X A series of heterobimetallic complexes of the type [Fe III M II L(µ-OAc)(OAc)(H 2 O)](ClO 4 )‚nH 2 O(2-5) and [{Fe III - Co III L(µ-OAc)(OAc)} 2 (µ-O)](ClO 4 ) 2 ‚3H 2 O(6) where H 2 L is a tetraaminodiphenol macrocyclic ligand and M II ) Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The 1 H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV-vis spectra of 2-5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (µ-acetate)bis(µ-phenoxide)-Ni II Fe III core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear Co III - Fe III units are bound by an Fe-O-Fe linkage. 6 crystallizes in the orthorhombic space group Ibca with a ) 17.577(4) Å, b ) 27.282(7) Å, c ) 28.647(6) Å, and Z ) 8. The two iron(III) centers in 6 are strongly antiferromagnetically coupled, J )-100 cm -1 (H )-2JS 1 ‚S 2 ), whereas the other two S 1 ) S 2 ) 5 / 2 systems, viz. [Fe 2 III (HL) 2 (µ-OH) 2 ](ClO 4 ) 2 (1) and the Fe III Mn II complex (5), exhibit weak antiferromagnetic exchange coupling with J )-4.5 cm -1 (1) and -1.8 cm -1 (5). The Fe III Ni II (3) and Fe III Co II (4) systems, however, exhibit weak ferromagnetic behavior with J ) 1.7 cm -1 (3) and 4.2 cm -1 (4). The iron(III) center in 2-5 exhibits quasi-reversible redox behavior between -0.44 and -0.48 V vs Ag/AgCl associated with reduction to iron(II). The oxidation of cobalt(II) in 4 occurs quasi-reversibly at 0.74 V, while both nickel(II) and manganese(II) in 3 and 5 undergo irreversible oxidation at 0.85 V. The electrochemical reduction of 6 leads to the generation of 4. Introduction Oxo- and hydroxo-bridged diiron units are of wide occurrence in biology and perform a range of activities such as oxygen transport (hemerythrin 1 ), hydroxylation of alkanes (methyl monooxygenase 2 ), phosphate ester hydrolysis (purple acid phosphatases, 3 PAP’s) and DNA synthesis (ribonucleotide reductase 4 ). Consequently, the structural, magnetic, spectro- scopic and redox properties, as also chemical reactivities of binuclear iron complexes have been the focus of intense activities. 5-11 The recognition of Fe 2 (µ-O)(µ-O 2 CR) 2 and Fe 2 (µ- O)(µ-O 2 CR) cores in the active sites of some of the diiron proteins have led to the production of a few excellent structural models. 12 The occurrence of a heterobimetallic Fe III Zn II active site in the PAP from kidney bean 13 has evoked considerable interest because PAP’s from bovine spleen and porcine uterin fluid ² Indian Association for the Cultivation of Science, Calcutta. ‡ Technische Hochschule, Darmstadt. § Universita ¨t Gesamthochschule Paderborn. X Abstract published in AdVance ACS Abstracts, March 15, 1996. (1) (a) Holmes, M. A.; Stenkamp, R. E. J. Mol. Biol. 1991, 220, 723. (b) Sheriff, S.; Hendrickson, W. A.; Smith, J. L. J. Mol. Biol. 1987, 197, 273. (c) Shiemke, A. K.; Loehr, T. M.; Sanders-Loehr, J. J. Am. Chem. Soc. 1986, 108, 2437. (2) (a) Rosenzweig, A. C.; Frederick, C. A.; Lippard, S. J.; Nordlund, P. Nature 1993, 366, 537. (b) Anderson, K. K.; Froland, W. A.; Lee, S.-K.; Lipscomb, J. D. New J. Chem. 1991, 15, 405. (c) Green, J.; Dalton, H. J. Biol. Chem. 1989, 264, 17698. (3) (a) True, A. E.; Scarrow, R. C.; Randall, C. R.; Holz, R. C.; Que, L., Jr. J. Am. Chem. Soc. 1993, 115, 4246. (b) Averill, B. A.; Davis, J. C.; Burman, S.; Zirino, T.; Sanders-Loehr, J.; Loehr, T. M.; Sage, J. T.; Debrunner, P. G. J. Am. Chem. Soc. 1987, 109, 3760. (c) Antanaitis, B. C.; Aisen, P. AdV. Inorg. Biochem. 1983, 5, 111. (4) (a) Nordlund, P.; Eklund, H. J. Mol. Biol. 1993, 232, 123. (b) Atta, M.; Nordlund, P.; Aberg, A.; Eklund, H.; Fontecave, M. J. Biol. Chem. 1992, 267, 20682. (5) (a) Feig, A. L.; Lippard, S. J. Chem. ReV. 1994, 94, 759. (b) Lippard, S. J. Angew. Chem., Int. Ed. Engl. 1988, 27, 344. (6) (a) Que, L., Jr. in Bioinorganic Catalysis; Reedijk, J., Ed.; Marcel Dekker: Amsterdam, 1993; p 347. (b) Que, L., Jr.; True, A. E. Prog. Inorg. Chem. 1990, 38, 97. (7) Kurtz, D. M., Jr. Chem. ReV. 1990, 90, 585. (8) Vincent, J. B.; Olivier-Lilley, G. L.; Averill, B. A. Chem. ReV. 1990, 90, 1447. (9) Sanders-Loehr, J. In Iron Carriers and Iron Proteins; Loehr, T. M., Ed.; VCH Publishers: New York, 1989; p 373. (10) Wilkins, P. C.; Wilkins, R. G. Coord. Chem. ReV. 1987, 7, 195. (11) Murray, K. S. Coord. Chem. ReV. 1974, 12, 1. (12) For example, see: (a) Armstrong, W. H.; Lippard, S. J. J. Am. Chem. Soc. 1983, 105, 4837. (b) Wieghardt, K.; Pohl, K.; Gebert, W. Angew. Chem., Int. Ed. Engl. 1983, 22, 727. (c) Armstrong, W. H.; Spool, A.; Papaefthymiou, G. C.; Frankel, R. B.; Lippard, S. J. J. Am. Chem. Soc. 1984, 106, 3653. (d) Chaudhuri, P.; Wieghardt, K.; Nuber, B.; Weiss, J. Angew. Chem., Int. Ed. Engl. 1985, 24, 778. (e) Turowski, P. N.; Armstrong, W. H.; Roth, M. E.; Lippard, S. J. J. Am. Chem. Soc. 1990, 112, 681. (f) Drueke, S.; Wieghardt, K.; Nuber, B.; Weiss, J.; Fleischhauer, H.-P.; Gehring, S.; Haase, W. J. Am. Chem. Soc. 1989, 111, 8622. (g) Norman, R. E.; Yan, S.; Que, L., Jr.; Backes, G.; Ling, J.; Sanders-Loehr, J.; Zhang, J. H.; O’Connor, C. J. J. Am. Chem. Soc. 1990, 112, 1554. (h) Dong, Y.; Menage, S.; Brennan, B. A.; Elgren, T. A.; Jang, H. G.; Pearce, L. L.; Que, L., Jr. J. Am. Chem. Soc. 1993, 115, 1851. 2292 Inorg. Chem. 1996, 35, 2292-2300 0020-1669/96/1335-2292$12.00/0 © 1996 American Chemical Society