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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 10
BKCSDE 21(10)
October 20, 2000 

Synthesis and Characterization of the Mixed-valence [FeIIFeIIIBPLNP(OAc)2](BPh4)2 Complex As a Model for the Reduced Form of the Purple Acid Phosphatase
Jeseung Lee, Dong J.Jung, Ho-Jin Lee, Kang-Bong Lee, Nam Hwi Hur, Ho G. Jang
[FeⅡ FeⅢ BPLNP(OAc)₂](BPh₄)₂ (1), a new model for the reduced form of the purple acid phosphatases, has been synthesized by using a dinucleating ligand, 2,6-bis[((2-pyridylmethyl)(6-methyl-2-pyridylmethyl)ami-no)methyl]-4-nitrophenol (HBPLNP). Complex 1 has been studied by electronic spectral, NMR, EPR, SQUID, and electrochemical methods. Complex 1 exhibits two strong bands at 498 nm (ε= 2.6 ×10³M-¹cm-¹) and 1363 nm (ε= 5.7 ×10²M-¹cm-¹) in CH₃CN. These are assigned to phenolate-to-FeⅢ and intervalence charge-transfer transitions, respectively. NMR spectrum of complex 1 exhibits sharp isotropically shifted resonances, which number is half of those expected for a valence-trapped species, indicating that electron transfer between FeⅡ and FeⅢ centers is faster than NMR time scale at room temperature. Complex 1 undergoes quasireversible one-electron redox processes. The FeⅢ₂/FeⅡFeⅢ and FeⅡFeⅢ/FeⅡ₂ redox couples are at 0.807 and 0.167 V ver-sus SCE, respectively. It has Kcomp = 5.9 ×10 1s(acetato) ligand combination sta-bilizes a mixed-valence FeⅡFeⅢ complex in the air. Interestingly, complex 1 exhibits intense EPR signals at g = 8.56, 5.45, 4.30 corresponding to mononuclear high-spin FeⅢ species, which suggest a very weak magnetic coupling between the iron centers. Magnetic susceptibility study shows that there is a very weak antiferromag-netic coupling (J = -0.78cm-¹, H = -2JS₁×S₂) between FeⅡ and FeⅢ centers. Thus, we can suggest that complex 1 has a very weak antiferromagnetic coupling between the iron centers due to the electronic effect of the nitro group in the bridging phenolate ligand.
1025 - 1030
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