[Fe(II)Fe(III)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)amino)methyl]-4-nitrophen ol (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 x 103 M-1cm-1) and 1363 nm (ε = 5.7 x 102 M.-. in CH3CN. These are assigned to phenolate-to-Fe(III) 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 Fe(II) and Fe(III) centers is faster than NMR time scale at room temperature. Complex 1 undergoes quasireversible one-electron redox processes. The Fe(III)2/Fe(II)Fe(III) and Fe(II)Fe(III)/Fe(II)2 redox couples are at 0.807 and 0.167 V versus SCE, respectively. It has K(comp) = 5.9 x 1010 representing that BPLNP/bis(acetato) ligand combination stabilizes a mixed-valence Fe(II)Fe(III) complex in the air. Interestingly, complex 1 exhibits intense EPR signals at g = 8.56, 5.45, 4.30 corresponding to mononuclear high-spin Fe(III) species, which suggest a very weak magnetic coupling between the iron centers. Magnetic susceptibility study shows that there is a very weak antiferromagnetic coupling (J = -0.78 cm-1, H = -2JS1· S2) between Fe(II) and Fe(III) 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.
|Number of pages||6|
|Journal||Bulletin of the Korean Chemical Society|
|Publication status||Published - 2000 Oct 20|
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