A New Model for the Reduced Form of Purple Acid Phosphates: Structure and Properties of [Fe2BPLMP(OAc)2](BPh4)2

摘要

[[FeⅡFeⅢBPLMP(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-methylphenol (HBPLMP). Complex I has been characterized by X-ray diffraction method as having (μ-phenoxo)bis(acetato)diiron core. Complex 1 was crystallized in the monoclinic space group C2/c with the following cell parameters: a=41.620(6) ?, b=14.020(3) ?, c=27.007(4) ?, β=90.60(2)°, and Z=8. The iron centers in the complex 1 are ordered as indicated by the difference in the Fe-O bond lengths which match well with typical FeⅢ-O and FeⅡ-O bond lengths. Complex 1 has been studied by electronic spectral, NMR, EPR, SQUID, and electochemical methods. Complex 1 exhibits strong bands at 592 nm, 1380 nm in CH3CN (ε = 1.0 × 103 , 3.0 × 102). These are assigned to phenolate-to-FeⅢ and intervalence charge-transfer transitions, respectively. Its NMR spectrum exhibits sharp isotropically shifted resonances, which number half of those expected for a valence-trapped species, indicating that electron transfer between FeⅡ and FeⅢ centers is faster than NMR time scale. This complex undergoes quasireversible one-electron redox processes. The FeⅢ2/FeⅡFeⅢ and FeⅡFeⅢ/FeⅡ2 redox couples are at 0.655 and -0.085 V vs SCE, respectively. It has Kcomp=3.3 × 1012 representing that BPLMP/bis(acetate) ligand combination stabilizes a mixed-valence FeⅡFeⅢ complex in the air. Complex 1 exhibits a broad EPR signal centered near g=1.55 which is a characteristic feature of the antiferromagnetically coupled high-spin FeⅡFeⅢ system (Stotal=1/2). This is consistent with the magnetic susceptibility study showing the weak antiferromagnetic coupling (J= - 4.6 cm-1, H= - 2JS1·S2) between FeⅡ and FeⅢ center.