Synthesis and characterization of the mixed-valence [(FeFeBPLNP)-Fe-II-B-III(OAc)(2)](BPh4)(2) complex as a model for the reduced form of the purple acid phosphatase
J. Lee et al., Synthesis and characterization of the mixed-valence [(FeFeBPLNP)-Fe-II-B-III(OAc)(2)](BPh4)(2) complex as a model for the reduced form of the purple acid phosphatase, B KOR CHEM, 21(10), 2000, pp. 1025-1030
[(FeFeBPLNP)-Fe-II-B-III(OAc)(2)](BPh4)(2) (1), a new model for the reduced
form of the purple acid phosphatases, has been synthesized by using a dinu
cleating ligand, 2,6-bis [((2-pyridplmethyl)(6-methyl-2-pyridylme no)methyl
]-4-nitrophenol (HBPLNP). Complex 1 has been studied by electronic spectral
, NMRI EPR, SQUID, and electrochemical methods. Complex 1 exhibits two stro
ng bands at 498 nm (epsilon = 2.6 x 10(3) M(-1)cm(-1)) and 1363 nm (epsilon
= 5.7 x 10(2) M(-1)cm(-1)) in CH3CN. These are assigned to phenolate-to-Fe
m 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 el
ectron transfer between Fen and Fem centers is faster than NMR time scale a
t room temperature. Complex 1 undergoes quasireversible one-electron redox
processes. The Fe-2(III)/(FeFeIII)-Fe-II and (FeFeIII)-Fe-II/Fe-2(II) redox
couples are at 0.807 and 0.167 V versus SCE, respectively. It has K-comp =
5.9 x 10(10) representing that BPLNP/bis(acetato) ligand combination sta b
ilizes a mixed-valence (FeFeIII)-Fe-II complex in the air. Interestingly, c
omplex 1 exhibits intense EPR signals at g = 8.56, 5.45, 4.30 corresponding
to mononuclear high-spin Fem species, which suggest a very weak magnetic c
oupling between the iron centers. Magnetic susceptibility study shows that
there is a very weak antiferromagnetic coupling (J = -0.78 cm(-1), H = -2JS
(1)(.)S(2)) between Fe-II and Fe-III centers. Thus, we can suggest that com
plex I has a very weak antiferromagnetic coupling between the iron centers
due to the electronic effect of the nitro group in the bridging phenolate l
igand.