TY - JOUR

T1 - Models for Iron-Oxo Proteins. MÖssbauer and EPR Study of an Antiferromagnetically Coupled FeIIINiII Complex

AU - Holman, T. R.

AU - Que, Larry

AU - Juarez-Garcia, C.

AU - Hendrich, M. P.

AU - Münck, E.

PY - 1990/1

Y1 - 1990/1

N2 - The bimetallic complex [FeIIINiII,BPMP(OPr)2](BPh4)2, where BPMP is the anion of 2,6-bis[(bis(2-pyridylmethyl) amino]methyl]-4-methylphenol, has been synthesized and its structure determined by X-ray diffraction methods as having a (μ-phenoxo)bis(μ-carboxylato) core. The complex crystallizes in the triclinic space group P1 with cell constants: a = 13.607 (3) Å, b = 13.700 (3) Å, c = 25.251 (7) Å, α = 77.29 (2)°,β = 78.25 (2)°, Γ = 61.73 (2)°, Z = 2, V= 4017 (4) Å3. The metal centers have distinct six-coordinate N3O3 environments and are separated by 3.378 (8) Å, similar to related complexes in this series. We have studied the complex with EPR and Mössbauer spectroscopy and magnetic susceptibility. All three techniques establish that the electronic ground state of the complex has spin S = 3/2. For T < 10 K the EPR spectra arc dominated by signals of the S = 3/2 multiplet. At higher temperatures, an additional resonance appears. It is centered at g = 4.2 and belongs to an excited multiplet with S = 5/2. We have studied the low-temperature Mössbauer spectra of the complex in external fields up to 6.0 T. Analysis of the well-resolved spectra yields D = 0.7 cm-1 and E/D = 0.32 for the zero-field splitting parameters of the S = 3/2 multiplet. Spectra taken in external fields H < 0.5 T reveal that D and E/D are distributed; a simple Gaussian distribution of E/D values fits the data quite well. The Mössbauer spectra show that the FeIII site is high-spin. It follows that the dinuclear complex consists of a ferric ion (S1 = 5/2) which is antiferromagnetically coupled to a high-spin (S2 = 1) NiII. Analysis of the temperature dependence of the g = 4.2 EPR signal yields J = +24 (3) cm-1 (J = JS1-S2); the susceptibility study agrees with this result. Analysis of the 57Fe magnetic hyperfine interaction with a spin coupling model yields A = -29.6 (2) MHz; this compares well with A(FeIII) = -29.5(2) MHz which we obtained here for the FeIII site of the isostructural FemZnn complex.

AB - The bimetallic complex [FeIIINiII,BPMP(OPr)2](BPh4)2, where BPMP is the anion of 2,6-bis[(bis(2-pyridylmethyl) amino]methyl]-4-methylphenol, has been synthesized and its structure determined by X-ray diffraction methods as having a (μ-phenoxo)bis(μ-carboxylato) core. The complex crystallizes in the triclinic space group P1 with cell constants: a = 13.607 (3) Å, b = 13.700 (3) Å, c = 25.251 (7) Å, α = 77.29 (2)°,β = 78.25 (2)°, Γ = 61.73 (2)°, Z = 2, V= 4017 (4) Å3. The metal centers have distinct six-coordinate N3O3 environments and are separated by 3.378 (8) Å, similar to related complexes in this series. We have studied the complex with EPR and Mössbauer spectroscopy and magnetic susceptibility. All three techniques establish that the electronic ground state of the complex has spin S = 3/2. For T < 10 K the EPR spectra arc dominated by signals of the S = 3/2 multiplet. At higher temperatures, an additional resonance appears. It is centered at g = 4.2 and belongs to an excited multiplet with S = 5/2. We have studied the low-temperature Mössbauer spectra of the complex in external fields up to 6.0 T. Analysis of the well-resolved spectra yields D = 0.7 cm-1 and E/D = 0.32 for the zero-field splitting parameters of the S = 3/2 multiplet. Spectra taken in external fields H < 0.5 T reveal that D and E/D are distributed; a simple Gaussian distribution of E/D values fits the data quite well. The Mössbauer spectra show that the FeIII site is high-spin. It follows that the dinuclear complex consists of a ferric ion (S1 = 5/2) which is antiferromagnetically coupled to a high-spin (S2 = 1) NiII. Analysis of the temperature dependence of the g = 4.2 EPR signal yields J = +24 (3) cm-1 (J = JS1-S2); the susceptibility study agrees with this result. Analysis of the 57Fe magnetic hyperfine interaction with a spin coupling model yields A = -29.6 (2) MHz; this compares well with A(FeIII) = -29.5(2) MHz which we obtained here for the FeIII site of the isostructural FemZnn complex.

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U2 - 10.1021/ja00177a024

DO - 10.1021/ja00177a024

M3 - Article

AN - SCOPUS:0025064777

VL - 112

SP - 7611

EP - 7618

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

IS - 21

ER -