Journal of Nuclear and Radiochemical Sciences, Vol. 7, No.1, pp. R13-R18, 2006

Mössbauer Spectroscopy –Nuclear Hyperfine Technique for Studying Dynamic Chemical
States of Iron Complexes–
Y. Maeda*
Department of Chemistry, Faculty of Sciences, Kyushu University. Hakozaki 6-10-1, Higashi-ku, Fukuoka, Japan.
Received: October 31, 2005
Mössbauer effect spectroscopy is one of the most important techniques for observing the dynamic phenomena ofelectronic states in solid. The Mössbauer spectra of mixed valence compounds show relaxation spectra if theelectronic states are changed dynamically between Fe2+ and Fe3+. The dynamic electronic states of mixed valencecompounds are discussed in connection with Mössbauer spectra of [Fe2 (bpmp)(ppa) 2 ]X 2 as examples. The
absorption spectra and cyclic voltammograms of the compounds were measured. The electronic states of themixed compounds are dependent on the species of their anions in the solid state.

1. Introduction
Dinuclear iron complexes with a variety of multidentate
ligands have been intensively studied due to the fact that dinuclear iron clusters in the active sites of metalloproteins play
important roles such as reversible dioxygen binding and/or activation. Significant examples are haemerythrin,1-3 the R2 subunitof ribonucleotide reductase,4 the hydroxylase component ofmethane monooxygenase,5-7 and purple acid phosphatase.8-10 In
order to understand the structural and spectroscopic propertiesof these diiron centers, mixed-valence dinuclear iron (II, III)
complexes with a septadentate polypyridine ligand (Hbpmp:
2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol)
were synthesized by Suzuki et al.,11 and diiron (II, III) complexes
with the ligands which contain imidazole derivatives instead ofpyridine groups (Hbimp),12 or which contain two phenols substituted for two pyridines13 were also reported.
The research of “bpmp” complexes is not only to study theproperties of model compounds for biological systems in solution, but also to elucidate valence states in the solid state,because the complexes with carboxylic acids having long
chains (CH 3 (CH 2 ) n COOH, n ≥ 3), show detrapped valence
states above 260 K.14 The rate of electron transfer in solid issensitive to the packing structure of the solid as the coupling of
the electronic state with vibrational coordinates leads to sensitivity to the structure. It should be said that packing structure
including the rearrangement of iron moieties of mixed-valence

Figure 1. Chemical structure of [Fe2 (bpmp)(ppa) 2] 2+*Corresponding author. E-mail: y.maescc@mbox.nc.kyushu-u.ac.jp

complexes is an important factor in determining the rate of
intramolecular electron transfer. In this study mixed-valenceµ-phenolate-bis (µ-carboxylate) diiron(II, III) complexes[Fe2 (bpmp)(ppa) 2 ](BF4) 2 ( 1 ), [Fe2 (bpmp)(ppa) 2 ](ClO4) 2 ( 2 ),[Fe2(bpmp)(ppa)2](PF6)2 ( 3 ), and [Fe2(bpmp)(ppa)2](BPh4)2 ( 4 )are prepared, where “Hppa” represents β-phenylpropionic acid,and the Mössbauer spectra of the complexes are discussed inconnection with the electron transfer rates. Chemical structureof [Fe2 (bpmp)(ppa)2] 2+ is drawn in Figure 1.
2. Experimental
Preparation of 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenol (Hbpmp). Bis(2-pyridylmethyl)amine (2.0 g,
10 mmol) was added dropwise to a solution of 2,6-bis (chloromethyl)-4-methylphenol (1.0 g, 5 mmol) in 50 mL methanol
below 10 ˚C. This solution was stirred for 30 minutes and methanol was removed by evacuation. The residue was dissolved inchloroform and washed twice with water. This chloroform solution was dried over anhydrous sodium sulfate and chloroform
was removed by evacuation. The residue was used as Hbpmp(2.6g, 5 mmol).
Preparation of [Fe IIFe III (bpmp)(ppa) 2 ](BF4 ) 2 (1). The
preparation of 1 is described as a representative example.
Synthesis of 1 was carried out in deoxygenated methanol solution under nitrogen atmosphere. A methanol (20 mL) solutionof iron(II) tetrafluoroborate (340 mg, 1 mmol) was stirred andadded to solution of Hbpmp (260 mg, 0.5 mmol) in methanol (20 mL), and 3-n-phenylpropionic acid (140 mg, 1 mmol),and triethylamine (100 mg, 1.0 mmol) was then added. The
solution was then exposed to an oxygen atmosphere(air) withstirring. Dark-green precipitates were collected by filtration,
washed with ethanol and ether, and dried in vacuum.
Anal. data for [Fe2 (bpmp)(ppa) 2](BF4) 2 (1): Calculated for
C 51 H 51 N6 Fe2 O5 B2 F 8 : C, 55.02; H, 4.62; N, 7.64; Fe, 10.03.
Found: C, 54.64; H, 4.55; N, 7.64; Fe, 9.89%.
Anal. data for [Fe2 (bpmp)(ppa) 2](ClO4) 2 (2): Calculated for
C51H51N6Fe2O13Cl2: C, 53.80; H, 4.51; N, 7.38; Fe, 9.81. Found:C, 53.25; H, 4.54; N, 7.46; Fe, 9.57%.
Anal. data for [Fe2 (bpmp)(ppa) 2](PF6) 2 (3): Calculated for
C 51 H 51 N6 Fe2 O 5 P 2 F12 : C, 49.82; H, 4.18; N, 7.64; Fe, 9.08.
Found: C, 54.64; H, 4.55; N, 7.64; Fe, 9.28%.
Anal. data for [Fe2 (bpmp)(ppa) 2](BPh4) 2 (4): Calculated for
C99H91N6Fe2O5B2 : C, 75.35; H, 5.81; N, 5.33; Fe, 7.08. Found:C, 74.22; H, 5.88; N, 5.49; Fe, 7.46%.
Microanalysis for carbon, hydrogen, and nitrogen was car-© 2006 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 06/30/2006

R14 J. Nucl. Radiochem. Sci., Vol. 7, No. 1, 2006

Maeda

Reflection and Absorption Spectra. Absorption spectra ofcomplexes 1 – 4 in acetonitrile solution were measured. An
absorption spectrum of 4 in acetonitrile solution is displayed in
Figure 2 as a representative example. The complexes giveabsorption bands in the visible region: λ =561 nm, ε =931
dm 3 cm -1 mol-1 for 1, λ =565 nm, ε =981 dm 3 cm -1 mol-1 for 2,
λ=561 nm, ε=1050 dm3cm-1mol-1 for 3, and λ=539 nm, ε=1108
dm3cm-1mol-1 for 4. These are assigned to charge transfer tran-∆ν1/2 (theor) = (2.31×103νmax)1/2

The electron delocalization coefficient α in a mixed-valencesystem is given by eq 215 where εmax is the molar extinction
coefficient of the IT band and d is the distance (Å) between
two metal centers associated with the IT transition. The α2value of 0.0065 (α = 0.081) is evaluated for complex 1 using
the d = 3.36 Å,14,16 νmax = 7794 cm-1, ∆ν1/2 = 4661 cm-1, and εmax
= 289 dm3 cm-1 mol-1.

α 2=∆ G* =

νmax
– Hab
4

(5)

3/2
νet = 2 π H ab ( kT νmax )–1/2
h

(6)

68

0
400

800

1200

1800

Wavelength/nm
Figure 2. Absorption spectrum of 4 in acetonitrile solution(1×10 -3
mol)

(4)

k et = νet exp – ∆ G
RT
68

200

(3)

The thermal rate constant for electron transfer is obtainedby eq 5.15

800

400

(2)

H ab = α · νmax

1000

ε /dm3 cm-1 mol -1

4.24×10-4 ε max ∆ ν 1/2
νmax d 2

Therefore, the mixed-valence bpmp complex 1 belongs to Class
II in the classification of Robin and Day17 on the base of the
Mössbauer spectra described later. The resonance energy
matrix element arising from orbital overlap between electron
donor and acceptor sites, Hab can be calculated from eq 3 toyield 631 cm-1 (7.5 kJ mol-1).18 The thermal free energy of electron transfer, ∆G *, for a symmetrical mixed-valence complex isgiven to be 15.8 kJ mol-1 by eq 4.19

1200

600

(1)

*

13

3. Results and Discussion

sitions from the pπ orbital of a bridging phenolato group to thehalf filled dπ* orbital of FeIII ions.11 The ligand field bands may
be obscured under the above CT band.
Complexes 1 – 4 show an additional broad absorption bandin near-IR region. The band is unambiguously assigned to theintervalence charge transfer transition ( IT ) of the mixedvalence complexes. The properties associated with these IT
bands for complexes 1 – 4 are collected in Table 1. The energyof the optical transition (νmax) for the IT band of complex 1 is7794 cm-1 and the width of half maximum (∆ν1/2) is 4661 cm-1.
The ∆ν1/2 value is compared to the theoretical value of 4243
cm-1 calculated by eq 1. The ratio of ∆ν1/2 (obsd) / ∆ν1/2 (theor)= 1.1 is commonly found for weakly to moderately coupledbinuclear mixed-valence dimers.

13

ried out at the Elemental Analysis Center, Kyushu University.
Quantitative analysis for iron was performed by atomic absorption analysis, using an Atomic Absorption / Flame Emission
Spectrometer AA-625-11 (Shimadzu).
Physical Measurements. Absorption and reflection spectra
were measured using a Shimadzu UV-3100PC self-recording
spectrophotometer in the region from 400 to 2000 nm.
Cyclic voltammetry of the complexes in acetonitrile wascarried out on an AC/DC Cyclic Polarograph P-900 (Yanaco)
at 293 K under argon atmosphere. A standard three-electrodesystem(BAS) was employed comprising a glassy carbon working electrode, a Ag-Ag+ - MeCN-NBu4ClO4 (RE-5, BAS), reference electrode and a platinum counter electrode in the region
from − 500 to 1200 mV. Ferrocene was used as a standard.
The observed values for the complexes were converted to redox
potentials versus SCE by using the following equation.
Redox potential for the complexes= observed value for a complex − observed value for
Ferrocene + 0.0739 (Ferrocene vs. Ag / AgCl) + 0.272 (Ag / AgCl
vs. SCE) V.
(1)
The Mössbauer spectra were measured using a Topologic
Mössbauer spectrometer with a 57Co/Rh source in the transmission mode. All isomer shifts are given relative to the center ofa spectrum for α - Fe at room temperature. The temperature
was controlled over 80 – 295 K using an Oxford Intelligent
temperature controller or over 5 – 295 K using a Lakeshore 331
temperature controller, and a Kenwood Regulated DC power
supply. The spectra were fitted by a Lorentzian line shape usinga software of IGOR PRO ( Wave Metrics Inc. ) on a personal
computer.

The νet term given by eq 6 is the frequency factor for electrontransfer. The calculated value of ket for complex 1 is 3.8 × 1014
s-1. The same arguments can be applied to complexes 2 – 4.
The calculated values of k et are similar to each other. Creutz
ha s p oi nt e d out t h at , i n a ser ies of m i xe d-va lenc e[Ru(bpy)2Cl] 2L complexes (where bpy is 2,2’-bipyridine and L
is the bridging ligand), there is a 100 fold increase in k et from107 to 109 s-1 as the metal-metal distance decreases from ~14 to~7 Å.17 Using this trend as a qualitative guide, it is not surprising that the ket values obtained for complex 1 – 4 are ~1014 since

Table 1: Spectrochemical Properties of the Mixed-valence Complexes.
Comp.

νmax/cm-1(ε /dm3cm-1mol-1)∆ν1/2 (obs)/cm-1∆ν1/2 (theo)/cm-1

α2

Hab /cm-1∆G*/ kJ mol-1

ket /s-1

12
3
47794 (289)7764 (282)7770 (251)7782 (288)

4661
4453
4628
4695

4243
4235
4237
4240

0.00650.00610.00560.0065

631
606
583
630

15.8
16.0
16.3
15.8

3.8 × 1014
3.5 × 1014
3.2 × 1014
3.8 × 1014

Mössbauer Spectroscopy-Nuclear Hyperfine Technique for Studying

the triply bridged diiron units in the complexes have relatively
short Fe–Fe distances ( ~3.4 Å).
Cyclic Voltammetry. Cyclic Voltammograms of the complexes were measured in acetonitrile at 293 K and are shown in
Figure 3. Two quasi-reversible waves corresponding to FeIIFeII/ FeII FeIII , E1 (V vs. SCE) and FeII FeIII / FeIII FeIII , E 2 (V vs.
SCE), couples are observed. The potentials observed for thecomplexes are E1= −0.089 V and E 2 = 0.646 V for 1, and E1=−0.094 V and E2 =0.631V for 2, E1=−0.084 V and E2 =0.641 V
for 3, and E1=−0.104 V and E2 =0.611 V for 4, being similar to
those observed for other [Fe2 (bpmp)L2](BF4)2 complex.14,19
The redox potentials of the complexes are dependent on thespecies of carboxylic acid. Peak-to-peak separations of these
two waves are 715 – 735 mV, and the ratios of the oxidation
currents (ipa) for the forward scan to the reduction currents (ipc)
for the reverse scan were close to unity for the both couples.
From the separation of the redox potentials of E1 and E2, comproportionation constants Kc (at 20 ˚C) of the following reaction are calculated from eq 7.
→ 2 ( FeII – FeIII )( FeIII – FeIII ) + ( FeII – FeII ) ←E2 − E1 = RT / FlnKc(7)

The E values of the FeIIFeIII bpmp complexes are well correlated with the electron donor ability of the bridging carboxylates; the complexes with carboxylic acids of the weak donor
ability is prefer low oxidation states. Equation 7 demonstrates
that the thermodynamic significance of peak separation of the
waves is its relationship to the comproportionation equilibrium
constant. The larger separation of the waves indicates the sub-J. Nucl. Radiochem. Sci., Vol. 7, No. 1, 2006 R15stantial stability of the diiron(II, III) ion over its corresponding
diiron(II, II) and diiron(III, III) species. For complexes 1 – 4,
Kc values calculated from eq 7 are 2.87 × 1012, 1.94 × 1012, 1.94
× 1012, and 1.31 × 1012, respectively. Therefore, in complexes 1– 4, mixed-valence states are highly stabilized in acetonitrile
solution.
Mössbauer spectroscopy. The Mössbauer spectra for thecomplexes were measured at various temperatures. The goodfits of the spectra to four Lorentzian line shapes for complex 1
were obtained at all temperatures. Each spectrum consists of
two doublets. One of the two doublets at 80 K is characteristicof high-spin FeII with an isomer shift (δ) of 1.14 mm s-1 and aquadrupole splitting (∆) of 2.75 mm s-1. The other is characteristic of high-spin FeIII with δ of 0.48 mm s-1 and ∆ of 0.56 mm
s-1. The area ratios of the two doublets are nearly 1:1. Upon
increasing temperature, the two doublets approach each otherbut still remain even at 295 K. The δ and ∆ values for highspin FeII at 295 K are 0.83 mm s-1, 1.27 mm s-1, and those forhigh-spin FeIII 0.57 mm s-1, 0.75 mm s-1 , respectively. The area
ratios of two doublets are 1:1. The result of the Mössbauer
spectra of complex 1 was comparable to that reported previously.16,20 The temperature dependence of the Mössbauer
parameters of complex 1 are plotted in Figures 4a and 4b withthose for other complexes.

1.4
1.2

(1)

δ / mm s-1

1.0

10 µA

0.8
0.6
0.4
0.2

(2)

0.0
100

150

200

250

Temperature / K
Figure 4a. Plots of the isomer shift vs. temperature for complexes 1–4.
Complex 1 (○), complex 2 (△), complex 3 (□), and complex 4 (◇).

(3)

(4)

∆ / mm s-1

2.5

2.0

1.5

1.0

0.5
100

150

200

250

Temperature / K
-1.0

-0.5

0

0.5

1.0

E / V vs. SCE
Figure 3. Cyclic voltammograms of the complexes 1–4.

Figure 4b. Plots of the quadrupole splitting vs. temperature forcomplexes 1–4. Complex 1 (○), complex 2 (△), complex 3 (□), andcomplex 4 (◇).

R16 J. Nucl. Radiochem. Sci., Vol. 7, No. 1, 2006

Maeda

1.00

1.00

295 K

295 K

0.97

Relative Transmission

0.98

1.00

1.00

250 K

200 K

0.97
0.96
1.00
80 K

0.95
-4

-2
0
2
-1
Velocity / mm s

4

Figure 5. Temperature dependence of the Mössbauer spectra of complex 2.

Relative Transmission

1.00

200 K

0.96
1.00

160 K

0.96
1.00

The Mössbauer spectra of complex 2 are illustrated in Figure
5. The Mössbauer spectra of complex 3 are similar to those ofcomplex 2. The Mössbauer spectra of complexes 2 and 3 at 80
K clearly show the characteristic FeII and FeIII doublets in anarea ratio of 1:1. At 295 K, complex 2 exhibits two doublets
assigned to high-spin FeII and FeIII with nearly equal area ratio.
On the other hand, the Mössbauer spectrum of complex 3 at
295 K exhibits two doublets assigned to high-spin FeII and FeIII
with a different area ratio. The area ratio of FeII and FeIII isabout 3:7. It is not easy to believe that this unequal area ratio
results entirely from a difference in the temperature dependence of the recoilless fraction of FeIII to FeII sites in thesematerials. Rather, it is proposed that the difference is due tothe analytical error for asymmetric absorption or due to a texture effect in the sample.21,22 Unfortunately, it is difficult toanalyze the spectra with an asymmetric doublet of FeII and asymmetric doublet of FeIII, but the temperature dependence ofδ and ∆ are similar to those observed for typical valence
trapped compounds.16
The Mössbauer spectra of complex 4 are shown in Figure 6.
Compared to the Mössbauer spectra of complexes 1 – 3, thespectra of complex 4 are considerably different. At 80 K, thespectrum is composed of two doublets assigned to FeII and FeIII
sites. The δ and ∆ values are 1.23 mm s-1 and 2.09 mm s-1
respectively, for FeII site, and 0.43 mm s-1, 0.81 mm s-1, respectively, for FeIII site. As the temperature is increased, these two
doublets gradually approach each other with line broadening tobecome a single average-valence doublet. The Mössbauer
spectrum at 295 K shows single average-valence doublet with δof 0.66 mm s-1 and ∆ of 0.89 mm s-1. The values of the δ and ∆are comparable to valence detrapped bpmp complexes reported
previously.14,23 However, the area ratio of FeII and FeIII is notequal at 80 K. The area ratios of FeII and FeIII at 80 K in complex 4 are 3:7. Also, ∆ value of FeIII site at 80 K, 0.81 mm s-1, isrelatively high as a high-spin FeIII species. Upon decreasing

80 K

0.94
1.00

5K
0.92

-4

-2

0

2

4

6

Velocity / mm s-1
Figure 6. Temperature dependence of the Mössbauer spectra of complex 4.

the temperature from 80 K, the area ratios of FeII and FeIII
gradually approach to 1:1. The area ratio of FeII and FeIII at 5
K is nearly 1:1. The δ value and ∆ value for FeII is 1.13 mm s-1
and 2.33 mm s-1 and those for FeIII is 0.50 mm s-1 and 0.69 mm
s-1, respectively. This result indicates that valence detrapping
occurs in complex 4 even at 80 K, and the valences are trapped
at 5 K. It is concluded that the valence delocalization in complex 4 takes place at the lowest temperature in the bpmp mixedvalence complexes studied until now. No bpmp mixed-valencecomplexes which show valence detrapping at 80 K have beenreported previously.24
The Mössbauer spectra of complexes 1 – 4 at 295 K are
illustrated in Figure 7 to compare the differences of electron

Mössbauer Spectroscopy-Nuclear Hyperfine Technique for Studying

1.00
(4)

0.96
1.00

Relative Transmission

(3)
0.98
1.00
(2)

0.98
1.00
(1)

0.95
-4

-2

0

2

4

6

Velocity / mm s-1
Figure 7. Mössbauer spectra for complexes 1–4 at 295 K. The solidlines represent theoretical fits obtained by the two-site relaxation
model.

transfer rate. Figure 7 and the results of the Mössbauer fitting
pa rameters clea rly show the electron transfer rate of[Fe2(bpmp)(ppa)2]2+ cations is sensitive to the species of counter
anions. Hendrickson et al. reported the sensitivities of anions tomixed-valence bimp complexes.12 [Fe2 (bimp)(AcO) 2] 2+ (where
AcO = acetate anion) shows a completely valence detrapped
Mössbauer spectrum at 290 K when anions are BF4-. The ClO4salt shows valence trapped spectrum even at 350 K. They concluded that the change in the counter anions can affect the rateof electron transfer of mixed-valence complexes because of theconsequence of the vibronic nature of the FeII FeIII center. If
there are appreciable intermolecular interactions between cations and anions in the crystals of FeIIFeIII complexes, then theseinteractions will tend to trap the valence. The complex will nothave enough thermal energy to make an interconversion
between two vibronic states of FeA II FeBIII and FeA III FeBII, overcoming interactions with neighboring molecules in the crystal.
However, if the thermal energy is large enough to overcome theinteractions or the interactions are weakened by changing inanions, complexes show the valence detrapped states.
In order to interpret the Mössbauer spectra of the complexes,
theoretical Mössbauer spectra are calculated by considering arelaxation model. The mathematical formalism which is applied
to this relaxation model is based on the quantum mechanicaldensity matrix equations of motion (dGi /dt) given by Wickmann.
25,26
The detail of the model and the fitting is described elsewhere.25,26 The probability of keeping FeII electronic state atsite A is nearly 0.8 and this result indicates that an excess elec-

J. Nucl. Radiochem. Sci., Vol. 7, No. 1, 2006 R17tron stays 80% of the time at site A and 20% of the time at site
B in complex 1. Therefore valence state of complex 1 isFe2.2+ Fe2.8+ at 295 K in Mössbauer timescale. This unusual
valence state of complex 1 is also reflected in the temperaturedependence of δ and ∆ as shown in Figures 4a and 4b.
Temperature dependence of δ and ∆ of complexes 2 and 3
exhibits typical behavior of valence trapped process between
80 K and 295 K.16 The δ of high-spin FeIII usually decrease
with increasing temperature except for complexes which experience a phase transition in the temperature measured, but δ of
FeIII site in complex 1 increases with increase in temperature,and the ∆ of high-spin FeIII are usually invariant with increasein temperature. However the ∆ of complex 1 increase withincrease in temperature. The line broadening of spectra, usually observed in the valence detrapping process, was notobserved in complex 1, and area ratios of FeII and FeIII remain
1:1 for all measured temperatures. Therefore, from theoreticalfittings of the spectra, complex 1 takes the unusual valence
state of Fe2.2+Fe2.8+ at 295 K in the Mössbauer timescale.
On the other hand, Mössbauer spectra of complex 2 exhibit
typical valence trapped spectra. The temperature dependenceof δ and ∆ are typical behavior of valence trapped complexes
and theoretical results of τ = 1.3 × 10 -6 s reflects that the electron transfer rate is slower than the Mössbauer timescale. The
same arguments can be applied to complex 3, and thus the theoretical fits of complex 3 are unreliable because the area ratioof FeII and FeIII for complex 3 is not equal at 295 K.
Compared to other complexes, complex 4 at 295 K shows
faster electron transfer than the Mössbauer timescale and only
an average spectrum is observed. Theoretical fitting of complex 4 describes τ = 2.9 × 10 -8 s at 295 K. As shown in Figure
6, line broading of spectra are observed with increasing thetemperature and the two doublets converged together above
200 K. This behavior of the spectra is observed in valence
detrapping processes and thus the complex 4 exhibits a valence
trapped to valence detrapped transition between 5 K and 295 Kin Mössbauer timescale.
Reference(1) A. L. Feig and S. J. Lippard, Chem. Rev. 94, 759 (1994).
(2) R. E. Stenkamp, L. C. Sieker, L. H. Jensen, and J. SandersLoehr, Nature(London) 291, 263 (1981); R. E. Stenkamp,
L. C. Sieker, and L. H. Jensen, J. Am. Chem. Soc. 106, 618(1984).
(3) P. C. Wilkins and R. G. Wilkins, Coord. Chem. Rev. 79,
195 (1987); R. G. Wilkins and P. C. Harrington, Adv.
Inorg. Biochem. 5, 51 (1983).
(4) L. Yhelander and P. Reichard, Annu. Rev. Biochem. 48,
133 (1979); P. Reichard and A. Ehrenberg, Science 221,
514 (1987); B. M. Sjöberg, T. M. Loehr, and J. SandersLoehr Jr., J. Biochem. 21, 96 (1982).
(5) J. G. Dewitt, J. G. Bensten, A. C. Rosenzweig, B. Hedman,
J. Green, S. Pilkington, G. C. Bensten, G. C.
Papaefthymiou, H. Dalton, K. O. Hodbson, and S. J.
Lippard, J. Am. Chem. Soc. 113, 9219 (1991).
(6) B. G. Fox, W. A. Froland, J. E. Dege, and J. D. Lipscomb,
J. Biol. Chem. 264, 10023 (1989).
(7) M. P. Woodl and H. Dalton, J. Biol. Chem. 259, 53 (1984).
(8) B. A. Averill, J. G. Davis, S. Burman, T. Zirino, J. SandersLoehr, T. M. Loehr, J. T. Sage, and P. G. Debrunner, J. Am.
Chem. Soc. 109, 3760 (1987); S. M. Kauzlarich,. B. K. Teo,T. Zirino, S. Burman, J.C. Davis, and B. A. Averill, Inorg.
Chem. 25, 2781 (1986).
(9) E. Sinn, G. J. O’Connor, J. de Jersey, and B. Zerner, Inorg.
Chim. Acta 78, L13 (1983).
(10) B.C. Antanaitis and P. Aisen, Adv. Inorg. Biochem. 5, 111(1983).
(11) M. Suzuki, A. Uehara, H. Oshio, K. Endo, M. Yanagi, S.

R18 J. Nucl. Radiochem. Sci., Vol. 7, No. 1, 2006
Kida, and K. Saito, Bull. Chem. Soc. Jpn. 60, 3547 (1987);
M. Suzuki, A. Uehara, H. Oshio, K. Endo, M. Yanagi, S.
Kida, and K. Saito, Bull. Chem. Soc. Jpn. 61, 3907 (1988).
(12) A. S. Borovik, B. P. Murch, and L. Que Jr., J. Am. Chem.
Soc. 109, 7190 (1987); M. S. Mashuta, R. J. Webb, K. J.
Oberhausen, J. F. Richardson, R. M. Buchanan, and D. N.
Hendrickson, J. Am. Chem. Soc. 111, 2745 (1989); M. S.
Mashuta, R. J. Webb, J. K. McCusker, E. A. Schmitt, K. J.
Oberhausen, J. F. Richardson, R. M. Buchanan, and D. N.
Hendrickson, J. Am. Chem. Soc. 114, 3815 (1992); A. S.
Borovik and L. Que Jr., J. Am. Chem. Soc. 110, 2345
(1988).
(13) A. Neves, M. A. de Brito, I. Vencato, V. Drago, K. Griesar,and W. Haase, Inorg. Chem. 35, 2360 (1996); C. Belle, I.
Gautier-Luneau, J. -L. Pierre, and C. Scheer, Inorg. Chem.
35, 3706 (1996).
(14) Y. Maeda, Y. Tanigawa, S. Hayami, and Y. Takashima,
Chem. Lett. 1992, 591 (1992); Y. Maeda, Y. Tanigawa, N.
Matsumoto, H. Oshio, M. Suzuki, and Y. Takashima, Bull.
Chem. Soc. Jpn. 67, 125 (1994); Y. Maeda, Y. Tanigawa, Y.
Ando, Y. Takashima, and N. Matsumoto, Acta Chim.
Hungarica, Models in Chem. 130, 55 (1993).
(15) A. S. Borovik, V. Papaefthymiou, L. F. Taylor, O. P.
Anderson, and L. Que Jr., J. Am. Chem. Soc. 111, 6183
(1989); T. Meyer, J. Chem. Phys. Lett. 64, 417 (1979); J.
Hopfield, J. Proc. Natl. Acad. Sci. U.S.A. 71, 3640 (1974);

Maeda
N. R. Kestner, J. Logan, and J. Jortner, J. Phys. Chem. 78,
2148 (1974).
(16) T. Manago, S. Hayami, H. Oshio, S. Osaki, H. Hasuyama,
R. H. Herber, and Y. Maeda, J. Chem. Soc. Dalton Trans.
1999, 1001 (1999).
(17) M. B. Robin and P. Day, Adv. Inorg. Chem. Radiochem.
10, 247 (1967).
(18) N. S. Hush, Prog. Inorg. Chem. 8, 391 (1967).
(19) C. Creutz, Prog. Inorg. Chem. 30, 1 (1983).
(20) T. Manago, S. Hayami, and Y. Maeda, J. Radioanal. Nucl.
Chem. 239, 267 (1999).
(21) G. S. Matouzenko, A. Bousseksou, S. A. Borshch, M.
Perrin, S. Zein, L. Salmon, G. Molnar, and S. Lecocq,
Inorg. Chem. 43, 227 (2004).
(22) J. P. Martin, J. Zarembowitch, A. Bousseksou, A. Dworkin,
J. G. Haasnoot, and F. Varret, Inorg. Chem. 33, 6325
(1994).
(23) T. Kambara, D. N. Hendrickson, M. Sorai, and S. M. Oh, J.
Chem. Phys. 85, 2895 (1986).
(24) Y. Maeda, A. Ishida, M. Ohba, S. Sugihara, and S. Hayami,
Bull. Chem. Soc. Jpn. 75, 2441 (2002).
(25) H. H. Wickman, Mössbauer Effect Methodology, Ed. I.
J. Gruverman, Plenum, New York Vol. 2, 39 (1966).
(26) H. H. Wickman, M. P. Klein, and D. A. Shirley, Phys. Rev.
152, 345 (1966).