Molecular and electronic structures of iron(II)/(III) complexes containing N,S-coordinated, closed-shell o-aminothiophenolato(1-) and o-iminothiophenolato(2-) ligands

Article abstract of DOI:10.1021/ic020617c

The coordination chemistry of the ligands o-aminothiophenol, H(abt), 4,6-di-tert-butyl-2-aminothiophenol, H[L^AP], and 1,2-ethanediamine-N,N′-bis(2-benzenethiol), H₄(′N₂S₂′), with FeCl₂ under strictly anaerobic and increasingly aerobic conditions has been systematically investigated. Using strictly anaerobic conditions, the neutral, air-sensitive, yellow complexes (μ-S,S)[Fe^II(abt)₂]₂ (1), (μ-S,S)[Fe^II(L^AP)₂]₂ · 8CH₃OH (2), and (μ-S,S)[Fe^II(′H₂N₂S₂ ′)]₂ · CH₃CN (3) containing high spin ferrous ions have been isolated where (abt)^1-, (L^AP)^1-, and (′H₂N₂S₂′)^2- represent the respective N,S-coordinated, aromatic o-aminothiophenolate derivative of these ligands. When the described reaction was carried out in the presence of trace amounts of O₂ and [PPh₄]Br, light-green crystals of [PPh₄][Fe^II(abt)₂(itbs)] · [PPh₄]Br (4) were isolated. The anion [Fe^II(abt)₂(itbs)]^- contains a high spin ferrous ion, two N,S-coordinated o-aminophenolate(1-) ligands, and an S-bound, monoanionic o-iminothionebenzosemiquinonate(1-) π radical, (itbs)^-. Complex 4 possesses an S_t = 3/2 ground state. In the absence of [PPh₄]Br and presence of a base NEt₃ and a little O₂, the ferric dimer (μ-NH,NH)[Fe^III(L^AP)(L^IP)]₂ (5a) and its isomer (μ-S,S)[Fe^III(L^AP)(L^IP)]₂ (5b) formed. (L^IP)^2- represents the aromatic o-iminothiophenolate(2-) dianion of H[L^AP]. The structures of compounds 2, 4, and 5a have been determined by X-ray crystallography at 100(2) K. Zero-field Moessbauer spectroscopy of 1, 2, 3, and 4 unambiguously shows the presence of high spin ferrous ions: The isomer shift at 80 K is in the narrow range 0.85-0.92 mm s^-1, and a large quadrupole splitting, |ΔE_Q|, in the range 3.24-4.10 mm s^-1, is observed. In contrast, 5a and 5b comprise both intermediate spin ferric ions (S_Fe = 3/2) which couple antiferromagnetically in the dinuclear molecules yielding an S_t = 0 ground state.

Full text of DOI:10.1021/ic020617c

Inorg. Chem. 2003, 42, 3208−3215
Molecular and Electronic Structures of Iron(II)/(III) Complexes Containing
N,S-Coordinated, Closed-Shell o-Aminothiophenolato(1−) and
o-Iminothiophenolato(2−) Ligands
Prasanta Ghosh, Ameerunisha Begum, Eckhard Bill, Thomas Weyhermu1ller, and Karl Wieghardt*
Max-Planck-Institut fu¨r Strahlenchemie, Stiftstrasse 34-36,
D-45470 Mu¨lheim an der Ruhr, Germany
Received October 14, 2002
The coordination chemistry of the ligands o-aminothiophenol, H(abt), 4,6-di-tert-butyl-2-aminothiophenol, H[LAP],
and 1,2-ethanediamine-N,N′-bis(2-benzenethiol), H (′N S ′), with FeCl2 under strictly anaerobic and increasingly
4
2 2
aerobic conditions has been systematically investigated. Using strictly anaerobic conditions, the neutral, air-sensitive,
II
II
II
yellow complexes (µ-S,S)[Fe (abt)2]2 (1), (µ-S,S)[Fe (LAP)2]2‚8CH OH (2), and (µ-S,S)[Fe (′H N S ′)]2‚CH CN (3)
3
2
2
2
3
containing high spin ferrous ions have been isolated where (abt)1-, (LAP)1-, and (′H N S ′)2- represent the respective
2
2 2
N,S-coordinated, aromatic o-aminothiophenolate derivative of these ligands. When the described reaction was carried
II
out in the presence of trace amounts of O and [PPh4]Br, light-green crystals of [PPh4][Fe (abt)2(itbs)]‚[PPh4]Br (4)
2
were isolated. The anion [Fe (abt)2(itbs)]- contains a high spin ferrous ion, two N,S-coordinated o-aminophenolate(1−)
II
ligands, and an S-bound, monoanionic o-iminothionebenzosemiquinonate(1−) π radical, (itbs)-. Complex 4 possesses
an S ) 3/2 ground state. In the absence of [PPh4]Br and presence of a base NEt3 and a little O , the ferric dimer
t
2
III
IP
III
IP
IP 2-
(µ-NH,NH)[Fe (LAP)(L )]2 (5a) and its isomer (µ-S,S)[Fe (LAP)(L )]2 (5b) formed. (L ) represents the aromatic
o-iminothiophenolate(2−) dianion of H[LAP]. The structures of compounds 2, 4, and 5a have been determined by
X-ray crystallography at 100(2) K. Zero-field Mo¨ssbauer spectroscopy of 1, 2, 3, and 4 unambiguously shows the
presence of high spin ferrous ions: The isomer shift at 80 K is in the narrow range 0.85−0.92 mm s-1, and a large
quadrupole splitting, |∆EQ|, in the range 3.24−4.10 mm s-1, is observed. In contrast, 5a and 5b comprise both
3
intermediate spin ferric ions (S ) /2) which couple antiferromagnetically in the dinuclear molecules yielding an
Fe
S ) 0 ground state.
t
Introduction
Sellmann et al.15,16 described the facile synthesis, crystal
structures, and spectroscopic properties of stable o-amino-
thiophenolato complexes of high-valent FeIV and even FeV.
The coordination chemistry of o-aminothiophenolato ligands
with iron ions has been fairly extensively studied since the
original paper by Larkworthy and Philips et al.1 in 1968 who
reported the dimeric complex (µ-S,S)[FeII(abt)2]2 where
(abt)1- represents the N,S-coordinated, aromatic monoanion
o-aminothiophenolate(1-). Since then a number of ferrous
and ferric complexes of this kind have been reported.2-14
(7) Sellmann, D.; Hannakam, M.; Knoch, F.; Moll, M. Z. Naturforsch.
1992, 47b, 1545.
(8) Karsten, P.; Maichle-Mo¨ssmer, C.; Stra¨hle, J. Z. Anorg. Allg. Chem.
1997, 623, 1644.
(9) Sellmann, D.; Emig, S.; Heinemann, F. W.; Knoch, F. Z. Naturforsch.
1998, 53b, 1461.
(10) Noveron, J. C.; Olmstead, M. M.; Mascharak, P. K. Inorg. Chem.
1998, 37, 1138.
(11) Noveron, J. C.; Herradova, R.; Olmstead, M. M.; Mascharak, P. K.
Inorg. Chim. Acta 1999, 285, 269.
(12) Sellmann, D.; Utz, J.; Heinemann, F. W. Inorg. Chem. 1999, 38, 5314.
(13) Sellmann, D.; Utz, J.; Heinemann, F. W. Inorg. Chem. 1999, 38, 459.
(14) Liaw, W.-F.; Lee, N.-H.; Chen, C.-H.; Lee, C.-M.; Lee, G.-H.; Peng,
S.-M. J. Am. Chem. Soc. 2000, 122, 488.
(15) Sellmann, D.; Emig, S.; Heinemann, F. W.; Knoch, F. Angew. Chem.
1997, 109, 1250; Angew. Chem., Int. Ed. Engl. 1997, 36, 1201.
(16) Sellmann, D.; Emig, S.; Heinemann, F. W. Angew. Chem. 1997, 109,
1808; Angew. Chem., Int. Ed. Engl. 1997, 36, 1734.
* To whom correspondence should be addressed. E-mail: wieghardt@
mpi-muelheim.mpg.de.
(1) Larkworthy, L. F.; Murphy, J. M.; Phillips, D. J. Inorg. Chem. 1968,
7, 1436.
(2) Elder, M. S.; Prinz, G. M.; Thornton, P.; Busch, D. H. Inorg. Chem.
1968, 7, 2426.
(3) Le Borgne, G.; Grandjean, D. Acta Crystallogr. 1973, B29, 1040.
(4) Sellmann, D.; Reineke, U. J. Organomet. Chem. 1986, 314, 91.
(5) Taka´cs, J.; Soo´s, E.; Nagy-Magos, Z.; Marko´, L. Inorg. Chim. Acta
1989, 166, 39.
(6) Sellmann, D.; Ka¨ppler, O. Z. Naturforsch. 1987, 42b, 1291.
3208 Inorganic Chemistry, Vol. 42, No. 10, 2003
10.1021/ic020617c CCC: $25.00 © 2003 American Chemical Society
Published on Web 04/10/2003

Structures of Fe(II)/(III) Complexes
Scheme 1. Ligand and Abbreviations
Scheme 2. Bond Lengths in N,S-Coordinated Anions
2. In addition, N,S-coordinated (L )
ISQ 1- and (itbs)1- radicals
display a quinoid type distortion of the six-membered ring
which is not observed in their closed-shell analogues. This
distortion comprises two alternating short C-C distances at
1.37 ( 0.01 Å and four longer ones at ∼1.415 ( 0.01 Å,
whereas in the closed-shell, aromatic mono- and dianions,
the six C-C bond lengths are equidistant at 1.39 ( 0.01 Å
(Scheme 2).
In the past, many authors have not explicitly considered
the presence of o-iminothionebenzosemiquinonate(1-) π
radicals in a given coordination compound but have invari-
ably derived the formal oxidation state of the central metal
ion by assuming the closed-shell o-iminothiophenolate di-
anion to be present. This practice leads to a situation where
the formal oxidation number and the physical or spectro-
scopic oxidation state differ by one unit.17
As it is possible to determine the true dn electron
configuration of the central metal ion and measure its
physical or spectroscopic oxidation state spectroscopically
(UV-vis, EPR, magnetic circular dichroism (MCD), or
X-ray absorption near edge (XANE) spectroscopy) and/or
magnetochemically, we decided to (re)investigate the coor-
dination chemistry of iron with o-aminothiophenol derived
ligands. This appeared to be very appealing because Mo¨ss-
bauer spectroscopy gives independent, valuable information
about the dn electron configuration in a given complex. We
will show in this work and a subsequent paper that physical
or spectroscopic oxidation states >III of the central iron ions
have not been reached in this chemistry.
In order to avoid solubility problems often encountered
in compounds containing the unsubstituted o-aminothio-
phenolates, we decided to use Sellmann’s ligands 4,6-di-
tert-butyl-2-aminothiophenol,6 H[LAP], and 1,2-ethanedi-
amine-N,N′-bis(2-benzenethiol),19 H2(′H2N2S2′).
In this paper, the first part of two successive papers, we
will describe the synthesis and spectroscopic characterization
of iron(II)/(III) complexes containing N,S-coordinated, closed-
shell o-aminothiophenolate(1-) or o-iminothiophenolato(2-)
ligands. In the second part (Ghosh, P.; Bill, E.; Weyher-
mu¨ller, T.; Wieghardt, K. J. Am. Chem. Soc., in press), we
will then discuss compounds containing N,S-coordinated
open-shell o-iminothionebenzosemiquinonate(1-) π radical
ligands. Scheme 3 summarizes the complexes prepared here.
In these latter two species, the deprotonated o-iminothio-
phenolate(2-) dianion was proposed to be present.
In contrast, in a recent publication we have shown17 that
o-aminothiophenolates are redox noninnocent ligands in
the sense that they can be N,S-coordinated to transition
metal ions (i) as closed-shell, aromatic o-aminothio-
phenolates(1-), (ii) as aromatic o-iminothiophenolate(2-)
dianions, and, contrary to common wisdom, also (iii) as open-
shell o-iminothionebenzosemiquinonate(1-) monoanions
(Scheme 1). Thus, we have established that it is experimen-
tally possible to distinguish between the two electronic
structures A and B by using high-quality, single crystal X-ray
crystallography.
The most distinctive structural features of an N,S-
coordinated o-iminothionebenzosemiquinonato(1-) π radical
are the experimentally observed, short C-S and C-N bond
lengths at 1.72 ( 0.01 and 1.36 ( 0.01 Å, respectively,
which are observed at 1.76 ( 0.01 and 1.40 ( 0.01 Å in the
aromatic dianions (LIP)2- or (ibt)2- shown in Schemes 1 and
Experimental Section
The ligand 4,6-di-tert-butyl-2-aminothiophenol (2-mercapto-3,5-
di-tert-butylaniline), H[LAP], was prepared by using the elegant route
(18) Chun, H.; Weyhermu¨ller, T.; Bill, E.; Wieghardt, K. Angew. Chem.
2001, 113, 2552; Angew. Chem., Int. Ed. 2001, 40, 2489.
(19) Corbin, J. L.; Work, D. E. Can. J. Chem. 1974, 52, 1054.
(17) Herebian, D.; Bothe, E.; Bill, E.; Weyhermu¨ller, T.; Wieghardt, K. J.
Am. Chem. Soc. 2001, 123, 10012.
Inorganic Chemistry, Vol. 42, No. 10, 2003 3209

Ghosh et al.
Scheme 3. Complexes Prepared in This Study
decanting the THF solvent, the crystals of 4 were separated
manually by using a needle and transferred to a vial in a glovebox.
Yield: 0.70 g (60%). Anal. Calcd for C66H57BrFeN3P2S3: C, 66.84;
H, 4.84; N, 3.54; Br, 6.74; S, 8.11; Fe, 4.71. Found: C, 66.8; H,
4.7; N, 3.5; Br, 6.2; Fe, 4.7; S, 8.1.
(µ-NH,NH)[FeIII(LAP)(LIP)]2 (5a). To a solution of the ligand
H[LAP] (0.50 g; 2.1 mmol) in dry O2-saturated CH3CN (50 mL)
was added under an argon blanketing atmosphere FeCl2 (0.13 g;
1.0 mmol). Triethylamine (0.20 g; 2.0 mmol) was added to this
yellow reaction mixture whereupon a rapid color change to green
was observed. After the solution was stirred for 1 h at ambient
temperature, a light blue-green precipitate of 5a formed which was
collected by filtration and dried under argon. Yield: 0.40 (76%).
Single crystals suitable for X-ray crystallography of 5a‚2CH3CN‚
CH2Cl2 were grown from a solution of CH2Cl2 (40 mL) and CH3CN
(20 mL) containing 100 mg of 5a by slow evaporation of the solvent
under argon. IR(KBr disk): ν(N-H) 3208, 3146, 3175, 3122, 3076,
3055. Anal. Calcd for C56H86Fe2N4S4: C, 63.74; H, 8.21; N, 5.31;
S, 12.15; Fe, 10.62. Found: C, 64.0; H, 8.2; N, 5.4; S, 12.2; Fe,
10.6.
(µ-S,S)[FeIII(LAP)(LIP)]2‚2CH3CN‚CH3OH (5b). When the same
reaction as described for 5a was carried out in dry, O2-saturated
CH3CN (30 mL) and dry CH3OH (10 mL) containing Li[OCH3]
(3 mmol), a brown precipitate of 5b was obtained. Yield: 0.47 g
(80%). IR(KBr disk): ν(N-H) 3314, 3280, 3264. After drying 5b
in vacuo for 12 h at 45 °C, the elemental analysis (C, H, N, S, Fe)
was nearly identical to that of 5a.
X-ray Crystallographic Data Collection and Refinement of
the Structures. A dark brown single crystal of 2, a yellow crystal
of 4, and a deep green specimen of 5a were coated with
perfluoropolyether, picked up with a glass fiber, and immediately
mounted in the nitrogen cold stream of the diffractometers to
prevent loss of solvent. Intensity data were collected at 100 K using
graphite monochromated Mo KR radiation (λ ) 0.71073 Å). Final
cell constants were obtained from a least-squares fit of a subset of
several thousand strong reflections. Data collection was performed
by hemisphere runs taking frames at 0.3° (Siemens SMART) and
1.0° (Nonius Kappa-CCD) in ω. A semiempirical absorption
correction using the program SADABS20 was performed on the
data set of 5a, and intensity data of 4 were corrected with
MulScanAbs21 while data of 2 were left uncorrected. Crystal-
lographic data of the compounds and diffractometer types used are
listed in Table 1. The Siemens ShelXTL22 software package was
used for solution, refinement, and artwork of the structure. The
structures were readily solved by direct methods and difference
Fourier techniques. All non-hydrogen atoms except some atoms in
disordered parts were refined anisotropically, and hydrogen atoms
attached to carbon atoms were placed at calculated positions and
refined as riding atoms with isotropic displacement parameters.
Hydrogens attached to nitrogen atoms were, where possible, located
from the difference map and refined with restrained N-H distances
using the SADI option. Disordered solvent molecules in 2 and 5a
were refined using a split atom model with restrained distances.
The bromide anion in 4 was split over two positions with refined
occupation factors of about 0.85 and 0.15 giving both positions
the equal displacement parameters.
described by Sellmann and Ka¨ppler6 with a slight modification. In
contrast to the original procedure, we have not prepared the zinc(II)
complex as a means for purification but oxidized the crude solution
containing the ligand with air instead which yields the disulfide
(C14H22NS)2 in quantitative yield as yellow crystalline and air-stable
1
solid. H NMR (500 MHz, CDCl3) δ ) 1.23 (s, 18H), 1.31 (s,
18H); 4.27 (4H), 6.56 (d, 2H), 6.76 (d, 2H). 13C NMR (100 MHz,
CDCl3) δ ) 31.08, 31.86, 34.80, 37.34, 110.74, 114.43, 151.17,
153.42, 153.92. 1,2-Ethanediamine-N,N′-bis(2-benzenethiol) has
been prepared as described in ref 19.
Syntheses of Complexes. (µ-S,S)[FeII(abt)2]2 (1). This very air-
sensitive complex has been described previously.1 We have used a
simplified route for its preparation. To a deaerated methanolic
solution (60 mL) of 2-aminothiophenol (0.50 g; 4.0 mmol) and
triethylamine (0.45 g; 4.0 mmol) was added under strictly anaerobic
conditions (glovebox) FeCl2‚4H2O (0.40 g; 2.0 mmol). The reaction
mixture was heated to reflux under an Ar atmosphere for 3 h during
which time a pale yellow, air-sensitive precipitate formed which
was filtered off. IR(KBr disk): νas(NH2) 3269, 3255 cm-1; νs(NH2)
3104, 3060 cm-1. Anal. Calcd for C24H24Fe2N4S4: C, 47.38; H,
3.98; N, 9.21; S, 21.08. Found: C, 47.1; H, 4.0; N, 9.1; S, 21.3.
(µ-S,S)[FeII(LAP)2]2‚8CH3OH (2). To a solution of 4,6-di-tert-
butyl-2-aminothiophenol (H[LAP]) (0.50 g; 2.0 mmol) and triethyl-
amine (0.2 g; ∼2.0 mmol) in dry CH3OH (60 mL) was added under
strictly anaerobic conditions (glovebox, Ar) FeCl2‚4H2O (0.20 g;
1.0 mmol). The yellow reaction mixture was stirred at 20 °C for
15 min and stored in a glovebox for 4 days within which time
yellow crystals of 2 were obtained. Yield: 0.70 g (70%). IR(KBr
disk): νas(NH2) 3298, 3267; νs(NH2) 3208 cm-1. Anal. Calcd for
C56H88Fe2N4S4 (after drying in vacuo): C, 63.62; H, 8.39; N, 5.30;
S, 12.13; Fe, 10.56. Found: C, 63.5; H, 8.4; N, 5.2; S, 12.3; Fe,
10.6.
(µ-S,S)[FeII(′H2N2S2′)]2‚CH3CN (3). To a degassed solution of
the ligand 1,2-ethanediamine-N,N′-bis(2-benzenethiol) (0.60 g; 2.2
mmol) in dry acetonitrile (40 mL) was added under an Ar blanketing
atmosphere FeCl2 (0.254 g; 2.0 mmol). Triethylamine (0.355 g)
was added dropwise with stirring at ambient temperature under
strictly anaerobic conditions (glovebox). Within 2 h of stirring, a
yellow, microcrystalline solid formed which was collected by
filtration, washed with acetonitrile, and dried. The material is very
air-sensitive and must be stored under Ar. Yield: 0.58 g (84%).
Anal. Calcd for C28H28N4S4Fe2‚CH3CN: C, 51.36; H, 4.45; N, 9.98;
S, 18.28. Found: C, 51.5; H, 4.3; N, 10.4; S, 18.0. IR(KBr disk):
ν(N-H) 3264 cm-1
.
[PPh4][FeII(abt)2(itbs)]‚[PPh4]Br (4). To a solution of the ligand
H[LAP] (0.38 g; 3.0 mmol) and triethylamine (0.3 g; 3.0 mmol) in
aerated tetrahydrofurane (60 mL) were added under an Ar pro-
tecting atmosphere FeCl2‚4H2O (0.20 g; 1.0 mmol) and [PPh4]Br
(0.42 g; 2.0 mmol). The mixture was stirred at ambient temperature
for 10 min and stored in a closed vessel under Ar for 2 days. During
this time, yellowish-green crystals of 4 grew on the walls of the
flask along with an amorphous yellow powder of probably 1. After
Physical Measurements. Electronic spectra of complexes were
recorded with an HP 8452 A diode array spectrophotometer
(20) Sheldrick, G. M. SADABS; Universita¨t Go¨ttingen: Go¨ttingen, Ger-
many, 1994.
(21) Spek, A. L. PLATON 99 program suite; Utrecht University: Utrecht,
The Netherlands, 1999.
(22) ShelXTL V.5; Siemens Analytical X-ray Instruments, Inc.: Madison,
WI, 1994.
3210 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures of Fe(II)/(III) Complexes
Table 1. Crystallographic Data for 2‚8CH3OH, 4, and 5a‚2CH3CN‚CH2Cl2
2
4
5a
chem formula
fw
C64H120Fe2N4O8S4
1313.58
C66H57BrFeN3P2S3
1186.03
C61H94Cl2Fe2N6S4
1222.26
space group
a, Å
b, Å
P1h, No. 2
10.7231(12)
11.727(2)
16.112(2)
83.38(2)
71.77(2)
71.40(2)
1823.6(4)
1
P212121, No. 19
12.5998(4)
19.5165(8)
23.3203(11)
90
90
90
5734.6(4)
4
P1h, No. 2
10.6430(8)
10.6610(8)
17.0322(12)
76.64(2)
72.79(2)
66.92(2)
1683.6(2)
1
c, Å
R, deg
â, deg
γ, deg
V, Å
Z
T, K
100(2)
100(2)
100(2)
F calcd, g cm-3
diffractometer
reflns collected/θmax
unique reflns/[I > 2σ(I)]
no. params/restraints
µ(Mo KR), cm-1
R1a/GOFb
wR2c (I > 2σ(I))
1.196
1.374
1.205
Nonius Kappa-CCD
13233/24.99
6335/4571
365/21
5.62
0.0711/1.063
0.1627
Nonius Kappa-CCD
49899/27.50
13137/11149
689/0
11.69
0.0600/1.037
0.1465
Siemens SMART
18536/33.19
11050/8025
381/3
6.74
0.0544/1.034
0.1641
a Observation criterion: I > 2σ(I). R1 ) ∑||Fo| - |Fc||/∑|Fo|. b GOF ) [∑[w(Fo - Fc )2]/(n - p)]1/2
.
c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]1/2 where
2
2
2
2
2
w ) 1/σ2(Fo ) + (aP)2 + bP, P ) (Fo + 2Fc )/3.
2
2
2
(range: 190-1100 nm). Temperature-dependent (2-298 K) mag-
netic susceptibilities of powdered samples of complexes were
measured with a SQUID magnetometer (MPMS Quantum Design)
in an external magnetic field of 1.0 T. The experimental data were
corrected for underlying diamagnetism by use of tabulated Pascal’s
constants and where appropriate for temperature-independent
paramagnetism, TIP. Mo¨ssbauer data were recorded on an alternat-
ing constant-acceleration spectrometer. The minimum experimental
line width was 0.24 mm s-1 (full width at half-height). The sample
temperature was maintained constant in an Oxford Instruments
Variox cryostat. Isomer shifts are quoted relative to R-Fe at 298
K.
Results and Discussion
Syntheses and Characterization of Complexes. The
reaction of the ligand o-aminothiophenol, H[abt], or 4,6-di-
tert-butyl-2-aminothiophenol, H[LAP], or 1,2-ethanediamine-
N,N′-bis(2-benzenethiol), H2(H2N2S2), and 2 or 1 equiv of
triethylamine in dry methanol or acetonitrile with FeCl2 under
strictly anaerobic conditions at ambient temperature affords
the yellow, microcrystalline, extremely air-sensitive com-
plexes (µ-S,S)[FeII(abt)2]2 (1), (µ-S,S)[FeII(LAP)2]2 (2), and
(µ-S,S)[FeII(′H2N2S2′)]2 (3), respectively. These compounds
consist of two N,S-coordinated, aromatic o-aminothio-
phenolato(1-) ligands and a high spin ferrous ion. Two such
monomeric units are connected via two thiolato bridges
rendering the FeII ions five-coordinate (FeN2S3).
Complex 1 has been described previously1 as an insoluble,
yellow powder. From variable-temperature (70-310 K)
magnetic susceptibility measurements, it was concluded1 that
two high spin ferrous ions (SFe ) 2) are antiferromagnetically
coupled with J ) -11.1 cm-1; converted according to the
notation of eq 1, g ) 2.07, yielding the diamagnetic ground
state St ) 0. We have repeated these measurements in the
range 4-300 K, and from a fit of the data to the Hamiltonian,
eq 1, the following parameters have been established: J )
-47 ( 4 cm-1, g ) 2.0 (fixed), D1 ) D2 ) 10 ( 5 cm-1;
E/D ) 0 (fixed), and a paramagnetic impurity of S ) 5/2 of
Figure 1. Temperature dependence of the magnetic moment, µeff, of
dinuclear 1 and 3 (top) and mononuclear 4 (bottom). The parameters for
the best fit are given in the text.
4.5% (or 5.6% for S ) 2). We note that the present (see
Figure 1) and the previous experimental data1 of 1 in the
range 80-300 K are in good agreement. The discrepancy
of J values is due to errors in the fitting procedure in ref 1.
2
H ) -2JBS ‚BS + [D (S2 - 1/ S (S + 1)] + g µ ‚BS ‚BB
∑
1
2
i
z,i
3
i
i
i
B
i
i)1
(1)
The structure of 1 can be composed of either two cis-
FeN2S2 or two trans-FeN2S2 monomers which are bridged
in both instances by two µ-thiophenolato groups.
Inorganic Chemistry, Vol. 42, No. 10, 2003 3211

Ghosh et al.
In order to obtain a more soluble analogue of 1, the dimeric
yellow complex (µ-S,S)[FeII(LAP)2]2‚8CH3OH (2) was syn-
thesized by using the described protocol but with the ligand
4,6-di-tert-butyl-2-aminothiophenol. The crystal structure
determination of 2 (see later) confirms the dimeric nature
of this species. The magnetic moment of 2 at 295 K is 4.2
µB per dimer which corresponds nicely to the value of 4.0
µB determined for 1 at this temperature.
Complex 4 is air-sensitive and was stored under argon in
a refrigerator. The crystal structure determination (see later)
clearly establishes the presence of the mononuclear mono-
anion [FeII(abt)2(itbs)]- containing a high spin ferrous ion,
two N,S-coordinated o-aminothiophenolato(1-) anions, (abt)1-,
and, in addition, a monodentate S-coordinated iminothione-
benzosemiquinonate(1-) radical, (itbs)1-•
.
The temperature dependence of the magnetic moment of
4 (3-290 K) shown in Figure 1 (bottom) was modeled
successfully by using the same spin Hamiltonian, eq 1, as
shown. The following parameters were obtained from a best
fit: a high spin ferrous ion (SFe ) 2) is antiferromagnetically
coupled to a ligand radical (Srad ) 1/2) with J ) -135 ( 25
cm-1; gFe ) 2.12 ( 0.1, grad ) 2.0 (fixed), |D|3/2 ) 5.0 cm-1
(fixed) yielding the observed St ) 3/2 ground state of 4. Thus,
trace amounts of oxygen have generated a ligand radical
anion under the described reaction conditions.
By using slightly different reaction conditions as already
described for the synthesis of 4, we have discovered that it
is also possible to selectively oxidize the FeII to FeIII ions.
Thus, the reaction of the ligand H[LAP] and FeCl2 (2:1) in
dry acetonitrile which was saturated with dioxygen with 2
equiv of triethylamine induces a color change from yellow
to green, and a bluish-green precipitate of (µ-NH,NH)-
[FeIII(LAP)(LIP)]2 (5a) formed in 76% yield.
By using 1,2-ethanediamine-N,N′-bis(2-benzenethiol) as
starting material in the preparation, yellow microcrystals of
(µ-S,S)[FeII(′H2N2S2′)]2‚CH3CN (3) were obtained. The
magnetic moment of 5.5 µB at 295 K indicates the dimeric
nature of 3. Figure 1 shows the temperature dependence of
the magnetic moment per dimer and a best fit which was
obtained with gFe ) 2.18 ( 0.2, J ) -35 ( 2 cm-1 (S1 )
S2 ) 2), |D| ) 10 ( 5 cm-1, a paramagnetic impurity S )
5/2 of 2% (or 2.5% for S ) 2), and øTIP ) 300 × 10-6 emu.
The protonation and oxidation level of the ligands in 5a
as one (LAP)1- and one (LIP)2- is corroborated by infrared
spectroscopy (νas, νs(NH2)- and ν(N-H)-stretching vibrations
are observed) and its crystal structure determination (see a
following section). The electron rich, N,S-coordinated di-
anion (LIP)2- acts as bridging ligand via the imido group to
form a dinuclear complex (FeN3S2 polyhedron).
When this reaction was carried out in an acetonitrile/
methanol mixture using lithium methoxide as a base, a brown
precipitate of presumably (µ-S,S)[FeIII(LAP)(LIP)]2‚2CH3CN‚
CH3OH (5b) was obtained in excellent yields. Figure 2 shows
the differing electronic spectra of 5a and 5b in CH2Cl2
solution under anaerobic conditions. We have not been able
to obtain single crystals of 5b for an X-ray structure
determination. Therefore, the proposed and shown (µ-
S,S)[FeIII(LAP)(LIP)]2 structure is tentative.
Since 1, 2, and 3 each contain a high spin ferrous ion and
the ligands are in their fully reduced forms, namely N,S-
coordinated o-aminothiophenolate, we decided to study the
reaction products under more aerobic (oxidizing) conditions.
To this end, we first used dioxygen saturated solvents but
performed the reactions under an argon blanketing atmo-
sphere (the solvents were not purged with argon). Thus, from
an aerated tetrahydrofuran solution of the ligand H[LAP] and
NEt3 and FeCl2‚4H2O (3:3:1) to which [PPh4]Br had been
added, yellow-green crystals of [PPh4][FeII(abt)2(itbs)]‚
[PPh4]Br (4) grew within 2 days under Ar at 20 °C on the
wall of the vessel in ∼70% yield. In addition, a small amount
of yellow, microcrystalline 1 precipitated which was decanted
off with the solvent. The yellow-green crystals were then
manually collected with a long needle under anaerobic
conditions.
3212 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures of Fe(II)/(III) Complexes
Figure 4. Structure of the monoanionic complex [FeII(abt)2(itbs)]- in
crystals of 4.
Figure 2. Electronic spectra of 5a and 5b in CH2Cl2 solution under an
argon atmosphere.
Table 2. Selected Bond Distances (Å)
Complex 2
Fe1-N1
Fe1-N2
Fe1-S1
Fe1-S2
Fe1-S2*
Fe1-Fe1*
S1-C1
N1-C2
C1-C2
C1-C6
C2-C3
2.134(4)
2.229(4)
2.382(2)
2.394(1)
2.397(2)
2.919(2)
1.790(5)
1.447(6)
1.401(6)
1.419(6)
1.378(7)
S2-C21
N2-C22
C21-C22
C21-C26
C22-C23
C23-C24
C24-C25
C25-C26
C3-C4
1.795(4)
1.451(6)
1.406(6)
1.417(6)
1.382(6)
1.384(6)
1.386(6)
1.396(6)
1.374(6)
1.408(6)
1.385(6)
C4-C5
C5-C6
Complex 4
Fe1-N1
Fe1-N2
Fe1-S3
Fe1-S2
Fe1-S1
S1-C1
N1-C2
C1-C6
C1-C2
C2-C3
C3-C4
C4-C5
C5-C6
2.242(4)
2.268(4)
2.351(1)
2.377(1)
2.441(1)
1.771(5)
1.443(6)
1.389(7)
1.409(6)
1.378(7)
1.394(7)
1.392(8)
1.376(7)
S2-C7
1.753(4)
1.444(5)
1.402(6)
1.411(6)
1.393(6)
1.379(6)
1.392(6)
1.383(6)
1.747(5)
1.356(8)
1.329(8)
1.446(8)
1.569(9)
1.28(1)
N2-C8
C7-C12
C7-C8
C8-C9
C9-C10
C10-C11
C11-C12
S3-C13
N3-C14
C13-C14
C13-C18
C14-C15
C15-C16
C16-C17
C17-C18
Figure 3. Structure of the dimer in crystals of 2.
In solution (CH2Cl2), both 5a and 5b are very sensitive
toward dioxygen. The resulting products are described in a
subsequent paper.
Crystal Structure Determination. The structures of
complexes 2, 4, and 5a have been determined by X-ray
crystallography at 100(2) K. As pointed out previously,17
the geometric features of N,S-coordinated ligands (LAP)1-,
(LIP)2-, and (LISQ 1- differ significantly (Scheme 2) and allow
)
the assignment of the protonation and oxidation level of a
ligand in a given complex.
Figure 3 shows the structure of the dinuclear bis(µ-
thiolato)diferrous complex 2. Clearly, each iron ion is N,S-
bound to two (LAP)1- ligands (in cis position relative to each
other). The two R-NH2 groups per monomer are not
equivalent. Therefore, the IR spectrum of 2 displays two
antisymmetric and two symmetric N-H stretching frequen-
cies (see Experimental Section). This renders the central iron
ions divalent. The rather long Fe-N and Fe-S bond
1.44(1)
1.33(1)
Complex 5a
1.928(2)
Fe1-N2
Fe1-N1
Fe1-N2*
Fe1-S2
Fe1-S1
Fe1-Fe1*
S1-C1
S2-C21
N1-C2
N2-C22
C1-C2
C1-C6
C2-C3
C3-C4
1.384(3)
1.408(3)
1.401(3)
1.402(3)
1.427(3)
1.394(3)
1.393(3)
1.403(3)
1.391(3)
2.013(2)
2.118(2)
2.206(1)
2.211(1)
2.7192(7)
1.771(2)
1.770(2)
1.458(3)
1.423(3)
1.400(3)
1.423(3)
1.394(3)
C4-C5
C5-C6
C21-C22
C21-C26
C22-C23
C23-C24
C24-C25
C25-C26
distances are indicative of a high spin configuration (SFe
)
anion [FeII(abt)2(itbs)]- as shown in Figure 4. The five-
coordinate anion consists of two N,S-coordinated o-amino-
thiophenolato(1-) ligands, bound in cis-position relative to
each other, and a monodentate, S-bound o-iminothione-
benzosemiquinonato(1-) π radical which is disordered in
crystals of 4 as was judged from the comparatively large
anisotropic thermal parameters of the one nitrogen and six
carbon atoms of this ligand. From the fact that the Mo¨ssbauer
2) (Table 2) in excellent agreement with the magnetic
susceptibility measurements and the Mo¨ssbauer spectrum
(see in a following section). Similar structures are proposed
for complexes 1 and 3.
Complex 4 contains in one quarter of a unit cell two
tetraphenylphosphonium cations, an uncoordinated bromide
anion, a water molecule of crystallization, and the mono-
Inorganic Chemistry, Vol. 42, No. 10, 2003 3213

Ghosh et al.
Table 3. Zero-Field Mo¨ssbauer Parameters of Complexes at 80 K
c
d
complex
δ, mm s-1 a
|∆EQ|, mm s-1 b
SFe
St
1
2
3
4
0.91
0.85
0.87
0.92 (50%)
0.88 (50%)
0.33
4.10
3.68
3.24
4.05
3.38
0.93
2.71
2
2
2
2
2
0
0
0
3
/
/
2
3
2
3
5a
5b
/
/
0
0
2
3
0.30
2
a Isomer shift vs R-Fe at 298 K. b Quadrupole splitting. c Local spin state
of iron ion. d Ground state of molecule.
Figure 5. Structure of the dimer in crystals of 5a.
spectrum of 4 displays two quadrupole doublets of very
similar isomer shift and quadrupole splitting parameters, we
conclude that the radical ligand (LISQ 1-
is statically disor-
)
dered over two positions in a hydrophobic cavity generated
by phenyl groups of two [PPh4]+ cations in the solid state.
It has not been possible to resolve this disorder by a split
atom model. The Fe-N and Fe-S bonds are long and
indicative of a central high spin ferrous ion as in 2.
The dimer in crystals of 5a shown in Figure 5 has a
different structure as compared to that of 2 (Figure 3). Two
(µ-imido) bridges are observed, and the two N,S-chelating
ligands differ in their respective level of protonation. Clearly,
two terminal (LAP)1- ligands are present, as well as two
dianionic, aromatic (LIP)2- ligands. The latter, electron richer
dianion forms the bridges via the R-NH- groups. The
oxidation level of both ligands is clearly aromatic: the C-S
bonds at 1.77 Å and the C-N bonds at 1.46 Å (terminal)
and 1.42 Å (bridging) are long, and the six-membered carbon
rings do not show quinoid type distortions but display six
nearly equivalent C-C bonds. It is noted the C-C bond
between the two carbon atoms which carry the sulfur donor
atom and the tert-butyl group, respectively, is always at
1.41-1.42 Å irrespective of the protonation or oxidation level
of the ligand. This is presumably a steric effect. This is true
for all structures reported here and for those described
previously.17 The geometrical features of the bridging (LIP)2-
ligand in 5a are very similar to those reported for a terminal
o-iminothiophenolate(2-) in square planar, diamagnetic
[(bpy)PtII(LIP)].23
Figure 6. Five-coordinate intermediate spin ferric complexes and their
Mo¨ssbauer parameters at 80 K.
Zero-Field Mo1ssbauer Spectroscopy. The zero-field
Mo¨ssbauer spectra of all complexes have been recorded at
80 K; the isomer shift (vs R-Fe at 295 K) and quadrupole
splitting parameters are given in Table 3.
The zero-field spectra of complexes 1, 2, and 3 display
each a single doublet in the narrow isomer shift range 0.83-
0.92 mm s-1 and quadrupole splitting range 3.38-4.10 mm
s-1. These values unequivocally indicate the presence of a
high spin ferrous ion (SFe ) 2) in each of these compounds.
Complex 4 containing the mononuclear anion [FeII(abt)2(itbs)]-
displays two such doublets (ratio 1:1) at δ ) 0.92 and 0.88
mm s-1, ∆EQ ) 4.05 and 3.38 mm s-1, which indicates the
presence of two structurally slightly different iron(II) ions.
As already pointed out, the S-coordinated (itbs)1- radical is
disordered in solid 4. Therefore, we suggest that the anion
exists in two different conformations in the solid state. It is
clear that both conformers contain a high spin ferrous ion.
The dinuclear complexes 5a and 5b both display a
quadrupole doublet at a similar isomer shift of 0.33 and 0.30
mm s-1, respectively, but significantly different quadrupole
splittings of 0.93 and 2.71 mm s-1. From magnetic suscep-
tibility data, the X-ray structure analysis of 5a, and from
their electronic spectra, it is concluded that both complexes
contain intermediate spin ferric ions (SFe ) 3/2) which couple
antiferromagnetically in the dimers yielding the observed
These considerations render the iron ions in 5a trivalent.
The Fe-N and Fe-S bonds are significantly shorter than
those in 2 and those expected for a high spin ferric ion.
Therefore, the local spin states at the ferric ions in 5a are
3
1
either intermediate or low spin (SFe ) /2 or /2) which are
intramolecularly antiferromagnetically coupled yielding an
St ) 0 ground state.
(23) Ghosh, P.; Begum, A.; Herebian, D.; Bothe, E.; Hildenbrand, K.;
Weyhermu¨ller, T.; Wieghardt, K. Angew. Chem., Int. Ed. 2003, 42,
563.
(24) Sawyer, D. T.; Srivatsa, G. S.; Bodini, M. E.; Schaefer, W. P.; Wing,
R. M. J. Am. Chem. Soc. 1986, 108, 936.
(25) Niarchos, D.; Kostikas, A.; Simopoulos, A.; Coucouvanis, D.; Pilt-
ingsrud, D.; Coffman, R. E. J. Chem. Phys. 1978, 69, 4411.
(26) Keutel, H.; Ka¨pplinger, I.; Ja¨ger, E.-G.; Grodzicki, M.; Schu¨nemann,
V.; Trautwein, A. X. Inorg. Chem. 1999, 38, 2320.
3214 Inorganic Chemistry, Vol. 42, No. 10, 2003

Structures of Fe(II)/(III) Complexes
diamagnetic ground state. Figure 6 summarizes some Mo¨ss-
bauer data for three genuine intermediate spin ferric com-
plexes. These data resemble closely those of 5a and 5b.
quinonate(1-) π radical ligand has been identified. The
aromatic tetradentate ligand (′H2N2S2′)2- has been identified
in the dimer (µ-S,S)[FeII(′H2N2S2′)]2 (3).
Acknowledgment. We thank the Alexander von Hum-
boldt Foundation and the Max-Planck Society for fellowships
to P.G. and A.B., respectively. We are grateful to the Fonds
der Chemischen Industrie for financial support.
Conclusion
We have shown in this part of our investigation of the
reactivity of o-aminothiophenols with iron(II)/(III) ions under
anaerobic, or dioxygen deficient, conditions that complexes
containing N,S-coordinated, aromatic, closed-shell mono- and
dianions, (LAP)1- or (abt)1-, (LIP)2- or (ibt)2-, are formed:
complexes 1 and 2 are high spin ferrous species whereas 5a
and 5b are intermediate spin ferric species. In one instance,
4, an S-coordinated monodentate o-iminothionebenzosemi-
Supporting Information Available: X-ray crystallographic
files, in CIF format, for compounds 2, 4, and 5a. Figure S1 showing
the Mo¨ssbauer spectra of complexes 1-4, 5a, and 5b. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC020617C
Inorganic Chemistry, Vol. 42, No. 10, 2003 3215