Synthesis, structure, and magnetic properties of the halide-bridged dimeric complex [(bpmaL1)Fe(μ-Cl)Cl]2

Article abstract of DOI:10.1016/j.ica.2012.09.010

Complexation of FeCl₂·4H₂O with N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline [bpmaL₁] gave air-stable dichloro-bridged binuclear iron(II) species (1a) having five-coordinated iron, which was characterised by X-ray crystallography and magnetic susceptibility. The geometry at each iron centre of 1a is a distorted trigonal bipyramid with two equivalent half-molecules providing overall C_i symmetry. One of the pyrazolyl nitrogen atoms (N1) and a chlorine atom (Cl2)^# form one apex of the distorted trigonal bipyramid. The magnetic parameters indicated only a weak antiferromagnetic coupling, despite the presence of two chloro ions, and dominant zero-field-splitting parameters. The relatively long Fe?Fe distance of 3.8118(6) A? within the chloro-bridged dimer excludes direct interaction between the iron(II) ions. Thus, the antiferromagnetic coupling between the two iron(II) ions of 1a is attributed to superexchange through the chloride ions. Compared to the analogous cobalt complexes, the activity of α-olefin polymerization towards ethylene, norbornene, 1-octene and methyl methacrylate (MMA) was virtually zero, 1a is the first bis-pyrazole based dinuclear and five-coordinated iron(II) complex.

Full text of DOI:10.1016/j.ica.2012.09.010

Inorganica Chimica Acta 394 (2013) 501–505
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Note
Synthesis, structure, and magnetic properties of thehalide-bridged dimeric complex
[(bpmaL1)Fe( -Cl)Cl]2
l
Minkyu Yang a, Eunhee Kim a, Jong Hwa Jeong a, Kil Sik Min b, Hyosun Lee a,
⇑
a Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu-City 702-701, Republic of Korea
b Department of Educational Chemistry, Kyungpook National University, 1370 Sankyuk-dong, Buk-gu, Daegu-City 702-701, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 3 June 2012
Received in revised form 18 September
2012
Accepted 18 September 2012
Available online 29 September 2012
Complexation of FeCl2ꢀ4H2O with N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline [bpmaL1] gave air-stable
dichloro-bridged binuclear iron(II) species (1a) having five-coordinated iron, which was characterised
by X-ray crystallography and magnetic susceptibility. The geometry at each iron centre of 1a is a dis-
torted trigonal bipyramid with two equivalent half-molecules providing overall Ci symmetry. One of
the pyrazolyl nitrogen atoms (N1) and a chlorine atom (Cl2)# form one apex of the distorted trigonal
bipyramid. The magnetic parameters indicated only a weak antiferromagnetic coupling, despite the pres-
ence of two chloro ions, and dominant zero-field-splitting parameters. The relatively long Feꢀ ꢀ ꢀFe dis-
tance of 3.8118(6) Å within the chloro-bridged dimer excludes direct interaction between the iron(II)
ions. Thus, the antiferromagnetic coupling between the two iron(II) ions of 1a is attributed to superex-
Keywords:
N,N-Bis{(1-H pyrazole-1-yl)methyl}aniline
Binuclear iron(II) complex
Magnetic susceptibility
change through the chloride ions. Compared to the analogous cobalt complexes, the activity of a-olefin
polymerization towards ethylene, norbornene, 1-octene and methyl methacrylate (MMA) was virtually
zero, 1a is the first bis-pyrazole based dinuclear and five-coordinated iron(II) complex.
Ó 2012 Elsevier B.V. All rights reserved.
a-Olefin polymerization
1. Introduction
of the research was to investigate the steric and electronic influ-
ences of the substituents on complex formation. Secondly, the
Coordination complexes with pyrazole-based chelating ligands
are of particular interest because of their many applications, e.g.
as industrial catalysts for olefin oligomerisation and polymerisa-
tion [1–3], as bioinorganic materials in pharmaceutical prepara-
tions [4–8], and as catalytic materials [9,10]. As catalysts for
olefin polymerisation, very little is known about bispyrazolyl li-
gand-based transition metal complexes [11–14] compared to espe-
cially those incorporating a tris-pyrazole ligand [15–20]. For
example, the groups of Gibson and co-workers [21] and Brookhart
and co-workers [22,23], independently discovered highly active tri-
dentate iron and cobalt complexes having 2,6-bis(imino)pyridines
as ligands. These were highly active for ethylene polymerisation.
Similarly, the chelate pyrazolyl ligands were reported firstly by
Driessen et al. [24], the transition metal complexes with bis-
pyrazolyl ligands, specifically iron-bispyrazolyl complexes have
been the best interested due to their spin state stability [25–30]
and applications as various catalyst precursors [31–34]. Herein,
we report the synthesis and characterisation of the iron(II) dimeric
catalytic behaviour of these modified methyl aluminoxane
(MMAO)-activated complexes was additionally investigated for
the polymerisation of
a-olefins [35,36]. Surprisingly, they were
catalytically inactive towards substrates containing the olefinic
moiety, even towards methyl methacrylate (MMA). In contrast,
the cobalt analogues [bpmaLn]CoCl2 [37], which was tetrahedral
monomeric Co(II) complexes, towards MMA are very reactive
towards MMA [36,38,39].
2. Experimental
2.1. Materials and instrumentation
All manipulations were performed using a combination of glove
box, high vacuum, and Schlenk techniques under an argon atmo-
sphere unless otherwise specified. Solvents were purified and de-
gassed by standard procedures. Other starting materials were
obtained from high-grade commercial suppliers and used without
further purification. 1H NMR (400 MHz, 600 MHz) and 13C NMR
(100.61 MHz, 150.85 MHz, respectively) were recorded on a Bruker
Advance Digital 400, 600 NMR spectrometer and chemical shifts
were recorded in ppm units using SiMe4 as an internal standard.
Coupling constants are reported in Hertz (Hz). Infrared (IR) spectra
were recorded on Bruker FT/IR-Alpha (neat) and the data are
complexes, namely [(bpmaLn)Fe(l-Cl)Cl]2, where specifically
(bpmaL1) refers to N,N-bis(pyrazolylmethyl)aniline, having substit-
uents on both the pyrazole ring and aniline ring units. The first goal
⇑
Corresponding author.
E-mail address: hyosunlee@knu.ac.kr (H. Lee).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.010

502
M. Yang et al. / Inorganica Chimica Acta 394 (2013) 501–505
reported in reciprocal centimetres. Melting point was measured by
Digital Melting Apparatus (IA9100). Elemental analysis and ICP
(Inductively Coupled Plasma) were performed by Fison-EA1108
and Thermo IRIS XDL duo, respectively. Magnetic susceptibilities
were measured in an applied field of 5000 Oe between 6 and
300 K on a Quantum Design MPMS superconducting quantum
interference device (SQUID) magnetometer. Diamagnetic correc-
tions were made [545.5 (1), 426.5 (2) and 534.8 ꢁ 10ꢂ6 (3) emu/
mol] by using Pascal’s constants.
2.2.4. Synthesis of [(bpmaL3)Fe(l-Cl)Cl]2 (3a)
The solution of ligand [bpmaL3] (1.00 g, 2.54 mmol) in dried
ethanol (50 mL) was added to the solution of FeCl2ꢀ4H2O
(0.510 g, 2.54 mmol) in dried ethanol (50 mL) at room tempera-
ture. The pale yellow solid was precipitated after stirring at room
temperature for 24 h. The solid was filtered and washed with fresh
cold ethanol (30 mL ꢁ 1) followed by washing with pentane
(30 mL ꢁ 2) to give pale yellow coloured crystalline solid. Yield
(0.94 g, 79.6%). m.p = 182–183 °C. Anal. Calc. for C40H54Cl4Fe2N10
:
C, 51.75; H, 5.86; N, 15.09. Found: C, 52.13; H, 6.19; N, 14.45%.
1H NMR (CDCl3, 400 MHz): d 7.76 ([–(N2C3H3)2–], s, 2H), 7.49
([–(N2C3H3)2–], s, 2H), 7.18 ([C6H3(CH)2 (CH3)4N–], s, 3H), 6.27
([–(N2C3H3)2–], s, 2H), 5.50 ([–N(CH)2–], s, 4H), 2.65 ([C6H3(CH)2
(CH3)4N–], s, 2H), 0.90([C6H3(CH)2(CH3)4N–], s, 6H), 1.05 ([C6H2
(CH3)4N–], s, 6H). IR (solid neat; cmꢂ1): 2922 (m), 2854 (m),
1739(w), 1709 (w), 1467 (m), 1454 (m), 1441 (m), 1405 (s), 1362
(m), 1322 (m), 1297 (m), 1252 (m), 1204 (m), 1170 (s), 1113 (m),
1099 (m), 1068 (s), 1053 (m), 989 (m), 973 (m), 948 (m), 917
(m), 899 (m), 866 (w), 812 (m), 781 (s), 769(s), 748 (s), 657 (w),
643 (m), 608 (s), 588 (s).
2.2. Synthesis of ligands and complexes
2.2.1. Preparation of ligands
(1-H Pyrazole-1-yl)methanol as starting material were
prepared in processes described elsewhere [21,32]. Ligands N,
N-Bis{(1-H-Pyrazole-1-yl)methyl}aniline,
[bpmaL1],
N,N-Bis
{(1-H-Pyrazole-1-yl)methyl}-2,4,6-trimethylaniline, [bpmaL2], N,
N-Bis{(1-H Pyrazole-1-yl)methyl}2,6-diisopropylaniline, [bpmaL3],
N,N-Bis{(3,5-dimethyl-1H-pyrazol-1-yl)methyl}-2,6-diisopropylan-
iline, [bpmaL4] was prepared by by a similar procedure as described
in the literature [36–39].
2.3. Representative polymerization procedure of MMA
Methyl methacrylate (MMA) was extracted with 10% sodium
hydroxide, washed with water, dried over magnesium sulfate,
and distilled over calcium hydride under reduced pressure before
2.2.2. Synthesis of [(bpmaL1)Fe(l-Cl)Cl]2 (1a)
The solution of ligand [bpmaL1] (1.00 g, 3.95 mmol) in dried
ethanol (50 mL) was added to the solution of FeCl2ꢀ4H2O
(0.780 g, 3.95 mmol) in dried ethanol (50 mL) at room tempera-
ture. The pale yellow solid was precipitated after stirring at room
temperature for 24 h. The solid was filtered and washed with
fresh cold ethanol (30 mL ꢁ 3) followed by washing with pentane
(30 mL ꢁ 3) to give pale yellow coloured crystalline solid (2.33 g,
77.5%). m.p = 138–139 °C. Anal. Calc. for C28H30Cl4Fe2N10: C, 44.24;
H, 3.98; N, 18.43. Found: C, 44.26; H, 3.98; N, 18.62%. 1H NMR
(DMSO, 400 MHz): d 7.77 ([–(N2C3H3)2–], s, 2H, J = 0.15 Hz), 7.43
([–(N2C3H3)2–], d, 2H, J = 0.15 Hz), 7.06 ([C6H5(CH3)3N–], s, 2H),
6.74 ([C6H5(CH3)3N–], d, 3H), 6.23 ([–(N2C3H3)2–], d, 2H, J = 0.38
Hz), 5.42 ([–N(CH2)2–], s, 2H), 5.34 ([–N(CH2)2–], s, 2H). IR (solid
neat; cmꢂ1): 1496 (w), 11468 (m), 1453 (w), 1400 (m), 1375 (w),
1335 (w), 1312 (w), 1289 (w), 1247 (w), 1218 (w), 1183 (m),
1145 (m), 1106 (w), 1098 (w), 1070 (m), 1045 (m), 977 (m), 931
(m), 892 (w), 871 (w), 849 (w), 829 (w), 808 (w), 779 (s), 766 (s),
721 (m), 697 (s), 678 (m), 656 (m), 639 (m), 619 (m), 610 (s), 590
(m), 579 (m), 570 (m).
use. To
(11.4 mg, 15.0
a
100-mL Schlenk flask containing [bpmaL]CoCl2
mol) in toluene (1 mL) was added MMAO (modi-
l
fied methylaluminoxane, 6.9 wt.% in toluene, 3.25 mL, [MMAO]0/
[Fe(II) catalyst]0 = 500) under a dry argon atmosphere. After the
mixture had been stirred at room temperature for 10 min, it was
transferred into MMA (5.0 mL, 47.0 mmol, [MMA]0/[F(II) cata-
lyst]0 = 3100). Then, the reaction flask was immersed in an oil bath
at 60 °C and stirred for 2 h. The resulting polymer was precipitated
in methanol (400 mL) and HCl (3 mL) was added with stirring for
10 min. The polymer was filtered and washed with methanol
(400 mL ꢁ 3) to give PMMA, which was vacuum-dried at 60 °C.
Additionally, polymerization was examined at different tempera-
tures (0, 25, 40, 50 °C) with 1a.
2.4. X-ray crystallographic analysis
An X-ray quality single crystal was mounted in a thin-walled
glass capillary on an Enraf-Noius CAD-4 diffractometer with Mo
Ka
radiation (k = 0.71073 Å). Unit cell parameters were determined
by least-squares analysis of 25 reflections (10° < h < 13°). Intensity
data were collected with h range of 1.83–25.46° in /2h scan mode.
Three standard reflections were monitored every 1 h during data
collection. The data were corrected for Lorentz-polarization effects
2.2.3. Synthesis of [(bpmaL2)Fe(l-Cl)Cl]2 (2a)
x
The solution of ligand [bpmaL2] (1.00 g, 3.39 mmol) in dried
ethanol (50 mL) was added to the solution of FeCl2ꢀ4H2O
(0.673 g, 3.39 mmol) in dried ethanol (50 mL) at room tempera-
ture. The pale yellow solid was precipitated after stirring at room
temperature for 48 h. The solid was filtered and washed with fresh
cold ethanol (30 mL ꢁ 3) followed by washing with pentane
(30 mL ꢁ 3) to give pale yellow coloured crystalline solid (0.75 g,
and decay. Empirical absorption corrections with
v-scans were ap-
plied to the data. The structure was solved by using Patterson
method and refined by full-matrix least-squares techniques on F
using SHELX-97 and SHELX-97 program packages. All non-hydrogen
atoms were refined positioned geometrically using riding model
with fixed isotropic thermal factors. The final cycle of the refine-
ment converged with R1 = 0.0363 and wR2 = 0.0864.
51.8%). m.p = 173–174 °C. Anal. Calc. for
C34H42Cl4Fe2N10: C,
48.37; H, 5.01; N, 16.59. Found: C, 48.08; H, 5.03; N, 16.43. 1H
NMR (DMSO, 400 MHz): d 7.96 ([–(N2C3H3)2–], s, 2H, J = 0.15 Hz),
7.42 ([–(N2C3H3)2–], d, 2H, J = 0.15 Hz), 6.66 ([C6H2(CH3)3N–], s,
2H), 6.46 ([–(N2C3H3)2–], s, 2H, J = 0.38 Hz), 5.13 ([–N(CH2)2–], s,
4H), 2.05 ([C6H2(CH3)3N–], d, 3H), 1.95 ([C6H2(CH3)3N–], d, 3H),
1.50 ([C6H2(CH3)3N–], s, 3H). IR (solid neat; cmꢂ1): 2922 (m),
2853 (w)1514 (w), 1482 (w), 1468 (w), 1451 (w), 1403 (m), 1352
(w), 1320 (w),1302 (m), 1250 (m), 1205 (w), 1189 (m), 1168 (m),
1157 (m), 1126 (m), 1098 (m), 1061 (m), 989 (w), 974 (m), 941
(m), 908 (w), 892 (w), 861 (w), 846 (m), 807 (w), 763 (s), 733
(m), 677 (m), 645 (m), 608 (m), 589 (s), 559 (w).
3. Results and discussion
The [(bpmaLn)Fe(l-Cl)Cl]2 complexes were readily prepared by
stirring a solution of FeCl2ꢀ4H2O with one equivalent of the
(bpmaLn) ligand [40] in dry ethanol at room temperature (Scheme
1). The complexes were isolated in high yield as air-stable micro-
crystalline yellow powders. However, the dimeric iron complex
[(bpmaL4)Fe(l-Cl)Cl]2 (4a) did not form with ligand ([bpmaL4],

M. Yang et al. / Inorganica Chimica Acta 394 (2013) 501–505
503
R3
R3
R1
N
N
N
N
R2
R2
R3
R3
R3
R2
R2
Cl
R2
N
R2
R1
N
R1
Cl Fe
Fe Cl
R3
N
N
.
FeCl2 4H2O
Cl
R3
N
N
N
R3
EtOH/rt
N
N
N
N
R3
R3
R3
R3
R1, R2, R3 = H: [bpmaL1]
[(bpmaL1)Fe(µ-Cl)Cl]2 (1a)
[(bpmaL2)Fe(µ-Cl)Cl]2 (2a)
R1, R2 = Me, R3 = H: [bpmaL2]
R1, R3 = H, R2 = CHMe2: [bpmaL3]
3a
)
[(bpmaL3)Fe(µ-Cl)Cl]2
(
Scheme 1. Synthetic scheme for the preparation of [(bpmaLn)FeCl-(l-Cl)]2 (1a–3a).
R1 = H, R2 = CHMe2, R3 = Me), presumably because of steric hin-
drance by the pyrazole substituent.
Dinuclear Fe complexes 1a–3a were very inert to ethylene,
1-octene and norbornene polymerization, for example, for ethylene
polymerization even at an ethylene pressure of 30 bar in toluene
media at various temperatures. This catalytic inactivity of Fe(II)
ity of 1a was 0.34 ꢁ 106 g/mol Fe h, while those of FeCl2ꢀ4H2O and
MMAO were only 0.21 ꢁ 105 g/mol Fe h and 0.14 ꢁ 105 g/mol Fe h
at 60 °C, respectively.
A single crystal of [(bpmaL1)Fe(l-Cl)Cl]2 (1a) was grown by
slowly evaporating a methylene chloride solution at room temper-
ature. The X-ray structure determination revealed a chloro-bridged
dimeric species with crystallographic inversion symmetry (Fig. 1).
Crystal structure data, details of data collection, and refinement
parameters for 1a are listed in Table 1. Selected bond lengths (Å)
and angles (°) for 1a are described in Fig. 1. The geometry at each
iron centre is best described as a distorted trigonal bipyramid (TBP)
with two equivalent half-molecules providing overall Ci symmetry.
One of the pyrazolyl nitrogen atoms (N1) and a chlorine atom
(Cl2)# form one apex of the distorted trigonal bipyramid. There is
complex as
compared to bis(imino)pyridine–Fe(II) complex which shows high
catalytic activity for ethylene polymerization and -olefin oligo-
a dimeric five-coordinated was totally different
a
merization. However, only precatalyst 1a could be activated with
MMAO to polymerize methyl methacrylate (MMA) to give PMMA
with Tg 120 °C. To confirm the catalytic activity of MMA polymer-
ization, blank polymerization of MMA was performed with starting
Fe complex, FeCl2ꢀ4H2O, and MMAO themselves at 60 °C. The activ-
C12
C11
C3
C13
C10
C14
C4
C2
N2
C9
C5
N3
C1
N1
N4
Cl2
N5
Fe
C6
C7
C8
Cl1
Fig. 1. ORTEP drawing and atom numbering of [(bpmaL1)Fe(l-Cl)Cl]2 (1a) with 40% of the thermal ellipsoid probability. Selected bond lengths (Å) and angles (°) are Fe–Cl(1)
2.2827 (6), N(1)–N(2) 1.355(2), Fe–Cl(2) 2.3545 (6), N(2)–C(4) 1.451(3), Fe–Cl(2)# 2.6367 (6), N(3)–C(9) 1.430(3), Cl(2)–Fe# 2.6367 (9), N(3)–C(5) 1.451(2), Fe–N(1) 2.1791
(17), N(4)–C(5) 1.466(3), Fe–N(5) 2.1345 (17), Fe–Fe# 3.8118 (6), Fe–Cl(2)–Fe# 99.431 (19); N(1)–N(2)–C(4) 120.78(16), Cl(1)–Fe–Cl(2) 136.63 (3), C(5)–N(3)–C(4) 114.47(15),
Cl(2)–Fe–Cl(2)#1 80.569 (19), N(5)–N(4)–C(5) 123.56(16), N(1)–Fe–Cl(1) 93.18 (5), N(4)–N(5)–Fe 132.46(13), N(5)–Fe–Cl(1) 112.05 (5), N(3)–C(5)–N(4) 114.61(16),
N(1)–Fe–Cl(2)#1 165.34 (5), C(9)–N(3)–C(5) 116.28(16), N(5)–Fe–Cl(2)#1 92.59 (5), C(9)–N(3)–C(4) 115.32(16).

504
M. Yang et al. / Inorganica Chimica Acta 394 (2013) 501–505
Table 1
8
Crystal data and structure refinement of [(bpmaL1)Fe(
l-Cl)Cl]2 (1a).
Empirical formula
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
C28H30Cl4Fe2N10
760.12
triclinic
7
6
5
4
ꢀ
P1
µ
µ
8.9804(5)
9.8764(5)
10.5081(8)
819.41(10)
b (Å)
c (Å)
V (Å3)
Z
Dcalc
1
1.540 Mg/m3
1.248 mmꢂ1
388
Absorption coefficient
F(000)
F(0000)
Crystal size (mm)
h (°)
Index ranges
389.35
0.50 ꢁ 0.40 ꢁ 0.30
2.20–25.47
ꢂ10 ꢃ h ꢃ 10
0 ꢃ k ꢃ 11
ꢂ12 ꢃ l ꢃ 11
3037 unique [Rint = 0.0097]
3304
Reflections collected/unique
Reflections observed (>2
r)
0
50
100
150
200
250
300
350
Data completeness
Refinement method
Data/restraints/parameters
Tmin, Tmax
1.000
Full-matrix least-squares on F2
3037/0/199
0.555, 0.688
0.530
Temperature, T, K
Fig. 2. Plot of
the best fit obtained.
leff (T) for [(bpmaL1)Fe(l-Cl)Cl]2 (1a) in a field of 1 T. Solid line shows
0
Tmin
Goodness-of-fit (GOF) on F2
1.114
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0296, wR2 = 0.0838
R1 = 0.0363, wR2 = 0.0864
0.595 and ꢂ0.358
magnetometer was used for the measurements. The effective mag-
netic moment, leff [=(8 B/Fe2 at 350 K. This va-
MT)1/2] was 7.43
lue is slightly larger than the 6.93 B expected for two independent
iron(II) ions (S = 2, Fe(II), g = 2). The value of eff(T) decreased with
Largest difference in peak and hole (e Åꢂ3
)
v
l
l
l
a substantial enlargement of the Cl1–Fe–Cl2 angle [136.63(3)°] and
a small contraction of the N5–Fe–Cl1 angle [112.05(5)°] in the
equatorial plane. The N1–Fe–Cl(2⁄) angle is slightly less than
180° [165.34(5)°], and the N1–Fe–N5 angle is substantially larger
[100.35(7)°] as a consequence of the bulky eight-membered
chelate ring. The angles between the three equatorial ligands,
Cl1–Fe–Cl2 [136.63(3)°], N5–Fe–Cl1 [112.05(5)°], and N5–Fe–Cl2
[110.22(5)°] total 358.86°. The Fe–N bond lengths are unexcep-
tional, whereas the terminal Fe–Cl bond [2.2827(6) Å] is shorter
than the bridging bond [2.3545(6) Å]. The chlorine atom bridges
are notably asymmetric with bond lengths of 2.3545(6) Å for
Fe–Cl2 and 2.6367(6) Å for Fe–Cl2#. Dinuclear, five-coordinate iron
complexes with bridging units such as oxygen and halide are abun-
dant [41–51]. However, trigonal bipyramidal diiron complexes,
especially those containing the bis-pyrazole chelate ligand and
decreasing temperature, consistent with the presence of a weak
antiferromagnetic interaction between the iron(II) ions. The leff
(T) data were fitted to an analytical expression for
v(T) for a
coupled S = 2 binuclear spin model based on the Hamiltonian
2
H = –2JS1ꢀS2 + 2DFe[Sz ꢂ 2] + g B(S1 + S2)ꢀB (S1 = S2 = 2) incorporat-
l
ing exchange coupling, zero-field splitting (D), and Zeeman inter-
action [54]. The fitting gave J = ꢂ0.86 cmꢂ1 with g = 2.15,
|D| = 1.332 cmꢂ1, and 0.9% paramagnetic impurities. The resulting
magnetic parameters indicated only a weak antiferromagnetic
coupling, despite the presence of chloro ions, and dominant zero-
field-splitting parameters [55]. The coupling constant J of 1a is
quite different than the ꢂ63.7 cmꢂ1 value for [(PhCN)2(Mes)2Fe2
{l-N = C(Mes)(Ph)}2] (Mes = 2,4,6-Me3C6H2), which is also a nitro-
gen-bridged dinuclear iron(II) system [56]. The relatively long
FeꢀꢀꢀFe distance (3.8118(6) Å) within the chloro-bridged dimer
rules out direct interaction between the iron(II) ions. Therefore,
the antiferromagnetic coupling between the two iron(II) ions of
1a is attributed to superexchange through the chloride ions.
bridged l
2-chloro group, are uncommon [48]. The molecular struc-
ture of 1a is similar to those of dichloro-(2-pyridylmethylidene)
(triphenylsilyl)amino iron(II) [52], [2-(iminoethyl)pyridine]iron(II)
[53], and bis(l2-chloro)-chloro-(2-(20-pyridyl)quinoxaline)iron(II).
In dichloro-(2-pyridylmethylidene)(triphenylsilyl)amino iron(II),
which has a trigonal bipyramidal environment about iron, the N2
and Cl1A atoms are arranged in axial positions (N2–Fe–Cl1A,
170.98(6)°) while the N1, Cl1, and Cl2 atoms form the trigonal
plane. The angles between the equatorial ligands are [N2–Fe1–
N1] 81.86(9)°, [N2A–Fe1–N1] 122.30(9)°, [N2–Fe1–N2A] 143.4(1)°,
and [N1–Fe–N1A] 102.7(1)°. For the [2-(iminoethyl)pyridine]
iron(II) complex, the pyridyl nitrogen atom N1 and Cl1 mark one
apex of the distorted trigonal bipyramid, with N1–Fe–Cl1 =
155.6(2)°. The angles between the three equatorial ligands are
[N9–Fe–Cl1⁄] 126.0(2)°, [N9–Fe–Cl2] 116.7(2)°, and [Cl1⁄–Fe–Cl2]
115.5(1)°. These angles define a distorted trigonal bipyramid
having an enlarged Cl–Fe–Cl angle [133.9(1)°] and asymmetric
chlorine bridges having lengths 2.511(1) Å [Fe–Cl2] and 2.391(1) Å
[Fe–Cl2⁄].
4. Conclusion
The first bispyrazole-containing binuclear and five-coordinated
iron(II) complex [(bpmaL1)Fe(l-Cl)Cl]2 (1a) have been structurally
characterised. In addition, the magnetic properties have been mea-
sured for the iron(II) bimetallic 1a. The magnetic property of di-
meric iron complex is best described as only
a
weak
antiferromagnetic coupling between the two iron(II) ions of 1a
and dominant zero-field-splitting parameters.
Acknowledgments
This research was supported under the Basic Science Research
Programs through the National Research Foundation of Korea
(NRF), funded by the Ministry of Education, Science, and Technol-
ogy (Grant No. 2009-0075742). This research was supported by Re-
search fund of Kyungpook National University, 2012.
The magnetic susceptibility (v) of 1a was measured from 6 to
350 K at 1 T field strength to study the effect of the structural
parameters on the magnetic properties (Fig. 2). An MPMS XL 7.0

M. Yang et al. / Inorganica Chimica Acta 394 (2013) 501–505
505
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