Syntheses, three types of hydrogen-bonded assembly structures, and magnetic properties of [FeIII(Him)2(hapen)]Y·solvent (Him = imidazole, hapen =N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, y = BPh4-, CF<

Article abstract of DOI:10.1016/j.ica.2013.01.021

Five iron(III) complexes of [Fe^III(Him)₂(hapen)] Y·solvent with five different counter anions were synthesized, where Him = imidazole, H₂hapen = N,N′-bis(2-hydroxyacetophenylidene) ethylenediamine, Y = BPh₄

Full text of DOI:10.1016/j.ica.2013.01.021

Inorganica Chimica Acta 399 (2013) 185–192
Contents lists available at SciVerse ScienceDirect
Inorganica Chimica Acta
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Syntheses, three types of hydrogen-bonded assembly structures,
III
and magnetic properties of [Fe (Him) (hapen)]Yꢀsolvent
2
0
(
Him = imidazole, hapen = N,N -bis(2-hydroxyacetophenylidene)ethylenediamine,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Y = BPh , CF SO , PF , ClO , and BF )
4
3
3
6
4
4
a
a
a
a
a,
⇑
Masataka Koike , Keishiro Murakami , Takeshi Fujinami , Koshiro Nishi , Naohide Matsumoto
,
b
Yukinari Sunatsuki
a
Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 1-1, Okayama 700-8530, Japan
b
a r t i c l e i n f o
a b s t r a c t
III
Article history:
Received 28 August 2012
Received in revised form 15 November 2012
Accepted 16 January 2013
Available online 5 February 2013
Five iron(III) complexes of [Fe (Him) (hapen)]Yꢀsolvent with five different counter anions were synthe-
2
0
sized,
where
Him = imidazole,
H
2
hapen = N,N -bis(2-hydroxyacetophenylidene)ethylenediamine,
4ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
III
Y = BPh (1), CF
ion has octahedral coordination geometry with N
hapen) and two nitrogen atoms of two imidazoles at the axial positions. The imidazole group is hydro-
3
SO
3
(2), PF
6
(3), ClO
4
(4), and BF
4
2
(5), and solvent = methanol or H O. Each Fe
2 2
O
donor atoms of the equatorial tetradentate ligand
(
gen-bonded to the phenoxo oxygen atom of hapen of the adjacent unit and/or to the counter anion or
solvent molecule, to give three types of assembly structures involving linear dimer, cyclic dimer, and
one-dimensional zigzag chain. Compound 1, with a cyclic dimer, and 2 and 3, with a one-dimensional
chain, showed spin-equilibrium behavior between high-spin (S = 5/2) and low-spin (S = 1/2) states,
whereas 4 and 5, with linear dimers, are high-spin complexes. Compound 3 shows abrupt spin transition
with small thermal hysteresis.
Keywords:
Iron(III)
Spin equilibrium
Imidazole
2 2
N O Schiff-base ligand
Hydrogen bonds
Assembly structures
Ó 2013 Elsevier B.V. All rights reserved.
1
. Introduction
the equatorial and axial ligands [6]. For example (see Scheme 1),
III
III
[
2 4 2 4
Fe (Him) (salen)]BPh and [Fe (Him) (acacen)]BPh are HS and
According to Tanabe–Sugano diagrams, which are based on the
LS complexes, respectively, where the axial ligand was fixed as
n
ꢁ
strong crystal-field theory of octahedral 3d metal complexes [1],
the electronic ground-state changes between low-spin (LS) and
imidazole (Him), and
N,N -bis(salicylidene)ethylenediamine, N,N -bis(acetylacetonylid-
H
2
salen,
H
2
acacen, and BPh
4
denote
0
0
n
high-spin (HS) states at spin crossover (SCO) points in 3d
ene) ethylenediamine, and tetraphenylborate, respectively [6].
III
(
4 6 n 6 7) metal complexes. It is known experimentally that the
Within the [Fe (Him)
2
L]BPh
4
(L = N
O
2 2
Schiff-base ligand) frame-
SCO phenomenon, interconversion between HS and LS states, is in-
duced by external perturbations, such as temperature, pressure,
pH, and light irradiation [2]. Among the SCO complexes reported
so far, Fe and Fe complexes have been the most intensively stud-
ied [2,3]. It has also been recognized for a long time that the Fe
sites in some heme proteins exhibit SCO behavior [4], which plays
a key role in their biological functions. From the viewpoint of
developing model compound of heme proteins, a number of iron
porphyrins have been synthesized and studied [5]. In 1975, in or-
work, salen provides a weak enough ligand field to give HS states
and acacen provides a strong enough ligand field to give LS states.
Later, Murray in 1987 and Real in 1998 synthesized SCO iron(III)
complexes with analogous symmetrical Schiff-base ligands [7].
II
III
Matsumoto in 1984 synthesized [Fe(Him)
the unsymmetrical ligand salacen (H
2
(salacen)]BPh
salacen = N-salicylidene-N -
4
using
0
2
acetylacetonylidene)ethylenediamine) in order to provide an inter-
mediate ligand field strength between those provided by salen and
acacen, and confirmed the spin-equilibrium properties of the com-
plex [8]. Nishida and Matsumoto also pointed out that suitable li-
der to obtain a simple SCO model compound, Nishida synthesized
III
a family of Fe complexes with N
2
O
2
Schiff-base ligands and two
2
gand field strength of the equatorial ligand H L can be supplied by
0
axial monodentate ligands, and showed that the spin states can
be tuned primarily by the total ligand field strength provided by
symmetrical Schiff-base ligands such as N,N -bis(benzoylacetony-
0
lidene)ethylenediamine (H
tophenylidene)ethylenediamine (H
In this study, using a symmetrical ligand, i.e., H
2
bzacen) and N,N -bis(2-hydroxyace-
2
hapen), respectively [6b,8b].
hapen, five iro-
(hapen)]Yꢀsolvent with five different
⇑
Corresponding author. Tel./fax: +81 96 342 3390.
E-mail address: naohide@aster.sci.kumamoto-u.ac.jp (N. Matsumoto).
2
III
n(III) complexes [Fe (Him)
2
0
020-1693/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2013.01.021

1
86
M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
5
0 mL of methanol was added a solution of ethylenediamine
(
0.05 mol, 3.01 g) in 50 mL of methanol, and the mixture was stir-
red for 1 h on a hot-plate. The resulting yellow crystalline material
was collected by suction filtration, washed with a small amount of
methanol, and dried in vacuo. Yield: 14.78 g (99%). Calc. for H2-
20 2 2
hapen (C18H N O ): C, 72.95; H, 6.80; N, 9.45. Found: C, 72.93;
H, 6.82; N, 9.32%. Mp = 193–196 °C. The precursor iron(III) complex
III
[
Fe Cl(hapen)]ꢀ0.5CH
3
OH was prepared according to the literature
method [8b].
III
2
.2.2. Preparation of iron(III) complex [Fe (Him)
2
(hapen)]Yꢀsolvent
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
(
Y = BPh
4
(1), CF SO
3 3
(2), PF
O)
(hapen)]BPh
OH (1 mmol, 0.40 g) in 30 mL of methanol
6
(3), ClO
4
(4), and BF
4
(5), and
solvent = methanol or H
2
III
2.2.2.1. [Fe (Him)
2
4
ꢀ2CH
3
OHꢀH
2
O (1). To a suspension
III
of [Fe Cl(hapen)]ꢀ0.5CH
3
was added an excess of imidazole (10 mmol, 0.68 g), and the mix-
ture was stirred for 10 min on a hot-plate and then filtered. To the
4
filtrate was added a solution of NaBPh (1 mmol, 0.34 g) in 5 mL of
methanol. The resulting solution was allowed to stand for several
hours, during which time dark-purple plate-like crystals precipi-
tated, and they were collected by suction filtration and dried in
III
air. Yield: 0.56 g (63%). Calc. for [Fe (Him)
2
(hapen)]BPh
4
ꢀ2CH3-
OHꢀH
2
O (C24
H
26
N
6
O
2
FeꢀBPh
4
ꢀ2CH
3
OHꢀH
2
O): C, 67.65; H, 6.36; N,
9
.47. Found: C, 67.59; H, 6.08; N, 9.90%.
III
2
.2.2.2. [Fe (Him)
2
(hapen)]CF
3
SO
3
ꢀ1.5H
2
O (2). Compound 2 was
prepared using a similar method as that used to prepare 1, using
III
NaCF
Him)
3
SO
3
instead of NaBPh
(hapen)]CF
45.33; H, 4.41; N, 12.69. Found: C, 45.07; H, 4.39; N, 12.94%.
4
. Yield: 0.40 g (60%). Calc. for [Fe (-
III
(salen)]+ (a), [FeIII(Him)
(hapen)] (d).
(acacen)]+ (b), [FeIII
Scheme 1. Structures of [Fe (Him)
2
2
2
2
3
SO
3 2
ꢀ1.5H O
(C24
H
26
N
6
O
2
FeꢀCF
3
SO O): C,
3
ꢀ1.5H
2
+
III
+
(
Him)
2
(salacen)] (c), and [Fe (Him)
III
2
.2.2.3. [Fe (Him)
2
(hapen)]PF
6
ꢀ2H
2
O (3). Compound 3 was pre-
4ꢁ
3
3ꢁ
6ꢁ
,
counter anions were synthesized, where Y = BPh , CF
SO , PF
, and solvent = crystal solvent (see Scheme 1). As
the equatorial ligand H hapen and the axial ligand imidazole are
fixed for the five complexes, and provide a ligand field strength
pared using a similar method as that used to prepare 1, using
ꢁ
ꢁ
ClO
4
, and BF
4
III
NaPF
(
1
6
instead of NaBPh
4
. Yield: 0.44 g (66%). Calc. for [Fe (Him)
O): C, 43.19; H, 4.53; N,
2
2
hapen)]PF O (C24
6
ꢀ2H
2
H
26
6
N O
2
FeꢀPF
6
ꢀ2H
2
2.59. Found: C, 43.13; H, 4.50; N, 13.05%.
III
+
2
around the SCO point, the complex-cation of [Fe (Him) (hapen)]
with various anions may give SCO complexes. Hence, these com-
plexes are suitable for investigating the details of the effects of
the counter anion and crystal solvent on the SCO properties. These
complexes gave a variety of assembly structures, constructed by
hydrogen-bonding, depending on the counter anion, and some
complexes showed SCO and others did not; we report their synthe-
ses, structures, and magnetic properties.
III
2
.2.2.4. [Fe (Him)
2
(hapen)]ClO
4
ꢀ0.5CH
3
OH (4). Compound 4 was
prepared using a similar method as that used to prepare 1, using
III
NaClO
4
instead of NaBPh
(hapen)]ClO
8.90; H, 4.69; N, 13.96. Found: C, 48.98; H, 4.65; N, 14.32%.
4
. Yield: 0.35 g (58%). Calc. for [Fe
OH (C24 OH): C,
(
Him)
2
4
ꢀ0.5CH
3
H
26
N
6
O
2
FeꢀClO
4
ꢀ0.5CH
3
4
III
2
.2.2.5. [Fe (Him)
2
(hapen)]BF
4
ꢀ0.5HimꢀH
2
O (5). Compound 5 was
prepared using a similar method as that used to prepare 1, using
III
2
. Experimental
NaBF
(
4
4
instead of NaBPh
hapen)]BF
ꢀ0.5HimꢀH
8.99; H, 4.84; N, 15.68. Found: C, 48.91; H, 4.80; N, 15.34%.
4
. Yield: 0.38 g (60%). Calc. for [Fe (Him)
2
4
2
O
(C24
26
H N
6
O
2
FeꢀBF ꢀ0.5HimꢀH O): C,
4
2
Caution! Perchlorate salts of metal complexes are potentially
explosive. Only small quantities of material should be prepared
and the samples should be handled with care.
2.3. Physical measurements
2.1. General
Elemental analyses (C, H, and N) were carried out by Miss. Kikue
Nishiyama at the Center for Instrumental Analysis of Kumamoto
University. Melting points were measured by METTLE FP90 Central
Processor. Magnetic susceptibilities were measured by a Quantum
Design MPMS-XL5 magnetometer in the temperature range of
All reagents and solvents used in this study are commercially
available from Tokyo Kasei Co., Ltd., Tokyo, Japan and Wako Pure
Chemical Industries, Ltd., Osaka, Japan, and were used without fur-
ther purification. All of the synthetic procedures were performed in
air.
ꢁ1
5–300 K at the 2 K min
under an applied magnetic field of
0.5 T. The calibration was performed with palladium metal. Correc-
tions for diamagnetism were applied using Pascal’s constants [10].
2
2
.2. Preparation of materials
2
.4. Crystallographic data collection and structure analyses
.2.1. Preparations of tetradentate ligand H
2
hapen and precursor
III
iron(III) complex [Fe Cl(hapen)]ꢀ0.5CH
3
OH
X-ray diffraction data were collected using a Rigaku RAXIS RA-
0
The tetradentate ligand, N,N -bis(2-hydroxyacetophenylid-
ene)ethylenediamine, was prepared according to the literature
PID imaging plate diffractometer using graphite monochromated
Mo K radiation (k = 0.71073 Å). The temperature of the crystal
was maintained at the selected value by means of a Rigaku cooling
a
[
9]. To a solution of 2-hydroxyacetophenone (0.1 mol, 13.63 g) in

M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
187
device within an accuracy of ±2 K. The X-ray diffraction data for all
five complexes were first collected at 296 K, and then the diffrac-
tion data at the lower temperatures for 2 and 3 were collected.
The data were corrected for Lorentz, polarization and absorption
effects. The structures were solved by a direct method, and ex-
panded using the Fourier technique [11]. Some of the crystal sol-
vents were not found on the D-Fourier. Hydrogen atoms were
fixed at the calculated positions and refined using a riding model.
All calculations were performed using the CrystalStructure crystal-
lographic software package [12].
3
. Results and discussion
3
.1. Synthesis and characterization of iron(III) complexes
III
–
–
–
[Fe (Him)
2
(hapen)]Yꢀsolvent [Y = BPh
4 3 3 6
(1), CF SO (2), PF (3),
–
–
ClO
4 4
(4), BF (5)]
The precursor FeIII complex [Fe Cl(hapen)]ꢀ0.5CH
III
OH was ob-
3
2
tained by mixing the ligand H hapen, iron(III) chloride anhydrate,
and triethylamine in a 1:1:2 M ratio in methanol. The Fe com-
(hapen)]Y (Y = BPh
(5)) with two imidazoles at the axial positions
and various counter anions were obtained as black plate-like crys-
III
Fig. 1.
properties; 1 BPh
v
M
T
vs.
T
plots for complexes 1–5, showing their various magnetic
III
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
6ꢁ
ꢁ
ꢁ
4
plexes [Fe (Him)
2
4
(1), CF
SO
3 3
(2), PF
6
(3),
4
(
); 2 CF
3
SO
3
(
); 3 PF ( ); 4 ClO
4
( ); and 5 BF
( ).
ꢁ
ꢁ
(4), BF
4
The solid lines for 4 and 5 represent the theoretical curves with the fitting
parameters given in the text.
ClO
4
III
tals by mixing [Fe Cl(hapen)]ꢀ0.5CH
3
OH, imidazole, and NaY
) in a 1:10:1 M ratio in meth-
anol. The C, H, and N elemental analyses agreed with the formula
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
4
(
Y = BPh
4
, CF
3
SO
3
, PF
6
, ClO
4
, BF
transition with thermal hysteresis is unusual for SCO FeIII com-
plexes. The
M
v T value above 150 K of 3 has a constant value of
III
[
Fe (Him)
2
(hapen)]Yꢀsolvent. Ground samples of complexes 1, 2,
3
ꢁ1
3
ꢁ1
ca. 4.4 cm mol K, which is compatible with 4.37 cm mol
K
and 3 showed thermochromism, whereas those of 4 and 5 did
not. The dark-purple color of the ground samples of 1 and 2 at
room temperature changed to a greenish-black color at liquid-
nitrogen temperature, and the dark-purple color of 3 at room tem-
perature changed to black at liquid-nitrogen temperature.
of the spin-only HS value. On lowering the temperature, the
v
M
T
value decreases abruptly at around 75 K, and then reaches a con-
3
ꢁ1
stant value of ca. 0.7 cm mol K below 40 K; this value is compa-
rable to the LS (S = 1/2) spin-only value and those of the reported
III
LS Fe complexes. The spin-transition temperature is evaluated
M
by calculating the derivative of dv T vs dT, giving T1/2 = 78 K.
3.2. Temperature-dependence of magnetic properties
Compounds 4 and 5 show essentially similar magnetic behav-
iors to each other. In the higher temperature region above ca.
3
The magnetic susceptibilities (
ples were measured in the temperature range 5–300 K under an
applied magnetic field of 0.5 T at a sweep rate of 2 K min . The
magnetic susceptibility was measured while lowering the temper-
ature from 300 to 5 K in the first run. Subsequently, the magnetic
susceptibility was measured while raising the temperature from
v
M
) of the polycrystalline sam-
40 K, the compounds have constant
v
M
T values of ca. 4.4 cm -
ꢁ1
mol K, which is compatible with the expected HS value of
S = 5/2. The T value decreases abruptly below 20 K. This abrupt
decrease in the magnetic behavior cannot be ascribed to spin tran-
sitions from HS to LS states, but is caused by second-order Zeeman
ꢁ1
v
M
3
2
g
effects for (t2g) (e ) species in axially distorted octahedral sur-
5
to 300 K in the second run. The
v
M
T vs. T plots for all five com-
roundings [10,13]. These magnetic behaviors can be analyzed
using Eq. (1) [10,14]. Eq. (1), for the average magnetic susceptibil-
ity, takes account of single-ion anisotropy, where gFe is the Lande g
plexes are shown in Fig. 1. The plots for the warming and cooling
modes are practically the same for all five complexes, showing
no thermal hysteresis.
B
factor for the Fe ion, k is Boltzmann’s constant, b is the Bohr
The experimental data were examined in terms of the spin-only
magneton, x = D/k T, where the parameter D is a measure of the
B
III
values of the HS (S = 5/2) and LS (S = 1/2) states of Fe ions with the
zero-field splitting, and N
a
is the temperature-independent para-
5
3
d
electronic configuration; the theoretical spin-only
v
M
T values
magnetism [14].
3
for the HS (S = 5/2) and LS (S = 1/2) states are 4.37 and 0.375 cm -
mol K, respectively. The
2
2
ꢁ2x
ꢁ1
3
ꢁ1
<
v
> ¼ Ng b =12k Tð19 þ 16=x þ ð9 ꢁ 11=xÞe
v
M
T value of 1 is 4.14 cm mol K at
Fe
B
ꢁ
6x
ꢁ2x
ꢁ6x
3
4
00 K, which is slightly smaller than the spin-only HS value of
þ ð25 ꢁ 5=xÞe Þ=ð1 þ e þ e Þ þ N
a
ð1Þ
3
ꢁ1
.37 cm mol K. On lowering the temperature, the
M
v T value
3
ꢁ1
The value of was used. The best fit was obtained when
gradually decreases to 3.07 cm mol K at 5 K; this value is much
larger than the spin-only LS value, showing an incomplete and very
gradual spin equilibrium. The
ꢁ
1
ꢁ4
3
ꢁ1
g
Fe = 2.01, D = 4.5 cm
,
and
Na
= 2.5 ꢂ 10 cm mol
for 4,
ꢁ
1
3
ꢁ1
and for corresponding values of 2.027, 3.5 cm
,
and Na =
v
M
T value of 2 is 3.94 cm mol K at
ꢁ4
3
ꢁ1
1
.7 ꢂ 10 cm mol for 5. The obtained fitting values are typical
3
00 K, which is smaller than the spin-only HS value. On lowering
3
of slightly distorted octahedral high-spin iron(III) environments [14].
the temperature, the
M
v T value decreases gradually to 1.33 cm -
ꢁ1
mol K at 5 K; this value is closer to the LS value than that of 1
is, but considerably larger than the LS value. Compound 2 shows
a gradual spin equilibrium over a wide temperature range. Com-
pound 3 shows a complete abrupt spin transition between the
3.3. Crystal structures
3.3.1. Crystal structures of 1–5 at 296 K
HS and LS states. The
v
M
T curves in the cooling and warming
The crystal structures of 1–5 were determined using
single-crystal X-ray diffraction at several temperatures. The crys-
tallographic data are listed in Table 1. Relevant coordination bond
distances and angles, and hydrogen-bond distances are given in
ꢁ1
modes measured at the sweeping rate of 2 K min show a small
but definite difference in the spin transition temperature region,
suggesting a very small thermal hysteresis. The present abrupt spin

1
88
M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
Table 1
Crystallographic data for BPh salt (1), CF
4ꢁ
3
3ꢁ 6ꢁ 4ꢁ 4ꢁ
SO salt (2), PF salt (3), ClO salt (4), and BF salt (5).
BPh
4
(1)
CF
FeB C25
635.42
monoclinic
3
SO
3
(2)
PF
6
(3)
ClO
4
(4)
BF
4
(5)
Formula
C
50
H
54
N
6
O
4
H
26
6
N O
5
FeF
3
C
24
H
26
N
6
O
2
FePF
6
C
24.5
H
28
N
6
O
6
FeCl C25.5H N O FeBF
30 7 3 4
Formula weight 869.67
Crystal system triclinic
631.32
monoclinic
601.83
triclinic
607.20
triclinic
Space group
P 1ꢀ (No. 2)
C2/c (No. 15)
C2/c (No. 15)
P 1ꢀ (No. 2)
P 1ꢀ (No. 2)
T (K)
296
296
200
103
296
200
103
296
296
a (Å)
b (Å)
c (Å)
12.120(7)
12.658(7)
15.544(9)
96.103(7)
104.876(6)
97.521(6)
2260(3)
2
24.668(2)
9.6459(7)
25.208(3)
90
113.893(2)
90
5484.2(8)
8
1.539
24.415(1)
9.5785(4)
25.0179(9)
90
113.502(2)
90
24.209(1)
9.5144(3)
24.8577(8)
90
113.186(2)
90
24.333(5)
9.636(2)
25.094(4)
90
113.557(5)
90
5394(2)
8
1.555
24.250(2)
9.5816(5)
24.823(2)
90
113.054(2)
90
24.085(1)
9.5517(4)
24.596(1)
90
112.746(2)
90
9.6826(7)
15.345(2)
18.770(2)
77.616(3)
84.515(2)
82.917(2)
2696.3(4)
4
9.678(2)
15.557(3)
18.599(3)
78.512(4)
85.155(4)
83.697(4)
2722.3(8)
4
a
(°)
b (°)
(°)
c
3
V (Å )
5365.4(4)
5263.1(4)
5307.2(6)
5218.3(4)
Z
D
calcd (g cmꢁ3) 1.278
1.573
7.091
1.604
7.229
1.580
7.054
1.607
7.174
1.482
7.108
1.481
6.189
0.1047, 0.2885
ꢁ
1
l
(mm
)
3.848
6.938
6.941
a
b
R , Rw
0.0730, 0.1612 0.0739, 0.2129 0.0694, 0.2159 0.0702, 0.2158 0.0870, 0.2396 0.0730, 0.2197 0.0756, 0.2239 0.0908, 0.2519
P
P
a
R = ||F
Rw = [ w(|F
o
| ꢁ |F
c
||/ |F
o
|.
P
P
b
2
2
2
2|2]1/2.
o
| ꢁ |F
c
|) / w|F
o
Table 2
Coordination bond distances (Å) and angles (°) for BPh salt (1), CF
4ꢁ
3
3ꢁ 6ꢁ
SO salt (2), and PF salt (3).
BPh
4
(1)
CF
3
SO
3
(2)
PF
296 K
2.105(7)
2.127(5)
2.164(5)
2.144(5)
1.883(4)
1.890(6)
2.135
6
(3)
296 K
296 K
200 K
103 K
200 K
2.102(6)
2.118(5)
2.159(4)
2.143(5)
1.890(4)
1.903(6)
2.131
103 K
Fe–N1
Fe–N2
Fe–N3
Fe–N5
Fe–O1
Fe–O2
1.969(6)
1.984(7)
2.033(8)
2.034(8)
1.858(6)
1.861(5)
2.005
2.107(6)
2.088(5)
2.141(4)
2.143(4)
1.880(4)
1.898(5)
2.120
2.080(6)
2.070(4)
2.118(4)
2.129(4)
1.881(3)
1.900(5)
2.099
2.039(5)
2.026(4)
2.073(4)
2.086(4)
1.881(3)
1.893(5)
2.056
2.092(7)
2.101(5)
2.130(4)
2.129(5)
1.879(4)
1.907(6)
2.114
<Fe–N>
O1–Fe–O2
O1–Fe–N1
O1–Fe–N3
O1–Fe–N5
O2–Fe–N2
O2–Fe–N3
O2–Fe–N5
N1–Fe–N2
N1–Fe–N3
N1–Fe–N5
N2–Fe–N3
N2–Fe–N5
91.8(3)
91.3(3)
90.1(3)
87.7(3)
91.8(3)
89.4(3)
92.0(3)
85.3(3)
87.7(3)
91.1(3)
92.8(3)
89.3(3)
101.50(17)
88.06(18)
92.38(15)
91.87(15)
89.1(2)
90.08(17)
91.57(19)
81.4(2)
87.76(18)
89.84(19)
89.27(16)
86.08(16)
99.69(16)
88.70(17)
92.35(14)
91.99(14)
89.73(18)
89.62(17)
91.78(18)
81.94(19)
88.30(17)
89.64(18)
89.41(15)
85.95(15)
95.83(15)
89.88(16)
92.04(14)
91.78(13)
90.92(17)
89.10(15)
91.39(16)
83.41(18)
89.10(16)
90.02(17)
89.52(15)
86.59(14)
101.9(2)
101.66(18)
88.62(19)
92.83(16)
93.27(15)
88.8(2)
89.36(19)
92.8(2)
81.0(2)
87.89(18)
88.8(2)
88.39(2)
84.99(16)
100.5(2)
89.1(2)
93.32(17)
93.20(17)
89.1(2)
89.0(2)
92.6(2)
81.4(3)
88.5(2)
88.5(3)
92.21(18)
93.49(19)
88.7(3)
89.9(3)
92.6(3)
80.9(3)
87.5(3)
88.8(3)
88.87(18)
84.8(2)
88.8(2)
87.77(17)
85.33(17)
Table 3
Hydrogen bond distances (Å) for BPh salt (1), CF
96 K.
4ꢁ
3ꢁ
6ꢁ
Compounds 4 and 5 have isomorphous structures and crystallized
3
SO salt (2), and PF salt (3) at
ꢀ
2
in a triclinic space group, P1 (No. 2), with Z = 4, and the unique unit
III
+
2
consists of two [Fe (Him) (hapen)] complex cations, two counter
4ꢁ
BPh salt (1)
⁄
anions, and crystal solvent molecules (see Table 4).
N6 ꢀ ꢀ ꢀO4
2.800(11)
2.821(11)
2.626(10)
O1ꢀ ꢀ ꢀO3
O3ꢀ ꢀ ꢀO4
ꢁ
The molecular structures of all the cationic part of compounds
III
1–5 are similar to each other. The molecular structure of the [Fe
+
CF
3
⁄
SO
3
salt (2)
(Him)
2
(hapen)] part of 1, and the atom numbering scheme, are
shown in Fig. 2, as a representative example. The Fe ion of the
complex cation has an octahedral coordination environment with
III
N6 ꢀ ꢀ ꢀO2
N4ꢀ ꢀ ꢀO8
ꢁ
2.911(7)
2.887(17)
PF
6
⁄
salt (3)
the N
and N
O
donor atoms of the equatorial tetradentate ligand hapen,
2
2
N6 ꢀ ꢀ ꢀO2
2.938(8)
2
donors of two imidazoles at the axial positions. The Fe–N
and Fe–O coordination bond distances are indicative of the spin
state. These Fe–N and Fe–O coordination bond distances in all five
complexes at 296 K are consistent with the reported bond lengths
for HS iron(III) complexes with similar Schiff-base ligands [6c,7,8].
The relative orientation of the imidazole rings is one of the param-
eters that determine the coordination core bond lengths and con-
sequently the spin state [3]. Fig. 2(b) shows the orientations of
the two imidazole rings, in which one imidazole ring bisects the
angles defined by the two N–Fe–O diagonals, and the other
imidazole ring is oriented nearly along the N–Fe–O diagonal.
Table 2 and 3 for 1-3 and in Table 4 for 4 and 5. Compound 1 crys-
ꢀ
tallized in a triclinic space group, P1 (No. 2), and the unique crys-
III
+
tallographic unit consists of one [Fe (Him)
2
(hapen)] , two
ꢁ
methanol molecules as the crystal solvent, and one BPh
4
anion.
Compounds 2 and 3 crystallized in an isomorphous monoclinic
space group, C2/c, and each unique unit consists of one
III
+
[
Fe (Him)
2
(hapen)] , two methanol molecules as the crystal sol-
ꢁ
ꢁ
vent, and one counter anion, i.e., CF
3
SO
3
, for 2 and PF
6
for 3.

M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
189
Table 4
the equatorial coordination plane at 296 K are indicative of the spin
state; high-spin compounds 4 and 5 have the large angle around
4ꢁ
Coordination bond distances and hydrogen bond distances and bond angle for ClO
salt (4) and BF salt (5) at 296 K.
ꢁ
1
03.5°, while SCO compounds 1, 2 and 3 have smaller angles of
ClO
4
BF
4
91.8°, 101.5° and 101.9°, respectively. Murray et al. demonstrated
that the five-membered chelate ring involving ethylenediamine
moiety is closely related to the spin state, (1) the envelope confor-
mation accepts the spin transition; (2) the gaushe or planar confor-
mation locks in high spin state [15]. Compounds 4 and 5 of high-spin
complexes have a gaushe conformation, while the other compounds
of SCO complexes 1–3 are closer to an envelope conformation, giving
a distortion of two benzene moieties. This result is accord with that
of Murray [15].
Bond distance
Fe1–N1
Fe1–N2
Fe1–N3
Fe1–N5
Fe1–O1
Fe1–O2
Fe1–N average
Fe2–N7
Fe2–N8
Fe2–N9
Fe2–N11
Fe2–O3
Fe2–O4
Fe2–N average
2.119(8)
2.116(8)
2.172(7)
2.142(7)
1.899(7)
1.909(6)
2.137
2.114(8)
2.093(7)
2.146(8)
2.159(8)
1.881(6)
1.918(6)
2.128
2.113(7)
2.114(7)
2.174(7)
2.150(6)
1.871(6)
1.913(6)
2.138
2.122(7)
2.096(7)
2.137(7)
2.156(7)
1.858(5)
1.931(5)
2.128
3.3.2. Three types of hydrogen-bonded assembly structures
As shown in Table 1, compounds 1–5 crystallized in three types
ꢀ
of crystal structures: 1 crystallized in a triclinic space group, P1
Hydrogen bond distance
N6ꢀ ꢀ ꢀO4
(No. 2); 2 and 3 crystallized in an isomorphous monoclinic space
group, C2/c; and 4 and 5 crystallized in an isomorphous triclinic
space group, P1 (No. 2), with Z = 4. As described below, three types
2.795(10)
2.60(2)
2.776(12)
2.96(3)
2.787(9)
N4ꢀ ꢀ ꢀO18 or F10
N12ꢀ ꢀ ꢀO6 or F2
N10ꢀ ꢀ ꢀN13 or O19
2.676(18)
2.681(16)
2.772(13)
ꢀ
of hydrogen-bonded assembly structures are generated.
III
Fig.
hapen)]ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ}
has an inversion center consisting of two Fe complex molecules,
3
shows the cyclic dimer structure, {ꢀ ꢀ ꢀ[Fe (Him)
2
Bond angle
(
2
, of 1. The cyclic dimer structure
O1–Fe1–O2
O1–Fe1–N1
O1–Fe1–N3
O1–Fe1–N5
O2–Fe1–N2
O2–Fe1–N3
O2–Fe1–N5
N1–Fe1–N2
N1–Fe1–N3
N1–Fe1–N5
N2–Fe1–N3
N2–Fe1–N5
O3–Fe2–O4
O3–Fe2–N7
O3–Fe2–N9
O3–Fe2–N11
O4–Fe2–N8
O4–Fe2–N9
O4–Fe2–N11
N7–Fe2–N8
N7–Fe2–N9
N7–Fe2–N11
N8–Fe2–N9
N8–Fe2–N11
104.5(3)
104.2(3)
87.7(3)
94.3(3)
90.3(3)
87.4(3)
91.9(3)
94.6(3)
80.6(3)
87.5(3)
84.8(3)
86.1(3)
87.8(3)
103.5(2)
88.2(3)
95.4(3)
91.0(3)
87.7(3)
88.7(3)
95.0(3)
80.7(3)
87.4(3)
87.6(3)
86.3(3)
86.4(3)
III
88.1(3)
93.4(3)
89.7(3)
87.1(3)
91.8(3)
94.0(3)
80.2(3)
88.6(3)
84.8(3)
87.1(3)
88.4(3)
103.8(3)
88.4(3)
94.2(3)
91.0(3)
87.2(3)
88.3(3)
94.6(3)
80.6(3)
88.2(3)
87.7(3)
87.1(3)
87.0(3)
III
+
2
i.e., [Fe (Him) (hapen)] , and four methanol molecules. One of
the two phenoxo oxygen atoms of hapen in the complex cation,
O(1), is hydrogen-bonded to the oxygen atom O(3) of the methanol
molecule, with a distance of O(1)ꢀ ꢀ ꢀO(3) = 2.821(11) Å. The oxygen
atom O(3) of methanol is further hydrogen-bonded to another
methanol, with a distance of O(3)ꢀ ꢀ ꢀO(4) = 2.626(10) Å. The oxygen
⁄
atom O(4) is further hydrogen-bonded to a nitrogen atom N(6) of
the coordinated imidazole of the adjacent complex unit, with a dis-
⁄
tance of O(4)ꢀ ꢀ ꢀN(6) = 2.800(11) Å. As a result, a cyclic dimeric
III
structure, {ꢀ ꢀ ꢀ[Fe (Him)
2
(hapen)]ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ}
2
, is con-
ion is not involved in the
ꢁ
structed by hydrogen-bonds. The BPh
4
cyclic dimer structure, and is present as the counter anion. The same
III
cyclic structure was found in [Fe ((Him)
2
(hapacen)]BPh
4
ꢀ2MeOH
[16], which showed spin equilibrium, where hapacen = N-(2-hydroxy-
acetophenylidene)-N -(acetylacetonylidene)ethylenediamine.
0
As the crystal structures of 2 and 3 are isomorphous, these two
complexes have essentially the same crystal structures. Fig. 4(a)
and (b) show parts of one-dimensional (1D) zigzag-chain structures
of 2 and 3, respectively. The 1D structure is constructed by intermo-
lecular hydrogen-bonding between a phenoxo oxygen, O(2), of the
⁄
complex cation and an imidazole nitrogen, N(6) , of the adjacent
Similar relative orientations of the two imidazole rings are found
for the other complexes.
The spin sate of [Fe (salX)(L) ] systems (salX = N O Schiff-
2 2
base ligand; L = pyridine or imidazole) has been explained by the
⁄
complex cation, with a distance of O(2)ꢀ ꢀ ꢀN(6) = 2.911(7) Å for 2
⁄
III
2 +
and O(2)ꢀ ꢀ ꢀN(6) = 2.938(8) Å for 3. The adjacent complex cations
are related by a two-fold screw axis along the b-axis and the
⁄
O(2)ꢀ ꢀ ꢀN(6) hydrogen-bond is repeated to form a 1D structure
structural parameters. For example, the O–Fe–O bond angles of
running along the b-axis. The remaining imidazole of the two imida-
Fig. 2. (a) ORTEP drawing of [FeIII(Him) (hapen)]+ part of 1, with the atom numbering scheme, at 200 K; the same atom numbering is used for 1–3. The thermal ellipsoids
2
were drawn at the 50% probability level. (b) View of the complex cation 1 projected on the planar tetradentate Schiff-base ligand at 296 K, showing the orientations of two
imidazole rings.

1
90
M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
Fig. 3. Cyclic dimer structure, {ꢀ ꢀ ꢀ[Fe(Him)
2
(hapen)]ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ(MeOH)ꢀ ꢀ ꢀ}
2
, of
ꢁ
BPh
4
salt (1). The structure has an inversion center and is constructed from three
kinds of hydrogen-bond: O(1)ꢀ ꢀ ꢀO(3) (phenoxoꢀ ꢀ ꢀmethanol), O(3)ꢀ ꢀ ꢀO(4) (metha-
nolꢀ ꢀ ꢀmethanol), and O(4)ꢀ ꢀ ꢀN(6) (methanolꢀ ꢀ ꢀimidazole).
6ꢁ
Fig. 5. (a) 1D zigzag-chain structure running along the b-axis of PF salt (3). (b)
Space filling representation of the rod-like chain.
zoles per complex cation is hydrogen-bonded to the counter anion
ꢁ ꢁ
3 6
in 2, but is not hydrogen-bonded to PF in 3.
CF
3
SO
The two adjacent complex-cations are related by a 2
Fe2 sites have different hydrogen-bonding environments. One
imidazole of the Fe2 site is hydrogen-bonded to the counter anion,
and the other imidazole of the Fe2 site is hydrogen-bonded to, or in
weak contact with, the methanol crystal solvent for 4, and an imid-
azole incorporated in the crystallization for 5. In contrast, one
imidazole of the Fe1 site is hydrogen-bonded to the phenoxo oxy-
gen of the Fe2 site to form a linear dimer structure, and the other
imidazole of the Fe1 site is hydrogen-bonded to the counter anion.
1
screw axis
along the b-axis and the resulting infinite 1D chain runs along the
b-axis. Each equatorial coordination plane and axially coordinated
imidazole group are tilted from the b-axis. Fig. 5 shows the 1D
structure and its space filling representation, showing a rod-like
structure. In the crystal lattice, rods are stacked along the b-axis,
and the anions occupy the space among the rods. A similar 1D
III
structure was found in [Fe (4-NH
2
4
Py)(L)]BPh ; 4-NH
2
Py = 4-ami-
nopyridine,
L = bis(3-methoxysalicylideneaminopropyl)amine)]
1D chain was formed by intermolecular
[
17], in which
a
3
.3.3. Structural deformation during spin transition
Compounds 2 and 3 showed spin equilibrium, and their crystal
amineꢀ ꢀ ꢀphenoxo hydrogen-bonds, and the compound showed an
abrupt spin transition.
structures at several temperatures were determined. The relevant
coordination bond distances are summarized in Table 2. The
Fe–N coordination bond distances of 2 at 296 K are is in the
range 2.088(5)–2.143(4) Å; these values are in the expected range
for HS Fe complexes with a Schiff-base N
As 4 and 5 are isomorphous, these two complexes have essen-
tially the same crystal structure. Fig. 6(a) and (b) show the linear
dimer structures of 4 and 5, respectively. The linear dimer struc-
ture is constructed by hydrogen-bonds between an imidazole
nitrogen, N(6), of the Fe1 site and a phenoxo oxygen, O(4), of the
III
4
O
2
environment [3]. The
corresponding distances at 103 K are in the range 2.026(4)–
.086(4); these values are shorter than those at 296 K, but are
adjacent complex cation Fe2 site, with
a
distance of
2
III
O(4)ꢀ ꢀ ꢀN(6) = 2.794(10) Å. As a result of the O(4)ꢀ ꢀ ꢀN(6) hydro-
gen-bond, the coordination bond distance of Fe1–O(2) is longer
than that of Fe1–O(1). As shown in Fig. 6(a) and (b), the Fe1 and
longer than those expected for the LS Fe complexes [3]. As a result
of the incomplete spin transitions for 2, the differences between the
average Fe–N bond distances at 296 and 103 K are less than 0.1 Å.
3ꢁ
6ꢁ
3
3ꢁ
Fig. 4. (a) 1D zigzag-chain structure running along the b-axis of CF
3
SO salt (2). (b) 1D zigzag-chain structure running along the b-axis of PF salt (3). Anions CF
SO and
ꢁ
PF
6
of 1 and 2 are disordered.

M. Koike et al. / Inorganica Chimica Acta 399 (2013) 185–192
191
4ꢁ
4ꢁ
Fig. 6. (a) Linear dimer structure of ClO salt (4). (b) Linear dimer structure of BF salt (5). The structure consists of two Fe sites, Fe1 and Fe2, with different hydrogen-
ꢁ
ꢁ
bonding environments. Anions ClO
4
and BF
4
of 4 and 5 are disordered.
The Fe–N(axial imidazole) distances change more significantly than
those of Fe–N(equatorial). The spin-transition temperature of 3 (ca.
plexes. Within a 1D chain constructed by intermolecular imidaz-
oleꢀ ꢀ ꢀphenoxo hydrogen bond, each equatorial coordination plane
and imidazole group concerning with the hydrogen bond of the
SCO site are tilted from the 1D axis (b-axis). Since the molecular
volume resulting from elongation of the metal–ligand distances
and the coordination geometry of individual SCO molecules
changes substantially during the spin transition, such structural
features can absorb the structural change raised from spin transi-
tion. By adapting this molecular design, SCO Fe(III) complex with
larger thermal hysteresis can be realized.
7
8 K) is lower than 103 K, the lowest temperature of our X-ray appa-
ratus, and the Fe–N coordination bond distances at 296, 200, and
1
03 K are in the expected range for HS FeIII complexes.
4
. Concluding remarks
Firstly the present study is carried out from these general view-
points on SCO complexes.
A series of complexes with the formula [Fe (Him)
were synthesized, where the metal-complex cation of [Fe (Him)
III
Acknowledgments
2
(hapen)]Y
III
2
+
(
hapen)] was fixed, and the molecular size and/or molecular shape
T. Fujinami and K. Nishi were supported by the Research Fel-
lowship for Young Scientists of the Japan Society for the Promotion
of Science, KAKENHI 00248556 and 00248498.
3
ꢁ
3
ꢁ
6
of the counter anion Y varied, i.e., 86.9 Å (CF
3
SO
3
), 73.0 Å (PF
),
3
ꢁ
3
ꢁ
4
5
4.4 Å (ClO
4
), and 53.4 Å (BF
) [18a]. The crystal packing of an
SCO molecule in a crystal lattice significantly affects the SCO prop-
erties [3a]. The counter anion [18] and the solvent molecule [19] in
the crystal lattice influence SCO properties caused by the molecu-
lar expansion and shrinkage indirectly but significantly. The cation
and anion packing in the crystal lattice depend on the anion size
and, as a result, three types of hydrogen-bonded assembly struc-
tures are generated: a SCO cyclic dimer in 1, SCO 1D chains in 2
and 3, and high-spin linear dimers in 4 and 5. Compound 3, in par-
ticular, shows a complete and abrupt spin transition with small
thermal hysteresis. As five complexes contain the same complex-
Appendix A. Supplementary data
CCDC 897460–897468 contain the supplementary crystallo-
III
ꢁ
graphic data for [Fe (Him) (hapen)]Yꢀsolvent (Y = BPh4 (1),
2
ꢁ
ꢁ
ꢁ
ꢁ
4
CF SO (2), PF6 (3), ClO (4), and BF (5)). These data can be
3
3
4
obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at http://dx.doi.org/10.1016/j.ica.2013.01.021.
III
+
III
2
cation of [Fe (Him) (hapen)] , whose Fe ion is coordinated by
4 2
N O
donor atoms of equatorial hapen and two axial Him, the vari-
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significantly influencing the SCO properties. It should be especially
emphasized that compound 3 with 1D chain shows abrupt spin
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