Syntheses, hydrogen-bonded assembly structures, and spin crossover properties of [FeIII(Him)2(n-MeOhapen)]PF6 (Him = imidazole and n-MeOhapen = N,N′-bis(n-methoxy-2-oxyacetophenylidene)ethylenediamine); n = 4, 5, 6)

Article abstract of DOI:10.1016/j.ica.2015.03.034

Three iron(III) complexes, [Fe^III(Him)₂(n-MeOhapen)]PF₆ (1: n = 4, 2: n = 5, 3: n = 6), where Him = imidazole and n-MeOhapen = N,N′-bis(n-methoxy-2-oxyacetophenylidene)ethylenediamine, were synthesized. Each Fe^III

Full text of DOI:10.1016/j.ica.2015.03.034

Inorganica Chimica Acta 432 (2015) 89–95
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Inorganica Chimica Acta
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Syntheses, hydrogen-bonded assembly structures, and spin crossover
properties of [FeIII(Him)2(n-MeOhapen)]PF6 (Him = imidazole and
n-MeOhapen = N,N0-bis(n-methoxy-2-oxyacetophenylidene)
ethylenediamine); n = 4, 5, 6)
a
a
a
b
Takeshi Fujinami a, , Mizuki Ikeda , Masataka Koike , Naohide Matsumoto , Tomohiro Oishi ,
⇑
Yukinari Sunatsuki c
a Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
b Technical Division, Faculty of Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
c Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 1-1, Okayama 700-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Three iron(III) complexes, [FeIII(Him)2(n-MeOhapen)]PF6 (1: n = 4, 2: n = 5, 3: n = 6), where
Him = imidazole and n-MeOhapen = N,N0-bis(n-methoxy-2-oxyacetophenylidene)ethylenediamine, were
synthesized. Each FeIII ion was coordinated by N4O2 donor atoms of equatorial n-MeOhapen and two axial
Him. The saturated FeC2N2 chelate ring involving the ethylenediamine moiety adopted a gauche con-
formation and the two phenylidene planes of [FeIII(Him)2(n-MeOhapen)]+ were oriented opposite to
the FeO2N2 coordination plane. Two adjacent [FeIII(Him)2(4-MeOhapen)]+ cations in 1 were connected
via PFꢀ6 ions by hydrogen bonds between the imidazole group and PFꢀ6 to give a one-dimensional chain.
Two adjacent cations in 2 were connected via hydrogen bonds between the phenylidene oxygen and imi-
dazole atoms to form a cyclic dimer structure. Two EtOH molecules were involved in a hydrogen-bonded
cyclic dimer structure in 3. Compounds 1 and 2 showed spin crossover behavior, but 3 showed incom-
plete spin crossover.
Article history:
Received 30 October 2014
Received in revised form 9 January 2015
Accepted 22 March 2015
Available online 3 April 2015
Keywords:
Iron(III) complex
Spin equilibrium
Imidazole
N2O2 Schiff-base ligand
Hydrogen bonds
Assembly structures
Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction
ligands exhibit SCO [2–5], and the SCO complexes with bidentate
or tridentate ligands are major groups in SCO studies [1,6]. The
Spin crossover (SCO) is
a
representative phenomenon of
FeII or FeIII sites in some heme proteins exhibit SCO properties
[7], and iron porphyrin derivatives have been studied as model
compounds [8]. As synthetic, yet simple model compounds,
Nishida first reported a family of FeIII complexes with N2O2
salen-type ligands at the equatorial plane and two monodentate
ligands (monodentate ligands such as pyridine and imidazole
derivatives) at the axial sites [FeIII(X)2(salen-type)]BPh4 [9] and
demonstrated that the ligand field of [FeIII(X)2(salen-type)]+ is
close to the SCO point and that some of them exhibit SCO.
Subsequently, Matsumoto [10], Murray [11], and Real [12]
reported SCO FeIII complexes with analogous N2O2 Schiff-base
ligands and revealed the relevant factors to determine the SCO
properties. Especially, Murray [11] pointed out that the con-
formation of the two phenylidene planes of [FeIII(X)2(salen-type)]+
with a one side opened salen-type ligand is related to ‘‘whether or
not SCO occurs’’. The favored conformation is not always achieved
for [FeIII(X)2(salen-type)]+, and even if SCO was observed, steep
SCO with hysteresis was not merely observed.
bistability in the electronic structure of metal complexes. SCO
complexes show inter-conversion between the high-spin (HS)
and low-spin (LS) states upon external physical perturbations such
as temperature, pressure, and light irradiation [1]. Steepness,
multi-step, and hysteresis in SCO profiles can be induced by
intermolecular cooperative effects [1].
Among metal complexes that exhibit SCO, SCO FeIII complexes
with a d5 electronic configuration generally exhibit a gradual spin
equilibrium [2] and show no thermal hysteresis with the exception
of a few complexes [3]. On the other hand, some SCO FeII com-
plexes with a d6 electronic configuration show steep spin transi-
tions that exhibit thermal hysteresis [1]. FeII and FeIII complexes
with a tetradentate planar ligand and two monodentate axial
⇑
Corresponding author. Tel./fax: +81 96 342 3385.
E-mail address: tfujinami@sci.kumamoto-u.ac.jp (T. Fujinami).
http://dx.doi.org/10.1016/j.ica.2015.03.034
0020-1693/Ó 2015 Elsevier B.V. All rights reserved.

90
T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
In previous papers, we revealed that ‘‘hapen-type’’ ligands in
6.31–6.28 (1H, q), 3.92 (2H, s), 3.79 (3H, s), 2.34 (3H, s). Here, s,
d, t, and indicate singlet, doublet, triplet, and quartet,
respectively.
[FeIII(X)2(hapen-type)]+ (Scheme 1) can give the suitable con-
formation due to the steric hindrance between the methyl group
on the phenylidene moiety and five-membered chelate ring
[10d]. Furthermore, an imidazole group as the axial ligand X in
[FeIII(X)2(hapen-type)]+ can form intermolecular hydrogen-bonds
to generate an assembly structure that may lead to cooperative
effects and modify the SCO profile. One of these complexes,
[FeIII(Him)2(hapen)]AsF6, showed steep SCO with thermal
hysteresis [4]. Some of SCO properties, such as steep, multi-step
spin transitions, hysteresis, and light-induced excited spin-state
trapping (LIESST), depend on the intermolecular hydrogen-bonds
among the SCO molecules [13]. In this study, three FeIII complexes
[FeIII(Him)2(n-MeOhapen)]PF6 (1: n = 4, 2: n = 5, 3: n = 6)
with three isomers of the new ‘‘hapen-type’’ ligand (n-
MeOhapen) were synthesized. In addition to the favorable con-
formation of the ‘‘hapen-type’’ ligand and intermolecular hydrogen
bond by imidazole group, the methoxy group may modify the
intermolecular interactions. From the above described three
points; (1) the molecular conformation of the two phenylidene
planes (2) intermolecular interactions by hydrogen bonds by with
the imidazole moiety, and (3) modification of the assembly struc-
ture by the methoxy group, we have synthesized three FeIII com-
plexes [FeIII(Him)2(n-MeOhapen)]PF6 (1: n = 4, 2: n = 5, 3:
n = 6)(Scheme 1), and reported here the syntheses, structures,
and SCO properties.
q
2.2.1.2. H2(5-MeOhapen). The tetradentate Schiff-base ligand H2(5-
MeOhapen) was prepared by a similar method to that used in the
preparation of H2(4-MeOhapen), using 5-methoxy-2-hydroxyace-
tophenone instead of 4-methoxy-2-hydroxyacetophenone.
A
yellow crystalline material was obtained as the product. Yield:
6.22 g (87%). Anal. Calc. for H2(5-MeOhapen) (C20H24N2O4): C,
67.40; H, 6.79; N, 7.86. Found: C, 67.19; H, 6.81; N, 7.77%.
mp = 251 °C. IR: mC
@
1614 cmꢀ1 1H NMR (CDCl3, 400 MHz,
.
N
ppm): d 7.04 (1H, d), 6.93–6.90 (1H, q), 6.87–6.84 (1H, d) 3.97
(2H, s), 3.77 (3H, s), 2.35 (3H, s).
2.2.1.3. H2(6-MeOhapen)ꢁ0.25EtOH. The tetradentate Schiff-base
ligand H2(6-MeOhapen)ꢁ0.25EtOH was prepared by
a similar
method to that used in the preparation of H2(4-MeOhapen), using
6-methoxy-2-hydroxyacetophenone instead of 4-methoxy-2-
hydroxyacetophenone. A yellow crystalline material was obtained.
Yield: 6.16 g (67%). Anal. Calc. for H2(6-MeOhapen)ꢁ0.25EtOH
(C20H24N2O4ꢁ0.25EtOH): C, 66.91; H, 6.99; N, 7.61. Found: C,
66.67; H, 6.91; N, 7.72%. mp = 197 °C. IR: mC
@
N
1600 cmꢀ1 1H
.
NMR (CDCl3, 400 MHz, ppm): d 7.17–7.13 (1H, t), 6.54–6.52 (1H,
q), 6.28–6.26 (1H, q), 3.91 (2H, s), 3.81 (3H, s), 2.47 (3H, s).
2.2.1.4. [FeCl(4-MeOhapen)]ꢁH2O 10. The precursor iron(III) complex
[FeIIICl(4-MeOhapen)]ꢁH2O was prepared according to the method
2. Experimental
applied for [FeIIICl(salen)]. To
a solution of H2(4-MeOhapen)
(0.01 mol, 3.56 g) in 150 mL of methanol, anhydrous FeIIICl3
(0.01 mol, 1.62 g) was added, and the mixture was stirred for
30 min on hot-plate at 65 °C. To the hot solution, a solution of tri-
ethylamine (0.02 mol, 2.02 g) in 10 mL of methanol was added
dropwise. The resulting black crystals were collected by suction fil-
tration, washed with a small amount of diethylether, and dried in
vacuo. Yield: 4.18 g (93%). Anal. Calc. for [FeCl(4-MeOhapen)]ꢁH2O
(C20H24N2O4FeClꢁH2O): C, 51.80; H, 5.22; N, 6.04. Found: C, 51.97;
2.1. General
All reagents and solvents used in the syntheses are commer-
cially available from Tokyo Kasei Co., Ltd., Tokyo, Japan and
Wako Pure Chemical Industries, Ltd., Osaka, Japan, and were used
without further purification. All of the synthetic procedures were
performed in air.
H, 4.96; N, 6.03%. IR: mC
@ .
1599 cmꢀ1
N
2.2. Preparation of materials
2.2.1.5. [FeCl(5-MeOhapen)]ꢁ0.5MeOH 20. Precursor complex 20 was
obtained as a black crystalline material by a similar method to that
used in the preparation of 10, using H2(5-MeOhapen) instead of
H2(4-MeOhapen). The product was obtained as black crystals.
Yield: 3.84 g (86%). Found: C, 53.13; H, 5.08; N, 6.24%. Calcd. for
[FeCl(5-MeOhapen)]ꢁ0.5MeOH (C20H24N2O4FeClꢁ0.5MeOH): C, 53.33;
2.2.1. Preparations of tetradentate ligand H2(n-MeOhapen) solvents
and precursor iron(III) complex [FeIIICl(n-MeOhapen)] solvents
2.2.1.1. H2(4-MeOhapen). To a solution of 4-methoxy-2-hydroxy-
acetophenone (0.05 mol, 8.31 g) in 50 mL of ethanol, a solution of
ethylenediamine (0.025 mol, 1.51 g) in 50 mL of ethanol was
added, and the mixture was stirred for 30 min on a hot plate at
60 °C. The resulting yellow crystalline material was collected by
suction filtration, washed with a small amount of ethanol, and
dried in vacuo. Yield: 7.30 g (82%). Anal. Calc. for H2(4-
MeOhapen) (C20H24N2O4): C, 67.40; H, 6.79; N, 7.86. mp = 254 °C.
H, 5.24; N, 6.07%. IR: mC
@ .
1614 cmꢀ1
N
2.2.1.6. [FeCl(6-MeOhapen)]ꢁ0.25EtOH 30. The precursor complex 30
was obtained as a black crystalline material by a similar method
to that used in the preparation of 10, using H2(6-MeOhapen) and
ethanol instead of H2(4-MeOhapen) and methanol. The product
Found: C, 67.09; H, 6.85; N, 7.86%. IR: mC
@ .
1583 cmꢀ1 1H NMR
N
(CDCl3, 400 MHz, ppm):
d
7.38–7.36 (1H, d), 6.36 (1H, d),
H
N
H
(b)
(a)
N
N
N
OCH3
4
6
3
H
3CO
OCH3
5
O
N
O
N
3
2
4
6
2
O
O
CH3
Fe3+
Fe3+
H
3CO
N
N
1
5
1
H
3C
H
3C
CH3
N
N
N
H
N
H
Scheme 1. (a) [FeIII(Him)2(n-MeOhapen)]+ (1: n = 4, 2: n = 5, 3: n = 6). (b) Favorable conformation of two phenylidene planes for SCO.

T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
91
was obtained as black crystals. Yield: 3.65 g (81%). Anal. Calc. for
[FeCl(6-MeOhapen)]ꢁ0.25EtOH (C20H24N2O4FeClꢁ0.25EtOH): C,
53.85; H, 5.18; N, 6.13. Found: C, 54.09; H, 5.46; N, 6.23%. IR:
using palladium metal. Corrections for diamagnetism were applied
using Pascal’s constants [14].
mC
@ .
1591 cmꢀ1
N
2.4. Crystallographic data collection and structure analyses
2.2.2. Preparation of iron(III) complex [FeIII(Him)2(n-
X-ray diffraction data were collected on a Rigaku RAXIS RAPID
imaging plate diffractometer using graphite monochromated Mo
MeOhapen)]PF6ꢁsolvents
2.2.2.1. [FeIII(Him)2(4-MeOhapen)]PF6 (1). To
a suspension of
Ka radiation (k = 0.71073 Å). The temperature of the crystal was
[FeIIICl(4-MeOhapen)]ꢁH2O (0.5 mmol, 0.22 g) in 10 mL of metha-
nol, an excess of imidazole (5 mmol, 0.34 g) was added, and the
mixture was stirred for 30 min on a hot-plate at 65 °C and subse-
quently filtered. A solution of NaPF6 (0.5 mmol, 0.09 g) in 5 mL of
methanol was added to the filtrate, and the resulting solution
was stirred for 15 min subsequently filtered. The resulting filtrate
was allowed to stand for several hours, during which time black
plate crystals precipitated; the crystals were collected by suc-
tion filtration, washed with diethyl ether, and dried in air.
Yield: 0.23 g (67%). Anal. Calc. for [FeIII(Him)2(4-MeOhapen)]PF6
(C26H30N6O4FePF6): C, 45.17; H, 4.37; N, 12.15. Found: C, 45.15;
maintained by a Rigaku cooling device within an accuracy of
2 K. The data were corrected for Lorentz, polarization, and absorp-
tion effects. The structures were solved by a direct method,
and expanded using the Fourier technique. Hydrogen atoms were
fixed at the calculated positions and refined using a riding model.
All calculations were performed using the CRYSTALSTRUCTURE crys-
tallographic software package [15].
3. Results and discussion
H, 4.68; N, 12.21%. IR: mC
@
1606 cmꢀ1 mN–H 3419 cmꢀ1
, , mP–F
N
3.1. Synthesis and characterization of iron(III) complexes
[FeIII(Him)2(n-MeOhapen)]PF6ꢁsolvents
821 cmꢀ1. Thermogravimetric analysis (TGA) was carried out
between room temperature and 145 °C using ca. 2 mg of the fresh
crystalline sample: In the heating mode, a 0.8% weight loss was
observed. In the cooling mode, the sample absorbed vapor to exhi-
bit a 0.8% weight increase.
The FeIII complexes [FeIII(Him)2(n-MeOhapen)]PF6ꢁsolvents (1:
n = 4, 2: n = 5, 3: n = 6) were obtained as black plate crystals by
mixing [FeIIICl(n-MeOhapen)], imidazole, and NaPF6 in a 1:10:1
molar ratio in methanol for 1 and 2, and in ethanol for 3. The C,
H, and N elemental analysis of complex 1 agreed with the formula
[FeIII(Him)2(4-MeOhapen)]PF6, demonstrating no existence of any
crystal solvents. With 1, the very gradual weight loss (within
0.1%) was observed in the heating mode in TGA. The elemental
analysis of 2 agreed with the formula [FeIII(Him)2(5-MeOhapen)]PF6ꢁ
0.5H2O. In the TGA, a 2.1% weight loss (0.8H2O) was observed in the
heating mode followed by a 1.1% weight increase (0.4 H2O) in the
cooling mode. The elemental analysis of 3 agreed with the formula
[FeIII(Him)2(6-MeOhapen)]PF6ꢁEtOH. In TGA, a 6.4% weight loss
(1EtOH) was observed in the heating mode and no weight increase
was observed in the cooling mode.
2.2.2.2. [FeIII(Him)2(5-MeOhapen)]PF6ꢁ0.5H2O (2). Compound 2 was
prepared using a similar method to that used in the preparation
of 1, using [FeIIICl(5-MeOhapen)]ꢁ0.5MeOH instead of [FeIIICl(4-
MeOhapen)]ꢁH2O. Black plate crystals were obtained as the pro-
duct. Yield: 0.20 g (57%). Anal. Calcd. for [FeIII(Him)2(5-
MeOhapen)]PF6ꢁ0.5H2O (C26H30N6O4FePF6ꢁ0.5H2O): C, 44.58; H,
4.46; N, 12.00. Found: C, 44.87; H, 4.42; N, 12.03%. IR: mC
@
N
1589 cmꢀ1 mN–H 3398 cmꢀ1 mP–F 817 cmꢀ1. TGA results of fresh
, ,
crystalline sample: In the heating mode, a 2.1% weight loss was
observed. In the cooling mode, the sample absorbed the vapor
and exhibited a 1.0% weight increase.
The ethanolic solutions of all complexes are shown in Fig. 1(a).
In the liquid state, 1 and 2 exhibited thermochromism, but 3
did not. The ethanolic solution of 1 was a deep red color at room
temperature, and changed to a bluish-green color at liquid-
nitrogen temperature. The ethanolic solution 2 was a violet color
at room temperature, and changed to an olive-green color at
2.2.2.3. [FeIII(Him)2(6-MeOhapen)]PF6ꢁEtOH (3). Compound 3 was
prepared using a similar method to that used in the preparation
of 1, using [FeIIICl(6-MeOhapen)]ꢁ0.25EtOH and ethanol instead of
[FeIIICl(4-MeOhapen)]ꢁH2O and methanol. Black plate crystals were
obtained as the product. Yield: 0.24 g (66%). Anal. Calc. for
[FeIII(Him)2(6-MeOhapen)]PF6ꢁEtOH (C26H30N6O4Fe-PF6ꢁEtOH): C,
45.60; H, 4.92; N, 11.39. Found: C, 45.71; H, 4.53; N, 11.58%. IR:
mC
@ , ,
1586 cmꢀ1 mN–H 3397 cmꢀ1 mP–F 825 cmꢀ1. TGA results of
N
fresh crystalline sample: In the heating mode, a 10.3% weight loss
was observed. In the cooling mode, a weight increase was not
observed.
2.3. Physical measurements
Elemental analyses (C, H, and N) were carried out at the
Center for Instrumental Analysis of Kumamoto University.
Melting points were measured by Yanako New Science Micro
Melting Point System MP-S3. 1H NMR spectra were measured by
on a Varian UnityInova AS400 with a static magnetic field of 9.4 T.
Infrared spectra were recorded at room temperature using a
PerkinElmer Frontier spectrometer with samples on ZnSe crystals.
Thermogravimetric analysis (TGA) was carried out on a TG/
DTA6200 (Seiko Instrument Inc.) instrument at a heating rate of
5 K minꢀ1 using ca. 5 mg samples. Magnetic susceptibilities were
measured by a Quantum Design MPMS-XL5 magnetometer in the
temperature range of 5–300 K at a sweep rate of 2 K minꢀ1 under
an applied magnetic field of 0.5 T. The calibration was performed
Fig. 1. (a) Thermochromism in ethanolic solutions of [FeIII(Him)2(n-
MeOhapen)]PF6ꢁsolvents. (1: n = 4, 2: n = 5, 3: n = 6) (b) thermochromism in the
solid state of [FeIII(Him)2(n-MeOhapen)]-PF6ꢁsolvents.

92
T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
The
slightly higher than 4.375 cm3 molꢀ1 K of the spin-only HS value.
Upon decreasing the temperature from 300 K to 5 K, the MT value
v
MT value of 1 was 4.5 cm3 molꢀ1 K at 300 K, which was
v
decreased and then reached a constant value of ca. 1.0 cm3 molꢀ1
K
at 5 K, but was larger than 0.375 cm3 molꢀ1 K of the spin-only LS
value. Compound 2 showed a more gradual spin equilibrium
than that of 1. The
which was slightly lower than the spin-only HS value. Upon
v
MT value of 2 was 4.1 cm3 molꢀ1 K at 300 K,
decreasing the temperature, the
vMT value decreased gradually
to 1.4 cm3 molꢀ1 K at 5 K, but was considerably larger than the
LS value. Compound 3 showed an incomplete spin equilibrium.
The
parable to the spin-only HS value. Upon decreasing the tempera-
ture, the
MT value decreased gradually to 2.8 cm3 molꢀ1 K at
v
MT value of 3 was 4.3 cm3 molꢀ1 K at 300 K, which was com-
v
5 K, but was considerably larger than the LS value.
3.3. Crystal structures
Fig. 2.
vMT vs. T plots for 1, 2, and 3.
3.3.1. Crystal structures of 1, 2, and 3
liquid-nitrogen temperature. The ethanolic solution of 3 was a yel-
lowish-brown color at room temperature did not show a color
change upon decreasing the temperature. The thermochromism
in the liquid state suggests SCO properties of isolated molecules.
The color of the ground sample of all complexes are shown in
Fig. 1(b). In the solid state, 1 and 2 showed thermochromism, but
3 did not. The color changes upon decreasing the temperature from
room temperature to liquid-nitrogen temperature were similar to
those of the ethanolic solutions. The thermochromism observed
in the solid state suggests SCO properties of the crystal state.
The crystal structures of 1, 2, and 3 were determined by
single-crystal X-ray diffraction analysis at various temperatures.
The crystallographic data are listed in Table 1. Relevant coordina-
tion bond distances, angles, and hydrogen-bond distances are
given in Table 2. The molecular structures of the [FeIII(Him)2
(n-MeOhapen)]+ part and the atom numbering scheme of all
complexes are shown in Figs. 3(a)–(c), in which the molecular
structures projected on the Schiff-base planes and the side views
are shown on the left and right side, respectively. Each FeIII ion
had an octahedral coordination environment with N2O2 donor
atoms of the tetradentate Schiff-base ligand at the equatorial plane
and N2 donors of two imidazoles at the axial positions. The
spin state of similar [FeIII(X)2(salen-type)]+ systems (salen-type =
salen-type N2O2 Schiff-base ligand; X = pyridine or imidazole)
was explained by structural parameters. The coordination bond
distances and angles are relevant parameters for the spin state.
The Fe–N coordination bond distances of 1 and 2 at 296 K were
in the range of those reported for HS FeIII complexes with similar
Schiff-base ligands [10–12]. The corresponding distances of 1 and
2 at 100 K were in the range of those reported for LS FeIII complexes
[10–12], and shorter than those at 296 K. The Fe–N distances of 3
were similar at 296 and 100 K, and were in the expected range
for HS state FeIII complexes. The O1–Fe–O2 bond angle is indicative
of the spin state; the values of 1 and 2 at 296 K were 98.90(14)° for
1 and 98.10(17)° for 2; these values were in the range of expected
3.2. Temperature-dependence of magnetic properties
The magnetic susceptibilities of the samples were measured in
the temperature range of 5–300 K under an applied magnetic field
of 0.5 T. The magnetic susceptibility was measured upon lowering
the temperature from 300 to 5 K in the first run and was subse-
quently measured while raising the temperature in the second
run. The
vMT vs. T plots for 1, 2, and 3 are shown in Fig. 2. The plots
of the data obtained in the heating and cooling modes were prac-
tically the same for the three complexes, and showed no thermal
hysteresis.
Complex 1 showed a spin equilibrium between the HS and LS
states. The
vMT curves in warming and cooling modes showed a
small difference in the spin transition temperature around 150 K.
Table 1
Crystallographic data for [FeIII(Him)2(n-MeOhapen)]PF6ꢁsolvents (1: n = 4, 2: n = 5, 3: n = 6).
[Fe(4-MeOhapen)]PF6 (1)
[Fe(5-MeOhapen)]PF6ꢁH2O (2)
[Fe(6-MeOhapen)]PF6ꢁEtOH (3)
Formula
Formula weight
Crystal system
Space group
T (K)
C
26H30N6O4FePF6
C26H30N6O4FePF6ꢁH2O
C26H30N6O4FePF6ꢁC2H5OH
691.37
monoclinic
C2/c
709.39
737.44
monoclinic
C2/c
170
monoclinic
C2/c
100
monoclinic
P21/n
monoclinic
P21/n
monoclinic
monoclinic
ꢀ
ꢀ
P1
P1
250
296
100
250
100
a (Å)
b (Å)
c (Å)
20.0759(5)
17.1908(6)
18.4139(5)
90
112.3140(7)
90
5879.1(3)
8
1.562
19.8295(6)
17.0362(7)
18.3305(6)
90
111.7182(8)
90
5752.9(4)
8
1.596
19.622(2)
16.912(2)
18.242(2)
90
111.354(2)
90
5638.0(8)
8
1.629
11.0207(5)
13.9014(6)
19.875(1)
90
98.420(2)
90
3012.2(3)
4
1.564
10.8257(6)
17.8663(9)
19.311(1)
90
98.986(2)
90
2863.2(3)
4
1.646
10.1273(4)
12.7833(5)
15.1387(7)
70.303(2)
80.113(2)
64.9446(9)
1670.6(1)
2
1.466
5.781
0.1027
0.3086
10.0342(4)
12.6380(5)
15.0402(7)
70.638(2)
80.499(1)
64.7394(9)
1626.7(1)
2
1.505
5.937
0.0379
0.1515
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc. (g cmꢀ3
)
l
(cmꢀ1
)
6.491
0.0590
0.1838
6.633
0.0609
0.1865
6.768
0.1274
0.3554
6.379
0.0759
0.2148
6.711
0.1246
0.3388
Ra
Rwb
a
R =
Rw = [
R
||Fo| ꢀ |Fc||/
R|Fo|.
b
R
w(|Fo2| ꢀ |Fc2|)2/
R .
w|Fo2|2]1/2

T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
93
Table 2
Coordination bond distances (Å), bond angles (°) and Hydrogen bond distances (Å) for [FeIII(Him)2(n-MeOhapen)]PF6ꢁsolvents (1: n = 4, 2: n = 5, 3: n = 6).
[Fe(4-MeOhapen)]PF6 (1)
[Fe(5-MeOhapen)]PF6ꢁH2O (2)
[Fe(6-MeOhapen)]PF6ꢁEtOH (3)
250 K
170 K
100 K
296 K
100 K
250 K
100 K
Bond lengths (Å)
Fe–N1
Fe–N2
Fe–N3
Fe–N5
Average <Fe–N>
Fe–O1
Fe–O2
2.093(3)
2.072(4)
2.173(5)
2.164(5)
2.125
1.875(4)
1.883(3)
1.879
2.015(3)
1.998(4)
2.089(5)
2.078(5)
2.045
1.881(4)
1.882(3)
1.881
1.945(6)
1.937(8)
2.013(9)
2.023(9)
1.980
1.875(7)
1.884(5)
1.879
2.073(5)
2.085(5)
2.133(6)
2.129(6)
2.105
1.885(4)
1.882(4)
1.883
1.938(8)
1.928(7)
1.980(9)
2.000(8)
1.962
1.893(6)
1.870(6)
1.881
2.105(4)
2.104(6)
2.169(4)
2.144(4)
2.131
1.893(5)
1.918(4)
1.906
2.1133(15)
2.103(3)
2.1434(16)
2.1590(16)
2.1297
1.8859(19)
1.9293(14)
1.908
Average <Fe–O>
Bond angles (°)
O1–Fe–O2
O1–Fe–N1
O2–Fe–N2
N1–Fe–N2
N1–Fe–N3
N1–Fe–N5
N2–Fe–N3
N2–Fe–N5
98.90(14)
88.63(15)
90.73(14)
81.88(15)
90.67(15)
88.08(15)
88.07(18)
89.12(16)
93.30(13)
90.83(14)
92.16(13)
83.83(13)
91.40(14)
88.56(14)
88.80(16)
90.39(15)
88.6(3)
92.2(3)
94.1(3)
85.2(3)
92.4(3)
89.5(3)
90.4(4)
91.8(4)
98.10(17)
90.44(18)
88.91(18)
82.55(19)
87.40(19)
88.90(20)
89.60(20)
89.00(19)
86.3(3)
94.0(3)
93.4(3)
86.3(3)
89.5(4)
91.9(4)
91.4(4)
91.7(3)
104.36(17)
87.97(18)
87.38(18)
80.53(18)
88.53(14)
87.18(14)
88.76(18)
87.89(18)
103.90(7)
88.51(7)
87.23(7)
80.60(6)
87.44(6)
86.87(6)
89.24(7)
87.55(7)
Hydrogen bond distances (Å)
N4Hꢁ ꢁ ꢁF1a (or O5b,c
N6Hꢁ ꢁ ꢁF3a (or O1b)
O5Hꢁ ꢁ ꢁO2
)
2.920(9)
3.059(8)
2.921(6)
3.047(6)
2.914(15)
3.029(12)
2.862(16)
2.949(7)
2.82(3)
2.850(10)
2.761(7)
2.759(9)
2.744(3)
2.751(3)
a
b
c
[Fe(4-MeOhapen)]PF6 (1).
[Fe(5-MeOhapen)]PF6ꢁH2O (2).
[Fe(6-MeOhapen)]PF6ꢁEtOH (3).
values for HS FeIII complexes [10–12]. The corresponding angles of
1 and 2 at 100 K were 88.6(3)° and 86.3(3)°, respectively, whose
values are closer to those of a regular octahedron than those at
296 K. The O1–Fe–O2 angles of 3 were 104.36(17)° at 296 and
104.36(17)° at 100 K, but were much distorted than those of 1
and 2.
Fig. 3 (left side) shows the orientations of the two imidazole
rings in the compounds. For 1 and 3, the two imidazole rings were
oriented nearly along the two N–Fe–O diagonals. For 2, one
imidazole ring bisected the angles defined by the two N–Fe–O
diagonals, and the other imidazole ring was oriented nearly along
the N–Fe–O diagonal. Fig. 3 (right side) shows the side view of the
Fig. 3. (a) (left side) Side view of the complex-cation. The thermal ellipsoids were drawn at the 50% probability level. (right side) ORTEP drawing of [FeIII(Him)2
(4-MeOhapen)]+ of 1 projected on the planar Schiff-base ligand with the selected atom numbering scheme at 100 K. (b) The molecular structures of 2. (c) The molecular
structure of 3 at 100 K.

94
T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
complex-cation. In all three complexes, the saturated five-mem-
bered chelate ring involving the ethylenediamine moiety adopted
the gauche conformation, in which two carbon atoms deviated at
opposite positions from the plane defined by FeN2 in all three com-
plexes and at all temperatures. Murray et al. demonstrated that the
five-membered chelate ring FeC2N2 is closely related to the spin
state, as the envelope conformation allows the spin transition,
and the gauche or planar conformation locks in high spin state
[11]. As demonstrated above, complexes 1–3 have gauche con-
formation, but the phenylidene planes were oriented opposite to
the FeO2N2 coordination plane. For example, the deviated distances
of C9 and C10 atoms from the FeN2 plane for 1 at 100 K were
+0.279 and ꢀ0.265 Å, respectively (+0.180 and ꢀ0.441 Å for 2,
+0.194 and ꢀ0.495 Å for 3). The dihedral angles of the benzene
rings A and B from the FeN2O2 plane for 1 were +14.56° and
ꢀ14.86°, respectively (+3.62° and ꢀ25.77° for 2, +10.04° and
ꢀ31.02° for 3). Benzene ring B was increasingly tilted from the
coordination plane in the following order: 1 < 2 < 3, suggesting that
the tilting of the benzene rings occurs due to the steric hindrance
between the methyl and n-methoxy group at the phenylidene
moiety. Complexes 1 and 2 with n-methoxy groups (n = 4 and 5)
may have a flexible conformation and may be suitable for a struc-
tural change from the HS to LS spin transition due to the small
steric hindrance. The large steric hindrance observed in 3 with
the 6-methoxy group may lock the N2O2 ligand conformation.
3.3.2. Three types of hydrogen-bonded assembly structures
Fig. 4(a)–(c) shows the assembly structures of 1, 2, and 3,
respectively. Complex 1 contained one-dimensional (1D) chain
structures. The 1D structure of 1 was composed of weak hydrogen
bonds between the imidazole nitrogen and PFꢀ6 ion. Specifically,
one PFꢀ6 anion bridges two adjacent [FeIII(Him)2(4-MeOhapen)]+
cations with hydrogen bonds of F(1)ꢁ ꢁ ꢁN(4) and F(3)ꢁ ꢁ ꢁN(6)⁄. The
adjacent cations are related by a two-fold screw axis along the b-
axis to form a 1D structure. In the crystal lattice, rods are stacked
along the b-axis, and the anions occupy the space among the rods.
Fig. 4(b) and (c) shows the two cyclic dimer structures of 2
and 3. Both cyclic dimer structures had an inversion center and
the PFꢀ6 ion was not involved in the cyclic dimer structure. In
complex 2, one of the two imidazoles was hydrogen bonded
to one of two phenoxo oxygen atoms of the adjacent complex-
cation with N(6)ꢁ ꢁ ꢁO(1)⁄ to form
a cyclic dimeric structure,
{ꢁ ꢁ ꢁ[FeIII(Him)2(5-MeOhapen)]ꢁ ꢁ ꢁ}2, while the other imidazole
N(4) is hydrogen bonded to a water molecule. In complex 3, one
of the two imidazoles is hydrogen bonded to the oxygen atom
O(5) of ethanol with N(4)ꢁ ꢁ ꢁO(5), while the other imidazole does
not form any hydrogen bonds. The oxygen atom O(5) is also hydro-
gen bonded to one of two phenoxo oxygen atoms of the adjacent
complex-cation with O(5)ꢁ ꢁ ꢁO(2) to form a cyclic dimer structure,
{ꢁ ꢁ ꢁ[FeIII(Him)2(hapen)]ꢁ ꢁ ꢁ(EtOH)ꢁ ꢁ ꢁ}2.
4. Concluding remarks
Three FeIII complexes [FeIII(Him)2(n-MeOhapen)]PF6 solvents
(1: n = 4, 2: n = 5, 3: n = 6) with three isomers of the new
‘‘hapen-type’’ ligand (n-MeOhapen) were synthesized. Three types
of hydrogen-bonded assembly structures were generated, includ-
ing a 1D chain in 1, and a cyclic dimer in 2 and 3, whose FeIII ion
was coordinated by N4O2 donor atoms of equatorial n-MeOhapen
and two axial Him. The saturated FeC2N2 chelate ring involving
the ethylenediamine moiety adopted a gauche conformation and
the two phenylidene planes of [FeIII(Him)2(n-MeOhapen)]+ were
oriented opposite to the FeO2N2 coordination plane, suggesting
that the tilting of the phenylidene planes occurs due to the steric
hindrance between the methyl and n-methoxy group at the
phenylidene moiety. Complex 1 and 2 showed SCO behavior, but
3 showed incomplete SCO. The N2O2 conformation in 1 and 2 with
n-methoxy groups (n = 4 and 5) may facilitate the structural
change from the HS to LS spin transition due to the small steric
hindrance. The ligand conformation in 3 with the 6-methoxy group
may promote the HS state, due to the large steric hindrance. These
results demonstrate that the conformation of the N2O2 Schiff-base
ligand is related to SCO behavior of the complexes.
Acknowledgment
T. Fujinami was supported by the Research Fellowship for
Young Scientists of the Japan Society for the Promotion of
Science, KAKENHI 00248556.
Appendix A. Supplementary material
CCDC 1030202–1030208 contains the supplementary crys-
tallographic data for [FeIII(Him)2(4-MeOhapen)]PF6 (1) at 100,
170 and 250 K, [FeIII(Him)2(5-MeOhapen)]PF6ꢁH2O (2) at 100 and
296 K, and [FeIII(Him)2(6-MeOhapen)]PF6ꢁEtOH (3) at 100 and
250 K, respectively. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.
uk/data_request/cif. Supplementary data associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/10.
1016/j.ica.2015.03.034.
Fig. 4. (a) 1D structure by hydrogen bonds between PFꢀ6 and imidazole of 1,
{ꢁ ꢁ ꢁ[Fe(Him)2(4-MeOhapen)]+ꢁ ꢁ ꢁPF6ꢀꢁ ꢁ ꢁ}1. (b) Cyclic dimer structure constructed by
hydrogen bond of imidazole. . .phenoxo oxygen of 2, {ꢁ ꢁ ꢁ[Fe(Him)2(5-
MeOhapen)]+ꢁ ꢁ ꢁ}2. (c) Cyclic dimer structure constructed from hydrogen-bonds
through ethanol of 3, {ꢁ ꢁ ꢁ[Fe(Him)2(6-MeOhapen)]+ꢁ ꢁ ꢁEtOHꢁ ꢁ ꢁ}2. The structures of 2
and 3 have an inversion center.

T. Fujinami et al. / Inorganica Chimica Acta 432 (2015) 89–95
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