Reprint of facial and meridional geometrical isomers of tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with Δ- And Λ-configurations and their enantio-discriminative assembly via imidazole?chloride hydrogen bonding and spin cross-over properties

Article abstract of DOI:10.1016/j.poly.2013.02.003

A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HL ^Me-Benz) reacts with Fe^IICl₂·4H ₂O and NaPF₆ at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) chloride hexafluorophosphate solvate with the formula of [Fe^II(HL ^Me-Benz)₃]Cl·PF₆·solvent. Meridional and facial geometrical isomers, i.e., mer-[Fe^II (HL ^Me-Benz)₃]Cl·PF₆·1.5H ₂O (1·PF₆·1.5H₂O) and fac-[Fe^II(HL^Me-Benz)₃]Cl·PF ₆·EtOH·H₂O (2·PF₆· EtOH·H₂O), were selectively crystallized from methanol and ethanol solutions, respectively. fac-[Fe^II(HL^Me-Benz) ₃]Cl·SbF₆·H₂O (2·SbF ₆·H₂O) and fac-[Fe^II(HL ^Me-Benz)₃]Cl·ClO₄·EtOH· H₂O (2·ClO₄·EtOH·H₂O) are synthesized in ethanol, using the corresponding anions. Each Fe^II ion has an octahedral coordination geometry with N₆ donor atoms from three bidentate ligands. All three imidazole groups in both the fac- and mer-[Fe^II(HL^Me-Benz)₃]²⁺ cations are hydrogen-bonded to neighboring three Cl^- ions, and each Cl ^- ion is hydrogen-bonded to three imidazole groups of three neighboring complex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex 1·PF₆·1.5H ₂O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-[Fe^II(HL^Me-Benz) ₃]²⁺?Cl^-}₃ units with an ΔΔΛ or ΛΛΔ configuration; the PF ₆^- ions occupy the spaces between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e., {fac-[Fe^II(HL^Me-Benz)₃]²⁺? Cl^-}₄. The tetranuclear structure comprises four homo-chiral fac-Δ- or fac-Λ-[Fe^II(HL^Me-Benz) ₃]²⁺ cations and four Cl^- ions interconnected by twelve imidazole-chloride hydrogen bonds to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cubane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the magnetic susceptibilities and Mo?ssbauer spectra reveal that the fac-complexes show incomplete spin crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS, S = 2) and low-spin (LS, S = 0) states.

Full text of DOI:10.1016/j.poly.2013.02.003

Polyhedron 52 (2013) 1489–1498
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Reprint of ‘‘Facial and meridional geometrical isomers of
tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II) with
D- and K-con
figurations and their enantio-discriminative assembly via imidazoleÁ Á Áchloride
hydrogen bonding and spin cross-over properties’’ q
Daisuke Furushou a, Tomotaka Hashibe a, Takeshi Fujinami a, Koshiro Nishi a, Hiroaki Hagiwara a,
Naohide Matsumoto a, , Yukinari Sunatsuki b, Masaaki Kojima b, Seiichiro Iijima c
⇑
a Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan
b Department of Chemistry, Faculty of Science, Okayama University, Tsushima-naka 3-1-1, Okayama 700-8530, Japan
c National Institute of Advanced Industrial Science and Technology, Umezono 1-1-1, Tsukuba 305-8568, Japan
a r t i c l e i n f o
a b s t r a c t
A bidentate 2-methylimidazol-4-yl-methylideneaminobenzyl ligand (HLMe-Benz) reacts with FeIICl2Á4H2O
and NaPF6 at a 3:1:1 molar ratio to yield a tris(2-methylimidazol-4-yl-methylideneaminobenzyl)iron(II)
chloride hexafluorophosphate solvate with the formula of [FeII(HLMe-Benz)3]ClÁPF6Ásolvent. Meridional
and facial geometrical isomers, i.e., mer-[FeII (HLMe-Benz)3]ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O) and fac-
[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O (2ÁPF6ÁEtOHÁH2O), were selectively crystallized from methanol and eth-
anol solutions, respectively. fac-[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6ÁH2O) and fac-[FeII(HLMe-Benz)3]ClÁ
ClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O) are synthesized in ethanol, using the corresponding anions. Each FeII
ion has an octahedral coordination geometry with N6 donor atoms from three bidentate ligands. All three
imidazole groups in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations are hydrogen-bonded to neighboring
three ClÀ ions, and each ClÀ ion is hydrogen-bonded to three imidazole groups of three neighboring com-
plex cations; this results in the formation of hydrogen-bonded assembly structures. mer-Complex
1ÁPF6Á1.5H2O forms a heterochiral two-dimensional (2D) network structure comprised of cyclic {mer-
Article history:
Received 26 April 2012
Accepted 29 June 2012
Available online 7 February 2013
Dedicated to Alfred Werner on the 100th
Anniversary of his Nobel prize in Chemistry
in 1913.
Keywords:
Iron(II) complex
Bidentate ligand
Geometrical isomer
Optical isomer
Hydrogen bond
Spin crossover
À
[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}3 units with an DDK or KKD configuration; the PF6 ions occupy the spaces
between the 2D layers. All the fac-complexes have isomorphous cubane-like tetrameric structures, i.e.,
{fac-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}4. The tetranuclear structure comprises four homo-chiral fac-
D- or fac-K-
[FeII(HLMe-Benz)3]2+ cations and four ClÀ ions interconnected by twelve imidazole-chloride hydrogen bonds
to form a chiral cubane supramolecule that encapsulates one counter anion. In the crystal lattice, the cub-
ane-like tetramers with opposite chiralities are alternately arrayed. The temperature dependence of the
magnetic susceptibilities and Mössbauer spectra reveal that the fac-complexes show incomplete spin
crossover behavior, while the mer-complex shows a gradual spin crossover between high-spin (HS,
S = 2) and low-spin (LS, S = 0) states.
Ó 2013 Published by Elsevier Ltd.
1. Introduction
In 1893, Werner published the first paper on coordination com-
pounds [1a]. In a subsequent paper published in 1902, he introduced
DOI of original article: http://dx.doi.org/10.1016/j.poly.2012.06.085
the terms ‘‘primary valence (Hauptvalenz)’’ and ‘‘secondary valence
(Nebenvalenz)’’ to explain the structures and physical properties of
coordination compounds [1b]. Taking CoCl3Á6NH3 as an example,
the number of CoÀCl bonds corresponds to a primary valence of 3
and the number of CoÀNH3 bonds corresponds to a secondary va-
lence of 6. Accordingly, Werner’s primary valence represents the
oxidation state, and the secondary valence represents the coordina-
tion number. In a complex, the central metal atom is bonded to a
definite number of atoms (coordination number) in a simple spatial
q
The publisher would like to inform the readership that this article is a reprint of
a previously published article. An error occurred on the publisher’s side which
resulted in the publication of this article in a wrong issue. As a consequence, the
publisher would like to make this reprint available for the reader’s convenience and
for the continuity of the special issue. For citation purposes, please use the original
publication details; D. Furushou et al./Polyhedron 44 (2012) 194–203’. The
publisher sincerely apologizes to the readership and in particular to the author of
the respective article and deeply regrets the inconvenience caused.
⇑
Corresponding author. Tel./fax: +81 96 342 3390.
E-mail address: naohide@aster.sci.kumamoto-u.ac.jp (N. Matsumoto).
0277-5387/$ - see front matter Ó 2013 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.poly.2013.02.003

1490
D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
geometric pattern [1a]; a coordination number of six is frequently
observed, and it corresponds to an octahedral geometry. In accord
with his theory, Werner successfully explained the number of geo-
metrical isomers that had been observed at that time. For example,
Werner explained the difference between the two isomers of
CoCl3Á4NH3, i.e., green trans- and purple cis-[CoCl2(NH3)4]Cl. His
theory also suggests the existence of optical isomers [2], which
was experimentallyconfirmedbytheopticalresolutionof chiralme-
tal complexes. The first optically-resolved complex was cis-[CoCl(N-
H3)(en)2]Br2 [2a]; later, he succeeded in the optical resolution of the
non-carbon-containing hexol [Co4(OH)6(NH3)12]X6 [2b]. The sec-
ondary valence is directed toward fixed positions in space, and it
forms the basis for the stereochemistry of metal complexes. How-
ever, Werner’s primary valence or oxidation state did not fully
explain the physical properties of metal complexes since many of
the physical properties of coordination compounds such as their
magnetic and electronic spectral properties are dictated by their
electronic structures. A new concept for primary valence (i.e., elec-
tronic configuration) was introduced via the crystal-field and/or
ligand-field theories [3], which are based on quantum mechanics.
In this study, we report an octahedral FeII complex hexacoordi-
arrangement of the ligands around the FeII ion. In this study, mer
and fac geometrical isomers, i.e., mer-[FeII(HLMe-Benz)3]ClÁPF6Á
1.5H2O (1ÁPF6Á1.5H2O) and fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O
(2ÁPF6ÁEtOHÁH2O), are selectively crystallized.
In addition to the stereochemistry of the [FeII(HLMe-Benz)3]2+
complex cation itself, the complex forms a supramolecular struc-
ture due to hydrogen bonding between the imidazole groups of
the complex cation and the ClÀ ions. All three imidazole groups
in both the fac- and mer-[FeII(HLMe-Benz)3]2+ cations form hydrogen
bonds with three neighboring ClÀ ions (i.e., NHÁ Á ÁClÀ) and each ClÀ
ion forms hydrogen bonds with three imidazole groups from three
complex cations. The 3:3 hydrogen bonds between the geometrical
and optical isomers of [FeII(HLMe-Benz)3]2+ and the ClÀ ions lead to a
variety of assembled structures. In the present case, the fac-com-
plex forms
a homo-chiral cubane-like tetramer, i.e., {fac-D-
[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}4 or {fac-
K
-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}4,
while the mer-complex forms a heterochiral two-dimensional
(2D) network structure comprised of cyclic {mer-[FeII
(HLMe-Benz)3]2+Á Á ÁClÀ}3 units with DDK or KKD configurations.
In addition to the stereochemistry of the complex cation itself
and the supramolecular structure, the FeII complex can interconvert
between two electronic states between high-spin (HS) and low-
spin (LS) states [4]. There are two possible electronic states for
the FeII complex with a d6 electronic configuration in an octahedral
coordination environment on the basis of the crystal-field theory
[4,5]: high-spin (HS, S = 2) and low-spin (LS, S = 0). According to
the Tanabe-Sugano diagram based on the strong crystal field theory
[4], the HS state changes to the LS state at the spin crossover point,
as the crystal field strength increases. Both the mer- and fac-FeII
complexes show SCO behavior similar to that of other FeII com-
plexes with polydentate ligands containing imidazole groups [6].
nated by three bidentate ligands [FeII(HLMe-Benz)3]2+
, where
HLMe-Benz denotes an non-equivalent bidentate chelate ligand de-
rived from a 1:1 condensation of 2-methyl-4-formylimidazole
and benzylamine, and the H of HLMe-Benz denotes the imidazole
NH hydrogen atom. As Werner’s theory predicts, this complex has
many possible geometrical and optical isomers. As shown in
Scheme 1, the [FeII(HLMe-Benz)3]2+ complex with a coordination
number of 6 and octahedral coordination geometry can form
meridional and facial geometrical isomers. The complex also has
D
- and
K
-optical isomers due to the clockwise and anti-clockwise
(1)
(2)
(3)
(4)
(a)
Cl
Cl
Cl
H
N
N
H
H
H
H
H
H
H
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Fe
N
N
N
N
N
N
N
N
N
N
Fe
N
N Fe
N
Fe
N
R
H
R
R
R
R
R
R
N
N
N
N
R
N
N
N
mer-Δ
N
N
N
H
H
H
Cl
Cl
Cl
H
N
meridional
(mer)
H
H
N
H
H
H
H
H
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
N
Fe
N
R
N
N
3
N
N
N
Fe
Fe
N Fe
N
N
Fe
N
R
R
R
R
H
R
R
R
N
R
N
N
N
R
N
N
N
Me
H
mer-Λ
N
N
N
N
H
H
H
N
H
N
N
FeII + 3
Cl
R
(b)
H
H
R
R
N
N
N
N
N
N
Fe
N
N
N
N
Fe
N
H
N
H
N
3
H
N
N
Fe
N
3
N
N
N
N
N
R
Cl
R
Cl
H
N
H
R
H
H
N
N
N
N
N
R
N
Fe
H
N
N
N
N
N
N
N
Fe
N
N
facial
(fac)
H
N
N
Cl
N
N
H
H
N
N
H
R
N
R = -CH2-Ph
N
R
R
R
N
fac-Δ
N
N
Fe
N
R
R
Fe
N
N
N
N
N
H
N
R
N
N
N
R
N
N
H
Fe
N
H
R
R
Cl
N
N
H
N
N
N
H
N
N
H
N
H
N
N
N
N
Cl
N
R
Cl
N
N
H
H
N
N
N
Fe
H
N
N
N
H
N
N
N
N
Fe
Cl
N
H
N
N
R
N
N
H
N
H
N
N
H
R
N
N
R
R
N
fac-Λ
N
N
Fe
Fe
N
N
N
N
H
N
R
N
N
H
N
H
N
R
Cl
R
Scheme 1. (1) The 1:3 reaction of an FeII ion and 2-methylimidazol-4-yl-methylideneaminobenzyl (abbreviated as HLMe-Benz) gives fac-[FeII(HLMe-Benz)3]2+ and mer-[FeII-
(HLMe-Benz)3]2+. (2) Optical isomers with
D- and K-configurations due to the clockwise and anti-clockwise arrangement of the ligands around the metal center. (3) Three
imidazole groups from each complex cation form hydrogen bonds with three ClÀ ions and each ClÀ ion forms hydrogen bonds with three imidazole groups of three complex
cations to form hydrogen-bonded assembly structures. (4) (a) Heterochiral 2D network structure with the net unit of a {mer-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}3 cyclic trimer. (b)
Homo-chiral cubane-like tetranuclear structure, i.e., {fac-
D
-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}4 or {fac-
K
-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}4.

D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
1491
It is known that SCO properties are significantly affected by weak
intermolecular hydrogen bonds [7]. The construction of supramo-
lecular assembly structures from hydrogen bonds between the
imidazole groups of the complex cation and the ClÀ ions and the
SCO properties are examined to elucidate the relationship between
assembly structure made by hydrogen bonds and SCO properties.
The isostructural cubane compounds with different sizes of anions,
i.e., fac-[FeII(HLMe-Benz)3]ClÁX with X = SbF6 (2ÁSbF6ÁH2O) and ClO4
(2ÁClO4ÁEtOHÁH2O), are also synthesized to examine the relation-
ship between SCO properties and encapsulated anion size. Part of
this study has been reported in Chemistry Letters [8].
solution was stirred at room temperature for 1 h and then filtered.
The filtrate was kept for a few days in a refrigerator, resulting
in the formation of large golden-yellow crystals. They were
collected by suction filtration. Yield: 0.22 g. Anal. Calc. for
fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O = C36H39FeN9ClPF6ÁEtOHÁH2O:
C, 50.82; H, 5.27; N, 14.03. Found: C, 50.74; H, 5.29; N, 13.85%.
TGA: 7.1% weight loss was observed.
2.3.3. Preparation of fac-[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6ÁH2O)
The 2ÁSbF6ÁH2O complex was prepared in a manner similar to the
manner in which 2ÁPF6ÁEtOHÁH2O was prepared, using NaSbF6 in-
stead of NaPF6. Yellow crystals precipitated and were collected. Anal.
Calc. for fac-[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O = C36H39FeN9ClSbF6ÁH2O:
C, 45.86; H, 4.38; N, 13.37. Found: C, 45.69; H, 4.59; N, 13.24%.
TGA: 1.9% weight loss was observed.
2. Experimental
Caution! Perchlorate salts of metal complexes are potentially
explosive. Only small quantities of material should be prepared
and samples should be handled with care.
2.3.4. Preparation of fac-[FeII(HLMe-Benz)3]ClÁClO4ÁEtOHÁH2O
(2ÁClO4ÁEtOHÁH2O)
The 2ÁClO4ÁEtOHÁH2O complex was prepared in a manner simi-
lar to the manner in which 2ÁPF6ÁEtOHÁH2O was prepared, using
NaClO4 instead of NaPF6. Yellow crystals precipitated and were col-
lected. TGA measurement for freshly prepared sample: 7.5% weight
loss was observed. The value corresponds to EtOH + H2O. Elemen-
tal analyses (dried sample). Anal. Calc. for fac-[FeII(HLMe-Benz)3]-
ClÁClO4Á2/3EtOHÁH2O = C36H39FeN9Cl2O4Á2/3EtOHÁH2O: C, 53.56;
H, 5.42; N, 15.05. Found: C, 53.89; H, 5.59; N, 14.95%.
2.1. General procedure
All chemicals and solvents were obtained from Tokyo Kasei, Ltd.
and Wako Pure Chemical Industries, Ltd.; they were reagent grade
and used without further purification. All the synthetic procedures
were carried out in an open atmosphere.
2.2. Synthesis of 2-methylimidazol-4-yl-methylideneaminobenzyl
(HLMe-Benz
)
2.4. Physical measurements
The HLMe-Benz ligand was prepared by mixing 2-methyl-4-
formylimidazole with benzylamine in a 1:1 molar ratio in methanol
or ethanol. The ligand solution was used for the synthesis of the FeII
complex without further purification or isolation. As described be-
low, the reaction solvent plays an important role in the selective
Elemental C, H, and N analyses were carried out at the Center
for Instrumental Analysis at Kumamoto University. Thermogravi-
metric analyses (TGA) were performed on a TG/DTA6200 (Seiko
Instrument Inc.). Except for the perchlorate salt, the samples
(ꢀ5 mg) were heated from room temperature to 180 °C in heating
mode and then from 180 °C to room temperature in cooling mode.
The 2 mg sample of the perchlorate salt was measured between
room temperature and 130 °C. Magnetic susceptibilities were mea-
sured using a Quantum Design MPMS XL5 magnetometer in the
temperature range of 5–300 K at a rate of 2 K minÀ1 under an ap-
plied magnetic field of 0.5 T. Calibration was performed using pal-
ladium metal. Corrections for diamagnetism were made using
Pascal’s constants [9].
formation of the facial and meridional isomers of [FeII(HLMe-Benz)3]2+
.
2.3. Synthesis of the FeII complexes
2.3.1. Preparation of mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O
(1ÁPF6Á1.5H2O)
For the in situ preparation of the HLMe-Benz ligand, a solution of
benzylamine (0.161 g, 1.5 mmol) in 5 mL of methanol was added to
a solution of 2-methyl-4-formylimidazole (0.165 g, 1.5 mmol) in
10 mL of methanol at room temperature. A solution of FeIICl2Á4H2O
(0.099 g, 0.5 mmol) in 10 mL of methanol was then added followed
by the addition of a solution of NaPF6 (0.105 g, 0.5 mmol) in 10 mL
of methanol. The resultant solution was stirred at room tempera-
ture for 1 h and then filtered. The filtrate was allowed to evaporate
slowly for a few days, resulting in the formation of orange-yellow
crystals with small amounts of red crystals. They were collected by
suction filtration. The red crystals were manually removed and the
orange–yellow crystals were collected. Yield: 0.25 g. Anal. Calc. for
mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O = C36H39FeN9ClPF6Á1.5H2O: C,
50.22; H, 4.92; N, 14.64. Found: C, 50.10; H, 4.86; N, 14.54%.
TGA: 3.1% weight loss was observed.
2.5. X-Ray crystal structure analyses
X-ray diffraction data were collected on a Rigaku RAXIS RAPID
imaging plate diffractometer using graphite monochromated Mo
Ka radiation (k = 0.71073 Å). The temperature of the crystal was
maintained at the selected value within an accuracy of 2 K via a
Rigaku cooling device. The diffraction data for complex
1ÁPF6Á1.5H2O were initially collected at 230 K; then, the crystal
was cooled to 150 K at a 10 K minÀ1 sweeping rate and diffraction
data were again collected. The temperature was then sequentially
lowered to 103 K and the diffraction data were collected. The data
were corrected for Lorentz, polarization, and absorption effects.
The structures were solved using the direct method [10] and ex-
panded using the Fourier technique [11]. The structures were re-
fined via a F2 full-matrix least-squares method with anisotropic
thermal parameters for all non-hydrogen atoms. Hydrogen atoms
were fixed in calculated positions and refined using a riding model,
with the exception of those bound to O(1) of the water molecule.
For 2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O, and 2ÁClO4ÁEtOHÁH2O, the dif-
fraction data were collected at 296 K and corrected for Lorentz,
polarization, and absorption effects. The structures were solved
by the direct method [10] and were expanded using the Fourier
technique [11]. The structures were refined by the F2 full-matrix
2.3.2. Preparation of fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O
(2ÁPF6ÁEtOHÁH2O)
For the in situ preparation of the HLMe-Benz ligand, a solution of
benzylamine (0.161 g, 1.5 mmol) in 5 mL of ethanol was added to a
solution of 2-methyl-4-formylimidazole (0.165 g, 1.5 mmol) in
10 mL of ethanol at room temperature. The resulting solution
was maintained at 50 °C with stirring for 30 min and then cooled
to room temperature.
0.5 mmol) in 10 mL of ethanol was added followed by a solution
of NaPF6 (0.105 g, 0.5 mmol) in 10 mL of ethanol. The resulting
A
solution of FeIICl2Á4H2O (0.099 g,

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D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
least-squares method with anisotropic thermal parameters for all
non-hydrogen atoms, except for the atoms in ethanol or water
molecules; the non-hydrogen atoms of ethanol or water molecules
were refined isotropically. Hydrogen atoms were fixed in calcu-
lated positions and were refined using a riding model with the
exception of those bound to the carbon and oxygen atoms of eth-
anol and water molecules. Attempts to obtain the structure at
low temperatures were unsuccessful due to the formation of cracks
in the crystal. All calculations were performed using the Crystal
Structure crystallographic software package [12].
Fig. 1. Solid-state thermochromism of 1ÁPF6Á1.5H2O and 2ÁPF6ÁEtOHÁH2O.
1ÁPF6Á1.5H2O at (a) room temperature and (b) 77 K, and 2ÁPF6ÁEtOHÁH2O at (c)
room temperature and (d) 77 K.
3. Results and discussion
Table 1
3.1. Synthesis and characterization of mer-[FeII(HLMe-Benz)3]
ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O), fac-[FeII(HLMe-Benz)3]
ClÁPF6ÁEtOHÁH2O (2ÁPF6ÁEtOHÁH2O), fac-[FeII(HLMe-Benz)3]
ClÁSbF6ÁH2O (2ÁSbF6ÁH2O), and fac-[FeII(HLMe-Benz)3]
ClÁClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O)
X-ray crystallographic data for mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O).
Compound
mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O
230 K
150 K
103 K
Formula
Formula weight
Crystal system
Space group
a (Å)
C36H42FeN9ClPF6O1.5
861.05
monoclinic
P21/c (No. 14)
10.1166(4)
20.0477(8)
19.9207(9)
91.3670(9)
4039.1(3)
4
The synthetic procedures were all performed in air. The 2-methyl-
imidazol-4-yl-methylideneaminobenzyl bidentateligand, which was
used in all the FeII complexes, was prepared via the 1:1 condensation
of 2-methyl-4-formylimidazole and benzylamine. The FeII complexes
were prepared by mixing the HLMe-Benz bidentate ligand, FeIICl2Á4H2O,
and NaY (Y = SbF6, PF6, and ClO4) at a 3:1:1 molar ratio. The mer-form,
i.e., mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O), was prepared
in methanol and formed orange rhombic crystals, while the fac-form,
i.e., fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O (2ÁPF6ÁEtOHÁH2O), was pre-
pared in ethanol and formed cubic yellow crystals; this demonstrates
that the reaction solvent plays an important role in the selective crys-
tallization of the fac and mer isomers. Analogous fac-complexes with
two different anions, i.e., fac-[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6Á
H2O) and fac-[FeII(HLMe-Benz)3]ClÁClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O),
were synthesized in ethanol in a manner similar to the manner in
which 2ÁPF6ÁEtOHÁH2O were synthesized using NaSbF6 and NaClO4,
respectively, instead of NaPF6. The two complexes were obtained as
yellow cubic crystals.
The C, H, and N elemental analyses of these complexes suggest
the presence of lattice solvents. Accordingly, the amounts of sol-
vents in the crystals were examined via TGA (see Supplementary
data); the samples were heated from room temperature to 160 °C
and then cooled to room temperature at a heating/cooling rate of
10 °C/min. A weight loss of 3.1%, which corresponds to 1.5 mole-
cules of H2O, was observed for 1ÁPF6Á1.5H2O in heating mode and
a weight increase of 0.5 molecules of H2O from atmospheric mois-
ture was observed in the subsequent cooling mode measurement.
A continuous weight loss of 7.1% corresponding to a molecule of
EtOH and H2O was observed for 2ÁPF6ÁEtOHÁH2O in the heating
mode. Heating 2ÁSbF6ÁH2O resulted in a weight loss of 1.9% corre-
sponding to one molecule of H2O. Due to the potential for explo-
sion of the perchlorate salt, a small sample of ꢀ2 mg was heated
to 130 °C for the analysis. A weight loss of 7.5%, which corresponds
to a molecule of EtOH and H2O, was observed for 2ÁClO4ÁEtOHÁH2O
in the heating mode; the weight loss occurred continuously.
These four complexes showed solid-state thermochromism
from yellow at ambient temperature to orange–red or orange at
77 K, which suggests SCO (Fig. 1).
10.0498(4)
19.8405(7)
19.7795(8)
91.5956(10)
3942.4(3)
4
9.9939(4)
19.6216(7)
19.6369(8)
91.6521(10)
3849.1(3)
4
b (Å)
c (Å)
b (°)
V (Å3)
Z
T (K)
230
150
103
Dcalc (g cmÀ3
)
1.416
1.451
1.486
l
(cmÀ1
)
5.494
5.628
5.765
Ra
0.0892
0.0900
0.0889
wRb
0.2679
0.2798
0.2772
a
R =
wR = [
R
||Fo| À |Fc||/
R|Fo|.
b
R
w(|Fo2| À |Fc2|)2/
R .
w|Fo2|2]1/2
mined via single-crystal X-ray diffraction analyses. Tables 1 and 2
show the crystallographic data and relevant coordination bond dis-
tances, angles, and intermolecular hydrogen bond distances,
respectively. 1ÁPF6Á1.5H2O crystallizes in a monoclinic space group,
i.e., P21/c (no. 14), with Z = 4 at all three temperatures; no crystallo-
graphic phase transition is observed. The unique crystallographic
unit comprises one complex mer-[FeII(HLMe-Benz)3]2+ cation, one
chloride ion, one hexafluorophosphate ion, and one water molecule
as a solvent. The additional half molecule of water that was indi-
cated by elemental and thermogravimetric analyses could not be
found.
Fig. 2 shows the molecular structure of the mer-[FeII(HLMe-Benz)3]2+
cation at 230 K and the selected atom numbering scheme. Three
ClÀ ions that are hydrogen bonded to the complex cation are also
shown (Fig. 2). In this cation, the FeII ion is octahedrally coordi-
nated by N6 donor atoms from three bidentate HLMe-Benz ligands.
Of the two possible geometrical isomers (i.e., facial and meridional),
the cation takes the meridional form with the three coordinated
imine nitrogen atoms or the three coordinated imidazole nitrogen
atoms in the meridional positions. By analyzing the Fe–N bond dis-
tances and N–Fe–N bond angles, the spin state can be identified. At
230 K, the Fe–N bond lengths are in the range of 2.136(5)–
2.239(5) Å, which are typical for similar HS FeII complexes with
N6 donor atoms. At 150 K and 103 K, the Fe–N bond lengths are
in the range of 2.089(5)–2.167(5) Å and 2.016(5)–2.054(5) Å,
respectively, which are shorter than the values expected for HS FeII
complexes and longer than those expected for LS complexes. The
average Fe–N bond length decreased by 0.152 Å from 2.188 Å at
230 K to 2.036 Å at 103 K; this difference is considerably smaller
than the value reported (ꢀ0.2 Å) for similar SCO complexes with
N6 ligands. The N–Fe–N bond angles are also indicative of the spin
state of the FeII ion since the angles at 103 K are closer to a regular
3.2. Structure and physical properties of mer-[FeII(HLMe-Benz)3]ClÁPF6Á
1.5H2O (1ÁPF6Á1.5H2O)
3.2.1. Crystal structures of 1ÁPF6Á1.5H2O
The crystal structures of 1ÁPF6Á1.5H2O at 230 K (HS state), 150 K
(intermediate between the HS and LS states), and 103 K were deter-

D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
1493
boring ClÀ ions with distances of N1Á Á ÁCl = 3.179(6) Å,
N4Á Á ÁCl⁄ = 3.089(7) Å, and N7Á Á ÁCl⁄⁄ = 3.190(7) Å; each ClÀ ion also
forms hydrogen bonds with three imidazole groups from three
mer-[FeII(HLMe-Benz)3]2+ at 230 K.
Table 2
Selected coordination bond lengths (Å), angles (°), and hydrogen-bond lengths (Å) for
mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O).
230 K
150 K
103 K
Due to the 3:3 imidazole-chloride hydrogen bonds, a 2D net-
work structure with a cyclic {mer-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}3 trimer
repeating unit is formed (Fig. 3(a)). Fig. 3(b) shows a side view of
the adjacent Àlayers, which reveals that the layer does not undulate
and the PF6 counter anions occupy the spaces between the
layers. The mer-[FeII(HLMe-Benz)3]2+ cation is also chiral with two
Bond lengths (Å)
Fe(1)–N(2)
Fe(1)–N(3)
Fe(1)–N(5)
Fe(1)–N(6)
Fe(1)–N(8)
Fe(1)–N(9)
Average Fe–N
2.136(5)
2.239(5)
2.166(5)
2.179(4)
2.204(6)
2.204(4)
2.188
2.089(5)
2.167(5)
2.109(5)
2.111(5)
2.132(6)
2.130(5)
2.123
2.016(5)
2.054(5)
2.034(6)
2.028(5)
2.045(6)
2.041(5)
2.036
possible optical isomers, i.e., mer-
D
-[FeII(HLMe-Benz)3]2+ and
mer- As shown in Fig. 3(c), each layer
K
-[FeII(HLMe-Benz)3]2+
.
Bond angles (°)
N(2)–Fe(1)–N(3)
N(2)–Fe(1)–N(5)
N(2)–Fe(1)–N(6)
N(2)–Fe(1)–N(8)
N(2)–Fe(1)–N(9)
N(3)–Fe(1)–N(5)
N(3)–Fe(1)–N(6)
N(3)–Fe(1)–N(8)
N(3)–Fe(1)–N(9)
N(5)–Fe(1)–N(6)
N(5)–Fe(1)–N(8)
N(5)–Fe(1)–N(9)
N(6)–Fe(1)–N(8)
N(6)–Fe(1)–N(9)
N(8)–Fe(1)–N(9)
76.9(2)
169.9(2
93.6(2)
99.8(2)
94.2(2)
95.9(2)
98.9(2)
166.4(2)
89.9 (2)
80.4 (2)
88.8(2)
92.8 (2)
94.5(2)
169.4(2)
77.0 (2)
78.0 (2)
171.4(2)
93.5(2)
99.0(2)
93.0(2)
95.7(2)
97.9(2)
168.4(3)
90.1(2)
81.6(2)
88.3(2)
82.9(2)
93.5(3)
170.7(2)
78.8(3)
80.5(2)
173.5(2)
92.4(2)
97.0(2)
91.9(2)
95.0(2)
96.4(2)
171.7(2)
89.9(2)
83.4(2)
88.1(2)
92.8(2)
91.7(2)
172.9(2)
82.2(2)
forms a heterochiral 2D network structure comprising cyclic
{mer-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}3 trimer units with DDK or KKD
configurations. It should be noted that the extended network
structures are similar at all three temperatures.
3.2.2. Magnetic properties of 1ÁPF6Á1.5H2O
The magnetic susceptibility of the ground sample was mea-
sured upon cooling from 300 to 5 K and then measured upon
warming from 5 to 300 K at a rate of 2 K minÀ1 under a 0.5 T mag-
netic field using a SQUID magnetometer. The vMT versus T plots are
shown in Fig. 4; vM is the molar magnetic susceptibility per Fe
atom and T is the absolute temperature.
Hydrogen bonds (Å)
N(1)Á Á ÁCl(1)
The
v
MT versus T plots of mer-[FeII(HLMe-Benz)3]ClÁPF6Á1.5H2O
3.179(6)
3.089(7)
3.190(7)
3.153
3.169(6)
3.104(6)
3.192(8)
3.155
3.173(6)
3.114(6)
3.184(7)
3.157
N(4)Á Á ÁCl(1)⁄
(1ÁPF6Á1.5H2O) showed SCO behavior. Above 200 K, a constant
N(7)Á Á ÁCl(1)⁄⁄
Average NÁ Á ÁCl
v
MT value of ꢀ4.0 cm3 K molÀ1 per iron atom was observed, which
is slightly higher than the spin-only HS FeII value and is compatible
with reported HS FeII (S = 2) complexes with similar bidentate li-
gands. At temperatures lower than 50 K, a plateau value of nearly
0.3 cm3 K molÀ1 was found, which is slightly larger than the theo-
Symmetry operations:
⁄x À 1, Ày + 1/2, z + 1/2.
⁄⁄x À 1, y, z.
retical value of LS FeII (S = 0) (
v
MT = 0 cm3 K molÀ1) and close to the
MT
reported value of LS FeII (S = 0). In the region of 60–180 K, the
v
value gradually changes between the HS and LS values. Compared
to gradual one-step SCO behavior, the SCO curve is unusual in the
wider temperature range: its curve shape and the vMT value at low
temperature suggest a cooperative effect due to the hydrogen-
bonded 2D network structure. The derivative of d MT versus
v
dT indicates a peak at 150 K with two shoulders at 130 and
90 K, which also suggests that the SCO is not a single transition
process.
3.2.3. Mössbauer spectra of 1ÁPF6Á1.5H2O
Representative Mössbauer spectra of mer-[FeII(HLMe-Benz)3]-
ClÁPF6Á1.5H2O (1PF6Á1.5H2O) are shown in Fig. 5. Deconvolution
analyses of the spectra were performed to determine the HS versus
total FeII molar fraction; the results are presented in Table 3. After
rapid cooling to 78 K, the Mössbauer spectra were recorded at 78,
120, 150, 200, and 250 K. The spectrum at 78 K consists of two
doublets that are attributed to the LS FeII species (d = 0.5 mm sÀ1
,
EQ = 0.27 mm sÀ1
,
D
area ratio of 82%) and HS FeII species
EQ = 2.24 mm sÀ1
area ratio of 18%). The
Fig. 2. Molecular structure of the complex cation of 1ÁPF6Á1.5H2O at 230 K showing
the selected atom numbering scheme. Coordinated imidazole and imine nitrogen
atoms are represented by blue and pink spheres, respectively. As shown, three blue
or three pink spheres take the meridional positions. Further, three imidazole groups
per complex cation are hydrogen bonded to three neighboring ClÀ ions (green
balls), whose positions are generated by symmetry operations: Cl⁄: x À 1, Ày + 1/2,
z + 1/2; Cl⁄⁄: x À 1, y, z. (Color online.)
D
(d = 1.11 mm sÀ1
,
,
Mössbauer spectral data at 78 K supports the magnetic susceptibil-
ity results that the
v
MT value at 78 K (0.3 cm3 K molÀ1) is larger
than expected for the LS (S = 0) state. At 120, 150, and 200 K, the
spectra comprise two doublets that are also attributed to LS and
HS FeII species. The ratio of HS species to HS + LS species increases
as the temperature increases; this indicates that the spin transition
occurs gradually over a wide temperature range. The spectrum
at 250 K consists only of a doublet, which is attributed to the
octahedron than those at 230 K (e.g., N(2)–Fe–N(3): 76.9(2)° at
230 K, 80.5(2)° at 103 K). These results are in agreement with the
Mössbauer and magnetic susceptibility results described later.
As shown in Fig. 2, the three imidazole nitrogen atoms of the
mer-[FeII(HLMe-Benz)3]2+ cation are hydrogen bonded to three neigh-
HS FeII species (d = 1.01 mm sÀ1 EQ = 1.65 mm sÀ1 at 250 K).
, D
The Mössbauer spectral results are consistent with the magnetic
susceptibility results.

1494
D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
Fig. 3. (a) 2D network structure with a net unit of the cyclic {mer-[FeII(HLMe-Benz)3]2+Á Á ÁClÀ}3 trimer. Three imidazole groups per mer-[FeII(HLMe-Benz)3]2+ cation are hydrogen
bonded to three neighboring ClÀ ions. (b) Side view of the adjacent layers showing that the layer does not undulate and the PF6À counter anions occupy the spaces between
the layers. (c) Heterochiral 2D layer. The mer-[FeII(HLMe-Benz)3]2+ cation is also a chiral species with two possible optical isomers, i.e., mer- -[FeII(HLMe-Benz)3]2+ and mer-
D K-
[FeII(HLMe-Benz)3]2+. The two enantiomorphs are represented in green and red. (Color online.)
Fig. 4. SCO behavior of 1ÁPF6Á1.5H2O represented by a
vMT per Fe versus T plot. vMT
was measured upon cooling from 300 to 5 K and upon warming from 5 to 300 K.
3.3. Crystal structures and physical properties of fac-complexes, i.e.,
fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O (2ÁPF6ÁEtOHÁH2O), fac-
[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6ÁH2O), and fac-[FeII(HLMe-Benz)3]
ClÁClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O)
Fig. 5. Selected Mössbauer spectra for 1ÁPF6Á1.5H2O recorded at 78, 120, 150, and
200 K.
À
of the PF6 ions is positioned at the four-fold rotation axis and
the other is at the three-fold and two-fold rotation axes. Table 5
shows relevant bond distances and angles as well as intermolecu-
lar hydrogen-bond distances.
3.3.1. Crystal structures of 2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O, and
2ÁClO4ÁEtOHÁH2O
Crystal structures of 2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O, and 2ÁClO4Á
EtOHÁH2O were determined via single-crystal X-ray diffraction
analyses at 296 K. A crystal structural diffraction study of complex
2ÁClO4ÁEtOHÁH2O at low temperatures was attempted in order
to elucidate the structural changes during the SCO transition;
however, rapid cooling to 103 K caused cracks to form in the
crystal while slow cooling of another crystal to 103 K at 1 K minÀ1
gave the unit cell parameters but structural determination was
unsuccessful.
The structure of 2ÁPF6ÁEtOHÁH2O is shown as an example in
Fig. 6, which contains the molecular structure of the complex
fac-[FeII(HLMe-Benz)3]2+ cation and three neighboring hydrogen
bonded ClÀ ions with their selected atom numbering schemes.
The FeII ion is octahedrally coordinated by N6 donor atoms from
three bidentate HLMe-Benz ligands. In the octahedron, each biden-
tate HLMe-Benz ligand occupies the facial coordination sites. By con-
sidering the Fe–N bond distances and N–Fe–N bond angles, the
spin state of the complex at 296 K can be identified. At 296 K,
the Fe–N distances are in the range of 2.187(3)–2.218(3) Å,
2.173(4)–2.224(5) Å, and 2.175(4)–2.221(4) Å for 2ÁPF6ÁEtOHÁH2O,
2ÁSbF6ÁH2O, and 2ÁClO4ÁEtOHÁH2O, respectively; these values are
typical for HS FeII bound to N6 donors Table 5.
Table 4 shows the crystallographic data for 2ÁPF6ÁEtOHÁH2O,
2ÁSbF6ÁH2O, and 2ÁClO4ÁEtOHÁH2O at 296 K. The three complexes
crystallize into a cubic space group, i.e., P-43n (No. 218), with
the general positions of Z = 24, which indicates that the three com-
plexes are isomorphous. The unit cell contains eight formula units
(e.g., [FeII(HLMe-Benz)3]ClÁPF6ÁEtOH H2O): one third of the formula is
a crystallographic unique unit that comprises one HLMe-Benz ligand
at the general position, Fe and Cl atoms positioned at their three-
As shown in Fig. 6, three imidazole groups per fac-[FeII-
(HLMe-Benz)3]2+ are hydrogen bonded to three neighboring ClÀ ions.
In all three complexes, the three imidazole-chloride hydrogen
bonds are equivalent; the N(1)ÁÁÁCl distances are 3.128(4),
À
fold rotation axis, and two crystallographic unique PF6 ions; one

D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
1495
Table 3
Mössbauer data for 1ÁPF6Á1.5H2O.
Temp.
(K)
da
D
EQ
Cb
Area ratio
(%)
Assignment
(mm sÀ1
)
(mm sÀ1
)
(mm sÀ1
)
250
200
1.01
1.04
0.48
1.07
0.48
1.09
0.50
1.11
0.51
1.65
1.86
0.27
2.09
0.28
2.18
0.27
2.24
0.27
0.25
0.25
0.26
0.24
0.29
0.25
0.24
0.26
0.26
100
93
7
70
30
47
53
18
82
HS FeII
HS FeII
LS FeII
HS FeII
LS FeII
HS FeII
LS FeII
HS FeII
LS FeII
150
120
78
a
Isomer shift data are reported to iron foil.
Full width at half-height.
b
Fig. 6. Molecular structure of the complex fac-[FeII(HLMe-Benz)3]2+ cation of
2ÁPF6ÁEtOHÁH2O viewed along the C3 axis with the selected atom numbering
scheme. Coordinated imidazole and imine nitrogen atoms are represented by blue
and pink spheres, respectively. Three imidazole groups per complex cation are
hydrogen bonded to three neighboring ClÀ ions (green spheres). (Color online.)
Table 4
X-Ray crystallographic data for fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O (2ÁPF6Á
EtOHÁH2O), fac-[FeII(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6ÁH2O) and fac-[FeII(HLMe-Benz)3]
ClÁClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O) at 296 K.
Compound
2ÁPF6ÁEtOHÁH2O
2ÁSbF6ÁH2O
2ÁClO4ÁEtOHÁH2O
Formula
Formula
weight
Crystal
system
Space group
a (Å)
C
38H47FeN9ClPF6O2 C36H41FeN9ClSbF6O C36H47FeN9Cl2O6
898.11
942.82
852.60
fac-[FeII(HLMe-Benz)3]2+ is a chiral species with two possible optical
isomers: fac-
It should be noted that each cubane-like tetranuclear structure
is formed from four homo-chiral fac-
-[FeII(HLMe-Benz)3]2+ or
fac-
-[FeII(HLMe-Benz)3]2+ moieties. Fig. 7(b) shows a homo-chiral
D K .
-[FeII(HLMe-Benz)3]2+ and fac- -[FeII(HLMe-Benz)3]2+
cubic
cubic
cubic
ꢀ
ꢀ
ꢀ
P43n (No. 218)
P43n (No. 218)
P43n
D
20.871 (3)
20.871 (3)
20.871 (3)
9092 (3)
8
296
1.312
4.918
0.0306
0.0789
20.877 (3)
20.877 (3)
20.877 (3)
9099 (2)
8
20.829 (3)
20.829 (3)
20.829 (3)
9036(3)
8
K
b (Å)
tetranuclear structure; the red molecule represents the fac-D-
c (Å)
[FeII(HLMe-Benz)3]2+ isomer. In the crystal lattice, homo-chiral
cubane-like tetramers formed from cations with opposite
V (Å3)
Z
chiralities (i.e., red fac-
K D-
-[FeII(HLMe-Benz)3]2+ and green fac-
T (K)
296
296
Dcalc (g cmÀ3
)
1.376
1.253
[FeII(HLMe-Benz)3]2+) are alternately arrayed, as shown in Fig. 7(c).
l
(cmÀ1
)
10.314
0.0323
0.0821
5.027
0.0339
0.0855
Ra
It should be noted that there are many possible assembly struc-
tures that can be constructed from the common motif of 3:3
NHÁ Á ÁClÀ hydrogen bonds between fac-[FeII(HLR)3]2+ and the ClÀ
ions (HLR denotes a bidentate chelate ligand derived from 2-
methyl-4-formylimidazole and a monoamine such as benzylamine
[13]). The assembly structures that have been found thus far for
fac-[FeII(HLR)3]ClÁPF6 (R = Me, Et, n-Pr, n-Bu, n-Pen, n-Hex,Á Á Á) in-
clude three kinds of 2D layers, a 1D ladder, and a cubane-like clus-
ter. Compounds with long alkyl groups or bulky substituents at the
monoamine moiety, e.g., fac-[FeII(HLMe-Bnz)3]ClÁPF6 and fac-
[FeII(HLn-Hex)3]ClÁPF6, tend to form cubane-like clusters [13a].
wRb
a
R =
wR = [
R
||Fo| À |Fc||/
R|Fo|.
b
R
w(|Fo2| À |Fc2|)2/
R .
w|Fo2|2]1/2
Table 5
Selected coordination bond lengths (Å), angles (°), and hydrogen-bond lengths (Å) for
2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O and 2ÁClO4ÁEtOHÁH2O at 296 K.
Compound
fac-[FeII
fac-[FeII
fac-[FeII
(HLMe-Benz)3]
ClÁPF6ÁEtOHÁH2O
(HLMe-Benz)3]
ClÁSbF6ÁH2O
(HLMe-Benz)3]
ClÁClO4ÁEtOHÁH2O
3.3.2. Magnetic properties of 2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O, and
2ÁClO4ÁEtOHÁH2O
Bond lengths (Å)
Fe(1)–N(2)
Fe(1)–N(3)
2.187(3)
2.218(3)
2.203
2.173(4)
2.224(5)
2.199
2.175(4)
2.221(4)
2.198
The magnetic susceptibilities of the ground samples were mea-
sured under a 0.5 T magnetic field using a SQUID magnetometer
upon cooling from 300 to 5 K and then again upon warming from
Average Fe–N
Bond angles (°)
N(2)–Fe(1)–N(3)
5 to 300 K at 2 K minÀ1. The
v
MT versus T plots for 2ÁPF6ÁEtOHÁH2O,
76.62(11)
3.128(4)
76.74(17)
3.138(5)
76.81(14)
3.109(5)
2ÁSbF6ÁH2O, and 2ÁClO4ÁEtOHÁH2O are shown in Fig. 8, where
vM is
Hydrogen bond (Å)
N(1)Á Á ÁCl(1)
the molar magnetic susceptibility per Fe and T is the absolute
temperature.
The
v
MT versus T plot of 2ÁPF6ÁEtOHÁH2O showed incomplete
SCO behavior. Above 120 K,
a
constant vMT value of
3.138(5), and 3.109(5) Å for 2ÁPF6ÁEtOHÁH2O, 2ÁSbF6ÁH2O, and
2ÁClO4ÁEtOHÁH2O, respectively.
ꢀ4.2 cm3 K molÀ1 per iron atom was found, which is slightly high-
er than the spin-only HS FeII value and is comparable with reported
values for HS FeII (S = 2) complexes. Upon lowering the tempera-
Although imidazole-chloride hydrogen bonding is a common
motif for the construction of assembly structures, the complexes
form tetrameric cubane-like structures through three NHÁ Á ÁCl
bonds. Fig. 7(a) shows that the cubane structure of {fac-[Fe-
(HLMe-Benz)3]2+Á Á ÁClÀ}4 is constructed by twelve NHÁ Á ÁCl hydrogen
bonds; each cubane encapsulates a counter anion, X, which is
subjected to disorder that is likely due to free rotation at 296 K.
ture to 50 K, the
v
MT value decreases to 2.25 cm3 K molÀ1, which
is half the HS value. This result indicates that a spin transition oc-
curs from the 4HS state of the tetrameric Fe4 molecule to a
2HS + 2LS state. Calculation of the derivative of dvMT versus dT re-
vealed a spin transition temperature, T1/2, of 80 K between the 4HS
and 2HS + 2LS states.

1496
D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
Fig. 7. (a) Cubane-like tetranuclear structure of 2ÁPF6ÁEtOHÁH2O constructed from twelve NHÁ Á ÁClÀ hydrogen bonds with a PF6 anion encapsulated by the cubane. The
disorder of the encapsulated PF6À ion is likely due to free rotation at 296 K. (b) Homo-chiral cubane-like tetranuclear aggregate in 2ÁPF6ÁEtOHÁH2O; the red molecule indicates
À
the fac-
K
-[Fe(HLMe-Benz)3]2+ isomer. (c) Packing diagram of 2ÁPF6ÁEtOHÁH2O. In the crystal lattice, cubane-like tetramers with opposite chiralities (i.e., red fac-
K-
[Fe(HLMe-Benz)3]2+ and green fac- -[Fe(HLMe-Benz)3]2+) are alternately arrayed. (Color online.)
D
Fig. 8. SCO behaviors of 2ÁPF6ÁEtOHÁH2O (red), 2ÁSbF6ÁH2O (green), and
2ÁClO4ÁEtOHÁH2O (purple) in the form of MT vs. T plots. (Color online.)
Fig. 9. Selected Mössbauer spectra of 2ÁPF6ÁEtOHÁH2O recorded at 78 and 120 K.
v
the Debye temperature of the FeIII impurity is much higher than
that of FeII, it becomes more apparent at higher temperatures
and appears to be relatively abundant [15]; however, the actual
percentage of the impurity is equal to the value determined from
the low-temperature spectrum: The spectrum at 78 K shows a
smaller percentage of the impurity, which means the content of
the FeIII impurity is low. Deconvolution analysis of the spectrum
was performed to determine the HS versus total FeII molar fraction,
and the results are presented in Table 6. After rapid cooling to 78 K,
Mössbauer spectra were recorded at 78, 120, 150, and 200 K. The
spectra at 120, 150, and 200 K comprise doublets that are
The
v
MT versus T plot of 2ÁSbF6ÁH2O also showed incomplete
SCO behavior. Above 100 K,
a
constant
vMT value of ꢀ4.2
cm3 K molÀ1 was found, which is slightly higher than the HS FeII va-
lue and is comparable with those reported for HS FeII (S = 2) com-
plexes with similar bidentate ligands. Upon lowering the
temperature to 10 K, the
which is half of the HS value. This result indicates that a spin tran-
sition occurs from the 4HS state of the tetrameric Fe4 molecule to
the 2HS + 2LS state. The calculation of the derivative of dvMT versus
dT revealed a spin transition temperature of 70 K between the 4HS
v
MT value decreases to ꢀ2.1 cm3 K molÀ1
,
and 2HS + 2LS states.
attributed to HS FeII species (d = 1.10 mm sÀ1 EQ = 0.76 mm sÀ1
, D
The
v
MT versus T plot of 2ÁClO4ÁEtOHÁH2O shows a multi-step
at 120 K). The spectrum at 78 K comprises two doublets attribut-
spin transition. Above 160 K,
a
constant vMT value of
able to HS and LS FeII species with a relative ratio 65:26.
ꢀ4.1 cm3 K molÀ1 is found, which is slightly higher than the HS FeII
value and is comparable with those reported for HS FeII (S = 2)
complexes with bidentate ligands. Upon lowering the temperature
3.3.4. Structural parameters of cubane and spin-crossover behavior
It is well known that the spin crossover properties are influenced
by intermolecular interactions, known as the ‘‘cooperative effect.’’
For these cubane complexes, the cooperative effect can be divided
into intra-cubane and inter-cubane interactions. The effects of in-
tra-cubane interactions on spin crossover can be evaluated by the
structural parameters of the cubane; in contrast, it is difficult to
evaluate the effects of inter-cubane interactions. Each cubane mol-
ecule encapsulates one counter anion at the center of its cavity. The
below 80 K, the
vMT value decreases to a steady value of
ꢀ1.0 cm3 K molÀ1, which is one quarter of the HS value. The
versus T plot also contains a shoulder at ꢀ120 K.
vMT
3.3.3. Mössbauer spectra of 2ÁPF6ÁEtOHÁH2O
As shown in Fig. 9, the Mössbauer spectra of 2ÁPF6ÁEtOHÁH2O
comprise signals attributable to HS and/or LS FeII species and a
broad peak attributable to an unidentified component. The uniden-
tified component is connected with the HS FeIII species and is likely
FeIII oxide fine particles, which have a small quadrupole splitting
and an isomer shift ranging from 0.3 to 0.4 mm sÀ1 [14]. Since
sizes of the anions were evaluated by quantum-chemical calcula-
tions to be 54.4 Å3, 73.0 Å3, and 88.7 Å3 for ClO4À, PF6À, and SbF6
,
À
respectively [16]. The structural parameters of the three HS (S = 2)

D. Furushou et al. / Polyhedron 52 (2013) 1489–1498
1497
Table 6
structural changes. The magnetic data is in accord with these re-
sults, which suggests that the observed SCO properties are mainly
due to intra-cubane interactions.
Mössbauer data for 2ÁPF6ÁEtOHÁH2O.
Temp.
(K)
da
D
EQ
Cb
Area ratio
(%)
Assignment
(mm sÀ1
)
(mm sÀ1
)
(mm sÀ1
)
Acknowledgement
200
150
120
78
1.05
0.34
0.57
0
0.21
0.86
83
17
HS FeII
Ferric
impurity
HS FeII
Ferric
impurity
HS FeII
Ferric
impurity
HS FeII
LS FeII
T. Hashibe, K. Nishi, T. Fujinami, and H. Hagiwara were sup-
ported by the Research Fellowship for young scientists of the Japan
Society for the Promotion of Science.
1.09
0.35
0.68
0
0.23
0.66
87
13
1.10
0.39
0.76
0
0.25
0.65
88
12
Appendix A. Supplementary data
1.12
0.51
0.38
0.85
0.19
0
0.23
0.20
0.48
65
26
9
CCDC 878434, 878435, 878436, 878437, 878438, and 878439
contains the supplementary crystallographic data for mer-[FeII-
(HLMe-Benz)3]ClÁPF6Á1.5H2O (1ÁPF6Á1.5H2O) at 230, 150, and 103 K, and
fac-[FeII(HLMe-Benz)3]ClÁPF6ÁEtOHÁH2O (2ÁPF6ÁEtOHÁH2O), fac-[FeII-
(HLMe-Benz)3]ClÁSbF6ÁH2O (2ÁSbF6ÁH2O) and fac-[FeII(HLMe-Benz)3]Cl
ÁClO4ÁEtOHÁH2O (2ÁClO4ÁEtOHÁH2O) at 296 K, respectively. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html, or from the Cambridge Crystallographic Data Centre,
12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.poly.2012.06.085.
Ferric
impurity
a
Isomer shift data are reported to iron foil.
Full width at half-height.
b
Table 7
Structural parameters of the cubane structure at 296 K.
Compound
2ÁSbF6ÁH2O
2ÁPF6ÁEtOHÁH2O
2ÁClO4ÁEtOHÁH2O
Fe–N(2) (Å)
Fe–N(3) (Å)
N(2)–Fe–N(3) (°)
N(1)Á Á ÁCl (Å)
FeÁ Á ÁCl (Å)
2.173(4)
2.224(5)
76.74(17)
3.138(5)
7.359
11.285
9.349
100.12
78.87
2.187(3)
2.218(3)
76.62(11)
3.128(4)
7.352
11.191
9.462
99.11
2.175(4)
2.221(4)
76.81(14)
3.109(5)
7.330
11.044
9.587
97.75
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