Magnetic and liquid crystalline property of long-alkyl chain appended iron (II) imidazole complexes

Article abstract of DOI:10.1016/j.jorganchem.2016.02.014

Fe[((py)im-C16)₃](BF₄)₂ (1) and Fe[((py)imH)₃](BF₄)₂ (2), the Iron(II) compounds with C16 long alkyl chain appended (py)imH and unmodified (py)imH [(py)imH = 2-(2-pyridyl)imidazole] have be

Full text of DOI:10.1016/j.jorganchem.2016.02.014

Accepted Manuscript
Magnetic and liquid crystalline property of long-alkyl chain appended Iron (II)
Imidazole complexes
Mohammad Razaul Karim, Hiroshi Takehira, Mohammed M. Rahman, Abdullah M.
Asiri, Md. Khairul Amin, Ryo Ohtani, Shinya Hayami
PII:
S0022-328X(16)30047-X
10.1016/j.jorganchem.2016.02.014
JOM 19398
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 27 October 2015
Revised Date: 8 February 2016
Accepted Date: 10 February 2016
Please cite this article as: M.R. Karim, H. Takehira, M.M. Rahman, A.M. Asiri, M.K. Amin, R. Ohtani,,
S. Hayami, Magnetic and liquid crystalline property of long-alkyl chain appended Iron (II) Imidazole
complexes, Journal of Organometallic Chemistry (2016), doi: 10.1016/j.jorganchem.2016.02.014.
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Magnetic and liquid crystalline property of long-alkyl chain appended
Iron (II) Imidazole complexes
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Mohammad Razaul Karima,b, Hiroshi Takehirab, Mohammed M. Rahmanc, Abdullah
M. Asiric, Md. Khairul Amina, Ryo Ohtani,b Shinya Hayamib,d,*
aDepartment of Chemistry, School of Physical Sciences, Shahjalal University of Science &
Technology, Sylhet-3114, Bangladesh
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bGraduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami,
Kumamoto, 860-8555, Japan.
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cCenter of Excellence for Advanced Materials Research (CEAMR) & Chemistry Department,
King Abdulaziz University, Jeddah 21589, P.O. Box 80203, Saudi Arabia;
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dJST, CREST, 5 Sanbancho, Chiyoda-ku, Tokyo, 102-0075, Japan.
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* Corresponding author
Prof. Shinya Hayami
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Phone: +81-96-342-3469. Fax: +81-96-342-3469
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Graduate School of Science and Technology, Kumamoto University, 2-39-1
Kurokami, Kumamoto, 860-8555, Japan.
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E-mail: hayami@sci.kumamoto-u.ac.jp
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Abstract
Fe[((py)im-C16)3](BF4)2 (1) and Fe[((py)imH)3](BF4)2 (2), the Iron(II) compounds
with C16 long alkyl chain appended (py)imH and unmodified (py)imH [(py)imH=2-(2-
pyridyl)imidazole] have been synthesized and characterized by NMR, IR spectra and
elemental analysis. For containing C16 long alkyl chain, complex 1 exhibits the liquid
crystalline property around room temperature. The magnetic study suggests that 1 exists
only in low spin state but 2 exhibits gradual spin crossover behavior. These observation
suggests the possibility for synchronizing liquid crystallinity and spin crossover behavior of
(py)imH complex in near future.
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Keywords: Iron(II); 2-(2-pyridyl)imidazole; Liquid crystal (LC); Spin crossover (SCO);
C16-alkylchain
1. Introduction
Appending long alkyl chains into ligand groups of metal complexes can result in
some unique physical and chemical phenomena including the synchronicity between spin-
state transitions and crystal-liquid crystal phase transitions. The nature of magnetic metal
center and the effect of thermal motion on long alkyl chains play the major role for such
external stimuli aided synergetic effect [1]. In a more specific way, the modulation of
temperature or intensity of irradiated photon can result in some change in spin state or phase
transition process. In molecular material chemistry the spin crossover (SCO) behavior
corresponds to spin state switching [2]. The mesogenic materials having liquid crystalline
(LC) properties and SCO behavior have attracted considerable interest in recent years. As
these materials can exhibit spin transition signals with phase transition phenomena at
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different temperature regions, they can be used as photo and thermo-chromic switching
materials [3]. Iron complex possesses wide interests in SCO chemistry since Cambi et al.
observed the SCO behavior in an iron (III) tris-dithiocarbamate complex at 1930 by
studding the temperature-dependent magnetic moments [4]. The first iron (II) SCO complex
was reported and recognized in 1964 and 1967, respectively [5]. SCO phenomenon
represents the external stimuli (e.g. temperature, pressure, magnetic field, light etc.) aided
reversible transformation of electronic arrangement between high spin (HS) and low spin
(LS) state in the complexes of first raw transition metal ions having 3dn (n = 4-7) electronic
configuration [6]. On the otherhand, the liquid crystalline property of metal complexes
having C16 long alkyl chain has been reported by several groups [7]. Liquid crystals of
transition-metal complexes, called metallomesogens are well known for their
multifunctional aspects [8]. The development of metallomesogens with functionalities
including spin-crossover, mixed-valence, magnetism, conductivity etc. are important for
achieving the co-occurrence of various physical properties in functional molecular-based
materials. Mononuclear iron (II) complexes with heterocyclic N-donor ligands are well
known for their spin-crossover behavior and low-temperature spin-trapping phenomenon. A
significant number of such compounds undergo thermal spin-transitions upon cooling or
heating [9]. Todate, a number or reports on the Iron complexes of (py)imH and its
derivatives has been reported so far [10]. Herein, we observed the mesogenic nature and
SCO behavior in (py)imH based Iron (II) complexes.
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(py)imH, a derivative of imidazole is one of the most important nitrogen containing
bioactive ligand. The ligand in its pure form is capable to form hydrogen bond [11]. It is a
bidentate ligand having both the pyridinic and pyrrolic N atoms functioning as the electron
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donors for the formation of coordination complexes [12]. Compared with the closely related
2,2ʹ-bipyridine, (py)imH can coordinate as a weaker σ donor and π acceptor ligand [13].
Previously, N-functionalized imidazole, its derivatives and complexes with some transition
metals were studied extensively for therapeutic applications including antibacterial,
antifungal and antitubercular agents [14]. The anomalous magnetic behavior of Iron (II)
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complexes with (py)imH having T2g-1A1g equilibrium was reported long before [15]. Also
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Goodgame et al. reported the cooperative thermal spin-transition behavior of
Fe[((py)imH)3](ClO4)2 [16]. Later, Wilson et al. reported the solution state equilibrium
between high and low spin state in Fe[((py)imH)3](BF4)2 [17]. In recent years the
temperature dependent variable magnetic properties of Iron complex of (py)imH having
phenyl derivatives have been studied by Michelle et al. [18]. (py)imH can be N-
functionalized through deprotonation by base [7]. Based on this previous observation in this
study, we attempt to insert long alkyl chain by replacing H from the pyrrolic N-H. Previous
abiotic study suggested that the activity and functionality of alkylated imidazole precursor
depends on the chain lengths. For example the biological functionality was found to be
pronounced when the alkyl chain have at least 12 carbons [19]. Apart from biological
application, almost no efforts have been noticed to justify the liquid crystalline nature and
magnetic behavior of (py)imH based materials. In this respect, we considered the N-
functionalization of (py)imH to devise functional metal complexes. By replacing the proton
in basic medium, we inserted C16 alkyl chain at (py)imH and synthesized corresponding
Iron (II) complexes 1 and 2. Complex 1 and 2 exhibited the liquid crystallinity and gradual
spin crossover property, respectively.
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2. Experimental Section
2.1. Materials
Pyridine-2-carboxaldehyde, glyoxal (40%), ammonia (25%), one bromohexadecane,
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sodium hydride, tetra-n-butylammonium bromide (TBAB), ethyl alcohol and
tetrahydrofuran (THF) was purchaged from Wako Chemical Co. Ltd. Pyridine-2-
carboxaldehyde was distilled at reduced pressure and was preserved on brown bottle by
wrapping aluminum foil until using. All other chemicals were used without further
purification except mentioned differently.
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2.2.
Instrumentation
Elemental analysis (C, H and N) were carried out at the Instrumental Analysis Center of
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Kumamoto University. H-NMR spectra were recorded on a JEOL (500-ECX)
Instrument (500 MHz) using deuterated solvents with TMS as internal reference. Magnetic
Susceptibilities were measured on a Quantum Design MPMS-5S. Samples were put into a
gelatin capsules and mounted inside plastic straws. They were then fixed at the end of the
sample transport rod and were conveyed inside the magnet core fitted with field strength
and temperature scanning facilities. Thermal analysis through differential scanning
calorimetry (DSC) was carried out on a SHIMADZU DSC 50 differential scanning
calorimeter. Powder X-ray diffraction (XRD) studies were performed on a Rigaku X-ray
diffractometer RAD-2A with a 2.0 kW Cu Ka X-ray. Polarized Optical Microscopy (POM)
was carried out on a polarization microscope (OPTICAL POL with a Yanagimoto factory
model MP-J3) micromelting point meter, devised by Nippon Chemical Industrial
Corporation.
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2.3.
Synthesis of (py)imH
The overall route for synthesis is depicted by scheme 1. The ligand was synthesized by
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some modification of Radziszewski method [20]. In a typical procedure, 5.0 g freshly
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distilled pyridine-2-carboxaldehyde in 5.0 ml EtOH at 0 C was added dropwise into 6.75
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ml glyoxal (dissolved in 5.0 ml EtOH) of 0 C and was stirred for 30.0 minutes. 19.2 ml
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ammonia at 0 C was added very slowly with constant stirring at 0 C for 4.0 hours. The
mixture was stirred further for 18.0 hours at room temperature to achieve a deep brown
solution. The volume of the content was then reduced to 30% by rotary evaporator. The
remaining content was extracted by diethyl ether (10 times × 30 ml). The ether from the
extracted was removed by rotary evaporator and a red oily product was found. It was
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distilled at 132.0 C under low pressure. Pale yellow needle like crystals were found. Yield
32%, melting point 136.0 oC. 1H-NMR (500 MHz, CDCl3): 8.46 (d, J = 4.8, 1H), 8.09 (d, J
= 7.6, 1H); 7.71 (td, J= 7.6, 3.8 1H); 7.68 (s, 1H), 7.18 (q, 1H), 7.13 (s, 1H). UV/Vis
(MeOH): 273 (11900), 294 (15600). IR (KBr): ca. 3352 w, 1614 s, 1595 s, 1508 m, 1481 s,
1458 s, 1414 s, 1379 m, 1307 s, 1280 m, 1252 m, 1171 m, 1150 s, 1136 s, 1107 m, 991 s,
955 s, 901 m, 789 s, 758 s, 737 s, 708 m, 621 s, 657 m, 499 m, 462 m, 430 w.
2.4.
Synthesis of (py)im-C16
NaH (0.024 g, 1.0 mmol) in 5.0 ml THF was cooled to 0 C. (py)imH (0.145 g, 1.0
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mmol) in 5.0 ml THF was added dropwise and was stirred for 30.0 hour in an ice bath. Then
the temperature of the solution was increased to room temperature and stirred for another
30.0 minutes. 0.01 g TBAB was then added as phase transfer catalyst followed by a slow
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addition of C16-Br (0.305 g, 1.0 mmol). Finally 10.0 ml THF was added and the mixture
was refluxed overnight at 65.0 oC. The solvent was then removed by stirring it in open air at
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65.0 C. The product was dissolved in chloroform and filtered. The solvent was removed
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and the final product was washed by water and dried under vacuum. Brown oily product
was found. 1H-NMR (500 MHz, CDCl3): 8.46 (d, J = 4.8, 1H), 8.09 (d, J = 7.6, 1H); 7.71 (td,
J = 7.6, 3.8, 1H); 7.68 (s, 1H), 7.18 (q, 1H), 7.13 (s, 1H); 1.22 (m, 31H, -CH2CH2CH2-). IR
(KBr): ca. 3448 w, 1605 s, 1578 s, 1556 m, 1535 m, 1472 m, 1425 s, 1371 m, 1310 m,
1263 s, 1150 m, 1123 s, 1088 m, 1063 s, 1032 s, 1031 m, 980 s, 953 m, 920 m, 780 s, 731 m,
704 s, 612 s.
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2.5.
Synthesis of 1 and 2
Previously, almost similar compound of 2 with different counter anion (BPh4) was
reported by Wilson et al [17]. Herein, we have introduced different counter anion. In a
typical synthetic method, NaBF4 (0.095 mg, 0.25 mmol), ascorbic acid (0.176 mg, 0.1
mmol) and FeCl2.4H2O (0.02 mg, 0.1 mmol) was dissolved in 10 ml MeOH by 10 minutes
stirring at room temperature. The solution was filtered and added dropwise into a solution of
(py)im-C16 (0.107 mg, 0.29 mmol) in 10.0 ml methanol under argon at room temperature.
The mixture was stirred for 4.0 hours and crystallized at room temperature. The product was
filtered from methanol, washed with water and finally was recrystallized from methanol.
After drying, red powder of 1 was found. Yield (0.11 g, 0.76%). Element. Anal. Calcd. For
C78H135B2F8FeN9: C, 63.12; H, 9.17; N, 8.49 Found: C, 63.40; H, 9.12; N, 8.56%. In a
similar way, 2 was synthesized using the ligand (py)imH. Element. Anal. Calcd. For
C24H21B2F8FeN9: C, 43.35; H, 3.18; N, 18.96 Found: C, 43.40; H, 3.22; N, 19.01%. The
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powdered and crystalline products of 1 and 2, respectively were obtained from slow
evaporation of solvent through the pinholes of parafilm cover at room temperature. The
crystals were larger in size, when they were precipitated from methanol at room temperature.
Crystals obtained from hot methanol or by rapid cooling using refrigeration were
comparatively smaller in size. Above room temperature, the solubility of the complexes
increases. Therefore, room temperature was preferred for obtaining the products.
3. Results and discussion
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3.1.
Synthesis and structure:
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For synthesizing (py)imH we followed the Debus-Radziszewski reaction [21], where a
dicarbonyl, an aldehyde and ammonia react to form imidazole or its derivatives. We used
glyoxal and pyridine-2-carboxaldehyde as the dicarbonyl and aldehyde. The reaction takes
place in two steps. In the first step, dicarbonyl and ammonia condense to give a diimine. In
second stage, the diimine condenses with the aldehyde. Therefore, glyoxal is necessary to
obtain diimine, which reacts with pyridine-2-carboxaldehyde to form (py)imH. The
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formation of (py)imH and its modification into (py)im-16 was confirmed by H-NMR and
IR spectra. The hydrogen atom attached to the pyrroline ring is labile and was possible to
substitute by -C16H31 alkyl group by base catalyzed reaction in presence of TBAB. TBAB is
an ionic compound which can be deionized to form (C4H9)4N+ (TBA+) and Br-. The function
of TBAB is similar to the mechanism of phase transfer catalyst reported previously by
Starks. [22] (py)im-16 is formed through a two step reaction. In the first step, (py)imH and
NaH reacts to form (py)im-Na+. Ionic (py)im-Na+ is sparingly soluble in organic phase,
which prohibits its interaction with Br-C16H31 dissolved in THF. Therefore, the phase
transfer catalyst TBAB is necessary to convert (py)im-Na+ into (py)im-TBA+ complex,
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which is soluble in THF. The polar part (N+) electrostatically bounds the (py)im- precursor,
whereas the non polar part (-C4H9) dissolves in THF. In the final stage (py)im-TBA+ reacts
with Br-C16H31 to form (py)im-16 and TBAB again. The Br- and Na+ form insoluble NaBr
salt and precipitated out from the system. TBAB therefore is necessary for successful
completion of the reaction.
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The NMR spectra for (py)imH matches with theoretical calculation and some previous
report [8]. Characteristic NMR peak at low field (1.22 (m, 31H, -CH2CH2CH2-)) confirms
the successful insertion of C16-long alkyl chain during the reaction. This NMR
spectroscopy based characterization for successful ligand alkylation process is well reported
[23]. The insertion of Fe2+ ion for formation of the complexes was followed by previous
report [12]. Unfortunately, we failed to get the single crystals, as it is expected that the
thermal motion of long alkyl chain could prohibits the crystal packing [24]. Even we
synthesized complex having the ligand with shorter alkyl chains (C1 and C4), stable crystal
packing was not possible to avail. As some alternative, elemental analysis and IR spectra
could confirm the formation of the complexes. Figure 1 represents the IR spectra of
(py)imH, (py)im-C16, 1 and 2. In Figure 1(a), the diffused peak at 3100-3500 cm-1 and the
sharp peak at 1595 cm-1 rises from the stretching and bending mood of vibration,
respectively for pyrrilic hydrogen atom bonded to N. This N-H bond is polar due to the
variation in electronegativity between N and H. Therefore, the positively charged hydrogen
atom takes part in intermolecular hydrogen bond and the resultant IR adsorption peak is
broad. The pyridinic, and pyrrilic C-N bond stretching frequencies lie within the range of
1250-1350 cm-1. When the pyrrilic H atom is substituted by C16 alkyl chain, the IR
spectrum of resulted (py)im-16 is characterized by the appearance of peaks at 2850 and
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2920 cm-1 (Figure 1b). These peaks are resulted from the stretching mood of aliphatic C-H
bond of long alkyl chain. In addition, the IR spectrum of (py)im-C16 shows the
disappearance of broad peak at 3100-3500 cm-1 due to the removal of pyrrilic H atom and
the breaking of the hydrogen bonded networks. The IR spectra in Figure 1c and Figure 1d
indicate the formation of complex 1 and 2 through clear indication for the existence of Fe-N
bond. When Fe2+ was inserted near the pyridinic and pyrrilic N, the characteristic IR
stretching frequencies of Fe-N bond formed at ~1000 cm-1 indicated the formation of iron
(py)imH/(py)im-C16 compounds [25]. Besides, the peaks position and intensity for
pyridinic and pyrrilic C-N bond in the ligands near 1300 cm-1 undergo some change in 1 and
2. When the ligands co-ordinate to Fe2+ ion, the electron density from C-N bond is partly
shifted to C-Fe bond, which is responsible for the respective change in the band intensity.
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3.2.
Liquid crystalline behavior of 1
The liquid-crystalline property of 1 was justified firstly by phase transition enthalpy
changes, which were measured by carrying out thermal analysis with DSC in a wide range
of temperature. As shown in Figure 2, an endothermic peak at 306 K (∆H = 53.81 kJmol-1)
on cooling process and an exothermic peak at 330 K (∆H = -41.58 kJmol-1) on heating
process were observed. These results indicate the possibility for crystal to mesophase phase
transition near room temperature. The meso-phase structure of 1 was further studied by
powder XRD and hot-stage polarized optical microscopy (POM). Figure 3 shows the
powder XRD patterns of the solid and mesophase states for 1 observed at 330 and 455 K,
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respectively. At room temperature, the XRD pattern displays two reflections at 2θ = 3.06
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(d-spacing = 28.38 Å) and 6.15 (d-spacing = 14.14 Å) in the small-angle region and a
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broad scattering halo centered at 21.2 (d-spacing = 4.43 Å) in the wide-angle region.
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However at 455 K, the XRD pattern reveals three reflections at 2θ = 2.52, 5.14 and 7.74
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with respective d-spacing values as 34.46, 16.91 and 11.24 Å in the small-angle region. The
ratio of the d-spacing values becomes 1:1/2:1/3 and could be indexed as the (001), (002) and
(003) reflections of a lamellar phase. Besides, a diffuse and broad scattering halo centered at
4.08 Å (2θ = 21.7 o) in the wide-angle region is indicative of the liquid-like order of the
aliphatic chains. POM images for 1 (Figure 4) show the conversion of the compounds
directly into isotropic liquid. At 330 K, typical fan shaped texture of lamellar phase during
heating and cooling process indicates the crystal to mesophase phase transformation.
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3.3.
Spin Crossover behavior of 1 and 2
Spin transitions between the high-spin (HS) and low-spin (LS) states for 1 and 2 were
investigated by the measurement of the molar magnetic susceptibility χm as function of the
temperature. Complex 1 exists only in low spin state within the temperature range 5-400 K
(Figure 5a). The χmT value is around 0.5 cm3Kmol-1 at 5 K and decrease slightly at higher
temperature. The rate of this lowering is comparatively higher at 5-25 K. Beyond 25 K, the
χmT values lie below 0.26 cm3Kmol-1 and represents the low spin state of Iron (II). The
cooling process resulted in the reversible thermal curve. The magnetic study indicates the
diamagnetic behavior of the complex. Slightly higher χmT values at low temperature are
insignificant but indicate the presence of impurity in 1. The product seems to adsorb traces
of impurity (FeCl2 or related ions) during precipitation. Though the result of elemental
analysis indicates the close match between calculated and experimental values for C, H and
N content in 1 and 2, there exist some possibility for the existence of adsorbed impurity.
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Especially, as 1 was found in powdered form, it is more likely to adsorb impurity. The
magnetic data for 1 was reproducible, while we repeated the experiment several times.
Apart from the impurity effect, any other reason behind this slightly higher susceptibility
values at low temperature is presently unknown. However, our future plan includes tuning
the length of alkyls chain to study the magnetic behavior of the series in details.
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The temperature dependent magnetic susceptibility for 2 reveals a gradual SCO
behavior without hysteresis loop in the temperature region from 5 to 400 K (Figure 5b).
This behavior is a typical phenomenon occurring in some Iron (II) complexes [7b]. The χmT
value is equal to 0.26 cm3Kmol-1 at 5 K and lies within the range of expected χmT value for
LS Iron (II) ions [26]. As the temperature is increased from 5 K, the χmT value remains
constant upto 150 K. Beyond 150 K, the χmT value gradually increases to 2.7 cm3Kmol-1 at
400 K and is consistent with HS state. Upon cooling process, the behavior of magnetic
susceptibility exhibits the reversible thermal curve.
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Soft metal complexes become interesting not only as some functional materials, but
also for the phase transitions with synchronicity between the central metal complex and the
long alkyl chains [27]. The liquid crystalline behavior of some metal complexes having long
alkyl chain (especially C16) is well reported [28]. We propose that the observed mesophase
structure of 1 around room temperature originates from the equilibrium between thermal
motion of the flexible C16 alkyl chain and its rigidity in crystal packing. The packing of
polar headed moiety ((py)im) with C16 alkyl tail in an atmosphere of bulk polar liquid
resulted in the diffraction pattern of lamellar phase. Previously, some complexes of (py)imH
with Fe2+ and Cr3+ was reported to exhibit octahedral crystal structure [29]. Therefore, we
also expect similar structure for 1. In octahedral packing the long alkyl chains are extended
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and supposed to limit the tilting motion of the packing through interchain interaction with
neighboring alkyl groups. Therefore, the liquid crystalline property could sustain around
room temperature. In future, we are intending to study further the liquid crystallinity, by
changing the counter anion and modulating the chain lengths. Present magnetic study
suggests the possibility for SCO behavior in (py)imH based Fe2+ complexes. Though the
increase in chain length renders the spin transition phenomenon, the liquid crystallinity was
availed with longer alkyl chain. Achieving simultaneous electron transitions across all
molecules to obtain abrupt SCO behavior is highly desirable. Establishing cooperativity
among the molecules is the primary condition for such achievement and the best way to
increase cooperativity between molecules is to functionalize the side chain by polar groups.
Our future endeavor includes such trials. The present form of this manuscript is important
for further advancement in this filed. This manuscript indicates the possibility of both the
SCO behavior and liquid liquid crystallinity in Iron based (Py)imH complex. We are
expecting the coalescence of these two functionalities in a single molecule in near future.
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4. Conclusion
We have synthesized novel (py)imH based Iron(II) complexes as [Fe((py)im-
C16)3](BF4)2 and [Fe((py)imH)3](BF4)2. The DSC track, powder XRD pattern and POM
images were indicative for the liquid crystalline lamellar phase of [Fe((py)im-C16)3](BF4)2.
[Fe((py)im-C16)3](BF4)2 exists only in low spin state, whereas, [Fe((py)imH)3](BF4)2
exhibits gradual SCO property with respect to the modulation of temperature. All these
complexes indicate the possibility of designing (py)imH based novel multifunctional
mesogenic materials in future.
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C6H31Br, NaH
EtOH
NH3
+ +
Distillation
TBAB, reflux in
THFunder Ar, 36 h
(b)
(a)
N
N
Fe
N
N
N
N
(c)
1
3 5 7 9 111315
(BF4)2
16
N
N
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2
FeCl2.4H2O, NaBF4
N
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Scheme 1. Synthesis of the ligand and complexes. (a) (py)imH, (b) (py)im-C16 and (c) 1
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4000 3500 3000 2500 2000 1500 1000
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(d)
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Wavenumber/cm-1
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Figure 1. IR spectra for charecterization of the ligands and complexes. (a) (py)imH, (b)
(py)im-C16 (c) 1 and (d) 2.
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1.5
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Cooling
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Figure 2. Temperature dependent phase transfer phenomenon. DSC curve of 1
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455 K
300 K
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2θ/O
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Figure 3. Study of the liquid crystaline phase. Powder XRD pattern for 1
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(a)
(b)
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Figure 4. Study of the liquid crysatalline phase by POM texture of 1 under crossed
polarizers at 330 during heating (a) and cooling (b)
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3.0
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Figure 5. Study of the the temperature dependent SCO behaviour. χmT versus T plots for
(a) and (b).
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Highlights
ꢀ Fe[((py)im-C16)3](BF4)2 and Fe[((py)imH)3](BF4)2 [(py)imH=2-(2-
pyridyl)imidazole] have been synthesized.
ꢀ Fe[((py)im-C16)3](BF4)2 exhibits the liquid crystalline property.
ꢀ Fe[((py)im-C16)3](BF4)2 exists only in low spin state.
ꢀ Fe[((py)imH)3](BF4)2 exhibits gradual spin crossover behavior.
Graphical Abstract
Fe2+
C16
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