Magnetic, photophysical and thermal properties of complexes of iron(II) with structurally different Schiff bases

Article abstract of DOI:10.14233/ajchem.2015.17829

Three Fe(II) complexes of structurally different Schiff bases i.e., [Fe(L1)₂](BF₄) (1), [Fe₂(OOC(CH₂)₁₄CH₃)₂(L₂)(H₂O)₂] (2) and [Fe₂(O

Full text of DOI:10.14233/ajchem.2015.17829

Asian Journal of Chemistry; Vol. 27, No. 7 (2015), 2359-2364
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17829
Magnetic, Photophysical and Thermal Properties of
Complexes of Iron(II) with Structurally Different Schiff Bases
*
NORBANI ABDULLAH , AFIQ AZIL, ANITA MARLINA and NUR LINAHAFIZZA M. NOOR
Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia
*
Corresponding author: Fax: +60 3 79674193; Tel: +60 3 79674264; E-mail: norbania@um.edu.my, anitamarlina@siswa.um.edu.my
Received: 16 April 2014; Accepted: 30 May 2014; Published online: 30 March 2015; AJC-17033
Three Fe(II) complexes of structurally different Schiff bases i.e., [Fe(L1)
Fe (OOC(CH (L )(H O) ]·2.5H O (3), were synthesized and characterised for potential uses as spin crossover and low band gap
materials with metallomesogenic properties. Complex 1 was obtained in a one-pot reaction involving Fe(BF with L1, while compounds
and 3 were obtained by step-wise reactions involving [Fe(OOC(CH (EtOH)] with H L2 and H L3, respectively. At room
temperature, compound 1 has a low-spin Fe(II) atom while both compounds 2 and 3 have two high-spin Fe(II) atoms. The values for the
optical band gap (E ) were 1.8 eV for compound 1, 1.9 eV for compound 2 and 2.3 eV for compound 3. These complexes were thermally
stable, with decomposition temperature of 260 °C for compound 1, 205 °C for compound 2 and 250 °C for compound 3. Complexes 1 and
exhibited mesomorphisms while 3 was not mesomorphic.
2
](BF
4
) (1), [Fe
2
(OOC(CH
2
)
14CH
3
)
2
(L
2
)(H
2
O)
2
] (2) and
[
2
2
)
14CH
3
)
2
3
2
4
2
)
4 2
2
2
)
14CH
3
)
2
2
2
g
2
Keywords: Iron(II), Schiff base, Spin crossover, Bandgap, Metallomesogen.
and H L3, respectively.A common feature of these complexes
2
INTRODUCTION
was the presence of linear 16-carbon alkyl chains, introduced
Fe(II) complexes made up of N-donor ligands are widely
investigated as spin crossover (SCO) materials. This is because
the valence electronic configuration of Fe(II) (3d ) may be
reversibly switched between low spin (LS, t2g ) and high spin
20
in order to lower their melting temperatures and to induce
21,22
mesomorphism (s)
.
6
6
4
2
g
(
HS, t2g
e ) state by external stimuli, such as temperature,
1
-6
pressure and light irradiation . More recently, Fe(II) comp-
lexes are attracting attention as potential photosensitizers in
N
N
N
H
C(H
C)15
(CH )15CH
2 3
3
2
7-9
dye-sensitized solar cells (DSSC) , to replace the more expen-
(a)
10-15
sive and toxic Ru(II) complexes . For these purposes, ligands
derived from Schiff bases are ideally suited as they are easy to
prepare, structurally versatile and form stable complexes with
1
6-19
most transition metal ions
This paper presents the syntheses of three structurally
different Schiff bases, L1, H L2 and H L3 (Fig. 1) and the
corresponding Fe(II) complexes. Ligand L1 was a neutral
-donor Schiff base, H L2 was a multi-N donor conjugated
Schiff base and H L3 has two N,O-donors separated by an
.
N
N
2
2
N
N
N
N
3
2
NH
HN
2
(b)
eight-carbon aliphatic chain. The main objective was to show
the effect of different donor atoms of the ligands on the struc-
tures, magnetic, photophysical and thermal properties of
Fe(II) complexes formed. [Fe(L1)
a one-pot reaction involving Fe(BF
Fe (OOC(CH (L )(H O) ] (2) and [Fe
CH (L )(H O) ]·2½H O (3) were formed in step-wise
reactions involving [Fe(OOC(CH (EtOH)] with H L2
2
](BF
4
)
2
(1) was formed in
O and L1, while
(OOC(CH
N
OH
N
4
)
2
·6H
2
[
2
2
)
14CH
3
)
2
2
2
2
2
2
)
14
OH
(c)
3
)
2
3
2
4
2
Fig. 1. Structural formulae of Schiff bases: (a) L1; (b) H
2
2
L2; and (c) H L3
2
)
14CH
3
)
2
2

2
360 Abdullah et al.
Asian J. Chem.
-
1
(
73.7 %).Anal. Calcd. for C34
H, 11.2 %. Found: C, 66.4; H, 12.5 %.
L2: An ethanolic mixture (30 mL) of pyrrole-2-carbo-
xaldehyde (11.69 g, 123 mmol) and 2,4-diamino-6-phenyl-
,3,5-triazine (11.52 g, 61.5 mmol) was refluxed for 3 h in the
H
68
O
5
Fe (612.8 g mol ): C, 66.6;
EXPERIMENTAL
All chemicals were analaR reagents and used as received.
H
2
The elemental analyses (CHN) were carried out on a Thermo
1
Finnigan Flash EA 1112. The H NMR spectra were recorded
1
in CDCl
3
and DMSO on a JEOL FT-NMR lambda 400 MHz
presence of a few drops of glacial acetic acid. A brownish
powder obtained was filtered from the hot reaction mixture,
washed with ethanol and dried in an oven at 100 °C. Yield:
spectrometer. The FTIR spectra were recorded for neat
-1
samples from 4000 to 450 cm on a Perkin-Elmer Frontier
FTIR spectrometer equipped with a diamond attenuated total
reflectance attachment. Magnetic susceptibility at room
temperature was determined on a Sherwood automagnetic
susceptibility balance by the Gouy method. The instrument
-1
1
6
5.8 g (68.3 %). Anal. Calcd. for C19
H
15
N
7
(341.4 g mol ): C,
1
6.9; H, 4.4; N, 28.7 %; found: C, 66.9; H, 4.9; N, 29 %. H
): 6.75 (d, 4H), 7.43-7.49 (d, 3H), (7.51 (s,
H), 8.23 (d, 2H), 8.25 (d, 2H), 11.3 (s, 2H).
Fe (OOC(CH (L )(H O) ] (2): [Fe(OOC(CH
(EtOH)] (0.15 g, 0.24 mmol) was added to an ethanolic
L2 (0.09 g, 0.26 mmol) and the
reaction mixture was refluxed for 3 h. The pale brown powder
formed was filtered from the hot reaction mixture, washed
with ethanol and dried in an oven at 100 °C. Yield: 0.21 g
NMR (DMSO-d
2
6
was calibrated using Hg[Co(NCS) ] and the molar suscep-
4
[
3 2
)
2
2
)
14CH
3
)
2
2
2
2
)
2 14
tibility value was corrected for the diamagnetism of the
constituent atoms using Pascal's constants. Variable tempe-
rature magnetic susceptibility was measured on a Quantum
Design MPMS XL EverCool SQUID magnetometer at Kinki
University, Higashiosaka-shi, Osaka, Japan. About 10 mg of
the sample was placed inside a gelatine capsule and inserted
halfway inside a drinking straw to a depth of about 10 cm
from the top. The straw was then inserted into the instrument.
The measurements were recorded at 1 Tesla (10,000 Gauss)
in the temperature range of 300-4 K. The raw data was analysed
using Microsoft Excel and IGOR Pro. The UV-visible spectrum
CH
suspension (25 mL) of H
2
-1
(
6
87.7 %). Anal. Calcd. for C51
H
79
N
7 6
O Fe
2
(997.9 g mol ): C,
1.4; H, 7.9; N, 9.8 %; found: C, 61.2; H, 7.6; N, 9.1 %.
L3: 2-Hydroxybenzaldehyde (4.88 g, 40 mmol) was
added to an ethanolic solution (100 mL) of 1,8-diaminooctane
2.89 g, 20 mmol) and the reaction mixture was refluxed for
h in the presence of a few drops of glacial acetic acid. The
yellow crystalline solid obtained from the cooled reaction
mixture was filtered, washed with ethanol and left to dry at
room temperature. Yield: 5.37 g (76.1 %). H NMR (CDCl
.2-1.7 (m, 4H), 3.5 (t, 1H), 6.8 (t, 1H), 6.9 (d, 1H), 7.2 (t,
H), 7.3 (d, 1H), 8.3 (s, 1H), 13.6 (s, 1H). Anal. Calcd. for
H
2
(
3
was recorded in CHCl and DMSO from 1200 to 400 nm on a
3
Shimadzu UV-visible-NIR 3600 spectrophotometer.
Thermogravimetric analysis (TGA) was done on a Perkin-
1
3
):
Elmer Pyris Diamond TG/DTA thermal instrument under N
2
1
1
C
3
-1
at a flow rate of 10 cm min . The temperature range was 50-
-1
9
00 °C and the scan rate was 20 °C min . Differential scanning
-1
22
H
28
N
2
O
2
(352.5 g mol ): C, 75; H, 8; N, 8 %; found: C,
5.3; H, 7.9; N, 8.2 %.
Fe (OOC(CH
Fe(OOC(CH
0.27 g, 0. 76 mmol) were refluxed in ethanol (100 mL) for
h. The brown powder formed was filtered and dried at room
temperature. Yield: 0.35 g (46.6 %). Anal. Calcd. for
calorimetry (DSC) was done on a Mettler Toledo DSC 822
calorimeter in the temperature range 25 °C to a maximum
7
[
2
2
)
14CH
3
)
2
(L3)(H
2
O)
4
]·2.5H
2
O (3):
L3
3
-1
2
50 °C under N at a flow rate of 20 cm min and a scan rate
2
[
(
3
2
)
14CH
3
)
2
(EtOH)] (0.42 g, 0.69 mmol) and H
2
-1
of 10 °C min . The scans were recorded during one heating-
and-cooling cycle for all complexes and the onset temperatures
were quoted for all peaks observed. Polarising optical
microscopy (POM) was carried out on an olympus polarizing
microscope equipped with a Mettler Toledo FP90 central
processor and a Linkam THMS 600 hot stage. The sample
was heated in an oven at 60 °C for a few days prior to the
-1
C
54
H
101
N
2
O
12.5Fe
2
(1090 g mol ): C, 59.4; H, 9.3; N, 2.6 %.
Found: C, 59.1; H, 8.8; N, 2.9 %.
RESULTS AND DISCUSSION
-1
analysis. The heating and cooling rates were 10 and 3 °C min ,
respectively and the magnification was 50x.
Syntheses and structural elucidation: Complex 1
([Fe(L1) ](BF ) was obtained as a dark purple powder in high
Syntheses
2
)
4 2
yield from a one-pot reaction involving 2,6-pyridinedicar-
boxaldehye, 1-aminohexadecane and iron(II) tetrafluroborate
hexahydrate (mole ratio 2:4:1, Scheme-I). It was soluble in
methanol, ethanol, dichoromethane and chloroform. Its
chemical formula was supported by CHN elemental analyses
and by IR spectroscopy discussed below.
[
Fe(L1)
2
](BF
4
)
2
(1): Fe(BF
4
)
2
·6H O (0.34 g, 1.01 mmol)
2
was added portionwise to a magnetically stirred methanolic
solution (25 mL) of 2,6-pyridinedicarboxaldehyde (0.28 g,
.07 mmol) and 1-aminohexadecane (0.97 g, 4.05 mmol) at
room temperature. The mixture was further stirred at room
temperature for 1 h. The purplish black powder obtained was
filtered and washed with diethyl ether. Yield: 1.1 g (77.2 %).
2
-1
Anal. Calcd. for C78
H, 10.3; N, 6 %. Found: C, 67.1; H, 11.4; N, 5.9 %.
Fe(OOC(CH (EtOH)]: FeSO ·7H O (5.10 g,
8.3 mmol) was added to a hot ethanolic solution (50 mL) of
CH (CH 14COONa (10.23 g, 36.7 mmol). The mixture was
H
142
N
6
2
B FeF
8
(1393.5 g mol ): C, 67.2;
2
4 CH (CH ) NH
3 2 15 2
O
O
[
2
)
14CH
3
)
2
4
2
N
1
3
2
)
Fe(BF ) ·6H O
4
2
2
heated for 0.5 h and the fine light brown powder formed was
filtered under suction, washed with distilled water followed
by ethanol and then dried in an oven at 60 °C. Yield: 8.3 g
[
Fe(L1) ](BF )
2 4 2
MeOH, RT, 1 h
Scheme-I: Equation for the preparation of compound 1

Vol. 27, No. 7 (2015)
Magnetic, Photophysical and Thermal Properties of Complexes of Iron(II) 2361
Its IR spectrum showed two strong peaks at 2916 and
-
1
2
850 cm for νasymCH
2
and νsymCH , respectively, a weak peak
2
-1
-1
at 1636 cm for νC=N, a strong peak at 1024 cm for νB-F of
–
23
-1
noncoordinated BF
νFe-N. From these, it may be inferred that L1 was coordinated
to Fe(II) ion as a neutral N -donor ligand (Fig. 2).
In contrast, complexes 2(Fe (OOC(CH (L2)(H
and 3 ([Fe (OOC(CH (L3)(H ]·2.5H O) were
obtained in high yields in step-wise reactions involving
Fe(OOC(CH (EtOH)] and H and H
4
ion and a medium peak at 519 cm for
3
2
)14CH )
2 3 2
2
O) ])
2
2
2
)
14CH
3
)
2
2
O)
4
2
(a)
[
2
)
14CH
3
)
2
2
L
2
2
3
L ,
respectively (Scheme-II). Both complexes were dinuclear with
octahedral Fe(II) centres. Complex 2 was soluble in DMSO
and THF, while complex 3 was soluble in chloroform and
dichloromethane. As for compound 1, the chemical formulae
for compounds 2 and 3 were supported by CHN elemental
analyses and IR spectroscopy.
(
b)
2
O
O
N
N
(i)
(ii)
+
+
H
2
L2
Complex2
N
H
H
2
N
H
N
NH
2
(i)
(ii)
2
2
N-(CH
2
)
8
-NH
2
H
2
L3
Complex 3
HO
Scheme-II: Equations for the preparation of compounds 2 and 3: (i) EtOH,
HOAc, 3 h reflux; (ii) [Fe(OOC(CH
reflux
2 3
)14CH )(EtOH)], EtOH, 3 h
The IR spectrum of compound 2 showed two broad peaks
-
1
centred at 3333 and 3138 cm for H-bonded H
2
O molecules,
two strong peaks at 2918 and 2850 cm for νasymCH and
, respectively, a strong peak at 1618 cm for ν(C=N),
-
1
2
-1
νsymCH
2
-1
a strong peak at 1530 cm for νasymCOO, a strong peak at 1393
-1
-1
cm for symCOO, a weak peak at 578 cm for ν(Fe-N) and a
-1
24
weak peak at 491 cm for ν(Fe-O) . For comparison, the IR
(c)
-1
spectrum of H
and a strong peak at 1615 cm for ν(C=N). Hence, it may be
inferred that in the formation of compound 2, H were doubly
2
L2 showed a weak peak at 3295 cm for ν(N-H)
Fig. 2. Proposed structures of: (a) compound 1 (BF ) ; (b) compound 2;
4
2
-
1
2
and (c) compound 3·2.5H O
2
L
2
Magnetic and photophysical properties: Complex 1 was
diamagnetic at room temperature as the value of its mass
deprotonated at pyrrole N-H, the iminyl nitrogen atoms
were not involved in the bonding and the binding mode of
–
susceptibility (χ ), determined by the Gouy method, was
g
CH
(
3
(CH
2
)
14COO ion to Fe(II) atoms was bidentate chelating
-1 25
negative. Its electronic absorption spectrum in chloroform
∆ = 137 cm ) (Fig. 2).
shows two strong intraligand bands at 473 nm (εmax = 6476
The IR spectrum of compound 3 showed a weak peak at
-
1
-1
-1
-1
-
1
-1
M cm ) and 576 nm (εmax = 7100 M cm ), a strong singlet
3
396 cm for water, two strong peaks at 2917 and 2849 cm
, respectively, a weak peak at 1612
1
metal-to-ligand charge transfer band ( MLCT) at 596 nm (εmax
for νasymCH
2
and νsymCH
2
-1
-1
9
-
1
-1
=
8710 M cm ) assigned to t2g → π* electronic transition
cm for νC=N, a strong peak at 1574 cm for νasymCOO, a
-1 -1
-1
and a weaker d-d band at 721 nm (εmax = 470 M cm ) assigned
strong peak at 1446 cm for νsymCOO, a medium peak at 592
1
1
26
-
1
-1
24
to A1g → T1g electronic transition . Hence, compound 1 was
a low-spin iron(II) complex. From this, it may be inferred that
L1 was a strong field ligand. From the electronic spectral data,
cm for νFe-N and a medium peak at 461 cm for ν(Fe-O) .
For comparison, the IR spectrum of H L3 showed a weak peak
2
-1
-1
at 3406 cm for ν(O-H), two strong peaks at 2919 cm and
-
1
the optical band gap (E
g
) for compound 1, calculated using
2
851 cm for νasymCH
2
and νsymCH , respectively and a strong
2
-1
the equation: E = hc/λ, where c = velocity of light, h = Planck
g
peak at 1633 cm for ν(C=N). Hence, it may be inferred that
27
constant and λ (absorption edge of CT band) = 688 nm) ,
was 1.8 eV.
in the formation of compound 3, the two phenolic O-H group
2
of H L3 was deprotonated and the phenolic oxygen and iminyl
In contrast, compound 2 was paramagnetic at room tempe-
nitrogen were coordinated to Fe(II) atom. In addition, the ∆
–
-1
rature. The value of χ
M
T (χ = molar magnetic susceptibility
M
value for CH
3
(CH )14COO ligand was 128 cm , suggesting a
2
25
and T = temperature in K), as determined by the Gouy method,
chelating binding mode to both Fe(II) centres (Fig. 2).

2
362 Abdullah et al.
Asian J. Chem.
3
-1
was 6.2 cm K mol at 298 K. The expected value for a dimeric
The electronic absorption spectrum of compound 3 in
28
3
-1
high spin Fe(II) octahedral complex is 6 cm K mol . From
these, it may be inferred that both Fe(II) atoms in the complex
were high spin, with negligible electronic communication
between the two Fe(II) centres. Thus, L2 ion was a weak
field ligand. The electronic absorption spectrum for the
complex in DMSO shows a shoulder at 488 nm (εmax = 3478
chloroform shows two overlapping bands at 468 nm (εmax =
-1 -1 -1 -1
114.3 M cm ) and 510 nm (εmax = 63.5 M cm ) assigned to
intraligand electronic transitions. The E
= 534 nm).
g
value was 2.3 eV (λonset
2–
Thermal properties: The thermal data (TGA and DSC)
for complexes 1-3 are shown in Table-1. The TGA traces are
shown in Fig. 4, while the DSC scans are shown in Fig. 5.
-1
-1
M cm ) assigned to the intraligand electronic transition and
a weak d-d band at 773 nm (εmax = 489 M cm ) assigned to
-1
-1
5
5
29,30
T
2g → E
g
electronic transition . The E
g
value, similarly
TABLE-1
THERMAL DATA FOR COMPLEXES 1-3
calculated as for compound 1 using λ = 630 nm, was 1.9 eV.
For compound 3, the value of χ T, as determined by the
Gouy method, was 4.17 cm K mol at 300 K. Since low spin
Fe(II) is diamagnetic (t2g ) and the expected χ
complex with two high spin Fe(II) atoms and g = 1.3 (see
below) is 2.54 cm K mol , it may be inferred that compound
comprised of two high spin Fe(II) atoms at this temperature .
Additionally for compound 3, its temperature-dependence
magnetic susceptibility was measured using a SQUID magne-
tometer in the temperature range 300-2 K. The experimental
-
1
M
TGA
Tdec (°C)
DSC Tonset/°C (∆H/kJ mol )
Heating
Complex
3
-1
Cooling
6
T value for a
260
62.6
89.6
+16.0) (+94.1)
44.5
(–54.1)
166. 57.6 40.6
M
1
2
3
–
–
–
(
29
3
-1
56.4
85.3
176.8
205
250
(
–11.7) (+64.2) (+55.6) (.31.8 –21.9 (–28.6
7*
+48.7)
31
3
7
–
–
–
–
–
(
* Two overlapping endotherms
curve of χ
M
T versus T (Fig. 3) shows a good fit with the theore-
The TGA trace for compound 1 (Fig. 4a) shows a gradual
tical curve constructed from the formula for a symmetrical
weight loss totaling 90.2 % on heating from 260 °C to about
28
–
4
dinuclear complex given below and inserting the values of g
6
40 °C. This may be due to the decomposition of BF
ion and
-1
=
1.3 and J (the isotropic interaction parameter) = -28.4 cm
L1 ligand (expected 93.3 %). The amount of residue above
this temperature was 9.8 %. For compound 2, the TGA trace
into the formulae:
(
Fig. 4b) shows a rapid weight loss of 90.4 % on heating from

E(S)
2
2
Ng β Σ S(S + 1) exp –
about 205 to 620 °C. This may be due to evaporation of
coordinated H
L2 ligands (expected 88.8 %). The amount of residue above
this temperature was 9.6 %. For compound 3, the TGA trace
s



kT 
–
χm =
2
O and decomposition of CH
3
(CH )14COO and
2

S 
Σ (2S + 1) exp –
S


kT


(
Fig. 4c) shows an initial weight loss of 4.1 % in the tempe-
rature range 100-250 °C, assigned to evaporation of lattice
O (expected 3.5 %). On further heating to about 660 °C, it
suffered a total weight loss of 78 %, assigned to loss of coordi-
J
E(S) = –
S(S + 1)
2
H
2
From Fig. 3, it is noted that the χ T values decreased
M
3
-1
3
-1
–
gradually from 4.15 cm K mol at 294 K to 2.03 cm K mol
nated H
8
1
2
O and decomposition of CH
5.1 %). The amount of residue above this temperature was
7.9 %.
3 2
(CH )14COO (expected
3
-1
at 8.8 K and then more rapidly to about 1.78 cm K mol at
K as a result of zero-field splitting. It is also noted that the g
4
value for compound 3 was significantly lower than the theore-
tical value (2.0023), suggesting a highly distorted octahedral
environment, expected for high spin Fe(II) atoms due to the
1
00
-1
80
weak Fe-L bonds. The low J value (-28.4 cm ) indicates a
weak antiferromagnetic interaction between the two Fe(II)
centres, postulated to occur through H-bonds between the
Complex 1
Complex 2
Complex 3
60
40
20
0
32
coordinated and lattice H O . The results suggest a normal
2
but incomplete SCO behaviour in this temperature range.
5
4
3
5
0
200
350
500
650
800
Temperature (°C)
Fig. 4. TGA traces of (a) compound 1; (b) compound 2; and (c) compound 3
2
Experimental χMT curve
For phase transitions, the DSC of complex 1 (Fig. 5a)
shows two endotherms on heating at 62.6 °C (∆H = +16.0 kJ
Fit χMT curve
1
-1
0
0
mol ) assigned to crystal-to-crystal transition and at 89.6 °C
50
100
150
200
250
300
-1
(
∆H = +94.1 kJ mol ) assigned to crystal-to-mesophase
Temperature (K)
transition. On cooling from 150 °C, there was an exotherm at
-1
Fig. 3. Plot of χ
M
T vs. T for compound 3
44.5 °C (∆H = -54.1 kJ mol ) assigned to mesophase-to-crystal

Vol. 27, No. 7 (2015)
Magnetic, Photophysical and Thermal Properties of Complexes of Iron(II) 2363
1
4
transition. The sample, sandwiched between two glass covers,
was then heated on a hot stage and the changes observed under
a polarized optical microscope (POM) were as follows: it
melted at about 89 °C and then cleared to an isotropic liquid
at 193 °C. On cooling from the isotropic liquid phase, batonetts
of smectic A developed at 133 °C, which transformed into the
smectic A phase at 126 °C (Fig. 6b). Hence, the complex has
liquid crystal properties of a calamitic mesogen. Similar
12
(a)
10
8
6
4
2
0
2
4
6
Heating
Cooling
-
-
-
33
mesophase was found for [Co(C16-terpy)
2
](BF
4
)
2
compound .
For compound 2, its DSC (Fig. 5b) shows three endo-
-1
therms on heating at 56.4 °C (∆H = +11.7 kJ mol ) assigned
-8
to H-bonds breaking involving coordinated water, at 85.3 °C
0
50
100
150
200
-
1
(
∆H = +64.2 kJ mol ) assigned to crystal-crystal transititon
Temperature (°C)
-1
and 176.8 °C (∆H = +55.6 kJ mol ) assigned to crystal-to-
mesophase transition. On cooling from 250 °C, three exo-
therms formed at 166.4 °C (∆H = -31.8 kJ mol ), 57.6 °C (∆H
-21.9 kJ mol ) and 40.6 °C (ÄH = -28.6 kJ mol ), all of
15
-1
-1
-1
10
5
=
(b)
which cannot be assigned with certainty. The sample, observed
under POM, was found to darken at about 83 °C and then
melted at about 175 °C. On cooling from 250 °C, an optical
texture was observed at 209 °C (Fig. 6c).
Heating
0
For compound 3, its DSC (Fig. 5c) shows two overlapping
-1
Cooling
endotherms on heating at 77 °C (∆Hcombined = -48 kJ mol ),
assigned to crystal-to-crystal and crystal-to-isotropic liquid
transitions (the latter was observed at 104 °C under POM). Its
DSC shows no peaks on cooling from 180 °C to room tempe-
rature and POM did not show any optical textures. Hence, it
may be concluded that 3 was not mesogenic.
-5
-10
0
50
100
150
200
250
300
Temperature (°C)
2
.0
1.5
.0
.5
Conclusion
(c)
Heating
1
[
2
Fe(L1) ](BF
4
) (1), [Fe
2
(OOC(CH
2
)
14CH
3
)
2
(L2) (H
2
O)
2
]
0
(
2) and [Fe (OOC(CH
2
2
)
14CH
3
)
2
(L3)(H O)
2
4
]·2.5 H O (3) were
2
0
new Fe(II) complexes of three structurally different Schiff
bases. These complexes were thermally stable (Tdec > 200 °C)
and except for compound 2, has melting temperatures lower
than 100 °C. Complex 1 has one low-spin Fe(II) atom, low
optical band gap (1.8 eV) and exhibited enantiotropic SmA
mesomorphism. Complex 2 has two high-spin Fe(II) atoms,
low optical bandgap (1.9 eV) and exhibited mesomorphism
-0.5
Cooling
-1.0
-1.5
0
50
100
150
200
Temperature (°C)
Fig. 5. DSC scans for one heating-cooling cycle of: compound 1 (a);
compound 2 (b); and compound 3 (c)
(
s). Complex 3 also has two high-spin Fe(II) atoms at room
(
a)
(b)
(c)
Fig. 6. Photomicrographs of: compound 1 on cooling from the isotropic liquid phase at 133 °C (a) and 126 °C (b); and compound 2 on cooling at 209 °C

2
364 Abdullah et al.
Asian J. Chem.
1
1
1
0. S. Günes and N.S. Sariciftci, Inorg. Chim. Acta, 361, 581 (2008).
1. N. Sekar and V.Y. Gehlot, Resonance, 15, 819 (2010).
2. A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, Chem. Rev.,
temperature with weak antiferromagnetic interaction and
incomplete SCO at low temperature, large optical bandgap
(
2.3 eV), but no liquid crystal properties. Hence, these comp-
1
10, 6595 (2010).
lexes are potential SCO materials, but only compound 1 is a
potential dye-sensitized solar cell material.
13. J. Song, Z. Luo, H. Zhu, Z. Huang, T. Lian, A.L. Kaledin, D.G. Musaev,
S. Lense, K.I. Hardcastle and L. Hill, Inorg. Chim. Acta, 363, 4381 (2010).
1
1
1
1
4. R.M. O'Donnell, P.G. Johansson, M. Abrahamsson and G.J. Meyer,
Inorg. Chem., 52, 6839 (2013).
5. P.G. Bomben, K.C.D. Robson, B.D. Koivisto and C.P. Berlinguette,
Coord. Chem. Rev., 256, 1438 (2012).
ACKNOWLEDGEMENTS
The authors acknowledge the Malaysia Ministry of
Education for High Impact Research Grant (UM.C/625/1/HIR/
MOHE/05) and University of Malaya for postgraduate research
grants (PV056-2012A and PG023-2013A). Thanks are also
due to Prof. MalcolmA. Halcrow, School of Chemistry, Univer-
sity of Leeds, Leeds, United Kingdom for useful suggestions
and Prof. Takayoshi Kuroda-Sowa, Department of Chemistry,
Faculty of Science and Engineering Kinki University, Osaka,
Japan for providing the use of Quantum Design MPMS XL
EverCool SQUID magnetometer.
6. V.B. Badwaik, R.D. Deshmukh and A.S. Aswar, J. Coord. Chem., 62,
2
037 (2009).
7. Y.-G. Li, D.-H. Shi, H.-L. Zhu, H. Yan and S.W. Ng, Inorg. Chim. Acta,
360, 2881 (2007).
1
1
8. P.G. Cozzi, Chem. Soc. Rev., 33, 410 (2004).
9. A.D. Garnovskii, A.L. Nivorozhkin and V.I. Minkin, Coord. Chem. Rev.,
1
26, 1 (1993).
2
0. A.M. Giroud-Godquin, Coord. Chem. Rev., 178-180, 1485 (1998).
21. G.S. Attard and P.R. Cullum, Liq. Cryst., 8, 299 (1990).
2
2
2. S.T. Ha, G.Y. Yeap and P.L. Boey, Int. J. Phys. Sci., 5, 2185 (2010).
3. J. Seo, S.T. Moon, J. Kim, S.S. Lee and K.M. Park, Bull. Korean Chem.
Soc., 24, 17 (2003).
2
4. B.C. Smith, Infrared Spectral Interpretation: A Systematic Approach,
CRC Press, United States (1998).
REFERENCES
2
2
5. G.B. Deacon and R.J. Philips, Coord. Chem. Rev., 33, 227 (1980).
6. A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, Amsterdam,
edn 2, p. 437 (1984).
7. C. Huang, Y. Chan, F. Liu, D. Tang, J. Yang, Y. Lai, J. Li and Y. Liu, J.
Mater. Chem., 1, 5402 (2013).
1
.
P. Gütlich and H.A. Goodwin, Spin Crossover in Transition Metal Com-
pounds, In: Topics in Current Chemistry, Springer, Berlin-Heidelberg,
pp. 233-235 (2004).
A. Abedi, V. Amani, R. Bocá, L. Dlhán, H.R. Khavasi and N. Safari,
Inorg. Chim. Acta, 395, 58 (2013).
C.Atmani, F. El Hajj, S. Benmansour, M. Marchivie, S. Triki, F. Conan,
V. Patinec, H. Handel, G. Dupouy and C.J. Gómez-García, Coord. Chem.
Rev., 254, 1559 (2010).
A.B. Gaspar, M. Seredyuk and P. Gütlich, J. Mol. Struct., 924-926, 9 (2009).
Y. Bodenthin, G. Schwarz, Z. Tomkowicz, M. Lommel, Th. Geue, W.
Haase, H. Möhwald, U. Pietsch and D.G. Kurth, Coord. Chem. Rev.,
2
2
3
.
.
2
2
8. O. Kahn, Molecular Magnetism,VCH Publishers Inc., NewYork (1993).
9. J.P. Jesson, S. Trofimenko and D.R. Eaton, J. Am. Chem. Soc., 89,
3
158 (1967).
3
3
0. G. Sowjanya, N.C.G. Reddy, S.L. Reddy, B.J. Reddy and R.L. Frost,
Spectrochim. Acta A, 71, 751 (2008).
1. P. Gütlich, A.B. Gaspar and Y. Garcia, Beilstein J. Org. Chem., 9, 342
4
5
.
.
(
2013).
2
53, 2414 (2009).
3
3
2. Y. Farina and D.A. Rice, Pertanika J. Sci. Technol., 3, 211 (1995).
3. S. Hayami, Y. Kojima, D. Urakami, K. Ohta and K. Inoue, Polyhedron,
6
7
8
9
.
.
.
.
P. Gütlich, Struct. Bond., 44, 83 (1981).
S. Ferrere and B.A. Gregg, J. Am. Chem. Soc., 120, 843 (1998).
S. Ferrere, Chem. Mater., 12, 1083 (2000).
2
8, 2053 (2009).
S. Ferrere, Inorg. Chim. Acta, 329, 79 (2002).