Structural and spectral studies of an iron(III) complex [Fe(Pranthas) 2][FeCl4] derived from 2-acetylpyridine-N(4), N(4)-(butane-1, 4-diyl) thiosemicarbazone (HPranthas)

Article abstract of DOI:10.1016/j.molstruc.2004.10.036

A novel iron(III) complex of 2-acetylpyridine N(4), N(4)-(butyl-1, 4-diyl) thiosemicarbazone (HPranthas), [Fe(Pranthas)₂]FeCl₄ was synthesized and physico-chemically characterized by means of partial elemental analysis, magnetic meas

Full text of DOI:10.1016/j.molstruc.2004.10.036

Journal of Molecular Structure 737 (2005) 61–67
www.elsevier.com/locate/molstruc
Structural and spectral studies of an iron(III) complex
[Fe(Pranthas)2][FeCl4] derived from 2-acetylpyridine-N(4),
N(4)-(butane-1, 4-diyl) thiosemicarbazone (HPranthas)
A. Sreekantha, Hoong-Kun Funb, M.R. Prathapachandra Kurupa,
*
aDepartment of Applied Chemistry, Cochin University of Science and Technology, Kochi, Kerala 682 022, India
bX-ray Crystallography Unit, School of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia
Received 5 July 2004; revised 8 October 2004; accepted 21 October 2004
Abstract
A novel iron(III) complex of 2-acetylpyridine N(4), N(4)-(butyl-1, 4-diyl) thiosemicarbazone (HPranthas), [Fe(Pranthas)2]FeCl4 was
synthesized and physico-chemically characterized by means of partial elemental analysis, magnetic measurements (polycrystalline state),
2
2
1
¨
UV–Vis and IR spectroscopies. The presence of spin-paired iron(III) cation with dxzdyzdxy ground state is revealed by the EPR and Mossbauer
spectral data. Structure of the free ligand HPranthas and the complex [Fe(Pranthas)2]FeCl4 were solved by single crystal X-ray diffraction.
The framework of iron(III) complex consists of a discrete monomeric cationic entity containing low spin iron(III) in a slightly distorted
octahedral environment. The metal ion is bonded to one sulfur and two nitrogens of each thiosemicarbazone molecule. The
tetrachloroferrate(III) ion acts as counterion.
q 2005 Elsevier B.V. All rights reserved.
¨
Keywords: Iron(III) complex; Thiosemicarbazone; Single crystal X-ray diffraction; Mossbauer spectrum; EPR spectrum; IR spectrum
1. Introduction
The success in therapeutic applications of N-heterocyclic
thiosemicarbazones for removing excess iron from iron-
loaded mice through chelation therapy is quite remarkable
[4]. 2-Acetylpyridine thiosemicarbazones were the first
thiosemicarbazones in which antimalarial activity was
detected, and the highest activity is reported when the
N(4) position is either disubstituted or part of a ring system
[5]. There are some reports on the iron(III) complexes of
biologically active 2-acetylpyridine thiosemicarbazones
[6,7]. Recently we have reported the copper(II) [8] and
iron(III) [9] complexes synthesized from 2-benzoylpyridine
N(4), N(4)-(butane-1, 4-diyl)thiosemicarbazone. This paper
stems from our interests in the investigation of some
biologically active 2-acetylpyridine thiosemicarbazones
and their metal complexes. In continuation of our
investigations on the thiosemicarbazones and semicarba-
zones and their metal complexes [10–12], we have
synthesized 2-acetylpyridine N(4), N(4)-(butane-1, 4-
diyl)thiosemicarbazone (HPranthas), and its iron(III) com-
plex using ferric chloride.
Thiosemicarbazones and their metal complexes have
been subject of interest in numerous studies because of their
chemical and biological properties [1,2]. Thiosemicarba-
zones generally exist in the thione form in the solid state but
exist as an equilibrium mixture of thione and thioenol forms
in solution (A and B) which is essential for their versatile
chelating behavior.
The well documented biological activities of several
heterocyclic thiosemicarbazones have been often attributed
to a chelation phenomenon with transition metal ions [3].
* Corresponding author. Tel.: C91 484 2575804; fax: C91 484 2577595.
E-mail address: mrp@cusat.ac.in (M.R. Prathapachandra Kurup).
0022-2860/$ - see front matter q 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2004.10.036

62
A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
2. Experimental
2.3. Synthesis of 4-methyl-4-phenyl-3-thiosemicarbazide
(1a)
2.1. General
A solution of carboxymethyl N-methyl N-phenyldithio-
carbamate in 20 ml 99% hydrazine hydrate and 10 ml of
water was heated on the rings of a steam bath. After 3 min
crystals begin to separate. Heating was continued for
22 min. The crystals were collected by filtration, washed
well with water and dried under a heat lamp. The crude
product was recrystallized from a mixture of 50 ml ethanol
and 25 ml of water. This gave 10.8 g of stout colorless rods
of 4-methyl-4-phenyl-3-thiosemicarbazide (1a). Mp 124–
125 8C.
2-Acetylpyridine (Aldrich), pyrrolidine (SRL), N-
methylaniline (Merck), thiosemicarbazide (SRL), carbon
disulfide (Merck), hydrazine hydrate (99%, SRL) and
ferric chloride (Merck) were used as received. All solvents
were distilled before use. 2-Acetylpyridine N(4), N(4)-
(butane-1, 4-diyl)thiosemicarbazone (HPranthas) was syn-
thesized (Scheme 1) by the following adoption of a
reported procedure [13].
2.2. Synthesis of carboxymethyl N-methyl
N-phenyldithiocarbamate
2.4. Pyrrolidine-1-thiocarboxylic acid hydrazide (1b)
A solution of 1.0 g of 1a in 5 ml of acetonitrile was
treated with 395 mg of pyrrolidine and the solution was
heated under reflux for 15 min. The solution was chilled and
the microporous off white crystals separated were collected
and washed with acetonitrile. This afforded 570 mg of 1b.
Mp 174–175 8C.
A mixture consisting of 12.0 ml (15.2 g, 0.2 mol) of CS2
and 21.6 ml N-methylaniline was treated with a solution of
8.4 g (0.21 mol) of NaOH in 250 ml water. After stirring at
room temperature for 4 h, the organic layer had disappeared.
At this point, the straw colored solution was treated with
23.2 g (0.20 mol) of sodium chloroacetate and allowed to
stand overnight for 17 h. The solution was acidified with
25 ml of conc. HCl and the solid which separated was
collected and dried. This afforded 39.7 g of pale buff colored
carboxymethyl N-methyl N-phenyldithiocarbamate. Mp
197–198 8C.
2.5. Synthesis of HPranthas
A solution 1 g (2 mmol) of 4-methyl-4-phenyl-3-
thiosemicarbazide in 5 ml of acetonitrile was treated
with 2 mmol of pyrrolidine-1-thiocarboxylic acid
Scheme 1.

A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
63
hydrazide (1b). The solution was heated at reflux for 2 h.
2.7. Physical methods
The solution was chilled and the crystals that separated
were collected and washed well with acetonitrile. This
afforded stout yellow rods of HPranthas in 65% yield. The
compound was recrystallized from methanol, mp 148 8C.
X-ray quality single crystals of the compound were grown
from a mixture of methanol and chloroform. Anal. Calcd
(Found) %: C, 58.21 (58.03); H, 6.57 (6.49); N, 22.39
(22.56). UV–Vis, cmK1(log 3, l molK1 cmK1): 34,480
(4.11), 30,120 (3.96), 32,250 (4.08). IR (cmK1): 1604 s,
Microanalyses were carried out using a Heraeus
Elemental Analyzer at CDRI, Lucknow, India. Infrared
spectra were recorded on a Shimadzu DR 8001 series FT-
IR instrument as KBr pellets in the range 400–4000 cmK1
and far IR spectra were recorded in the range 50–
500 cmK1 on a NICOLET MAGNA 550 FT-IR spec-
trometer using polyethylene pellets at RSIC, IIT, Bombay,
India. Electronic spectra were recorded in the 900–250 nm
range in a diffused reflectance mode in MgO matrix in
1
1118 m, 1380 s, 843 sh. H NMR (CDCl3–TMS) d (ppm):
1
N(2)H, 8.63 s; C(11)H, 8.12 d; C(10)H, 7.61 dd; C(9)H,
7.79 dd; C(8)H, 7.58 d; C(12)H3, 2.2 s; C(1-4)H, 3.48–
3.62 m. 13C{1H} NMR d (ppm): C(5), 185.32; C(6),
151.13; C(7), 147.92; C(11), 137.19; C(8), 124.10; C(9),
119.77; C(10); 119.13, C(12), 13.66; C2 and C3, 52.11;
C1 and C4, 65.79.
Ocean Optics SD 200 fiber optic Spectrophotometer. H
and 13C NMR spectra were obtained in a Brucker DRX
500 instrument using CDCl3 as the solvent and TMS as
the internal reference. Magnetic measurements were made
in the polycrystalline state on a home built simple Gouy
balance using Hg[Co(SCN)4] as calibrant. EPR spectrum
was recorded in a Bruker ESP300, X-band CW spec-
trometer operating at 9.52 GHz equipped with a liquid
nitrogen cryostat. The spectrum was recorded with a
modulation amplitude of 0.05 (0.1) mT and 100 kHz
modulation frequency, and the field was calibrated by
using 2,2-diphenyl-1-picrylhydrazyl (DPPH) with a g
2.6. Synthesis of [Fe(Pranthas)2]FeCl4
To a methanolic solution of ferric chloride (1 mmol)
was added a solution of HPranthas (1 mmol) in chloro-
form and refluxed for 30 min. The resulting deep green
colored solution was evaporated to half its volume. On
cooling dark brown shining crystals of the compound
which separated out (yield, 70%) were washed with ether
and dried over P4O10 in vacuo. X-ray quality single
crystals of the compound were grown by slow evaporation
of a methanolic solution of the complex in 7 days. Anal.
Calcd (Found) %: C, 38.54 (38.53); H, 4.00 (4.04); N,
14.91 (14.98).
¨
value of 2.0036. Mossbauer spectrum was recorded on a
constant-acceleration spectrometer with multi channel
analyzer using a 57Co source in a rhodium matrix at
Inter University Consortium, Indore, India.
2.8. X-ray crystallography
A pale yellow monoclinic crystal of HPranthas and a
dark brown triclinic crystal of Fe(Pranthas)2FeCl4 having
Table 1
Crystal data and structure refinement parameters
HPranthas
Fe(Pranthas)2FeCl4
Empirical formula
Formula weight (M)
Temperature (T), K
C12H16N4S
248.35
293
C24H30Cl4Fe2N8S2
748.18
293(2)
˚
Wave length (Mo Ka), A
Crystal system/Space group
Unit cell dimensions
0.71073
0.71073
Monoclinic, P21/c
˚
Triclinic, P-1
˚
˚
˚
aZ15.627 A, aZ90.0008; bZ22.115 A,
aZ8.7431(7) A, aZ82.619(2)8; bZ13.4881(11) A,
bZ87.482(2)8; cZ14.4522(12) A, gZ75.535(2)8
1636.5(2)
˚
˚
bZ94.3628; cZ7.444 A, gZ90.0008
2565.1
3
˚
Volume (V), A
Z, Calculated density (r), mg mK3
Absorption coefficient (m), mmK1
F(000)
8, 1.286
2, 1.518
0.237
1.370
1056
0.52!0.40!0.20 mm3
2.61–25.00
764
0.44!0.26!0.26 mm3
2.24–25.00
Crystal size
q Range for data collection (8)
Limiting indices
K17%h%8, K24%k%22, K8%l%8
25.00, 92.8%
K8%h%10, K15%k%16, K17%l%15 1.095
25.00, 97.7%
Completeness to 2q
Max. and min. transmission
Goodness-of-fit on F2
Final R indices [IO2s(I)]
R indices (all data)
0.9542 and 0.8869
1.112
0.7172 and 0.5840
1.095
R1Z0.0861, wR2Z0.2135
R1Z0.1200, wR2Z0.2373
˚
0.468 and K0.432 e A
R1Z0.0564, wR2Z0.1175
R1Z0.0753, wR2Z0.1296
0.507 and K0.372 e AK3
K3
Largest diff. peak and hole

64
A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
appropriate dimensions were sealed in a glass capillary,
and intensity data were measured at room temperature
(293 K) on an Bruker 1-k ccs diffractometer equipped
two crystallographically independent molecules A and B in
the asymmetric unit of the compound HPranthas with bond
lengths and angles which agree with each other and are
within normal ranges. Both molecules are related by a local
pseudo-twofold rotation axis and exist in an E configuration
about the C6–N3 and C5–N2 bonds relative to the N3–N2
bond. The S and hydrazine N3 atoms are in Z configuration
with respect to the C5–N2 bond. In both molecules the five
membered pyrrolidine ring is not planar and tends towards
an envelope conformation. In both molecules, the relative
conformations of the pyridine ring and the methyl group
with respect to the plane of the thiosemicarbazone are
conditioned by the sp2 hybridized carbon atom. The C5–S1
˚
with graphite-monochromated Mo Ka (lZ0.71073 A)
radiation. The trial structure was obtained by direct
methods using SHELXL-97 and refined by full-matrix least
squares on F2 (SHELXS-97) [14]. The non-hydrogen atoms
were refined with anisotropic thermal parameters. All
hydrogen atoms were geometrically fixed and allowed to
refine using a riding model. Absorption corrections were
employed using j-Scan. The crystallographic data along
with details of structure solution refinements are given in
Table 1.
˚
˚
(1.692(4) A) and C6–N3 (1.293(6) A) bond lengths are
typical of double bond character in agreement with
previously reported thiosemicarbazone derivatives [17,18].
3. Results and discussion
The complex is dark brown and readily soluble in
polar organic solvents. From the analytical data it can
be formulated as either [Fe(Pranthas)2]FeCl4 or
[FePranthasCl2] but the crystallographic and spectroscopic
as well as spectroscopic data indicated that the FeClK4 anion
was formed in the reaction. The compound was found to
be a 1:1 electrolyte [15] in DMF with Lm value near to
105 UK1 cm2 molK1. The cation centre of the complex is
expected to contain two deprotonated ligands attached to
low-spin iron(III). Magnetic moment has been determined
for the complex at room temperature in the polycrystalline
state, which was found to be 4.35 BM, on a per ion basis,
which is consistent with one high-spin iron and one low-spin
iron(III) in the molecule [7,16]. The complete assignment of
the two spin states of the complex was done on the basis of
3.2. Molecular and crystal structure
of [Fe(Pranthas)2][FeCl4]
Fig. 2 shows the molecular structure of the compound
along with atom numbering scheme. Table 3 presents
selected bond lengths and angles. The low-spin iron(III) ion
has a distorted octahedral coordination in the complex. The
pattern of coordination is similar to that observed in
complexes of similar type [9,19,20]. The two molecules of
monodeprotonated ligand, coordinate to iron via pyridyl
nitrogens, azomethine nitrogens and thiolato sulfurs in a
meridional arrangement to form four five membered chelate
rings. The crystallographic asymmetric unit contains a
[Fe(Pranthas)2] cation and a tetrachloroferrate [FeCl4]K
anion.
¨
EPR and Mossbauer measurements.
There is a slight shortening of the Fe–N(azomethine)
bond distance compared to Fe–N(py) distances; this may
be attributed to the fact that the azomethine nitrogen is a
stronger base compared with the pyridyl nitrogen. The two
azomethine nitrogen atoms are trans to each other, while
the pyridyl nitrogen atoms and thiolato sulfur atoms are in
3.1. Molecular and crystal structure of HPranthas
Fig. 1 shows the molecular structure of HPranthas and
Table 2 lists the selected bond lengths and angles. There are
Fig. 1. ORTEP diagram of the compound HPranthas, with 50% ellipsoidal probability. Hydrogen atoms are shown as smaller spheres of arbitrary radii.

A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
65
Table 2
Selected bond lengths and angles of HPranthas
Table 3
Selected bond lengths and angles of complex
˚
Bond angles (8)
Bond lengths
Bond angles
Bond lengths (A)
Fe(1)–N(7)
S(1A)–C(5A)
N(1A)–C(5A)
N(2A)–C(5A)
N(2A)–N(3A)
N(3A)–C(6A)
C(1A)–C(2A)
X–H/Cg
1.692(4)
1.347(6)
1.349(6)
1.364(5)
1.293(6)
1.511(9)
C(5A)–N(1A)–C(4A)
124.0
1.918(3)
N(7)–Fe(1)–
N(3)
176.48(16)
80.47(15)
103.03(15)
98.98(14)
95.42(11)
85.12(11)
89.18(10)
164.56(11)
85.52(11)
90.97(11)
165.57(11)
C(5A)–N(2A)–N(3A) 121.4
C(6A)–N(3A)–N(2A) 118.6
Fe(1)–N(3)
Fe(1)–N(8)
Fe(1)–N(4)
Fe(1)–S(1)
Fe(1)–S(2)
Fe(2)–Cl(2)
Fe(2)–Cl(3)
Fe(2)–Cl(4)
Fe(2)–Cl(1)
S(1)–C(5)
1.928(3)
N(7)–Fe(1)–
N(8)
C(2A)–C(3A)–C(4A)
105.3
N(1A)–C(5A)–N(2A) 114.7
1.986(3)
N(3)–Fe(1)–
N(8)
N(2A)–C(5A)–S(1A)
˚
124.0
˚
H/Cg (A) X/Cg (A)
:X–H/
Cg (8)
146.67
1.986(3)
N(7)–Fe(1)–
N(4)
C9–H9BA–Cg(4)a
2.8854 3.6978
2.2151(13)
2.2194(13)
2.1820(19)
2.1831(19)
2.187(2)
N(7)–Fe(1)–
S(1)
aZx, 1/2Ky, 1/2Cz Cg(4)ZN4B,C7B,C8B, C9B, C10B, C11B
˚
˚
N(3)–Fe(1)–
S(1)
D–H/A
H/A (A)
D/A (A)
:D–H/
A (8)
136
N(8)–Fe(1)–
S(1)
N2A–H2AC/N4A
N2B–H2Bc/N4B
C3B–H3BC/S1Ab
bZ1Cx, y, z
1.93
1.95
2.83
2.6184
2.6249
3.7531
135
N(4)–Fe(1)–
S(1)
160
N(7)–Fe(1)–
S(2)
2.1929(17)
1.741(4)
N(3)–Fe(1)–
S(2)
cis positions. The tetrachloroferrate anion present in the
molecule is in a slightly distorted tetrahedral geometry
N(8)–Fe(1)–
S(2)
˚
with equal bond lengths (w2.187 A) and angles
(w109.468).
C–H/p interactions
H/Cg
X/Cg
3.1062
3.2959
3.2420
3.9134
3.8528
X–H/Cg
102.19
100.24
100.10
148.28
145.42
C(12)–H(12A)/Cg(4)a 2.7738
C(23)–H(23A)/Cg(1)a 3.0009
C(23)–H(23A)/Cg(3)a 2.9469
C(22)–H(22A)/Cg(7)b 3.0917
3.3. IR and electronic spectra
C(13)–H(13B)/Cg(8)c
3.0146
Table 4 lists the assignments of IR bands most useful for
the establishment of the mode of coordination of the
thiosemicarbazone and its iron(III) complex. Coordination
of the azomethine nitrogen is indicated by the lowering of
the band at 1604 to 1597 cmK1. The band is not a pure
vibrational CaN stretching, but it contains also a contri-
bution from CaC vibrations of the pyridyl ring [21]. Two
bands at z1380 and 843 cmK1 were assigned to the C–S
stretching and bending mode of vibrations. These bands are
observed at lower energy in the complex, indicating
H-bonding interactions
D/A
2.82
H/A
3.6626
D–H/A
152
C(9)–H(9A)/Cl(3)
Equivalent position code
Cg(1)ZFe(1), S(1), C(5),
N(2), N(3)
aZx, y, z, bZK1Cx, y, z, cZ1Cx, y, z Cg(3)ZFe(1), N(4), C(8),
C(6), N(3)
Cg(4)ZFe(1), N(8), C(20),
C(18), N(7)
Cg(7)ZN(4), C(12), C(11),
C(10), C(9), C(8)
Cg(8)ZN(8), C(20), C(21),
C(22), C(23), C(24)
coordination of thiolato sulfur. Another band which is
considered to be sensitive to coordination is n(N–N) which
is raised in energy due to coordination because of the
increased double bond character. The newly formed CaN
bond due to the deprotonation of the ligand is also observed
z1648 cmK1
.
The far-IR spectrum of the complex has a broad split
band assignable to n3(FeCl4) at 376 cmK1. This splitting
may be due to the steric factors which reduce the symmetry
from tetrahedral [22,23]. Similarly the band corresponding
to n4 at 123 cmK1 is also found to be split due to site effects.
The other two stretching modes n1 and n2 are found at 325
and 100 cmK1, respectively. Bands at 526 and 353 cmK1
were assigned to the Fe–N vibrations of the azomethine and
pyridyl nitrogen coordination, respectively. The Fe–S bond
Fig. 2. ORTEP diagram of the compound [Fe(Pranthas)2]FeCl4 with 50%
ellipsoidal probability. Hydrogen atoms are omitted for clarity.
stretching vibrations is found at 419 cmK1
.

66
A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
Table 4
common for low spin octahedral complexes [26]. The
observed anisotropic character is due to rhombic distortion
common for spin paired iron(III) complexes. The small
deviation of the anisotropic g values from 2.0 suggests that
the unpaired electrons is in the dxy orbital with a dx2zdy2zdx1y
ground state configuration. It is interesting to note a sharp
but small signal corresponding to gZ4.264 indicating the
presence of high spin species which was identified as
[FeCl4]K anion. The absence of ligand hyperfine splitting of
the highest g-values indicate no interaction of the unpaired
electron with the imine nitrogen.
IR spectral data of the ligand and it’s iron(III) complex
Compound
HPranthas
n(CaN)
n(NaC)
n(NaN)
n/d(CaS)
1604 s
–
1118 s
1193 s
n(Fe–S)
1380 s, 843 w
1239 m, 839 w
n(FeCl4)
Fe(Pranthas)2- 1597 s
1648 s
n(Fe–Npy)
FeCl4
n(Fe–Nazo
)
Fe(Pranthas)2- 526 w
FeCl4
353 s
419 m
376 s, 325 s,
123 s, 100 s
All values are in cmK1
.
The electronic spectra of the ligand and its iron(III)
complex in the UV region are dominated by two intense
intraligand bands around 37,030 and 29,850 cmK1 assigned
to p/p* and n/p* transitions, while coordination has
little effect on these bands. Usually n/p* transitions
involving N and S occur at a lower energy than p/p*. The
bands at 14,990 and 24,210 cmK1 in the spectrum of the
complex were assigned to d/p* transitions. These
transitions also involve S/Fe and other ligand to metal
charge transfer transitions. The band at 10,250 cmK1 is due
to d/d band which correspond to 2T2g/2T1g transition of
the d5 spin-paired systems [24].
¨
3.5. Mossbauer spectrum
¨
The Mossbauer spectrum of the complex was recorded at
298 K in order to understand and confirm the spin behavior of
¨
the system. The Mossbauer parameters calculated from the
spectra were compared with a-iron as a standard. The
positive dis value shows that the excited state is not
necessarily larger than the ground state. The high intensity
doublet in the spectrum the complex with an isomer shift
approximately at K0.13 mm sK1, characterized by a quad-
rupolar splitting DEqz2.21 mm sK1, is ascribed to the 2T2g
ground state of low spin iron(III) [27]. The 1:1 ratio between
the quadrupole split spectra is not strictly observed due to the
anisotropic absorption known as Goldansky–Karyagin
effect. The spectrum also showed of another broad,
3.4. Electron paramagnetic resonance spectrum
The EPR spectrum of the complex was recorded at 110 K
in DMF glass and spin Hamiltonian parameters were
obtained after the spectral simulations performed by Easy-
Spin package [25]. The spectrum was resolved into well-
defined rhombic symmetry with three g values viz. 2.20,
2.15 and 1.99. Fig. 3 shows the EPR spectrum of the
complex recorded in a DMF glass. This type of feature is
less intense signal corresponding to disz0.12 mm sK1
,
DEqz0.675 mm sK1 ascribed to tetrahedral high spin
iron(III) species [28]. Similar features were observed in the
spectrum of an iron(III) complex reported elsewhere [9],
where it was found that there was no change in the spectral
features even when the temperature was lowered to 20 K.
The observation of the broad line with unresolved quad-
rupolar splitting is assumed to be due to much slower spin
relaxation due to the orbital electrons of iron (Fig. 4).
Fig. 3. EPR spectrum of the complex in a solution of DMF at 110 K:
experimental spectrum (blue), simulated best fit spectrum (red). (For
interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
¨
Fig. 4. Mossbauer spectrum of the complex (298 K).

A. Sreekanth et al. / Journal of Molecular Structure 737 (2005) 61–67
67
[8] A. Sreekanth, M.R.P. Kurup, Polyhedron 22 (2003) 3321.
[9] A. Sreekanth, M.R.P. Kurup, Polyhedron 23 (2004) 1225.
4. Supplementary information
[10] A. Sreekanth, S. Sivakumar, M.R.P. Kurup, J. Mol. Struct. 655 (2003)
47.
Crystallographic data for the structural analysis has been
deposited with the Cambridge Crystallographic Data center,
CCDC 228088 for compound HPranthas and CCDC 228089
for compound [Fe(Pranthas)2]FeCl4. Copies of this infor-
mation maybe obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2, IEZ, UK (fax: C
44-1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
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¨ ¨
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Acknowledgements
One of the authors A.S. would like to thank the Cochin
University of Science and Technology for a Research
Fellowship. The authors are thankful to Dr Ajay Gupta,
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