Synthesis, EPR and M?ssbauer spectral studies of new iron(III) complexes with 2-benzoylpyridine-N(4), N(4)-(butane-1,4-diyl) thiosemicarbazone (HBpypTsc): X-ray structure of [Fe(BpypTsc)2]FeCl 4·2H2O and the free ligand

Article abstract of DOI:10.1016/j.poly.2004.01.006

Three novel iron(III) complexes of 2-benzoylpyridine N(4), N(4)-(butyl-1,4-diyl) thiosemicarbazone (HBpypTsc), [Fe(BpypTsc) ₂]ClO₄ (1), [Fe(BpypTsc)₂]NO₃ (2) and [Fe(BpypTsc)₂]FeCl₄ (3) were synthesized and physico-chemically characterized by means of partial elemental analyses, magnetic measurements (polycrystalline state), UV-Vis and IR spectroscopies. The spin Hamiltonian parameters, isomer shifts and quadrupolar splitting values of the complexes were assigned by variable temperature EPR and M?ssbauer spectra. The presence of a spin-paired iron(III) cation with d_xz ²d_yz²d_xy¹ ground state is revealed by the simulated EPR spectral data. The structures of the free ligand HBpypTsc and one of the complexes [Fe(BpypTsc)₂]FeCl ₄ (3) were solved by single crystal X-ray diffraction which authenticated a FeN₄S₂ octahedral coordination in the complex, as envisaged from the spectral data. All complexes except [Fe(BpypTsc)₂]FeCl₄ (3) were found to be low-spin S=1/2 (²T_2g), whereas 3 was found to have both low-spin ( ²T_2g) and high-spin (⁶A₁) centres.

Full text of DOI:10.1016/j.poly.2004.01.006

Polyhedron 23 (2004) 969–978
www.elsevier.com/locate/poly
€
Synthesis, EPR and Mossbauer spectral studies of new
iron(III) complexes with 2-benzoylpyridine-N(4),
N(4)-(butane-1,4-diyl) thiosemicarbazone (HBpypTsc):
X-ray structure of [Fe(BpypTsc)2]FeCl4 ꢀ 2H2O and the free ligand
1
Anandaram Sreekanth , M.R. Prathapachandra Kurup
*
Department of Applied Chemistry, Cochin University of Science and Technology, Kochi 682 022, Kerala, India
Received 11 August 2003; accepted 9 December 2003
Abstract
Three novel iron(III) complexes of 2-benzoylpyridine N(4), N(4)-(butyl-1,4-diyl) thiosemicarbazone (HBpypTsc),
[Fe(BpypTsc)2]ClO4 (1), [Fe(BpypTsc)2]NO3 (2) and [Fe(BpypTsc)2]FeCl4 (3) were synthesized and physico-chemically character-
ized by means of partial elemental analyses, magnetic measurements (polycrystalline state), UV–Vis and IR spectroscopies. The spin
Hamiltonian parameters, isomer shifts and quadrupolar splitting values of the complexes were assigned by variable temperature
2
2
1
€
EPR and Mossbauer spectra. The presence of a spin-paired iron(III) cation with dxzdyzdxy ground state is revealed by the simulated
EPR spectral data. The structures of the free ligand HBpypTsc and one of the complexes [Fe(BpypTsc)2]FeCl4 (3) were solved by
single crystal X-ray diffraction which authenticated a FeN4S2 octahedral coordination in the complex, as envisaged from the spectral
data. All complexes except [Fe(BpypTsc)2]FeCl4 (3) were found to be low-spin S ¼ 1=2 (2T2g), whereas 3 was found to have both
low-spin (2T2g) and high-spin (6A1) centres.
Ó 2004 Elsevier Ltd. All rights reserved.
€
Keywords: Iron(III) complexes; Thiosemicarbazone; Single crystal X-ray diffraction; Mossbauer spectra; EPR spectra; IR spectra
1. Introduction
phenomenon with transition metal ions [5]. The success
in therapeutic applications of N-heterocyclic thiosemic-
arbazones for removing excess iron from iron-loaded
mice through chelation therapy is quite remarkable [6].
We have previously examined the chelation behavior of
some O–N–S and N–N–S donor thiosemicarbazones
with several transition metal ions with the aim of gain-
ing more information about their nature of coordination
and related structural, spectral and biological properties
[7–11]. There are some interesting reports on the ir-
on(III) complexes of biologically active 2-acetylpyridine
thiosemicarbazones [12,13]. This paper discusses the
syntheses and spectral studies of three iron(III) com-
plexes with the title ligand 2-benzoylpyridine N(4),
N(4)-(butane-1,4-diyl)thiosemicarbazone (HBpypTsc)
(Scheme 1). A previously reported complex of a
2-acetylpyridine thiosemicarbazone prepared from
FeCl3, gave a stoichiometry FeLCl2 which suggested it
to be a five-coordinate iron(III) complex having an
The discovery of a low-spin (S ¼ 1=2) non-heme
[FeIIIN2S3] centre in the enzyme nitrile hydratase has
raised interest in mononuclear model iron(III) com-
plexes with N, S coordination [1,2]. Several groups have
structurally characterized iron(III) complexes with NxSy
coordination and compared their spectroscopic proper-
ties with the biological iron site [3,4]. The well-docu-
mented biological activities of several heterocyclic
thiosemicarbazones have often attributed to a chelation
* Corresponding author. Tel.: +91-484-2575804; fax: +91-484-
2577595.
E-mail addresses: sran@esr.phys.chem.ethz.ch (A. Sreekanth),
mrp@cusat.ac.in (M.R.P. Kurup).
1
€
Present address: Laboratorium fur Physikalische Chemie, Eid-
genossische Technische Hochschule, Honggerberg, CH-8093, Zurich,
€
Switzerland. Tel.: +41-1-6325702; fax: +41-1-6321538.
0277-5387/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.01.006

970
A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
12
11
1
N
8
S
2
14
10
3
MeOH
N
H
N
N
13
N
N
1
4
15
9
+
dil. HOAc
reflux
H
2
H2N
N
17
7
6
3
4
16
S
O
5
Scheme 1.
intermediate spin state [14]. However the structural in-
formation as well as the spectral information obtained
for a similar compound, 3 in our case, confirmed that
the previous report could be incorrectly formulated.
rated to half its volume. On cooling dark brown shining
crystals of compound 1 separated out and were washed
with ether and dried over P4O10 in vacuo.
2.4. Synthesis of [Fe(BpypTsc)2]NO3 (2)
2. Experimental
To a methanolic solution of ferric nitrate (1 mmol)
was added a solution of HBpypTsc (2 mmol) in chlo-
roform and the mixture was refluxed for 30 min. The
resulting deep green colored solution was evaporated to
half of its volume. On cooling dark brown shining
crystals of compound 2 separated out and were washed
with ether and dried over P4O10 in vacuo.
2.1. General
2-Benzoylpyridine (Lancaster), ferric chloride
(Merck) and ferric nitrate (Merck) was used as received.
Ferric perchlorate was prepared from ferric carbonate
by digesting it with perchloric acid followed by evapo-
rating the solution on a sand bath followed by sub-
sequent cooling. Caution! Perchlorate salts are
potentially explosive and should be handled with care.
Pyrrolidine-1-thiocarboxylic acid hydrazide was syn-
thesized by adopting and modifying a reported proce-
dure [15]. All solvents were distilled before use.
2.5. Synthesis of [Fe(BpypTsc)2]FeCl4 (3)
To a methanolic solution of ferric chloride (1 mmol)
was added a solution of HBpypTsc (1 mmol) in chloro-
form and the mixture was refluxed for 30 min. The re-
sulting deep green colored solution was evaporated to half
its volume. On cooling dark brown shining crystals of
compound 3 separated out and were washed with ether
and dried over P4O10 in vacuo. X-ray quality single
crystals of the compound were grown by the slow
evaporation of a methanolic solution of the complex in
7 days.
2.2. Synthesis of HBpypTsc
To a solution of pyrrolidine-1-thiocarboxylic acid
hydrazide (0.1 mol) and 2-benzoylpyridine (0.1 mol) in
20 mL methanol, 2 drops of conc. acetic acid was added
and the reaction mixture was heated under reflux for 5 h.
The reaction mixture was kept for 3 days where the deep
yellow colored crystals of HBpypTsc began to separate
in a decent yield with satisfactory analytical data. X-ray
quality single crystals of the compound were grown
from a solution of the compound HBpypTsc in chlo-
roform layered with methanol in 3 days. Melting point
2.6. Physical methods
Microanalyses were carried out using a Heraeus El-
emental 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
cmꢁ1 and far-IR spectra were recorded in the range 50–
500 cmꢁ1 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 Ocean Optics SD 200 fiber optic Spectropho-
tometer. Magnetic measurements were made in the
polycrystalline state on a home built simple Gouy bal-
ance using Hg[Co(SCN)4] as calibrant. EPR spectra
were recorded in a Bruker ESP300, X-band CW spec-
trometer operating at 9.52 GHz equipped with a liquid
1
185–186 °C. H NMR d (ppm): NH, 14.3, singlet 1H;
8.73, doublet, aromatic, 1H, J ¼ 7:5 Hz; 8.5, aromatic,
doublet, 1H; 7.1–7.8, aromatic, multiplet, 7H, 3.8, ali-
phatic, multiplet, 4H, 1.9, aliphatic, multiplet, 4H.
2.3. Synthesis of [Fe(BpypTsc)2]ClO4 (1)
To a methanolic solution of ferric perchlorate (1
mmol) was added a solution of HBpypTsc (2 mmol) in
chloroform and the mixture was refluxed for 30 min.
The resulting deep green colored solution was evapo-

A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
971
Table 1
Crystal data and structure refinement parameters
HBpypTsc
17H18N4S
310.41
[Fe(BpypTsc)2]FeCl4 ꢀ 2H2O (3)
C34H38Cl4Fe2N8O2 S2
Empirical formula
Formula weight, M
Temperature, T (K)
C
908.34
293(2)
298(2)
0.70930
ꢀ
Wavelength, Mo Ka (A)
0.70930
triclinic
Crystal system
Space group
Unit cell dimensions
orthorhombic
P21P21P21
ꢁ
P1
ꢀ
a (A)
9.95
10.77
9.64
15.15
ꢀ
b (A)
ꢀ
c (A)
14.89
90.00
16.24
114.57
a (°)
b (°)
c (°)
90.00
90.00
93.79
101.76
3
ꢀ
Volume, V (A )
1596.3
4, 1.292
2082.1
2, 1.449
Z, Calculated density, q (Mg mꢁ3
)
Absorption coefficient, l (mmꢁ1
F ð000Þ
)
0.205
656
1.094
932
Crystal size (mm)
h Range for data collection
Limiting indices
0.35 ꢂ 0.35 ꢂ 0.30
2.33–24.90
0.275 ꢂ 0.175 ꢂ 0.150
1.40–24.92
0 6 h 6 11, 0 6 k 6 12,
0 6 l 6 17
0 6 h 6 11, ꢁ17 6 k 6 17,
ꢁ19 6 l 6 19
5912/5912 ½Rint ¼ 0:000ꢃ
24.92, 80.8
Reflections collected/Unique
Completeness to 2h (°, %)
Maximum and minimum transmission
Goodness-of-fit on F 2
1526/1526 ½Rint ¼ 0:000ꢃ
24.90, 94.1
1.000 and 0.989
1.075
1.000 and 0.969
1.134
Final R indices ½I > 2rðIÞꢃ
R1 ¼ 0:0332, wR2 ¼ 0:0777
R1 ¼ 0:0387, wR2 ¼ 0:0825
0.174 and )0.224
R1 ¼ 0:0605, wR2 ¼ 0:1535
R1 ¼ 0:0895, wR2 ¼ 0:1726
1.287 and )0.405
R indices (all data)
Largest difference peak and hole (e A
ꢁ3
ꢀ
)
nitrogen cryostat. The spectra were measured 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
value of 2.0036. NMR spectra were recorded on a
Bruker DRX 500 instrument using CDCl3 as the solvent
and TMS as the internal reference at the Sophisticated
Instruments Facility, Indian Institute of Science, Ban-
galore, India. The tentative structure of the compound
HBpypTsc was assigned on the basis of different NMR
experiments, based on the couplings and connectivities
of the signals observed. The 1H resonances were as-
signed on the basis of chemical shifts, multiplicities and
coupling constants from 1H NMR experiments. The
assignments of the NH and OH hydrogens were made
by comparison with the spectra recorded on deuterium
exchange. The carbon types were determined by 13C-
Spin Echo Fourier Transform (SEFT) experiments.
HBpypTsc having appropriate dimensions were sealed
in a glass capillary, and intensity data were measured at
room temperature (293 K) on an Nonius MACH3 dif-
fractometer equipped with graphite-monochromated
ꢀ
Mo Ka (k ¼ 0:71073 A) radiation. The trial structure
was obtained by direct methods using SHELXL-97 and
refined by full-matrix least squares on F 2
(SHELXS-97)
[16,17]. The non-hydrogen atoms were refined with an-
isotropic thermal parameters. All hydrogen atoms were
geometrically fixed and allowed to refine using a riding
model. Absorption corrections were employed using w-
scan. The crystallographic data along with details of
structure solution refinements are given in Table 1.
3. Results and discussions
3.1. Syntheses
€
Mossbauer spectra were recorded on a constant-accel-
eration spectrometer with multi channel analyzer using a
57Co source in a Rhodium matrix at Inter University
Consortium, Indore, India.
The ligand HBpypTsc was synthesized by a direct
condensation of the ketone with the thiosemicarbazide.
In the H NMR spectrum the signal for N(2)H is ob-
1
served at a low field of d ¼ 14:35 ppm and this signal
disappears on deuterium exchange, which is consistent
with the Z configuration of the thiosemicarbazone
moiety. The low frequency multiplets at d ¼ 3:8 (4H)
2.7. X-ray crystallography
A dark brown triclinic crystal of the [Fe(BpypTsc)2]-
FeCl4 (3) and a deep yellow orthorhombic crystal of

972
A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
and 1.9 (4H) ppm were attributed to pyrrolidine ring
protons C14 and C15, respectively, which are chemically
and magnetically equivalent with C17 and C16 (the
numbering scheme of HBpypTsc is given in Scheme 1).
Aromatic protons of the pyridine and phenyl ring ap-
pear at d ¼ 8:73, doublet, aromatic, 1H, J ¼ 7:5 Hz; 8.5,
aromatic, doublet, 1H and 7.1–7.8, aromatic, multiplet,
7H, respectively. The carbon atoms were assigned on the
basis of proton decoupled 13C and 13C- Spin Echo
Fourier Transform NMR spectra. Eighteen signals were
observed in the 13C NMR spectrum, which are assigned
as follows. Signals at d ¼ 177:0 and 177.6 ppm were
attributed to C(1)@N(2) and C(13)@S(1) of the thio-
semicarbazone moiety. Aromatic carbons of the pyri-
dine and phenyl ring of the 2–benzoylpyridine moiety
appear at d ¼ 121:5 (C5), 123.8 (C4), 126.1 (C6), 128.4
(C10), 129.2 (C11), 129.6 (C3), 129.9 (C9), 137.3 (C7),
143.9 (C2), 148.0 (C9), 149.2 (C12), 152.8 (C8), whereas
the peaks at d ¼ 53:4, 50.4, 26.6 and 24.3 were assigned
to aliphatic carbons C14, C17, C15 and C16, respec-
tively, of the pyrrolidine ring.
S1
C4
C5
C6
C3
C14
C13
N2
C15
C1
N4
N3
C2
C7
C17
C8
N1
C16
C9
C12
C10
C11
Fig. 1. ORTEP diagram of the compound HBpypTsc, with 54% el-
lipsoidal probability. Hydrogen atoms are shown as smaller spheres of
arbitrary radii.
3.2. Molecular and crystal structure of compound
HBpypTsc
All complexes were dark brown and are readily sol-
uble in polar organic solvents. Their stoichiometries and
partial elemental analysis data are shown in Table 2.
Analytical data shows a 1:2:1 ratio of iron, ligand and
anions for FeL2X [X ¼ ClO4, FeCl4ꢁ, NO3]. From the
analytical data obtained for compound 3 two formula-
tions are possible: [Fe(BpypTsc)2]FeCl4 or [FeB-
pypTscCl2], but from the crystallographic as well as the
spectroscopic data it is clear the compound isolated is
the former one consisting of an ion pair. The com-
pounds were 1:1 electrolytes [18] in DMF with Km val-
ues near to 95 Xꢁ1 cm2 molꢁ1. The cation centre of all
the complexes are expected to contain two deprotonated
ligands attached to an iron(III) centre. Magnetic mo-
ments have been determined for all the complexes at
room temperature in the polycrystalline state. Iron(III)
is known to exist in three states with S ¼ 5=2 (6A1,
l ¼ 5:92 BM), 3/2 (4A2, l ¼ 3:87 BM) and 1/2 (2T2,
l ¼ 1:73 BM)[19]. The magnetic moments of the com-
pounds 1 and 2 are 1.89 and 2.33 BM, respectively, in-
dicating these compounds are typical low spin
compounds. The high values of susceptibility for com-
pound 3 indicate the presence of a high spin centre in the
molecule [20,21]. The complete assignment of the spin
states of the complexes were done on the basis of EPR
Fig. 1 shows the molecular structure of the com-
pound along with the atom numbering scheme. The
molecule exists in the E conformation around the N2–
N3 bond. The structure reveals quasicoplanarity in the
plain of the thiosemicarbazone but both the aromatic
rings are bifurcated. The molecular structure reveals
that the compound exists in the thione form. Table 3
illustrates selected bond lengths and angles.
The compound has two double bonds in the thio-
ꢀ
semicarbazone moiety viz. C1–N2 1.295 A and C13–S1
ꢀ
1.681 A which are consistent with the previously re-
ported cases. The planarity in the thiosemicarbazone is
revealed by a smaller dihedral angle of the N2–N3–C13–
S1 (0.9°) skeleton. A considerable amount of ring bi-
furcation from the plane of the thiosemicarbazone is
indicated by the dihedral angles C1–N2–N3–C13
()176.9°) and C8–C1–C2–C7 ()44.7°). The S and pyr-
idyl N1 atoms are in E configuration with respect to the
C1–N2 bond. The five-membered pentamethyleneimine
(pyrrolidine) ring is not planar and tends towards an
envelope conformation [22]. The smaller dihedral angles
between the pyridyl ring and the phenyl ring of the 2-
benzoylpyridine moiety and thiosemicarbazone moiety
C2–C1–C8–C9 ()28.2°) and N3–N2–C1–C8 (2.2°), is
due to a resonance effect between the p systems. Pyridyl
nitrogen N1 is intramolecularly hydrogen bonded to
€
and Mossbauer measurements.
Table 2
Stoichiometries and partial elemental analysis of the complexes
Compounds
Stoichiometries
l (BM)
Anal. Calc. (Found) (%)
C
H
N
[Fe(BpypTsc)2]ClO4 (1)
[Fe(BpypTsc)2]NO3 (2)
[Fe(BpypTsc)2]FeCl4 (3)
C34H34ClFeN8O4S2
C34H34FeN9O3S2
C34H34Cl4Fe2N8S2
52.74 (52.75)
55.40 (55.43)
46.80 (46.81)
4.40 (4.43)
4.65 (4.65)
3.93 (3.93)
14.45 (14.48)
17.09 (17.11)
12.85 (12.85)
1.89
2.33
4.38

A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
973
Table 3
ꢀ
Selected bond lengths (A) and angles (°) of HBpypTsc
Bond lengths
Bond angles
S(1)–C(13)
N(1)–C(12)
N(1)–C(8)
N(2)–C(1)
N(2)–N(3)
N(3)–C(13)
1.681(3)
1.341(4)
1.342(4)
1.295(4)
1.366(3)
1.360(4)
C(1)–N(2)–N(3)
C(13)–N(3)–N(2)
N(1)–C(8)–C(9)
N(1)–C(8)–C(1)
N(1)–C(12)–C(11)
N(3)–C(13)–S(1)
118.4(2)
121.1(2)
121.7(3)
117.5(2)
123.9(4)
124.0(2)
ꢀ
ꢀ
X–Hꢀ ꢀ ꢀCg
Hꢀ ꢀ ꢀCg (A)
2.8518
3.2937
Xꢀ ꢀ ꢀCg (A)
\X– Hꢀ ꢀ ꢀCg (°)
126.85
145.44
C12–H12ꢀ ꢀ ꢀCg(3)a
3.6071
4.1282
C16–H16ꢀ ꢀ ꢀCg(2)b
ꢀ
ꢀ
D–Hꢀ ꢀ ꢀA
Hꢀ ꢀ ꢀA (A)
Dꢀ ꢀ ꢀA (A)
\D–Hꢀ ꢀ ꢀA (°)
N3–H103ꢀ ꢀ ꢀN1c
C11–H11ꢀ ꢀ ꢀN2c
1.94
2.59
2.659
3.409
136
153
Cg(2) ¼ N1, C8, C9, C10, C11, C12; Cg(3) ¼ C2, C3, C4, C5, C6, C7.
Cg, centroid; D, donor and A, acceptor.
a Equivalent position code: 1=2 ꢁ x; 1 ꢁ y; 1=2 þ z.
b Equivalent position code: 1 ꢁ x; ꢁ1=2 þ y; 1=2 ꢁ z.
c Equivalent position code: x; y; z.
ꢀ
N3–H10 at 2.65 A distance forming a six-membered
ring.
Fig. 2 shows the molecular structure of the compound
along with the atom numbering scheme. The low-spin
iron(III) ion has a distorted octahedral geometry in the
complex. The pattern of coordination is similar to that
observed in similar types of complexes [23]. The two
molecules of monodeprotonated ligand, coordinate to
iron via pyridyl nitrogens, azomethine nitrogens and
thiolato sulfur atoms to form four five membered che-
3.3. Molecular and crystal structure of compound 3
The compound Fe(BpypTsc)2FeCl4 ꢀ 2H2O (3) crys-
tallizes with two molecules of water of crystallization.
Table 4 presents the selected bond lengths and angles.
Table 4
Selected bond lengths and angles of compound 3
ꢀ
Bond lengths (A)
Bond angles (°)
Fe(1)–N(2)
Fe(1)–N(6)
Fe(1)–N(5)
Fe(1)–N(1)
Fe(1)–S(2)
Fe(1)–S(1)
S(1)–C(13)
N(2)–C(1)
N(2)–N(3)
Fe(2)–Cl(4)
Fe(2)–Cl(3)
Fe(2)–Cl(2)
Fe(2)–Cl(1)
1.916(4)
1.928(5)
1.980(5)
1.984(5)
2.201(19)
2.225(19)
1.749(6)
1.309(7)
1.358(6)
2.156(2)
2.168(2)
2.171(2)
2.196(2)
N(2)–Fe(1)–N(6)
N(2)–Fe(1)–N(5)
N(6)–Fe(1)–N(5)
N(2)–Fe(1)–N(1)
N(6)–Fe(1)–N(1)
N(5)–Fe(1)–N(1)
N(2)–Fe(1)–S(2)
N(6)–Fe(1)–S(2)
N(5)–Fe(1)–S(2)
N(1)–Fe(1)–S(2)
N(2)–Fe(1)–S(1)
N(6)–Fe(1)–S(1)
N(5)–Fe(1)–S(1)
175.4(2)
102.2(2)
81.6(2)
81.1(2)
101.9(2)
86.8(2)
91.06(15)
85.55(16)
165.38(15)
89.13(16)
85.30(15)
92.03(15)
90.19(16)
ꢀ
ꢀ
C–Hꢀ ꢀ ꢀp
Hꢀ ꢀ ꢀCg (A)
2.7053
2.7790
Xꢀ ꢀ ꢀCg (A)
X–Hꢀ ꢀ ꢀCg (°)
113.95
104.77
C12–H12ꢀ ꢀ ꢀCg(4)a
C29–H29ꢀ ꢀ ꢀCg(3)a
3.1962
3.1651
ꢀ
ꢀ
H-bonding interactions
O1–H102ꢀ ꢀ ꢀO2b
O2–H103ꢀ ꢀ ꢀO1c
Hꢀ ꢀ ꢀA (A)
Dꢀ ꢀ ꢀA (A)
D–Hꢀ ꢀ ꢀA (°)
0.94
1.70
1.65
2.78
2.0425
2.3247
2.3247
3.6489
131
128
122
145
O1–H104ꢀ ꢀ ꢀO2d
C14–H14Aꢀ ꢀ ꢀS2
Cg(3) ¼ Fe1, N1, C8, C1, N2, Cg(4) ¼ Fe1, N5, C25, C18, N6.
a x; y; z.
b 2 ꢁ x; 1 ꢁ y; ꢁz.
c 1 þ x; 1 þ y; z.
d 1 ꢁ x; 1 ꢁ y; ꢁz.

974
A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
while the pyridyl nitrogen atoms and thiolato sulfur
Cl4
atoms are in cis positions. The ligands are orthogonal to
the metal ion, with the NNS coordination in a merido-
nal fashion [24]. The chelate rings are almost planar.
There exist strong C–Hꢀ ꢀ ꢀ p interactions between these
metal containing chelate rings Cg(3) and Cg(4) with
pyridyl ring protons. The tetrachloroferrate anion
present in the molecule is slightly distorted tetrahedral
Fe2
Cl1
N1
Cl2
Cl3
ꢀ
with equal bond lengths (ꢄ2.187 A) and angles
C8
N2
(ꢄ109.46°).
C1
N5
Fe1
3.4. IR spectra
C18
N7
N6
S2
N3
In Table 5 we have compiled the assignments of IR
bands most useful for the establishment of the mode of
coordination of thiosemicarbazone ligands in their ir-
on(III) coordination. Coordination of the azomethine
nitrogen is indicated by the lowering of the band at 1630
cmꢁ1 by 30–50 cmꢁ1. The band is not a pure vibrational
band of C@N stretching, but it is a combination band of
C@C vibrations of the pyridyl ring also [25]. Two bands
ꢅ1340 and 840 cmꢁ1 were assigned to the C–S stretching
and bending mode of vibrations. These bands also shift
to lower energies in all complexes compared to the li-
gand, indicating the coordination of the thiolato sulfur.
Another band which is considered to be sensitive to
coordination is m(N–N) which is raised in energy due to
coordination because of the increased double bond
character. The newly formed C@N bond due to the
deprotonation of the ligand is also observed ꢅ1630
cmꢁ1. The spectra of the complexes showed an increase
in pyridyl ring in-plane and out-of-plane bending mode
C30
C13
N4
S1
Fig. 2. ORTEP diagram of the compound[Fe(BpypTsc)2]FeCl4 ꢀ 2H2O
(3) with 50% ellipsoidal probability. Hydrogen atoms and lattice water
molecules are omitted for clarity.
late rings. The crystallographic asymmetric unit con-
tains a [Fe(BpypTsc)2] cation and a tetrachloroferrate
(FeClꢁ4 ) anion along with two molecules of lattice water.
Coordination lengthens the ligands C13–S1 and C1–
ꢀ
N2 bonds to 1.749 and 1.309 A, respectively, and this is
an explicit indication of the deprotonation followed by
the coordination of the ligand moiety. 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,
of vibrations at ꢅ440 and 650 cmꢁ1
.
Table 6 shows the polyatomic anionic vibrations
along with the M–L stretching vibrations observed in
the far-IR and IR regions. Fig. 3 shows the far-IR
spectra of the complexes. The spectra of compound 1
Table 5
Ligand vibrational data of the complexes
Compound
m(C@N)
m(N@C)
m(N@N)
m=d(C@S)
HBpypTsc
1630 s
1594 s
1594 s
1595 m
1118 s
1163 s
1108 s
1111 s
1342 s, 842 w
1240 m, 843 w
1202 s, 839 w
1204 s, 844 w
[Fe(BpypTsc)2]ClO4 (1)
[Fe(BpypTsc)2]NO3 (2)
[Fe(BpypTsc)2]FeCl4 (3)
1627 s
1628 s
1645 m
All values are in cmꢁ1
.
Table 6
Far-IR and anionic vibrational data of the complexes
Compound
m(Fe–Nazo
)
m(Fe–Npy
)
m(Fe–S)
m(Xa)
[Fe(BpypTsc)2]ClO4 (1)
[Fe(BpypTsc)2]NO3 (2)
[Fe(BpypTsc)2]FeCl4 (3)
515 w
585 w
528 w
354 w
364 w
352 s
452 w
450 w
419 s
470 w, 1105 s, 619 w
698 w, 839 w, 1379 s, 1289 s
374 s, 320 s, 134 w, 110 s
All values are in cmꢁ1
a ClO4, FeCl4, NO3.
.

A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
975
3.5. Electronic spectra
Table 7 shows the electronic spectral values in solid-
state DRS mode. Fig. 4 shows the electronic spectrum of
compound 3. The UV region is dominated by two in-
tense intra ligand bands at ꢄ36 000 and 29 000 cmꢁ1
assigned to p ! pꢆ and n ! pꢆ transitions.
Usually n ! pꢆ transitions involving N and S atoms
occur at a lower energy than p ! pꢆ. Bands which are
between 36 000 and 30 000 cmꢁ1 in the spectrum of the
complexes having pyridyl ligands have been assigned to
p ! pꢆ and n ! pꢆ transitions and the bands between
15 000 and 27 000 cmꢁ1 are assigned to d ! pꢆ transi-
tions, S ! Fe and other ligand-to-metal charge transfer
transitions. The bands below 15 000 cmꢁ1 are due to
2
2
d ! d bands which correspond to a T2g ! T1g tran-
sition of the d5 spin-paired systems [29]. A comparison
of the spectra of 1, 2 and 3 shows no significant differ-
ences indicating that electronic spectra of the cations
dominate the spectral properties [30]. Therefore the spin
forbidden transitions between 13 700 and 16 600 cmꢁ1 of
[FeCl4]ꢁ are too weak to be observed. Unfortunately the
electronic spectra of low-spin iron(III) compounds have
not been adequately characterized.
Fig. 3. Far-IR spectra of the iron(III) complexes.
had broad split bands assignable to m3(ClO4) ꢅ 1105
cmꢁ1, it is unlikely that the perchlorate ion is bound
directly to the iron(III) centre since there is no indication
of splitting of m4(ClO4) ꢅ 619 cmꢁ1. This is also con-
firmed by the absence of m1(ClO4) ꢅ 920 cmꢁ1. Besides
these m2(ClO4) is also observed ꢅ470 cmꢁ1. All these
bands are split due to the strong H-bonding interactions
in the molecule [26]. A similar splitting occurs in the
m3(FeCl4) ꢅ 374 cmꢁ1 band in the spectrum of com-
pound 3. This splitting may be due to the steric factors
which reduce the symmetry from tetrahedral [27]. Sim-
ilarly the band corresponding to m4 ꢅ 134 cmꢁ1 is also
found to be split due to site effects. The other two
stretching modes m1 and m2 are found at approximately
330 and 114 cmꢁ1, respectively, in the spectrum of
compound 3. The spectrum of compound 2 has two
strong bands at 1389 and 1289 cmꢁ1 corresponding to m1
and m4 of the nitrato group. The absence of a combi-
nation band ꢅ1740 cmꢁ1 assignable to m1 þ m4 indicates
the ionic nature of the group [28]. Bands at ꢅ515 and
355 cmꢁ1 are assigned to the Fe–N vibrations of the
azomethine and pyridyl nitrogen coordination, respec-
tively. Fe–S bond stretching vibrations are found ap-
proximately at 420 cmꢁ1 in the spectra of the complexes.
Fig. 4. UV–Vis-NIR spectrum of compound 3 (insight: UV region).
Table 7
Electronic spectral data of the complexes
Compound
p ! pꢆ
43 300
36 5136
36 630
37 037
n ! pꢆ
29 240, 29 760
LMCT
d ! d
–
HBpypTsc
–
[Fe(BpypTsc)2]ClO4 (1)
[Fe(BpypTsc)2]NO3 (2)
[Fe(BpypTsc)2]FeCl4 (3)
30 487
29 585
30 211
26 737, 15 503
24 509, 15 822
24 390, 211 416, 15 974
10 362
10 373
10 438
All values are in cmꢁ1
.

976
A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
3.6. Electron paramagnetic resonance spectra
The EPR spin Hamiltonian parameters of the ir-
on(III) complexes obtained after the spectral simula-
tions performed by EasySpin package [31] are presented
in Table 8. Figs. 5–7 show the EPR spectra of the
complexes recorded under different conditions. The
EPR of the d5 iron(III) is expressed by the spin Ham-
iltonian [32,33],
H ¼ b½gxHx ꢀ Sx þ gyHy ꢀ Sy þ gzHz ꢀ Szꢃ
with S ¼ 1=2 and g ¼ 2:00:
The polycrystalline EPR spectra of compound 3 consist
of a single broad line with a Dpk (peak-to-peak) value
ꢄ27 mT and a comparatively higher g value ꢄ2.25. This
feature does not change even when the temperature is
lowered to 100 K. This is indicative of the presence of a
mixture of spin species in the system. The observed g
value ꢅ2.0 and a nearly isotropic spectra indicate spin–
spin relaxation via dipole–dipole interactions. However
the solid-state spectra of the other two compounds 1 and
2 are rhombic in nature with three g values. This type of
feature is common for low spin octahedral complexes
[34]. The observed anisotropic character is due to
rhombic distortion common for spin paired iron(III)
complexes.
285
325
365
B [mT]
o
Fig. 5. EPR spectrum of compound 1 in the polycrystalline state: upper
trace at 298 K, lower trace at 100 K. Dotted lines shows the simulated
best fit spectra of the compound.
The isotropic spectrum of complex 3 in the poly-
crystalline state changes to a rhombic spectrum in frozen
solution in DMF. Since the gav values obtained at both
temperatures are similar, it is likely that lattice effects in
the solid state may account for this change from iso-
tropic to rhombic and it is common for spin paired ir-
on(III) complexes. The small deviation of the
anisotropic g values from 2.0 suggests that the unpaired
electron is in the dxy orbital with a d2xzdy2zdx1y ground state
configuration. It was interesting to note a sharp but
small signal corresponding to g ¼ 4:2603 indicating the
presence of a high spin species which was identified as
the [FeCl4]ꢁ anion. The spectra of the compounds 1 and
2 recorded in dichloromethane at 100 K also show an-
isotropic spectra with three g values corresponding to a
low spin octahedral iron(III) system. However the
spectral features were not resolved probably due to poor
glass formation.
285
325
[mT]
B
o
Fig. 6. EPR spectrum of compounds 1 and 2 in a solution of dichlo-
romethane at 100 K: upper trace compound 1, lower trace compound
2. Dotted lines show the simulated best fit spectra of the compounds.
Table 8
EPR spectral data of the complexes
Compound
State
Temperature (K)
g1
g2
g3
[Fe(BpypTsc)2]ClO4 (1)
powder
powder
CH2Cl2
powder
powder
CH2Cl2
powder
powder
DMF
298
100
100
298
100
100
298
100
100
2.1990
2.1984
2.1803
2.1899
2.1897
2.1866
2.1495
2.1466
2.1400
2.1465
2.1462
2.1460
2.0026
2.0052
2.0010
2.0036
[Fe(BpypTsc)2]NO3 (2)
[Fe(BpypTsc)2]FeCl4(3)
2.0032
2.0027
2.2594, Dpk ¼ 30 mT
2.1490, Dpk ¼ 27 mT
1.9981, 4.2603
2.1935
2.1432

A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
977
1.005
1.000
0.995
0.990
0.985
0.980
0.975
0.970
0.965
-4
-2
0
2
4
Velocity (mms-1)
135
175
215
255
295
335
375
B [mT]
o
€
Fig. 8. Mossbauer spectrum of compound 1 (298 K).
Fig. 7. EPR spectrum of compound 3 in a solution of DMF at 100 K:
upper trace experimental spectrum, lower trace simulated best fit
spectrum.
20 K
1.00
0.98
0.96
0.94
0.92
3.7. M€ossbauer spectra
€
Mossbauer spectra of the complexes were recorded at
298 and 20 K in order to understand and confirm the
€
spin behavior of the systems. The Mossbauer parame-
298 K
ters calculated from the spectra are presented in Table 9,
and Figs. 8–10 show the spectra of the complexes. All
values were compared with a-iron as a standard.
The high intensity doublet in the spectra of all the
complexes with an isomer shift approximately at )0.12
1.00
0.98
0.96
0.94
mm sꢁ1
, characterized by a quadrupolar splitting
DEq ꢅ 2:1 mm sꢁ1, is ascribed to the low spin T2g
ground state of low spin iron(III) [35]. These values
change a little when the temperature is lowered. The
signals in the low temperature spectra were more in-
tense. The 1:1 ratio between the quadrupole split spectra
is not strictly observed due to the anisotropic absorption
known as the Goldansky–Karyagin effect. The spectra
of compound 3 is unusually interesting with the presence
of another broad signal corresponding to dis ꢅ 0:12
mm sꢁ1 DEq ꢅ 0:67 mm sꢁ1, ascribed to a tetrahedral
high spin iron(III) species [36]. The observation of the
broad line with unresolved quadrupolar splitting is as-
2
-5
-4
-3
-2
-1
0
1
2
3
4
5
Velocity (mms-1)
€
Fig. 9. Mossbauer spectra of compound 2 at different temperatures.
sumed to be due to much slower spin relaxation due to
the orbital electrons of iron. The high spin signal is
temperature dependent and in the 20 K spectrum of
compound 3 the signal is found to be shifted compared
to the 298 K spectrum, and it was found to be more
intensified. There are no changes between the 298 and 20
Table 9
€
Mossbauer spectral data of the complexes
Compound
Temperature (K)
Spin
dis (mm sꢁ1
)
DEq (mm sꢁ1
)
[Fe(BpypTsc)2]ClO4 (1)
[Fe(BpypTsc)2]NO3 (2)
298
298
20
1/2
1/2
1/2
1/2
1/2
5/2
5/2
)0.17 (2T2g
)0.11 (2T2g
)0.12 (2T2g
)0.10 (2T2g
)0.11 (2T2g
)
)
)
)
)
2.231 (2T2g
2.351 (2T2g
2.352 (2T2g
2.110 (2T2g
2.241 (2T2g
0.925 (6A1)
0.625 (2T2g
)
)
)
)
)
[Fe(BpypTsc)2]FeCl4 (3)
298
20
298
20
0.17 (6A1)
0.12 (2T2g
)
)
All values are relative to a-iron.

978
A. Sreekanth, M.R.P. Kurup / Polyhedron 23 (2004) 969–978
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0.992
0.984
298 K
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-4
-3
-2
-1
0
1
2
3
4
5
Velocity (mmS-1)
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Inorg. Met.- Org. Chem. 28 (1998) 1415.
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without any magnetic interactions in the molecules [37].
€
€
University of Gottingen, Gottingen, Germany, 1997.
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3.8. Supplementary information
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Crystallographic data for the structural analysis has
been deposited with the Cambridge Crystallographic
Data centre, CCDC 217178 for compound HBpypTsc
and CCDC 217177 for compound [Fe(BpypTsc)2]-
FeCl4 ꢀ 2H2O (3). Copies of this information may be ob-
tained free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 IEZ, UK (fax: +44-1223-336-033;
E-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.ca-
m.ac.uk).
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Acknowledgements
One of the authors (A.S.) thanks the Cochin Uni-
versity of Science and Technology for a Research Fel-
lowship. The authors are thankful to the National Single
Crystal X-ray Diffraction Facility, IIT, Bombay for the
X-ray diffraction studies and Dr. Ajay Gupta, Inter-
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ETH, Zurich, 2003.
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[32] B. Bleaney, M.C.M. OÕBrien, Proc. Phys. Soc. London Sect. B 69
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spectral experiments. M.R.P. Kurup is thankful to the
Science, Technology and Environment Department
(STED), Govt. of Kerala for financial assistance.
[33] J.S. Griffith, The Theory of Transition Metal Ions, Cambridge
University Press, London, 1961.
[34] Y. Nishida, A. Sumita, K. Hayashida, H. Olishima, S. Kida, Y.
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