Crystal structure and magnetic behaviour of a five-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone

Article abstract of DOI:10.1016/j.ica.2007.03.045

The crystal structure and magnetic properties of a penta-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone, [Fe(H₂mthpy)Cl₂](CH₃C₆H₄SO₃), are reported. The synthesised ligand and the metal complex were characterised by spectroscopic methods (¹H NMR, IR, and mass spectroscopy), elemental analysis, and single crystal X-ray diffraction. The complex crystallises as dark brown microcrystals. The crystal data determined at 100(1) K revealed a triclinic system, space group P over(1, ?) (Z = 2). The ONSCl₂ geometry around the iron(III) atom is intermediate between trigonal bipyramidal and square pyramidal (τ = 0.40). The temperature dependence of the magnetic susceptibility (5-300 K) is consistent with a high spin Fe(III) ion (S = 5/2) exhibiting zero-field splitting. Interpretation of these data yielded: D = 0.34(1) cm^-1 and g = 2.078(3).

Full text of DOI:10.1016/j.ica.2007.03.045

Inorganica Chimica Acta 360 (2007) 3896–3902
www.elsevier.com/locate/ica
Crystal structure and magnetic behaviour of a five-coordinate
iron(III) complex of pyridoxal-4-methylthiosemicarbazone
*
Eddy W. Yemeli Tido, Esther J.M. Vertelman, Auke Meetsma, Petra J. van Koningsbruggen
Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
Received 22 November 2006; received in revised form 14 March 2007; accepted 24 March 2007
Available online 7 April 2007
Paper presented in the MAGMANet-ECMM, European Conference on Molecular Magnetism.
Abstract
The crystal structure and magnetic properties of a penta-coordinate iron(III) complex of pyridoxal-4-methylthiosemicarbazone,
[Fe(H2mthpy)Cl2](CH3C6H4SO3), are reported. The synthesised ligand and the metal complex were characterised by spectroscopic meth-
ods (1H NMR, IR, and mass spectroscopy), elemental analysis, and single crystal X-ray diffraction. The complex crystallises as dark
ꢀ
brown microcrystals. The crystal data determined at 100(1) K revealed a triclinic system, space group P1 (Z = 2). The ONSCl2 geometry
around the iron(III) atom is intermediate between trigonal bipyramidal and square pyramidal (s = 0.40). The temperature dependence of
the magnetic susceptibility (5–300 K) is consistent with a high spin Fe(III) ion (S = 5/2) exhibiting zero-field splitting. Interpretation of
these data yielded: D = 0.34(1) cmꢀ1 and g = 2.078(3).
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Crystal structure; Penta-coordinate; Iron(III); Pyridoxal-4-methylthiosemicarbazone; Zero-field splitting
1. Introduction
specific redox reactions is crucial for the enzymatic activity
[6,7]. Both the diiron(III) centre as well as the organic rad-
ical are therefore important targets in anticancer therapy
focusing on the development of RR inhibitors.
Nowadays there is a lot of interest in the design of iron
chelators having potential as anti-tumor agents – the most
promising of these being tridentate ligands containing a
thiosemicarbazone entity [1–3].
The 3-aminopyridine-2-carboxaldehyde thiosemicarba-
zone (triapine, Fig. 1) is a very strong iron chelator and in
the body it is likely that the iron chelate is the active species
that quenches the active site tyrosyl radical required by RR
for its enzymatic activity [8]. At the time of its discovery, the
N,N,S-chelating triapine was considered as the most effec-
tive inhibitor of RR yet identified [9]. Further research
focused on the synthesis, determination of the iron-chela-
tion efficiency and study of the promising antiproliferative
activity of pyridoxal isonicotinoyl hydrazone (PIH)
(Fig. 1) [9–12]. Pyridoxal N(4)-substituted thiosemi-
carbazones can be considered as derivatives of both these
classes of active anti-tumor drugs, and the organic com-
pound [13] as well as its Cu(II) complexes [14] have indeed
been found to inhibit cell growth, but not to such an extent
that it leads to a programmed cell death.
In fact, iron ions are crucial for cell growth and it is gen-
erally accepted that tumor cells are more sensitive to iron
deprivation than normal cells, which may to a major extent
be associated with cancer cells expressing higher levels of
the iron-containing enzyme ribonucleotide reductase
(RR) [4]. RR is a multisubunit enzyme responsible for
the reduction of ribonucleotides to their corresponding
deoxyribonucleotides, which are building blocks for
DNA [5]. Active RR contains an oxygen-linked diferric
centre and a tyrosyl radical and their interplay involving
*
Corresponding author. Tel.: +31 50 3634363; fax: +31 50 3634315.
E-mail address: p.j.van.koningsbruggen@rug.nl (P.J. van Konings-
bruggen).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.03.045

E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
3897
10.00 g (49 mmol) of pyridoxal hydrochloride (99%) was
dissolved in 80 ml of water with constant stirring, and
was added to 5.17 g (49 mmol) of 4-methyl-3-thiosemicar-
bazide (97%) dissolved in 40 ml of water. The mixture
was kept at 40 ꢁC for 120 min. After the mixture was
cooled to room temperature, deep yellow needle-like crys-
tals were isolated by filtration, washed with water and dried
in vacuo for two days. Yield: 9.0 g, 63%. Anal. Calc. for
C10H15ClN4O2S: C, 41.31; H, 5.20; N, 19.27; S, 11.03.
Found: C, 41.30; H, 5.18; N, 19.10; S, 11.11%. M.p.:
228 ꢁC. H2mthpy Æ HCl is soluble in water, warm ethanol,
but scarcely dissolves in acetone, chloroform and metha-
HO
NH2
N
N
H
N
H
N
NH2
N
N
S
N
O
OH
CH3
a
b
HO
H
N
H
N
N
CH3
N
S
OH
1
CH3
nol, even when warmed. H NMR (300 MHz, DMSO-d6/
c
d ppm): 11.40 (bs, 1H, OH py), 9.93 (bs, 1H, NH-2), 8.59
(m, 2H, py CHN + NH-4), 7.93 (s, 1H, py), 5.29 (t, 1H,
OH), 4.56 (d, 2H, py CH2O), 2.99 (d, 3H, CH3N), 2.42
(s, 3H, CH3 py). MS (ionisation mode: EI+) m/z (%): 254
(98), 165 (100), 150 (27), 116 (7), 74 (31), 57 (39).
Fig. 1. Schematic representation of 3-aminopyridine-2-carboxaldehyde
thiosemicarbazone (triapine; a), pyridoxal isonicotinoyl hydrazone (PIH;
b), pyridoxal-4-methylthiosemicarbazone (H2mthpy; c).
2.1.2. Synthesis of [Fe(H2mthpy)Cl2](CH3C6H4SO3)
A
Although there have been numerous studies involving
the synthesis and characterisation of N-substituted pyri-
doxal thiosemicarbazone complexes of various metal ions
[13–15], there is no report on X-ray crystal structure deter-
minations of iron(III) compounds of those ligands. Still,
the synthesis and characterisation of several Fe(III) com-
pounds of various compositions have been reported, such
as bis-ligand complexes of formulae [Fe(HL)2]Cl Æ xH2O
(H2L = pyridoxal-4R-thiosemicarbazone, R = H, (x = 0,
2) [16], R = CH3, C2H5, C6H5, (x = 0) [17]), which appear
to contain the monodeprotonated ligand. In addition, a
mono-ligand compound of formula [Fe(H2L)(OH2)Cl2]Cl
(H2L = pyridoxal-thiosemicarbazone) [18] has been re-
ported, which does contain the ligand in its neutral form.
In this paper, we present the X-ray crystal structure of
solution of Fe(CH3C6H4SO3)3 Æ 6H2O (0.339 g;
0.5 mmol) in 15 ml of ethanol, was added dropwise with
constant stirring to a solution of pyridoxal-4-methylthio-
semicarbazone Æ HCl (0.291 g; 1 mmol) in 20 ml of ethanol.
The resulting dark brown solution was stirred and heated
mildly for about 20 min before being allowed to stand at
room temperature for three days. The dark brown micro-
crystals were isolated by filtration, washed with ethanol
and diethylether, and dried in a well ventilated space for
24 h. Yield: 0.23 g, 82%. M.p. > 280 ꢁC. Anal. Calc. for
C17H21Cl2N4O5S2Fe: C, 36.97; H, 3.83; N, 10.15; S,
11.61. Found: C, 38.08; H, 4.06; N, 10.15; S, 11.95%.
The complex is soluble in water, ethanol, and in acidic
and basic solutions in the pH range from 0 up to 14; it is
sparingly soluble in methanol and acetone.
dichloropyridoxal-4-methylthiosemicarbazone
iron(III)
p-toluenesulfonate, [Fe(H2mthpy)Cl2](CH3C6H4SO3) (H2-
mthpy = pyridoxal-4-methylthiosemicarbazone), with the
objective to inequivocally identify the coordination behav-
iour of the ligand towards Fe(III), as well as to assess its
ionic form and tautomeric structure. In addition, the mag-
netic behaviour of this material is reported.
2.2. Physical measurements
Infrared spectra were recorded on KBr pellets on an
Interspec 200-X FT-IR spectrometer in the range between
4000 and 400 cmꢀ1 with a resolution of 1 cmꢀ1. Routine
EI+ spectra were measured with the MS route JMS-600H
1
2. Experimental
sector mass spectrometer (JEOL). H NMR spectra were
recorded in DMSO-d6 with a Varian VXR 300 spectro-
meter with TMS as standard. Elemental analysis was
carried out at the Microanalytical Department of the Uni-
versity of Groningen, using the Euro EA Elemental Ana-
lyzer from the EuroVector Instrument and Software
Company. The magnetic measurements were performed
on a Quantum Design magnetometer with a superconduc-
ting quantum interface device. The sample was prepared by
putting exactly 22.8 mg of the compound between two
pieces of cotton wool in a gelcap. The magnetic field was
kept constant at 0.1 T while the temperature was raised
from 5 to 300 K. The collected raw data were corrected
for molecular diamagnetism.
Pyridoxal hydrochloride (99%) has been purchased from
Aldrich, whereas 4-methyl-3-thiosemicarbazide (97%) and
iron(III) p-toluenesulfonate (Fe(CH3C6H4SO3)3 Æ 6H2O)
have been purchased from Acros. All chemicals were used
without further purification.
2.1. Preparations
2.1.1. Synthesis of pyridoxal-4-methylthiosemicarbazone
hydrochloride (H2mthpy Æ HCl)
H2mthpy Æ HCl has been prepared according to a modi-
fication of the procedure described in the literature [17,19].

3898
E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
Table 1
2.3. X-ray crystallography
Crystal data and refinement details of the structure determination of
[Fe(H2mthpy)Cl2](CH3C6H4SO3)
A parallelepiped-shaped dark brown coloured crystal
with the dimensions of 0.19 · 0.17 · 0.14 mm was mounted
on top of a glass fiber and aligned on a Bruker SMART
APEX CCD diffractometer (Platform with full three-circle
goniometer). The diffractometer was equipped with a 4 K
CCD detector set 60.0 mm from the crystal. The crystal
was cooled to 100(1) K using the Bruker KRYOFLEX
low-temperature device. Intensity measurements were per-
formed using graphite monochromated Mo Ka radiation
from a sealed ceramic diffraction tube (SIEMENS). Gener-
ator settings were 50 kV/40 mA. SMART [20] was used for
preliminary determination of the unit cell constants and
data collection control. The intensities of reflections of a
hemisphere were collected by a combination of three sets
of exposures (frames). Each set had a different / angle
for the crystal and each exposure covered a range of 0.3ꢁ
in x. A total of 1800 frames were collected with an expo-
sure time of 10.0 s per frame. The overall data collection
time was 9.0 h. Data integration and global cell refinement
was performed with the program SAINT [20]. The final unit
cell was obtained from the xyz centroids of 3065 reflections
after integration. Intensity data were corrected for Lorentz
and polarisation effects, scale variation, for decay and
Formula
C
552.26
triclinic
17H21Cl2N4O5S2Fe
Formula weight (g molꢀ1
Crystal system
)
ꢀ
Space group
Crystal colour
Crystal description
Crystal dimensions (mm)
Unit cell dimensions
P1
dark brown
parallelepiped-shaped
0.19 · 0.17 · 0.14
˚
a (A)
8.265(1)
10.944(1)
13.534(2)
98.519(2)
90.445(2)
100.958(2)
1187.8(3)
2
1.544
100(1)
0.71073
10.71
566
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
Volume (A )
Z
Dcalc (g cmꢀ3
)
Temperature (K)
˚
Radiation (A)
l (Mo Ka) (cmꢀ1
)
F(000)
Number of unique data
Number of data with [Fo P 4.0r(Fo)]
R(F)a, wR(F2)b
5280
4153
0.0590, 0.1667
a
R(F) = (iFoj ꢀ jFci)/jFoj for Fo > 4.0r(Fo).
P
P
b
2
wR(F2) = [ [w(Fo ꢀ Fc2)2]/ [w(Fo2)2]]1/2 with w = 1/[r2(Fo2) +
(aP)2 + bP] and P = [max(Fo2,0) + 2Fc2]/3 and weighting scheme:
a = 0.0784, b = 3.0568.
absorption:
a multi-scan absorption correction was
applied, based on the intensities of symmetry-related reflec-
tions measured at different angular settings (SADABS) [21],
2
and reduced to Fo . The program suite SAINTPLUS was used
respectively; ultimately the suggested a (=0.0784) and b
(=3.0568) were used in the final refinement.
for space group determination (XPREP) [20].
The unit cell [22] was identified as triclinic, space group
P1: the E-statistics were indicative of a centrosymmetric
Crystal data and numerical details on data collection
and refinement are given in Table 1. Neutral atom scatter-
ing factors and anomalous dispersion corrections were
taken from International Tables for Crystallography [28].
All refinement calculations and graphics were performed
on a HP XW6200 (Intel XEON 3.2 Ghz)/Debian-Linux
computer at the University of Groningen with the program
packages SHELXL [29] (least-square refinements), a locally
modified version of the program PLUTO [30] (preparation
of illustrations) and PLATON [31] package (checking the final
results for missed symmetry with the MISSYM option, sol-
vent accessible voids with the SOLV option, calculation of
geometric data and the ORTEP [31] illustrations).
ꢀ
space group [23]. Reduced cell calculations did not indicate
any higher metric lattice symmetry [24] and examination of
the final atomic coordinates of the structure did not yield
extra crystallographic or metric symmetry elements [25,26].
The structure was solved by direct methods using the
program SIR2004 [27]. The positional and anisotropic dis-
placement parameters for the non-hydrogen atoms were
refined. The hydrogen atoms were generated by geometri-
cal considerations, constrained to idealised geometries,
and allowed to ride on their carrier atoms with an isotropic
displacement parameter related to the equivalent displace-
ment parameter of their carrier atoms.
Final refinement on F2 carried out by full-matrix least-
squares techniques converged at wR(F2) = 0.1667 for
5280 reflections and R(F) = 0.0590 for 4153 reflections with
Fo P 4.0r(Fo) and 284 parameters. A final difference Fou-
rier map revealed features within the range ꢀ1.0 to +1.1(1)
3. Results and discussion
3.1. General
A spectroscopic study has been carried out in order to
identify the tautomeric as well as the ionic form of pyri-
doxal-4-methylthiosemicarbazone in DMSO-d6 solution
and in the solid state. Evidence of the solid compound
being the HCl adduct appears from the IR spectrum in
which a band at 2851 cmꢀ1 could be addressed as the
m(N–H+) stretching vibration confirming that the nitrogen
atom of the pyridine ring bears a proton. Also in DMSO-d6
solution the compound is present in this zwitterionic form
3
˚
e/A located near the S1 and Fe positions.
The positional and anisotropic displacement parameters
for the non-hydrogen atoms and isotropic displacement
parameters for hydrogen atoms were refined on F2 with
full-matrix least-square procedures minimizing the func-
P
2
2
2
tion Q = h[w(j(Fo ) ꢀ k(Fc )j)2], where w = 1/[r2(Fo ) +
2
2
(aP)2 + bP], P = [max(Fo ,0) + 2Fc ]/3, F0 and Fc are the
observed and calculated structure factor amplitudes,

E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
3899
as could be deduced from the N–H proton resonance
1
observed at 8.59 ppm in the H NMR spectrum. In addi-
tion, the IR spectrum of H2mthpy Æ HCl shows a strong
absorption at 1000 cmꢀ1 which could be assigned to the
m(C@S) vibration of the free ligand indicating that it is
present in the thione form. The presence of this as the sole
isomer in the solid state is in agreement with the absence of
the m(S–H) band at ca. 2550 cmꢀ1. Also in solution the
Schiff base remains predominantly as the thione tautomer
which is concomitant with the absence of the S—H proton
resonance at ca. 4.00 ppm in the 1H NMR spectrum
recorded in DMSO-d6. These results are in agreement with
the crystal structure of the hydrochloric salt of pyridoxal-4-
methylthiosemicarbazone in which the thione form could
˚
˚
be identified by the short C@S bond of 1.669(5) A in con-
junction with the C–N(amine) bond of 1.339(6) A, the lat-
ter being significantly shorter than a normal C–N bond,
and with the presence of a hydrogen atom on the hydrazi-
nic nitrogen [32]. The solid state structure of
H2mthpy Æ HCl is stabilised by an intramolecular hydrogen
bond between the OH of the phenol and the azomethine
nitrogen atom [32].
Fig. 2. ORTEP drawing of [Fe(H2mthpy)Cl2](CH3C6H4SO3).
IR spectroscopy provides a useful method for assessing
the coordination mode of the ligand in the present Fe(III)
compound. The m(C@N) band at 1615 cmꢀ1 of the free
ligand is shifted by 5 cmꢀ1 to lower values in the infrared
spectrum of the complex indicating the coordination of
the azomethine nitrogen. On the opposite side, the hydrazi-
nic m(N–N) band shifts to higher wavenumbers (from
1237 cmꢀ1 of the free ligand to 1251 cmꢀ1 of the complex)
because of the reduction in the repulsion between lone
pairs of electrons on the nitrogen atoms as a consequence
of coordination via the azomethine nitrogen atom, which
probably causes a certain degree of delocalisation of
charge. Coordination of the phenolate group is indicated
by the disappearance of the OH stretching vibration – as
observed for the free ligand at 3198 cmꢀ1 – in the IR spec-
trum of the complex.
3.2. Description of the structure of
[Fe(H2mthpy)Cl2](CH3C6H4SO3)
Fig. 3. Packing arrangement of [Fe(H2mthpy)Cl2](CH3C6H4SO3) dis-
played in the unit cell.
The compound crystallises in the triclinic space group
P1 with Z = 2. The asymmetric unit consists of one for-
ꢀ
Table 2
Selected
[Fe(H2mthpy)Cl2](CH3C6H4SO3)
mula unit without an atom at a special position. The
identification of the atoms and the configuration of the
cation- and anion-moiety are shown in the ORTEP [31]
drawing of Fig. 2; the packing of the molecules is shown
in the unit cell displayed in Fig. 3. Relevant information
on bond lengths and angles is given in Table 2.
˚
(A)
bond
lengths
and
bond
angles
(ꢁ)
for
Fe–Cl1
Fe–Cl2
Fe–S1
Fe–O1
Fe–N1
S1–C9
N3–C9
N4–C9
N1–N3
N1–C1
2.2555(13)
2.2505(14)
2.3650(13)
1.915(3)
2.237(4)
1.725(4)
1.368(6)
1.317(5)
1.372(5)
1.302(6)
Cl1–Fe–Cl2
Cl1–Fe–S1
Cl1–Fe–O1
Cl1–Fe–N1
Cl2–Fe–S1
Cl2–Fe–O1
Cl2–Fe–N1
S1–Fe–O1
S1–Fe–N1
O1–Fe–N1
C4–N2–C5
107.66(5)
111.18(5)
107.53(10)
91.51(10)
89.20(5)
The [Fe(H2mthpy)Cl2]+ unit contains an Fe(III) ion in
an ONSCl2 environment formed by the neutral tridentate
chelating O,N,S pyridoxal-4-methylthiosemicarbazone
ligand together with two monodentate coordinating chlo-
ride anions. The Fe-donor atom distances involving the
97.38(9)
160.27(10)
136.54(10)
79.26(9)
80.75(12)
124.3(4)
˚
chlorides are Fe–Cl1 = 2.2555(13) A and Fe–Cl2 = 2.2505
˚
(14) A. The distances to the ligand donor atoms are Fe–
Standard deviations in the last decimal place are given in parentheses.

3900
E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
˚
˚
˚
S1 = 2.3650(13) A, Fe–O1 = 1.915(3) A and Fe–N1 =
(1) A, for S1, N1, N3, C9 and Fe for the five-membered thi-
˚
2.237(4) A. Pyridoxal-4-methylthiosemicarbazone appears
osemicarbazide ring, severally. These geometric features
are associated with the O1–Fe–N1 bite angle of
80.75(12)ꢁ originating from the six-membered chelate ring
being only marginally larger than the S1–Fe–N1 bite angle
of 79.26(9)ꢁ involving the five-membered chelate ring of
H2mthpy. The Fe(III) ion is lifted by 0.5522(7) A out of
the least-squares plane through the [O1, N1, S1, Cl2] basal
plane in the direction of the axial Cl1 atom.
The p-toluenesulfonate anion is involved in intensive
hydrogen bonding with pyridoxal-4-methylthiosemicarbaz-
one (Table 3). The O6 of the sulfonate sets up a hydrogen
bonding network with the O2 hydroxy methyl substituent
to be in its neutral zwitterionic form, i.e. it is deprotonated
at the phenolic oxygen O1 whereas it is protonated at the
pyridine N2 and the hydrazinic N3. Protonation of N2 is
evident from the value of the C4–N2–C5 pyridyl angle of
124.3(4)ꢁ, which has significantly increased with respect
to the C–N–C angle of about 120ꢁ that could be expected
for a non-protonated pyridyl-N. In addition, protonation
of N3 is in line with the ligand being in the thione form,
i.e. having a typical short C9 = S1 distance of 1.725(4) A
and adjacent carbon–nitrogen bond lengths which are typ-
ical for a single bond (C9–N3 = 1.368(6) A, C9–N4 =
1.317(5) A). These bond distances are in agreement with
˚
˚
˚
˚
˚
attached to the pyridyl ring (O2–H22 = 0.84 A, H22. . .O6
= 1.94 A, O2. . .O6 = 2.772(4) A, O2–H22. . .O6 = 170ꢁ)
and with the pyridyl N2 of a symmetry related ligand
˚
˚
the literature values [32].
X-ray structural data of Fe(III) bis-ligand compounds
of the dianion of R-salicylaldehyde thiosemicarbazone
reveal that the Fe–S, Fe–O and Fe–N distances typically
are of the order of 2.44 A, 1.96 A and 2.12 A for high spin
Fe(III), severally, whereas these are 2.23 A, 1.94 A and
1.96 A for low spin Fe(III), severally [33]. Comparison with
these iron ligand bond lengths indicates that the Fe(III) ion
is in the high spin state in the present compound, albeit
involving a rather long Fe–N1 distance of 2.237(4) A,
which may be related to the more relaxed Fe(III) geometry
in the five-coordinate complex.
The ONSCl2 geometry about the Fe(III) ion may be
described as intermediate between trigonal bipyramidal
and square pyramidal and is characterised by a s value of
0.40. The s index of trigonality which is also designated
as the general descriptor of five-coordinate centric mole-
cules is given as s = (b ꢀ a)/60, where a and b are the
two largest basal angles in a five-coordinate complex. For
a perfectly tetragonal pyramidal geometry, s is equal to
zero, while it becomes unity for a perfectly trigonal bipyra-
midal geometry [34]. The basal plane of this geometric fig-
ure may be defined by the atoms [Cl2, S1, N1, O1] yielding
iron-donor atom binding angles deviating considerably
from the ideal value of 90ꢁ, i.e. Cl2–Fe–O1 = 97.38(9)ꢁ,
N1–Fe–O1 = 80.75(12)ꢁ, S1–Fe–N1 = 79.26(9)ꢁ and S1–
Fe–Cl2 = 89.20(9)ꢁ. This is a major consequence of the
strain exerted by the chelating ligand located in this basal
plane which tends to thrive towards planarity as well as
to optimising the metal-donor atom bond lengths to these
suitable for high spin Fe(III). Particularly, the binding of
the ligand involving the formation of two metallocycles –
˚
(N2–H32 = 0.88 A, H32. . .O6 (1 ꢀ x, 1 ꢀ y, 1 ꢀ z) =
˚
˚
1.90 A, N2. . .O6 (1 ꢀ x, 1 ꢀ y, 1 ꢀ z) = 2.752(5) A, N2–
H32. . .O6 (1 ꢀ x, 1 ꢀ y, 1 ꢀ z) = 163ꢁ), whereas O7
establishes a hydrogen bond with the hydrazinic N3 of a
˚
˚
˚
˚
˚
˚
˚
symmetry related ligand (N3–H33 = 0.88 A, H33. . .O7
˚
˚
(1 + x, y, z) = 1.98 A, N3. . .O7 (1 + x, y, z) = 2.732(5) A,
N3–H33. . .O7 (1 + x, y, z) = 143ꢁ). The structure is
additionally stabilised by a hydrogen bond between the
secondary amine group N4 and the O2 hydroxy methyl
group of two symmetry related ligands (N4–H34 =
˚
˚
˚
0.88 A, H34. . .O2 (2 ꢀ x, ꢀy, 1 ꢀ z) = 2.08 A, N4. . .O2
˚
(2 ꢀ x, ꢀy, 1 ꢀ z) = 2.864(5) A, N4–H34. . .O2 (2 ꢀ x,
ꢀy, 1 ꢀ z) = 149ꢁ).
3.3. Magnetic properties
The product of the magnetic susceptibility and the tem-
perature (vMT) measured in the temperature range 5–
300 K is shown in Fig. 4. At 300 K, the vMT value is
3.86 cm3 molꢀ1 K, which is close to the spin-only value for
the high spin iron(III) ion (S = 5/2). The vMT value remains
virtually constant until about 60 K, after which it decreases
relatively abruptly reaching a value of 2.84 cm3 molꢀ1 K at
5 K. This behaviour may be understood as arising from the
zero-field splitting of high spin Fe(III). The magnetic data
were fitted using the following equation:
ꢀ
ꢁ
Ng2b2 0:14 þ 5:12eꢀ3:23X þ 23:85eꢀ6:83X
vM
¼
ð1Þ
4kT
1 þ eꢀ3:23X þ eꢀ6:83X
a
five-membered thiosemicarbazide S,N-chelate ring
Table 3
together with a six-membered pyridoxilydene N,O-chelate
ring – appears to be associated with a severe deviation from
planarity of the iron-ligand framework. The angle between
the least-squares planes through these five-membered and
six-membered rings is 21.93(14)ꢁ. The distances of the cor-
responding atoms to these least-squares planes are
˚
Geometry of intra- and intermolecular hydrogen bonds (A, ꢁ) for
[Fe(H2mthpy)Cl2](CH3C6H4SO3)
˚
˚
˚
D–H. . .A
D–H (A)
H. . .A (A)
D. . .A (A)
D–H. . .A (ꢁ)
O2–H22. . .O6
N2–H32. . .O6a
N3–H33. . .O7b
N4–H34. . .O2c
0.84
0.88
0.88
0.88
1.94
1.90
1.98
2.08
2.772(4)
2.752(5)
2.732(5)
2.864(5)
170
163
143
149
˚
˚
˚
˚
ꢀ0.207(3) A, ꢀ0.156(3) A, ꢀ0.009(4) A, 0.161(4) A, 0.004
˚
˚
(4) A and 0.207(1) A for O1, N1, C1, C2, C6 and Fe for
the six-membered pyridoxilydene ring, severally, and
Standard deviations in the last decimal place are given in parentheses.
Atoms marked with a letter are generated by the symmetry operations:
a = 1 ꢀ x, 1 ꢀ y, 1 ꢀ z; b = 1 + x, y, z; c = 2 ꢀ x, ꢀy, 1 ꢀ z.
˚
˚
˚
˚
ꢀ0.141(1) A, ꢀ0.179(3) A, 0.091(3) A, 0.093(4) A, 0.137

E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
3901
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.ica.
2007.03.045.
4.0
3.8
3.6
3.4
3.2
3.0
2.8
References
[1] C. Shipman Jr., S.H. Smith, J.C. Drach, D.L. Klayman, Antiviral
Res. 6 (1986) 197.
0
50 100 150 200 250 300
T/K
´
[2] S. Padhye, G.B. Kauffman, Coord. Chem. Rev. 63 (1985) 127.
[3] D.X. West, S.L. Dietrich, I. Thientanavanich, C.A. Brown, A.E.
Liberta, Transit. Met. Chem. 19 (1994) 195.
[4] J. Yuan, D.B. Lovejoy, D.R. Richardson, Blood 104 (2004) 1450.
[5] J. Shao, B. Zhou, B. Chu, Y. Yen, Curr. Cancer Drug Targets 6
(2006) 409.
Fig. 4. Temperature dependence of
(CH3C6H4SO3). The solid line corresponds to the fit using the parameters
described in the text.
vMT for [Fe(H2mthpy)Cl2]-
[6] A. Jordan, P. Reichard, Annu. Rev. Biochem. 67 (1998) 71.
[7] P. Nordlund, H. Eklund, J. Mol. Biol. 232 (1993) 123.
[8] J. Shao, B. Zhou, A.J. Di Bilio, L. Zhu, T. Wang, C. Qi, J. Shih, Y.
Yen, Mol. Cancer Ther. 5 (2006) 586.
[9] D.B. Lovejoy, D.R. Richardson, Blood 100 (2002) 666.
[10] J.L. Buss, F.M. Torti, S.V. Torti, Curr. Med. Chem. 10 (2003) 1021.
[11] J.L. Buss, B.T. Greene, J. Turner, F.M. Torti, S.V. Torti, Curr. Top.
Med. Chem. 4 (2004) 1623.
[12] D.R. Richardson, E.H. Tran, P. Ponka, Blood 86 (1995) 4295.
[13] M. Belicchi Ferrari, F. Bisceglie, E. Leporati, G. Pelosi, P. Tarasconi,
Bull. Chem. Soc. Jpn. 75 (2002) 781.
[14] M. Belicchi Ferrari, F. Bisceglie, G. Pelosi, P. Tarasconi, R. Albertini,
P.P. Dall’Aglio, S. Pinelli, A. Bergamo, G. Sava, J. Inorg. Biochem.
98 (2004) 301.
where, X = D/kT, D is the zero-field splitting parameter, g
´
is the Lande factor and the other symbols have their usual
meanings. Eq. (1) is the theoretical equation for the mag-
netic susceptibility resulting from the axial and rhombic
zero-field splitting for an S = 5/2 ion [35]. The best fit
has been obtained with the parameters D = 0.34(1) cmꢀ1
and g = 2.078(3) with a correlation coefficient of 0.98 and
a reduced v2 of 0.0015.
4. Conclusion
[15] V.M. Leovac, V.S. Jevtovic, L.S. Jovanovic, G.A. Bogdanovic, Rev.
J. Serb. Chem. Soc. 70 (2005) 393.
[16] M. Mohan, P.H. Madhuranath, A. Kumar, M. Kumar, N.K. Jha,
Inorg. Chem. 28 (1989) 96.
[17] N.S. Gupta, M. Mohan, N.K. Jha, W.E. Antholine, Inorg. Chim.
Acta 184 (1991) 13.
[18] V.S. Jevtovic, L.S. Jovanovic, V.M. Leovac, L.J. Bjelica, J. Serb.
Chem. Soc. 68 (2003) 929.
Dichloropyridoxal-4-methylthiosemicarbazone iron(III)
p-toluenesulfonate has been obtained by reacting iron(III)
p-toluenesulfonate hexahydrate with pyridoxal-4-methyl-
thiosemicarbazone hydrochloride followed by crystallisa-
tion at room temperature. The crystal structure revealed
a five-coordinate Fe(III) ion in an ONSCl2 environment
that is intermediate between trigonal bipyramidal and
square pyramidal. To the best of our knowledge this is
the first instance in which coordination of this set of donor
atoms to iron has been crystallographically identified. The
ligand is in its neutral zwitterionic form, i.e. it is deproto-
nated at the phenolic-O whereas it is protonated at the pyr-
idine-N and the hydrazinic-N, and coordinates to Fe(III)
by using its thione-S, phenolic-O, and azomethine-N.
The magnetic data are consistent with the behaviour
typical for a high spin Fe(III) ion subjected to zero-field
splitting. The D value of 0.34(1) cmꢀ1 that has been deter-
mined for the present five-coordinate Fe(III) compound
(s = 0.40) is of the same magnitude as the zero-field split-
ting parameter of 0.79 cmꢀ1 that has been reported for
chloro-(N-p-nitrobenzoylimido-meso-tetraphenylporphiri-
nato)iron(III) (s = 0.65).
[19] M. Belicchi Ferrari, G. Fava Gasparri, E. Leporati, C. Pelizzi, P.
Tarasconi, G. Tosi, J. Chem. Soc., Dalton Trans. (1986) 2455.
[20] Bruker, SMART, SAINTPLUS and XPREP Area Detector Control and
integration Software, Smart Apex Software Reference Manuals
Bruker Analytical X-ray instruments Inc., Madison, Wisconsin,
USA, 2000.
[21] G.M. Sheldrick, SADBAS Version 2.03. Multi-Scan Absorption Cor-
rection Program, University of Go¨ttingen, Germany, 2001.
[22] A.J.M. Duisenberg, J. Appl. Crystallogr. 25 (1992) 92.
[23] M.R. Snow, E.R.T. Tiekink, Acta Crystallogr. B44 (1988) 676.
[24] A.L. Spek, J. Appl. Crystallogr. 21 (1988) 578.
[25] Y. Le Page, J. Appl. Crystallogr. 20 (1987) 264.
[26] Y. Le Page, J. Appl. Crystallogr. 21 (1988) 983.
[27] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascar-
ano, L. De Caro, C. Giacovazzo, G. Polidori, R. Spagna, J. Appl.
Crystallogr. 38 (2005) 381.
[28] A.J.C. Wilson (Ed.), International Tables for Crystallography, vol. C,
Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992.
[29] G.M. Sheldrick, SHELXL-97 Program for the Refinement of Crystal
Structures, University of Go¨ttingen, Germany, 1997.
[30] A. Meetsma, PLUTO Molecular Graphics Program. Version of
March 2006. University of Groningen, The Netherlands, 2006.
[31] A.L. Spek, (2006). PLATON Program for the Automated Analysis of
Molecular Geometry (A Multipurpose Crystallographic Tool), Ver-
sion of February 2006. University of Utrecht, The Netherlands. A.L.
Spek, J. Appl. Crystallogr. 36 (2003) 7.
Appendix A. Supplementary material
CCDC 628129 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data
[32] U. Abram, K. Ortner, R. Gust, K. Sommer, J. Chem. Soc., Dalton
Trans. (2000) 735.

3902
E.W. Yemeli Tido et al. / Inorganica Chimica Acta 360 (2007) 3896–3902
[33] V.V. Zelentsov, in: V.I. Spitsyn (Ed.), Advances In Inorganic
Chemistry, MIR Publishers, 1983, p. 122.
[34] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J.
Chem. Soc., Dalton Trans. (1984) 1349.
[35] C.-H. Chen, Y.-Y. Lee, B.-C. Liau, S. Elango, J.-H. Chen, H.-Y.
Hsieh, F.-L. Liao, S.-L. Wang, L.-P. Hwang, J. Chem. Soc., Dalton
Trans. (2002) 3001.