Synthesis and crystal structure characterization of iron(II), cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane

Article abstract of DOI:10.1016/j.poly.2009.02.039

Three new mononuclear complexes of nitrogen-sulfur donor sets, formulated as [Fe^II(L)Cl₂] (1), [Co^II(L)Cl₂] (2) and [Ni^II(L)Cl₂] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synt

Full text of DOI:10.1016/j.poly.2009.02.039

Polyhedron 28 (2009) 1261–1264
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and crystal structure characterization of iron(II), cobalt(II) and
nickel(II) complexes with 1,3-bis(2-pyridylmethylthio)propane
Animesh Patra a, Sandipan Sarkar a, Michael G.B. Drew b, Ennio Zangrando c, Pabitra Chattopadhyay a,
*
a Department of Chemistry, Burdwan University, Golapbag, Burdwan 713 104, India
b Department of Chemistry, Reading University, Reading RG6 6AD, Berks, UK
c Dipartimento di Scienze Chimiche, Via Licio Giorgieri 1, 34127 Trieste, Italy
a r t i c l e i n f o
a b s t r a c t
Three new mononuclear complexes of nitrogen–sulfur donor sets, formulated as [FeII(L)Cl2] (1),
[CoII(L)Cl2] (2) and [NiII(L)Cl2] (3) where L = 1,3-bis(2-pyridylmethylthio)propane, were synthesized
and isolated in their pure form. All the complexes were characterized by physicochemical and spectro-
scopic methods. The solid state structures of complexes 1 and 3 have been established by single crystal
X-ray crystallography. The structural analysis evidences isomorphous crystals with the metal ion in a dis-
torted octahedral geometry that comprises NSSN ligand donors with trans located pyridine rings and
Article history:
Received 22 January 2009
Accepted 19 February 2009
Available online 11 March 2009
Keywords:
Iron(II)
Cobalt(II)
Nickel(II) complex
Nitrogen–sulfur ligands
chlorides in cis positions. In dimethylformamide solution, the complexes were found to exhibit FeII/FeIII
,
CoII/CoIII and NiII/NiIII quasi-reversible redox couples in cyclic voltammograms with E1/2 values (versus
Ag/AgCl at 298 K) of +0.295, +0.795 and +0.745 V for 1, 2 and 3, respectively.
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
cobalt(II) and nickel(II) complexes with 1,3-bis(2-pyridylmethyl-
thio)propane (L) having two pyridinic-N and two thioether-S do-
Considerable attention has been paid to the coordination chem-
istry of nitrogen–sulfur donor ligands towards transition metal
ions [1–7] because these complexes can present many characteris-
tics of related biological systems containing metal ions in the same
coordination environment. Thus it is a challenge for chemists to
design appropriate ligand frames with the purpose of synthesizing
metal complexes with predetermined properties. Structural [8–17]
and reactivity [18–20] studies could provide useful insight into the
chemistry and biochemistry of bio-active molecules. The interest
in the coordination chemistry of S-ligated transition metal com-
plexes arises in part from the fact that they mimic the ligation of
certain biomolecules in proteins.
The first crystal structure of [NiFe] hydrogenase enzyme ex-
tracted from ‘Desulforibrio gigas’ showed the active site containing
an unexpected disulfur bridged heterobimetallic Ni–Fe core, and in
addition two cystein groups were bound to nickel [15–17]. For the
modelling of the active site, imidazole and thioether containing li-
gands are most relevant. Several NxSy ligands have been designed
where the nitrogen belongs to aromatic systems such as pyridine,
imidazole and benzimidazole and their reactivity towards transi-
tion metals have been investigated, in particular with copper(II)
to mimic blue copper proteins such as plastocyanine [10].
nors. Detailed structures of [FeII(L)Cl2] (1) and [NiII(L)Cl2] (3),
established by single crystal X-ray crystallography, are also in-
cluded. The study of the electrochemical behavior of all three com-
plexes shows MII/MIII quasi-reversible redox couples in the cyclic
voltammograms.
2. Experimental
2.1. Materials and physical measurements
All chemicals and reagents were obtained from commercial
sources and were used as received, unless otherwise stated. Sol-
vents were distilled from an appropriate drying agent. The organic
ligand 1,3-bis(2-pyridylmethylthio)propane (L) was synthesized
following the procedure as stated in our earlier report [21].
The C, H, N elemental analyses were performed on a Perkin–El-
mer model 2400 elemental analyzer. The metal contents in the
complexes were analyzed by using a Varian Atomic Absorption
spectrophotometer (AAS) model-AA55B, GTA equipped with a
graphite furnace. The electronic absorption spectra were recorded
on a JASCO UV–Vis/NIR spectrophotometer model V-570. IR spec-
tra were obtained by a JASCO FT-IR spectrometer model 460 plus
using KBr disks. Room temperature magnetic susceptibilities were
recorded using a vibrating sample magnetometer PAR 155 model.
Molar conductances (KM) were measured in a systronics conduc-
tivity meter 304 model in dimethylformamide with a complex
As part of our continuing interest on nitrogen–sulfur polyden-
tate chelators [21], herein we report an account on the iron(II),
* Corresponding author. Tel.: +91 342 2558339; fax: +91 342 2530452.
E-mail address: pabitracc@yahoo.com (P. Chattopadhyay).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.02.039

1262
A. Patra et al. / Polyhedron 28 (2009) 1261–1264
concentration of ꢀ10ꢁ3 mol Lꢁ1. The redox behaviors of the com-
plexes were examined on a computer controlled EG&G PAR model
270 VERSTAT electrochemical instrument using a Ag/AgCl elec-
trode with TBAP as the supporting electrolyte. All the measure-
ments were made at 298 K in dimethylformamide solution for a
complex concentration range of 10ꢁ3–10ꢁ4 mol Lꢁ1 using dry dini-
trogen for 3–4 min in order to remove dissolved oxygen.
the crystal positioned at 90 mm from the image plate). Mo Ka radi-
ation (k = 0.71073 Å) was used for both data collections. Cell refine-
ment, indexing and scaling of the data sets were carried out using
programs CRYSALIS [22], DENZO and SCALEPACK [23]. An absorption cor-
rection was applied to 1 by the ABSPACK program [24]. Both struc-
tures were solved using direct methods with the SHELXS97 program
and refined by the full-matrix least-squares method based on F2
with all observed reflections [25]. Hydrogen atoms were fixed at
geometrical positions. As the complexes were located on a crystal-
lographic twofold axis, the central methylene C(8) atom results
was disordered over two sites (0.5 occupancy each). All the calcu-
lations were performed using the WINGX System, Version 1.70.01
[26].
2.2. Preparation of the complexes
The complexes were synthesized following a common proce-
dure, as described below, using the respective metal(II) chloride
salts and 1,3-bis(2-pyridylmethylthio)propane (L) in a 1:1 mole ra-
tio. To a methanolic solution (15 mL) of L (276.0 mg, 1.0 mmol), ir-
on(II) chloride tetrahydrate (1.0 mmol) (for 1), cobalt(II) chloride
hexahydrate (1.0 mmol) (for 2) or nickel(II) chloride hexahydrate
(for 3) was added dropwise, stirring the mixture for an hour. The
reaction mixture was refluxed for 3 h and then kept at room tem-
perature. The pure crystallized product was obtained from this
solution by allowing slow evaporation of the solvent. The product
was collected by filtration followed by washing with water and
methanol, and dried in vacuo.
3. Results and discussion
3.1. Synthesis and characterization
The organic ligand 1,3-bis(2-pyridylmethylthio)propane (L) was
synthesized by the reaction of the respective alkyl dithiol com-
pound with 2-picolyl chloride in the presence of sodium ethoxide.
The complexes were obtained in good yields from the reaction of
the corresponding metal salt with an equimolar amount of the
respective organic moiety in methanol medium. All the complexes
are monomeric in nature and are sparingly soluble in common or-
ganic solvents. The complex conductivity measurements in
dimethylformamide show conductance values in range 42–
52Ko molꢁ1 cmꢁ1, which suggest that the complexes exist in solu-
[Fe(L)Cl2] (1): Yield: 70–75%; Anal. Calc. for C15H18Cl2FeN2S2: C,
43.15; H, 4.31; N, 6.71; Fe, 13.42. Found: C, 43.18; H, 4.32; N, 6.79;
Fe, 13.50%. IR (cmꢁ1): mC@N 1468; mC–S 758. Magnetic moment (
l,
B.M.): 5.45. Conductivity (Ko, X
ꢁ1 cm2 molꢁ1) in DMF: 45.
[Co(L)Cl2] (2): Yield: 71–75%; Anal. Calc. for C15H18Cl2CoN2S2: C,
42.86; H, 4.29; N, 6.67; Co, 14.03. Found: C, 43.12; H, 4.15; N, 6.5 1;
Co, 13.91%. IR (cmꢁ1): mC@N 1472; mC–S 761. Magnetic moment (
l,
tion as non-electrolytes. The magnetic moment (
perature of iron(II) in (1) is 5.45 B.M., which indicates a high-spin
octahedral iron(II) complex; the values of for the cobalt(II) and
l) at room tem-
B.M.): 4.91. Conductivity (Ko, X
ꢁ1 cm2 molꢁ1) in DMF: 52.
[Ni(L)Cl2] (3): Yield: 80–85%; Anal. Calc. for C15H18Cl2N2NiS2: C,
l
42.85; H, 4.29; N, 6.67; Ni, 13.99. Found: C, 42.99; H, 4.18; N, 6.79;
nickel(II) complexes are 4.91 and 3.08 B.M., respectively.
Ni, 14.08%. IR (cmꢁ1): mC@N 1470; mC–S 760. Magnetic moment (
l,
B.M.): 3.08. Conductivity (Ko
, X
ꢁ1 cm2 molꢁ1) in DMF: 42.
3.2. Structures of complexes 1 and 3
2.3. X-ray crystal structure analysis
The X-ray structural analyses evidence that the crystals of 1 and
3 are isomorphous, and an ORTEP view of complex 1 is shown in
Fig. 1, together with the atom numbering scheme. The metal re-
sides on a crystallographic twofold axis bisecting the Cl–M–Cl
and S–M–S angles. Thus the methylene C(8) atom of the organic
moiety is disordered over two positions (each of occupancy 0.5),
and only one orientation is displayed in Fig. 1. The tetradentate
NSSN ligand is wrapped around the metal in such a way that the
pyridine rings are in trans positions and the metal ion completes
the highly distorted octahedral coordination sphere with two chlo-
rides located in cis positions. The present coordination pattern of L
Single crystals of complexes 1 and 3 suitable for X-ray diffrac-
tion analysis were grown by slow evaporation of methanolic solu-
tions at ambient temperature. Crystallographic data and details of
the refinements are provided in Table 1. Diffraction data for 1 were
collected at 150(2) K using the Oxford Diffraction X-Calibur CCD
System (321 frames, counting time of 2 s, the crystal positioned
at 50 mm from the CCD). The experiment for 2 was carried out at
room temperature on a Nonius DIP-1030H system (45 frames,
Table 1
Crystallographic data for 1 and 3.
1
3
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C15H18Cl2FeN2S2
417.18
150(2)
orthorhombic
Pbcn
14.315(2)
8.4443(9)
14.5516(18)
1759.0(4)
4
C15H18Cl2N2NiS2
420.04
293(2)
14.312(3)
8.551(2)
14.678(3)
1796.3(7)
b (Å)
c (Å)
Volume (Å3)
Z
qcalc (g/cm3)
F(000)
1.575
856
1.553
864
h range (°)
2.80–30.00
1.395
2.77–29.64
1.606
l
(Mo K
a )
) (mmꢁ1
Unique reflections/data I > 2
r
(I)
2528/1011
0.0854/0.2129
0.891
1.596, ꢁ1.604
2402/1600
0.0348/0.0943
0.888
0.491, ꢁ0.476
Fig. 1. ORTEP drawing (ellipsoids at 50% probability) of complex [Fe(L)Cl2] (1). The
molecule is located on a twofold axis and only one position for the disordered C(8)
methylene is shown. The same atom numbering is applied to the isomorphous
complex [Ni(L)Cl2] (3), substituting Fe with Ni.
Final R1/wR2 indices [I > 2
r(I)]
Goodness-of-fit
D
q
(e Aꢁ3
)

A. Patra et al. / Polyhedron 28 (2009) 1261–1264
1263
758–761 cmꢁ1, which are assignable to
in addition to the other characteristic bands of the organic moie-
ties. This observation supports the presence of the ligand frame
mC@N and
m
C–S, respectively,
Table 2
Coordination bond distances (Å) and angles (°) for 1 and 3.
1, M = Fe
3, M = Ni
containing the pyridine ring and the C–S bond, and mC–S is generally
Bond distance (Å)
observed in the free ligand in the range of 780–790 cmꢁ1 [21].
The electronic absorption spectra of complexes 1–3 were re-
corded at room temperature using dimethylformamide as the sol-
vent and the data tabulated in Table 3. All the spectra in the high
energy region (below 400 nm) exhibit bands corresponding to
M–N(1)
M–S(1)
M–Cl(1)
2.099(5)
2.440(2)
2.384(2)
2.104(2)
2.451(1)
2.392(1)
Bond angles (°)
N(1)–M–N(10)
N(1)–M–Cl(10)
N(1)–M–Cl(1)
N(1)–M–S(1)
N(1)–M–S(10)
Cl(1)–M–Cl(10)
Cl(1)–M–S(1)
Cl(1)–M–S(10)
S(1)–M–S(10)
167.4(3)
95.35(15)
93.16(15)
82.40(15)
89.23(15)
94.90(9)
84.20(6)
177.51(5)
96.80(9)
166.48(9)
95.50(5)
93.63(5)
82.22(5)
88.77(5)
94.88(4)
84.38(3)
177.54(2)
96.45(3)
*
*
transitions. In addition, charac-
intramolecular
p
?
p
and n ?
p
teristic bands for the complexes were detected as follows.
In the electronic spectrum of [Fe(L)Cl2], a prominent peak
around 475 nm with a shoulder at about 752 nm was observed,
corresponding to MLCT and d–d transitions, respectively. The elec-
tronic spectrum of 2 shows bands at 425, 560 and 967 nm, assign-
able to the transitions 4T1g ? 4T1g(P), 4T1g ? 4A2g(F) and
4T1g ? 4T2g(F), respectively. The position of these bands indicates
an octahedral geometry about the CoII ion [29]. The spectrum of
3 exhibits bands at 475, 685 and 873 nm, which may be assigned
Primed atoms at ꢁx,y,ꢁz + 1/2.
was also detected in the neutral [Ni(L)(ONO2)2] derivative [27], but
it is noteworthy that in the trigonal bipyramidal copper(II) com-
plex [Cu(L)Cl]+ [21] a pyridine-N and a thioether-S reside at the ax-
ial positions whereas the equatorial sites were occupied by the
other N and S donors and by the chloride ligand. The coordination
bond lengths and angles of 1 and 3, listed in Table 2, show only
minor differences related to the metal ionic radii. The M–N bond
3
3
3
to A2g(F) ? 3T1g(P), A2g(F) ? 3T1g(F) and A2g(F) ? 3T2g(F) transi-
tions, respectively. These observations suggest an octahedral
geometry of the NiII ion [30].
3.4. Electrochemistry
The redox properties of the complexes were examined by cyclic
voltammetry using a Pt-disk working electrode and a Pt-wire
auxiliary electrode in dry dimethylformamide using [n-Bu4N]ClO4
as the supporting electrolyte. Voltammetric data are set out in
Table 3.
lengths are comparable within their e.s.d.’s (2.099(5) and
0
2.104(2) ÅA in 1 and 3, respectively), while the values of the M–S
0
and M–Cl distances differ by c0a. 0.01 ÅA, being of 2.440(1),
0
2.451(1) ÅA and 2.384(2), 2.392(1) ÅA in 1 and 3, respectively. The
bond angles subtended at the metal differ by less than 1° in the
two structures, but they deviate considerably from the ideal octa-
hedral values and the N–M–N angle of 167° (mean value for the
two structures) shows the highest deviation. In fact the pyridine
rings of the ligand are bent with respect to the S2Cl2 plane, forming
a dihedral angle of 80.57° (mean value), likely induced by ligand
constraints upon coordination, while the dihedral angle made by
the trans located pyridine planes is 55.3(2)° and 54.9(1)° in 1
and 3, respectively. The bond distances and geometrical distortions
of 3 agree with those found in [Ni(2,20-(2,5-dithiahexamethylene)
dipyridine)Cl2] [28] while small differences are evidenced when
compared with the disordered crystal structure of [Ni(L)(ONO2)2]
[7].
The voltammetric response for [Fe(L)Cl2] (1) exhibits an oxida-
tive couple at the E1/2 value of +0.295 V, assigned to the FeII/FeIII
pair, [29] with a peak potential separation (DEp) of 120 mV and
cathodic to anodic current intensity ratio of 0.97. The cyclic vol-
tammogram of [Co(L)Cl2] (2) shows a quasi-reversible peak for
the CoII/CoIII redox couple at E1/2 of 0.795 V with
DEp of
195 mV. The cyclic voltammogram of [Ni(L)Cl2] (3) exhibits a
quasi-reversible NiII/NiIII redox couple centered at 0.745 V versus
Ag/AgCl. Here, the E1/2 value for complex 3 lies at the higher side
of the range generally measured, 0.3–0.8 V, for the NiIII/NiIII oxi-
dation potential data for thioether containing nickel(II) com-
plexes, [31] indicating that NiII is fairly stabilised in 3. No
cathodic response, recommended for NiII ? NiI reduction, was
observed for 3 up to ꢁ1.51 V. The voltammetric parameters were
studied in the scan rate interval 50–400 mV sꢁ1. The ratio be-
tween the cathodic peak current and the square root of the scan
3.3. Spectroscopic properties
The infrared spectra of all the complexes exhibit characteristic
strong to medium intensity bands in the regions 1468–1472 and
rate (Ipc/ ) is approximately constant. The peak potential
m1/2
shows a small dependence on the scan rate. The ratio Ipc to Ipa
is close to unity. From these data, it can be deduced that the re-
dox couple is related to a quasi-reversible one-electron transfer
process controlled by diffusion.
Table 3
UV–Vis spectral and electrochemical data.a
Compound UV–Vis dataa
Electrochemical datab
4. Conclusion
a
a
k (nm)
Epc
(V)
Epa
(V)
E1/2
Reversibility
(Ipc/Ipa
(
e
, dm3 molꢁ1 cmꢁ1
)
(V)
)
The synthesis and characterization of three new mononuclear
complexes of iron(II), cobalt(II) and nickel(II) with a N2S2 donor
set have been performed. No inert atmosphere (i.e. dinitrogen) is
required for the synthesis of the iron(II) and cobalt(II) complexes,
but these are prone to aerial oxidation. Structural characterization
of 1 and 3 by X-ray diffraction indicates isomorphous crystals with
the metal ion in an octahedral geometry with the chloride and py
ligands occupying cis and trans positions, respectively. All the com-
plexes manifest very similar redox behavior in dimethylformamide
solution, showing MII/MIII redox couples in the cyclic voltammo-
grams, but no cathodic response for the MII/MI redox process.
1
2
3
212(9530), 261(8310),
332(3010), 475(975),
752(108)
210(9000), 257(6300),
337(2820), 425(89),
560(186), 967(22)
210(10230), 258(7430),
328(2915), 475(221),
685(520), 873(31)
+0.235 +0.355 +0.295 0.97
+0.600 +0.990 +0.795 1.03
+0.665 +0.825 +0.745 0.93
a
In DMF.
Data recorded in mV, at 298 K and scan rate 100 mV sꢁ1; E1/2 = (Epc + Epa)/2; Ipc
b
/
Ipa is constant for scans in the range of 50–400 mV sꢁ1
.

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A. Patra et al. / Polyhedron 28 (2009) 1261–1264
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Acknowledgements
Financial support from the Council of Scientific and Industrial
Research (CSIR), New Delhi, India, is gratefully acknowledged.
We thank EPSRC and the University of Reading for funds for the
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