Structural, vibrational, thermal and magnetic investigation of novel Co(II), Cu(II), Zn(II) and Hg(II) crystalline metal complexes with 2-amino-5-benzylmercapto-1,3,4-thiadiazole: A low weight model of protonated copolymer resin

Article abstract of DOI:10.1016/j.jpcs.2004.11.004

The 2-amino-5-benzylmercapto-1,3,4-thiadiazole (C₉H ₉N₃S₂) is a low weight model of a protonated copolymer resin used as a metal uptake agent. New monomeric crystalline metal complexes of C₉H₉N₃S₂ with Co(II), Cu(II), Zn(II) and Hg(II) were synthesized and investigated in order to facilitate the interpretation of the metal/resin binding mode. These materials have been studied by single crystal X-ray Diffraction and FTIR Spectroscopy at room temperature. Crystal data for these triclinic phases are reported. All frameworks consist of discrete monomeric units that provide crystalline stability through a network of hydrogen bond interactions. The Co(II), Zn(II) and Hg(II) ions are surrounded by a tetrahedral arrangement of two thioether monodentate ligands (each one coordinating by a N(1)_thiadiazole atom) and two chlorine atoms. The Cu(II) ion is coordinated by four thioether monodentate ligands (each one coordinating by a N(1)_thiadiazole atom) and one chlorine atom as nearest neighbor in a distorted square pyramidal polyhedron. The spectroscopic data are consistent with the structural model. FTIR spectra evidence changes in the H-bonds in the crystal packing when coordination with these divalent ions is present. Magnetic susceptibility at room temperature for Cu(II) and Co(II) complexes, EPR spectrum at room temperature for Cu(II) complex and thermal properties for all complexes were measured. These results could be useful for the interpretation of the binding mode of M(II)/1,3,4-thiadiazole-2-amino-5-thiol in protonated copolymer resin which are used as uptake agents of toxic metallic ions.

Full text of DOI:10.1016/j.jpcs.2004.11.004

Journal of Physics and Chemistry of Solids 66 (2005) 936–945
www.elsevier.com/locate/jpcs
Structural, vibrational, thermal and magnetic investigation
of novel Co(II), Cu(II), Zn(II) and Hg(II) crystalline metal
complexes with 2-amino-5-benzylmercapto-1,3,4-thiadiazole:
a low weight model of protonated copolymer resin
a
b
G.E. Camı , M. Liu Gonzalez , F. Sanz Ruiz , J.C. Pedregosa
b
a,
*
´
´
a
´ ´ ´ ´
Area de Quımica General e Inorganica ‘Dr. G.F.Puelles’, Facultad de Quımica, Bioquımica y Farmacia, CONICET PIP-4929,
Universidad Nacional de San Luis, Chacabuco y Pedernera, 5700 San Luis, Argentina
´
S.C.S.I.E. (Unidad de Rx)—Facultad de Fısica, Universidad de Valencia, Av. Moliner 50, 46100 Burjassot, Valencia, Spain
b
Received 14 July 2004; accepted 16 November 2004
Abstract
The 2-amino-5-benzylmercapto-1,3,4-thiadiazole (C9H9N3S2) is a low weight model of a protonated copolymer resin used as a metal
uptake agent. New monomeric crystalline metal complexes of C9H9N3S2 with Co(II), Cu(II), Zn(II) and Hg(II) were synthesized and
investigated in order to facilitate the interpretation of the metal/resin binding mode. These materials have been studied by single crystal X-ray
Diffraction and FTIR Spectroscopy at room temperature. Crystal data for these triclinic phases are reported. All frameworks consist of
discrete monomeric units that provide crystalline stability through a network of hydrogen bond interactions. The Co(II), Zn(II) and Hg(II)
ions are surrounded by a tetrahedral arrangement of two thioether monodentate ligands (each one coordinating by a N(1)thiadiazole atom) and
two chlorine atoms. The Cu(II) ion is coordinated by four thioether monodentate ligands (each one coordinating by a N(1)thiadiazole atom) and
one chlorine atom as nearest neighbor in a distorted square pyramidal polyhedron. The spectroscopic data are consistent with the structural
model. FTIR spectra evidence changes in the H-bonds in the crystal packing when coordination with these divalent ions is present. Magnetic
susceptibility at room temperature for Cu(II) and Co(II) complexes, EPR spectrum at room temperature for Cu(II) complex and thermal
properties for all complexes were measured. These results could be useful for the interpretation of the binding mode of M(II)/1,3,4-
thiadiazole-2-amino-5-thiol in protonated copolymer resin which are used as uptake agents of toxic metallic ions.
q 2005 Elsevier Ltd. All rights reserved.
Keywords: D. Crystal structure
1. Introduction
metal ions [4,5]. Thus, a protonated copolymer resin based
on poly(styrene-codivinylbenzene) that incorporates 2-
amino-1,3,4-thiadiazole-5-thiol in its structure has been
used to extract gold and platinum. The binding mode of
gold/resin has been investigated by using a low molecular
weight derivative thioether: 2-amino-5-benzylmercapto-
1,3,4-thiadiazole [6], although its complex structure was
not thoroughly studied.
The structural and electronic modifications in 1,3,4-
thiadiazole ring derivative crystalline compounds with
diverse substituents and their metal complexes have been
particularly interesting due to their pharmacological proper-
ties and inhibition activity on carbonic anhydrase enzyme
[1–3]. In addition, some of these 1,3,4-thiadiazole ring-
containing ligands can be efficient uptake agents of toxic
The 1,3,4-thiadiazole ring allows different substituents at
positions 2 and 5. In the last years the structures and
spectroscopic behavior of some crystalline 1,3,4-thiadiazole
ligands containing –SO2NH2 (sulfonamido) and –SH (thiol)
groups at these positions (particularly position 2) and their
* Corresponding author. Tel.: C54 2652 423789x117; fax: C54 2652
430224.
E-mail address: jpedreg@unsl.edu.ar (J.C. Pedregosa).
0022-3697/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2004.11.004

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
937
Fig. 1. Molecular structure of 5-amino-2-benzylmercapto-1,3,4-thiadiazole.
metal complexes were determined in our laboratory [7–15].
The interactions of metal ions with these ligands have been
widely studied [16–22]. We are interested in analyzing
ligand versatility, crystal packing, H-bond strength in the
lattice, structural modifications, influence of different
substituents at ring positions 2 and 5, coordination sites
and vibrational, thermal and magnetic behavior of new
crystalline metal complexes of 1,3,4-thiadiazole structurally
related ligands.
4-thiadiazole-2-thiol and 1.8 mL (15.32 mmol) of benzyl-
bromide. The reaction was followed by TLC. After 18 hs,
the obtained precipitate was filtered and washed with
distilled water. The filtrate was hydrolyzed with distilled
water. The resulting solid was filtered and dried with P4O10
in a dryer. Thus, C9H9N3S2 (MP 428 K, 97% yield) was
obtained as a white solid which was crystallized using
CH2Cl2-absolute ethanol (5:1). The product was character-
ized by FTIR, NMR, HRMS and the structure was refined
by the single crystal X-ray technique. Our results were
coincident with the structural data previously reported [6].
Complexes. One millimole of the corresponding M(II)
chloride Zn, Co, Hg and Cu and 2 mmol of the ligand were
dissolved in 50 mL of absolute ethanol, with stirring at room
temperature (r.t.) for 2 h. Prismatic crystals of the
complexes were obtained by solvent evaporation at r.t.
after 2 weeks.
The versatility of 1,3,4-thiadiazole derivative thioethers
as ligands in crystalline metal complexes has not received
much attention. As far as we know, information on the
structural and spectroscopic behavior is also very scarce.
Although some crystal thioether structures have been
determined [6–12], there is no previous data of their metal
complex structures determined by single crystal X–ray
technique.
In order to obtain a wider insight of the general properties
of new crystalline phases we have synthesized and analyzed
the structure, coordination sites and vibrational, magnetic
and thermal behavior of Zn(II), Co(II), Hg(II) and Cu(II)
complexes with 2-amino-5-benzylmercapto-1,3,4-thiadia-
zole (C9H9N3S2). This ligand is a low weight model of the
protonated copolymer resin mentioned above (Fig. 1).
2.2. X-ray crystallography
X-ray measurements were carried out for [Co(C9H9N3
S2)2Cl2], [Zn(C9H9N3S2)2Cl2] and [Hg(C9H9N3S2)2Cl2] at
293 K on an Enraf–Nonius CAD-4 Single-Crystal Diffract-
ometer using Mo Ka radiation with a graphite crystal
˚
monochromator (lZ0.7173 A). The unit cell dimensions
were determined from the angular settings of 25 reflections
with q between 1 and 258 for [CoL2Cl2], 6 and 12.958 for
[ZnL2Cl2] and 1.6 and 258 for [HgL2Cl2], and refined with
CAD-4 software [23] and HKL Denzo and Scalepack
programs [24]. The space group was determined as triclinic
2. Experimental
2.1. Synthesis
ꢀ
P1 from no systematic absences. The intensity data were
The syntheses of the ligand and metal complexes were
performed by using analytical grade reagents according to
the following procedures.
collected with the uK2q scan technique and at variable
scan rate, with a maximum scan time of 60 s per reflection.
On all reflections, profile analysis was performed [25].
Lorentz and polarization corrections were applied and the
data were reduced to Fo values [26]. The structures were
solved using SIR92 [27]. Isotropic least-squared refinement
on F2 was performed using SHELX97 [28]. During the final
Ligand. 2-amino-5-benzylmercapto-1,3,4-thiadiazole
(C9H9N3S2) was obtained by complete reaction of 0.4 g
(17.38 mmol) of Na8 in 100 mL of absolute ethanol, in Ar
inert atmosphere and stirring at room temperature (r.t.);
followed by addition of 2 g (15.04 mmol) of 5-amino-1,3,

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
938
stage the non-hydrogen atoms were refined. All hydrogen
atoms positions were Fourier map located. The minimized
function was:
between 4000 and 2000 cmK1, and better than 2 cmK1 in
the remaining ranges.
h
i1=2
X
X
2.4. Thermal and magnetic measurements
uðF02 KFc2Þ2=
uðF02Þ2
;
TG-DTA measurements were made with Shimadzu
TGA-51 and DTA-50 equipment, using platinum pan in
air atmosphere and at a heating rate of 10 8C/min from r.t. to
1273 K.
2
w Z 1=½s2ðF02Þ Cð0:0828PÞ ꢀ
with sðF02Þ from counting statistic and PZðMaxðF02OÞC
2!Fc2Þ=3. The absorption correction was performed by
semiempirical PSISCANS method [29]. The figures were
made with ORTEP [30]. Atomic scattering factors were
calculated with PARST [31].
EPR spectra of polycrystalline samples were recorded at
X band frequencies (9.7 GHz, 100 kHz) using a Bru¨ker ER
200 Spectrometer.
Magnetic susceptibility measurements were carried out
at r.t. with a CAHN-2000 Susceptometer, operating at
6 kGauss, using Hg[Co(NCS)4] as calibrant and correcting
diamagnetism with the appropriate Pascal constants [34].
X-ray measurements were carried out for [Cu(C9H9N3
S2)4Cl]Cl at 293 K on a Nonius Kappa-CCD Single Crystal
˚
Diffractometer, using Mo Ka radiation (lZ0.7173 A). The
images were collected using the oscillation method, with 28
oscillation and 180 s exposure time per image. Data
collection strategy was calculated with the COLLECT program
[32]. Data reduction and cell refinement were performed
with the HKL Denzo and Scalepack programs. The unit cell
dimensions were determined from 7484 reflections (with q
between 2.910 and 26.7338). Crystal structure was solved by
direct methods using the SIR97 program [33]. Anisotropic
least-squares refinement was carried out with SHELX97. All
non-hydrogen atoms were anisotropically refined. Hydro-
gen atoms were located in a difference Fourier map.
Geometrical calculations were calculated with PARST.
The crystallographic plots were made with ORTEP.
3. Results and discussion
3.1. Crystal structure
Complex structures consist of discrete monomeric units
that provide crystalline stability through a network of
hydrogen bond interactions.
Crystal data and structure refinement for the four
complexes are given in Table 1. Fig. 2 shows the ORTEP
drawing of the monomer unit structure of Co(II), Zn(II) and
Hg(II) isostructural complexes, detailing the atomic num-
bering scheme. Fig. 3 shows the ORTEP drawing of the
Cu(II) complex. Relevant bond distances and angles for
each structure are detailed in Table 2. Fig. 4 shows the unit
cell of the Co(II), Zn(II) and Hg(II) complexes, whereas
Fig. 5 shows the unit cell for the Cu(II) complex.
2.3. Spectroscopic data
´ ´
FTIR spectra were recorded on a Nicolet Protege 460
Spectrometer provided with a CsI beamsplitter in the 4000
to 225 cmK1 range, using thin KBr pellet technique for the
solid samples. Spectral resolution was better than 4 cmK1
Table 1
Crystal data and refinement of [Co(C9H9N3S2)2Cl2], [Cu(C9H9N3S2)4Cl]Cl, [Zn(C9H9N3S2)2Cl2] and [Hg(C9H9N3S2)2Cl2]
Complex
[CoL2Cl2]
[CuL4Cl]Cl
[ZnL2Cl2]
[HgL2Cl2]
Empirical formula
Formula weight
Temperature (K)
C18H18Cl2CoN6S4
576.45
C36H36Cl2CuN12S8
1027.69
C18H18Cl2ZnN6S4
582.89
C18H18Cl2HgN6S4
718.11
293(2)
293(2)
293(2)
293(2)
˚
Wave length (A)
0.71073
ꢀ
Triclınic, P1
0.71073
ꢀ
Triclınic, P1
0.71073
ꢀ
Triclınic, P1
0.71073
ꢀ
Triclınic, P1
Crystal system and space group
´
´
´
´
Unit cell dimensions
˚
a (A)
˚
B (A)
9.713(4)
10.013(2)
12.3703(13)
89.073(13)
85.298(17)
89.53(2)
1186.0(5)
2
11.5510(3)
12.3490(3)
17.1140(5)
108.3500(10)
92.7360(10)
97.3580(15)
2287.91(11)
2
9.648(2)
10.0626(16)
12.365(2)
89.078(19)
85.693(18)
81.637(14)
1184.3(4)
2
9.6155(12)
10.0786(12)
12.531(3)
88.939(18)
85.708(19)
82.156(9)
1199.6(3)
2
˚
C (A)
a (degrees)
b (degrees)
g (degrees)
3
˚
Volume (A )
Z
Density (calculated) (Mg/m3)
1.614
1.492
1.635
1.988
Absorption coefficient (mmK1
)
1.320
1.002
1.635
7.006
F(000)
586
1054
592
692
Crystal size (mm)
(0.3!0.25!0.23)
(0.35!0.18!0.04)
(0.15!0.20!0.25)
(0.3!0.2!0.15)

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
939
radius. The N(1B)–M–N(1A) and Cl(1)–M–Cl(2) angles are
approximately 100 and 1208 respectively, in the Co(II) and
Zn(II) complexes, and about 90 and 1368, respectively, in
the Hg(II) complex, thus indicating a greater distortion of
the tetrahedral geometry in the latter complex.
In the Cu(II) complex the ligand–metal ratio is 4:1. The
geometry around the Cu(II) ion is best described as distorted
square pyramidal with four N(1)thiadiazole atoms in the basal
plane and one chlorine atom in apical position. It is
interesting to note that the Cu(II) ion presents an octahedral
geometry in other similar complexes [17,18,37] suggesting
that the steric effect due to the benzyl substituent forces the
Cu(II) ion into a penta-coordinated geometry in the
thioether complex.
The M(II)–Cl bond length in the Cu(II) complex
˚
(2.6627 A) is longer than the same bond in Co(II), Zn(II)
˚
and Hg(II) complexes (2.2460, 2.2246 and 2.383 A,
Fig. 2. ORTEP diagram of [Co(C9H9N3S2)2Cl2], [Zn(C9H9N3S2)2Cl2] and
[Hg(C9H9N3S2)2Cl2].
respectively). The Jahn–Teller effect present in ions with
t26ge3g configuration is responsible of the observed distortion
in the Cu(II) coordination polyhedron.
3.1.1. Coordination polyhedron
Co(II), Zn(II) and Hg(II) complexes are isostructural and
are coordinated in tetrahedral geometry by two thioether
molecules and two chlorine atoms. The ligand-metal ratio is
2:1. Each ligand coordinates through the N(1)thiadiazole atom
in monomeric units. In these complexes the M(II)–N bond
3.1.2. Ligand conformation
The four metal complexes described in this work present
a modified ring N(1)–N(2) bond distance compared to the
same bond distance in the free ligand (see Table 2). It is
remarkable that this distance remains unchanged in the
same case for M(II)–sulfonamide complexes where the
ligand is not coordinating through Nthiadiazole atoms [14,15].
These facts correlate positively with coordination occurring
through one Nthiadiazole atom in the complexes studied here.
˚
length is about 2 A, in agreement with other complexes with
aromatic ring ligands [19,35,36]. The corresponding
distance for the Hg(II) complex is much longer
˚
(2.351–2.361 A) and similar to the Hg(II)–Cl bond length
˚
(2.368–2.383 A) (see Table 2) according to the larger ionic
Fig. 3. ORTEP diagram of [Cu(C9H9N3S2)4Cl]Cl.

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
940
Table 2
Relevant bond distances and bond angles for [Co(C9H9N3S2)2Cl2], [Cu(C9H9N3S2)4Cl]Cl, [Zn(C9H9N3S2)2Cl2], [Hg(C9H9N3S2)2Cl2] and free ligand (with
e.s.d.’s in parenthesis)
Bond
[CoL2Cl2]
[CuL4Cl]Cl
[ZnL2Cl2]
[HgL2Cl2]
Free ligand
˚
2.023(4) A
˚
2.018(4) A
˚
2.2460(14) A
˚
2.2382(13) A
˚
2.015(2) A
˚
2.027(2) A
˚
2.6627(9) A
˚
2.043(2) A
˚
2.046(2) A
˚
2.2246(8) A
˚
2.2315(7) A
˚
2.361(9) A
˚
2.351(10) A
˚
2.383(3) A
˚
2.368(3) A
M–N(1A)
M–N(1B)
M–Cl(1)
–
–
–
–
–
–
M–Cl(2)
–
˚
2.009(2) A
˚
2.021(2) A
˚
1.315(4) A
˚
1.399(3) A
˚
1.292(4) A
˚
1.738(3) A
˚
1.746(3) A
˚
0.87(4) A
Cu–N(1C)
Cu–N(1D)
C(1)–N(1)
N(1)–N(2)
N(2)–C(2)
C(1)–S(1)
C(2)–S(1)
N(3)–H(1)
N(3)–H(2)
C(2)–S(2)
–
–
–
–
–
–
˚
1.337(5) A
˚
1.397(5) A
˚
1.271(6) A
˚
1.708(5) A
˚
1.744(4) A
˚
0.99(6) A
˚
0.72(6) A
˚
1.748(5) A
˚
1.325(3) A
˚
1.395(3) A
˚
1.281(3) A
˚
1.732(3) A
˚
1.745(3) A
˚
0.93(4) A
˚
0.81(3) A
˚
1.746(3) A
˚
1.292(15) A
˚
1.376(13) A
˚
1.293(15) A
˚
1.767(12) A
˚
1.740(13) A
˚
0.86(1) A
˚
0.86(1) A
˚
1.741(13) A
˚
1.308(3) A
˚
1.382(3) A
˚
1.291(3) A
˚
1.738(2) A
˚
1.736(3) A
˚
0.85(3) A
˚
0.87(3) A
˚
1.740(2) A
˚
0.78(4) A
˚
1.744(3) A
˚
1.758(5) A
˚
1.734(3) A
˚
1.752(3) A
˚
1.718(14) A
–
˚
1.344(6) A
˚
1.332(4) A
˚
1.335(4) A
˚
1.310(15) A
˚
1.331(3) A
C(1)–N(3)
˚
1.331(6) A
˚
1.329(4) A
˚
1.327(4) A
˚
1.334(17) A
–
Angle
N(1B)–M–N(1A)
N(1B)–M–Cl(2)
N(1A)–M–Cl(2)
N(1B)–M–Cl(1)
N(1A)–M–Cl(1)
Cl(2)–M–Cl(1)
Cl(1)–Cu–N(1A)
Cl(1)–Cu–N(1B)
Cl(1)–Cu–N(1C)
Cl(1)–Cu–N(1D)
N(1A)–Cu–N(1B)
N(1B)–Cu–N(1C)
N(1C)–Cu–N(1D)
N(1D)–Cu–N(1A)
N(1A)–Cu–N(1C)
N(1B)–Cu–N(1D)
101.30(16)8
108.48(10)8
–
98.53(9)8
106.33(7)8
89.6(4)8
106.1(3)8
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
110.84(10)8
106.62(11)8
–
109.23(6)8
109.28(6)8
108.7(3)8
101.5(3)8
–
109.06(10)8
119.00(6)8
–
110.15(7)8
120.92(3)8
104.6(3)8
136.35(13)8
–
–
–
–
–
–
–
–
–
–
–
95.38(8)8
92.18(7)8
93.11(7)8
101.00(7)8
88.86(9)8
92.28(9)8
87.67(9)8
89.27(9)8
171.38(10)8
166.81(10)8
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
Where M is Co, Zn or Hg.
The contiguous N(1)–C(1) bond length in the complexes is
also modified compared to the free ligand. For instance,
Co(II), Cu(II) and Zn(II) complexes present an increased
N(1)–C(1) bond length and consequently a decrease in
double bond character, while the Hg(II) complex shows a
decreased bond length and therefore an increased double
bond character [38]. The C(1)–N(3) bond distance is
modified in all four complexes. All these changes are
associated to coordination through the ring N(1) atom as
well as to different hydrogen bond interactions in the lattice
with the subsequent electron delocalization of negative
charge through these bonds. As occurs in some 1,3,4-
thiadiazole sulfonamides, the N(1) atom is the best donor
atom because there is a significant interaction between the
1,3,4-thiadiazole ring and the substituted amino group: the
negative differential charge on N(3) is able to move through
the N(3)–C(1)–N(1) bonds and stabilizes the decrease of
negative charge in N(1) generated upon coordination [8].
The N(2)–C(2), C(2)–S(1) and C(1)–S(1) bond distances
in 1,3,4-thiadiazole, the C(2)–S(2) and S(2)–C(3) bond
distances in the 5-position substituent, as well as the angle
between the thiadiazole ring and benzyl group, are not
modified in the complexes compared to the values observed
for the free ligand. These observations indicate that the
substituent at ring position 5 does not participate in the
coordination with the metal ion and thus does not affect
complex formation.
3.1.3. Crystal packing
Interaction between monomeric units occurs through a 3-
D network of hydrogen bonds that give rise to ligand and
complex crystalline structures. The 3-D crystal structure of
the free ligand is stabilized by Namino–H/N(1)thiadiazole and
N
amino–H/N(2)thiadiazole [6], whereas in the complexes
these interactions are Namino–H/N(1 or 2)thiadiazole and
amino–H/Cl.
N
3.2. Vibrational behavior
The overlapped FTIR spectra of [Co(C9H9N3S2)2Cl2]
(which is typical for all four complexes) and free ligand are

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
941
Fig. 4. Unit cell of Co(II), Zn(II) and Hg(II) isostructural complexes.
Fig. 5. Unit cell of Cu(II) complex.

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
942
band in the complexes spectra is due to the new Namino
H/Cl bond, in accordance with the crystal packing.
–
Because of the rigidity of the penta-atomic ring, the
vibrational spectra cannot be interpreted in terms of localized
vibrations, as many atoms of the ring are involved in several
modes [13,41]. Our asignment for each of the 1,3,4-
thiadiazole ring modes (see Table 3) was done in agreement
with that performed by Edwards et al. [46] and our previous
work on Cu(II) complexes with related ligands [10,11].
In the complexes spectra, the nCaN and nN–N modes
are shifted to lower frequencies than the corresponding to
the free ligand. This is consistent with X-ray diffraction data
that shows that the coordination site is located on
N(1)thiadiazole atom. Hence, the C–N and N–N bond
distances are modified upon coordination and complex
formation. No significant changes are observed for other
vibrational modes.
Fig. 6. FTIR spectra of [Co(C9H9N3S2)2Cl2] compared with the C9H9N3S2
free ligand.
In previous works [10,11], nM–N stretching modes have
been difficult to identify because of the presence of weak
bands corresponding to the ligand and lattice modes at low
frequencies. However, in Cu(II) complexes with acetazola-
mide and 5-amino-1,3,4-thiadiazole-2-thiol a band at
370 cmK1 was tentatively assigned to nCu–N stretching
mode [10,11]. In the present work, nM(II)–N modes cannot
be identified due to the mentioned overlapping effects.
shown in Fig. 6. As far as we know, these spectra are
reported here for the first time.
The most significant FTIR band assignments are listed in
Table 3. These vibrational spectra were analyzed on the
basis of general references [39,40] and by comparison with
other related compounds [10,11,13,41–45].
In comparison to the free ligand spectrum, the spectra of
the metal complexes show interesting changes which are
associated with N(1)thiadiazole atom coordination and differ-
ent H-bond interactions, and are in agreement with the
molecular structures and crystalline lattices.
3.3. Thermal behavior
The free ligand spectrum shows two bands at 3292 and
3104 cmK1, which both correspond to the nNH stretching
3.3.1. TG-DTA studies of 2-amino-5-benzylmercapto-1,3,4-
thiadiazole
modes of the Namino–H/N(1)thiadiazole and Namino
H/N(2)thiadiazole interactions. The presence of a third
–
The thermogravimetric curve shows that the ligand is
stable up to 443 K. Beyond this temperature, an important
Table 3
FTIR assignation for [Co(C9H9N3S2)2Cl2], [Cu(C9H9N3S2)4Cl]Cl, [Zn(C9H9N3S2)2Cl2] and [Hg(C9H9N3S2)2Cl2]
Mode
[CoL2Cl2] (cmK1
)
[CuL4Cl]Cl (cmK1
)
[ZnL2Cl2] (cmK1
)
[HgL2Cl2] (cmK1
)
nN–H/X
3388(s)
3269(s)
3179(s)
1620(sh)
1608(s)
1505(s)
3357(s)
3265(s)
3170(s)
1602(s)
3393(s)
3277(s)
3185(s)
1620(sh)
1609(s)
1506(s)
3406(s)
3296(s)
3190(s)
1608(s)
dN–H/X (in plane)
nC–N thiadiazole ring
1512(m)
1494(w)
1244(m)
1070(m)
1028(m)
767(m)
1509(s)
1495(s)
1238(m)
1067(m)
1025(m)
769(s)
nC–C benzyl ring
nN–N thiadiazole ring
1250–1236(d,w)
1071(m)
1025(m)
776(sh)
766(m)
1236–1202(d,m)
1072(m)
1025(m)
dN–H/X (out of plane)
nC–S
767(s)
655(m)
646(w)
560(w)
655(m)
619(m)
560(w)
478(m)
421(m)
401(w)
348(m)
322(m)
294(w)
656(m)
614(m)
559(m)
478(m)
412(w)
374(w)
324(w)
293(m)
620(m)
560(w)
Network modes
478(w)
470(w)
441(w)
291(w)
423(m)
402(w)
381(w)
339(m)
305(m)
s, strong; m, medium; w, weak; sh, shoulder; d, doublet.

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
943
loss of weight takes place in the 443–651 K temperature
range, probably due to decomposition of the major part of
the molecule: both rings and amino group (experimental:
80%, calculated: 79.3%). Finally, there is a continuous loss
of weight until total sample volatilization is reached at
873 K.
The DTA curve shows three endothermic processes that
proceed at 434, 568 and 703 K. The first one is the melting
point, whereas the others are the first and second steps of
decomposition.
3.3.2. TG-DTA studies of the complexes
The thermograms of the complexes reveal that pyrolitic
decomposition occurs in three steps. The first one
corresponds to a weight loss in the 443–651 K temperature
range, probably due to the decomposition of the major part
of the molecule. Immediately after the first step, a second
step takes places; it does not correspond to the metallic
sulfide that can be observed in the thiadiazolic sulfonamide
thermogram [8]. Finally, the last decomposition occurs in
the third step and the remaining residue corresponds to the
particular metallic oxide as follows: experimental: 13.32G
1.00% (calculated 14.22%) of the Co(II) complex, as CoO;
experimental: 7.94G1.00% (calculated 8.73%) of the
Cu(II) complex, as CuO; and experimental: 13G1.00%
(calculated 13.92%) of the Zn(II) complex, as ZnO. These
residues were characterized by powder X-ray diffraction
analysis [47] (ZnO: JCPDS card 890511, CoO: JCPDS card
780431, and CuO: JCPDS card 895899). In the case of
Hg(II) complex, the third step occurs at 718–868 K
temperature range with continuous weight loss until total
volatilization of the sample.
Fig. 7. EPR spectrum of [Cu(C9H9N3S2)4Cl]Cl at 298 K.
in the Cu(II) complex. This result is comparable to those
obtained for other Cu(II) complexes with the same geometry
described by Alzuet and co-workers [48].
No hyperfine structure is observed, probably on account
of the exchange interaction that appears in concentrated
systems, particularly if it consists of monomeric complexes
as in the present case. In polycrystalline powder EPR
spectra, g-values are not necessarily associated to metallic
sites because the resultant spectrum is the average of all the
sites included in the unit cell. In fact, if the unit cell includes
two or more symmetry related sites, a false isotropic
spectrum that expresses the symmetry of the unit cell
instead of that of the individual sites is observed.
Considering that the Zn(II) and Cu(II) are not isostruc-
tural complexes, the copper-doped zinc technique, which
was useful for other similar five-coordinated complexes
[49], cannot be employed in this case.
For all complexes, DTA curves show an endothermic
process around 434 K that corresponds to the rupture of the
coordinated bond and simultaneous melting of the ligand.
Subsequently, another endothermic process occurs at 552,
553, 579 and 542 K for Zn(II), Co(II), Hg(II) and Cu(II)
complexes, respectively, which corresponds to the first
weight loss. Following, a small peak is associated to the
second loss of weight at 733 K (exothermic) for the Zn(II)
complex, 807 K (endothermic) for the Co(II) complex,
718 K (endothermic) for the Hg(II) complex and 664 K
(exothermic) for the Cu(II) complex. Finally, the last
process that occurs is exothermic for Zn(II), Co(II) and
Cu(II) complexes at 866, 895 and 694 K, respectively; while
the Hg(II) complex curve shows an endothermic peak at
814 K corresponding to total sample volatilization.
3.4.2. Magnetic moment
3.4.2.1. Magnetic Moment of [Cu(C9H9N3S2)4Cl]Cl. The
magnetic moment value (at r.t.) of the [Cu(C9H9N3S2)4
Cl]Cl complex is 1.34 MB; somewhat smaller than the spin
moment only. This is not consistent with the presence of the
unpaired electron in monomeric Cu(II) complexes [50] and
is uncommon in mononuclear Cu(II) complexes. Smaller
values than those corresponding to the spin moment are
characteristic of dimeric and trimeric complexes that can
exhibit ferromagnetic or antiferromagnetic couplings [51].
This can be illustrated with the values found for dinuclear
Cu(II) dicarboxylate complexes (1.4 MB) [52].
3.4. Magnetic properties
Our results are not easy to interpret. It seems reasonable
to assume that the two sublattices with a distance around
˚
5 A are exchange coupled, since a direct Cu–Cu exchange is
3.4.1. EPR spectrum
The polycrystalline powder EPR spectrum of the Cu (II)
complex measured at r.t. (Fig. 7) shows a wide signal with
gZ2.063. The spectrum does not change when temperature
is lowered to 110 K. The experimental g value obviously
does not reflect the square pyramidal coordination geometry
rather improbable. The exchange presumably occurs
through an overlapping between the bulky ligand rings of
different [Cu(C9H9N3S2)4Cl]Cl polyhedrons. This overlap-
ping is strongly dependent on electronic density, as has
been observed for similar monomeric complexes with

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G.E. Camı et al. / Journal of Physics and Chemistry of Solids 66 (2005) 936–945
944
1,3,4-thiadiazole ring [48]. However, additional investi-
gations are needed.
the X-ray crystallographic facilities. J.C. P. is member of
CONICET.
3.4.2.2. Magnetic moment of [Co(C9H9N3S2)2Cl2]. Banci
et al. [53] establishes a correlation between meff. and the
geometry for Co(II) complexes. Values of 3.98–4.82 MB
are to be expected when tetrahedral geometry is present.
In the case of [Co(C9H9N3S2)2Cl2], the greater exper-
imental value (4.58 MB) for the magnetic moment probably
indicates an orbital contribution to this moment. This is
expected when the Co(II) ion is in tetrahedral coordination,
which has an A term as the ground state and a T excited one.
A very good agreement between the experimental and
calculated moment is observed.
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