Mercury complexes with the ligand benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone

Article abstract of DOI:10.1016/j.ica.2009.08.029

The Schiff base benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone (LH) and its complexes [Hg(NO₃)(LH)₂]NO₃ (1), [Hg(L)₂] (2), [Hg(LH)₂(μ-X)₂HgX₂] [X = Cl (3), Br (4)], [HgI(LH)(μ-

Full text of DOI:10.1016/j.ica.2009.08.029

Inorganica Chimica Acta 363 (2010) 1275–1283
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Mercury complexes with the ligand benzaldehyde-N(4),N(4)-
dimethylthiosemicarbazone
*
Elena López-Torres , M. Antonia Mendiola
Departamento de Química Inorgánica, C/Francisco Tomás y Valiente, 7, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 May 2009
Received in revised form 14 August 2009
Accepted 23 August 2009
Available online 28 August 2009
The Schiff base benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone (LH) and its complexes [Hg(NO3)
(LH)2]NO3 (1), [Hg(L)2] (2), [Hg(LH)2(l-X)2HgX2] [X = Cl (3), Br (4)], [HgI(LH)(l-I)2HgI(LH)] (5) and
[HgI2(LH)] (6) have been synthesized and characterized by IR, mass spectrometry, 1H and 13C NMR and
by single crystal X-ray diffraction. All the complexes were obtained in ethanol and complex 2, in which
the ligand is deprotonated, in addition needs the presence of basic medium. From mercury(II) iodide two
complexes with the same molar ratio but with different structures were isolated. In all the complexes the
ligand acts as a NS chelate, except in complex 5 in which is only S-donor. The coordination number of the
mercury ion and the structures of the complexes depend on the counterion. Complexes 1, 2 and 6 are
monomeric species but with different coordination spheres: N2S2O2 with a distorted octahedral arrange-
ment in complex 1, and N2S2 or NSI2 in a pseudo-tetrahedral geometry in complexes 2 and 6, respectively.
However, 3, 4 and 5 are binuclear complexes with two halido bridges, but they show two different struc-
tures. In 3 and 4, each mercury ion has a different environment giving an asymmetric structure, one is
bonded to two NS-ligands and two halido bridges in a distorted octahedral geometry, and the other
one has a tetrahedral environment formed by four halido ligands. In complex 5 both mercury ions are
equivalent with a SI3 distorted tetrahedral coordination sphere, formed by one S-bonded ligand, one ter-
minal iodido and two iodido bridges.
Dedicated to Jonathan R. Dilworth.
Keywords:
Bidentate ligands
Structure elucidation
Mercury(II) complexes
Benzaldehyde
Thiosemicarbazones
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
ible, often with distorted trigonal or tetrahedral coordination
geometries [5–7].
Industrial and also dental use of mercury has led to significant
environmental pollutions. In addition, atmospheric oxidation and
also methylation to methylmercury in natural waters caused se-
vere contamination via the food chain. Despite far-reaching efforts
to reduce the pollution, even currently, metallic mercury used for
small scale gold mining or gold ore processing is causing both
acute and chronic poisoning [1–3].
Mercury(II) is known to affect the central nervous system and
also has renal, gastrointestinal and hematologic toxicity [2]. The
high affinity of Hg(II) for sulfur-containing biomolecules, in partic-
ular, proteins with cysteine residues, has been proposed to inhibit
or deactivate the biological function of several enzymes [3,4]. Che-
lating agents such as D-penicillamine (H2Pen@HSC(CH3)2–
CH(NH3)+COOÀ) and BAL (2,3-dimercaptopropanol) have been clin-
ically used for detoxification and efficiently reduce plasma levels of
mercury(II) [2–4]. Often, very stable forms include linear com-
plexes with two sulfur ligands; nevertheless, the Hg–S bonds are
labile and for higher coordination numbers the structures are flex-
Thiosemicarbazones have been extensively studied due to their
pharmacological properties and their coordinative behavior to-
wards transition metal ions [8–10]. However, very few mer-
cury(II) complexes with thiosemicarbazones are known,
although they are good candidates as chelating agents for this me-
tal ion. Some of them are based on potentially tridentate ligands,
such as 2-acetylpyridine thiosemicarbazone, 2-pyridineforma-
mide thiosemicarbazone, benzaldehyde thiosemicarbazone or
their N(4) substituted thiosemicarbazones [11–13]. Reaction of
these thiosemicarbazones with Hg(II) halides give rise to five-
coordinate compounds with formula [Hg(LH)X2] (X = Cl, Br or I)
in which the coordination occurs through the pyridine and the
azomethine nitrogen atoms and the thiocarbonyl group [14,15].
Although they are less known these thiosemicarbazones can also
form binuclear or polynuclear complexes in which the sulfur or
the halogen atom acts as a bridge between metal centers [11,12]
and, in some cases, they also behave as S-monodentate ligands
to form complexes with formula [Hg(LH)2X2], where the mercury
atom is in a tetrahedral arrangement [16,17]. Polymerization is
rare and only one coordination polymer with a thiosemicarbazone
ligand is reported [16]. In our group, we have explored the
reactivity of a N2S2 bis(thiosemicarbazone) [18] and a potentially
* Corresponding author. Tel.: +34 914972376; fax: +34 914974833.
E-mail address: elena.lopez@uam.es (E. López-Torres).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.08.029

1276
E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
bidentate triazine 3-thione ligand [19], both derived from benzil
and thiosemicarbazone, with mercury (II) nitrate and methylmer-
cury chloride. In the three complexes characterized by X-ray dif-
fraction, the ligands were only bonded to the mercury through
the sulfur atom, giving a linear arrangement, results that point
out the high affinity of mercury for the thiocarbonyl group and
for a low coordination number.
In this paper we report the synthesis of the ligand benzalde-
hyde-N(4),N(4)-dimethylthiosemicarbazone LH and its complexes
derived from the reaction with HgX2 (X = Cl, Br, I or NO3). We have
obtained complexes with different Hg:LH ratio and with the ligand
being neutral or deprotonated. The complexes have been charac-
terized using NMR, IR and mass spectrometry. The X-ray single
crystal structures of the complexes and the thiosemicarbazone
LH are also reported.
2.2.2. Preparation of the complexes
2.2.2.1. [Hg(NO3)(LH)2]NO3 (1). A solution of LH (0.100 g,
0.48 mmol) in ethanol (10 mL) was mixed with Hg(NO3)2ÁH2O
(0.082 g, 0.24 mmol). The mixture was stirred at room temperature
for 2 h. The yellow precipitate was filtered off, washed with etha-
nol and diethyl ether and dried in vacuo. Yield 75%. MS (FAB): m/
z (%): 614.9 (100) [HgL(LH)]+. 1H NMR ([D6]DMSO, d ppm): 9.0 (s,
1H, NH), 8.4 (d, 1H, CH), 7.8 (m, 2H, Ph), 7.5 (m, 3H, Ph), 3.2 (s,
6H, CH3). 13C NMR ([D6]DMSO, d ppm): 168.4 (CS), 153.0 (CN),
135.3, 132.7, 131.4, 129.3, 129.0, 128.4, 126.7, 125.6 (Ph), 41.4
(CH3). IR (KBr, cmÀ1):
(CH)Me 2931, (NO)NO3 1768, 1698, 1537,
1590, (NO)NO3 1384,1315, (CS) 930.
m(NH) 3216,
m
(CH) 3118,
m(CH)Ph 3060,
m
m
m
(CN) 1603, d(NCS)
m
m
Single crystals suitable for X-ray diffraction analysis were ob-
tained from the mother liquor.
2.2.2.2. [Hg(L)2] (2). A solution of LH (0.100 g, 0.48 mmol) in etha-
nol (10 mL) with LiOHÁH2O (0.020 g, 0.48 mmol) was mixed with
Hg(NO3)2ÁH2O (0.082 g, 0.24 mmol). The mixture was stirred at
room temperature for 4 h and the scarce solid was separated by fil-
tration and discarded. A crystalline yellow solid was formed from
evaporation of the filtrate overnight that was filtered off, washed
with cold ethanol and diethyl ether and dried in vacuo. Yield
80%. (FAB): m/z (%): 614 (100) [M+H]+. 1H NMR (CDCl3, d ppm):
8.4 (s, 1H, CH), 8.2 (d, 1H, Ph), 7.5–7.2 (m, 4H, Ph), 3.2 (s, 6H,
CH3). 13C NMR (CDCl3, d ppm): 153.1 (CS), 146.8 (CN), 134.0,
132.7, 131.4, 129.6, 129.2, 128.3. 128.1, 128.0 (Ph), 40.1, 39.6
2. Experimental
2.1. Physical measurements
Microanalyses were carried out using a LECO CHNS-932 Ele-
mental Analyzer. IR spectra in the 4000–400 cmÀ1 range were re-
corded as KBr pellets on a Jasco FT/IR-410 spectrophotometer.
Fast atom bombardment (FAB) mass spectra were recorded on a
VG Auto Spec instrument using Cs as the fast atom and m-nitro-
benzylalcohol (mNBA) as the matrix. Electrospray Ionization (ESI)
mass spectra were performed with an ion trap instrument LCQ
Deca XP plus (Thermo Instruments). An ESI source was used in po-
sitive ionization mode. The instrumental parameters were set as
follows: mass range scanned from m/z 500 to 2000; Source Voltage
(KV): 4.5; Seath gas flow rate: 11; Capillary Temperature (C): 250;
Capillary Voltage (V): 38 and Tube Lens Voltage (V): 30. Conductiv-
ity data were measured using freshly prepared DMF solutions (ca.
10À3 M) at 25 °C with a Metrohm Herisau model E-518 instrument.
1H and 13C spectra were recorded on a spectrometer Bruker AMX-
300 using CDCl3 or DMSO-d6 as solvents and TMS as internal
reference.
(CH3). IR (KBr, cmÀ1):
d(NCS) 1590, 1567, (CS) 877.
m(CH) 3071, m(CH)Ph 3021, m(CH)Me 2920,
m
Single crystals suitable for X-ray diffraction analysis were ob-
tained by slow evaporation of the mother liquor.
This complex was also obtained from HgX2 (Cl, Br or I) under the
same reaction conditions.
2.2.2.3. [Hg(LH)2(l-Cl)2HgCl2] (3). A solution of LH (0.100 g,
0.48 mmol) in ethanol (10 mL) was mixed with HgCl2 (0.132 g,
0.48 mmol). The mixture was stirred at room temperature for
4 h. The light yellow solid formed was filtered off, washed with
ethanol and dried in vacuo. Yield 94%. (ESI): m/z: 614 [HgL(LH)]+.
1H NMR ([D6]DMSO, d ppm): 11.0 (s, 1H, NH), 8.4 (s, 1H, CH), 7.8
(m, 2H, Ph), 7.4 (m, 3H, Ph), 3.3 (s, 6H, CH3). 13C NMR ([D6]DMSO,
d ppm): 174.5 (CS), 149.4 (CN), 133.6, 131.0, 129.6, 128.2 (Ph), 42.6
2.2. Synthesis of the ligands and complexes
All the reagents and solvents were commercially obtained and
used without further purifications.
(CH3). IR (KBr, cmÀ1):
(CH)Me 2930, d(NCS), 1602, 1577,
This complex was also obtained working in a LH:HgX2 2:1 mo-
lar ratio.
Single crystals suitable for X-ray diffraction analysis were ob-
tained by recrystallization in DMSO.
m
(NH) 3192,
m
(CH) 3121,
m(CH)Ph 3055, 3022,
m
m(CS), 968.
2.2.1. Preparation of benzaldehyde-N(4),N(4)-
dimethylthiosemicarbazone, (LH)
The compound LH was prepared by condensation of benzalde-
hyde and N(4),N(4)-dimethylthiosemicarbazide. Benzaldehyde
(0.5 mL, 4.9 mmol) was added over a solution of N(4),N(4)-dimeth-
ylthiosemicarbazide (0.500 g, 4.5 mmol) in ethanol:water 1:1
(15 mL). The yellow solution was stirred at room temperature for
3 h. The white solid formed was collected by filtration, washed
thoroughly with distilled water, ethanol and diethyl ether and
dried in vacuo. Yield 70%. Anal. Calc. for C10H13N3S: C, 57.97; H,
6.28; N, 20.28; S, 15.46. Found: C, 57.94; H, 6.21; N, 20.25; S,
15.44. MS (FAB): m/z (%): 208.1 (100) [M+H]+. 1H NMR (CDCl3, d
ppm): 9.0 (s, 1H, NH), 7.7 (s, 1H, CH), 7.6 (m, 2H, Ph), 7.4 (m, 3H,
Ph), 3.5 (s, 6H, CH3). 1H NMR ([D6]DMSO, d ppm): 10.9 (s, 1H,
NH), 8.2 (s, 1H, CH), 7.6 (m, 2H, Ph), 7.4 (m, 3H, Ph), 3.2 (s, 6H,
CH3). 13C NMR (CDCl3, d ppm): 181.8 (CS), 142.9 (CN), 134.1,
2.2.2.4. [Hg(LH)2(l-Br)2HgBr2] (4). The reaction was carried out
using the procedure described above but using HgBr2 (0.172 g,
0.48 mmol) instead of HgCl2. Yield 90%. (ESI): m/z: 614 [HgL(LH)]+.
1H NMR (CDCl3, d ppm): 8.8 (s, 1H, NH), 7.6 (s, 1H, CH), 7.4 (m, 2H,
Ph), 7.3 (m, 3H, Ph), 3.4 (s, 6H, CH3). 1H NMR ([D6]DMSO, d ppm):
8.4 (s, 1H, CH), 7.8 (m, 2H, Ph), 7.4 (m, 3H, Ph), 3.3 (s, 6H, CH3). 13
C
NMR ([D6]DMSO, d ppm): 173.2 (CS), 150.9 (CN), 133.2, 131.3,
129.2, 128.5 (Ph), 42.4 (CH3). IR (KBr, cmÀ1):
(NH) 3195, (CH)
3138, (CH)Ph 3061, 3000, (CH)Me 2928, d(NCS), 1601, 1580,
(CS) 966.
This complex was also obtained working in a LH:HgX2 2:1 mo-
lar ratio.
Single crystals suitable for X-ray diffraction analysis were ob-
tained by recrystallization in DMSO.
m
m
m
m
m
130.5, 129.2, 127.5 (Ph), 44.5 (CH3). IR (KBr, cmÀ1):
(CH) 3165, (CH)Ph 3009, (CH)Me 2925, 2894,
d(HNCS) 1551, (CS) 1020.
m
(NH) 3229,
m
m
m
m(CN) 1600,
m
Single crystals suitable for X-ray diffraction analysis were ob-
2.2.2.5. [HgI(LH)(l-I)2HgI(LH)] (5) and [HgI2LH] (6). The reaction
tained from the mother liquor.
was carried out following the procedure described for 3 but HgI2

E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
1277
(0.220 g, 0.48 mmol) was used instead of HgCl2. Data for the yellow
solid formed (5): Yield 88%. (ESI): m/z: 535.9 [HgI(LH)]+. 1H NMR
([D6]DMSO, d ppm): 11 (s, 1H, NH), 8.5 (s, 1H, CH), 7.8 (m, 2H,
Ph), 7.5 (m, 3H, Ph), 3.3 (s, 6H, CH3). 13C NMR ([D6]DMSO, d
ppm): 173.4 (CS), 151.5 (CN), 133.0, 131.5, 129.2, 128.6 (Ph), 42.7
Single crystals suitable for X-ray diffraction analysis were ob-
tained by recrystallization in DMSO.
2.3. Crystallography
(CH3). IR (KBr, cmÀ1):
(CH)Ph 3061,
3015, (CH)Me 2969, (CN) 1599, d(HNCS) 1570, m(CS) 959. Data
m(NH) 3279,
m(CH) 3138,
m
Single crystal X-ray diffraction measurement were performed
using a Bruker AXS Kappa Apex-II diffractometer equipped with
an Apex-II CCD area detector using a graphite monochromator
m
m
for the light yellow crystalline material formed from the filtrate
(6): Yield: 7%. (ESI): m/z: 535.9 [HgI(LH)]+ 1H NMR (CDCl3, d
ppm): 9.1 (s, 1H, NH), 7.8 (s, 1H, CH), 7.6 (m, 2H, Ph), 7.4 (m, 3H,
Ph), 3.4 (s, 6H, CH3). 13C NMR (CDCl3, d ppm): 171.8 (CS), 157.0
(CN), 131.3, 129.5, 128.8, 126.7(Ph), 41.5 (CH3). IR (KBr, cmÀ1):
(Mo Ka radiation, k = 0.71073 Å). The substantial redundancy in
data allows empirical absorption corrections (SADABS) [20] to be ap-
plied using multiple measurements of symmetry-equivalent
reflections. The raw intensity data frames were integrated with
the SAINT program, which also applied corrections for Lorentz and
polarization effects [21].
m
(NH) 3232,
1551, 1569,
Complex 5 was also obtained working in a LH:HgX2 2:1 molar
ratio.
m
(CH) 3167,
m(CH)Ph 3015, m(CH)Me 2925, d(NCS),
m
(CS) 953.
The software package SHELXTL version 6.10 was used for space
group determination, structure solution and refinement. The
Table 1
Crystallographic data for LH and complexes 1ÁH2O, 2 and 3.
LH
1ÁH2O
2
3
Empirical formula
Formula weight
Temperature
C10H13N3S
207.29
100(2) K
C20H28HgN8O7S2
757.21
100(2) K
C20H24HgN6S2
613.16
100(2) K
C20H26Cl4Hg2N6S2
957.57
100(2) K
Wavelength
Crystal system
Space group
0.71073 Å
orthorhombic
Pbca
0.71073 Å
monoclinic
P2(1)/c
0.71073 Å
monoclinic
P2/n
0.71073 Å
monoclinic
C2/c
Unit cell dimensions
a = 13.225(3) Å
b = 8.343(4) Å b = 90°
c = 18.993(6) Å
a
= 90°
a = 10.8557(9) Å
a
= 90°
a = 19.207(2) Å
b = 6.3971(6) Å
b = 112.545(5)°
c = 19.215(2) Å
2180.6(4) Å3
4
a
c
= 90°
= 90°
a = 19.1465(5) Å
b = 11.2707(3) Å
b = 125.1560(10)°
a
= 90°
= 90°
b = 18.7596(16) Å
b = 104.360(3)°
c = 13.6196(12) Å
2687.0(4) Å3
4
c = 90°
c
= 90°
c = 16.0073(7) Å
2824.18(16) Å3
4
c
Volume
Z
Density (calculated)
Absorption coefficient
F(0 0 0)
2095.5(12) Å3
8
1.314 Mg/m3
0.273 mmÀ1
880
1.872 Mg/m3
5.939 mmÀ1
1488
1.868 Mg/m3
7.269 mmÀ1
1192
2.252 Mg/m3
11.407 mmÀ1
1792
Reflections collected
Independent reflections
Completeness to h
Goodness-of-fit on F2
12 875
2218 [Rint = 0.0960]
95.2%
32 600
5883 [Rint = 0.0780]
99.3%
41 329
4444 [Rint = 0.0694]
99.8%
88 269
4343 [Rint = 0.0513]
99.9%
1.002
1.120
1.037
1.142
Final R indices [I > 2
r
(I)]
R1 = 0.0454,
wR2 = 0.1036
R1 = 0.0914,
wR2 = 0.1238
0.303 and À0.229 e.ÅÀ3
R1 = 0.0414, wR2 = 0.0958
R1 = 0.0765, wR2 = 0.1214
1.752 and À2.260 e.ÅÀ3
R1 = 0.0378, wR2 = 0.0985
R1 = 0.0210, wR2 = 0.0691
R indices (all data)
R1 = 0.0585, wR2 = 0.1171
1.488 and À2.695 e.ÅÀ3
R1 = 0.0302, wR2 = 0.0733
0.769 and À0.949 e.ÅÀ3
Largest difference in peak and
hole
Table 2
Crystallographic data for complexes 4, 5.2DMSO and 6.
Identification code
4
5.2DMSO
6
Empirical formula
Formula weight
Temperature
C20H26Br4Hg2N6S2
1135.41
100(2) K
C24H38Hg2I4N6O2S4
1479.62
100(2) K
C10H13HgI2N3S
661.68
100(2) K
Wavelength
Crystal system
Space group
0.71073 Å
monoclinic
C2/c
0.71073 Å
triclinic
0.71073 Å
triclinic
ꢀ
ꢀ
P1
P1
Unit cell dimensions
a = 19.2278(8) Å
a
= 90°
a = 9.2624(5) Å
a
= 98.324(3)°
a = 7.7735(11) Å
a = 89.794(10)°
b = 11.5883(8) Å b = 126.045(5)°
b = 10.8890(7) Å b = 104.164(3)°
b = 10.3408(19) Å b = 71.431(7)°
c = 16.2968(10) Å
2936.0(3) Å3
4
c
= 90°
c = 11.2364(7) Å
974.98(10) Å3
1
c
= 112.903(3)°
c = 11.1497(16) Å
780.6(2) Å3
2
c = 67.953(7)°
Volume
Z
Density (calculated)
Absorption coefficient
F(0 0 0)
2.569 Mg/m3
16.053 mmÀ1
2080
2.520 Mg/m3
11.275 mmÀ1
676
2.815 Mg/m3
13.931 mmÀ1
592
Reflections collected
Independent reflections
Completeness to h
Goodness-of-fit on F2
50 524
4542 [Rint = 0.0732]
99.5%
67 891
5014 [Rint = 0.0447]
99.5%
17 896
3109 [Rint = 0.0510]
97.8%
1.029
1.194
1.085
Final R indices [I > 2
R indices (all data)
Largest difference in peak and hole
r
(I)]
R1 = 0.0477, wR2 = 0.1180
R1 = 0.0828, wR2 = 0.1373
3.518 and À3.808 e.ÅÀ3
R1 = 0.0135, wR2 = 0.0321
R1 = 0.0148, wR2 = 0.0326
0.564 and À0.852 e.ÅÀ3
R1 = 0.0241, wR2 = 0.0601
R1 = 0.0287, wR2 = 0.0637
2.170 and À1.265 e.ÅÀ3

1278
E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
structures were solved by direct methods (SHELXS-97) [22], com-
pleted with difference Fourier syntheses, and refined with full-ma-
Hg:LH ratio. In contrast, complexes 5 and 6 show the fragment
[HgI(LH)]+, corresponding to a 1:1 ratio.
2
trix least-squares using SHELXL-97 minimizing
x
(F0 ÀFc2). Weighted
R factors (Rw) and all goodness of fit S are based on F2 and conven-
tional R factors (R) are based on F [23]. All non-hydrogen atoms
were refined with anisotropic displacement parameters. All scat-
tering factors and anomalous dispersions factors are contained in
the SHELXTL 6.10 program library. Experimental details of the X-ray
structural analysis as well as the crystallographic data are summa-
rized in Tables 1 and 2.
3.2. Crystal structures
The structure determination of LH shows (Fig. 1) that in the so-
lid state the thiosemicarbazone exists in the thione form, sup-
ported by the presence of hydrazinic hydrogens and a C–S
distance of 1.678(3) Å, which is much shorter than a single C–S
bond and where N(1) and S(1) are in a cis disposition. The ligand
core is deviated from planarity, with a mean deviation of 0.79 Å
for S(1) from the least-squares plane. The aromatic ring is forming
a dihedral angle of 11.21° with this plane. The molecules form
hydrogen bonds between the NH group and the sulfur atom
[N(2)–H(2)Á Á ÁS(1)#1 3.431(3) Å, 165(83)° #1 1Àx + 1/2, y + 1/2, z],
forming infinite chains running parallel to the b axis. These chains
are linked through SÁ Á ÁS interactions (3.48 Å, sum of the Van der
Waals radii 3.60 Å) along the a axis, leading a 2D network.
In all the complexes but 5 the N,S-coordination mode of the li-
gand affords one five-membered chelate ring. Coordination of mer-
cury induces more electronic delocalization, which can be
confirmed by the decrease in the C(2)–N(2) bond distance and
the increase in the distance corresponding to the C–S groups ob-
served in all the metal derivatives (Table 3). In complex 2 the li-
gand is in the thiol form, since deprotonation leads to the
formation of a new C@N bond and the CS bond distance is close
to the value expected for a single bond (Table 3). The Hg–S bonds
are quite strong in all the complexes and are much shorter than the
Hg–N bonds. In complexes 5 and 6 these bonds are the largest due
to the presence of strong Hg–I bonds that weaken the Hg–S ones.
3. Results and discussion
3.1. Synthesis
Benzaldehyde-N(4),N(4)-dimethylthiosemicarbazone, (LH) was
prepared by condensation of benzaldehyde and N(4),N(4)-dimeth-
ylthiosemicarbazide in ethanol:water 1:1. The new molecule was
unambiguously characterized by spectroscopic methods, as de-
tailed in the Section 2, and by single crystal X-ray diffraction
studies.
The synthesis of the complexes was carried out in ethanol, and
in the case of complex 2, also in the presence of the basic medium
provided by LiOHÁH2O (Scheme 1). The structures of the complexes
mainly depend on the counterion used. In the complexes the ligand
behaves as a neutral molecule unless lithium hydroxide is used,
which induces its deprotonation. Conductivity data indicate that
the complexes are molecular species, except the nitrate derivative
[Hg(NO3)(LH)2]NO3 (1) [24]. The mass spectra of complexes 1, 2, 3
and 4 show a peak corresponding to [Hg(L)(LH)]+ indicating a 1:2
H
N
N
Me2N
[Hg(LH)2(µ-X)2HgX2]
X
X
X
X
Hg
S
X=Cl 3
X=Br 4
Hg
S
N
N
H
NMe2
Me2N
O
N
S
HgX2
N
N
Me2N
Hg
X=Cl, Br
O
N
O
S
N
N
S
Hg
NO3
S
HN
HgX2 + LiOH.H2O
Hg(NO3)2.H2O
NMe2
NH
N
N
S
X=Cl, Br, I, NO3
N
H
NMe2
NMe2
[HgL2] 2
LH
HgI2
[Hg(NO3)(LH)2]NO3 1
precipitate
filtrate
NMe2
I
N
I
S
HN
Hg
Hg
NH
I
S
N
I
I
N
Hg
Me2N
I
HN
S
[HgI(LH)(µ-I)2HgI(LH)] 5
[Hg(LH)I2] 6
Me2N
Scheme 1.

E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
1279
Fig. 1. Molecular structure of LH with 50% probability ellipsoids; bond lengths (Å): C(1)–N(1), 1.276(3); N(1)–N(2), 1.371(3); N(2)–C(2), 1.356(3); C(2)–N(3), 1.341(3); C(2)–
S(1), 1.678(3); N(3)–C(3), 1.448(4); N(3)–C(4), 1.455(3); bond angles (°): C(1)–N(1)–N(2), 115.4(2); C(2)–N(2)–N(1), 120.5(2); N(3)–C(2)–N(2), 115.2(2); N(3)–C(2)–S(1),
122.58(18); N(2)–C(2)–S(1), 122.26(19).
Table 3
Selected bond distances (Å) of the ligand skeleton in LH and its complexes.
LH
1ÁH2O
2
3
4
5.2DMSO
6
C(1)–N(1)
C(5)–N(4)
N(1)–N(2)
N(4)–N(5)
N(2)–C(2)
N(5)–C(6)
C(2)–N(3)
C(6)–N(6)
C(2)–S(1)
C(6)–S(2)
1.276(3)
1.281(8)
1.288(8)
1.371(8)
1.376(7)
1.352(9)
1.356(9)
1.327(9)
1.326(8)
1.720(7)
1.718(7)
1.285(9)
1.296(9)
1.377(8)
1.357(8)
1.294(9)
1.327(9)
1.363(11)
1.349(9)
1.769(8)
1.768(8)
1.280(5)
1.262(11)
1.281(3)
1.273(7)
1.371(3)
1.356(3)
1.341(3)
1.678(3)
1.379(4)
1.343(4)
1.317(4)
1.727(3)
1.384(9)
1.342(10)
1.321(10)
1.711(8)
1.384(3)
1.346(3)
1.328(3)
1.723(2)
1.385(6)
1.343(6)
1.327(7)
1.713(5)
Fig. 2. Molecular structure of 1 with 50% probability ellipsoids, hydrogen atoms, the nitrate and the water molecule are omitted for clarity; bond lengths (Å): Hg(1)–S(1),
2.3576(18); Hg(1)–S(2), 2.3683(18); Hg(1)–N(4), 2.534(5); Hg(1)–N(1), 2.784(5); Hg(1)–O(2), 2.790(6); Hg(1)–O(1), 2.837(6); bond angles (°): S(1)–Hg(1)–S(2), 166.90(7);
S(1)–Hg(1)–N(4), 116.60(13); S(2)–Hg(1)–N(4), 75.40(12); S(1)–Hg(1)–N(1), 70.44(11); S(2)–Hg(1)–N(1), 109.52(12); N(4)–Hg(1)–N(1), 76.52(17); S(1)–Hg(1)–O(2),
89.34(15); S(2)–Hg(1)–O(2), 95.25(15); N(4)–Hg(1)–O(2), 93.99(18); N(1)–Hg(1)–O(2), 149.78(17); S(1)–Hg(1)–O(1), 86.21(15); S(2)–Hg(1)–O(1), 88.49(14); N(4)–Hg(1)–
O(1), 134.23(18); N(1)–Hg(1)–O(1), 148.55(18); O(2)–Hg(1)–O(1), 44.41(17).

1280
E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
The asymmetric unit of complex
1
contains one
[Hg(NO3)(LH)2]+ cation, one NO3À and a water molecule. In the cat-
ion, the mercury ion is bonded to two N,S-donor ligands and to a
bidentate nitrato group in a strongly distorted octahedral arrange-
ment, due to the small bite of the NO3 ligand, with the sulfur atoms
in the axial positions (Fig. 2). As far as we know, this complex rep-
resents the first example of a mercury complex crystallographi-
cally characterized containing a thiosemicarbazone ligand and a
nitrato group. Within the ligands bond distances are very similar
to those of free LH, although the backbone is more planar and
the phenyl ring is more canted, since the angle that forms with
the ligand skeleton is 22.50°. The phenyl groups are located on
opposite sides, thus minimizing steric hindrance, which is ob-
served in all the complexes containing two ligands bonded to the
same mercury atom. In the literature there are few reports about
crystalline structures of Hg compounds with bidentate nitrato
ligands, and only two with a N2S2O2 environment (any provided
by nitrato), but the Hg–O bond distances falls within the range of
other Hg–O bonds reported [25]. There is an extended network
of hydrogen bonds involving the amine and nitrato groups, the
nitrate anion and the water molecule (Table 4), leading a 3D
architecture.
The asymmetric unit of complex 2 is formed by two crystallo-
graphically-distinct units of [HgL2], in which each metal ion is
bonded to two deprotonated ligands in a bidentate mode, giving
a N2S2 environment (Fig. 3). The s4 parameter is 0.57 and 0.55
for Hg(1) and Hg(2), respectively, so the geometry is intermediate
Fig. 4. Molecular structure of 3 with 50% probability ellipsoids, hydrogen atoms
omitted for clarity. Data for 3; bond lengths (Å): Hg(1)–S(1), 2.3732(8); Hg(1)–N(1),
2.748(3); Hg(1)–Cl(1), 3.0387(12); Hg(2)–Cl(2), 2.4653(10); Hg(2)–Cl(1),
2.4888(12); bond angles (°): S(1)#1–Hg(1)–S(1), 177.87(4); S(1)#1–Hg(1)–N(1),
71.54(6); S(1)–Hg(1)–N(1), 106.72(6); S(1)#1–Hg(1)–Cl(1), 102.20(3); S(1)–Hg(1)–
Cl(1), 79.48(3); N(1)–Hg(1)–Cl(1). 109.65(7); Cl(2)#1–Hg(2)–Cl(2), 105.79(5);
Cl(2)#1–Hg(2)–Cl(1), 114.50(4); Cl(2)–Hg(2)–Cl(1), 110.65(4); Cl(1)#1–Hg(2)–
Cl(1), 101.01(6); Hg(2)–Cl(1)–Hg(1), 90.29(4). Data for 4; bond lengths (Å):
Hg(1)–S(1), 2.3819(19); Hg(1)–N(1), 2.764(7); Hg(1)–Br(1), 3.1317(10); Hg(2)–
Br(2), 2.5788(9); Hg(2)–Br(1), 2.6204(10); bond angles (°): S(1)#1–Hg(1)–S(1),
177.82(10); S(1)#1–Hg(1)–N(1), 106.98(14); S(1)–Hg(1)–N(1), 71.22(14); S(1)#1–
Hg(1)–Br(1), 102.00(5); S(1)–Hg(1)–Br(1), 79.68(5); N(1)–Hg(1)–Br(1), 150.54(13);
N(1)–Hg(1)–Br(1)#1, 108.59(14); Br(1)–Hg(1)–Br(1)#1, 81.51(4); Br(2)#1–Hg(2)–
Br(2), 107.22(5); Br(2)#1–Hg(2)–Br(1)#1, 110.60(3); Br(2)–Hg(2)–Br(1)#1,
112.98(3); Br(2)–Hg(2)–Br(1), 110.60(3); Br(1)#1–Hg(2)–Br(1), 102.56(5), Hg(2)–
Br(1)–Hg(1), 87.97(3). Symmetry transformations used to generate equivalent
atoms: #1 Àx, y, Àz + 1/2.
between tetrahedral and square-planar (s4 = 0 for SP and s = 1 for
Td) [26]. Due to electronic delocalization after deprotonation, the
ligand backbones are flat, with maximum deviations from the
Table 4
Hydrogen bonds for 1 [Å and °].
D–HÁ Á ÁA
d(D–H)
d(HÁ Á ÁA)
d(DÁ Á ÁA)
<(DHA)
N(5)–H(5A)Á Á ÁO(6)
N(2)–H(2)Á Á ÁO(7)
0.88
0.88
0.89(2)
0.90(2)
2.07
1.89
1.86(5)
1.89(3)
2.887(9)
2.734(8)
2.623(13)
2.785(9)
154.1
160.5
142(7)
173(9)
O(7)–H(7D)Á Á ÁO(5)
O(7)–H(7E)Á Á ÁO(3)#1
Symmetry transformations used to generate equivalent atoms: #1 Àx + 1, y + 1/2,
Àz + 1/2.
Fig. 3. Molecular structure of 2 with 50% probability ellipsoids, hydrogen atoms omitted for clarity; bond lengths (Å): S(2)–Hg(2), 2.3570(17); S(1)–Hg(1), 2.3612(19); Hg(2)–
N(4), 2.537(6); Hg(1)–N(1), 2.532(6); bond angles (°): S(2)–Hg(2)–S(2)#1, 163.83(10); S(2)–Hg(2)–N(4), 118.98(13); S(2)#1–Hg(2)–N(4), 74.34(13); N(4)–Hg(2)–N(4)#1,
80.6(3); S(1)#2–Hg(1)–S(1), 156.00(10); S(1)–Hg(1)–N(1)#2, 76.18(13); S(1)–Hg(1)–N(1), 123.74(13); N(1)#2–Hg(1)–N(1), 80.8(3). Symmetry transformations used to
generate equivalent atoms: #1 Àx + 1/2, y, Àz + 1/2 #2 Àx + 3/2, y, Àz + 1/2.

E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
1281
least-squares planes of À0.069 Å for N(2) and À0.026 Å for N(6).
The phenyl ring is canted 14.19° in the unit containing Hg(1) and
29.89° in the unit containing Hg(2).
including the phenyl ring, lies almost in the same plane (dihedral
angle 4.27°). The iodido bridges, as well as occurs with Cl and Br,
are quite asymmetric, but the distances are within the range found
in related structures [30,31]. The DMSO molecules are linked by
hydrogen bonds with the amine groups [N(2)–H(2)Á Á ÁO(1)#2
2.857(3) Å, 152.6°, #2 xÀ1, y, zÀ1], and short I(2)Á Á ÁI(2) contacts,
3.86 Å, form infinite chains along the b axis.
The molecular structure of complex 6 is formed by one mercury
ion bonded to one neutral ligand through the imine nitrogen and
the sulfur atom and to two iodidos (Fig. 6), giving rise to a NSI2
Complexes 3 and 4 are isomorphous, having the same structure,
so they will be discussed together and only pictures corresponding
to 3 will be depicted. Both complexes consist of HgX42À units with
two of the XÀ ligands acting as bridges to link the [Hg(LH)2]2+
moieties (Fig. 4). This leads to one mercury ion with N2S2X2 environ-
ment in a distorted octahedral arrangement and to another metal
with a X4 coordination in a tetrahedral disposition (s4 is 0.96 for
complex 3 and 0.97 for complex 4). The ligands can be considered
planar, with maximum deviations from the least-squares planes of
0.081 Å for C(2) in complex 3 and 0.069 Å for N(1) in complex 4.
The phenyl rings form dihedral angles of 29.73° and 27.93° in com-
plexes 3 and 4, respectively. The halogen bridges are quite asymmet-
ric, with one bond distance much longer than the other, although the
largest are within the range of other complexes found in the
literature [27–29]. The molecules are held together by hydrogen
bonds between the terminal halogen groups and the amine groups
forming infinite chains running along b [N(2)–H(2)Á Á ÁCl(2)#2
3.286(3) Å, 168(5)°; N(2)–H(2)Á Á ÁBr(2)#2 3.492(7) Å, 169(6)° #2 x,
yÀ1, z].
environment in a distorted tetrahedral geometry (s4 = 0.80). The li-
gand can be considered planar being the maximum deviation from
the least-squares plane of 0.0661 Å for N(2), and with the phenyl
ring forming a dihedral angle of 17.64°. The molecules are forming
dimers through hydrogen bonds between I(1) and the amine group
[N(2)–H(2)Á Á ÁI(1)#1 3.977(5) Å, 162.0°, #1 Àx + 1, Ày + 1, Àz].
These dimers are linked by I(2)Á Á ÁI(2) contacts with a distance of
2.93 Å, and I(1)Á Á ÁI(1) with a distance of 3.88 Å, which are slightly
shorter than the sum of the Van der Waals radii, 3.96 Å, giving rise
to a 2D structure in the ac plane.
3.3. Infrared spectra
The asymmetric unit of complex 5 recrystallized in DMSO con-
tains one molecule of the complex and two of DMSO. The
[HgI(LH)(l-I)2HgI(LH)] units are centrosymmetric with the inver-
sion point located in the middle of the Hg–Hg distance. Each mer-
cury atom has a SI3 coordination, provided by one neutral S-
bonded ligand, one terminal iodido and two iodido bridges, giving
The band corresponding to m(N–H) is observed, except in com-
plex 2, indicating that the ligand behaves as a neutral molecule,
but is deprotonated in complex 2. The coordination by sulfur in-
duces the band at 1020 cmÀ1 is shifted to lower frequency. All
the spectra show a band assigned to the
m(C–H), which is clearly
a distorted tetrahedral geometry, with s4 = 0.82 (Fig. 5). The ligand,
shifted in complex 2, in which the ligand has lost the acidic hydro-
Fig. 5. Molecular structure of 5 with 50% probability ellipsoids; bond lengths (Å): Hg(1)–S(1), 2.4863(6); Hg(1)–I(2), 2.6751(2); Hg(1)–I(1), 2.7535(2); Hg(1)–I(1)#1,
3.2297(2); bond angles (°): S(1)–Hg(1)–I(2), 122.094(15); S(1)–Hg(1)–I(1), 114.274(16); I(2)–Hg(1)–I(1), 122.623(7); S(1)–Hg(1)–I(1)#1, 93.148(15); I(2)–Hg(1)–I(1)#1,
98.111(6); I(1)–Hg(1)–I(1)#1, 88.342(6); Hg(1)–I(1)–Hg(1)#1, 91.658(6). Symmetry transformations used to generate equivalent atoms: #1 Àx, Ày, Àz + 1.

1282
E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
Fig. 6. Molecular structure of 6 with 50% probability ellipsoids; bond lengths (Å): Hg(1)–S(1), 2.4926(14); Hg(1)–I(2), 2.6764(5); Hg(1)–I(1), 2.6853(5); Hg(1)–N(1), 2.687(4);
bond angles (°): S(1)–Hg(1)–I(2), 112.73(4); S(1)–Hg(1)–I(1), 123.83(4); I(2)–Hg(1)–I(1), 122.488(16); S(1)–Hg(1)–N(1), 72.06(9); I(2)–Hg(1)–N(1), 116.81(9); I(1)–Hg(1)–
N(1), 90.98(9).
gen atom. The spectrum of complex 1 shows several bands corre-
mers, but complexes 3, 4 and 5 show a dinuclear structure. Com-
pounds 3 and 4 contain two different mercury ions: one has a
N2S2X2 coordination sphere that has not been observed to date in
any crystal structure reported, while the other one is bonded to
four halide ions. In contrast, in complex 5 both mercury atoms
have a SI3 coordination, since the ligand is only bonded through
the sulfur atom.
Complexes 3 and 4, consisting in dinuclear species containing
two mercury atoms with different coordination environments,
one octahedral and one tetrahedral, are scarce and represents the
first example of this kind of compounds with a thiosemicarbazone
ligand.
sponding to nitrate and nitrato groups, which support the presence
-
of NO3 acting both as ligand and counterion.
3.4. NMR spectra
The new compounds were also characterized by NMR spec-
troscopy. The spectrum of the ligand displays well-resolved 1H
NMR signals, which correlate well with the hydrogen atoms pres-
ent in the molecule. The 13C NMR spectrum of LH also show the
signals corresponding to the carbon atoms expected for the
condensation product between benzaldehyde and N(4),N(4)-
dimethylthiosemicarbazide.
In the 1H NMR (CDCl3) spectrum of complex 2, the absence of
the N–H signal is consistent with the thiosemicarbazone being
deprotonated. The 1H NMR spectra of the rest of the complexes
confirm that the ligand is in its neutral form. Spectrum of complex
4 in [D6]DMSO, does not show the signal corresponding to the NH
proton, although it is observed in CDCl3. In the 13C NMR spectra,
the signals corresponding to the imine carbons and the thiocarbon-
yl groups are clearly shifted on complexation.
Acknowledgement
We thank César J. Pastor from the SIdI of the UAM for the crystal
measurements and DGICYT for financial support (Project CT2005-
07788/BQU).
Appendix A. Supplementary material
CCDC 733645, 733646, 733647, 733648, 733649, 733650 and
733651 contain the supplementary crystallographic data for 1, 2,
3, 4, 5, 6 and LH. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.ica.2009.08.029.
4. Conclusions
The reactions were carried out in ethanol and the behavior of
the ligand, as monoanion or as a neutral molecule, only depends
on the presence or the absence of lithium hydroxide. On the other
hand, the ligand:mercury ratio in the complexes does not depend
on the stoichiometry used in the reaction and their structures are
only determined by the counterion used. Thus from nitrate a 1:2
complex was obtained, while from chloride, bromide or iodide,
all the complexes show a 1:1 ratio. Complexes 1, 2 and 6 are mono-
References
[1] U. Skyllberg, P.R. Bloom, J. Qian, C.-M. Lin, W.F. Bleam, Environ. Sci. Technol. 40
(2006) 4174.

E. López-Torres, M.A. Mendiola / Inorganica Chimica Acta 363 (2010) 1275–1283
1283
[2] B.O. Leung, F. Jalilehvand, V. Mah, Dalton Trans. (2007) 4666.
[3] T. Roza, N.C. Teixoto, A. Welter, E.M.M. Flores, M.E. Pereira, Basic Clin.
Pharmacol. Toxicol. 96 (2005) 302.
[4] T.W. Clarkson, L. Magos, Crit. Rev. Toxicol. 36 (2006) 609.
[5] E.E. Hoffmeyer, S.P. Singh, C.J. Dona, A.R.S. Ross, R.J. Huhes, I.P. Pickering, G.N.
George, Chem. Res. Toxicol. 19 (2006) 753.
[17] E. Bermejo, A. Castiñeiras, T. Perez, R. Carballo, W. Hillar, Z. Anorg. Allg. Chem.
627 (2001) 2377.
[18] E. López-Torres, D.G. Calatayud, M.A. Mendiola, C.J. Pastor, J.R. Procopio, Z.
Anorg. Allg. Chem. 632 (2006) 2471.
[19] E. López-Torres, M.A. Mendiola, C.J. Pastor, Polyhedron 25 (2006) 1464.
[20] G.M. Sheldrick, SADABS Version 2.03, Program for Empirical Absorption
Corrections, Universität Göttingen: Göttingen, Germany, 1997–2001.
[21] G.M. Sheldrick, SAINT+NT (Version 6.04) SAX Area-Detector Integration Program,
Bruker AXS, Madison, WI, 1997–2001.
[22] G.M. Sheldrick, SHELXTL (Version 6.10) Structure Determination Package, Bruker
AXS, Madison, WI, 2000.
[23] G.M. Sheldrick, M. SHELXS-97, Program for Structure Solution, Acta Crystallogr.
Sect. A 46 (1990) 467.
[24] W.J. Geary, Coord. Chem. Rev. 7 (1971) 81.
[25] L.-J. Baker, G.A. Bowmaker, P.C. Healy, B.W. Skelton, A.H. White, J. Chem. Soc.,
Dalton Trans. (1992) 955.
[26] L. Yang, D.R. Powell, R.P. Houser, Dalton Trans. (2007) 955.
[27] S.Y. Lee, S. Park, H.J. Kim, J.H. Jung, S.S. Lee, Inorg. Chem. 47 (2008) 1913.
[28] X.-F. Wang, Y. Lv, T.-a. Okamura, H. Kawaguchi, G. Wu, W.-Y. Sun, N. Ueyama,
CrystGrowthDes 7 (2007) 1125.
[29] M.S. Bharara, T.H. Bui, S. Parkin, D.A. Atwood, Inorg. Chem. 44 (2005) 5753.
[30] S.J. Lee, J.H. Jung, J. Seo, I. Yoon, K.-M. Park, L.F. Lindoy, S.S. Lee, Org. Lett. 8
(2006) 1641.
[6] U. Abram, A. Castiñeiras, I. García-Santos, R. Rodríguez-Riobó, Eur. J. Inorg.
Chem. (2006) 3079.
[7] J.S. Casas, A. Castiñeiras, M.D. Couce, M. García-Vega, M. Rosende, A. Sánchez, J.
Sordo, J.M. Varela, E.M. Vázquez-López, Polyhedron 27 (2008) 2436.
[8] D.X. West, S.B. Padhye, P.B. Sonawane, Struct. Bonding 76 (1991) 1.
[9] J.S. Casas, M.S. Tasende, J. Sordo, Coord. Chem. Rev. 209 (2000) 197.
[10] T.S. Lobana, R. Sharma, G. Bawa, S. Khanna, Coord. Chem. Rev. 253 (2009) 977.
[11] E. Bermejo, A. Castiñeiras, I. García-Santos, D.X. West, Z. Anorg. Allg. Chem. 630
(2004) 1096.
[12] E. Bermejo, A. Castiñeiras, I. García-Santos, D.X. West, Polyhedron 22 (2003)
1147.
[13] T.S. Lobana, A. Sánchez, J.S. Casas, A. Castiñeiras, J. Sordo, M.S. García-Tasende,
E.M. Vázquez-López, J. Chem. Soc., Dalton Trans. (1997) 4289.
[14] T.S. Lobana, Rekha, R.J. Butcher, T.W. Failes, P. Turner, J. Coord. Chem. 58
(2005) 1369.
[15] E. Bermejo, A. Castiñeiras, R. Dominguez, R. Carballo, C. Maichle-Mossmer, J.
Strahle, D.X. West, Z. Anorg. Allg. Chem. 625 (1999) 961.
[16] A. Castiñeiras, R. Carballo, T. Pérez, Polyhedron 20 (2001) 441.
[31] M.S. Bharara, S. Parkin, D.A. Atwood, Inorg. Chem. 45 (2006) 211.