In situ generation of functionalized 1,2,4-triazole-5-thiones containing pyridine or pyrazine moieties and their coordination to HgII

Article abstract of DOI:10.1039/c6ce00338a

The reaction of 2-cyanopyridine or 2-cyanopyrazine with N-methylthiosemicarbazide afforded (Z)-2-(amino(pyridin-2-yl)methylene)-N-methylhydrazinecarbothioamide (HPyAm4M) and (Z)-2-(amino(pyrazin-2-yl)methylene)-N-methylhydrazinecarbothioamide (HPzAm4M), respectively. Prolonged heating under reflux in methanol in the synthesis of these thiosemicarbazones led to the formation of 4-methyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione (HMPytat, 1) and 4-methyl-5-pyrazin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione (HMPztat, 2) by oxidative cyclization of the starting thiosemicarbazones. Reactions of thiosemicarbazones with mercury(II) salts gave new complexes of general formulae [Hg(tat)X] (3, 4) and [Hg(Htat)₂X₂] (5, 7, 9-11), along with [Hg₃(HEPytat)₂(EPytat)₂Cl₄]·3H₂O (6) and [Hg(EPytat)(HEPytat)I]·H₂O (8) (Htat = general 1,2,4,-triazole-5-thione). The complexes were isolated as solids and were characterized by elemental analysis, mass spectrometry and IR, ¹H NMR and ¹³C NMR spectroscopy. Recrystallization of the complexes from DMSO gave the compounds [Hg(MPytat)₂]_n (3a), [Hg(HMPytat)₂Br₂]·H₂O (4a), [{Hg(HEPytat)(μ²-NS-EPytat)Cl₂}₂Hg] (6a), [Hg(EPytat)₂]_n (6b), [Hg(MPztat)₂]_n (10a) and [Hg(EPztat)₂]_n (11a) (HEPytat = 4-ethyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione and HEPztat = 4-ethyl-5-pyrazin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione). These complexes were studied by single-crystal X-ray diffraction. The structural analysis revealed the versatility of heterocyclic functionalized 1,2,4-triazole-5-thiones to coordinate to mercury(II) in the thione and thiolate forms through the use of various donor atoms to give different and interesting crystalline packings. The supramolecular assemblies observed in the solid state were analysed. These elegant assemblies are formed by a combination of several noncovalent interactions, including intermolecular hydrogen-bonding supramolecular synthons and aromatic-aromatic interactions. The short Hg?Hg distance of 3.660 ? indicates the presence of a probable mercurophilic interaction in 6a.

Full text of DOI:10.1039/c6ce00338a

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In situ generation of functionalized 1,2,4-triazole-
-thiones containing pyridine or pyrazine moieties
and their coordination to Hg †
5
Cite this: CrystEngComm, 2016, 18,
428
II
3
Elena Bermejo, Alfonso Castiñeiras,* Isabel García-Santos and Raúl Rodríguez-Riobó
The reaction of 2-cyanopyridine or 2-cyanopyrazine with N-methylthiosemicarbazide afforded (Z)-2-
(
aminoIJpyridin-2-yl)methylene)-N-methylhydrazinecarbothioamide (HPyAm4M) and (Z)-2-(amino(pyrazin-
-yl)methylene)-N-methylhydrazinecarbothioamide (HPzAm4M), respectively. Prolonged heating under reflux
in methanol in the synthesis of these thiosemicarbazones led to the formation of 4-methyl-5-pyridin-2-yl-
2
2
,4-dihydro-[1,2,4]triazole-5-thione (HMPytat, 1) and 4-methyl-5-pyrazin-2-yl-2,4-dihydro-[1,2,4]triazole-
-thione (HMPztat, 2) by oxidative cyclization of the starting thiosemicarbazones. Reactions of thio-
5
semicarbazones with mercuryIJII) salts gave new complexes of general formulae [Hg(tat)X] (3, 4) and
HgIJHtat) ] (5, 7, 9–11), along with [Hg (HEPytat) (EPytat) Cl ]·3H O (6) and [Hg(EPytat)(HEPytat)I]·H O (8)
Htat = general 1,2,4,-triazole-5-thione). The complexes were isolated as solids and were characterized
[
X
2 2
3
2
2
4
2
2
(
1
13
by elemental analysis, mass spectrometry and IR, H NMR and C NMR spectroscopy. Recrystallization of
the complexes from DMSO gave the compounds [Hg(MPytat)
2
]
n
(3a), [Hg(HMPytat)
2
Br
2
]·H
2
O
(4a),
(11a)
2
[
{Hg(HEPytat)(μ -NS-EPytat)Cl
2 2
}
Hg] (6a), [Hg(EPytat)
]
2 n
(6b), [Hg(MPztat) (10a) and [Hg(EPztat) ]
2
]
n
2 n
(HEPytat = 4-ethyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione and HEPztat = 4-ethyl-5-pyrazin-
2-yl-2,4-dihydro-[1,2,4]triazole-5-thione). These complexes were studied by single-crystal X-ray diffrac-
tion. The structural analysis revealed the versatility of heterocyclic functionalized 1,2,4-triazole-5-thiones
to coordinate to mercury(II) in the thione and thiolate forms through the use of various donor atoms to
give different and interesting crystalline packings. The supramolecular assemblies observed in the solid
state were analysed. These elegant assemblies are formed by a combination of several noncovalent inter-
actions, including intermolecular hydrogen-bonding supramolecular synthons and aromatic–aromatic in-
teractions. The short Hg⋯Hg distance of 3.660 Å indicates the presence of a probable mercurophilic
interaction in 6a.
Received 8th February 2016,
Accepted 2nd April 2016
DOI: 10.1039/c6ce00338a
www.rsc.org/crystengcomm
Introduction
of 1,2,4-triazole can be synthesized by intramolecular cycliza-
3
tion of substituted thiosemicarbazones. Thiosemicarbazones
1
,2,4-Triazoles and their derivatives represent an interesting
are polyfunctional compounds that cyclize readily and form
five- or six-membered heterocyclic compounds and, as a con-
sequence, their reactions can be performed under a wide vari-
ety of conditions. Numerous different routes can be found for
the synthesis of cycles but previous studies suggest that thio-
semicarbazones are typical substrates that undergo ring-
closure processes to afford the corresponding triazole and
thiadiazole derivatives, normally in the presence of a metal
class of heterocyclic compounds that have a wide spectrum of
biological activities. In addition, 1,2,4-triazoles are very useful
ligands in coordination chemistry because of their different
binding behaviours, either bidentate-bridging or mono-
dentate, depending on the position and nature of the substit-
uent on the triazole ring. Furthermore, a 3-substituted triazole
thiol can function as a uninegative monodentate or neutral
bridging ligand to two metal centres or as a bridge between
two metal centres in the azolato or thiolato form. Derivatives
1
2
4
salt. In particular, formamide thiosemicarbazones, as well as
1,2,4-triazole-5-thiones and 1,3,4-thiadiazoles, can also form
1,2,4-triazole-5-amine derivatives (Scheme 1). 1,2,4-Triazole-5-
thiones, along with their corresponding thiosemicarbazones,
can show a thione–thiol tautomerism in solution, whereas in
the solid state, they are present only in the thione form. The
latter are very versatile systems as they can form mono-, di-
and polynuclear metal complexes as a result of two different
coordination modes: as a monodentate ligand through the
sulfur atom or as a bidentate bridge through the sulfur and
Department of Inorganic Chemistry, Faculty of Pharmacy, University of Santiago
de Compostela, E-15782 Santiago de Compostela, Spain.
E-mail: alfonso.castineiras@usc.es
†
Electronic supplementary information (ESI) available. CCDC 1452050 (1),
452051 (2), 1452052 (3a), 1452053 (4a), 1452054 (6a), 1452055 (6b), 1452056
1
(10a) and 1452057 (11a). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c6ce00338a
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Experimental section
Materials
All reagents and solvents were commercially available ex-
cept for 2-pyridineformamide NIJ4)-methylthiosemicarbazone
7
(
HPyAm4M),
2-pyridineformamide NIJ4)-ethylthiosemicar-
8
bazone (HPyAm4E), 2-pyrazineformamide NIJ4)-methylthio-
semicarbazone (HPzAm4M) and 2-pyrazineformamide NIJ4)-
9
ethylthiosemicarbazone (HPzAm4E), which were prepared as
reported previously.
Elemental analyses for carbon, hydrogen and nitrogen were
performed on a Fisons-Carlo Erba 1108 microanalyser. Mass
spectra were obtained using a Micromass AutoSpec spectrome-
ter for ESI. Fourier transform infrared (FT-IR) spectra were
−1
recorded from KBr disks (4000–400 cm ) or polyethylene-
−1
sandwiched Nujol mulls (500–100 cm ) with a Bruker IFS-66V
spectrophotometer and are reported in the synthesis section
using the following abbreviations: vs = very strong, s = strong,
m = medium, w = weak, vw = very weak, sh = shoulder, br =
1
13
broad. H and C NMR spectra were obtained from DMSO-d6
solutions at room temperature using a Varian Mercury 300 in-
strument. Chemical shifts, in ppm, are reported relative to
Scheme 1 Cyclization process of formamide thiosemicarbazones.
Me Si using the solvent signal as reference.
4
nitrogen atoms. However, 1,2,4-triazole-5-thiones functional-
ized with aromatic heterocycles have an increased number of
donor atoms and they can behave as chelating polydentate li-
gands. As in thiolates, the sulfur atom of the aforementioned
derivatives can coordinate simultaneously to two metal cen-
tres. The presence of the soft thione donor group allows the
Crystal structure determinations
Diffraction data were obtained using Enraf Nonius CAD4,
Bruker Smart CCD-1000 or Bruker X8 Kappa APEXII diffrac-
tometers from crystals mounted on glass fibres. Data were
corrected for Lorentz and polarization effects and for absorp-
2
+
2+
+
+
+
stabilization of soft acids such as Pt , Pd , Cu , Ag , Au ,
1
0
11
2
+
2+
tion following psi-scan or multi-scan types. The structures
Cd and Hg and, in such circumstances, the coordinative
possibilities are increased considerably. From this perspec-
tive, an important factor to consider when choosing a metal
ion that allows intermolecular association in the complexes
with 1,2,4-triazole-5-thione is the Lewis acidity of the metal
atom. The greater the Lewis acidity of the central atom, the
greater the likelihood of the appearance of M–S interactions
dominating the stabilization of the crystal structure. In this
case, the greater soft–soft interaction between mercuryIJII) and
sulfur should favor supramolecular aggregation patterns. Mer-
cury–sulfur chemistry is of great interest due to the biological
1
2
were solved by direct methods, which revealed the positions
2
of all non-hydrogen atoms. These were refined on F by a
full-matrix least-squares procedure using anisotropic dis-
1
2
placement parameters. All hydrogen atoms were located in
difference maps, and the positions of O–H and N–H hydro-
gens were refined (others were included as riders); the isotro-
pic displacement parameters of H atoms were constrained to
1
.2Ueq of the carrier atoms. Molecular graphics were gener-
1
3
ated using DIAMOND. The crystal data, experimental de-
tails and refinement results are summarized in Table 1.
5
and environmental importance of the metal and, in particu-
Preparation of the 1,2,4-triazole-5-thiones
lar, the structural chemistry of mercuryIJII) thiolates provides a
fascinating variety of assemblies that contain both common
HgIJII) coordination geometries, i.e., linear and tetrahedral,
and, among them, bridging thiolate ligands are common,
Sodium (0.092 g, 4.0 mmol) was added to MeOH (25 mL), which
14
had been dried over Mg and I2, and the solution was stirred
until complete dissolution was achieved. 2-Pyridinecarbonitrile
(2.60 g, 25 mmol) or 2-pyrazinecarbonitrile (2.63 g, 25 mmol)
was added and the mixture was stirred for 30 min. 4-Methyl-3-
thiosemicarbazide (2.63 g, 25 mmol) was added in small por-
tions over a period of 1 h. A further quantity of MeOH (20 mL)
was added and the mixture was heated under reflux for a mini-
mum of 4 h. The resulting solution was allowed to cool with
stirring for 24 h and the resulting solid was filtered off.
Recrystallization from hot methanol and slow evaporation of
MeOH at room temperature produced yellow crystals of
HMPytat and dark yellow crystals of HMPztat after a period
of approximately 10 d.
6
with a wide range of Hg–S distances. We report here the re-
sults of structural investigations into the 1,2,4-triazole-5-
thione-based structures 1 and 2, which are formed by oxidative
cyclization of thiosemicarbazones. In addition, we describe
the structural characterization of six new 1,2,4-triazole-5-
thione HgIJII) complexes (3a, 4a, 6a, 6b, 10a and 11a) obtained
in the same oxidative cyclization of thiosemicarbazones, in the
presence of HgIJII) halides, where the combination of metal co-
ordination and weak interactions such as hydrogen bonding
and aromatic–aromatic interactions results in extensive supra-
molecular networks.
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Table 1 Crystal data and structure refinement for the compounds listed
Compound
HMPytat (1)
HMPztat (2)
2 2 2 2 2
[HgIJHMPytat) Br ]·H O (4a) [{HgIJEPytat)IJHEPytat)Cl } Hg] (6a)
Empirical formula
8 8 4
C H N S
7 7 5
C H N S
C H18Br HgN OS
16 2 8 2
36 4 3 16 4
C H38Cl Hg N S
Formula weight
Temperature/K
192.24
293
193.24
293
762.91
293
1566.63
293
Wavelength/Å
1.54184
0.71073
0.71073
0.71073
Crystal system
Space group
Monoclinic
Monoclinic
Triclinic
P¯1
Triclinic
P¯1
1
P2 /c
1
P2 /n
Unit cell dimensions
a/Å
b/Å
c/Å
α/°
β/°
γ/°
11.447(4)
5.0219(9)
15.967(3)
90
91.41(2)
90
917.6(4)
4
1.392
5.5577(12)
14.228(3)
10.921(2)
90
100.939(4)
90
864.7(3)
4
1.484
7.7077(6)
9.726(2)
10.608(2)
12.611(3)
104.613(4)
109.647(4)
95.734(4)
1161.1(5)
1
16.2385IJ14)
18.9449IJ14)
80.783(9)
86.817(9)
86.277(8)
2333.2(3)
4
2.172
10.226
1440
3
Volume/Å
Z
Calc. density/Mg m
Absorp. coeff./mm
−
3
2.240
10.351
738
−1
2.784
400
0.331
400
FIJ000)
Crystal size
ϑ range/°
Limiting indices/h, k, l
Refl. collected/unique (Rint
Completeness ϑ/°
Absorp. correct.
Max./min. transm.
Data/parameters
0.62 × 0.14 × 0.12
3.86–75.05
−14/14, 0/6, 0/19
1967/1890 (0.010)
99.9/67.68
Psi-scan
1.000/0.379
1890/121
1.040
0.55 × 0.25 × 0.21
2.39–27.47
−7/7, 0/18, 0/14
8146/1977 (0.027)
99.9/25.24
SADABS
1.000/0.898
1977/121
1.058
0.25 × 0.15 × 0.10
2.34–27.97
−10/0, −21/21, −24/24
12049/11239 (0.091)
100.0/25.24
Psi-scan
1.000/0.720
11 230/541
0.962
0.39 × 0.31 × 0.12
1.80–26.41
−12/9, −13/13, −15/15
12 171/4717 (0.049)
99.6/25.24
SADABS
1.000/0.464
4717/289
)
2
Goodness-of-fit on F
0.978
Final R indices
R indices (all data)
Largest diff. peak/hole
R
R
1
= 0.058, wR
= 0.058, wR
2
= 0.153
= 0.153
R
R
1
= 0.039, wR
= 0.053, wR
2
= 0.105
= 0.113
R
R
1
= 0.067, wR
= 0.269, wR
2
2
= 0.174
= 0.246
R
R
1
= 0.029, wR
= 0.044, wR
2
2
= 0.061
= 0.066
1
2
1
2
1
1
0.499/−0.523
[HgIJMPytat)
14HgN
0.219/−0.314
[HgIJEPytat)
18HgN
2.294/−2.479
0.928/−1.308
Compound
]
2 n
(3a)
]
2 n
(6b)
[HgIJMPztat)
2
]
n
(10a) [HgIJEPztat)
]
2 n
(11a)
Empirical formula
16
C H
8
S
2
18
C H
S
8 2
14
C H
12HgN10
S
2
16
C H
16HgN10
S
2
Formula weight
Temperature/K
583.06
293
611.11
293
585.05
100
613.10
293
Wavelength/Å
0.71073
0.71073
0.71073
0.71073
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
C2/c
Orthorhombic
Pna2
Monoclinic
P2 /n
1
1
Unit cell dimensions
a/Å
b/Å
c/Å
α/°
β/°
γ/°
21.6688IJ14)
11.3368IJ17)
8.2128(5)
90
107.851(6)
90
1920.4(3)
4
2.017
13.282(2)
18.980(4)
8.270(3)
90
90.328(8)
90
2084.7(9)
4
1.947
7.1597(2)
6.3074(2)
38.1938IJ10)
90
90
90
1724.80(9)
4
2.253
9.190
1112
14.646(16)
10.045(11)
15.852(17)
90
116.057IJ16)
90
2095(4)
4
1.944
3
Volume/Å
Z
Calc. density/Mg m
Absorp. coeff./mm
−
3
−1
8.251
1112
7.606
1176
7.571
1176
FIJ000)
Crystal size
ϑ range/°
0.48 × 0.16 × 0.12
3.07–29.97
0.25 × 0.15 × 0.15
2.14–27.96
0.40 × 0.04 × 0.03
2.13–30.85
0.16 × 0.14 × 0.07
1.58–26.42
Limiting indices/h, k, l
Refl. collected/unique (Rint
Completeness ϑ/°
−28/30, −15/0, −11/0
2965/2784 (0.032)
99.8/25.24
−17/17, −25/0, −10/0
2686/2516 (0.072)
99.9/25.24
0/10, 0/9, −49/43
28 560/4359 (0.037)
99.2/25.24
−18/16, 0/12, 0/19
17 778/4297 (0.034)
100.0/25.24
SADABS
)
Absorp. correct.
Psi-scan
Psi-scan
SADABS
Max./min. transm.
Data/parameters
Goodness-of-fit on F
0.915/0.737
2784/124
1.018
0.972/0.756
2516/133
0.945
0.770/0.120
4359/247
1.200
1.000/0.609
4297/262
1.055
2
Final R indices
R indices (all data)
Largest diff. peak/hole
R
R
1
= 0.037, wR
= 0.097, wR
2
= 0.080
= 0.093
R
R
1
= 0.053, wR
= 0.207, wR
2
= 0.101
= 0.132
R
R
1
= 0.027, wR
= 0.030, wR
2
2
= 0.054
= 0.055
R
R
1
= 0.031, wR
= 0.053, wR
2
2
= 0.059
= 0.065
1
2
1
2
1
1
1.299/−1.801
0.881/−1.883
3.041/−3.930
0.667/−0.715
4
-Methyl-3-(pyridin-2-yl)-1H-1,2,4-triazole-5IJ4H)-thione
C 50.2, H 4.1, N 29.2, S 16.3%; calc. for C H N S (192.25), C
8 8 4
50.0, H 4.2, N 29.1, S 16.7%. ESI MS, m/z: 192, [C H N S] .
8 8 4
+
(
HMPytat, 1). Yield: 1.25 g (26%). Elemental analysis: found,
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Scheme 2 Synthesis of 3-pyridine- and 3-pyrazine-1,2,4-triazole-5-thiones.
Scheme 3 Plausible mechanism for the formation of 1,2,4-triazole-5-thiones from formamide thiosemicarbazones.
Scheme 4 Proposed structures for the HgIJII) complexes 3–11.
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Fig. 1 (a) Perspective view of the asymmetrical unit of 1. (b) Molecular packing diagram of H-bonding interactions including supramolecular
2
homosynthons of R
2
(8) motif (orange dashed lines). (c) Network arrangement of 1 formed through intermolecular hydrogen bonding interactions.
Symmetry code: (a) −x, −y, 1 − z.
−
1
IR (νmax/cm ): 3110s, 3055s ν(NH), 1596s, 1550s, 1530s
under reduced pressure and washed with ethanol to provide
white (Cl), pale-yellow (Br) or yellow (I) solids.
ν(CN + CC), 1081m ν(NN), 788m ν(CS), 625s Δ(CCC),
1
4
05vw ϕ(CC). H NMR (DMSO-d , ppm): 14.0 (1H, s, N13H),
[HgIJMPytat)Cl], 3. Yield: 94 mg (88%). Elemental analysis:
6
8
.4 (1H, d, C11H), 7.9 (1H, td, C13H), 7.8 (1H, d, C14H), 7.4
found, C 22.6, H 1.5, N 13.2, S 7.4%; calc. for C
(427.28), C 22.5, H 1.6, N 13.1, S 7.5%. FAB MS, m/z: 585.1,
8
H
7
ClHgN
4
S
1
3
+
(
1H, m, C12H), 3.8 (3H, m, C18H). C NMR (DMSO-d
ppm): 173.4 (C17), 151.3 (C15), 149.4 (C11), 145.4 (C16),
33.8 (C13), 125.4 (C12), 123.1 (C14), 36.1 (C18).
-Methyl-3-(pyrazin-2-yl)-1H-1,2,4-triazole-5IJ4H)-thione
HMPztat, 2). Yield: 0.82 g (17%). Elemental analysis: found,
C 43.3, H 3.6, N 36.0, S 17.1%; calc. for C S (193.25), C
3.5, H 3.7, N 36.2, S 16.6%. ESI MS, m/z: 193, [C
6
,
−1
[Hg(HMPytat)2]; 429.0, [Hg(H MPytat)Cl]. IR (νmax/cm ):
2
1
1590s ν(CN), 993m ν(NN), 790m ν(CS), 292m ν(Hg–S), 244s
1
4
ν(Hg–Cl). H NMR (DMSO-d
6
, ppm): 8.7 (2H, d, H1), 8.03 (1H,
1
3
(
d, H4), 8.0 (1H, td, H3), 7.5 (1H, m, H2), 3.9 (3H, s, Me).
C
7
H
7
N
5
NMR (DMSO-d , ppm): 154.5 (C7), 152.5 (C6), 149.0 (C1), 147.3
6
+
4
7
H N
7 5
S] .
IR (νmax/cm ): 3097s, 2941s ν(NH), 1613s, 1557s, 1530s
ν(CN + CC), 1021m ν(NN), 793m ν(CS), 629s Δ(CCC), 407vw
(C5), 137.6 (C3), 124.3 (C2), 122.7 (C4), 33.7 (Me).
Recrystallization from DMSO/EtOH or DMF/acetone and,
after filtration, slow evaporation of the solvents from the fil-
−1
1
ϕ(CC). H NMR (DMSO-d
6
, ppm): 13.7 (1H, s, N13H), 8.7 (1H, d,
2 n
trate afforded colourless prisms of [HgIJMPytat) ] (3a) over a
C11H), 9.4 (1H, d, C14H), 8.7 (1H, d, C12H), 3.1 (3H, s, C18H).
period of 12/16 d.
13
6
C NMR (DMSO-d , ppm): 177.1 (C17), 145.9 (C15), 142.8 (C11),
[HgIJMPytat)Br], 4. Yield: 89 mg (61%). Elemental analysis:
found, C 20.6, H 1.4, N 12.0, S 6.0%; calc. for C BrHgN
471.73), C 20.4, H 1.5, N 11.9, S 6.8%. FAB MS, m/z: 391.3,
140.6 (C16), 144.8 (C12), 143.8 (C14), 31.2 (C18).
H
8 7
4
S
+
(
Synthesis of the complexes
−1
[Hg(MPytat)]. IR (νmax/cm ): 1589s ν(CN), 993m ν(NN), 789m
1
The title complexes were obtained using the general proce-
dure described below. Thiosemicarbazone (0.25 mmol) and
HgX2 (X = Cl, Br or I) (0.25 mmol) were mixed in absolute
EtOH (25 mL). The resulting mixture was stirred and heated
under reflux for 2 h. The mixture was allowed to cool over-
night and the resulting crystalline precipitate was filtered off
ν(CS), 281m ν(Hg–S), 207m ν(Hg–Br). H NMR (DMSO-d
8.7 (2H, s,b, H1), 8.0 (1H, d,b, H4), 7.9 (1H, t, H3), 7.5 (1H, s,b,
H2), 3.9 (3H, s, Me). C NMR (DMSO-d , ppm): 33.9 (Me).
6
The clear solution was left to crystallize at ambient tem-
perature and, after several days, colourless crystals suitable
6
, ppm):
13
2 2
for crystal determination corresponding to [HgIJHMPytat) Br ]
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Fig. 2 (a) Perspective view of the asymmetrical unit of 2. (b) Molecular packing diagram of H-bonding interactions including supramolecular
2
homosynthons of R
2
(8) motif (orange dashed lines). (c) Network arrangement of 2 formed through intermolecular hydrogen bonding interactions.
Symmetry code: (a) 3 − x, 1 − y, −z.
·
H O (4a) were obtained. Recrystallization from DMSO and
(C1), 146.8 (C5), 137.7 (C3), 124.6 (C2), 122.9 (C4), 41.1 (CH2),
14.6 (CH ).
2
slow evaporation of the solvent from the filtrate afforded
3
colourless prisms of [Hg(MPytat)
0 d.
HgIJHMPytat)
2
]
n
(3a) over a period of 15–
The mother liquor was allowed to crystallize at room tem-
perature for two weeks to provide colourless crystals of
[Hg (HEPytat) (EPytat) Cl ] (6a). A portion of the solid obtained
3 2 2 4
2
[
2
I
2
], 5. Yield: 83 mg (40%). Elemental analy-
sis: found, C 22.9, H 1.8, N 13.7, S 8.4%; calc. for
after filtration was dissolved in DMSO and the mixture was
allowed to evaporate at room temperature. Colourless prisms
+
C H HgI N S (838.88), C 22.9, H 1.9, N 13.4, S 7.6%. FAB
1
6
16
2 8 2
−1
MS, m/z: 193, [H
2
MPytat]. IR (νmax/cm ): 3487s–3315s ν(NH),
of [Hg(EPytat)
[HgIJHEPytat)
found, C 27.5, H 2.6, N 16.6, S 8.3%; calc. for C H Br HgN S
8 2
]
2 n
(6b) were obtained after a period of 13 d.
1
611–1587s ν(CN + CC), 997m ν(NN), 845m ν(CS), 287m
2
Br ], 7. Yield: 140 mg (49%). Elemental analysis:
2
1
ν(Hg–S), 139m ν(Hg–I). H NMR (DMSO-d , ppm): 8.7 (2H, dd,
6
18 20
2
+
H1), 8.0 (4H, m, H3 + H4), 7.5 (2H, m, H2), 3.9 (6H, s, Me).
(772.93), C 28.0, H 2.6, N 14.5, S 8.3%. FAB MS, m/z: 207.0,
1
3
−1
C NMR (DMSO-d
6
, ppm): 159.9 (C7), 151.2 (C6), 149.0 (C1),
[H
2
EPytat]. IR (νmax/cm ): 3384s, 3311s ν(NH), 1556s ν(CN),
1
47.3 (C5), 137.5 (C3), 124.2 (C2), 122.7 (C4), 33.3 (Me).
Recrystallization from DMSO and slow evaporation of the
999m ν(NN), 792s ν(CS), 297m, 226m (Hg–S), 190m, 183w
1
ν(Hg–Br). H NMR (DMSO-d
H3 + H4), 7.5 (2H, dd, H2), 4.5 (4H, q, CH
NMR (DMSO-d , ppm): 156.1 (C7), 151.4 (C6), 149.2 (C1), 147.3
6
, ppm): 8.7 (2H, d, H1), 8.0 (4H, m,
13
solvent from the filtrate afforded colourless prisms of
HgIJMPytat) ] (3a) over a period of 12 d.
2
), 1.3 (6H, t, CH
3
).
C
[
2
n
6
[Hg
3
(HEPytat)
2
(EPytat)
2
Cl
4
]·3H
2
O, 6. Yield: 109 mg (27%).
(C5), 137.5 (C3), 124.2 (C2), 122.6 (C4), 41.1 (CH
2
), 14.9 (CH
3
).
Elemental analysis: found, C 26.8, H 2.4, N 13.2, S 8.2%; calc.
for C H Cl Hg N O S (1620.69), C 26.7, H 2.7, N 13.8, S
Recrystallization from DMSO at ambient temperature for
12 d afforded colourless prismatic crystals of [HgIJEPytat) ] (6b).
3
6
44
+
4
3
16
3
4
2 n
7
6
.9%. FAB MS, m/z: 207.0, [H
2
EPytat]; 442.9, [Hg(HEPytat)Cl];
]; 1223.1,
2
[HgIJEPytat)IJHEPytat)I]·H O, 8. Yield: 147 mg (78%). Ele-
13.0, [Hg(HEPytat) ]; 1016.9, [Hg(EPytat-(H))
2
4
mental analysis: found, C 28.5, H 2.3, N 14.5, S 8.6%; calc. for
−1
+
[Hg (EPytat) ]. IR (ν /cm ): 3447s,b ν(OH + NH), 1588–
C H HgIN OS (757.04), C 28.6, H 2.8, N 14.8, S 8.5%. FAB
2
4
max
18 21
8
2
−1
1
566s ν(CN), 995m ν(NN), 793m ν(CS), 298m ν(Hg–S), 252s
2
MS, m/z: 207.0, [H EPytat]. IR (νmax/cm ): 3432s,b ν(OH + NH),
1
ν(Hg–Cl). H NMR (DMSO-d
6
, ppm): 8.7 (1H, d, H1), 8.0 (2H,
1630–1570s ν(CN + CC), 998m ν(NN), 792m ν(CS), 339s
1
d, H3 + H4), 7.5 (1H, t, H2), 4.5 (2H, q, CH ), 1.3 (3H, t,
ν(Hg–N), 291m ν(Hg–S), 153m ν(Hg–I). H NMR (DMSO-d6,
2
1
3
CH
3
). C NMR (DMSO-d
6
, ppm): 158.1 (C7), 151.0 (C6), 149.3
ppm): 8.7 (2H, m, H1), 8.0 (1H, m, H4), 8.0 (1H, m, H3), 7.5
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CrystEngComm
Table 2 Selected bond lengths and angles for the compounds listed
a
[
HgIJHMPytat)
2 2 2
Br ]∙H O (4a)
2 2
[{HgIJEPytat)IJHEPytat)Cl } Hg] (6a)
Bond lengths [Å]
HgIJ1)–SIJ11)
HgIJ1)–SIJ12)
HgIJ1)–BrIJ11)
HgIJ1)–BrIJ12)
2.525(5)
HgIJ2)–SIJ21)
HgIJ2)–SIJ22)
HgIJ2)–BrIJ21)
HgIJ2)–BrIJ22)
2.524(5)
2.478(5)
2.763(2)
2.549(2)
HgIJ1)–SIJ1)a
HgIJ1)–SIJ1)
HgIJ1)–ClIJ1)
HgIJ1)–ClIJ2)
2.3570(15)
2.3570(15)
3.1121(13)
3.3623(18)
HgIJ2)–SIJ2)
2.4469(14)
2.478(5)
2.765(2)
2.549(2)
HgIJ2)–ClIJ1)
HgIJ2)–ClIJ2)
HgIJ2)–NIJ13)
2.5319(15)
2.4191(13)
2.332(4)
HgIJ1)–HgIJ2)
3.6600(8)
Angles [°]
SIJ11)–HgIJ1)–SIJ12)
a
112.02(16)
102.29(14)
106.30(12)
102.29(14)
127.26(16)
100.61(7)
SIJ21)–HgIJ2)–SIJ22)
SIJ21)–HgIJ2)–BrIJ21)
SIJ21)–HgIJ2)–BrIJ22)
SIJ22)–HgIJ2)–BrIJ21)
SIJ22)–HgIJ2)–BrIJ22)
BrIJ21)–HgIJ2)–BrIJ22)
113.03(16)
105.60(13)
107.95(12)
101.80(13)
125.99(15)
99.38(7)
SIJ1)–HgIJ1)–SIJ1)
SIJ1)–HgIJ1)–ClIJ1)
180
SIJ2)–HgIJ2)–NIJ13)
SIJ2)–HgIJ2)–ClIJ1)
NIJ13)–HgIJ2)–ClIJ1)
SIJ2)–HgIJ2)–ClIJ2)
NIJ13)–HgIJ2)–ClIJ2)
ClIJ1)–HgIJ2)–ClIJ2)
118.53(11)
115.51(5)
87.64(11)
113.58(5)
110.24(10)
108.44(6)
SIJ11)–HgIJ1)–BrIJ11)
SIJ11)–HgIJ1)–BrIJ12)
SIJ12)–HgIJ1)–BrIJ11)
SIJ12)–HgIJ1)–BrIJ12)
BrIJ11)–HgIJ1)–BrIJ12)
103.12(4)
76.88(4)
86.95(5)
93.05(5)
76.77(4)
a
S(1) –HgIJ1)–ClIJ1)
SIJ1)–HgIJ1)–ClIJ2)
S(1) –HgIJ1)–ClIJ2)
ClIJ1)–HgIJ1)–ClIJ2)
a
a
Symmetry transformations: a: −x, −y, −z.
Selected bond lengths and angles [°] for the compounds listed
[
HgIJMPytat)
]
2 n
(3a)
[HgIJEPytat)
]
2 n
(6b)
[HgIJMPztat)
]
2 n
(10a)
2 n
[HgIJEPztat) ] (11a)
Bond lengths [Å]
a
HgIJ1)–NIJ3)
2.286(4)
2.286(4)
2.4872(15)
2.4872(15)
HgIJ1)–NIJ3)a
HgIJ1)–NIJ3)b
HgIJ1)–SIJ1)
2.378(7)
2.378(7)
2.426(3)
2.426(3)
HgIJ1)–NIJ23)
HgIJ1)–SIJ1)
HgIJ1)–SIJ1)
HgIJ1)–SIJ2)
2.457(6)
HgIJ1)–NIJ22)
HgIJ1)–NIJ26)
HgIJ1)–SIJ1)
2.656(5)
2.666(5)
2.376(3)
b
HgIJ1)–NIJ3)
HgIJ1)–SIJ1)
HgIJ1)–SIJ1)
2.8040(19)
2.4451(18)
2.4219(19)
4.1330(3)
4.1330(3)
c
c
a
HgIJ1)–SIJ1)
HgIJ1)–SIJ2)
2.372(3)
a
b
a
HgIJ1)–HgIJ1)
4.3772(4)
4.347(4)
HgIJ1)–HgIJ1)
4.2960(15)
4.1721(16)
HgIJ1)–HgIJ1)
HgIJ1)–HgIJ1)
b
a
b
SIJ1)–SIJ1)
SIJ1)–SIJ1)
Angles [°]
a
b
a
NIJ3) –HgIJ1)–NIJ3)
116.4(2)
NIJ3)–HgIJ1)–NIJ3)b
NIJ3)–HgIJ1)–SIJ1)
94.4(4)
102.5(2)
105.4(2)
105.4(2)
102.5(2)
NIJ22)–HgIJ1)–NIJ26)
NIJ22)–HgIJ1)–SIJ1)
NIJ26)–HgIJ1)–SIJ1)
92.55(15)
102.33(11)
91.64(11)
a
NIJ3) –HgIJ1)–SIJ1)
104.24(13)
109.60(12)
109.60(12)
104.24(13)
NIJ23)–HgIJ1)–SIJ1)
a
89.90(16)
99.30(15)
b
a
b
NIJ3) –HgIJ1)–SIJ1)
NIJ3) –HgIJ1)–SIJ1)
NIJ23)–HgIJ1)–SIJ1)
a
c
c
NIJ3) –HgIJ1)–SIJ1)
NIJ3)–HgIJ1)–SIJ1)
b
c
a
c
NIJ3) –HgIJ1)–SIJ1)
NIJ3) –HgIJ1)–SIJ1)
NIJ23)–HgIJ1)–SIJ2)
100.05(15)
NIJ22)–HgIJ1)–SIJ2)
NIJ26)–HgIJ1)–SIJ2)
90.25(10)
96.95(11)
c
c
a
SIJ1)–HgIJ1)–SIJ1)
113.05(8)
SIJ1)–HgIJ1)–SIJ1)
138.49(12)
SIJ1)–HgIJ1)–SIJ1)
112.03(6)
98.92(6)
143.27(7)
SIJ2)–HgIJ1)–SIJ1)
SIJ2)–HgIJ1)–SIJ1)
164.45(6)
a
SIJ2)–HgIJ1)–SIJ1)
Symmetry transformations
a: −x, −y, −z
a: −x + 1, y, −z + 1/2
b: x, −y + 1, z + 1/2
c: −x + 1, −y + 1
a: x − 1/2, −y + 1/2, z
b: x + 1/2, −y + 1/2, z
b: x, −y, z − 1/2
c: −x, y, −z − 1/2
1
3
(
(
1
1H, m, H2), 4.5 (2H, q, CH
DMSO-d , ppm): 156.5 (C7), 151.0 (C6), 149.3 (C1), 148.1 (C5),
37.7 (C3), 124.7 (C2), 122.8 (C4), 40.7 (CH ), 14.4 (CH ).
2
), 1.3 (3H, t, CH
3
). C NMR
2 2
[HgIJHMPztat) Cl ], 10. Yield: 66 mg (40%). Elemental
6
analysis: found, C 22.9, H 1.8, N 13.7, S 8.4%; calc. for
C H Cl HgN S (657.96), C 25.6, H 2.1, N 21.3, S 9.7%.
2
3
14 14
2
10 2
+
−1
[
HgIJHEPytat)
I
2 2
], 9. Yield: 74 mg (34%). Elemental analysis:
HgN
866.93), C 24.9, H 2.3, N 12.9, S 7.4%. FAB MS, m/z: 207.3, [H -
FAB MS, m/z: 193.2, [HMPztat]. IR (νmax/cm ): 3487–3315s
found, C 25.5, H 2.0, N 13.6, S 7.7%; calc. for C18
(
H
20
I
2
8
S
2
ν(NH), 1611–1587s ν(CN + CC), 997m ν(NN), 845m ν(CS),
+
1
307m ν(Hg–S), 239s ν(Hg–Cl). H NMR (DMSO-d , ppm): 8.7
2
6
−1
EPytat]. IR (νmax/cm ): 3406–3324s ν(NH), 1586–1520s, ν(CN
CC), 998s ν(NN), 854s ν(CS), 261m ν(Hg–S), 143m ν(Hg–I).
H NMR (DMSO-d , ppm): 8.7 (2H, d, H1), 8.0 (4H, m, H3 +
(2H, dd, H1), 8.0 (4H, m, H3 + H4), 7.5 (2H, m, H2), 3.9 (6H,
1
3
+
6
s, Me). C NMR (DMSO-d , ppm): 159.9 (C7), 151.2 (C6),
1
149.0 (C1), 147.3 (C5), 124.2 (C2), 122.7 (C4), 33.3 (CH3).
Recrystallization from DMSO and slow evaporation of the
solvent from the filtrate afforded colourless needle-like crys-
6
13
H4), 7.5 (2H, s,b, H2), 4.5 (4H, d,b, CH
NMR (DMSO-d , ppm): 158.6 (C7), 150.8 (C6), 150.8 (C1), 149.2
C5), 137.6 (C3), 124.5 (C2), 122.7 (C4), 40.9 (CH ), 14.6 (CH ).
2
), 1.3 (6H, t, CH
3
).
C
6
(
tals of [HgIJMPztat) ] (10a) over a period of 20–25 d.
2
3
2 n
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Table 3 Classical hydrogen bonding parameters [Å, °] for the compounds listed
Compound
D–H⋯A
NIJ13)–HIJ13A)⋯SIJ1)
D–H
H⋯A
D⋯A
∠DHA
Symmetry
a
1
0.97(3)
2.32(3)
3.281(3)
172(3)
−x, −y, −z + 1
a
2
NIJ13)–HIJ13A)⋯SIJ1)
0.84(2)
2.46(2)
3.294(2)
176(2)
−x + 3, −y + 1, −z
x + 1, y, z
4a
NIJ13)–HIJ13)⋯BrIJ21)
NIJ23)–HIJ23)⋯OIJ2)
0.86
0.86
0.86
0.86
2.51
1.90
2.56
1.83
3.340(15)
2.75(2)
3.405(16)
2.69(2)
2.87(2)
2.87(2)
3.35(1)
3.43(2)
161.3
172.2
166.8
174.6
a
NIJ33)–HIJ33)⋯BrIJ11)
NIJ43)–HIJ43)⋯OIJ1)
OIJ1)⋯NIJ31)
OIJ2)⋯NIJ11)
a
OIJ1)⋯BrIJ21)
x + 1, y, z
x − 1, y, z
b
OIJ2)⋯BrIJ11)
6a
NIJ23)–HIJ23)⋯NIJ12)
0.84(5)
1.95(5)
2.789(6)
171(5)
Fig. 3 (a) Perspective view of the asymmetrical unit of 4a showing intermolecular hydrogen bonding interactions (orange dashed lines). (b)
Arrangement in the strip-like packing parallel to the a axis. (c) View of the layered network of 4a showing the intermolecular interactions and de-
tails of π–π stacking.
13
[
HgIJHEPztat) Cl ], 11. Yield: 58 mg (34%). Elemental analysis:
7.5 (2H, s,b, H2), 4.5 (4H, d,b, CH ), 1.3 (6H, t, CH ). C NMR
2 3
2
2
found, C 25.5, H 2.0, N 13.6, S 7.7%; calc. for C16
H
18Cl
2
HgN10
S
2
(DMSO-d
124.5 (C2), 122.7 (C4), 32.9 (CH
Recrystallization from DMSO and slow evaporation of the
solvent from the filtrate afforded yellow plate-like crystals of
2 n
[HgIJEPztat) ] (11a) over three weeks.
6
, ppm): 158.6 (C7), 150.8 (C6), 150.8 (C1), 149.2 (C5),
), 29.6 (CH ).
+
(
686.01), C 28.0, H 2.6, N 20.4, S 9.3%. FAB MS, m/z: 190.1,
2
3
−1
[C H N ]. IR (ν /cm ): 3406–3324s ν(NH), 1586–1520s ν(CN
9
12
5
max
+
CC), 998m ν(NN), 854m ν(CS), 311m ν(Hg–S), 243s ν(Hg–Cl).
1
H NMR (DMSO-d
6
, ppm): 8.7 (2H, d, H1), 8.0 (4H, m, H3 + H4),
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Table 4 Intermolecular π⋯π interaction parameters (Å, °) for the compounds listed
CrystEngComm
a
Compound
π⋯π
CgIJI)⋯CgIJJ)
α
Rings
Symmetry
a
1
CgIJ1)⋯CgIJ2)
3.709
5.14
Cg(1): (N12/N13/C17/N14/C16)
Cg(2): (N11/C11/C12/C13/C14/C15)
x, y − 1, z
x, y + 1, z
b
a
CgIJ2)⋯CgIJ1)
CgIJ1)⋯CgIJ2)
3.709
3.572
5.14
12.72
2
Cg(1): (N12/N13/C17/N14/C16)
Cg(2): (N11/C11/C12/N16/C14/C15)
x + 1, y, z
x − 1, y, z
b
a
CgIJ2)⋯CgIJ1)
CgIJ3)⋯CgIJ4)
3.572
3.942
12.72
5.75
4a
Cg(3): (N11/C11/C12/C13/C14/C15)
Cg(4): (N21/C21/C22/C23/C24/C25)
−x + 1, −y, −z + 1
−x + 2, −y, −z + 1
b
a
b
c
CgIJ3)⋯CgIJ4)
CgIJ4)⋯CgIJ3)
CgIJ4)⋯CgIJ3)
CgIJ7)⋯CgIJ8)
3.928
3.942
3.928
3.796
5.75
5.75
5.75
8.06
Cg(7): (N31/C31/C32/C33/C34/C35)
Cg(8): (N41/C41/C42/C43/C44/C45)
−x + 1, −y + 1, −z
c
a
CgIJ8)⋯CgIJ7)
CgIJ2)⋯CgIJ4)
3.796
3.486
8.06
4.16
6
3
a
a
Cg(2): (N22/N23/C27/N24/C26)
Cg(4): (N21/C21/C22/C23/C24/C25)
−x + 2, −y + 1, −z + 1
−x + 1/2, −y + 1/2, −z + 1
a
a
CgIJ4)⋯CgIJ2)
CgIJ1)⋯CgIJ2)
3.486
3.919
4.16
5.39
Cg(1): (N2/N3/C7/N4/C6)
Cg(2): (N1/C1/C2/C3/C4/C5)
a
a
a
a
CgIJ2)⋯CgIJ1)
CgIJ2)⋯CgIJ2)
CgIJ7)⋯CgIJ7)
CgIJ7)⋯CgIJ7)
3.919
3.908
3.935
3.935
5.39
3.00
7.00
7.00
6
1
b
0a
Cg(2): (N1/C1/C2/C3/C4/C5)
Cg(7): (N21/C21/C22/N26/C24/C25)
−x, y, −z + 1/2
x − 1/2, −y + 3/2, z
x + 1/2, −y + 3/2, z
a
CgIJI)⋯CgIJJ): distance between ring centroids; α: dihedral angle between planes I and J.
Fig. 4 (a) Molecular structure of 6a showing intramolecular hydrogen bonding (orange dashed lines). Symmetry code: (a) −x, −y, −z. (b) Details of
the coordination geometry of each Hg atom including the weak Hg⋯Cl interactions. (c) Fragment of the crystal packing showing details of π–π
stacking.
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Fig. 5 (a) Polymeric structure of 3a and details of the eight-membered ring. (b) One-dimensional ladder structure of 3a along the c axis. (c) Per-
spective view of the 1D chain in the ab plane. Symmetry codes: (a) −x, −y, −z; (b) x, −y, −0.5 + z; (c) −x, y, −0.5 − z; (d) −x, −y, −1 − z.
thiosemicarbazones and 1,2,4-triazole-5-thiones. Thus, in the
H NMR spectra, the –CH signals appear at around 2.8 ppm
3
Results and discussion
1
4
(
5
-Methyl-3-(pyridin-2-yl)-1H-1,2,4-triazole-5IJ4H)-thione
HMPytat, 1) and 4-methyl-3-(pyrazin-2-yl)-1H-1,2,4-triazole-
IJ4H)-thione (HMPztat, 2) were synthesized according to the
in HAmPy4M or HAmPz4M and around 3.9 ppm in HMPytat
or HMPztat, whereas the –CH –CH signals are observed at
2
3
around 4.50 and 1.28 ppm in HMPytat and HMPztat, respec-
tively, and these are displaced downfield in HAmPy4E or
procedure described in the Experimental section. The reac-
tions of 2-pyridine- or 2-pyrazineformamide thiosemicarbazone
NIJ4)-methyl or -ethyl monosubstituted derivatives with HgIJII)
halides proceed in a straightforward manner, although some
of the results are very dependent on the type of thio-
semicarbazone and the salt. For example, treatment of NIJ4)-
methyl and -ethyl thiosemicarbazone derivatives (HAmPy4M,
13
HAmPz4E. In the C NMR spectra, the shielded signal corre-
sponds to CS, in the range of 154–160 ppm, and the sig-
nals due to –CH at around 33.5 ppm and –CH –CH at
3 2 3
around 41.0 and 14.7 ppm confirm the cyclization of the
thiosemicarbazones. Small amounts of samples of the solids
obtained after filtration were dissolved in DMSO for NMR ex-
periments. The resulting solutions were allowed to stand at
room temperature for several days to afford compounds 3a,
4a, 6a, 6b, 10a and 11a as crystalline solids.
The proposed cyclization mechanism to form 1,2,4-triazole-
5-thiones suggests the nucleophilic attack of the N4 thioamide
of the formamide thiosemicarbazone on the azomethine car-
II
HAmPz4M, HAmPy4E and HAmPz4E, respectively) with Hg
salts in a 1 : 1 molar ratio under reflux did not produce the
expected free 1,2,4-triazole-5-thione derivatives but instead
gave rise to neutral mercuryIJII) complexes of the ligands in var-
iable yields. The general method employed to prepare the final
compounds is outlined in Scheme 2. At room temperature,
these reactions gave rise to mixtures of compounds in
which the starting thiosemicarbazone (Htsc) and 1,2,4-
triazole-5-thione (Htat) were present in complexes of general
formulae [HgIJHtsc) X ], [Hg(tat)X] (3, 4) and [Hg(Htat) X ] (5,
bon, with the elimination of a molecule of NH (Scheme 3).
3
This cyclization was also observed in 2-pyridinethiosemi-
3
,15
carbazone derivatives in the presence of AgIJI).
The EI(+) mass spectra showed the molecular ion peaks,
which are the base peaks in the spectra of the 1,2,4-triazole-5-
thione ligands HMPytat and HMPztat. The complex formation
was also investigated by mass spectrometry. The parent ions of
the complexes were not observed in the mass spectra. However,
2
2
2 2
7, 9–11), along with [Hg
3 2 2 4 2
(HEPytat) (EPytat) Cl ]·3H O (6) and
[Hg(EPytat)(HEPytat)I]·H
2
O (8). The presence of these com-
1
13
pounds was confirmed by H and C NMR spectroscopy as the
methyl and ethyl signals have different chemical shifts for
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Fig. 6 (a) Polymeric structure of 6b. (b) One-dimensional ladder structure of 6b along the c axis. (c) Perspective view of the 1D chain in the ab
plane. Symmetry codes: (a) 1 − x, y, 0.5 − z; (b) x, 1 − y, 0.5 + z; (c) 1 − x, 1 − y, −z; (d) 1 − x, 1 − y, 1 − z.
in the FAB-MS spectrum of [HgIJMPytat)Br], the ion attribut-
[Hg
·H
3
(HEPytat)
2
(EPytat)
2
Cl
4
]·3H
2
O
and [Hg(EPytat)(HEPytat)I]
+
−1
able to [LM] was observed. The molecular ions corre-
2
O showed a ν(O–H) band at 3447 and 3432 cm , respec-
+
sponding to compounds [L M] were observed for com-
tively, and this confirms the presence of water molecules in
these complexes. Coordination through the pyridine nitrogen
atom was demonstrated by the shift to higher frequencies of
the ν(CN) and ν(CC) (1539 cm ), α(CCC) (626 cm ) and
ϕ(CC) (403 cm ) ring vibrations. In the 500–100 cm re-
2
plexes
[Hg(MPytat)Cl]
and
3 2 2 4
[Hg (HEPytat) (EPytat) Cl ].
+
Additionally, evidence for [LMCl] ions was also found for
these complexes. Furthermore, the presence of peaks in
the FAB-MS spectra at m/z = 1016.9 and 1223.1, which cor-
−
1
−1
−
1
16
−1
+
+
respond to [Hg(EPytat-H)
4
]
and [Hg
2
(EPytat)
4
] , respectively,
gion, most of the complexes exhibited bands in the ranges
−
1
−1
for [Hg (HEPytat) (EPytat) Cl ] is consistent with the polynu-
260–320 cm and 310–350 cm ; these bands were not ob-
served in the spectra of the free ligands and are attributed to
ν(HgS) and ν(HgN), respectively. The spectra of all the com-
plexes also contain one or two bands in the sub-300 cm re-
gion and these are typical of metal–halogen vibrations.
3
2
2
4
clear nature of this compound. The FAB-MS data for
complexes [Hg(HMPytat) ], [Hg (HEPytat) (EPytat) Cl ],
Hg(HEPytat) Br ], [Hg(EPytat)(HEPytat)I] and [Hg(HEPytat) I ]
I
2 2
3
2
2
4
−
1
[
2
2
2 2
1
7
showed ion peaks at m/z = 193 and 207, which correspond
to L + 1H and L, respectively, for [Hg(HMPztat) Cl ].
2
2
The probable coordination geometry of complexes 3–11,
which contain the thione/thiol form of the triazole ligands
and halido as co-ligands, is shown in Scheme 4. The coordi-
nation geometries of complexes 5, 7, 9, 10 and 11 are proba-
bly discrete molecules in which each metal centre is coordi-
nated in a distorted tetrahedral fashion by two halido ligands
and two neutral 1,2,4-triazole-5-thione molecules acting as
monodentate thione S-donor ligands. In contrast, complexes
3 and 4 are likely to contain a linear polymeric structure with
mercuryIJII) ions tetrahedrally bonded through thiolate and
halido alternate bi-bridges. Complex 6 has the same molecular
structure as 6a (vide supra) and it is a trinuclear compound in
which the central Hg atom is bonded centrosymmetrically to
The IR data for the ligands and complexes are given in the
Experimental section. The spectra of the free 1,2,4-triazole-5-
thione ligands are consistent with the presence of the thione
form in the solid state. The absence of ν(SH) at approximately
−
1
2
500 cm and the presence of a broad and intense ν(NH)
−
1
band in the 3100–2900 cm region confirm the presence of
the thione form. The latter band is absent in the spectra of
the complexes of MPytat and EPytat and this indicates depro-
tonation of the ligands. In the remaining complexes, the
ν(NH) band appeared as a weaker absorption in the 3400–
−
1
3
300 cm region, which represents a high energy relative to
the uncoordinated ligands. The shifts to lower frequencies of
−
1
−
ν(CS), i.e., at 788–793 cm in the free ligands, are the result
two sulfur atoms from two [EPytat] ligands. Each 1,2,4-
triazole-5-thiolate forms a bridge through the N atom to a
1
of coordination through the thiocarbonyl sulfur atom.
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Fig. 7 Molecular packing diagram and weak intermolecular C–H⋯S and π–π stacking interactions (orange dashed lines) leading to the
supramolecular structure in 3a along the c axis.
second mercuryIJII) ion, which is also tetrahedrally coordinated
by another neutral HEPytat and two chlorido ligands that
interact weakly with the central mercuryIJII) ion. On the basis
of the experimental data outlined above, compound 8 must be
a dimer in which the two mercuryIJII) ions are bonded through
two thiolate S,N bridges and the tetrahedral environment of
each metal centre is completed by a sulfur atom of a neutral li-
gand in its thione form and an iodide group.
ular hydrogen bond in 1 [C18–H18⋯S1: 3.196(3) Å]. The for-
mation of hydrogen bonds leads to a herringbone pattern
when the structure is viewed in the bc plane for 1 (Fig. 1c)
and the ab plane for 2 (Fig. 2c), forming an infinite 2D
network.
2 2 2
Crystal structure of [HgIJHMPytat) Br ]·H O (4a). The
asymmetric unit of compound 4a contains two molecules of
the complex (I for Hg1 and II for Hg2) and two crystallization
water molecules (O1 and O2), as shown in Fig. 3a. Selected
bond lengths and angles are given in Table 2. Each central
mercury(II) ion is coordinated in a distorted tetrahedral fash-
ion by two bromides and two neutral HMPytat molecules,
which act as monodentate thione S-donor ligands in a similar
Crystal structures of the triazole ligands
The crystal structures of 1 and 2 are depicted in Fig. 1a and
2
a. Selected bond lengths and angles are provided in Table
S1.† The triazole and pyridine or pyrazine rings are essentially
coplanar in both compounds. The angles between the planes
defined by the triazole ring and the pyridyl or pyrazinyl
groups are 5.1IJ2)° and 12.7IJ1)°, respectively. The bond lengths
in the five-membered triazole heterocycles are in good agree-
2 2
way to those found in [Hg(L) Br ] (L = 3-amino-5-mercapto-
2
0
1,2,4-triazole). The dihedral angles between planes Br1–Hg–
Br2 and S1–Hg–S2 are 83.4(1)° and 94.0(1)° for molecules I
and II, respectively. The four-coordinate metrical parameter
1
8
21
ment with the tabulated values. In the two compounds, the
S1–C17 bond lengths of 1.679(3) and 1.682(2) Å are consistent
with a high double bond character – as observed in 1,2,4-
4
τ , as proposed by Houser, has values of 0.90 and 0.91, re-
spectively, and these are consistent with a pseudotetrahedral
environment for both molecules. There is a significant differ-
ence between the two Hg–Br bond distances and a less
marked difference between the two Hg–S bond distances
(Table 3), but the average values for both sets of distances
[Hg–Br, 2.656(2) Å; Hg–S, 2.501(5) Å] are comparable with
those found in HgBr2 complexes with thione ligands, an
1
9
triazole-5-thiones. In the two compounds, a weak inter-
molecular hydrogen bond links the sulfur atom of one mole-
cule to the NH group of the adjacent one [N13–H⋯S1a:
3
.281(3) Å for 1 and 3.294(2) Å for 2], which generates a cyclic
2
bimolecular homosynthon with an R (8) graph-set motif
2
2
0,22
(Table 3, Fig. 1b and 2b). In addition, there is an intramolec-
2 2
HgS Br chromophore and a terminal Hg–Br group.
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Fig. 8 Molecular packing diagram and weak intermolecular C–H⋯S and π–π stacking interactions (orange dashed lines) leading to the
supramolecular structure in 6b along the c axis.
Small differences in bond distances and angles between the
HMPytat ligands of 4a are within their combined esd values,
except for the angles between rings (Table S1†). However, in
comparison with the free ligand, the most significant differ-
ences concern the C–S bond distances and the angle between
the planes defined by the triazole cycle and pyridyl rings. In
the four ligands, the mean exocyclic C–S bond length of
have as acceptors towards N23–H23 and N43–H43 hydrogens
and presumably as donors in the direction of Br21 and Br11
e
b
(b: x − 1, y, z) [O1⋯Br21, 3.35(1) Å; O2⋯Br11, 3.43(2) Å]. These
hydrogen bonds are responsible for the different conforma-
tions of the ligand in the two complex molecules. When the
HMPytat molecules only participate in a hydrogen bond as a
donor through the triazole N–H with the oxygen atoms of the
water molecules (N23–H23⋯O1 and N43–H43⋯O2), the an-
gles between the planes containing the triazoles and pyridyl
rings are 19.1(8)° and 12.5(1)°, respectively, in contrast to the
value of 5.1(2)° in free HMPytat. However, when the ligands
are involved in two hydrogen bonds from the triazole ring
(N13–H13⋯Br21 and N33–H33⋯Br11) and to the pyridyl ring
(O1⋯N31 and O2⋯N11), the loss of planarity with respect to
free HMPytat is significantly greater [32.8(8)° and 28.8(8)° in
molecules I and II, respectively] (Fig. 3b). The final result of
the intramolecular hydrogen bonding is that complex mole-
cules are arranged in a strip-like packing arrangement parallel
to the a axis, as can be seen in Fig. 3b and c. Intermolecular
π–π stacking interactions between the pyridyl rings, with cen-
troid–centroid separations of 3.796–3.942 Å, are also responsi-
ble of the formation of 2D polymers (Table 4). These two-
dimensional networks are stacked together along the crystallo-
graphic a axis (Fig. 3c).
1
.713(18) Å lies in the range observed in other thione
22b,23
complexes
and is only about 0.03 Å longer than the corre-
sponding value observed in the free ligand. This modest bond
elongation is consistent with a reduction in the π-character of
these bonds upon coordination, but is in contrast to the ob-
6
served value of 1.726(5) Å in [AgIJEPytat)] (HEPytat = 4-ethyl-5-
pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione), where the li-
3a
gand is deprotonated. Furthermore, the presence of several
groups that are capable of interacting via hydrogen bonds in-
fluences the conformation and orientation of the HMPytat
moieties within the complex. The intramolecular hydrogen
e
bonds N13–H13⋯Br21 and N33–H33⋯Br11 (e: x + 1, y, z) af-
fect the arrangement of only one of the two HMPytat mole-
cules of each complex, with the other one arranged in an al-
most anti-parallel manner to the former – probably due to the
hydrogen bonds involving the solvated water molecules
(Table 3). In fact, the oxygen atoms of water (O1 and O2) be-
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Fig. 9 (a) One-dimensional chain structure of 10a. (b) Six-membered metallacycle and boat configuration in the core of 10a. (c) Molecular packing
diagram of the C–H⋯N interactions in complex 10a along the a axis. Symmetry codes: (a) −0.5 + x, 0.5 − y, z; (b) 0.5 + x, 0.5 − y, z.
Fig. 10 (a) Perspective view of the polymeric structure of 11a. (b) Details of the tri-coordination of the ligand in 11a. (c) View of the twelve-
membered metallacycle in complex 11a. Symmetry codes: (a) 0.5 − x, 0.5 + y, 1.5 − z; (b) 0.5 + x, 0.5 − y, 0.5 + z; (c) 0.5 − x, −0.5 + y, 1.5 − z.
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Fig. 11 (a) Molecular packing diagram of weak C–H⋯N and π–π stacking interactions in complex 10a along the b axis. (b) View of intrapolymeric
C–H⋯N and π–π stacking interactions in complex 10a. (c) View of interpolymeric C–H⋯N and π–π stacking interactions in complex 10a.
2
−
Crystal structure of [{HgIJHEPytat)IJμ -NS-EPytat)Cl
2
}
2
Hg]
at 2.447(1) Å, and one nitrogen atom of the [EPytat] ligand,
(
6a). The molecular structure of 6a is a centrosymmetric tri-
which acts as an NS bidentate bridging ligand to Hg1 at
2.332(4) Å. These bond lengths are within the expected range
for mercury(II) chlorido complexes containing thione and
mer. X-ray analysis showed the rare presence of two different
mercury(II) species in the asymmetric unit, as shown in
Fig. 4a. Selected bond lengths and angles are given in
Table 2. The Hg1 atom is bonded centrosymmetrically to
1
7,25
heterocycles as ligands.
3.660(1) Å. This value lies in the range of intermetallic dis-
The Hg⋯Hg separation is
−
26
two sulfur atoms from two [EPytat] ligands with an Hg–S dis-
tances usually suggested for mercurophilic interactions.
tance of 2.357(2) Å. This distance is typical of linearly coordi-
nated mercury. However, the presence of a pair of extra
chloride atoms per asymmetric unit at 3.112(1) Å for Cl1 and
Mercurophilic interactions have been reported/calculated
with Hg···Hg distances ranging from 3.570 Å to 4.484 Å.
2
4
27
28
The wide range can be partially attributed to the acceptable
value of the van der Waals radius of mercury, which has been
3
.362(2) Å for Cl2 from Hg1, i.e., at the upper limit of the
2
9
sum of the van der Waals radii of mercury (1.55 Å) and chlo-
rine (1.75 Å), suggests that a description in terms of a (2 + 4)
coordination would also be possible. If these weak interac-
tions are considered, the coordination of Hg1 can be de-
scribed as very distorted octahedral (Fig. 4b). Since mercury
is in the centre of symmetry, the S–Hg–S angle is 180°. The
monoanionic ligand coordinates in a bidentate bridging fash-
reported to be from 1.71 up to 2.2 Å, with the latter being
considered as a better estimate than others.
A lengthening of the C–S bonds for the two coordinated li-
gands with respect to the free 1,2,4-triazole-5-thiones is ob-
served [C17–S1, 1.741(5) Å and C27–S2, 1.704(5) Å] (Table S1†).
The coordination significantly alters the double-bond character
of the C–S group. This lengthening is observed to a lesser ex-
tent in the neutral (thione) ligand than that in the thiolate li-
gand. On the other hand, the reduction in the π-character of
the carbon–sulfur bonds is accompanied by a corresponding
increase in the π-character of the triazole carbon–nitrogen
bond, mainly the thioamide carbon–nitrogen bonds (C17–N13
and C27–N23). On average, the thioamide carbon–nitrogen dis-
tance is reduced from 1.335(3) Å in the free 1,2,4-triazole-5-
thiones to 1.308(6) Å in the thiolate ligand and 1.324(6) Å in
the thione ligand. The extent of the redistribution of the
π-electron density within the coordinated ligands is entirely
2
ion (S,N). Thus, the di-coordinate [Hg(EPytat) ] unit employs
its triazole N13 donor atom to connect to another
[
HgCl (HEPytat)] unit to form the trimer 6a, as shown in
2
2
Fig. 4a. In this way, the Hg2 atom is coordinated in a (Cl SN)
distorted tetrahedral environment. The dihedral angle be-
tween planes Cl1–Hg2–Cl2 and N13–Hg3–S2 is 78.55(1)° and
2
1
the four-coordinate metrical parameter τ
4
is 0.89, which is
consistent with a pseudotetrahedral description. The Hg2
atom is bonded to two terminal chlorido ligands at 2.429(1)
and 2.532(2) Å, one sulfur atom of a neutral HEPytat ligand
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Fig. 12 (a) View of the two-dimensional network of complex 11a extending in the bc plane. (b) Details of the weak C–H⋯S interactions in 11a. (c)
Perspective view of the crystal packing of 11a along the b axis.
consistent with, and typical of, thione/thiol–sulfur coordina-
for the angles N–Hg–N and S–Hg–S, where the smallest angle
in 3a is 113.05(8)° (S–Hg–S) and the largest angle is 116.4(2)°
(N–Hg–N). In contrast, in the case of 6b, the largest angle is
S–Hg–S = 138.49(2)° and the smallest angle is N–Hg–N =
94.4(4)° (Table 2). Each mercury atom is in a twofold rota-
tion axis and is coordinated to two triazole nitrogen atoms
and two sulfur atoms of four ligand molecules, which are re-
lated by symmetry to form linear polymeric chains in the di-
rection of the crystallographic c axis (Fig. 5b and 6b).
3
0
tion. Another significant difference between the two coordi-
nated ligands is that the pyridyl ring in the thiolate ligand is
rotated by 11.3IJ2)° with respect to the triazole group, while in
the thione ligand, the rotation is only 4.2IJ4)°.
It is noteworthy that the triazole ligands are oriented be-
tween them, thus an intramolecular hydrogen bond with the
neutral ligand N23–H serving as a donor and the anionic li-
gand N12 serving as an acceptor is created [N23⋯N12,
2.789(6) Å; N23–H23⋯N12, 171IJ5)°] (Table 3, Fig. 4c). The crys-
Two mercury atoms are bi-bridged by two 1,2,4-triazole-5-
thiolato ligands in a head-to-tail arrangement (Fig. 5) similar to
tal lattice is characterized by the absence of classical hydrogen
bonds, but the packing is governed by π–π stacking interac-
tions between neutral triazole rings of the nearest-neighbour
molecules, with centroid–centroid separations of 3.489 Å (α =
that found in complex dimers [HgIJ1-meimz2S)
2
(1-meimz2SH)]
2
3
2
(1-meimz2SH 1-methylimidazoline-2(3H)-thione)
=
and
[Hg (mmtrz) (Hmmtrz) ] (Hmmtrz = 3-mercapto-4-methyl-4H-
2
4
2
31
33
4
.16°, β = 11.35° and γ = 15.51°) (Table 4). These noncovalent
1,2,4-triazole) and in the one-dimensional metal–organic co-
ordination polymer [Hg(mmtrz)
3
3
interactions allow the primary structure formed by dynamic
coordination chemistry to organize further into a more ex-
tended multidimensional assembly.
2 n
] ,
with Hg–N bond lengths
of 2.286(4) Å and Hg–S bond lengths of 2.4872(15) Å in 3a, and
2.378(7) Å and 2.426(3) Å, respectively, in 6b. The Hg–N dis-
tances are consistent with the corresponding distances ob-
Crystal structures of [HgIJMPytat)
2 n 2 n
] (3a) and [Hg(EPytat) ]
3
4
(6b). The molecular structures of complexes 3a and 6b are
served in Hg(II) thiolates with an additional N-donor ligand
shown in Fig. 5 and 6, respectively. The complexes crystal-
but are higher than those found in 3a. The Hg–S distances are
lized in the C2/c space group and each Hg(II) centre adopts a
shorter than the distribution found in the Cambridge Struc-
2
1
35
distorted tetrahedral geometry (τ = 0.90), with the greatest
tural Database (CSD) for the Hg–S distances in Hg⋯thio-
4
36
deviation from the ideal value of the bond angles observed
carboxamide and that found in 4a, but are comparable to the
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corresponding distance found in 3a. The chain contains eight-
membered rings that consist of alternate Hg and S atoms and
C–N bonds. The octagonal rings are non-planar. However, the
geometry defined by the two Hg atoms and the two S atoms
can be considered as rectangular, with C–N bonds present
Fig. 9a). This dual mode of coordination to metal centres is
different to that found in compounds 3a and 6b, and it re-
sults in the formation of six-membered rings with a distorted
boat conformation [torsion angle Hg1–C27–N23–S1
=
12.73(6)°, Fig. 9b]. This distortion can be basically attributed
to the different atoms that make up the ring (C, N, S, Hg) and
the various bond lengths. In the six-membered rings, the
Hg⋯Hg and S⋯S separations are 4.133 and 3.979 Å, respectively.
Single-crystal X-ray diffraction measurements of complex
11a revealed that it is a two-dimensional coordination poly-
mer of the molecular formula [HgIJEPztat) ] (Fig. 10a). It was
2 2 2
above and below the plane (Fig. 5). The Hg S (CN) core can
also be viewed as consisting of an Hg S plane with an addi-
2
2
tional C–N on each side of the plane to form a relaxed chair
configuration. The deformation observed in the chair configu-
ration acquired by 3a [torsion angle Hg–N–C–S = 10.890(6)°] is
distinct from that of 6b [torsion angle Hg–N–C–S = 7.459(17)°].
This situation is probably due to the steric effects of the ethyl
group and its packing, in comparison with the methyl group,
2
n
found that complex 11a crystallizes in the monoclinic space
group P2 /n. The crystallographic parameters are given in
1
37
resulting in restricted vibrational motion in the crystal. The
Hg⋯Hg distances [4.377 Å (3a) and 4.296 Å (6b)] are much lon-
ger than the sum of the van der Waals radii and indicate that a
mercurophilic interaction does not occur. Despite having simi-
lar octagonal frameworks, the Hg⋯Hg distances are longer for
Table 1. The asymmetric unit consists of an Hg(II) center and
two 1,2,4-triazole-5-thione ligands. The divalent mercury ion
has a four-coordinate structure composed of two thiolate sul-
furs, a pyrazine nitrogen and one triazole nitrogen atom from
two deprotonated triazole-thione ligands, and their arrange-
ment is considerably distorted from the ideal tetrahedral ge-
ometry. The S1–Hg1–S2 angle [164.45(6)°] is much wider than
the other bond angles around the metal centre [90.25(10)–
3
a compared to those observed in 6b. However, these distances
are comparable to those found in [Hg (mmtrz) (Hmmtrz)
and [Hg(mmtrz) (4.288 and 4.343 Å, respectively) but are
significantly higher than those in [Hg(1-meimz2S) (1-
2
4
2
]
3
3
2 n
]
102.33(11)°]. The molecular structure of 11a can be best de-
2
3
2
21
meimz2SH)]
2
(4.054 Å).
4
scribed as a distorted see-saw geometry (τ = 0.73), with the
In the crystal lattice of both compounds (Fig. 7 and 8),
weak intermolecular non-classical hydrogen bonding interac-
tions are observed. In 3a, these are formed between the C2–H
nearly linear S1–Hg1–S2 forming the plank and the N22–
Hg1–N26 forming the pivot. The N22–Hg1–N26 and S1–Hg1–
S2 planes are nearly perpendicular to one another, with a di-
hedral angle of about 84.5°. The average Hg1–S and Hg1–N
d
bonds as donors and S1 atoms (d: x + 1/2, −y + 1/2, z + 1/2)
as acceptors, while in 6b, they are formed between C1–H
bond distances are 2.374 Å and 2.661 Å, respectively
d
bonds as donors and S1 atoms (d: −x + 1/2, y − 1/2, −z − 1/2)
(Table 2), and these are slightly shorter than the correspond-
ing distances found in complexes 3a, 4a, 6a, 6b and 11b,
which is attributable to the decrease in the coordination
number in 11a in comparison to the other Hg(II) complexes.
The 1,2,4-triazole-5-thione in both ligands has a distinct
coordinative behaviour. A monoanionic ligand coordinates in
a monodentate terminal fashion through the thiolate S1
atom. The other ligand is also monoanionic and acts as a
tridentate system through the thiolate S2 atom, the triazole
N22 atom and the pyrazine N26 atom, coordinating three dif-
ferent mercury ions as a threefold bridge (Fig. 10b). Thus, ev-
ery two mercury atoms are bi-bridged by two 1,2,4-triazole-5-
pyrazine ligands in a head-to-tail arrangement (Fig. 10c),
which leads to twelve-membered rings with a chair conforma-
tion in each layer, with both ligands contained in the same
plane and HgIJII) atoms located above and below this plane
with an Hg⋯Hg separation of 6.472(5) Å. The two ligand
molecules differ in their conformation around the triazole–
pyrazine C–C bond. In molecule 1 (containing S1), both rings
are ‘trans’ with respect to each other [torsion angle C14–C15–
C16–N12 = −18.4IJ1)°], whereas in molecule 2 (containing S2),
they are ‘cis’ [torsion angle C2–C25–C26–N22 = 20.4IJ8)°].
The crystal structure of compound 10a is stabilized by
intramolecular C–H⋯S interactions and intermolecular C–
H⋯N interactions. There are two types of C–H⋯N interac-
as acceptors (Table S2†). In compound 3a, this packing is
reinforced by pairs of weak π–π stacking interactions between
pyridine and triazole rings of the nearest-neighbour chains
3
1
(
(
head-to-tail), with centroid–centroid separations of 3.919 Å
Table 4, Fig. 7). However, in 6b, the π–π stacking interac-
tions are established between pyridine rings of the nearest li-
gands in the same chain (face-to-face with respect to one an-
other), with centroid–centroid separations of 3.908 Å (α = 3°,
β = 9.88°, γ = 9.88°) (Table 4, Fig. 8).
2 n 2 n
Crystal structures of [HgIJMPztat) ] (10a) and [Hg(EPztat) ]
(
11a). Compound 7 crystallizes in the orthorhombic Pna2 space
1
group. The structure obtained from single-crystal X-ray diffrac-
tion data reveals that compound 10a is a neutral 1D framework
that extends along the a axis. The repeat unit of each 1D ribbon
−1
contains one Hg(II) centre coordinated to two MPztat ligands.
The detailed coordination environment of each ligand and the
coordination polyhedron of the Hg(II) centre are shown in
Fig. 9a; the bond lengths and bond angles are listed in
Table 2. The Hg(II) centre in 10a has a geometry between
distorted tetrahedral and see-saw distorted by coordination to
−1
three S atoms and one N atom from four different MPztat li-
21
4
gands (τ = 0.90). In the polymeric chains, two mercury atoms
are S,N-bridged by a triazole ligand with Hg–N and Hg–S bond
distances of 2.457(6) and 2.422(2) Å, respectively. A second
triazole ligand forms asymmetric thiolato bridges between the
same mercury atoms, with Hg–S bond distances of 2.804(2) Å
c
tions and the C12–H12⋯N26 (c: −x + 3/2, y − 1/2, z − 1/2)
interaction results in the formation of a sheet-like structure
b
for Hg1–S and 2.445(2) Å for S1–Hg1 (b: x + 1/2, −y + 1/2, z;
(Fig. 11a). These sheets are further connected by C18–H⋯N
3444 | CrystEngComm, 2016, 18, 3428–3446
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and C28–H⋯N interactions (Table S2†). The molecular pack-
ing is further stabilized by π–π stacking interactions
Y. Sert, A. A. El-Emam, E. S. Al-Abdullah, A.-M. S. Al-Tamimi,
Ç. Çırak and F. Ucun, Spectrochim. Acta, Part A, 2014, 126,
280–290.
(Fig. 11b and c) between the pyrazine rings, with a centroid–
centroid distance of around 3.93 Å and a displacement angle
2 (a) J. G. Haasnoot, Coord. Chem. Rev., 2000, 200–202,
131–185; (b) M. H. Klingele and S. Brooker, Coord. Chem.
Rev., 2003, 241, 119–132; (c) G. Aromí, L. A. Barrios, O.
Roubeau and P. Gamez, Coord. Chem. Rev., 2011, 255,
485–546; (d) R. E. Sabzi, A. Nikoo, Y. Nikzad, M. Bahram, K.
Akbari and N. Samadi, Am. J. Anal. Chem., 2012, 3, 437–442.
3 (a) A. Castiñeiras, I. García-Santos, S. Dehnen and P.
Sevillano, Polyhedron, 2006, 25, 3653–3660; (b) R. Chmekh, I.
Tapsoba, H. Medini, E. Maisonhaute, M. L. Benkhoud and
K. Boujlel, J. Electroanal. Chem., 2007, 599, 85–90; (c) A. A.
Hassan, A. M. Shawky and H. S. Shehatta, J. Heterocycl.
Chem., 2012, 49, 21–37.
25
of 7° (Table 4). In contrast to compound 10a, compound
1a does not have π–π stacking interactions. In addition to
1
the C18–H18A⋯N11 and C24–H24⋯S1 intramolecular inter-
actions (Fig. 12a and b), in compound 11a, the molecular ar-
d
rangement is consolidated by C12–H12⋯S2 intermolecular
interactions (Fig. 12b) (d: x + 1/2, −y + 3/2, z − 1/2). The other
b
intermolecular interaction is C28–H28B⋯N21 (b: −x, −y + 2,
−
z + 1) (Table S2†). These two weak interactions generate a
three-dimensional network (Fig. 12c).
Conclusions
4
(a) P. Lo Meo, M. Gruttadauria and R. Noto, ARKIVOC,
005, 114–129; (b) R. M. Shaker, ARKIVOC, 2006, 59–112.
We have developed a strategy for the controllable in situ gen-
eration of functionalized 4-substituted 1,2,4-triazole-5-thiones
under mild reaction conditions from 2-pyridine- and
2
5
(a) Mercury and its Effects on Environment and Biology in
Metal Ions in Biological Systems, ed. A. Sigel and H. Sigel,
Marcel Decker, New York, 1997, vol. 34; (b) K. M. Rice, E. M.
Walker Jr, M. Wu, Ch. Gillette and E. R. Blough, J. Prev.
Med. Public Health, 2014, 47, 74–83.
2
-pyrazineformamide thiosemicarbazones. The coordination
chemistry of the ligands has been investigated with
mercuryIJII) ions in each coordination compound. The struc-
tural diversity of these materials is reflected in the variety of
coordination polyhedra for the mercury sites and by the mo-
lecular aggregations, ranging from essentially isolated mono-
nuclear to 3-dimensional arrays. A possible design element to
control the molecular aggregation can be based on the steric
profile of the substituents of the 1,2,4-triazole-5-thione/
thiolate ligands, although this principle may not be universal.
The crystals studied here show intra- and intermolecular clas-
sical hydrogen-bonding interactions, which lead to the forma-
tion of intriguing 3D networks that are reinforced by weak C–
H⋯S and C–H⋯N hydrogen bonding as well as by inter- and
intramolecular aromatic–aromatic interactions in some com-
pounds. Our results may be important to understand, on the
one hand, the oxidative cyclization of functionalized formam-
ide thiosemicarbazones aimed at the preparation of 1,2,4-
triazole-5-thione derivatives, and on the other hand, the solid-
state architectures of organic–inorganic materials containing
the thione/thiolate system. The investigation herein reported
also reflects that the comprehensive understanding of weak
intermolecular forces governing crystal packing should poten-
tially enable the rational design of solids. Parallel studies of
CdIJII) and ZnIJII) are in progress to compare packing patterns.
6
7
A. Morsalia and M. Y. Masoomi, Coord. Chem. Rev.,
2
009, 253, 1882–1905.
D. X. West, J. K. Swearingen, J. Valdés-Martínez, S. Hernández-
Ortega, A. K. El-Sawaf, F. van Meurs, A. Castiñeiras, I. García
and E. Bermejo, Polyhedron, 1999, 18, 2919–2929.
8
9
E. Bermejo, A. Castiñeiras, L. Fostiak, I. García-Santos, K.
Swearingen and D. X. West, Z. Anorg. Allg. Chem., 2005, 631,
7
28–738.
E. Labisbal, A. Sousa-Pedrares, A. Castiñeiras, J. K. Swearingen
and D. X. West, Polyhedron, 2002, 21, 1553–1559.
1
1
0 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta
Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen.
Crystallogr., 1968, 24, 351–359.
1 G. M. Sheldrick, SADABS, Program for Empirical Absorption
Correction of Area Detector Data, University of Göttingen,
Germany, 2001.
1
1
1
1
2 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
2
015, 71, 3–8.
3 K. Brandenburg and H. Putz, Diamond, version 3.2, Crystal
Impact GbR, Bonn, Germany, 2009.
4 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory
Chemicals, Pergamon Press, Oxford, 3rd edn, 1988.
5 A. Castiñeiras, I. García-Santos, S. Nogueiras, I. Rodríguez-
González and R. Rodríguez-Riobó, J. Mol. Struct., 2014, 1074,
Acknowledgements
1
–18.
6 C. Airoldi and A. S. Gonçalves, J. Inorg. Nucl. Chem.,
978, 40, 1817–1818.
Financial support from ERDF (EU), Ministerio de Ciencia e
Innovación (Spain) and the Xunta de Galicia (Spain) under re-
search projects (Project MAT2010-15594) and thematic net-
works (R2014/004 and CTQ2015-71211-REDT) is gratefully
acknowledged.
1
1
1
7 E. Bermejo, R. Carballo, A. Castiñeiras, R. Domínguez, A. E.
Liberta, C. Maichle-Mössmer, M. M. Salberg and D. X. West,
Eur. J. Inorg. Chem., 1999, 965–973.
1
8 Structure Correlations, ed. H.-B. Bürgi and J. D. Dunitz, vol.
References
2
, VCH, Weinheim, Germany, 1994.
1
(a) N. Demirbas, R. Ugurluoglu and A. Demirbas, Bioorg.
Med. Chem., 2002, 10, 3717–3723, and references therein; (b)
19 F. Heshmatpoura, M. Ghassemzadeh, M. Semsarha and B.
Neumüller, Z. Anorg. Allg. Chem., 2007, 633, 465–469.
This journal is © The Royal Society of Chemistry 2016
CrystEngComm, 2016, 18, 3428–3446 | 3445

View Article Online
Paper
CrystEngComm
2
2
2
0 M. Baraldi, W. Malavasi and R. Grandi, J. Chem. Crystallogr.,
998, 26, 63–66.
1 L. Yang, D. R. Powell and R. P. Houser, Dalton Trans.,
007, 955–964.
2 (a) E. Bermejo, A. Castiñeiras, I. García-Santos and D. X.
West, Z. Anorg. Allg. Chem., 2005, 631, 2011–2019; (b) F.
Isaia, M. C. Aragoni, M. Arca, C. Caltagirone, C. Castellano,
F. Demartin, A. Garau, V. Lippolis and A. Pintus, Dalton
Trans., 2011, 40, 4505–4513; (c) D. M. S. Paqhaleh, L.
Hashemi, V. Amani, A. Morsali and A. A. Aminjanov, Inorg.
Chim. Acta, 2013, 407, 1–6.
J.-Y. Saillard, Inorg. Chem., 2004, 43, 4012–4018; (g) M. R.
Haneline and F. Gabbaï, Angew. Chem., Int. Ed., 2004, 43,
5471–5474; (h) U. Patel, H. B. Singh and G. Wolmerhauser,
Angew. Chem., 2005, 117, 1715–1717; (i) H. Schmidbaur and
A. Schier, Organometallics, 2015, 34, 2048–2066; ( j) L. K.
Rana, S. Sharma and G. Hundal, Cryst. Growth Des.,
2016, 16, 92–107.
1
2
27 (a) F. Zamora, M. Sabat, M. Janik, C. Siethoff and B. Lippert,
Chem. Commun., 1997, 485–486; (b) S. Das, C.-H. Hung and
S. Goswami, Inorg. Chem., 2003, 42, 8592–8597; (c) M. R.
Haneline, M. Tsunoda and F. P. Gabbaï, J. Am. Chem. Soc.,
2002, 124, 3737–3742; (d) J. B. King, M. R. Haneline, M.
Tsunoda and F. Gabbaï, J. Am. Chem. Soc., 2002, 124,
9350–9351.
28 W.-Y. Wong, Coord. Chem. Rev., 2007, 251, 2400–2427.
29 (a) S. S. Batsanov, J. Chem. Soc., Dalton Trans., 1998, 1541–1546;
(b) K. R. Flower, V. J. Howard, S. Naguthney, R. G. Pritchard, J. E.
Warren and A. T. McGown, Inorg. Chem., 2002, 41, 1907–1912.
30 E. S. Raper, Coord. Chem. Rev., 1985, 61, 115–184.
31 Ch. Janiak, J. Chem. Soc., Dalton Trans., 2000, 3885–3896.
32 N. A. Bell, W. Clegg, J. R. Creighton and E. S. Raper, Inorg.
Chim. Acta, 2000, 303, 12–16.
2
2
3 (a) J. L. White, J. M. Tanski, D. G. Churchill, A. L. Rheingold
and D. Rabinovich, J. Chem. Crystallogr., 2003, 33, 437–445;
(
b) E. Bermejo, A. Castiñeiras, I. García-Santos and D. X.
West, Z. Anorg. Allg. Chem., 2005, 631, 2011–2019.
4 (a) D. Matković-Čalogović, D. Mrvoš-Sermek, Z. Popovića and
Ž. Soldina, Acta Crystallogr., Sect. C: Cryst. Struct. Commun.,
2
004, 60, m44–m46; (b) Y. Durust, C. Altug, C. Bozkurt and
F. R. Fronczek, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 2005, 61, m442–m444; (c) X.-Y. Tang, J.-X. Chen,
G.-F. Liu, Z. I.-G. Ren, Y. Zhang and J.-P. Lang, Eur. J. Inorg.
Chem., 2008, 2593–2600.
2
2
5 E. Bermejo, R. Carballo, A. Castiñeiras, R. Domínguez, A. E.
Liberta, C. Maichle-Mössmer and D. X. West, Z. Naturforsch.,
B: J. Chem. Sci., 1999, 54, 777–787.
33 A. Bharti, P. Bharati, M. K. Bharty, R. K. Dani, S. Singh and
N. K. Singh, Polyhedron, 2013, 54, 131–139.
34 E. Bermejo, A. Castiñeiras, I. García-Santos and D. X. West,
Polyhedron, 2003, 22, 1147–1154.
6 (a) P. Pyykkç and M. Straka, Phys. Chem. Chem. Phys.,
2
000, 2, 2489–2493; (b) M. A. Omary, R. M. Kassab, M. R.
Haneline, O. Elbjeirami and F. Gabbaï, Inorg. Chem.,
003, 42, 2176–2178; (c) U. Patel, H. B. Singh and G.
35 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58,
380–388.
2
36 A. Kováes, D. Nemesok, G. Pokol, K. M. Szécsényi, V. M.
Leovac, Z. K. Jaćimović, I. R. Evans, J. A. K. Howard, Z. D.
Tomic and G. Grester, New J. Chem., 2005, 28, 833–840.
37 M. S. Bharara, S. Parkin and D. A. Atwood, Inorg. Chem.,
2006, 45, 7261–7268.
Wolmerhauser, Angew. Chem., 2003, 115, 1743–1745; (d)
W. Y. Wong, L. Liu and J. X. Shi, Angew. Chem., 2003, 115,
4
198–4202; (e) W. Y. Wong, G. L. Lu, L. Liu, J. X. Shi and Z.
Lin, Eur. J. Inorg. Chem., 2004, 2066–2077; ( f ) A. Vega and
3446 | CrystEngComm, 2016, 18, 3428–3446
This journal is © The Royal Society of Chemistry 2016