New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties

Article abstract of DOI:10.1016/j.poly.2010.08.012

The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chloride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear Pd^II-complex [(PPh ₃)Pd(HL1)Cl]Cl·2CH₃CN

Full text of DOI:10.1016/j.poly.2010.08.012

Polyhedron 29 (2010) 3036–3045
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Polyhedron
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New mono- and binuclear Pd(II) complexes containing 1,2,4-triazole moieties
a
a
a
Mitra Ghassemzadeh a, , Samira Bahemmat , Masoomeh Mahmoodabadi , Babak Rezaii-Rad ,
⇑
Hassan Hosseini Monfared b, Effat Mottefakeri b, Bernhard Neumüller c
a Chemistry and Chemical Engineering Research Center of Iran, Iran
b Department of Chemistry, Faculty of Sciences, Zanjan University, Zanjan, Iran
c Fachbereich Chemie, Philipps Universität, Marburg, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of AMTT (AMTT = 4-amino-3-methyl-1,2,4-triazol-5-thione, HL1) with palladium(II) chlo-
ride and triphenylphosphane as a co-ligand in acetonitrile afforded the mononuclear PdII-complex
[(PPh3)Pd(HL1)Cl]Clꢀ2CH3CN (1). The complex [(PPh3)Pd(HL1)I]Clꢀ1/2H2O (2) was prepared via halogen
exchange between 1 and sodium iodide in methanol/acetonitrile. The first binuclear palladium(II) com-
plex containing singly deprotonated HL1, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Clꢀ1/3H2OꢀCH3OH (3), was pre-
pared by the reaction of HL1 with palladium(II) chloride and triphenylphosphane in the presence of
sodium acetate in methanol.
Received 2 May 2010
Accepted 7 August 2010
Available online 21 August 2010
Keywords:
1,2,4-Triazoles
Palladium(II) complexes
S,N ligands
All the complexes have been characterized by a combination of FT-IR-, 31P NMR-spectroscopy, elemen-
tal analyses and mass spectrometry. The molecular structures of the complexes were determined by
X-ray diffraction studies. The unit cell of 2 exhibits two crystallographically independent complexes,
while the unit cell of 3 contains three crystallographically independent molecules. While the triazole
moiety in 1 and 2 acts as a bidentate chelating ligand, the deprotonated triazole compound in 3 acts
as a bridging agent between two metal centers. Single-crystal X-ray diffraction revealed that the packing
mode of the heterocycle by the phenyl rings of the PPh3 moiety is responsible for the interesting observed
‘‘sandwich” effect. The X-ray structure of the complex [Pd(py)4]Cl2ꢀ1/2H2O (4) is also reported.
Ó 2010 Elsevier Ltd. All rights reserved.
‘‘Sandwich” effect
1. Introduction
thiol tautomerism in solution (forms I and II), as illustrated in
Scheme 1.
The chemistry of 1,2,4-triazole and its derivatives has received
considerable attention because of their effective biological impor-
tance and applications. They are known to possess significant anti-
tumor, antibacterial, fungicidal, hypotensive, hypothermic and
antiinflammatory activities [1–8]. In addition to these applications,
the coordination chemistry of 1,2,4-triazoles as a ligand is widely
studied [9] and reviewed [10,11]. Up to 200 single crystal X-ray
determinations of metal complexes with 1,2,4-triazoles as ligands
well demonstrate the growing interest in the chemistry of this
class of ligands. Metal complexes of 1,2,4-triazole and its deriva-
tives often exhibit enhanced biological activities compared to the
uncomplexed ligands [12–17].
Therefore, such ligands exhibit various coordination modes as
thioxo groups and triazoline nitrogen atoms are present on each
heterocyclic ring [26–28]. Some of the observed coordination
modes of the 1,2,4-triazole ring system to metal centers are pre-
sented in Scheme 2.
We have previously reported the synthesis and molecular struc-
ture of CuI- and AgI-complexes containing AMTT and its Schiff-
bases, in which the ligand acts either as S-monodentate (form A,
Scheme 2) or bidentate N,S-chelating (form B, Scheme 2), and have
found that such heterocycles can be used as good stabilization
agents for soft metal ions in low oxidation states [29–31]. We have
recently reported the synthesis and characterization of the silver(I)
complex [{[Ag(AETT)]NO3}2]n (AETT = 4-amino-5-ethyl-2H-1,2,
4-triazole-3(4H)-thione) with new coordination modes between
silver(I) ions and the sulfur atoms of the 1,2,4-triazole-3-thione
moieties, as shown in Scheme 3. These coordination modes lead
to the formation of a 10-membered Ag–S ‘‘mosaic” pattern and
cause a two dimensional endless framework [32].
Among the 1,2,4-triazole derivatives, the mercapto- and thione-
substituted 1,2,4-triazole ring systems have also been studied and
reviewed [18–25]. 4-Amino-5-methyl-2H-1,2,4-triazole-3(4H)-
thione (AMTT, HL1) shows, as a weak monoprotic acid, thione–
The present work concerns the synthesis and characterization
of mono- and binuclear palladium(II) complexes of sulfurated tria-
zole AMTT with triphenylphosphane as a co-ligand.
⇑
Corresponding author. Tel.: +98 21 44 58 07 20; fax: 98 21 44 58 07 62.
E-mail address: mghassemzadeh@ccerci.ac.ir (M. Ghassemzadeh).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.08.012

M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
3037
H
N
2. Experimental
N
N
N
S
HS
2.1. Materials
Me
Me
N
N
NH2
NH2
All chemicals except 4-amino-3-methyl-1,2,4-triazol-5-thione
[33] were purchased from Merck or Fluka and were used without
further purification. Complex 4 is produced by the recrystallization
of [PdL2]Cl2 (L = 4-amino-3-hydrazinyl-6-methyl-1,2,4-triazin-
5(4H)-one) from pyridine as a pale yellow solid mass and is iden-
tified as the same complex reported by Drew et al., namely
I
II
Scheme 1. Thione (I) and thiol (II) tautomers of AMTT.
H
N
H
N
H
N
N
.
N
N
M2
[Pd(Py)4]Cl2 3H2O [34,35].
M1
S
S
S
Me
Me
Me
N
N
N
NH2
NH2
NH2
2.2. Physical measurements
M1
M1
A
B
C
IR spectra were recorded (KBr) on a Perkin–Elmer 883 spec-
trometer. Melting points were recorded on a Büchi B545 melting
point apparatus and are uncorrected. 1H NMR and 31P NMR spectra
were recorded on a Bruker-AQS AVANCE 300 MHz using TMS
(d = 0.0 ppm) as an internal standard and 85% aqueous H3PO4 as
an external standard. Mass spectra were recorded on a Fisons
Instruments Trio 1000 spectrometer (EI = 70 eV). Elemental analy-
ses (C, H and N) were performed on a ThermoFinigan Flash EA 1112
series elemental analyzer.
M2
H
N
H
N
M3
N
N
M2
S
S
Me
Me
N
N
NH2
NH2
M1
M1
E
D
Scheme 2. Potential binding modes of AMTT to metal centers.
M1
2.3. Synthesis
H
N
H
N
N
N
M2
M2
M1
2.3.1. Synthesis of [(PPh3)Pd(HL1)Cl]Cl.2CH3CN (1)
S
S
R
R
N
N
A solution of HL1 (0.13 g, 1 mmol) in methanol/acetonitrile
(20 mL, 1/1) was treated with a solution of palladium(II) chloride
(0.17 g, 1 mmol) in the same solvent mixture (20 mL) and stirred
for 2 h at room temperature. After completion of the reaction,
which was monitored by thin layer chromatography (TLC) using
NH2
NH2
M2A
M2d
F
G
Scheme 3.
Table 1
Crystallographic data for 1, 2, 3 and 4.
Compound
1
2
3
4
Empirical formula
Formula mass
Crystal size (mm)
Crystal system
Space group
a [pm]
C
25H27Cl2N6PPdS
C21H22ClIN4O0.5PPdS
670.21
C58H54.67Cl3N4O1.33P3Pd2S
1273.18
C20H26Cl2N4O3Pd
547.75
0.31 ꢁ 0.21 ꢁ 0.19
Monoclinic
Cc
651.86
0.42 ꢁ 0.15 ꢁ 0.1
Monoclinic
P21/c
1906.4(2)
1326.0(1)
1122.9(1)
90
97.11(1)
90
2816.7(4)
4
0.49 ꢁ 0.38 ꢁ 0.32
0.37 ꢁ 0.32 ꢁ 0.31
Triclinic
Triclinic
ꢀ
ꢀ
P1
P1
1146.6(1)
1399.8(2)
1748.1(3)
100.34(2)
106.53(2)
90.01(2)
2642.2(7)
4
1493.6(1)
2511.6(2)
2594.1(2)
115.56(1)
97.73(1)
99.76(1)
8405(1)
6
1251.6(1)
1273.5(2)
1524.7(2)
90
107.50(1)
90
2317.8(5)
4
1.57
b [pm]
c [pm]
a
[°]
b [°]
c
[°]
V [pm3 ꢁ 106]
Z
Dcalc. [g cmꢂ3
]
1.537
1.685
1.509
Absorption correction
(Mo K
) [cmꢂ1
T [K]
2hmax [°]
Numerical
10.05
193
Numerical
21.29
193
Numerical
9.52
193
Numerical
10.59
193
l
a
]
52.10
52.16
51.94
52.32
Index range
h
k
l
ꢂ23 ? 23
ꢂ16 ? 16
ꢂ13 ? 13
27 186
ꢂ13 ? 14
ꢂ17 ? 17
ꢂ21 ? 21
25 854
ꢂ18 ? 18
ꢂ30 ? 30
ꢂ31 ? 31
82 940
ꢂ15 ? 15
ꢂ15 ? 15
ꢂ18 ? 18
11 260
Reflections collected
Unique reflections (Rint
)
5504 (0.0891)
3629
338
9561 (0.0692)
6394
552
30493 (0.0414)
19554
1929
4528 (0.0368)
3952
272
Reflections with Fo > 4
Parameters
r(Fo)
Flack parameter
R1
wR2 (all data)
0.00(3)
0.0282
0.0356
0.077a
0.495
0.0494
0.1320b
1.826
0.0396
0.0986c
1.157
0.0596d
0.43
Maximum residual electron density [e pmꢂ3 ꢁ 10ꢂ6
]
2
w ¼ 1=½r2ðFo2Þ þ ð0:0384 ꢀ PÞ ꢃ; P ¼ ½maxðFo2; 0Þ þ 2 ꢀ F2c ꢃ=3.
a
b
c
2
w ¼ 1=½r2ðF2oÞ þ ð0:0757 ꢀ PÞ ꢃ.
2
w ¼ 1=½r2ðF2oÞ þ ð0:0579 ꢀ PÞ ꢃ.
2
w ¼ 1=½r2ðF2oÞ þ ð0:0317 ꢀ PÞ ꢃ.
d

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M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
H2N
N
H2N
N
Pd(PPh3)Cl
S
Pd(PPh3)I
S
b
.
Cl 1/2H2O
.
Cl 2CH3CN
NH
NH
N
N
a
1
2
NH2
N
S
N
NH
c
HL1
H2N
N
Pd(PPh3)Cl
S
.
.
Cl 1/3H2O MeOH
N
N
Pd(PPh3)2Cl
3
Scheme 4. (a) PdCl2, PPh3 in MeOH/MeCN; (b) NaI in MeOH/MeCN; and (c) PdCl2, PPh3, NaOAc (2:3:1) in MeOH/MeCN.
ethylacetate/hexane (1/1 v/v) as the eluent, the reaction mixture
was treated with triphenylphosphane (0.26 g, 1 mmol) and was
stirred for a further 2 h. Completion of the reaction was monitored
by TLC using the same eluent as mentioned above. The reaction
mixture was filtered, washed with cold acetonitrile and dried at
room temperature. Yield: 0.48 g, 84%, mp: 225 °C, Anal. Calc. for
C
21H21Cl2N4PPdS (569.78): C, 44.27; H, 3.71; N, 9.83. Found: C,
44.20; H, 3.69; N, 9.97%. IR (KBr) [
m
/cmꢂ1]: 3047 s, 3022 s, 2872
s, 2762 s, 1969 w, 1899 w, 1604 m, 1506 s, 1479 s, 1433 s, 1390
m, 1357 m, 1311 w, 1184 m, 1097 s, 1072 w, 997 s, 748 s, 690 s,
534 s, 509 s, 451 w. EI-MS (70 eV): m/z 262 (PPh3), 130 (HL1).
31P NMR (d/ppm, CDCl3): 29.89 (s).
2.3.2. Synthesis of [(PPh3)Pd(HL1)I]Clꢀ1/2H2O (2)
A
solution of 1 (0.56 g, 1 mmol) in methanol/acetonitrile
(20 mL, 1/1) was treated with sodium iodide (0.15 g, 1 mmol) at
room temperature and stirred for 3 h. After completion of the reac-
tion (TLC), the crude product was filtered and washed with water
(2 ꢁ 10 mL), dried and characterized as a pure material. Single
Fig. 2. Molecular structures of the cations in complex 2 (thermal ellipsoids at the
40% probability level), the hydrogen atoms of the phenyl rings are omitted for
clarity. Selected bond lengths [pm] and angles [°]: Pd1–N1 212.1(5), Pd1–P1
224.4(2), Pd1–S1 231.9(2), Pd1–I1 260.26(9), S1–C1 171.3(7), C1–N2 135.1(9),
N2–C2 139.0(9), C2–N3 133(1), N3–N4 135.9(9), N4–C1 133.8(9), N2–N1 142.6(8),
N1–Pd1–P1 177.9(2), N1–Pd1–S1 87.8(2), P1–Pd1–S1 94.03(6), N1–Pd1–I1 88.4(2),
P1–Pd1–I1 89.80(5), C1–N2–C2 109.0(6), N2–C2–N3 108.2(6), C2–N3–N4 105.6(6),
N3–N4–C1 112.6(6), N4–C1–N2 104.5(6); Pd2–N6 212.1(5), Pd2–P2 224.2(2), Pd2–
S2 231.2(2), Pd2–I2 259.99(8), S2–C4 171.1(7), C4–N5 136.3(9), N5–C5 139.0(9),
C5–N7 128.7(9), N7–N8 139.3(9), N8–C4 132.3(9), N6–Pd2–S2 87.8(1), P2–Pd2–S2
94.23(6), N6–Pd2–I2 88.1(1), P2–Pd2–I2 89.85(5), C1–S1–Pd1 95.1(3), H7–O1–H8
102.7, H9–O2–H10 142.1, C4–N5–C5 108.1(5), N5–C5–N7 110.1(6), C5–N7–N8
104.9(6), N7–N8–C4 112.4(6), N8–C4–N5 104.2(6).
Fig. 1. Molecular structure of the ion pair in complex 1 (thermal ellipsoids at the
40% probability level), the hydrogen atoms of the phenyl rings are omitted for
clarity. Selected bond lengths [pm] and angles [°]: Pd1–N2 214.6(3), Pd1–P1
225.2(1), Pd1–Cl1 229.9(1), Pd1–S1 230.1(1), S1–C1 172.4(4), C1–N1 133.8(5), N1–
N2 141.1(5), N1–C2 138.1(5), C2–N3 130.5(5), N3–N4 137.0(5), N2–Pd1–Cl1
89.6(1), P1–Pd1–Cl1 89.67(4), N2–Pd1–S1 87.1(1), P1–Pd1–S1 93.78(4), C1–S1–
Pd1 95.6(1), C2–N1–C1 108.7(3), N1–C1–N4 104.9(3), C1–N4–N3 112.4(4), N4–N3–
C2 104.9(3), N3–C2–N1 109.1(4).

M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
3039
crystals suitable for X-ray analysis were obtained by recrystalliza-
tion from a methanol solution of 2. Yield: 0.60 g, 90%, mp: 228 °C,
Anal. Calc. for C21H21ClIN4PPdS (677.28): C, 39.01; H, 3.72; N, 8.27.
mp: 245 °C. Anal. Calc. for
C
58H54Cl3N4OP3Pd2S (1267.26) C,
54.97; H, 4.29; N, 4.42. Found: C, 54.89; H, 4.30; N, 4.45%. IR
(KBr), [m
/cmꢂ1): 3350, 1620, 1471, 1431, 748–696. 1H NMR (d/
Found: C, 38.94; H, 3.70; N, 8.30%. IR (KBr) [
m
/cmꢂ1]: 3188 w, 2978
ppm, CDCl3): 1.24 (s, 3H, CH3), 7.35–7.72 (m, 45H, 3PPh3). 31P
NMR (d/ppm, CDCl3): 23.53, 30.43. MS (70 ev) m/z: 129 (L1), 262
(PPh3).
w, 2939 m, 2854 m, 2690 m, 2634 m, 2387 m, 2351 m, 2333 m,
1799 w, 1768 w, 1714 s, 1612 s, 1516 m, 1460 w, 1375 w, 1332
s, 1226 m, 1166 w, 1126 vw, 1068 w, 1012 w, 977 w, 918 w, 887
w, 858 w, 715 m, 671 w, 609 vw, 520 m, 490 w, 459 w. EI-MS
(70 eV): m/z 130 (HL1), 262 (PPh3). 31P NMR (d/ppm, CDCl3):
35.74 (s).
2.4. Crystal structure analyses of 1, 2, 3 and 4 (Table 1)
Table 1 shows the crystallographic data of complexes 1–4. The
crystals of 1, 2, 3 and 4 were covered with perfluorinated oil and
mounted on the top of a glass capillary under a flow of cold gas-
eous nitrogen. The orientation matrix and unit cell dimensions
were determined from 8000 ( 1–3, Stoe IPDS I) and from 5000
2.3.3. Synthesis of [(PPh3)2ClPd(L1)Pd(PPh3)Cl]Clꢀ1/3H2OꢀCH3OH (3)
To a solution of HL1 (0.13 g, 1 mmol) in methanol (20 mL), a
solution of sodium acetate (0.08 g, 1 mmol) in water (2 mL) was
added. The obtained solution was treated with palladium chloride
(0.35 g, 2 mmol) and stirred for 1 h. After completion of the reac-
tion, which was monitored by TLC using ethyl acetate/ petroleum
ether (1/2) as the eluent, the orange reaction mixture was treated
with a solution of triphenylphosphane (0.78 g, 3 mmol) in same
the solvent (10 mL) and was stirred for a further 3 h. After comple-
tion of the reaction (TLC test), the solid was filtered and washed
with cold methanol (2 ꢁ 5 mL). The filtrate was kept at 4 °C to give
bright orange single crystals after a few days. Yield: 1.20 g, 95%,
(4, Stoe IPDS II) reflections (graphite-monochromated Mo-K
a
NH2
N
S
N
N
III
Scheme 5. Hückel aromaticity in L1.
Fig. 3. Molecular structures of the cations in complex 3 (thermal ellipsoids at the 40% probability level). Selected bond lengths [pm] and angles [°]: Pd1–N2 216.2(3), Pd1–P1
225.1(1), Pd1–S1 228.7(1), Pd1–Cl1 230.19(11), Pd2–N4 202.7(3), Pd2–Cl2 229.5(1), Pd2–P2 234.1(1), Pd2–P3 234.7(1), S1–C1 171.1(4), C1–N1 135.4(5), N1–C2 138.1(5), C2–
N3 131.1(5), N3–N4 138.7(5), N4–C1 131.3(5), N2–Pd1–S1 88.14(9), P1–Pd1–S1 88.30(4), N2–Pd1–Cl1 90.50(9), P1–Pd1–Cl1 93.09(4), N4–Pd2–P2 91.96(9), Cl2–Pd2–P2
88.20(4), N4–Pd2–P3 90.61(9), Cl2–Pd2–P3 90.09(4), C1–N1–C2 107.5(3), N1–C2–N3 108.7(3), C2–N3–N4 106.6(3), N3–N4–C1 109.8(3), N4–C1–N1 107.4(4); Pd3–N6
215.3(3), Pd3–P4 225.2(1), Pd3–S2 229.2(1), Pd3–Cl3 231.9(1), Pd4–N8 202.5(3), Pd4–Cl4 230.4(1), Pd4–P5 233.7(1), Pd4–P6 235.0(1), S2–C4 171.4(4), C4–N5 136.4(5), N5–
C5 137.0(5), C5–N7 130.9(5), N7–N8 138.4(5), N8–C4 131.8(5), N6–Pd3–S2 88.09(9), P4–Pd3–S2 92.17(4), N6–Pd3–Cl3 89.04(9), P4–Pd3–Cl3 90.70(4), N8–Pd4–P5 89.81(9),
Cl4–Pd4–P5 90.44(4), N8–Pd4–P6 89.94(9), Cl4–Pd4–P6 90.36(4), C4–N5–C5 107.9(3), N5–C5–N7 109.2(4), C5–N7–N8 106.1(3), N7–N8–C4 110.6(3), N8–C4–N5 106.1(3);
Pd5–N10 215.9(3), Pd5–P7 225.4(1), Pd5–S3 229.3(1), Pd5–Cl5 232.1(1), Pd6–N12 202.9(3), Pd6–Cl6 230.1(1), Pd6–P8 235.1(1), Pd6–P9 236.8(1), S3–C7 171.9(4), C7–N9
135.8(5), N9–C8 136.9(5), C8–N11 130.7(5), N11–N12 139.0(5), N12–C7 131.5(5), N10–Pd5–S3 87.52(9), P7–Pd5–S3 92.83(4), N10–Pd5–Cl5 89.28(9), P7–Pd5–Cl5 90.46(4),
N12–Pd6–P8 90.60(9), Cl6–Pd6–P8 89.92(4), N12–Pd6–P9 90.70(9), Cl6–Pd6–P9 89.71(4), C7–N9–C8 107.4(3), N9–C8–N11 109.2(4), C8–N11–N12 106.5(3), N11–N12–C7
109.4(3), N12–C7–N9 107.4(4).

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M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
radiation, k = 71.073 pm). The intensities were corrected for Lor-
entz and polarization effects. In addition, absorption corrections
were applied numerically. The structures were solved by direct
methods (SIR-92 for 1, 2 and 4 and SHELXS-97 for 3) and refined
3. Results and discussion
3.1. Synthesis and characterization of 1, 2 and 3
against F2 by full-matrix least-squares using the program SHELXL
-
As depicted in Scheme 4, complex 1 can be obtained as orange
solid mass by the reaction of HL1 with palladium chloride and tri-
phenylphosphane in a 1:1:1 molar ratio in methanol/acetonitrile.
The treatment of 1 with sodium iodide in a molar ratio of 1:1 in
the same solvent mixture gave complex 2 as a reddish powder,
and complex 3 can be prepared by the treatment of a solution of
97. The position of carbon bonded hydrogen atoms were calculated
for ideal positions and all hydrogen atoms except H1–H3 (free
refinement) in 2 were refined with a common displacement
parameter. Programs used were SIR-92 [36], SHELXS-97 [37], SHELXL
-
97 [38], SHELXTL-PLUS [39] and PLATON [40].
Fig. 4. A view of the structure of complex 1, showing the hydrogen bonding interactions between the cations and anions. The phenyl rings and methyl groups are omitted for
clarity.
Fig. 5. The packing diagram of 1 showing the hydrogen bonding between the cations and anions.

M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
3041
HL1 containing sodium acetate with palladium(II) chloride and tri-
phenylphosphane in methanol as bright red-orange crystals.
All the complexes are air-stable. The results of the elemental
analyses, together with IR and 31P NMR data, allow us to postulate
Fig. 8. Representation of the cation in 4 (thermal ellipsoids at the 40% probability
level). Selected bond lengths [pm] and angles [°]:Pd1–N4 201.9(3), Pd1–N1
203.2(3), Pd1–N3 203.8(3), Pd1–N2 203.9(3), N4–Pd1–N1 90.1(1), N4–Pd1–N3
88.5(1), N1–Pd1–N2 89.9(1), N3–Pd1–N2 91.4(1).
Fig. 6. Representation of hydrogen bonds involving cations and anions in
complex 2.
Fig. 7. The packing diagram of 2.

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M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
complexes 1, 2 and 3 being obtained. In IR spectra of the com-
plexes, the absorptions at 1479 and 1433 cmꢂ1 (1), 1460 and
1430 cmꢂ1 (2), and 1471 and 1431 cmꢂ1 (3) can be assigned to
C@Nring stretching vibrations. The absorptions around 3188–
3350 cmꢂ1 can be assigned to NH2 vibrations in 1–3. The P–C
vibrations of the PPh3 moiety are found in the range 744–
691 cmꢂ1 [41]. The mass spectra of 1, 2 and 3 show only the main
peak of the corresponding ligand and co-ligand triphenylphos-
phane (m/z = 130 (HL1) for 1 and 2, 129 (L1) for 3 and m/z = 262
(PPh3) for all complexes). The 31P NMR spectra of 1 and 2 in CDCl3
showed a sharp single peak at d 29.89 ppm (1) and d 35.74 ppm (2).
Consistent with the structure of 3, the solution 31P NMR spectrum
in CDCl3 showed two 31P resonances at d 30.43 ppm for the mono
phosphane coordinated palladium atom and at d 23.53 ppm for the
two-fold phosphane coordinated metal center. The 1H NMR spec-
trum of complex 3 shows pronounced changes with respect to
the free ligand (HL1), which means that the signal assigned to
the triazole proton disappears as a consequence of deprotonation.
3.2. Crystal structures of 1, 2 and 3
Complex 1 crystallizes in the monoclinic space group P21/c,
while 2 and 3 crystallize in the triclinic space group P1. Complexes
ꢀ
1 and 2 consists of [(PPh3)Pd(HL1)X]+ cations (X = Cl (1) and X = I
(2)) and chloride anions. Cations of both complexes contain the
[(PPh3)Pd(HL1)] core, in which the heterocycle HL1 acts as a biden-
tate chelating ligand and coordinates to the metal center via its
hydrazine nitrogen atom and its thione sulfur atom, like form B
as shown in Scheme 2 (Figs. 1 and 2). To complete the square pla-
nar arrangement around the palladium ion in these complexes, the
fourth coordination places in 1 and 2 are occupied by one chlorine
atom and one iodine atom. Complex 2 consists of two crystallo-
graphically independent molecules, as depicted in Fig. 2.
Complex 3 consists of three crystallographically independent
molecules (Fig. 3) and can be described as complex 1 with an addi-
tional coordination to a [(PPh3)2ClPd]-moiety through its deproto-
nated endocyclic NH-group. Therefore, the ligands act as a uni- as
well as a bidentate chelating ligand and coordinate to the metal
centers using one of their endocyclic nitrogen atoms (
coordination to Pd2, Pd4 and Pd6) and their thiol sulfur atom and
hydrazine nitrogen atom (
2-N,S-coordination to Pd1, Pd3 and
l
1-N-
l
Pd5). The other coordination positions around Pd1, Pd3 and Pd5
are occupied by one chlorine atom and one triphenylphosphane
molecule, while the positions around Pd2, Pd4 and Pd6 are occupied
by one chlorine atom and two triphenylphosphane moieties.
In the cations of 3, [(PPh3)2ClPd(L1)Pd(PPh3)Cl]+, the singly
deprotonated 1,2,4-triazole heterocycles (L1) act as a bridging
agent between two palladium atoms and show Hückel aromaticity
as shown in Scheme 5.
The Pd–P bond length of 225.2(1) pm in 1, and mean Pd–P bond
lengths of 224.3 pm in 2, 225.23 pm by one triphenylphosphane
coordinated a metal center and 234.9 pm by the two-fold triphen-
ylphosphane coordinated the palladium atoms in 3 are shorter than
the sum of the single bond radii for palladium and phosphorus, i.e.
Fig. 9. View of the hydrogen bonds in 4 involving chloride anions and water
molecules.
Fig. 10. The packing diagram of 4 showing the hydrogen bonding between cations and anions.

M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
3043
241 pm [42], and fall in the lower range (221–246 pm) of PdII–PPh3
bond reference values (230.2 pm) encountered in 248 entries [43].
The Pd–S bond distances of 230.1(1) pm (1), mean 231.55 pm
(2) and mean 229.06 pm (3) are comparable with those reported
for strong Pd–S coordination as observed in the complexes
[(AMTTO)Pd(PPh)3Br]Br.MeOH (Pd–S: 227.5(2) pm) [44] and
tion arrangement is responsible for the formation of chains along
the [0 0 1] direction (Fig. 5).
The chloride anions in 2 act as a bridging agent between the cat-
ions (Fig. 6). The Cl1 atoms coordinate to three N–H-moieties (one
intramolecular hydrogen bonding to one NH2-group and two inter-
molecular hydrogen bondings to the NH2- and NH-groups of the
adjacent cation, N1–H1ꢀ ꢀ ꢀCl1: 315.6(6) pm, N6–H4ꢀ ꢀ ꢀCl1:
314.5(6) pm and N8–H6ꢀ ꢀ ꢀCl1: 311.3(8) pm). The Cl2 anions are
responsible for the connections via hydrogen bonding between
two layers (by coordination to the NH2- and NH-groups of the mol-
ecules of other layers, N4–H3ꢀ ꢀ ꢀCl2a: 311.4(7) pm, N6–H5ꢀ ꢀ ꢀCl2b:
315.6(6) pm). Each Cl2 anion coordinates to the NH2-moiety of
the adjacent molecule via hydrogen bonding, simultaneously
(N1–H2ꢀ ꢀ ꢀCl2: 313.4(6) pm). These coordination modes lead to a
2D-layers parallel to (0 0 1) as shown in Fig. 7. It is noteworthy
to mention, that in all the complexes, the five-membered heterocy-
cles are planar.
[Pd2(
l
-H3L)2]ꢀ2DMSO (H3L = two-fold deprotonated 3,5-diacyl-
1,2,4-triazole-bis(4-methylthiosemicarbazone; Pd–S: 226.3(3)
pm) [45].
The Pd–Cl bond distances of 229.9(1) pm in 1 and mean
231.39 pm by Pd1, Pd3 and Pd5 and mean 230 pm by Pd2, Pd4
and Pd6 in 3 are in good agreement with the observed distances
in a series of triphenylphosphane-chlorine-palladium complexes,
such as [(AMTTO)Pd(PPh3)Cl]ClꢀCH3OH (Pd–Cl: 231.14(6) pm) [46].
The mean Pd–I bond distance of 260.12 pm in 2 is similar to those
observed in [(AMTTO)Pd(PPh3)I]ꢀ2CH3OH (Pd–I: 261.58(9) pm) [44].
Each cation in 1 acts as a bridging agent between its own chlo-
ride anion through its NH-group and the anions of two adjacent
molecules through the hydrogen atoms of their NH2-moieties via
hydrogen bonding (N2–H1ꢀ ꢀ ꢀCl2b: 326.2(4) pm, N2–H2ꢀ ꢀ ꢀCl2a:
333.0(4) pm and N4–H3ꢀ ꢀ ꢀCl2: 308.9(4) pm, Fig. 4). This coordina-
A similar interesting chloride–hydrogen bonding composition
can be observed in the palladium(II) complex [Pd(Py)4]Cl2ꢀ1/2H2O
(4). Complex 4 crystallizes in the monoclinic space group Cc with
a Flack-parameter of 0.00(3) and consists of [Pd(Py)4]+-cations
Fig. 11. Molecular structures of three crystallographically independent complexes of 3 showing the hydrogen bonding between the cations and two Clꢂ-ions.

3044
M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
and chloride anions (Fig. 8). Although the molecules are nearly
centrosymmetric, the structure could not be transformed into
space group C2/c, which was confirmed by the Flack parameter.
This was checked by standard procedures with the program PLATON
[40]. In addition, the unit cell of 4 shows that Cc is the correct space
group.
M2
N
N
S
R
N
NH2
M1
H
The palladium center in the square planar cation is surrounded
by four pyridine molecules. The chloride anions and the solvent
molecules in 4 are responsible for the formation of a network of
hydrogen bridges parallel to (0 0 1) as illustrated in Fig. 9 and
Fig. 10 (O1–H1ꢀ ꢀ ꢀCl2a: 320.3(5) pm, O1–H2ꢀ ꢀ ꢀCl2a: 320.3(5) pm,
Scheme 6.
hindrance induced by the bulky phenyl rings of the three
coordinated triphenylphosphane groups in 3 is responsible for
the deviation from the planar geometry observed in 1 and 2, since
no significant differences are found between the bond distances
and bond angles in the corresponding ligands in the complexes.
In each cation of 3, the triphenylphosphane ligands of the sec-
ond palladium ion are trans-positioned. According to this coordina-
tion arrangement, the five-membered heterocycle is packed by two
phenyl rings of the triphenylphosphane molecule like a sandwich
.
O2–H3ꢀ ꢀ ꢀCl1a: 315.9(5) pm, O2–H4ꢀ ꢀ ꢀ Cl2b: 311.1(5) pm, O3–
H5ꢀ ꢀ ꢀCl2c: 314.5(5) pm, O3–H6ꢀ ꢀ ꢀCl1b: 317.1(5) pm).
The dihedral angles between the ‘‘best” planes through the
PdN4-plane (A: Pd1 N1 N2 N3 N4) and the planes through pyridine
molecules (B: N1 C1 C2 C3 C4 C5, C: N2 C6 C7 C8 C9 C10, D: N3 C11
C12 C13 C14 C15, E: N4 C16 C17 C18 C19 C20) are (A, B) 97, (A, C):
63, (A, D): 94 and (A, E) 74°.
Complex 3 contains one water molecule and six methanol mol-
ecules per three complex molecules. In each complex, the hydra-
zine amine moiety of the five-membered heterocycles acts as a
bridging agent between two chloride anions using its two hydro-
gen atoms (Fig. 11). They link the chloride anion of the same
complex to the anion of the adjacent one via hydrogen bonding
(N2–H1ꢀ ꢀ ꢀCl7a: 324.3(3) pm, N2–H1–Cl7a: 163°; N2–H2ꢀ ꢀ ꢀCl7:
323.8(4) pm, N2–H2–Cl7: 164°; N6–H3ꢀ ꢀ ꢀCl9b: 332.6(5) pm, N6–
H3–Cl9b: 159°; N6–H4-Cl8: 313.1(4) pm, N6–H4–Cl8: 175°;
N10–H5ꢀ ꢀ ꢀCl8b: 329.6(3) pm, N10–H5–Cl8b: 159°; N10–H6ꢀ ꢀ ꢀ
Cl9: 320.9(4) pm, N10–H6–Cl9: 169°). The chloride ion Cl9 acts
as a bridging agent between one methanol molecule and the water
molecule via hydrogen bonding (O1–H7ꢀ ꢀ ꢀCl9: 323.5(5) pm, O1–
H7–Cl9: 126° and O5–H12ꢀ ꢀ ꢀCl9: 310(2) pm, O5–H12–Cl9: 130°).
Fig. 12 represents the unit cell of complex 3.
with a
p-stacking effect. The shortest distances between the cen-
tral lying atoms of the heterocycles in the sandwiches from the
phenyl rings are N3ꢀ ꢀ ꢀC59: 326.0(5) pm, N7ꢀ ꢀ ꢀC94: 318.3(5) pm
and N11ꢀ ꢀ ꢀC144: 313.0(5) pm.
4. Conclusion
In conclusion, we have synthesized and characterized two
mononuclear and the first binuclear palladium complex containing
the well known 4-amino-3-methyl-1,2,4-triazol-5-thione moiety.
According to the determined crystal structures, we found that
the 1,2,4-triazole moiety acts as a bidentate chelating ligand
through its sulfur and nitrogen atoms, while the singly deproto-
nated triazole moiety acts as a bridging agent between two metal
centers. It can simultaneously act as a bidentate chelating agent
through its thiole sulfur atom and hydrazine nitrogen atom to
one metal center and as a uni-dentate agent via its endocyclic
nitrogen atom to the other metal center. Consequently, this new
The dihedral angle between the ‘‘best” planes in the non-planar
complexes of 3 (A: Pd1 P1 Cl1 N2 S1; B: Pd2 Cl2 P2 P3 N4; C: Pd3
P4 Cl3 N6 S2; D: Pd4 P5 P6 Cl4 N8; E: Pd5 Cl5 P7 S3 N10 and F: Pd6
P8 P9 Cl6 N12) are 101 (A, B), 110 (C, D) and 119° (E, F). The steric
Fig. 12. The packing diagram of 3.

M. Ghassemzadeh et al. / Polyhedron 29 (2010) 3036–3045
3045
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