Synthesis, characterization and crystal structures of palladium(II) complexes containing neutral, one and twofold deprotonated 1,2,4-triazine species

Article abstract of DOI:10.1016/j.poly.2011.03.048

The synthesis and characterization of three new palladium(II) complexes of 4-amino-6-ethyl-1,2,4-triazine-3-thion-5-one (AETTO, H₃L), [PdCl ₂(H₃L)]·H₂O (1), [Pd₂Cl ₂(H₂L)(PPh

Full text of DOI:10.1016/j.poly.2011.03.048

Polyhedron 30 (2011) 1760–1766
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, characterization and crystal structures of palladium(II) complexes
containing neutral, one and twofold deprotonated 1,2,4-triazine species
a
b
b
Mitra Ghassemzadeh a, , Samira Bahemmat , Masoumeh Tabatabaee , Salameh Nassiri ,
⇑
Bernhard Neumüller c
a Faculty of Analytical and Inorganic Chemistry, Chemistry and Chemical Engineering Research Center of Iran, P.O. Box 14335-186, Tehran, Iran
b Department of Chemistry, Yazd Branch, Islamic Azad University
c Anorganische 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:
Received 24 December 2010
Accepted 17 March 2011
Available online 19 April 2011
In memory of Prof. Dr. H.C. Kurt Dehnicke
The synthesis and characterization of three new palladium(II) complexes of 4-amino-6-ethyl-1,2,4-tri-
azine-3-thion-5-one (AETTO, H3 L), [PdCl2(H3L)]ꢀH2O (1), [Pd2Cl2(H2L)(PPh3)3]NO3ꢀ2CH3CN (2) and
[Pd(HL)(PPh3)2] (3), are reported. All the synthesized compounds are air-stable and were characterized
by elemental analyses, IR, NMR spectroscopy and mass spectrometry. In addition, the molecular struc-
tures of the complexes have been determined by X-ray single crystal diffraction. On the basis of the crys-
tallographic data, the neutral ligand in 1 and the deprotonated ligands in 2 and 3 act as bidentate NS
donors. The singly deprotonated ligand in 2 acts as a bridging agent between two metal centers in the
binuclear PdII-complex.
Keywords:
1,2,4-Triazines
Pd(II) complexes
N,S-ligands
Ó 2011 Elsevier Ltd. All rights reserved.
Crystal structures
1. Introduction
The 3-thione substituted derivatives of 1,2,4-triazine can exist
in two tautomeric thione (I) and thiol (II) forms (Scheme 1), there-
The chemistry of compounds containing N and S donor atoms is
of special interest since they display a broad spectrum of physico-
chemical properties and biological activities. The coordination
chemistry of such ligands has also attracted considerable attention
due to the variety of coordination possibilities associated with
them. It is known that metal complexes of biologically active
compounds may have enhanced activities compared to the non-
coordinated ligands [1–11]. Among the N,S donor ligands, thiosem-
icarbazide and thiocarbohydrazide and their derivatives constitute
an interesting class with enormous biological activities [12–20]. On
the other hand, 1,2,4-triazines and their derivatives – as condensa-
tion products from the reaction of thiocarbohydrazides with
fore they can coordinate to metal centers in several fashions, such
as a unidentate ligand using the sulfur or nitrogen atom according
to the ‘‘Pearson principle’’, as a N,S-bidentate chelating agent or as
singly deprotonated unidentate or bidentate anions.
Recently, we have reported the behavior of such ligands towards
late transition metals such as silver(I), copper(I), copper(II), palla-
dium(II) and platinum(II) ions [30–36]. In our investigations in this
research field we have found that 6-aza-2-thiothymine (ATT) – a
representative of the 1,2,4-triazine derivatives – acts as a unidentate
ligand in methanol/acetonitrile in a 4:1 ratio to form the air-stable
complex [Pd(ATT)4]Cl2ꢀ8MeOH [33], while 4-amino-6-methyl-
1,2,4-triazine-3-thione-5-one (AMTTO), as an another member of
the family, acts as a bidentate neutral chelating agent in a 1 + 1 fash-
ion towards palladium(II) halides in the same solvent mixture to
give the complexes [Pd(AMTTO)X2]ꢀMeOH (X = Cl, Br and I) [36].
We have also reported the study of the latter against other nucleo-
philes like triphenylphosphane [36]. In this communication, we
wish to report the results of our studies on the syntheses, character-
ization and molecular structure of new mono- and binuclear palla-
dacycles containing another representative of this family.
a-keto acids – are well-known compounds. Some of them are
found in natural materials, exhibit biological activities and can be
used for various purposes since they are associated with diverse
pharmacological and biological activities such as analgesic-anti-
inflammatory [21–23], antibacterial [24–26], anti-asthmatic [27]
and antifungal [28] activities. A variety of synthetic methods are
known for the preparation of their substituted derivatives. Metal
complexes of 1,2,4-triazine derivatives such as S,N-heterocycles,
amino acids and proteins often exhibit enhanced biological
activities compared to the uncomplexed ligand [1,29].
2. Experimental
2.1. General considerations
⇑
All chemicals were purchased from Merck and Fluka and were
used without further purification. IR spectra were recorded on a
Corresponding author. Tel.: +98 21 44 58 07 06; fax: +98 21 44 58 07 62.
E-mail address: mghassemzadeh@ccerci.ac.ir (M. Ghassemzadeh).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.03.048

M. Ghassemzadeh et al. / Polyhedron 30 (2011) 1760–1766
1761
2.3.2. Synthesis of complex 1
To a solution of H3L (0.17 g, 1 mmol) in methanol/acetonitrile
(20 mL, 1:1) was added palladium(II) chloride (0.17 g, 1 mmol),
and the reaction mixture was stirred for 5 h at room temperature.
After completion of the reaction, which was monitored by TLC
using ethyl acetate/petroleum ether (1:2), a yellowish precipitate
was filtered off and washed with cold methanol (5 mL). The filtrate
was stored at room temperature for one week to yield brownish
crystals suitable for X-ray diffraction measurements. Yield:
0.31 g, 90%, m.p.: 258 °C. Elemental analysis: Anal. Calc. for
C5H8Cl2N4OPdS (349.53): C, 17.18; H, 2.31; N, 16.03. Found: C,
Scheme 1. Thione (I) and thiol (II) tautomeric forms in 3-thione-1,2,4-triazines.
Shimadzu spectrometer 470 (KBr pellets 4000–400 cmꢁ1). Melting
points were recorded on a Büchi apparatus B-545 and are uncor-
rected. The 1H and 13C NMR (H3L) were recorded on a Bruker
Avance 500 MHz spectrometer and the 31P NMR spectra were
recorded on Bruker 400 MHz and 500 MHz spectrometers using
TMS (d = 0.0 ppm) as the internal standard and 85% aqueous
H3PO4 as an external standard. Mass spectra were recorded on a
Fisons Instruments Trio 1000 spectrometer. Elemental analyses
were performed on a Thermo Finigan Flash EA 1112 series elemen-
tal analyzer.
17.09; H, 2.33; N, 15.99%. IR (KBr) [m
, cmꢁ1]: 3188 w, 2978 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
(30 eV): m/z 278 (Pd(H3L)), 172 (H3L). 1H NMR (d, DMSO-d6,
500 MHz): 1.09 (t, J = 7.40 Hz, 3H, CH3), 2.59 (q, J = 7.40 Hz, 2H,
CH2), 5.90 (s, 1H, NH).
2.2. Crystal structure analyses of H3L, 1, 2 and 3 (Table 1)
2.3.3. Synthesis of complex 2
A solution of H3L (0.05 g, 0.3 mmol) in methanol/acetonitrile
(1:1, 30 mL) containing sodium acetate (0.02 g, 0.3 mmol) was
treated with palladium(II) chloride (0.11 g, 0.6 mmol) and triphen-
ylphosphane (0.23 g, 0.9 mmol) and stirred for 3 h before a solu-
tion of silver nitrate (0.05 g, 0.3 mmol) in the same solvent
(15 mL) was added. The reaction mixture was stirred for further
3 h. After completion of the reaction, which was monitored by
TLC using ethyl acetate and petroleum ether (1:2 v/v) as the eluent,
the reaction mixture was filtered off and washed with cold meth-
anol. The filtrate was kept at 4 °C to give yellowish crystals after
few weeks. Yield: 0.33 g, 85%, m.p.: 328 °C. Elemental analysis:
Anal. Calc. for C59H52Cl2N5O4P3Pd2S (1303.81): C, 54.35; H, 4.02;
Selected crystals of H3L, 1, 2 and 3 were covered with perfluo-
rinated oil and mounted on the top of a glass capillary under a flow
of cold gaseous nitrogen. The orientation matrix and the unit cell
dimensions were determined from 2000 (H3L, Stoe IPDS II), 6000
(1, Stoe IPDS I), 10 000 (2, Stoe IPDS II) and 12 000 (3, Stoe IPDS
II) reflections (graphite-monochromated Mo
K
a
radiation
(k = 71.073 pm)). The intensities were corrected for Lorentz and
polarizations effects. In addition, absorption corrections were
applied for 1, 2 and 3 (numerical). The structures were solved by
direct methods for all compounds using SHELXS-97 for H3L and
SIR-92 for the complexes 1–3, they and were refined against F2 by
full-matrix least-squares using the program SHELXL-97. The hydro-
gen atoms H1–H3 in H3L, H2–H5 in 1, H1 and H2 in 2 and H1 for
3 were freely refined, while the remaining hydrogen atoms in H3
L, 1, 2 and 3 were calculated in ideal positions and were refined
with a common displacement parameter. The hydrogen atom of
the NH-group in 1 was fixed at 85 pm. The programs used were
SHELXS-97 [37], SHELXL-97 [38], SIR-92 [39], SHELXTL-PLUS [40] and
PLATON [41].
N, 5.37. Found: C, 54.20; H, 4.04; N, 5.34%. IR (KBr) [m
, cmꢁ1]:
3421 w, 3051 w, 2970 w, 2929 w, 2875 m, 1685 m, 1633 m,
1435 w, 1381 m, 1361 m, 1240 w, 1163 w, 1095 m, 997 vw, 921
w, 748 s, 694 s, 565 w, 532 s, 511 m, 445 w. EI-MS (30 eV): m/z
277 (Pd(H2L)), 262 (PPh3), 171 (H2L). 1H NMR (d, CDCl3 + DMSO-
d6, 500 MHz): 1.16 (t, J = 7.45 Hz, 3H, CH3), 2.72 (q, J = 7.45 Hz,
2H, CH2), 7.32–7.65 (m, 15H,
3
PPh3). 31P NMR (d, CDCl3,
161.97 MHz): 29.15 (s), 30.10 (s), 32.07.
2.3. Synthesis of H3L, 1, 2 and 3
2.3.4. Synthesis of complex 3
2.3.1. Synthesis of H3L
AETTO was prepared according to a modified literature proce-
dure for the preparation of AMTTO using 2-oxobutyric acid as
A solution of H3L (0.17 g, 1 mmol) in methanol/acetonitrile (1:1,
30 mL) was treated with sodium acetate (0.16 g, 2 mmol) and stir-
red for 3 h. To this solution was added [PdCl2(PPh3)2] (0.7 g,
1 mmol) under stirring. After 3 h and completion of the reaction,
which was monitored by TLC using ethyl acetate and petroleum
ether (1:2 v/v) as the eluent, the reaction mixture was filtered
off, washed with water (5 mL) and cold methanol (2 ꢂ 5 mL). The
filtrate was kept at 4 °C to give amber colored crystals after few
days. Yield: 0.66 g, 83%, m.p.: 274 °C. Elemental analysis: Anal.
Calc. for C41H36N4OP2PdS (801.14): C, 61.46; H, 4.53; N, 6.99.
the
(172.21): C, 34.87; H, 4.68; N, 32.53. Found: C, 34.68; H, 4.70; N,
32.49%. IR (KBr) [
, cmꢁ1]: 3290 s, 3238 s, 3016 m, 2978 s, 2937
a-keto acid [42]. M.p.: 127 °C, Anal. Calc. for C5H8N4OS
m
s, 2914 s, 2756 s, 1656 m, 1593 s, 1546 s, 1517 s, 1462 s, 1432 s,
1396 m, 1373 m, 1348 sh, 1309 sh, 1244 s, 1132 m, 1091 s, 968
s, 881 s, 804 s, 711 s, 675 s, 619 s, 569 s, 530 s, 487 s, 443 s, 428
s. MS (70 eV) m/z 172. 1H NMR (d, CDCl3, 500 MHz): 1.25 (t,
J = 7.42 Hz, 3H, CH3), 2.76 (q, J = 7.42 Hz, 2H, CH2), 6.20 (br, 2H,
NH2), 10.77 (s, 1H, NH). 13C NMR (d, CDCl3, 500 MHz): 10.61 (s,
CH3), 24.26 (s, CH2), 148.92 (C@N), 149.84 (C@O), 169.04 (C@S).
Found: C, 60.98; H, 4.51; N, 7.01%. IR (KBr) [m
, cmꢁ1]: 3296 m,
3051 m, 2974 w, 2918 m, 2360 w, 1967 w, 1614 s, 1544 m, 1483
m, 1435 s, 1369 m, 1265 s, 1192 w, 1161 w, 1093 m, 1074 w,
Scheme 2. Mesomeric forms of the AETTO-anions.

1762
M. Ghassemzadeh et al. / Polyhedron 30 (2011) 1760–1766
1055 w, 995 w, 931 w, 846 vw, 746 m, 694 s, 518 s, 455 w, 424 w.
EI-MS (30 eV): m/z 276 (Pd(HL)), 262 (PPh3), 170 (HL). 1H NMR (d,
DMSO-d6): 1.05 (t, J = 7.4 Hz, 3H, CH3), 2.59 (q, J = 7.4 Hz, 2H, CH2),
5.90 (s, 1H, NH), 7.31–7.48 (m, 30H, 6Ph). 31P NMR (d, DMSO-d6,
202 MHz): 27.65 (br), 28.02 (br).
The dinuclear PdII complex 2 can be obtained by the treatment
of H3L with palladium(II) chloride, triphenylphosphane, sodium
acetate and silver(I) nitrate in a molar ratio of 1:2:3:1:1 in acetoni-
trile/methanol, in accordance with Eq. (2).
ð2Þ
Complex 3 can be prepared by the reaction of H3L with
palladium(II) chloride and triphenylphosphane in the presence of
sodium acetate (1:1:2:2) in methanol/acetonitrile, according to
Eq. (3).
3. Results and discussion
The reaction of H3L with PdCl2 in methanol/acetonitrile gave
complex 1 in good yields.
ð1Þ
ð3Þ
Table 1
Crystallographic data for H3L and 1–3.
Compound
H3L
1
2
3
Empirical formula
Formula mass
Crystal size (mm)
Crystal system
Space group
a (pm)
C5H8N4OS
172.21
0.12 ꢂ 0.11 ꢂ 0.04
monoclinic
P21/c
1519.4(1)
666.4(1)
801.0(1)
90
103.71(1)
90
787.93(2)
4
C5H10Cl2N4O2PdS
367.53
C63H58Cl2N7O4P3Pd2S
1385.83
C41H36N4OP2PdS
801.14
0.17 ꢂ 0.04 ꢂ 0.03
monoclinic
P21/n
1016.9(1)
1936.0(1)
1843.3(1)
90
93.48(1)
90
0.38 ꢂ 0.05 ꢂ 0.04
0.23 ꢂ 0.14 ꢂ 0.13
tetragonal
triclinic
ꢀ
ꢀ
P421c
P1
1883.6(1)
1883.6(1)
660.4(1)
90
90
90
2343.1(4)
8
2.084
1247.2(1)
1456.4(1)
1900.5(1)
73.19(1)
83.30(1)
65.91(1)
3016.8(4)
2
b (pm)
c (pm)
a
(°)
b (°)
(°)
c
Volume [pm3 ꢂ 106]
3622.2(4)
4
1.469
Z
Dcalc (g cmꢁ3
)
1.452
1.526
Absorption correction
none
3.58
numerical
22.04
numerical
8.53
numerical
6.98
l
(cmꢁ1) (Mo K
a)
Temperature [K]
2hmax (°)
293(2)
52.26
293(2)
52.32
100(2)
51.78
100(2)
51.86
Index range
h
k
l
ꢁ18 ? 18
ꢁ8 ? 8
ꢁ9 ? 9
5314
ꢁ23 ? 21
ꢁ23 ? 20
ꢁ8 ? 8
10267
ꢁ15 ? 15
ꢁ17 ? 17
ꢁ23 ? 23
42920
ꢁ12 ? 11
ꢁ23 ? 23
ꢁ22 ? 22
27273
Reflections collected
Unique reflections (Rint
)
1503 (0.0692)
796
120
2312 (0.0471)
1712
161
11700 (0.0495)
8539
740
6900 (0.0755)
4424
455
Reflections with Fo > 4
Parameters
r(Fo)
Flack parameter
R1
wR2 (all data)
–
0.01(6)
0.0325
–
–
0.0613
0.1623a
0.18
0.032
0.0334
0.0514d
0.36
0.0604b
0.601
0.0731c
0.855
Maximum residual electron density ((e pmꢁ3) ꢂ 10ꢁ6
)
a
b
c
w = 1/[
w = 1/[
w = 1/[
w = 1/[
r
r
r
r
2(Fo2) + (0.0685P)2]; P = [max(Fo2, 0) + 2Fc2]/3.
2(Fo2) + (0.0273P)2].
2(Fo2) + (0.0427P)2].
2(Fo2) + (0.0138P)2].
d

M. Ghassemzadeh et al. / Polyhedron 30 (2011) 1760–1766
1763
Fig. 3. Molecular structure of 1 (thermal ellipsoids at the 40% probability level).
Selected bond lengths [pm] and angles [°]: Pd1–N2 202.0(5), Pd1–S1 224.7(2), Pd1–
Cl2 228.8(2), Pd1–Cl1 232.3(2), S1–C1 169.7(6), N1–C1 135.7(7), N1–C2 140.3(8),
N1–N2 143.0(6), N3–C3 129.8(9), N3–N4 135.2(8), N4–C1 132.9(7), O2–H4 81(8),
O2–H5 78(9); N2–Pd1–S1 87.3(1), N2–Pd1–Cl2 178.5(2), S1–Pd1–Cl2 92.08(7), N2–
Pd1–Cl1 88.4(1), S1–Pd1–Cl1 175.68(6), Cl2–Pd1–Cl1 92.23(6), C1–S1–Pd1 97.2(2),
N1–N2–Pd1 114.8(3), H4–O2–H5 97(8).
In contrast to Eq. (1), the reactions according to Eqs. (2) and (3)
give complexes 2 and 3 incorporating the anionic ligands III and IV
(Scheme 2). This result is obtained by abstraction of one HCl mol-
ecule from 2 and two HCl molecules from 3 by the sodium acetate
as a base. The coordination of the sulfur atom leads to additional
acidification of the amine functions, as shown in Scheme 2.
Furthermore, the reaction mixture of Eq. (2) undergoes a chlo-
ride–nitrate anion exchange reaction in the presence of silver(I)
nitrate.
Complexes 1–3 were found to be air-stable crystalline solids. In
accordance with the structures of the compounds, the 31P NMR
spectrum of 2 in CDCl3 exhibit three signals at d = 29.15, 30.10
and 32.07 ppm and the 31P NMR spectrum of 3 in DMSO-d6 show
Fig. 1. Molecular structure of H3L (thermal ellipsoids at the 30% probability level).
Selected bond lengths [pm] and angles [°]: S1–C1 164.8(5), O1–C2 121.5(5), N1–C2
137.9(6), N1–C1 138.4(6), N1–N2 141.3(6), N3–C3 130.0(6), N3–N4 133.5(5), N4–
C1 136.7(6), C4–C52 137(1), C4–C51 146(1); C2–N1–C1 124.6(4), C2–N1–N2
117.9(4), C1–N1–N2 117.4(4), C3–N3–N4 116.6(4), N3–N4–C1 129.4(4), C52–C4–
C3 117.6(7), C51–C4–C3 116.5(7).
Fig. 4. Molecular structure of 2 (thermal ellipsoids at the 40% probability level,
most of hydrogen atoms are omitted for clarity). Selected bond lengths [pm] and
angles [°]: Pd1–N3 202.8(2), Pd1–Cl1 229.97(8), Pd1–P2 232.90(9), Pd1–P1
238.39(9), Pd2–N2 210.3(3), Pd2–P3 223.87(9), Pd2–S1 227.43(8), Pd2–Cl2
232.22(8), S1–C1 171.7(3), O1–C2 121.6(4), N1–C1 136.6(4), N1–C2 139.4(4), N1–
N2 143.0(4), N3–C1 132.0(4), N3–N4 137.3(3), N4–C3 129.0(4), N5–O3 1.240(4),
N5–O4 1.245(4), N5–O2 1.257(4); N3–Pd1–Cl1 175.84(8), N3–Pd1–P2 90.07(8),
Cl1–Pd1–P2 87.02(3), N3–Pd1–P1 90.62(8), Cl1–Pd1–P1 92.38(3), P2–Pd1–P1
178.13(3), N2–Pd2–P3 177.14(9), N2–Pd2–S1 85.63(7), P3–Pd2–S1 96.02(3), N2–
Pd2–Cl2 91.11(7), P3–Pd2–Cl2 87.54(3), O3–N5–O4 120.3(3), O3–N5–O2 119.5(3),
O4–N5–O2 120.2(3).
Fig. 2. The packing diagram for H3L.

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M. Ghassemzadeh et al. / Polyhedron 30 (2011) 1760–1766
recorded at a lower voltage (30 eV) showed additionally new sig-
nals at m/z = 278 (1), m/z = 277 (2) and m/z = 276 (3), which can
be assigned to the corresponding PdL-fragmentations of the
complexes.
Table 1 shows the crystallographic data of the compounds and
Figs. 3–5 illustrate the molecular structures of complexes 1, 2
and 3, respectively.
3.1. Crystal structures of compound H3L, 1, 2 and 3
3.1.1. Compound H3L
Compound H3L crystallizes in the monoclinic space group P21/c.
The basic six-membered ring skeleton in this compound is planar
(Fig. 1). The bond distances in the triazine six-membered heterocy-
cle are in good agreement with those observed in AMTTO [44]. The
ethyl group is disordered with an occupancy factor of 0.5:0.5 for
C51:C52. The S1–C1 bond length in H3L with a mean value of
164.8(5) pm is significant for high double bond character. In H3L,
the NH2-group of each ligand is linked to the sulfur and oxygen
atoms via weak intramolecular hydrogen bondings (N2–H1ꢀ ꢀ ꢀO1:
298.0(6) pm and N2–H1–O1: 109(7)°, N2–H2ꢀ ꢀ ꢀS1: 267.0(6) pm
and N2–H2–S1: 99(6)°), while the NH-group links to the oxygen
atom of the adjacent molecule via hydrogen bonding (N4–
H3ꢀ ꢀ ꢀO1a: 282.0(6) pm and N4–H3–O1a: 162(7)°). The latter is
responsible for the formation of double-layers parallel to (1 0 0)
(Fig. 2). There are weak hydrogen bonds between the packed mol-
ecules in the double-layers, whose ‘‘edges’’ are shielded with the
disordered ethyl-tail.
Fig. 5. Molecular structure of 3 (thermal ellipsoids at the 40% probability level,
most of hydrogen atoms are omitted for clarity). Selected bond lengths [pm] and
angles [°]: Pd1–N2 199.2(3), Pd1–P1 230.22(8), Pd1–P2 230.73(8), Pd1–S1
230.73(8), S1–C1 173.7(4), O1–C2 123.2(4), N1–C1 134.9(4), N1–C2 139.8(4), N1–
N2 137.1(4), N3–C3 130.8(4), C1–N4 133.2(4); N2–Pd1–P2 170.46(9), N2–Pd1–P1
90.96(9), P1–Pd1–P2 98.38(3), N2–Pd1–S1 83.60(9), P2–Pd1–S1 87.09(3), S1–Pd1–
P1 174.40(4), C1–S1–Pd1 98.40(1).
two broad signals at d = 27.65 and 28.02 ppm, indicating the non-
equivalence of the phosphorus atoms as consequence of the asym-
metric S,N coordination of the HL ligand. In the IR spectra of 1–3,
the observed absorptions at 459 cmꢁ1 for 1, 445 cmꢁ1 for 2 and
455 cmꢁ1 for 3 can be assigned to Pd–N vibrations [43]. C@O–
and C@N– vibrations can be observed as two bands at 1656 and
1593 cmꢁ1 for H3 L, at 1714 and 1612 cmꢁ1 for 1, at 1685 and
1633 cmꢁ1 for 2 and at 1614 and 1544 cmꢁ1 for 3. The P–C vibra-
tions of PPh3-moiety are observed in the range 748–694 cmꢁ1 for
2 and 746–694 cmꢁ1 for 3. Each IR spectra exhibit two bands for
the valence vibrations for the NH2-groups at 3290 and
3238 cmꢁ1 (H3L), 3250 and 3188 cmꢁ1 (1), 3296 and 3251 cmꢁ1
(2), while the spectrum of 3 shows only one absorption at
3296 cmꢁ1 as consequence of the deprotonation of the NH2 moiety
in 3. The mass spectra of the complexes recorded at 70 eV showed
only the signals of the corresponding ligands in 1–3 (m/z = 172 (1),
m/z = 171 (2) and m/z = 170 (3)) and the signal of the triphenyl-
phosphane moiety for 2 and 3 at m/z = 262, while the spectra
3.1.2. Complexes 1, 2 and 3
Complexes [PdCl2(H3L)]ꢀH2O (1, Fig. 3) and [Pd(HL)(PPh3)2] (3,
Fig. 5) are neutral molecules, whereas complex 2 consist of
[(PPh3)2ClPd(H2L)Pd(PPh3)Cl]+-cations and nitrate anions (Fig. 4).
The structural data of the complexes show that 1 incorporates H3L
in its neutral form, while the corresponding ligands in 2 and 3 are
mono and twofold deprotonated AETTO moieties, respectively.
In all the complexes 1–3, the corresponding ligand acts as
chelating and coordinates to the metal center via its sulfur and
hydrazine nitrogen donors in a
j
2-N,S-coordination mode, form-
ing a five-membered chelate ring. In the case of complex 2, the
singly deprotonated AETTO-ligand coordinates additionally to a
second metal ion through one of its endocyclic nitrogen atoms
(j
1-N-coordination mode). The square planar geometry around
the metal centers in 1 and 3 are completed by two chlorine atoms
Fig. 6. The packing diagram of 1 involving hydrogen bonding.

M. Ghassemzadeh et al. / Polyhedron 30 (2011) 1760–1766
1765
and two triphenylphosphane molecules, respectively. The square
planar arrangement about the palladium centers in 2 is completed
by one chloride ligand and two trans-positioned triphenylphos-
phane molecules for Pd1 and one triphenylphosphane molecule
and one chloride ligand for Pd2. The latter is oriented cis to the
amine group of the heterocycle, indicating the strong influence
and twofold deprotonated AETTO. To our knowledge, among the
palladacycles containing 4-amino-6-alkyl/aryl-1,2,4-triazine-3-
thione as a ligand, complex 3 is the first example having a twofold
deprotonated species. Due to the determined molecular structures
of the complexes, the corresponding ligand acts as bidentate N,S-
chelating one to the metal centers. In the case of the binuclear
complex, the singly deprotonated triazine moiety acts as a bridge
between two metal centers via its endocyclic nitrogen atom.
of the
p-acids C@S and PPh3. A similar coordination mode is ob-
served in the tetrameric palladium(II) complex [Pd(L)]4ꢀ2C7H8,
where L is the twofold deprotonated Schiff-base (E)-4-(2-hydrox-
ybenzylideneamino)-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-
5(2H)-one [45].
Appendix A. Supplementary data
The graphical representation of 1 (Fig. 3) shows, except for the
disordered ethyl group (occupancy factor 0.65:0.35 for C51:C52), a
basically planar framework.
The Pd–Cl distances in 1 (232.3(2) and 228.8(2) pm) and those
in 2 (229.97(8) and 232.22(8) pm) are very similar to those in
[Pd(AMTTO)Cl2]ꢀCH3OH (232.2(2) and 228.9(1) pm) [44] and
[Pd(AMTTO)Cl(PPh3)]ClꢀCH3OH (231.14(6) pm) [46]. The strong
trans-influence of the sulfur atoms in comparison with the nitro-
gen atom is responsible for the observed differences in the Pd–Cl
distances.
CCDC 712072, 712073, 712074 and 773397 contains the sup-
plementary crystallographic data for compounds H3L, 1, 2 and 3.
These data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax:
(+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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bridges, which is formed between the amine group of the hetero-
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In conclusion, we have synthesized and characterized two
mononuclear and one binuclear complex containing neutral, mono

1766
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