The influence of substituents at C2 carbon atom of thiosemicarbazones {R(H)C2=N3-N2(H)-C 1(=S)-N1H2} on their dentacy in Pt II/PdII complexes: Synthesis, spectroscopy, and crystal structures

Article abstract of DOI:10.1002/zaac.200700538

The coordination chemistry of platinum(II) with a series of thiosemicarbazones {R(H)C²=N³-N²(H)-C ¹(=S)-N¹H₂, R = 2-hydroxyphenyl, H ₂stsc; pyrrole, H₂ptsc; phenyl, Hbtsc} is described. Reactions of trans-PtCl₂(PPh₃)₂ precursor with H₂stsc (or H₂ptsc) in 1:1 molar ratio in the presence of Et₃N base yielded complexes, [Pt(η³- O, N³, S-stsc)(PPh₃)] (1) and [Pt(η³- N⁴, N ³, S-ptsc)(PPh₃)] (2), respectively. Further, trans-PtCl₂(PPh₃)₂ and Hbtsc in 1:2 (M:L) molar ratio yielded a different compound, [Pt(η²- N³, S-btsc)(η¹-S-btsc)(PPh₃)] (3). Complex 1 involved deprotonation of hydrazinic (-N²H-) and hydroxyl (-OH) groups, and stsc^2- is coordinating via O, N³, S donor atoms, while complex 2 involved deprotonation of hydrazinic (-N²H-) and -N ⁴H groups and ptsc^2- is probably coordinating via N ⁴, N³, S donor atoms. Reaction of PdCl ₂(PPh₃)₂ with Hbtsc-Me {C₆H ₅(CH₃)C²=N³-N²(H)-C ¹(=S)-N¹H₂} yielded a cyclometallated complex [Pd(η³-C, N³, S-btsc-Me)(PPh₃)] (4). These complexes have been characterized with the help of analytical data, spectroscopic techniques {IR, NMR (¹H, ³¹P), U.V} and single crystal X-ray crystallography (1, 3 and 4). The effects of substituents at C² carbon of thiosemicarbazones on their dentacy and cyclometallation are emphasized.

Full text of DOI:10.1002/zaac.200700538

DOI: 10.1002/zaac.200700538
The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones
{R(H)C2؍N3-N2(H)-C1(؍S)-N1H2} on their Dentacy in PtII/PdII Complexes:
Synthesis, Spectroscopy, and Crystal Structures
Tarlok S. Lobana*,a, Gagandeep Bawaa, Geeta Hundala, and M. Zellerb
a Amritsar / India, Department of Chemistry, Guru Nanak Dev University
b Youngstown/USA, Department of Chemistry, Youngstown Universitry
Received October 16th, 2007; accepted November 28th, 2007.
Abstract. The coordination chemistry of platinum(II) with a series
of thiosemicarbazones {R(H)C2ϭN3-N2(H)-C1(ϭS)-N1H2, R ϭ
2-hydroxyphenyl, H2stsc; pyrrole, H2ptsc; phenyl, Hbtsc} is de-
scribed. Reactions of trans-PtCl2(PPh3)2 precursor with H2stsc (or
H2ptsc) in 1 : 1 molar ratio in the presence of Et3N base yielded
complexes, [Pt(η3- O, N3, S-stsc)(PPh3)] (1) and [Pt(η3- N4, N3,
S-ptsc)(PPh3)] (2), respectively. Further, trans-PtCl2(PPh3)2 and
Hbtsc in 1 : 2 (M : L) molar ratio yielded a different compound,
[Pt(η2- N3, S-btsc)(η1-S-btsc)(PPh3)] (3). Complex 1 involved de-
protonation of hydrazinic (-N2H-) and hydroxyl (-OH) groups, and
stsc2Ϫ is coordinating via O, N3, S donor atoms, while complex 2
involved deprotonation of hydrazinic (-N2H-) and -N4H groups
atoms. Reaction of PdCl2(PPh3)2 with Hbtsc-Me {C6H5(CH3)C2ϭ
N3-N2(H)-C1(ϭS)-N1H2} yielded
cyclometallated complex
a
[Pd(η3-C, N3, S-btsc-Me)(PPh3)] (4). These complexes have been
characterized with the help of analytical data, spectroscopic tech-
niques {IR, NMR (1H, 31P), U.V} and single crystal X-ray crystal-
lography (1, 3 and 4). The effects of substituents at C2 carbon of
thiosemicarbazones on their dentacy and cyclometallation are em-
phasized.
Keywords: Platinum; Salicylaldehyde thiosemicarbazone; Pyrrole-2-
carbaldehyde thiosemicarbazone; Benzaldehyde thiosemicarba-
zone; Cyclometallation; Deprotonation
and ptsc2Ϫ is probably coordinating via N4, N3,
S donor
Introduction
dinegative tridentate coordinating via O, N3, S or C, N3, S
donor atoms in complexes 9 and 10, respectively. Fourth
site is occupied by the halogen atoms (4 - 6, 8), PPh3 (10)
or S atom of anionic (7) or neutral (9) thiosemicarbazone
ligands. It was observed that the phenyl rings with the
donor substituents at C4 position were involved in the coor-
dination to the metal (8, 9), whereas its absence led to the
cyclometallation in complex 10.
Thiosemicarbazones (structure I, Chart 1) are an important
class of organic ligands [1], and are currently being explored
for their analytical applications [2], variable bonding modes
[3] and for their biological relevance [4Ϫ5]. Palladium(II)
and platinum(II) complexes of thiosemicarbazones have ex-
hibited antitumor, antibacterial and antifungal activities
[4Ϫ10]. For example, a square planar complex [PtLCl] con-
taining 2-acetylpyridine thiosemicarbazone-N-Me dis-
played cytotoxicity against the cisplatin resistant and sensi-
tive ovarian cancer cell lines, A2780 and A2780/Cp8 [8].
A literature survey reveals that the thiosemicarbazone
chemistry of palladium(II) has been more widely investi-
gated than that of platinum(II). Chart 1 depicts the re-
ported mononuclear square planar PtII complexes [6Ϫ10].
Pyridine based thiosemicarbazones (structure I) are unineg-
ative tridentate in [PtLCl] (4-6) [6, 8] and [PtL2] (7) [9].
Thiosemicarbazones based on phenyl rings with substitu-
ents formed complexes [PtLCl] (8), [PtL(H2L)] (9) [7] and
[PtL(PPh3)] (10) [10]. A ligand (L) is uninegative tridentate
coordinating via N4, N3, S in 4-7, P, N3, S in 8 and it is
* Prof. Tarlok S. Lobana
Department of Chemistry
Guru Nanak Dev University
Amritsar-143005 / India
E-mail: tarlokslobana@yahoo.co.in
Chart 1
Z. Anorg. Allg. Chem. 2008, 634, 931Ϫ937
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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T. S. Lobana, G. Bawa, G. Hundal, M. Zeller
0.06 mmol) followed by the addition of Et3N base (1 mL), and the
mixture was stirred for 3 h during which a clear light orange-yellow
solution was formed along with the formation of solid Et3NHϩClϪ
at the bottom of the flask. The contents were filtered to re-
move Et3NHϩClϪ and the filtrate allowed to evaporate at room
In the present paper, we report the bonding behaviour of
thiosemicarbazones with different rings (R1 ϭ 2-hydroxy-
phenyl, pyrrole, phenyl; R2ϭ H) as shown in Chart 2.The
rings may coordinate or undergo metallation process after
activation of C4-H bond. The fourth site (Y) was kept con-
stant and was occupied by PPh3. The work has been ex-
tended to PdII to study the influence of a bulkier R2 sub-
stituent (e.g. Me in place of H). This study is a part of our
interest in the chemistry of platinum group metals with the
N, S donors and earlier we reported [Pd(η3-O, N3, S-
stsc)(PPh3)] and [Pd(η3-N4, N3, S-ptsc)(PPh3)] with above
mentioned ligands [11, 12].
temperature. The yellow orange crystals of product
1 were
formed. Yield: 0.026 g, 76 %; m.p. 220-222 °C. Anal.Calcd for
C26H23N3OPPtS·C7H8(C33H31N3OPPtS): C, 53.29; H, 4.17; N,
5.6; Found: C, 53.0; H, 4.10; N, 5.41 %.
Main I.R. bands (KBr, cmϪ1), ν(NH), 3431s, 3290s, ν(C-H) 3047w, ν(CϭN)
ϩ δNH2 ϩ ν(CϭC) 1627s, 1600s, 1583s, ν(C-S) 813s, ν(P-C) 1099s. UV-Vis
spectrum (CH2Cl2, λmax/nm, ε/L molϪ1 cmϪ1): 413 (5.51 x 103), 365 (9.08 x
103), 239 (8.44 x 103). 1H NMR (δ, CDCl3), δ ϭ 8.54 (d, 1H, C2H, J ϭ
11.7), 7.63-7.76 (m, 8H, o-PhϩC4,6), 7.41-7.55 (m, 10H, m, p-Ph), 6.73 (dd,
1H, C5H, J ϭ 8.7), 4.82 (s, 2H, NH2). 31P NMR (CDCl3),δ ϭ Ϫ78.533
[1J(PtP) ϭ 4868 Hz].
Compound 2 was prepared similarly.
[Pt(η3-N4,N3,S-ptsc)(PPh3)] (2) Yield: 72 %; m.p. 190 °C. Anal.-
Calcd for C24H21N4PPdS: C, 46.08; H, 3.36; N, 8.96; Found: C,
46.12; H, 3.59; N, 8.11 %.
Main I.R. bands (KBr, cmϪ1), ν(NH) 3495s, 3292s, ν(C-H) 3050w, ν(CϭN)
ϩ δNH2 ϩ ν(CϭC) 1606s, 1589s, 1514s, ν(C-S) 819s, ν(P-C) 1095s. UV-Vis
spectrum (CH2Cl2, λmax/nm, ε/L molϪ1 cmϪ1) 430 (1.04 x 104), 314 (1.56 x
104), 245 (2.08 x 104). 1H NMR (δ, CDCl3, J, Hz), δ ϭ 7.90 (d, 1H, C2H,
J ϭ 7.8), 7.45-7.69 (m, 16H, o, m, p-PhϩC4), 6.62 (d, 1H, C6H, J ϭ 3), 5.88
(dd, 1H, C5H, J ϭ 2.1), 5.71 (s, 2H, NH2). 31P NMR (CDCl3), δ ϭ Ϫ94.4
[1J(PtP) ϭ 3530 Hz]
[Pt(η2-N3,S-btsc)(η1-S-btsc)(PPh3)] (3). To PtCl2(PPh3)2 (0.05 g,
0.06 mmol) suspended in toluene (15 mL) was added solid Hbtsc
(0.023 g, 0.12 mmol) followed by the addition of Et3N base (2 mL),
and the mixture was stirred for 3 h during which a clear lightyellow
solution was formed along with the formation of solid Et3NHϩClϪ
at the bottom of the flask. The contents were filtered to remove
Et3NHϩClϪ and the filtrate allowed to evaporate at room tempera-
ture. The yellow orange crystals of product 3 were formed. Yield:
76 %; m.p. 215 °C. Anal.Calcd for C34H31N6PPtS2: C, 50.18; H,
3.8; N, 10.30; Found :C, 50.55; H, 4.01; N, 10.42 %.
Chart 2
Experimental Section
Main I.R. bands (KBr, cmϪ1), ν(NH) 3443s, 3340s, 3267w, 3245w ν(C-H)
3070w, 3081, ν(CϭN) ϩ δNH2 ϩ ν(CϭC) 1600s, 1569s, 1541s, ν(C-S) 800s,
ν(P-C) 1097s. UV-Vis spectrum (CH2Cl2, λmax/nm, ε/L molϪ1 cmϪ1) 366 (1.69
x 104), 300 (2.21 x 104), 249 (2.19 x 104). 1H NMR (δ, CDCl3), δ ϭ 9.05 (s,
Materials and Techniques
Platinum(II) dichloride, salicylaldehyde, pyrrole-2-carbaldehyde
and benzaldehyde were obtained from Sigma Aldrich Ltd. The
thiosemicarbazone ligands were prepared by the reported methods
[13]. The starting platinum precursor PtCl2(PPh3)2 was prepared by
stirring a mixture of PtCl2 and PPh3 in acetonitrile for 2 h [14].
Elemental analyses for C, H and N were carried out using Thermo-
electron FLASHEA1112 analyser. The melting points were deter-
mined with a Gallenkamp electrically heated apparatus. U.V spec-
tra were recorded using UV-160 Shimadzu spectrophotometer. The
IR spectra were recorded using KBr pellets on a PyeϪUnicam
SP3-300 spectrophotometer. The 1H NMR spectra were recorded
on a JEOL AL 300 FT spectrometer at 300 MHz in CDCl3 with
TMS as the internal reference. The 31P NMR spectra were recorded
at 121.5 MHz with TMP {(CH3O)3P} as the external reference
taken as zero position.
2H, C2H), 7.18-7.74 (m, Ph-H ϩ ring protons of tsc), 5.08 (s, 2H, NH2). 31
NMR (CDCl3), δ ϭ Ϫ102.02.
P
[Pd(η3-C,N3,S-btsc-Me)(PPh3)] (4) To PdCl2(PPh3)2 precursor
(0.05 g, 0.07 mmol) suspended in toluene (15 mL) was added solid
Hbtsc-Me (0.014 g, 0.14 mmol), followed by the addition of Et3N
base (1 mL), and the mixture was stirred for 3 h during which a
clear light orange solution was formed along with Et3NHϩClϪ,
separating in solution at the bottom of the flask. The solution was
filtered to remove Et3NHϩClϪ and allowed to evaporate at room
temperature, and after evaporation, yellow orange crystals of prod-
uct were formed Yield 76 %, mp 250 °C. Anal.Calcd. for
C27H24N3PPdS: C 57.86, H 4.28, N 7.50; Found: C 57.53, H, 4.5,
N 7.08 %.
IR bands (KBr pellets, cmϪ1) ν(N-H), 3516b, 3448sh, 3334w (-NH2), ν(Cϭ
N) ϩ δNH2 ϩ ν(CϭC) 1588s, 1508b; ν(C-S), 840s; ν(P-CPh) 1089s. 1H NMR
(CDCl3) /δ: 7.64-7.70 (m, o-H, 6H), 7.35-7.46 (m, m, p-H, 9H), 6.29 (q, C5H,
1H, J ϭ 4.5), 6.49 (t, C6H, 1H, J ϭ 6), 6.85 (t, C7H, 1H, J ϭ 7.8), 7.08 (d,
C8H, 1H, J ϭ 7.5), 4.86 (s, -NH2, 2H), 2.35 (s, CH3, 3H)
Synthesis of the complexes
[Pt(η3-O,N3,S-stsc)(PPh3)] (1). To PtCl2(PPh3)2 (0.05 g, 0.06 mmol)
suspended in toluene (15 mL) was added solid H2stsc (0.012 g,
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The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones
Table 1 Crystal Data and Refinement details for 1, 3 and 4.
1
3
4
Empirical formula
M
T/K
C33H31N3OPPtS
743.73
295(2)
C34H31N6PPt S2
813.83
100(2) K
C27H24N3PPdS
559.92
100(2)
Crystal system
Space group
Unit cell dimensions
triclinic
P1
triclinic
P1
triclinic
P1
¯
¯
¯
˚
a/A
9.740(5)
10.0108(6)
10.1951(6)
16.2316(10)
105.2090(10)
90.2280(10)
98.2820(10)
1580.41(16)
2
9.8710(12)
11.3204(13)
12.3388(15)
89.603(2)
74.098(2)
67.0721(2)
1213.0(3)
2
˚
b/A
11.878(5)
13.619(5)
75.410(5)
75.810(5)
87.130(5)
1478.2(11)
2
˚
c/A
α/°
β/°
γ/°
3
˚
V/A
Z
Dcalcd /mg mϪ3
1.788
12.972
1.710
4.657
1.533
0.938
μ/mmϪ1
Reflections collected
Unique reflections
R indices (all data)
14681
4131
R1 ϭ 0.0636,
wR2 ϭ 0.1313
R1 ϭ 0.0528,
wR2 ϭ 0.1250
0.887 and Ϫ1.830
16481
7823
R1ϭ 0.0234,
wR2 ϭ 0.0552
R1 ϭ 0.0250,
wR2 ϭ 0.0561
2.625 and Ϫ1.150
12626
6003
R1ϭ 0.0272,
wR2 ϭ 0.0727
R1ϭ 0.0258,
wR2 ϭ 0.0712
0.41 and Ϫ0.492
Final R indices [I>2σ(I)]
Ϫ3
˚
Largest diff. peak and hole /e A
X-ray crystallography
(-OH) groups, yielding the complex [Pt(stsc)(PPh3)] (1)
(Scheme 1). Similarly, the ligand H2ptsc deprotonated
hydrazinic (-N2H-) and -N4H groups, and yielded complex
[Pt(ptsc)(PPh3)] (2). The x-ray crystallography showed that
stsc2Ϫ is coordinating via O, N3, S donor atoms in 1 (vide
infra). In compound 2, the coordination by ptsc2Ϫ is prob-
The data for compound 1 was collected at 293 K, on a Siemens
P4 diffractometer. The θϪ2θ technique was used to measure the
intensities up to a maximum of 2θ ϭ 50° with graphite monochro-
˚
matized Mo-Kα radiator (λ ϭ 0.71073 A). Cell parameters were
refined in the θ range, 10-12.5° using XSCANS [15]. The data were
corrected for Lorentz and polarization factors. An empirical psi
absorption correction was applied. The structure was solved by the
direct methods, and refined by the full matrix least squares meth-
ods based on F2. All the nonhydrogen atoms were refined aniso-
tropically, and hydrogen atoms were assigned calculated positions.
Scattering factors from the International Tables for X-ray crystal-
lography were used [16]. Data reduction, structure solution, refine-
ment and molecular graphics were performed using SHELXTL-PC
[17] and WinGX [18].
A single crystal of compound 3 was mounted on a Bruker AXS
SMART APEX CCD diffractometer equipped with a graphite
˚
monochromator and Mo-Kα radiation (λ ϭ 0.71073 A). The unit
cell dimensions and intensity data were measured at 100(2) K. The
structure was solved by the direct methods, and refined by the full
matrix least square based on F2 with anisotropic thermal param-
eters for the non-hydrogen atoms using Bruker SMART (data col-
lection) and Bruker SAINT (cell refinement), Bruker SHELXTL
(data reduction and computing molecular graphics, structure solu-
tion and (structure refinement)]. Amine hydrogen atoms were lo-
cated in the difference density Fourier map, however the N-H dis-
˚
tances were restrained to be 0.88 A within a standard deviation of
˚
0.02 A. All other hydrogen atoms were placed in the calculated
positions and all hydrogen atoms were refined with an isotropic
displacement parameter 1.5 (methyl) or 1.2 times of hydrogen
atoms at all other adjacent carbon atoms.
Results and Discussion
Synthesis
1
Reaction of PtCl2(PPh3)2 with H2stsc in the presence of tri-
ethylamine deprotonated hydrazinic (-N2H-) and hydroxyl
Scheme 1 PtCl2(PPh3)2 (i, ii); /2PtCl2(PPh3)2 (iii); Et3N, toluene
(i-iii).
Z. Anorg. Allg. Chem. 2008, 931Ϫ937
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933

T. S. Lobana, G. Bawa, G. Hundal, M. Zeller
ably occurring via N4, N3, S donor atoms. Thus, there was
no activation of C-H bonds in both the complexes and the
rings used their donor groups for coordination. Earlier it
has been reported that PdII with H2stsc and H2ptsc has
formed compounds similar to 1 and 2, respectively [11].
methyl group for R2 again has led to cyclometallation as
shown for PdII complex 4 (Scheme 2).
Chart 3
It is highlighted here that the reaction of PtCl2(PPh3)2
with Hbtsc (R1 ϭ Ph, R2 ϭ H) in 1 : 1 molar ratio was
carried out for obtaining the anticipated complex, [Pt(η3-C4,
N3, S-btsc)(PPh3)] similar to compound 10, but no isolable
product could be obtained. However, further addition of
one mole of Hbtsc yielded [Pt(btsc)2(PPh3)] (3), and X-ray
crystallography has confirmed that one ligand (as btscϪ) is
N3, S chelating and second (btscϪ) is η1-S-bonded (vide
infra). Thus compound 3 has not involved cyclometallation
as expected. A close analysis of complexes of PdII/PtII
(Charts 1 and Chart 3) [10, 19] reveals that cyclometallation
of aromatic rings (R1) occurred only when R2 substituent
at C2 is bulky group such as methyl or ethyl. In order to give
further credence to this important observation, reaction of
PtCl2(PPh3)2 with a thiosemicarbazone for R1 ϭ Ph, R2 ϭ
Me (see structure II, Chart 2) was carried out, but no crys-
talline product could be obtained. However, a similar reac-
tion with palladium(II) yielded a cyclometallated product,
[Pd(η3-C4, N3, S-btsc-Me)(PPh3)] (4) (Scheme 2) in which
phenyl ring binds to Pd metal {Hbtsc-Me ϭ Ph(Me)C2ϭ
N3-N2(H)-C1(ϭS)-N1H2}.
Chart 4
I.R. Spectroscopy
The IR spectra of the complexes reveal the presence of
ν(NϪH) bands due to (-NH2) group in the range
3278Ϫ3495 cmϪ1
.
The
bands
in
the
region
3100Ϫ3150 cmϪ1 expected due to ϪN2H group in the free
ligands [13] are found to be absent in the spectra of their
complexes 1Ϫ3, and it supports the anionic form of the
ligands. The ν(CϪH) bands due to the aromatic ring are
observed for all the complexes in the region near
3050 cmϪ1. Further, δ(NH2) ϩ ν(CϭN) ϩ ν(C-C) vibration
modes are unresolved, and are assigned in the range
1635Ϫ1515 cmϪ1. The thioamide band, which contains
considerable ν(CS) character is less intense in the complexes
and is found at a lower frequency {ν(C-S), 800-819 cmϪ1
}
suggesting coordination of the metal through sulfur [13,
19]. The presence of PPh3 in complexes 1-4 is confirmed by
the presence of a characteristic ν(C-P) bands in the range,
1095Ϫ1099 cmϪ1
.
Crystal structures of complexes
The atomic numbering schemes for 1 and 3 are given in
Figures 1 and 2 respectively, and selected bond angles and
bond lengths are listed in Table 2. Both the compounds
Scheme 2
¯
crystallized in triclinic crystal systems with space groups P1
in each case. A molecule of toluene is present as solvent of
crystallisation in complex 1, which is also supported by the
elemental analysis. The ligand salicylaldehyde thiosemicar-
bazone is coordinating as a dianion (stsc2Ϫ) after depro-
tonation of hydrazinic (-N2H-) and hydroxyl (-OH) protons
The steric effect of R2 group appears to push R1 group
closer to the metal for cyclometallation (see Chart 4). Since
R2 ϭ H in Hbtsc, low steric effect may explain the lack of
cyclometallation in compound 3. But introduction of
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The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones
˚
Table 2 Important bond lengths/A and bond angles/° of comple-
xes 1, 3 and 4.
1
N(1)-Pt
2.032(6)
2.014(6)
1.731(8)
1.302(11)
S-Pt
P-Pt
N1-N2
O1-C1
2.234(2)
2.2576(19)
1.369(9)
1.315(9)
O(1)-Pt
C(8)-S
C8-N2
O1-Pt-N1
O1-Pt-S
N1-Pt-S
93.1(3)
176.60(16)
83.79(19)
O1-Pt-P
N1-Pt-P
S-Pt-P
89.91(17)
176.34(18)
93.27(7)
3
P1-Pt1
Pt1-S1
C19-N2
C19-S1
N2-N3
2.2466(6)
2.2769(6)
1.308(3)
1.755(3)
1.396(3)
Pt1-S2
N3-Pt1
C27-N5
C27-S2
N5-N6
2.3461(6)
2.118(2)
1.314(3)
1.7552(3)
1.405(3)
N3-Pt-P1
N3-Pt1-S1
P1-Pt1-S1
176.51(6)
82.28(6)
94.32(2)
N3-Pt1-S2
P1-Pt1-S2
S1-Pt1-S2
95.13(4)
88.26(2)
177.20(2)
Figure 1 Structure of complex [Pt(η3- O, N3, S-stsc)(PPh3)] (1)
with atomic numbering Scheme.
4
N(1)-Pd(1)
C(1)-Pd(1)
Pd(1)-S(1)
2.0326(15)
2.0411(19)
2.3464(6)
P(2)-Pd(1)
N(1)-N(2)
C(9)-S(1)
2.2513(5)
1.376(2)
1.758(2)
N(1)-Pd(1)-C(1)
N(1)-Pd(1)-P(2)
C(1)-Pd(1)-P(2)
81.47(7)
177.05(5)
95.83(6)
N(1)-Pd(1)-S(1)
C(1)-Pd(1)-S(1)
P(2)-Pd(1)-S(1)
82.26(5)
163.45(6)
100.493(18)
176.6(2)° and N-Pt-P, 176.3(2)°} and the complex is
square planar.
In the mononuclear complex 3, platinum(II) is coordinat-
ing to two thiosemicarbazone ligands. One ligand is unineg-
ative bidentate coordinating via N3 and S donor atoms for-
ming a five membered chelate ring with the Pt1-N3 and
˚
Pt1-S1 bond distances of 2.118(2) and 2.277(6) A, respec-
tively, with a the bite angle N3-Pt-S of 82.28(6)°. The other
thiosemicarbazone ligand in anionic form is coordinating
Figure 2 Structure of complex [Pt(η2-N3,S-btsc)(η1-S-btsc)(PPh3)]
(3) with atomic numbering Scheme.
in complex 1. The thiosemicarbazone ligand is tridentate
coordinating via O, N3 and S donor atoms with Pt-O,
Pt-N and Pt-S bond distances of 2.014(6), 2.032(6) and
˚
2.234(2) A, respectively. The Pt-N and Pt-S bond distances
are longer than those observed in complexes of the type
[Pt(L)Cl], where L is monoanion of the pyridine based
thiosemicarbazones reported in the literature (ca. Pt-N, 1.95
˚
and Pt-S, 2.25 A) [6, 8]. The fourth site is occupied by phos-
phorus atom of the coordinating PPh3 molecule with a
3
˚
Pt-P distance of 2.258(2) A. The bite angles O-Pt-N and
N3-Pt-S of 93.1(3)° and 83.8(2)° respectively are compar-
able with those of analogous complex [Pd(stsc)(PPh3)] [11].
The two trans angles are quite close to linearity {O1-Pt-S,
Figure 3 Structure of complex [Pd(η3-C,N3,S-btsc-Me)(PPh3)] (4)
with atomic numbering Scheme.
Z. Anorg. Allg. Chem. 2008, 931Ϫ937
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
935

T. S. Lobana, G. Bawa, G. Hundal, M. Zeller
through S atom only with a longer Pt1-S2 bond distance,
2.3461(6) A. A comparison of these bond lengths with com-
(MǞLCT) and d-d bands, the band at around 245 nm is
assignable to thiosemicarbazone moiety (πǞπ*transitions).
˚
plex 1 and literature reports reveal that both the Pt-S as
well as Pt-N bond lengths are comparatively longer [6, 8].
The trans bond angles of complexes, {N-Pt-P, 176.51(6)°;
S-Pt-S, 177.20(2)°}, are nearly linear and the geometry is
distorted square planar.Figure 3 shows molecular structure
of the cyclometallated product, [Pd(η3-C4, N3, S-btsc-
Me)(PPh3].
The mononuclear complex 4 involves the cyclometall-
ation of the phenyl ring at C2 to PdII. Thus the ligand is
dianionic coordinating via C, N3, S donor atoms. The bond
parameters lie in the usual range [11Ϫ12].
Conclusion
The substituents at C2 position affect the stoichiometry as
well as the bonding modes of thiosemicarbazones. For ex-
ample, in PtII complexes, the presence of a substituent (R1)
at C2 with ionisable hydrogens (e.g. 2-hydorxyphenyl, 1;
pyrrole ring, 2) made the ligands, H2stsc and H2ptsc to be-
have as dinegative tridentate ligands (O, N3, S, 1 or N4, N3,
S, 2) after the loss of ϪOH and -N2H (H2stsc) or N4H and
N2H (H2ptsc) protons in the complexes. Fourth site of
square plane is occupied by PPh3 ligand.Complex 3 with
R1 as phenyl ring did not involve activation of C4-H bond,
rather two thiosemicarbazonates (btscϪ) coordinate in a
different manner, one is η1-S- bonded and the second is
η2-N3, S-chelated. It is inferred from these studies that the
bulky substituent R2 at C2 carbon(e. g. Me, Et, etc.) appears
responsible for the activation of a C-H bond of aryl (R1)
ring followed by cyclometallation in complexes [10, 19]. For
R1 ϭ phenyl, and R2 ϭ Me, palladium(II) has yielded a
cyclometallated product, [Pd(η3-C4, N3, S-btsc-Me)(PPh3)]
(4) in which phenyl ring metallates Pd metal {Hbtsc-Me ϭ
Ph(Me) C2ϭN3-N2(H)-C1(ϭS)-N1H2}. For R1 ϭ furan and
R2 ϭ Me, cyclometallation is also encountered in PtII com-
plexes [22].
NMR spectroscopy
The signals due to ϪN2H protons which appear around
11.2 ppm in the free ligands [13] were absent in the spectra
of their complexes 1Ϫ3. It supports deprotonation during
complexation in all these complexes. Additionally in com-
plexes 1 and 2, the absence of ϪOH (9.87 ppm, H2stsc) and
ϪN4H- (11.34 ppm, H2ptsc) proton signals respectively
confirmed their deprotonation. Thus in complexes 1 and 2,
the thiosemicarbazone ligands are behaving as dianions.
The ϪNH2 protons appear as single peaks in all the com-
plexes due to the free rotation of the N1H2 group along the
C1-N1 bond axis. The free ligands exhibit two broad peaks
due to the restricted rotation of the ϪN1H2 group along
the C1-N1 bond axis at room temperature [13]. The peaks
due to C2H and ring protons are given in the experimental
section, however, the phenyl ring (R1) protons of complex
3 could not be identified due to their overlapping with the
signals of PPh3 group. The 31PNMR of complexes 1 and 2
shows peaks at Ϫ78.8 and Ϫ94.4 ppm with 195Pt satellites.
The 1J(195Pt-31P) coupling constants (4868 and 3530 Hz for
complex 1 and 2 respectively) of both the complexes are in
the usual range [20] though it is greater for complex 1 than
for complex 2. The obvious reason for this seems to be the
difference in electronegativity of O atom in complex 1 vis-
Supplementary data is available from CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: ϩ44-12336033; e-mail:
deposit@ccdc.cam.ac.uk) on request quoting the deposition number
CCDC 662656, 662657 and 666777 for compounds 1, 3 and 4
respectively.
Acknowledgements. Financial assistance to one of us (GB) from
CSIR New Delhi (F.No. 9/254(155)-EMR-1) is gratefully acknowl-
edged.
References
`
a-vis that of N atom in complex 2. Due to low solubility of
[1] D. X. West, S. Padhye, P. B. Sonawane, Struct. Bonding
(Berlin) 1991, 76, 4. (b) S. Padhye, G. B. Kauffman, Coord.
Chem. Rev. 1985, 63, 127. (c) D. X. West, A. E. Liberta, S. B.
Padhye, R. C. Chikate, P. B. Sonawane, A. S. Kumbhar, R. G.
Yerande, Coord. Chem. Rev.. 1993, 123, 49. (d) J. S. Casas, M.
S. Garcia-Tasende, J. Sordo, Coord. Chem. Rev. 2000, 209, 197.
[2] a) R. K. Mahajan, T. P. S. Walia, Sumanjit, T. S. Lobana,
Anal. Sci. 2006, 22, 389. b) R. K. Mahajan, I. Kaur, T. S.
Lobana, Talanta 2003, 59, 101. c) R. K. Mahajan, T. P. S.
Walia, Sumanjit, T. S. Lobana, Talanta 2005, 67, 755. d) R.
K. Mahajan, R. Kaur, T. S. Lobana, Indian J. Chem. Sect A
2006, 45, 639.
[3] a) M. Maji, S. Ghosh, S. K. Chattopadhyay, T. C. W. Mak,
Inorg. Chem. 1997, 36, 2938. b) L. J. Ashfield, A. R. Cowley,
J. R. Dilworth, P. S. Donnelly, Inorg, Chem. 2004, 43, 4121. c).
A. R. Cowley, J. R. Dilworth, P. S. Donnelly, E. Labisbal, A.
Sousa, J. Am. Chem. Soc. 2002, 124, 5270. (d) T. S. Lobana,
S. Khanna, R. J. Butcher, A. D. Hunter, M. Zeller, Inorg.
Chem. 2007, 46, 5826.
complex 3, 195Pt satellites could not be observed.
Electronic Absorption Spectroscopy
The electronic absorption spectra of platinum(II) complexes
are indicative of their square planar geometry. In the visible
region of the square planar PtII complexes, three spin al-
lowed singlet-singlet d-d transitions are predicted [21]. The
1
ground state is A1g and the excited states corresponding
1
1
1
the three transitions are A2g, B1g and Eg in order of in-
creasing energy. Strong charge transfer transitions interfere
and prevent the observation of all the expected bands. The
very intense band at 366-430 nm is assignable to a combi-
nation of sulfurǞPtII, and charge transfer {(L(π)ǞMCT}
and PtII d-d bands [6, 8]. The band at 300-365 nm is assign-
able to a combination of metal-ligand charge transfer
936
www.zaac.wiley-vch.de
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 931Ϫ937

The Influence of Substituents at C2 Carbon Atom of Thiosemicarbazones
[4] a) D. Kovala-Demertzi, M. A. Demertzis, V. Varagi, A. Papag-
eorgiou, D. Mourelatos, E. Mioglou, Z. Lakovidou, A. Kotsis,
Chemotherapy 1998, 44, 421. b) D. Kovala-Demertzi, J. R.
Miller, N. Kourkoumelis, S. K. Hadjikakou, M. A. Demertzis,
Polyhedron 1999, 18, 1005. (c) D. Kovala-Demertzi, M. A. De-
mertzis, A. Castineiras, D. X. West, Polyhedron 1998, 17, 3739.
[5] A. G. Quiroga, J. M. Perez, I. Lopez-Solera, J. R. Masaguer,
A. Luque, P. Roman, A. Edwards, C. Alonso, C. Novarro-
Ranninger, J. Med. Chem. 1998, 41, 1399.
[6] D. Kovala-Demertzi, M. A. Demertzis, J. R. Miller, C. Papa-
dopoulou, C. Dodorou, G. Filousis, J. Inorg. Biochem. 2001,
86, 555. b) K. I. Goldberg, J. Valdez- Martinez, G. Espinosa-
Perez, L. J. Ackerman, D. X. West, Polyhedron 1999, 18, 1177.
[7] L. Papathanasis, M. A. Demertzis, P. N. Yadav, D. Kovala-
Demertz, C. Prentjas, A. Castin˜eiras, S. Skoulika, D. X. West,
Inorg. Chim. Acta 2004, 357, 4113.
[12] T. S. Lobana, G. Bawa, R. J. Butcher, B.-J. Liaw, C.-W. Liu,
Polyhedron 2006, 25, 2897.
[13] T. S. Lobana, A. Sanchez, J. S. Casas, A. Castineiras, J. Sordo,
M. S. Garcia-Tasende, E. M. Vazquez-Lopez, J. Chem. Soc.
Dalton Trans. 1997, 4289.
[14] W. L. Steffen, G. J. Palenik, Inorg. Chem. 1976, 15, 2432.
[15] XSCANS, Siemens Analytical X-ray Instruments Inc., Madi-
son, WI, USA, 1994.
[16] International Tables for X-ray Crystallography, vol. C,
Kluwer, Dordrecht, The Netherlands, 1995.
[17] G. M. Sheldrick, SHELXTL-PC, release 5.03, Siemens Ana-
lytical X-Ray Instruments Inc., Madison, WI, USA, 1995.
[18] G. X. Win, L. J. Farrugia, J. Appl. Cryst. 1999, 32, 837.
[19] a) J. M. Vila, M. T. Pereira, J. M. Ortigueira, M. Grana, D.
Lata, A. Suarez, J. J.Fernandez, A. Fernandez, M. Lopez-
Torres, H. Adams, J. Chem. Soc. Dalton Trans. 1999, 4193. b)
A. Amoedo, M. Grana, J. Martinez, T. Pereira, M. Lopez-
Torres, A. Fernandez, J. J. Fernandez,J. M. Vila, Eur. J. Inorg.
Chem. 2002, 613. c) J. Martinez, L. A. Adrio, J. M. Antelo,
M. Teresa-Pereira, J. J. Fernandez, J. M. Vila, Polyhedron 2006,
25, 2848.
[8] D. Kovala-Demertzi, P. N. Yadav, M. A. Demertzis, M. Coluc-
cia, J. Inorg. Biochem. 2000, 78, 347.
[9] D. Kovala-Demertzi, M. A. Demertzis, E. Fillov, A. A. Panta-
zaki, P. N. Yadav, J. R. Miller, V. Zheng, D. A. Kyriakidis,
Biometals 2003, 16, 411.
[10] D. Vazquez-Garcia, A. Fernanadez, J. J. Fernanadez, M. Lo-
pez-Torres, A. Suarez, J.-M. Ortigueira, J. M. Vila, H. Adams,
J. Organomet. Chem. 2000, 595, 199.
[11] a) T. S. Lobana, G. Bawa, A. Castineiras, R. J. Butcher, Inorg.
Chem. Comm. 2007, 10, 506. b) T. S. Lobana, G. Bawa, G.
Hundal, A. P. S. Pannu, R. J. Butcher, B.-J. Liaw, C.-W. Liu,
Polyhedron 2007, 26, 4993.
[20] D. Chan, L. Cronin, S. B. Duckett, P. Hupfield, R. N. Perutz,
New J. Chem. 1998, 511.
[21] A. B. P. Lever, Inorganic Electronic Spectroscopy, Elsevier, New
York: 1984.
[22] L. Adrio, J. M. Antelo, J. M. Ortiguera, D. Lata, M. T. Pereira,
M. Lopez-Torres, J. M. Vila, Z. Anorg. Allg. Chem. 2007,
633, 1875.
Z. Anorg. Allg. Chem. 2008, 931Ϫ937
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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