Transition metal complexes of 2-formylpyridinethiosemicarbazone (HFpyTSC) and X-ray crystal structures of [Pd(FpyTSC)(PPh3)]PF6and [Pd(FpyTSC)(SCN)]

Article abstract of DOI:10.1016/j.ica.2010.04.018

The syntheses of five new complexes of the 2- formylpyridinethiosemicarbazone ligand (HFpyTSC) with Pd(II) and Rh(III) ions are described, viz., [Pd(FpyTSC)(PPh₃)]PF₆, [Pd(FpyTSC)(SCN)], [Pd(FpyTSC)Br], [Pd(HFpyTSC)₂]Br

Full text of DOI:10.1016/j.ica.2010.04.018

Inorganica Chimica Acta 363 (2010) 2526–2532
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Inorganica Chimica Acta
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Transition metal complexes of 2-formylpyridinethiosemicarbazone (HFpyTSC) and
X-ray crystal structures of [Pd(FpyTSC)(PPh3)]PF6 and [Pd(FpyTSC)(SCN)]
a,**
Shadia A. Elsayed a, Ahmed M. El-Hendawy b, Sahar. I. Mostafa c, , Ian S. Butler
*
a Department of Chemistry, McGill University, Montreal QC, Canada H3A 2K6
b Chemistry Department, Faculty of Science, Mansoura University, Damietta, Egypt
c Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The syntheses of five new complexes of the 2-formylpyridinethiosemicarbazone ligand (HFpyTSC) with
Pd(II) and Rh(III) ions are described, viz., [Pd(FpyTSC)(PPh3)]PF6, [Pd(FpyTSC)(SCN)], [Pd(FpyTSC)Br],
[Pd(HFpyTSC)2]Br2 and [Rh(FpyTSC)(PPh3)2Cl]ClO4. The formulation of the complexes is discussed in
terms of their elemental analyses and IR, Raman, NMR (1H, 13C and 31P), mass and electronic spectra.
The X-ray crystal structures of [Pd(FpyTSC)(PPh3)]PF6 and [Pd(FpyTSC)(SCN)] show that the HFpyTSC
ligand coordinates to the central Pd(II) ion in a planar conformation through the pyridyl nitrogen, the
azomethine nitrogen and the deprotonated thiol sulphur atom. Thus, HFpyTSC is a versatile ligand that
usually acts as a mononegative tridentate ligand bonding through Npy, NC@N and C–SÀ while, in the case
of [Pd(HFpyTSC)2]Br2, it behaves as a neutral bidentate ligand via NC@N and C@S.
Received 13 February 2010
Received in revised form 6 April 2010
Accepted 13 April 2010
Available online 24 April 2010
Keywords:
Palladium
Rhodium
Thiosemicarbazone
Molecular spectra
X-ray crystallography
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
N and S donor ligands [16,17], we now report the synthesis and
spectral characterisation of some new Pd(II) and Rh(III) complexes
Thiosemicarbazones have been known for many years as an
important class of versatile multi-donor ligands in coordination
chemistry and they have been shown to have a variety of applica-
tions in biological and analytical fields [1,2]. Thiosemicarbazones
are considered to be mixed hard–soft chelating agents as they con-
tain both N and S atoms in the thiosemicarbazone moiety. This
dual character gives them the ability to bind metal ions in either
a neutral or anionic manner [3,4]. The members of one of the most
famous families of thiosemicarbazones have a tridendate kernel
and encompasses ligands derived from 2-formylpyridine which
show antitumour activity [5–7]. This activity is due to their ability
to inhibit the biosynthesis of DNA [8]. In most cases, these thio-
semicarbazones act as tridentate ligands that coordinate to metal
ions through N,N,S centres [9] and their coordination behaviour
depends on the nature of metal ions concerned.
containing 2-formylpyridinethiosemicarbazone (HFpyTSC) as the
primary ligand, together with as the X-ray crystal structures of
[Pd(FpyTSC)(PPh3)] and [Pd(FpyTSC)(SCN)].
2. Experimental
All reagents were purchased from Alfa/Aesar and all manipula-
tions were performed under aerobic conditions using materials
and solvents as received. [Pd(PPh3)2Cl2] was prepared from
K2PdCl4 and PPh3 in aqueous ethanolic solution [18]. Li2PdBr4
was prepared in situ from PdCl2 and LiBr according to the literature
method [19]. Warning: perchlorate salts are potentially explosive;
such compounds should be used in small quantities and treated
with the utmost care at all times.
Dichloromethane (DCM) and dimethylformamide (DMF), which
were used in electronic spectroscopy measurements, were dried
over molecular sieves. DMSO-d6 was used for the NMR measure-
ments and was referenced against TMS.
There are a number of papers in the literature describing the
interaction of thiosemicarbazone and substituted thiosemicarba-
zones derived from 2-formylpyridine with Pd(II) [10,11], Ru(II)
[12,13], Cu(II) [9,14], Fe(II), Fe(III), Co(III) and Rh(III) [15]. As a con-
tinuation of our previous research on the coordination chemistry of
2.1. Preparation of HFpyTSC
2-Formylpyridine (1.07 g, 10 mmol) in ethanol (2 mL) was
added dropwise to thiosemicarbazide (0.914 g, 10 mmol) in hot
EtOH-water (V/V, 1:1; 80 mL) followed by the addition of few
drops of glacial acetic acid. The reaction mixture was refluxed for
* Corresponding author. Tel.: +20 12 3696735; fax: +20 50 2246781.
E-mail addresses: sihmostafa@yahoo.com (Sahar. I. Mostafa), ian.butler@mcgill.
ca (I.S. Butler).
**
Corresponding author.
0020-1693/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2010.04.018

S.A. Elsayed et al. / Inorganica Chimica Acta 363 (2010) 2526–2532
2527
3.5 h. Upon cooling, the white solid was filtered off, washed with
water, ethanol and re-crystallized from ethanol. Yield 65%, m.p.
201 °C. Elemental Anal. Calc. for C7H8N4S: C, 46.6; H, 4.4; N, 31.1;
(H(C@N),s); 7.99 (N(4)H2). 13C NMR in DMSO-d6 (d, ppm): 158.91
C(2); 125.79 C(3); 141.44 C(4); 125.33 C(5); 149.92 C(6); 146.65
(C(C@N)); 184.37 (C(C@S)). UV–Vis (in DMF): kmax (nm): 474,
367, 328. Mass spectrum (m/e): 364.9 [Pd(FpyTSC)Br]+.
S, 17.8. Found: C, 46.5; H, 4.3; N,31.2; S, 17.6%. IR (cmÀ1):
m
as(NH2),
(N–N), 998;
(N–N), 995; (C@S),
3432;
m
m
s(NH2), 3255;
m
(NH), 3150;
m(C@N), 1608; m
(C@S), 819. Raman (cmÀ1):
m(C@N), 1607;
m
m
2.2.4. Cis-[Pd(HFpyTSC)2]Br2
824. 1H NMR in DMSO-d6 (d, ppm): 8.54 (H(3),d); 7.81 (H(4),t),
7.35 (H(5),t); 8.27 (H(6),d); 8.07 (H(C@N),s); 11.63 (N(3)H,s);
8.17, 8.35 (N(4)H2). 13C NMR in DMSO-d6 (d, ppm): 154.01 C(2);
120.90 C(3); 137.21 C(4); 124.79 C(5); 149.98 (C(6); 143.23
(H(C@N)); 179.02 (C(C@S)). UV–Vis (in DMC): kmax (nm): 447,
320. Mass spectrum (m/z): 180.
PdCl2 (0.044 g, 0.25 mmol) was added to HBr (1 mmol) and the
mixture was heated under reflux until a dark red solution was ob-
tained. A methanolic solution of HFpyTSC (0.09 g, 0.5 mmol;
20 mL) was added to this solution. The yellow precipitate which
formed was isolated, washed with water, methanol and dried in
air. Yield 70%, m.p. >300 °C. Conductivity data (10À3 M in DMF):
kM = 97.0
C14H18Br2N8PdS2: C, 26.8; H, 2.9; N, 17.8; S, 10.2, Found: C, 26.5;
H, 2.6; N, 17.4; S, 9.9%. IR (cmÀ1):
as(NH2), 3376; s(NH2), 3276;
(C@N), 1631; (N-N), 1050; (C@S), 807; (M–N), 454. Raman
(cmÀ1):
(C@N), 1606; (N–N), 1026; (C@S), 817; (M–N), 425,
(M–S), 347. 1H NMR in DMSO-d6 (d, ppm): 8.59, 8.56 (H(3),d);
ohmÀ1 cm2 molÀ1
.
Elemental
Anal.
Calc.
for
2.2. Preparation of complexes
m
m
2.2.1. [Pd(FpyTSC)(PPh3)]PF6
m
m
m
m
HFpyTSC (0.045 g, 0.25 mmol) in a methanolic solution of KOH
(0.014 g, 0.25 mmol; 15 mL) was added to a suspension of [Pd
(PPh3)2Cl2] (0.17 g, 0.25 mmol) in methanol (20 mL). The yellow
solution obtained was stirred overnight. A yellow complex was
formed upon the addition of a saturated aqueous solution of ammo-
nium hexafluorophosphate. Yield 89%, m.p. 288 °C. Conductivity
data (10À3 M in DMF): kM = 32.0 ohmÀ1 cm2 molÀ1 Elemental Anal.
Calc. for C25H22F6N4P2PdS: C, 43.3; H, 3.2; N, 8.1; S, 4.6%. Found: C,
m
m
m
m
m
8.09, 7.88 (H(4),t), 7.54, 7.41 (H(5),t); 8.27, 8.08 (H(6),d); 7.89,
8.07 (H(C@N),s); 11.68, 11.70 (N(3)H); 8.10, 7.99 (N(4)H2). 13C
NMR in DMSO-d6 (d, ppm): 158.51, 158.67 C(2); 121.74, 124.76
C(3); 141.20, 141.92 C(4); 125.46, 126.09 C(5); 149.67, 149.08
C(6); 146.42, 146.51 (C(C@N)); 178.84, 184.13 (C(C@S)). UV–Vis
(in DMF): kmax (nm): 473, 337.
43.5; H, 3.1; N, 8.1; S, 4.2%. IR (cmÀ1):
3367; k(C@N), 1603; (N–N), 1023; (C@S), 767;
man (cmÀ1):
(C@N), 1612; (N–N), 1024; (C@S), 763;
455,
(M–S), 355. 1H NMR in DMSO-d6 (d, ppm): 8.17 ((H3),d);
m
as(NH2), 3479;
(M–N), 446. Ra-
(M–N),
ms(NH2),
m
m
m
2.2.5. [Rh(FpyTSC)(PPh3)2Cl]ClO4
m
m
m
m
Hydrated rhodium trichloride (0.104 g, 0.4 mmol) was added to
an aqueous solution of 3M HClO4 (10 mL; pH = 1.5). HFpyTSC
(0.166 g, 0.8 mmol) in ethanol (15 mL) was added and the reaction
mixture was refluxed for 3 h. Triphenylphosphine (0.22 g,
0.82 mmol) in hot ethanol (10 mL) was added and the reaction
mixture was further refluxed for 3 h. Following this procedure, a
yellow orange precipitate was obtained, which was then filtered
off while hot, washed with hot water, hot ethanol and dried in
vacuo. Yield 40%, m.p. >300 °C. Conductivity data (10À3 M in
m
8.13 (H(4),t), 7.18 (H(5),t); 7.84 (H(6),d); 7.09 (H(C@N),s); 8.12
(N(4)H2). 13C NMR in DMSO-d6 (d, ppm): 159.91 C(2); 126.55
C(3); 142.11 C(4); 126.94 C(5); 150.91 (C(6); 142.11 (C(C@N));
180.03 (C(C@S)). UV–Vis (in DMF): kmax (nm): 473, 365.
2.2.2. [Pd(FpyTSC)(SCN)]
PdCl2 (0.035 g, 0.2 mmol) was added to KSCN (0.077 g,
0.8 mmol) in MeOH–water (V/V,1:1; 10 mL), the reaction mixture
was heated and stirred until a dark red solution of K2[Pd(SCN)4]
was formed. To this solution, HFpyTSC (0.036 g, 0.2 mmol) in
methanol (10 mL) was added. The resulting yellow precipitate
was collected, washed with water, methanol and dried in air. Yield
DMF): kM = 77.0 ohmÀ1 cm2 molÀ1 Elemental Anal. Calc. for
.
C
43H39Cl2N4O4P2RhS: C, 54.7; H, 4.2; N, 5.9; S, 3.4. Found: C,
54.6; H, 4.0; N, 6.1; S, 3.2%. IR (cmÀ1):
as(NH2), 3376; s(NH2),
3276; (C@N), 1616; (N–N), 1025; (C@S), 780; (M–N), 464. Ra-
man (cmÀ1):
(C@N), 1602; (N–N), 1029; (C@S), 726; (M–N),
447, (M–S), 416;
(M–Cl), 224. 1H NMR in DMSO-d6 (d, ppm):
m
m
m
m
m
m
m
m
m
m
80%, m.p. 298 °C. Conductivity data (10À3
M
in DMF):
m
m
kM = 2.0 ohmÀ1 cm2 mol1 Elemental Anal. Calc. for C8H7N5PdS2: C,
8.06 (H(3),d); 7.83 (H(4),t); 6.91 (H(5),t); 7.73 (H(6),d); 7.94
(N(4)H2). 13C NMR in DMSO-d6 (d, ppm): 157.57 C(2); 125.60
C(3); 139.94 C(4); 125.91 C(5); 151.48 C(6); 143.00 (C(C@N));
181.14 (C(C@S)). UV–Vis (in DMF): kmax (nm): 580, 480, 390. Mass
.
28.0; H, 2.1; N, 20.4; S, 18.7. Found: C, 27.9; H, 2.0; N, 20.2; S,
18.7%. IR (cmÀ1):
m
as(NH2), 3400;
(C@S), 766;
(M–N), 435. Raman (cmÀ1):
(N–N), 1021; (C@S), 766; (M–N), 435; (M–S), 345;
(M–SCN), 2109. 1H NMR in DMSO-d6 (d, ppm): 8.22 (H(3),d);
m
s(NH2), 3289;
m
(C@N), 1638;
m
(N–N), 1022;
m
m
m(C@N),
1606;
m
m
m
m
spectrum
(m/e):
841
[Rh(FpyTSC)(PPh3)2Cl]+,
579
m
[Rh(FpyTSC)(PPh3)]+.
7.80 (H(4),t), 7.57 (H(5),t); 8.18 (H(6),d); 7.93 (H(C@N),s); 8.09
(N(4)H2).13C NMR in DMSO-d6 (d, ppm): 158.95 C(2); 121.68
C(3); 141.80 C(4); 125.07 C(5); 148.71 C(6); 146.55 (C(C@N));
182.19 (C(C@S)). UV–Vis (in DCM): kmax (nm): 470, 321. Mass spec-
trum (m/e): 342.03 [Pd(FpyTSC)(SCN)]+; 311.3 [Pd(FpyTSC)(CN)]+.
2.3. Physical measurements
Elemental analyses (C,H,N,S) were carried out in the Depart-
ment of Chemistry at the University of Montreal. Infrared spectra
were recorded on a Nicolet 6700 Diamond ATR spectrometer in
the 4000–200 cmÀ1 range. Raman spectra were measured on an in-
Via Renishaw spectrometer using 785-nm laser excitation. NMR
spectra were measured on Varian Mercury 200-, 300- and 500-
MHz spectrometers. Mass spectra were recorded using MS25RFA
spectrometer. Electronic spectra were obtained using a Hewlett-
Packard 8453 spectrophotometer. X-ray diffraction measurements
were performed at the X-Ray Crystal Structure Unit, University of
Montreal, using a Bruker Platform diffractometer, equipped with
a Bruker MART 4K Charged-Coupled Device (CCD) Area Detector
using the program APEX II and a Nonius Fr591 rotating anode (cop-
per radiation) equipped with Montel 200 optics. The crystal-to-
detector distance was 5 cm and the data collection was carried
out in the 512 Â 512 pixel mode. The initial unit cell parameters
2.2.3. [Pd(FpyTSC)Br]
HFpyTSC (0.045 g, 0.25 mmol) was dissolved in a methanolic
solution of KOH (0.014 g, 0.25 mmol) and Li2PdBr4 (0.25 mmol)
was added. The reaction mixture was stirred at room temperature
for 24 h. The orange product was filtered off, washed with water,
methanol and dried in air. Yield 76%, m.p. >300 °C. Conductivity
data (10À3 M in DMF): kM = 8.0 ohmÀ1 cm2 molÀ1. Elemental Anal.
Calc. for C7H7BrN4PdS: C, 23.0; H, 1.9; N, 15.3; S, 8.8. Found: C,
22.9; H, 2.0; N, 15.3; S, 8.7%. IR (cmÀ1):
3276; (C@N), 1629; (N–N), 1024; (C@S), 778;
Raman (cmÀ1):
(C@N), 1605; (N–N), 1026; (C@), 788;
430, (M–S), 343;
(M–Br), 276. 1H NMR in DMSO-d6 (d, ppm):
8.61 (H(3),d); 8.09 (H(4),t), 7.55 (H(5),t); 7.74 (H(6),d); 7.90
m
as(NH2), 3427;
(M–N), 430.
(M–N),
ms(NH2),
m
m
m
m
m
m
m
m
m
m

2528
S.A. Elsayed et al. / Inorganica Chimica Acta 363 (2010) 2526–2532
were determined by the least-squares fit of the angular setting of
strong reflections, collected by a 10.0 degree scan in 33 frames over
three different parts of the reciprocal space (99 frames total). One
complete sphere of data was collected.
and HBr with HFpyTSC in methanol. Finally, the perchlorate com-
plex, [Rh(FpyTSC)(PPh3)2Cl]ClO4, was isolated from the reaction
of hydrated RhCl3 with HFpyTSC in presence of PPh3 and HClO4
in ethanol at pH 1.5. All the new complexes are microcrystalline
or powder-like, stable under normal laboratory conditions and sol-
uble in DMF and DMSO.
2.4. X-ray crystallography
3.1. Vibrational spectra
Orange needle crystals, suitable for X-ray analysis of
[Pd(FpyTSC)(PPh3)]PF6 and [Pd(FpyTSC)(SCN)] were obtained by
slow evaporation of the complexes in acetonitrile and DMF-DCM
(1:2), respectively. Crystals of the two complexes were mounted
on the diffractometer and the unit cell dimensions and intensity
data were measured at 200 K. The structures were solved by the
least-squares fit of the angular setting of strong reflections based
on F2. The relevant crystal data and experimental conditions along
with the final parameters are summarised in Table 1.
Some vibrational spectroscopic data have been reported for 2-
formylpyridinethiosemicarbazone, 2-formylpyridine substituted
thiosemicarbazones and a number of their complexes [9–14,
21–23]. The characteristic IR and Raman bands observed for 2-
formylpyridinethiosemicarbazone (HFpyTSC) and the new com-
plexes described here, together with the proposed vibrational assign-
ments, are presented in the experimental section. The HFpyTSC
molecule (Fig. 1) has a thioamide moiety [–NH–C(@S)–NH2] which
can exhibit thione–thiol tautomerism (Fig. 2) [23]. In the IR and Ra-
3. Result and discussion
man spectra, the absence of a m
(SH) band at ca. 2600 cmÀ1 indi-
cates that HFpyTSC ligand is predominantly in the thione form in
the solid state [23,24]. In solution and in the presence of metal
ions, however, it may convert to the deprotonated thiol [23]. The
free HFpyTSC ligand exhibits a strong IR band at 1608 cmÀ1, which
The Section 2 describes the synthesis of the new complexes of
2-formylpyridinethiosemicarbazone (HFpyTSC) and lists their ele-
mental analyses and spectroscopic data, which are in excellent
agreement with the assigned formulae. The complexes
[Pd(FpyTSC)(SCN)] and [Pd(FpyTSC)Br] are non-electrolytes in
DMF at room temperature while other isolated complexes
is characteristic of the m(HC@N) group; this vibration appears as a
strong band at 1607 cmÀ1 in the Raman spectrum. It is expected
that coordination of the nitrogen centre to the metal ion will re-
duce the electron density in the azomethine link and thus shift
[Pd(FpyTSC)(PPh3)]PF6,
[Rh(FpyTSC)(PPh3)2Cl]ClO4
and
[Pd(HFpyTSC)2]Br2 behave as 1:1, 1:1 and 1:2 electrolytes, respec-
tively [20]. The [Pd(FpyTSC)(PPh3)]PF6 complex was prepared from
the reaction of [Pd(PPh3)2Cl2] with HFpyTSC and KOH in methanol.
The [Pd(FpyTSC)(SCN)] complex was obtained from the reaction of
K2[Pd(SCN)4] and HFpyTSC in methanol, while the reaction of
Li2[PdBr4] with HFpyTSC in MeOK produced [Pd(FpyTSC)Br]. The
[Pd(HFpyTSC)2]Br2 complex was isolated from the reaction of PdCl2
the m(HC@N) vibration to lower wavenumbers [25]. In the spectra
of the complexes, this band is observed in the 1631–1603 cmÀ1 re-
gion, supporting coordination via the azomethine nitrogen centre
[26]. The band at 3150 cmÀ1 in the free ligand, arising from
m
(NH), is not observed in the complexes [12]. Also, the medium-in-
tense IR band at 819 cmÀ1 for HFpyTSC, attributable to the
m(C@S)
vibration (observed at 824 cm-1 in the Raman), is shifted to lower
Table 1
The details of crystals and experimental data for [Pd(FpyTSC)(PPh3)]+ and [Pd(FpyTSC)(SCN)].
[Pd(FpyTSC)(PPh3)]+
[Pd(FpyTSC)(SCN)]
Empirical formula
Formula weight
T (K)
C
25H22F6N4P2PdS
C8 H7 N5 Pd S2
343.71
150
692.87
200
k (A)
1.54178
monoclinic
P21/c
1.54178
monoclinic
C2/c
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
13.5473 (2)
19.2958 (3)
11.2618 (2)
90
17.9299 (5)
7.3128 (2)
17.6064 (4)
90
a
(°)
b (°)
113.808 (1)
90
2693.38 (7)
4
1.709
8.001
103.974 (1)
90
2240.19(10)
8
2.038
16.687
c
(°)
V (Å3)
Z
DCalc (g cmÀ3
)
Absorption coefficient (mmÀ1
F(0 0 0)
)
1384
1344
Crystal size (mm)
h range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Absorption correction
Maximum and minmum transmission
Refinement method
0.30 Â 0.10 Â 0.04
0.20 Â 0.04 Â 0.02
3.57–72.41
5.08–72.52
À16 6 h 6 15, À23 6 k 6 22, À12 6 l 6 13
17 702
5065 [Rint = 0.057]
À21 6h 6 21, À8 6 k 6 7, À21 6 l 6 21
14 303
2158 [Rint = 0.038]
semi-empirical from equivalents
0.7162 and 0.3724
full-matrix least-squares on F2
2158/3/154
semi-empirical from equivalents
0.7261 and 0.4133
full-matrix least-square on F2
5065/0/360
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.049
1.124
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0438, wR2 = 0.1367
R1 = 0.0455, wR2 = 0.1388
0.622 and À1.183
R1 = 0.0253, wR2 = 0.0662
R1 = 0.0275, wR2 = 0.0671
0.739 and À0.769
Largest difference in peak and hole (e/Å3)
Largest difference in peak and hole
0.00030(2)

S.A. Elsayed et al. / Inorganica Chimica Acta 363 (2010) 2526–2532
2529
4
and two doublets at d 8.27 and 8.54 ppm due to H(6) and H(3),
respectively. The singlets at d 8.07 and 11.63 ppm are assigned to
H(CH@N) and N(3)H, respectively. The two hydrogen atoms in
the terminal nitrogen, N(4)H2, are not equivalent and are assigned
to the pair of broad singlets at d 8.17 and 8.35 ppm, indicating re-
stricted rotation about the S@C-NH2 group [16]. No resonance is
observed near d 4.0 ppm, characteristic to SH, indicating that the
HFpyTSC ligand is present in the thione form [35].
5
6
3
2
∗
CH
N
1
2
N
3
NH
In the 1H NMR spectra of the complexes, the resonance arising
from the N(3)H proton is not observed, while those associated with
the azomethine nitrogen (CH@N), N(4)H2 and pyridine protons are
shifted downfield. This feature is indicative of a decrease in the
electron density caused by electron withdrawal by the metal ions
from the deprotonated thiol sulphur, azomethine nitrogen and
pyridine nitrogen centres [31]. In the 1H NMR spectrum of
[Pd(HFpyTSC)2]Br2, the resonance arising from N(3)H proton is ob-
served at d11.69 ppm, while the pyridine protons signals undergo
marginal shifts, indicating the non-involvement in coordination.
These data confirm the neutral bidentate character of HFpyTSC
via the thione sulphur and azomethine nitrogen centres. Also, the
spectrum of [Pd(HFpyTSC)2]Br2 shows two resonances for each
proton assigned to cis-configuration around Pd(II) [36]. The 1H
NMR spectra of [Pd(FpyTSC)(PPh3)]PF6 and [Rh(FpyTSC)(PPh3)2Cl]-
ClO4 show complicated multiplets at d 7.15–8.5 assigned to PPh3
which overlap with the FpyTSCÀ protons [29]. The PPh3 protons
experience downfield shifts compared to the free PPh3 [29]. In
the spectrum of [Pd(FpyTSC)(PPh3)]PF6, the PPh3 protons show
an upfield shift when compared to [Pd(PPh3)Cl2]. This shift is inter-
preted in terms of the stronger bonding of FpyTSC- to Pd(II) com-
pared to chloride [37].
4
NH2
S
Fig. 1. Structure of 2-formylpyridinethiosemicarbazone (HFpyTSC).
∗
∗
CH
CH
N
N
N
N
NH
N
S
NH2
HS
NH2
Fig. 2. Thione–thiol tautomeric forms of 2-formylpyridinethiosemicarbazone
(HFpyTSC).
energy in the complexes, indicating that coordination takes place
through the deprotonated thiol sulfur centre [27]. These data are
further supported by the shift of mas(NH2) and ms(NH2) stretches
The 31P NMR spectrum of [Pd(FpyTSC)(PPh3)]PF6 in DMSO-d6
consists of a sharp singlet at d 28.44 ppm, suggesting the presence
of one coordinated PPh3 group in the complex. On the other hand,
the spectrum of [Rh(FpyTSC)(PPh3)2Cl]ClO4 shows two singlets at d
13.32 and 14.42 ppm, indicating the presence of two PPh3 in a cis-
configuration [38].
near 3430 and 3250 cmÀ1, respectively, to lower wavenumbers
upon complexation [28–30]. The free HFpyTSC ligand shows an in-
tense band near 995 cm-1 assigned to the
m(N–N) stretch. In the
complexes, this band is shifted to higher energies, as a conse-
quence of coordination through the imine nitrogen atom [31]. Fur-
thermore, the pyridine ring deformation mode at 562 cmÀ1 in the
free ligand is shifted to near 590 cmÀ1 in the complexes indicating
participation of the pyridine nitrogen centre in coordination [23].
The Raman and IR spectral data suggest mononegative tridentate
N,N,SÀ coordinaton of the HFpyTSC ligand. In the case of
The 13C NMR spectrum of HFpyTSC in DMSO-d6 has been mea-
sured and assigned, and agrees with the published data [16]. The
spectrum shows seven resonances at d 120.90, 124.79, 137.21,
143.23, 149.98, 154.01 and 179.02 ppm, assigned to C(3), C(5),
C(4), C(CH@N), C(6), C(2) and C(C@S), respectively. In the com-
plexes, the resonances for the carbon atoms adjacent to the coordi-
nation sites, C(CH@N) and C(C@S), C(2) and C(6), are shifted
downfield relative to their positions in the free ligand [14]. This
feature may be due to an increase in the pyridine ring current in
C(2) and C(6) brought about by coordination to pyridine nitrogen
centre [39]. In the spectrum of [Pd(HFpyTSC)2]Br2, the C(CH@N)
and C(C@S), C(2) resonances are clearly shifted downfield with re-
spect to the other resonances. Also, each carbon atom shows two
resonances confirming the cis-configuration observed in the 1H
NMR spectrum.
[Pd(HFpyTSC)2]Br2, the m(NH) stretch is shifted to lower wavenum-
ber since the thione sulphur is taking part in coordination. Also, as
there is no shift observed in the pyridine ring deformation mode,
i.e., HFpyTSC acts as a neutral bidentate (N,S) ligand [31].
The presence of the coordinated PPh3 groups in
[Pd(FpyTSC)(PPh3)]PF6 and [Rh(FpyTSC)(PPh3)2Cl]ClO4 is mani-
fested by the strong IR bands near 1100 and 750 cmÀ1, attributed
to the
m
(P–C) and d(C–CH) vibrations, respectively [32]; the former
À
band overlaps with the ClO4 stretching vibration in the spectrum
of the Rh(III) complex. The IR spectrum of [Rh(FpyTSC)(PPh3)2Cl]-
ClO4 exhibits a strong band at 1091 cmÀ1 and a medium-intense
band at 625 cmÀ1 due to
m
3(F2) and
m
4(F2) modes of the uncoordi-
3.3. Electronic spectra
À
nated ClO4 ion [33]. The complex [Pd(FpyTSC)(PPh3)]PF6 displays
a strong IR vibration at 828 cmÀ1 arising from the ionic PF6 [34]. Fi-
nally, the new complexes show additional far-IR and Raman bands
The electronic spectrum of HFpyTSC in DCM shows two absorp-
*
p transitions of
tion bands at 447 and 320 nm attributable to n ?
at ca. 450, 350 and 280 cmÀ1 that can be attributed to
m(M–N),
the thiosemicarbazone thioamide moiety and the pyridine ring,
respectively [31]. These bands are shifted to higher energies upon
complexation [34]. The electronic spectra of the complexes in DMF
or DCM in the 200–900 nm regions contain intense bands associ-
ated with ligand-to-metal charge transfer (LMCT) transitions and
weaker bands assigned to d–d transitions [37].
m
(M–S) and m(M–X) modes, respectively [31,32].
3.2. NMR spectra
The 1H NMR spectroscopic data for HFpyTSC and its complexes
in DMSO-d6 are reported in the experimental section, and in close
agreement with the reported data [16]. The spectrum of the free
HFpyTSC (see Fig. 1 for numbering scheme) exhibits two triplets
at d 7.35 and 7.81 ppm assigned to H(5) and H(4), respectively
The electronic spectra of the Pd(II) complexes exhibit bands
near 470 and 320 nm due to 1A1g ? 1Bg and 1A1g ? 1Eg transitions,
respectively, in
a square-planar configuration [40]. In the
[Pd(FpyTSC)(PPh3)]PF6 complex,the absorption band at 370 nm is

2530
S.A. Elsayed et al. / Inorganica Chimica Acta 363 (2010) 2526–2532
*
assigned to a mixture of charge transfer from Pd(II) to the
p
orbi-
tal of PPh3 and d–d bands [41,42]. The electronic spectrum of
[Rh(FpyTSC)(PPh3)2Cl]ClO4 shows bands at 580, 480 and 390 nm,
which resemble those of six-coordinated octahedral Rh(III) com-
plexes and may be assigned to 1A1g ? 3T1g
,
1A1g ? 1T1g and
1A1g ? 1T2g transitions, respectively [29,42].
3.4. Mass spectra
The mass spectrum of HFpyTSC is in agreement with the as-
signed formula (m/z 180; Calcd 180), and matches the previously
published data [43]. The mass spectra of the complexes
[Pd(FpyTSC)(SCN)], [Pd(FpyTSC)Br] and [Rh(FpyTSC)(PPh3)2Cl]ClO4
are reported here and their molecular ion peaks are in agreement
with the assigned formulae. The mass spectrum of
[Pd(FpyTSC)(SCN)] shows fragmentation patterns corresponding
to succesive degradations of the molecule. The first signal at m/e
342.03 (Calcd. 343.4) is in agreement with the molecular ion of
the complex, [Pd(FpyTSC)(SCN)]+, with 50% abundance. The spec-
trum exhibits one more peak at 311.3 corresponding to
[Pd(FpyTSC)(NC)]+. The mass spectrum of [Pd(FpyTSC)Br] shows a
signal at m/e 364.9 (Calcd. 364.4) with 100% abundance. The spec-
trum of [Rh(FpyTSC)(PPh3)2Cl]ClO4 shows signals at 841 (Calcd.
Fig. 4a. Structure of [Pd(FpyTSC)(SCN)] with numbering scheme.
840.8)
and
579
(Calcd.
579)
corresponding
to
[Rh(FpyTSC)(PPh3)2Cl]+ and [Rh(FpyTSC)(PPh3)]+ fragments,
respectively [29].
3.5. X-ray crystal structures of [Pd(FpyTSC)(PPh3)]PF6 and
[Pd(FpyTSC)(SCN)]
In order to verify the proposed coordination modes of 2-formyl-
pyridinethiosemicarbazone
(HFpyTSC)
ligand
in
[Pd(FpyTSC)(PPh3)] and [Pd(FpyTSC)(SCN)], their structures were
determined by X-ray crystallography. The atomic numbering
schemes for the two complexes are given in Figs. 3 and 4, respec-
tively, and selected bond angles and bond lengths are listed in Ta-
bles
2 and 3, respectively. The [Pd(FpyTSC)(PPh3)]PF6 and
[Pd(FpyTSC)(SCN)] complexes crystallize in the monoclinic space
groups P21/c and C2/c, respectively.
In the case of [Pd(FpyTSC)(PPh3)]PF6, the structure shows that
FpyTSC- is coordinated to Pd(II) in the expected tridentate fashion
via pyridine nitrogen N(1), azomethine nitrogen N(2) and deproto-
nated thiol S(1), forming two five-membered chelate rings with
Fig. 4b. Hydrogen bonding interaction in the lattice of [Pd(FpyTSC)(SCN)].
Npy–Pd–NN@C {N(1)–Pd(1)–N(2)} and NN@C–Pd–S {N(2)–Pd(1)–
S(1)} bite angles of 80.12(13)o and 83.00(11)o, respectively. The li-
gand shows a Z, E, Z configurations about the bonds C(5)–C(6),
C(6)–N(2) and N(3)–C(7) for the donor centres N, N, and S, respec-
tively. Also, a triphenylphosphine is coordinated to Pd(II) centre,
which is trans to N(2). The strong coordination of Pd(II) to the azo-
methine nitrogen compared to the pyridyl nitrogen is due to the
higher basicity of N(2) [19]. In the complex, the bond distances
C(7)–N(3), 1.317(6) Å and C(6)–N(2), 1.288(6) Å are not intermedi-
ate between single and double bonds, but they are closer to double
bonds. Also, the N(2)–N(3), 1.372(5) Å bond length is very close to
a single bond (Table 2). Moreover, The C(7)–S(1) bond length in the
complex (1.771(4) Å) is intermediate between a C–S double bond
(1.62 Å) and a C–S single bond (1.82 Å), indicating that this bond
maintains a partial double bond character [44]. The trans P(1)–
Pd(1)–N(2) bond angle 175.64(10)o is close to linearity, while the
N(1)–Pd(1)–S(1) bond angle of 163.66(9)o deviates significantly
from linearity [10,45]. The palladium ion is thus nested in a NNSP
core, which is distorted from the ideal square-planar configuration,
as observed from the bond angles and bond lengths around Pd(II).
Fig. 3. Structure of [Pd(FpyTSC)(PPh3)]PF6 with numbering scheme.

S.A. Elsayed et al. / Inorganica Chimica Acta 363 (2010) 2526–2532
2531
Table 2
The Pd-N(1), Pd–N(2), Pd–S and Pd–P distances are all quite normal
[46].
Selected bond lengths (Å) and bond angles (o) for [Pd(FpyTSC)(PPh3)]+.
Bond lengths (Å)
Bond angles (o)
The X-ray crystal structure of complex [Pd(FpyTSC)(SCN)]
(Fig. 4a) shows that FpyTSCÀ is coordinated to palladium in the
same tridentate manner as in [Pd(FpyTSC)(PPh3)]PF6, and a thiocy-
anato-sulfur atom has taken up the fourth coordination site on the
Pd(II) in planar configuration. Thus, Pd(II) has an NNSS coordina-
tion sphere around it. The observed bond lengths, Pd–N(7),
1.982(2) Å, Pd–N(1), 2.077(3) Å, Pd–S(1), 2.3276(7) Å, Pd–S(8),
2.2523(7) Å in the complex are longer than those found in other re-
ported square-planar palladium(II) complexes with N,S-donors
[44]. The data show that [Pd(FpyTSC)(SCN)] has short N(7)–N(8)
(1.360(3) Å) and long C(8)–S(8) (1.763(3) Å) bond lengths (Table 3)
compared with other reported complex. The observed Pd–S(SCN)
bond length of 2.3276(7) Å and the N(7)–Pd–S(11) bond angle of
177.94(7)o are normal [47,48], while the N(1)–Pd(1)–S(8) angle
of 165.46(7)o is quite deviated from linearity [49]. An examination
of the packing pattern in the [Pd(FpyTSC)(SCN)] crystal shows that
Pd(1)–N(2)
Pd(1)–N(1)
Pd(1)–S(1)
Pd(1)–P(1)
S(1)–C(7)
N(1)–C(1)
N(1)–C(5)
N(2)–C(6)
N(2)–N(3)
N(3)–C(7)
N(4)–C(7)
N(4)–H(4A)
N(4)–H(4B)
C(1)–C(2)
C(1)–H(1)
C(2)–C(3)
C(2)–H(2)
C(3)–C(4)
C(3)–H(3)
C(4)–C(5)
C(4)–H(4)
C(5)–C(6)
C(6)–H(6)
P(1)–C(21)
P(1)–C(31)
P(1)–C(11)
2.023(3)
2.097(3)
2.2469(10)
2.2774(9)
1.771(4)
1.340(5)
1.354(5)
1.288(6)
1.372(5)
1.317(6)
1.333(5)
0.82(5)
0.92(6)
1.379(6)
0.9500
1.385(6)
0.9500
1.378(7)
0.9500
N(2)–Pd(1)–N(1)
N(2)–Pd(1)–S(1)
N(1)–Pd(1)–S(1)
N(2)–Pd(1)–P(1)
N(1)–Pd(1)–P(1)
S(1)–Pd(1)–P(1)
C(7)–S(1)–Pd(1)
C(1)–N(1)–C(5)
C(1)–N(1)–Pd(1)
C(5)–N(1)–Pd(1)
C(6)–N(2)–N(3)
C(6)–N(2)–Pd(1)
N(3)–N(2)–Pd(1)
C(7)–N(3)–N(2)
C(7)–N(4)–H(4A)
C(7)–N(4)–H(4B)
H(4A)–N(4)–H(4B)
N(1)–C(1)–C(2)
N(1)–C(1)–H(1)
C(2)–C(1)–H(1)
C(1)–C(2)–C(3)
C(1)–C(2)–H(2)
C(3)–C(2)–H(2)
C(4)–C(3)–C(2)
C(4)–C(3)–H(3)
C(2)–C(3)–H(3)
C(3)–C(4)–C(5)
C(3)–C(4)–H(4)
C(5)–C(4)–H(4)
N(1)–C(5)–C(4)
N(1)–C(5)–C(6)
C(4)–C(5)–C(6)
N(2)-C(6)–C(5)
N(2)–C(6)–H(6)
C(5)–C(6)–H(6)
N(3)–C(7)–N(4)
N(3)–C(7)–S(1)
N(4)–C(7)–S(1)
80.12(13)
83.54(11)
163.66(9)
175.64(10)
102.65(9)
93.68(4)
95.94(15)
118.7(3)
130.8(3)
110.5(3)
121.3(3)
115.1(3)
123.5(3)
111.2(3)
121(3)
126(4)
113(5)
122.3(4)
118.9
118.9
119.3(4)
120.4
120.4
119.1(4)
120.5
120.5
three
intermolecular
hydrogen
bonding
interactions,
1.392(6)
0.9500
1.448(5)
0.9500
1.817(4)
1.818(4)
1.819(4)
N(11,SCN)ÁÁÁH(N(9)H2) and two N(8)ÁÁÁH(N(9)H2), are active in the
lattice (Fig. 4b).
Acknowledgements
This research was supported by a NSERC (Canada) Discovery
grant (ISB) and a Scholarship from the Minsitry of Higher Educa-
tion, Egypt (E.S.).
119.0(4)
120.5
120.5
121.6(4)
116.8(4)
121.6(4)
117.4(4)
121.3
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2010.04.018.
121.3
118.5(4)
125.6(3)
115.9(4)
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C(6)–C(5)–C(4)
N(1)–C(6)–C(5)
N(1)–C(6)–C(7)
C(5)–C(6)–C(7)
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81.05(10)
84.48(7)
165.46(7)
177.94(7)
98.79(7)
95.73(3)
95.22(10)
100.28(11)
119.3(3)
129.9(2)
110.69(18)
120.8(2)
115.5(2)
123.62(18)
111.9(2)
121.7(3)
119.3(3)
119.5(3)
118.9(3)
121.2(3)
115.4(3)
123.3(3)
117.3(3)
117.9(3)
117.4(2)
124.8(2)
178.1(3)
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