Palladium(II) and platinum(II) complexes of 2-hydroxy acetophenone N(4)-ethylthiosemicarbazone - Crystal structure and description of bonding properties

Article abstract of DOI:10.1016/j.ica.2004.06.048

Reaction of H₂PtCl₄ and K₂PdCl₄ with 2-hydroxyacetophenone N(4)-ethylthiosemicarbazone, H₂Ap4Et, afforded [Pt(Ap4Et)(H₂Ap4Et)] and [Pd(Ap4Et)(H₂Ap4Et)]. Their crystal and molecular structures are reported and represent the first 1:2 thiosemicarbazone complexes with ligands having both different formal charge and denticity. Reaction of H₂PtCl₄ and K₂PdCl ₄ with 2-hydroxyacetophenone N(4)-ethylthiosemicarbazone, H ₂Ap4Et, afforded [Pt(Ap4Et)(H₂Ap4Et)] and [Pd(Ap4Et)(H₂Ap4Et)]. Their crystal and molecular structures are reported and represent the first 1:2 thiosemicarbazone complexes with ligands having both different formal charge and denticity. The dianion, Ap4Et ^2-, coordinates in a planar conformation to palladium(II) or platinum(II) via the phenolato O, imine N and thiolato S atoms, while the neutral molecule exhibits monodentate coordination by the thione S atom. Intra-, intermolecular hydrogen bonds and C-H?π contacts lead to aggregation and a supramolecular assembly. Electronic, IR, and NMR spectral data, as well as electrochemical measurements, are included. The pK_a values of the poorly water soluble H₂Ap4Et were obtained spectrophotometrically in aqueous solutions of constant ionic strength.

Full text of DOI:10.1016/j.ica.2004.06.048

Inorganica Chimica Acta 357 (2004) 4113–4120
www.elsevier.com/locate/ica
Palladium(II) and platinum(II) complexes of 2-hydroxy acetophenone
N(4)-ethylthiosemicarbazone – crystal structure and description
of bonding properties
a
a,
a
Leuteris Papathanasis , Mavroudis A. Demertzis *, Paras Nath Yadav ,
a,
a
b
Dimitra Kovala-Demertzi *, Christos Prentjas , Alfonso Castin˜eiras ,
a
Stavroula Skoulika , Douglas X. West
c
a
Department of Chemistry, University of Ioannina, 45110 Ioannina, Greece
Departamento de Qu´ımica Inorga´nica, Universidad de Santiago de Compostela, E-15706 Santiago de Compostela, Spain
b
c
Department of Chemistry 351700, University of Washington, Seattle, Washington 98195-1700, USA
Received 29 January 2004; accepted 12 June 2004
Available online 28 July 2004
Abstract
Reaction of H2PtCl4 and K2PdCl4 with 2-hydroxyacetophenone N(4)-ethylthiosemicarbazone, H2Ap4Et, afforded [Pt(A-
p4Et)(H2Ap4Et)] and [Pd(Ap4Et)(H2Ap4Et)]. Their crystal and molecular structures are reported and represent the first 1:2 thio-
semicarbazone complexes with ligands having both different formal charge and denticity. The dianion, Ap4Et2ꢀ, coordinates in
a planar conformation to palladium(II) or platinum(II) via the phenolato O, imine N and thiolato S atoms, while the neutral mol-
ecule exhibits monodentate coordination by the thione S atom. Intra-, intermolecular hydrogen bonds and C–Hꢁ ꢁ ꢁp contacts lead to
aggregation and a supramolecular assembly. Electronic, IR, and NMR spectral data, as well as electrochemical measurements, are
included. The pKa values of the poorly water soluble H2Ap4Et were obtained spectrophotometrically in aqueous solutions of con-
stant ionic strength.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Palladium(II); Platinum(II); Thiosemicarbazone; Crystal structures; Spectroscopy; Protonation constants
1. Introduction
of their transition-metal complexes [3–5]. Thiosemi-
carbazones usually bind to a metal ion as bidentate
N,S-donor ligands, when a third donor site (D) is incor-
porated into the ligands, like Tscs of 2-hydroxyaceto-
phenone, normally D,N,S-tricoordination takes place
[6,7]. Examples are also known where such ligands, in
addition to displaying D,N,S-tricoordination, bridge a
second metal ion through the sulfur [8–10] or oxygen
[11–13]. The present report has emerged from our con-
tinuous study on the coordination chemistry and on bi-
ological activities of Tscs with platinum metals. We
report here the structures and spectral properties of
[Pd(Ap4Et)(H2Ap4Et)] (2) and [Pt(Ap4Et)(H2Ap4Et)]
Thiosemicarbazone derivatives are of considerable in-
terest due to their antibacterial, antimalarial, antiviral
and antiitumor activities [1,2]. In our laboratory, the
chemistry of thiosemicarbazones has been an extremely
active area of research primarily because of the benefi-
cial biological (viz., antiviral and antitumor) activities
*
Corresponding authors. Tel.: +30265098425; fax: +302650448425.
E-mail addresses: mdemert@cc.uoi.gr (M.A. Demertzis), dkovala@
cc.uoi.gr (D. Kovala-Demertzi).
0020-1693/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.06.048

4114
L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
(3), where H2Ap4Et represents 2-hydroxyacetophenone
N(4)-ethylTsc, 1, and Ap4Et the dianion. To our knowl-
edge, this is the first report of 1:2 Tsc complexes with
different formal charge and denticity.
sonal computer and a Methrom 691 pH-meter.
H2Ap4Et possesses two function groups, –NH and –
OH, with dissociative hydrogens, which undergo two de-
protonation steps as a function of pH. For convenience,
in this paragraph H2Ap4Et is designated as H2A. In
aqueous solutions, there are four independent species
(i.e., H3A+, H2A, HAꢀ and A2ꢀ). Thus, there are three
separate dissociation steps given by Eqs. (1)–(3)
2. Experimental
2.1. Materials and physical measurements
Ka1
H3Aþ þ H2O ꢀ H2A þ H3Oþ
H2A þ H2O Kꢁa2 HAꢀ þ H3Oþ
HAꢀ þ H2O Kꢁa3 A2ꢀ þ H3Oþ
ð1Þ
ð2Þ
ð3Þ
Solvents were purified and dried according to standard
procedures. Infrared and far-infrared spectra were re-
corded with a Perkin–Elmer Spectrum GX FT-IR spec-
trophotometer using KBr pellets (4000–400 cmꢀ1) and
nujol mulls between polyethylene disks (400–40 cmꢀ1).
1H (250.13 MHz) and 13C (62.90 MHz) NMR spectra
were recorded with a Bruker AMX-400 spectrometer at
room temperature and referenced to DMSO or CHCl3.
UV spectra were recorded on a JASCO V-570 spectro-
The law of mass-action for these equations, based on the
molar absorptivities of the various species, takes the
form,
þ
eH A ꢀ eo
H2A
Ka1 ¼ ½H3Oþꢂ
Ka2 ¼ ½H3Oþꢂ
Ka3 ¼ ½H3Oþꢂ
ð4Þ
ð5Þ
ð6Þ
3
photometer. 2 and 3 were studied by the extended-Huckel
¨
eo ꢀ e
method using the CACAO PC Beta-Version 5.0 package
[14]. Electrochemical measurements were made using an
AUTOLAB PGSTAT30 potentiostat with a platinum
microsphere as working electrode, CHI102 CH Instru-
ments (2 mm diameter), a platinum wire auxiliary elec-
trode and an Ag/AgCl reference electrode in a three
electrode configuration. Ferrocene was added at the end
of each experiment and used as an internal standard. All
potentials are reported relative to ferrocenium/ferrocene
(Fe+/Fc, E1/2 = 0.173 V in DMF); under the experimental
conditions used (scan rate 100 mV sꢀ1). Et4NClO4 (0.1 M)
was used as supporting electrolyte, the solutions were
1 · 10ꢀ3 M in complex, and carried out under a dinitrogen
atmosphere.
eH A ꢀ eo
2
ꢀ
eo ꢀ eHA
ꢀ
eHA ꢀ eo
eo ꢀ eA2ꢀ
ꢀ
þ
respectively. The terms eo; eA2ꢀ ; eHA ; eH A and eH A are
2
3
the molar absorptivities of the observed solution, doubly
negative ionized, singly negative ionized, molecular and
positively charged species, respectively. In order to find
the dissociation constants, the values of the molar ab-
sorptivities must be experimentally determined. How-
ever, in this particular instance a direct application of
relationships (4) and (6) for Ka1 and Ka3 determination
þ
is impossible, since eH A and eA2ꢀ cannot be determined
3
2.2. Dissociation constants
in solutions with ionic strength equal to 0.1. Ideally, A2ꢀ
and H3A+ predominate at very high alkaline or very low
Due to the low solubility of H2Ap4Et, as well as its
high ka1 and low Ka3 values, spectrophotometry was
used to study the dissociation constants. Aqueous
H2Ap4Et solutions of constant ionic strength were pre-
pared with distilled water obtained from a borosilicate
autostill BICASA Spa, Model BE-115/R and used to de-
termine dissociation constants by a methology reported
previously [10,15]. A 1 · 10ꢀ4 M stock solution of
H2Ap4Et was initially prepared by suspending the ap-
propriate amount of the compound in a water bath in
0.01 M KOH until dissolution occurred, cooling to
room temperature, filling the flask to the required vol-
ume with 0.01 M KOH solution and mixing thoroughly.
Exactly 5.0 · 10ꢀ5 M working ligand solutions, having
different H3O+ ion concentrations and constant ionic
strength (l = 0.1), were then prepared with standard
HCl or KOH and KCl solutions. All absorption spectra
and pH measurements were made at 25 ꢁC with a Jasko
590 UV/VIS/NIR spectrophotometer guided by a per-
Fig. 1. Electronic absorption spectra of the conjugate pair H2A–HAꢀ
in the pH region 6.81–10.45.

L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
4115
acid solutions, respectively. Perhaps the equilibrium
steps (2) and (3) occur to an extent simultaneously,
and the value of the common species HAꢀ cannot also
be determined directly from absorption spectra. There-
fore, instead of using relationships (4)–(6), it is expedient
to use a proper rearrangement of them in the form,
perature. The resulting light yellow powder was filtered
off, washed with cold methanol and ether and dried in
vacuo over silica gel, finally redried at 70 ꢁC in vacuo
over P4O10; decomposition point 206 ꢁC, yield 42%.
IR (KBr): 1580 m(C‚N), 1563 m(C‚N), 810 m(C‚S),
748 m(C–S), 481 m(Pd–N), 353 and 325 m(Pd–S), 445
m(Pd–O); Elemental analyses are consistent with
C22H28N6O2S2Pd (Calc.: C, 45.6; H, 4.8; N, 14.5; S,
11.2. Found: C, 45.8; H, 5.1; N, 14.8; S, 11.2%).
eo ꢀ e
H2A
½H3Oþꢂ
þ
eo ¼ e
ꢀ Ka1
ð7Þ
ð8Þ
ð9Þ
H3A
[Pt(Ap4Et)(H Ap4Et)] (3) was prepared from the
2
1
eo ¼ eHA
þ
ðeH A ꢀ eoÞ½H3Oþꢂ
ꢀ
2
reaction of 1 (0.8 mmol) in ethanol (10 ml) with the
2ꢀ
Ka2
stock solution of PtCl4 (20 ml, 0.4 mmol). A stock
2ꢀ
1
PtCl4
solution was prepared by dissolving PtCl2
eo ¼ eA2ꢀ
þ
ðeHA ꢀ eoÞ½H3Oþꢂ
ꢀ
(2.66 g, 10 mmol) in concentrated HCl under reflux, fil-
tering to remove the turbidity caused by undissolved
material, neutralizing with Na2CO3 and diluting with
distilled water up to 250 mL (pH 6.0–6.5) to yield a so-
lution of 0.04 M Na2PtCl4. The pH of the reaction solu-
tion was adjusted to 9.0–10.0 with aqueous NEt3, and
the reaction mixture stirred for 3 days at room temper-
ature. The yellow powder was filtered off, washed with
cold ethanol and ether and dried as above; decomposi-
tion point 222 ꢁC, yield 60%. IR(KBr): 1581 m(C‚N),
1561 m(C‚N), 811 m(C‚S), 748 m(C–S), 479 m(Pt–N),
352 and 339 m(Pt–S), 442 m(Pt–O); Elemental analyses
are consistent with C22H28N6O2S2Pt (Calc.: C, 39.6; H,
4.3; N, 12.6; S, 9.6. Found: C, 40.0; H, 4.2; N, 11.9; S,
10.6%). Slow evaporation of dilute DMF solutions of
2 and 3 provided yellow crystals suitable for X-ray struc-
tural analysis.
Ka3
respectively [10]. These relationships are useful to find
the concentration dissociation constants of the ligand.
2.3. X-ray crystallography
Yellow crystals of 2 and 3 were mounted on glass fi-
bers and used for data collection. Cell constants and an
orientation matrix for data collection were obtained by
least-squares refinement of 25 reflections in the range
8.919 < h < 16.162ꢁ with a Nonius MACH3 diffracto-
meter for 2 and 21 reflections in the range of
9.73 < h < 11.58ꢁ on a Bruker-P4 diffractometer for 3.
Data were collected at room temperature using the x-
˚
scan technique with Mo Ka radiation (x = 0.71073 A)
at 293 K, corrected for Lorentz and polarization effects,
and empirical absorption corrections (x-scans for 2 and
DIFABS for 3) were made [16]. The structures were
solved by direct methods and subsequent difference
Fourier maps, and refined on F2 by a full-matrix least-
squares procedure using anisotropic displacement
parameters [17]. Hydrogen atoms were located in their
3. Results and discussion
3.1. Dissociation constants
˚
calculated positions (C–H 0.93–0.97 A) and were refined
The concentration dissociation constants of 1 were
determined and the 95% confidence limits of their log-
arithms were found to be equal to pKa1 = 1.75 0.02,
pKa2 = 8.81 0.04 and pKa3 = 12.96 0.01. pKa1 is as-
signed to the dissociation of the protonated Tsc moi-
ety by comparison with protonated thiosemicarbazide,
pKa = 1.70–1.87 [20], pKa2 to the hydroxyl group by
comparison with acetylphenol, pKa = 9.89–9.94 [20]
and pKa3 to the thiol/thioamide group. The replace-
ment of the N(2)-hydrogen in a Tsc moiety by a me-
thyl group prevents the observation of the third
dissociation constant adding credence to our assign-
ment [21]. The relative standard deviation of the
slopes, their confidence limits, the correlation coeffi-
cients, the analytical wavelengths and the pKas of
the above relationships are shown in Table 1. In
aqueous solutions in the pH region from 1.62 to
12.81, there are four independent species (i.e., H3A+,
H2A, HAꢀ and A2ꢀ) and two of them are shown
by the electronic absorption spectra in Fig. 1.
using a riding model. The O–H and N–H hydrogen
atoms were initially positioned at site determined from
difference maps and allowed to refine using, respectively,
the AFIX-148 and AFIX-48 controls in SHELXL-97.
Atomic scattering factors are from ‘‘International
Tables for X-ray Crystallography’’ [18]. Drawings were
made using PLATON [19].
2.4. Preparation of compounds
H2Ap4Et (1) was prepared by reacting equimolar
amounts of 2-hydroxyacetophenone (2 mmol) and ethyl
thiosemicarbazide (2 mmol) in 10 ml methanol as de-
scribed in the literature [8].
[Pd(Ap4Et)(H2ApEt)] (2) was synthesized by react-
ing 1 (0.8 mmol) in 10 methanol with an aqueous solu-
tion of K2PdCl4 (0.4 mmol). The pH of the solution
was adjusted to 9.0–9.5 by addition of aqueous NH3
and the reaction mixture stirred for 24 h at room tem-

4116
L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
Table 1
Analytical parameters of calibration graphs for acid–base properties of 1
RSD of slope (%)
Confidence limit of slope
Correlation coefficient
Wavelength k (nm)
pKa
2.87
3.28
4.66
ꢀ1.79 · 102 8.10 · 10ꢀ4a
6.51 · 108 7.30 · 107b
ꢀ9.20 · 1012 1.48 · 1010c
0.9989
0.9934
0.9999
287
308
285
pKa1 = 1.79
pKa2 = 8.81
pKa3 = 12.96
a
n = 9.
n = 9.
n = 7.
b
c
3.2. Synthesis
The interaction of K2PdCl4 and H2PtCl4 with 1 in ba-
sic solution (pH ca. 9) and 1:2 molar ratio afforded the
complexes 2 and 3, Scheme 1.
However, two other complexes have been obtained
by the reaction of Li2PdCl4 in methanol or aqueous
K2PdCl4 with 1 by using different molar ratios and
changing the pH. The mononuclear complex [Pd(HA-
p4Et)Cl] is prepared in methanol (1:1 molar ratio) and
[Pd(Ap4Et)]3 in the pH range of 9–10 (1:1 molar ratio).
[Pd(Ap4Et)]3 can also be formed from the monomer on
dissolution in DMF or directly from Li2PdCl4 and 1 in
methanol–ammonia solution [8]. When Na2PtCl4 reacts
with 1 in methanol or aqueous solutions using different
molar ratios and pH values, 3 is the only product
formed.
Fig. 2. ORTEP diagram of 2 with the labeling scheme.
3.3. Molecular structures
Perspective views of 2 and 3 with the atomic number-
ing schemes are shown in Figs. 2 and 3, respectively and
crystal data are given in Table 2, together with refine-
ment details. Selected bond distances and angles are
listed in Table 3.
The ligands are not equivalent, one being dianionic
and tridentate with O,N,S donation; the other ligand
is neutral and monodentate using only the sulfur atom,
S(2), to coordinate to the metal. The coordination envi-
ronment, MONSS, is essentially planar with a maximum
˚
deviation from the least-squares plane of 0.058(2) A
˚
for N(22) and 0.060(1) A for N(21) for 2 and 3, res-
pectively. The dianionic, tridentate ligand has a ZEZ
Fig. 3. ORTEP diagram of 3 with the labeling scheme.
CH3
70 CH3
H
N
NHC2H5
HO
N
N
NHC2H5
7
5
S
Li2PdCl4/MeOH
/H2O/MeOH
N
4
3
8
M
6
1
O
2
H2PtCl4
S
2
S
OH
NHC2H5
N
N
H
H3C
Scheme 1. The reaction path for the synthesis of 2 and 3.

L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
4117
Table 2
Crystal data, data collection and structure refinement
Compound
2
3
Formula
C22H28N6O2PdS2
579.02
triclinic
C22H28N6O2PtS2
665.70
triclinic
Formula weight
Crystal system
Space group
ꢀ
ꢀ
P1
7.2792(8)
P1
7.336(2)
˚
a (A)
˚
b (A)
13.475(3)
13.506(2)
13.508(2)
13.567(2)
73.350(10)ꢁ
74.5900(10)ꢁ
83.380(10)ꢁ
1240.6(4)
2
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
73.607(19)ꢁ
83.608(13)ꢁ
75.251(13)ꢁ
1227.9(4)
3
˚
V (A )
Z
2
1.566
Dx (g cmꢀ3
F(000)
l (mmꢀ1
Crystal size (mm)
)
1.782
652
5.854
592
0.957
)
0.20 · 0.25 · 0.10
3.96–24.64
8 6 h 6 0
ꢀ15 6 k 6 15
ꢀ15 6 l 6 15
4448
0.20 · 0.10 · 0.15
1.93–25.00
0 6 h 6 8
ꢀ14 6 k 6 14
ꢀ14 6 l 6 14
4555
h range (ꢁ)
hkl Range
Reflections collected
Reflections unique (Rint
)
4093 (0.1014])
4093/0/299
0.0031(18)
R1 = 0.0546, wR2 = 0.1050
R1 = 0.1884, wR2 = 0.1615
0.944
4216 (0.0377)
4216/0/299
Data/restraints/parameters
Extinction coefficient
Final R indices
R1 = 0.0434, wR2 = 0.0978
R1 = 0.0583, wR2 = 0.1050
1.033
R indices (all data)
Goodness-of-fit
ꢀ3
˚
max/min Dq (e A
)
0.031 and ꢀ0.029
0.836 and ꢀ1.049
Table 3
˚
Selected bond distances (A) and angles (ꢁ) for 2 and 3
2
3
Pd(1)–N(21)
Pd(1)–O(21)
Pd(1)–S(2)
1.9681(14)
Pt(1)–N(21)
Pt(1)–O(21)
Pt(1)–S(2)
2.007(6)
2.008(6)
2.238(2)
2.317(2)
1.711(9)
1.771(10)
1.358(11)
1.329(9)
1.297(10)
1.377(9)
1.350(10)
1.311(10)
1.462(11)
1.298(10)
1.400(9)
1.278(12)
1.366(11)
1.456(12)
1.9946(15)
2.2281(15)
2.3213(14)
1.6582(14)
1.7346(15)
1.3528(14)
1.3596(15)
1.2284(14)
1.4096(14)
1.3431(14)
1.3514(15)
1.4528(14)
1.2876(15)
1.4206(14)
1.3281(15)
1.3612(15)
1.3938(15)
Pd(1)–S(1)
S(1)–C(18)
S(2)–C(28)
Pt(1)–S(1)
S(1)–C(18)
S(2)–C(28)
O(11)–C(11)
O(21)–C(21)
N(11)–C(17)
N(11)–N(12)
N(12)–C(18)
N(13)–C(18)
N(13)–C(19)
N(21)–C(27)
N(21)–N(22)
N(22)–C(28)
N(23)–C(28)
N(23)–C(29)
O(11)–C(11)
O(21)–C(21)
N(11)–C(17)
N(11)–N(12)
C(18)–N(12)
C(18)–N(13)
N(13)–C(19)
N(21)–C(27)
N(21)–N(22)
N(22)–C(28)
N(23)–C(28)
N(23)–C(29)
N(21)–Pd(1)–O(21)
N(21)–Pd(1)–S(2)
O(21)–Pd(1)–S(2)
N(21)–Pd(1)–S(1)
O(21)–Pd(1)–S(1)
S(2)–Pd(1)–S(1)
92.46(2)
87.65(2)
N(21)–Pt(1)–O(21)
N(21)–Pt(1)–S(2)
O(21)–Pt(1)–S(2)
N(21)–Pt(1)–S(1)
O(21)–Pt(1)–S(1)
S(2)–Pt(1)–S(1)
93.4(2)
86.4(2)
178.335(7)
173.897(7)
91.43(2)
178.40(18)
174.4(2)
90.33(17)
90.00(9)
88.599(19)

4118
L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
configuration based on the C(11)–C(16), N(12)–C(17)
and N(13)–C(10) bonds, while the monodentate ligand
shows an EEZ configuration with respect to the same
bonds. These structures with tridentate/monodentate
bonding, rather than bis-bidentate, result from the pref-
erential binding of sulfur over nitrogen to palladium(II)
and platinum(II), the high stability of the tricyclic ring
system of the tridentate ligand and the tendency of the
ligands to retain planar structures. The ligand planarity
is indicated by the dihedral angle between the mean
planes of the phenol ring and M–S–C–N–N and the
mean planes of the phenol ring and the M–N–C–C–C–
O, 2.89(2) and 0.69(2)ꢁ, respectively, for 2 and 4.24(2)
and 2.86(2)ꢁ for 3. The negative charge of the dianionic
ligand is delocalized over the Tsc moiety and the S–C
bond distances are consistent with increased single bond
character, while the imine C–N distances and both thio-
amide C–N distances indicate considerable double bond
character (Table 2). The S–C bond distances for the
monodentate ligand are consistent with double bond
character, indicating a neutral molecule in the thione
form, protonated on N(13). The bond distances
O(21)–C(21) and O(11)–C(11) are indicative of a single
bond, shortened by the neighborhoods of the phenyl
ring, as expected for protonated O(11) and metallated
O(21) oxygens (Table 3). The M–O, M–N and M–S
bond distances are similar to those found in other palla-
dium(II) and platinum(II) complexes [9,22]. The mono-
mers of 2 and 3 form hydrogen-bonded dimers linked by
two N(14)–Hꢁ ꢁ ꢁS(2) hydrogen bonds, involving the
N(14)H hydrogen atom of the monodentate ligand
and the adjacent sulfur atom S(2) of the tridentate lig-
ands and vice versa of centro-symmetrically related pairs
of molecules. The observed hydrogen-bonding pattern is
Fig. 4. Intra- and intermolecular hydrogen bonds of 3.
of the DA = AD type. N(13)–H intramolecularly hydro-
gen bonds to coordinated O(21) and intermolecularly to
S(2) in 2 and 3 (Fig. 4).
The crystal packing is determined by C–H fi p inter-
actions, which are listed in Table 4 and shown in the
packing diagram in Fig. 5.
3.4. Spectroscopy
1
The H NMR spectrum of 1 shows two signals for
OH, 10.77, 12.60 ppm, and NH, 8.63, 8.33 ppm, which
is consistent with about one-third of the mixture being
the O–Hꢁ ꢁ ꢁN hydrogen bonding isomer [11–13]. Two
sets of peaks are also present for a number of the hydro-
gen and carbon atoms of 1 consistent with two isomers
and 2 and 3 also show two sets of peaks because of dif-
Table 4
Intra- and intermolecular hydrogen bonding and C–H–p stacking interactions for 2 and 3a
2
3
Donor D
Acceptor A
H ꢁ ꢁ ꢁ A
2.246
D ꢁ ꢁ ꢁ A
D-H ꢁ ꢁ ꢁ A
Donor D
AcceptorA
H ꢁ ꢁ ꢁ A
D ꢁ ꢁ ꢁ A
D–H ꢁ ꢁ ꢁ A
N(13)
N(14)
N(14)
C(12)
C(15)
O(21)
N(12)
S(2)i
O(11)ii
O(21)iii
2.746(4)
2.682(4)
3.488(3)
3.471(4)
3.439(5)
121.61
104.31
140.69
161.78
161.37
O(11)
N(13)
N(14)
N(14)
C(110)
C(15)
N(12)
O(21)
N(12)
S(2)xi
S(2)xii
O(21)iii
2.1020
2.3564
2.2324
2.7845
2.8161
2.6707
2.613(11)
2.801(9)
2.639(11)
3.515(8)
3.667(13)
3.103(10)
148.50
120.81
105.59
136.29
148.28
107.50
2.3365
2.7795
2.5756
2.5448
H ꢁ ꢁ ꢁ Cg
2.981
2.886
X ꢁ ꢁ ꢁ Cg
3.889
3.832
3.836
3.597
3.666
C–H ꢁ ꢁ ꢁ Cg
158.18
168.93
H ꢁ ꢁ ꢁ Cg
2.986
2.997
X ꢁ ꢁ ꢁ Cg
3.851
3.914
3.717
3.848
3.621
C–H ꢁ ꢁ ꢁ Cg
150.42
159.98
C(110)
C(210)
C(270)
C(270)
C(29)
Cg(3)iv
Cg(3)v
Cg(2)vi
Cg(1)vii
Cg(4)vii
C(110)
C(210)
C(270)
C(270)
C(29)
Cg(3)iv
Cg(3)viii
Cg(1)ix
Cg(2)x
Cg(4)ix
3.008
2.708
2.783
145.32
154.18
151.70
2.926
2.932
2.709
140.50
159.91
156.92
Symmetry operations; i: 1ꢀx, ꢀy, ꢀ1ꢀz; ii: 2ꢀx, ꢀ1ꢀy, ꢀ1ꢀz; iii: 1 + x, y, z; iv: ꢀ1 + x, y, z; v: ꢀ1 + x, 1 + y, z; vi: 1ꢀx, ꢀy, ꢀz; vii: ꢀx, ꢀy, ꢀz;
viii: 1 + x, y, 1 + z; ix: ꢀ1ꢀx, 2ꢀy, 1ꢀz; x: ꢀx, 2ꢀy, 1ꢀz; xi: ꢀx, 1ꢀy, 1ꢀz; xii: ꢀ1ꢀx, 1ꢀy, 1ꢀz.
a
Cg(1) and Cg(2) are the centroids of the rings M(1)–S(2)–N(22) N(23) and M(1)–O(21) N(22)–C(21)–C(26)–C(27), respectively, where M is Pd or
Pt; Cg(3) and Cg(4) are the centroids of the phenyl rings C(11)–C(12)–C(13)–C(14)–C(15)–C(16) and C(21)–C(22)–C(23)–C(24)–C(25)–C(26),
respectively.

L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
4119
Fig. 5. A view of the extended network of the intermolecular hydrogen bonds in 2 along the b axes.
1
ferent bonding of the ligands. Comparison of the H
NMR spectra of 2 and 3 with the spectrum of 1 shows
small upfield shifts for C(3)H, C(4)H and C(5)H, indi-
cating increased electron density at these sites on com-
plexation. These shifts, as well as downfield shifts for
C(2)H and C(70)H3, result from coordination of the
phenoxy oxygen and imine nitrogen atoms. Downfield
shifts are also observed for the imine carbon, C(7) indi-
cating decreased electron density on coordination. How-
ever, C(8) is shifted upfield considerably in the spectra of
2 and 3 due to greater back p-bonding for thiolato func-
tion than the imine function.
The electronic absorption spectra of 1–3 exhibit
bands at ca. 300 and 330 nm and of 2–3 do have a shoul-
der at 400–420 nm. The absorptions in the ultraviolet re-
gion are assignable to transitions within the ligand
orbitals and that in the visible region is probably due
to charge transfer transition involving metal and ligand
Fig. 6. Cyclic voltammograms (100 mV sꢀ1) of 1–3 in DMF (1.0 mM) in the range +2.0–2.0 V. The quoted potentials are vs. ferrocene/ferrocenium.

4120
L. Papathanasis et al. / Inorganica Chimica Acta 357 (2004) 4113–4120
orbitals [22]. For a better understanding of the nature of
the transition in the visible region, qualitative EHMO
calculations have been performed using the crystallo-
graphic coordinates for 2 and 3. The highest occupied
molecular orbital (HOMO) of 2 is composed of dxz,
dyz and dx2-y2 orbitals from palladium and the HOMO
of 3 has a major contribution from the dxz, dyz and
dxy orbitals from platinum. The lowest unoccupied mo-
lecular orbital (LUMO) of 2 and 3 is entirely localized
on different parts of the thiosemicarbazone ligands.
The HOMO energy is isolated, suggesting that the as-
signment of the lowest energy electronic transition can
be assigned to the computed HOMO-LUMO. Hence,
the absorption in the visible region may be assigned to
charge transfer transition occurring from the filled d or-
bitals of palladium or platinum to the vacant p* orbitals
of the thiosemicarbazone ligands.
Committee of University of Ioannina, Professor S. Dak-
aris, for in part funding of this research.
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