Synthesis, solution and spectral studies of palladium(II) complexes with 2-hydroxyacetophenone N(3)-propylthiosemicarbazone. Crystal structure of a tripalladium complex

Article abstract of DOI:10.1016/S0020-1693(02)00710-7

The reactions of palladium(II) salts with 2-hydroxyacetophenone N(3)-propylthiosemicarbazone, H₂Ap3Pr, are described. The synthesis and spectral characterization of a new triangular, trinuclear palladium(II) complex with the dianion, Ap3Pr^2-, are reported. The X-ray crystal structure determination of [Pd(Ap3Pr₂)]₃·DMF shows it to contain a chair-form hexagon of alternating Pd and S atoms to form a molecular bowl. The spectrophotometric characterization of H₂Ap3Pr is also reported.

Full text of DOI:10.1016/S0020-1693(02)00710-7

Inorganica Chimica Acta 332 (2002) 204–209
www.elsevier.com/locate/ica
Note
Synthesis, solution and spectral studies of palladium(II) complexes
with 2-hydroxyacetophenone N(3)-propylthiosemicarbazone.
Crystal structure of a tripalladium complex
Paras N. Yadav a, Mavroudis A. Demertzis a,*, Dimitra Kovala-Demertzi a,*,
Alfonso Castineiras b, Douglas X. West c
a Inorganic and Analytical Chemistry, Department of Chemistry, Uni6ersity of Ioannina, 45110 Ioannina, Greece
b Departamento de Qu´ımica Inorga´nica, Uni6ersidad de Santiago de Compostela, E-15706 Santiago de Compostela, Spain
c Department of Chemistry 351700, Uni6ersity of Washington, Seattle, WA 98195-1700, USA
Received 11 July 2001; accepted 12 December 2001
Abstract
The reactions of palladium(II) salts with 2-hydroxyacetophenone N(3)-propylthiosemicarbazone, H2Ap3Pr, are described. The
synthesis and spectral characterization of a new triangular, trinuclear palladium(II) complex with the dianion, Ap3Pr2−, are
reported. The X-ray crystal structure determination of [Pd(Ap3Pr2)]3·DMF shows it to contain a chair-form hexagon of
alternating Pd and S atoms to form a molecular bowl. The spectrophotometric characterization of H2Ap3Pr is also reported.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Trinuclear triangulo palladium (II); 2-Hydroxyacetophenone N(3) propylthiosemicarbazone; One-dimensional extended network;
Crystal structures; Dissociation constants
as a homogeneous catalyst in a large number of or-
ganic synthese [7]. Structures of both triangular and
linear trinuclear palladium(II) complexes have been
determined and have been reviewed [8]. For the Group
10 metals Ni, Pd, and Pt, M3 triangulo clusters do not
just act as building blocks for larger cluster com-
pounds, but in addition they display a broad chem-
istry which increases on descending the triad [8,9].
Palladium compounds were found to exhibit poten-
tially interesting biological activity [10]. Also, palladiu-
1. Introduction
Thiosemicarbazones of salicylaldehyde and 2-hy-
droxyacetophenone have recently attracted consider-
able attention because of their potential biological
properties [1] and catalytic activity [2]. Binuclear cop-
per(II) and nickel(II) [3] complexes of these types of
N(3)-substituted thiosemicarbazones have phenoxy
bridging based on spectral and structural characteriza-
tion. Recently, two trinuclear palladium complexes [4]
with sulfur bridging and a trinuclear nickel(II) com-
plex with both NiꢀO,OꢀNi and NiꢀS,OꢀNi bridging
patterns have been reported [5]. Palladium, in the form
of the metal, as well as mononuclear and trinuclear
compounds, is one of the best catalysts for a whole
host of reactions [6]. For example, palladium acetate,
Pd3(m-OAc)6, a trinuclear with a triangular arrange-
ment of acetato bridged palladium atoms, is employed
m(II)
complexes
of
2-formylpyridine
and
2-acetylpyridine N(4)-substituted thiosemicarbazones
have been studied with regard to their structural and
biological properties, and some of them have shown
remarkable antitumor activity [10]. Therefore, we con-
tinue to expand our studies of palladium(II) complexes
to include other potentially tridentate thiosemicarba-
zone ligands and report here the structure of a trinu-
clear palladium(II) complex of 2-hydroxyacetophenone
N(3)-propylthiosemicarbazone,
[Pd(Ap4Pr2)]3·DMF,
* Corresponding authors. Fax: +30-651-44825.
E-mail address: dkovala@cc.uoi.gr (D. Kovala-Demertzi).
which has PdꢀSꢀPd bridging.
0020-1693/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0020-1693(02)00710-7

P.N. Yada6 et al. / Inorganica Chimica Acta 332 (2002) 204–209
205
2. Experimental
mixture was stirred for 24 h at room temperature (r.t.),
and the resulting orange powder was filtered, washed
with methanol followed by ether and dried in vacuo
over silica gel. Calc. for [Pd(HAp3Pr)Cl]: C, 36.75; H,
4.11; Cl, 9.04; N, 10.7. Found: C, 36.50; H, 4.02; Cl,
9.40, N, 10.52%, m.p. 235 °C; yield: 78%.
2.1. Syntheses
Solvents were purified and dried according to stan-
dard procedures.
2.1.3. [Pd(Ap3Pr)]3 (3)
2.1.1. 2-hydroxyacetophenone
[Pd(Ap3Pr)]3 was prepared from the reaction of
K2PdCl4 (1 mmol) and H2Ap3Pr (1 mmol) in 25 ml of
H2O, by adjusting the pH of the reaction to approxi-
mately 9.5 with drops of a 1.0 M NH3 solution. Calc.
for [Pd(Ap3Pr)]3: C, 40.52; H, 4.25; N, 11.81. Found:
C, 40.20; H, 4.30; N, 12.20%; m.p.\300 °C; yield:
84%.
N(3)-propylthiosemicarbazone, H2Ap3Pr (1)
H2Ap3Pr was prepared by reacting equimolar
amounts of 2-hydroxyacetophenone (2 mmol), hydra-
zine hydrate (2 mmol) and propylisothiocyanate (2
mmol) in 10 ml methanol. The bright yellow powder
was filtrated and washed with cold methanol and dried
in 6acuo under silica gel at 50 °C for 1 h, yield 35%;
melting point (m.p.) 195 °C.
2.1.4. [Pd(Ap3Pr)]3·DMF (4)
2.1.2. [Pd(HAp3Pr)Cl] (2)
Slow evaporation of dimethylformamide solutions of
either 2 or 3 gives orange–brown crystals of the com-
plex [Pd(Ap3Pr)]3·DMF, 4, suitable for X-ray structural
analysis.
[Pd(HAp3Pr)Cl] was prepared by reacting lithium
tetrachloropalladate (1.2 mmol) prepared in situ from
palladium chloride and lithium chloride in methanol
and H2Ap3Pr (1 mmol) in methanol. The reaction
2.2. Physical measurements
Table 1
Crystal data and structure refinement for [Pd(Ap3P)]3·DMF
Infrared (IR) and far-IR spectra were recorded on a
Perkin–Elmer Spectrum GX FT-IR spectrophotometer
using KBr (4000–400 cm−1) and polyethylene pellets
(400–40 cm−1). Electronic spectra were recorded on a
JASCO V-570 spectrophotometer UV–VIS–NIR.
[Pd(Ap3P)]3DMF
Empirical formula
Formula weight
Temperature (K)
C39H52N10O4Pd3S3
1140.29
293(2)
,
Wavelength (A)
0.71073
triclinic
Crystal system
Space group
2.3. Structure determination
(
P1 (no. 2)
Unit cell dimensions
A yellow, prismatic crystal of [Pd3(Ap3Pr)3]·DMF
was mounted on a glass fiber and used for data collec-
tion. Cell constants and an orientation matrix for data
collection were obtained by least-squares refinement of
the diffraction data from 25 reflections in the range of
6.93BqB14.13° in a Enraf Nonius MACH3 auto-
matic diffractometer [11,11a]. Data were collected at
,
a (A)
9.682(7)
15.815(5)
16.069(6)
98.06(3)
101.27(4)
107.12(5)
2254(2)
2
1.680
1.374
1148
0.20×0.20×0.20
1.32–27.47
05h512, −205k519,
−205l520
10956/10338 [Rint=0.0318]
100.0
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
V (A )
3
,
Z
Dcalc (Mg m3)
293 K using Mo Ka radiation (u=0.71073 A) and the
,
Absorption coefficient (mm−1
F(000)
)
ꢀ-scan technique, and corrected for Lorentz and polar-
ization effects (Lp) [11b]. A semi-empirical absorption
correction („-scans) was made [11c] The structure was
solved by direct methods [11d] and subsequent differ-
ence Fourier maps, and refined on F2 by a full-matrix
least-squares procedure using anisotropic displacement
parameters [11e]. One of the propyl groups
(C29ꢀC210ꢀC211) showed disorder. All hydrogen
atoms were located in their calculated positions (CꢀH,
Crystal size (mm)
q Range for data collection (°)
Index ranges
Reflections collected/unique
Completeness to 2q=27.47 (%)
Absorption correction
Max/min transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F
Final R indices [I\2|(I)]
R indices (all data)
Largest difference peak and hole 0.826 and −1.195
„-scans
0.775, 0.570
full-matrix least-squares on F2
10338/0/537
,
0.93–0.97 A) and were refined using a riding model.
‚
2
1.007
Atomic scattering factors from ‘International Tables
for X-ray Crystallography’ [11f]. Molecular graphics
are from PLATON98 [11g] and a summary of the crystal
data, experimental details and refinement results are
listed in Table 1.
R1=0.0397, wR2=0.0989
R1=0.0671, wR2=0.1106
−3
,
(e A
)

206
P.N. Yada6 et al. / Inorganica Chimica Acta 332 (2002) 204–209
with dissociative hydrogens, which undergo two depro-
tonation steps as a function of pH. In addition,
H2Ap3Pr, is also susceptible to a single protonation.
Therefore, in aqueous solutions there are four indepen-
dent species (i.e., H3A+, H2A, HA− and A2−) properly
shown by separate absorption spectra of the conjugate
acid–base pairs. Fig. 1 is an example of the pair
H3A+–H2A. Thus, there are three separate dissociation
steps given by Eqs. (1)–(3):
Scheme 1.
K
a1
H3A++H2O X H2A+H3O+
(1)
(2)
(3)
K
a2
H2A+H2O X HA−+H3O+
K
a3
HA−+H2O X A2− +H3O+
The law of mass-action for these equations, based on
the molar absorptivities of the various species, takes the
form:
mH A+ −mo
Ka1=[H3O+]
Ka2=[H3O+]
Ka3=[H3O+]
(4)
(5)
(6)
3
mo−mH A
2
mH A−mo
2
mo−mHA
−
Fig. 1. Absorption spectra of the conjugate H3A+–H2A pair in the
pH region 1.36–6.58.
mHA− −mo
mo−mA
2−
respectively. The terms mo, m 2−, m −, mH A and mH A
+
2.4. Dissociation constants
A
HA
2
are the molar absorptivities of the observed soluti3on,
doubly negative ionized, singly negative ionized, molec-
ular and positively charged species, respectively. In
order to find the dissociation constants, the values of
the molar absorptivities must be experimentally deter-
mined. However, in this particular instance a direct
application of relationships (Eqs. (4) and (6)) for Ka1
Due to the low solubility of H2Ap3Pr, as well as its
high ka1 and low ka3 values, spectrophotometry was
used to study the dissociation constants. Aqueous
H2Ap3Pr 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
determine dissociation constants by a methology re-
ported previously [12]. A 1×10−4 M stock solution of
H2Ap3Pr was initially prepared by suspending in a
water bath the appropriate amount of the compound in
0.01 M KOH until dissolution occurred, cooling to r.t.,
filling the flask to the required volume with 0.01 M
KOH solution and mixing thoroughly. Exactly 5.0×
10−5 M working ligand solutions, having different
H3O+ ion concentrations and constant ionic strength
(v=0.1), where 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-
sonal computer and a Methrom 691 pH-meter.
and Ka3 determination is impossible, since mH A and
+
3
mA
2−
cannot be determined in solutions with ionic
strength equal to 0.1. Ideally, A2− and H3A+ predom-
inate at very high alkaline or very low acid solutions,
respectively. Perhaps the equilibrium steps (2) and (3)
occur to an extent simultaneously, and the value of the
common species HA− cannot also be determined di-
rectly from absorption spectra. Therefore, instead of
using relationships (Eqs. (4)–(6) it is expedient to use a
proper rearrangement of them in the form:
mo−mH A
2
mo=mH A+ −Ka1
(7)
(8)
(9)
[H3O+]
3
1
Ka2
mo=mHA
+
(mH A−mo)[H3O+]
−
2
1
Ka3
mo=mA
+
(mHA− −mo)[H3O+]
2−
3. Results and discussion
respectively, [13]. These relationships are useful to find
the concentration dissociation constants of the ligand.
The relative standard deviation (R.S.D.) of the slopes,
their confidence limits, the correlation coefficients, the
analytical wavelengths and the pKa of the above rela-
tionships are shown in Table 2.
3.1. Concentration dissociation constants
2-Hydroxyacetophenone N(3)-propylthiosemicarba-
zone, H2Ap3Pr, Scheme 1, designated in this paragraph
as H2A, possesses two function groups, ꢀNH and ꢀOH,

P.N. Yada6 et al. / Inorganica Chimica Acta 332 (2002) 204–209
207
Table 2
Analytical parameters of calibration graphs for acid–base properties of H2Ap3Pr
Equation
R.S.D. of slope (%)
Confidence limit of slope
Correlation Coefficient
Analytical wavelength (nm)
pKa values
Eq. (7)
Eq. (8)
Eq. (9)
2.87
3.28
4.66
−1.64×10−291.11×10−3 a
6.89×10895.22×107 b
358×101394.29×1012 c
0.9971
0.9957
0.9946
247
306
280
pKa1=1.79
pKa2=8.84
pKa3=13.55
a n=9.
b n=10.
c n=7.
A good approach of confidence limit for the pKa
values is pKa1=1.7990.03, pKa2=8.8490.03 and
pKa3=13.5590.05. The first of them (pKa1=1.79) is
assigned to the dissociation of the protonated thiosemi-
carbazone moiety by comparison toprotonated
thiosemicarbazide, which has a value of 1.70–1.87 [14].
The second one (pKa2=8.84) is assigned to the hy-
droxyl group by comparison with acetylphenol, which
has a value of 9.89–9.94 [14] and the third value
(pKa3=13.55) to the thiol–thioamide group. The re-
placement of the N(2)-hydrogen by a methyl group
prevents the observation of the third dissociation con-
stant adding credence to our assignment [15].
view of [Pd(Ap4Pr)]3·DMF with the atomic numbering
scheme is shown in Fig. 2 and selected bond distances
and angles are listed in Table 3. The dianionic, triden-
tate ligand has a ZEZ configuration about the bonds
C11ꢀC16, N12ꢀC17 and N13ꢀC10 for the oxygen, ni-
trogen and sulfur donor centers. The whole structure
forms into a type of bowl with the (3Pdꢀ3S) ring as the
base. This type of core has been reported previously for
palladium complexes [4]. The core of 4 consists of a
six-membered ring of alternating Pd(II) and S atoms in
a chair configuration. The remaining two sites of each
square planar Pd(II) center are occupied by the imine
nitrogen and the phenoxy oxygen.
The distances between the palladium centers
[Pd(1)ꢀPd(2), 3.404(2); Pd(2)ꢀPd(3), 4.171(3); and
Pd(1)ꢀPd(3), 3.872(3) A] indicate that there is no direct
bond between the palladium atoms. However, a very
weak interaction can be postulated in agreement with
the reported values for polynuclear palladium com-
3.2. Molecular structure of [Pd(Ap3Pr)]3·DMF (4)
,
The interaction of K2PdCl4 with H2Ap4Pr in acid
and basic solution (pH ca. 4–9) afforded the mononu-
clear and trinuclear complexes 2–4 according to the
reactions:
,
plexes (2.549(2)–3.539(1) A) [8]. The three bond angles
K2PdCl4+H2Ap4Pr
“[Pd(HAp4Pr)Cl], 2+2KCl+2HCl
CH OH–H O–NH OH
3
2
4
3K2PdCl4+3H2Ap4Pr ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢁ [Pd(Ap4Pr)]3, 3
+6KCl+6HCl
’
[Pd(Ap4Pr)]3, 3+DMF“[Pd(Ap4Pr)]3 DMF, 4
’
[Pd(Ap4Pr)], 2+DMF“[Pd(Ap4Pr)]3 DMF, 4+HCl
The X-ray crystal structure of complex 4 shows it to
be a triangular, trinuclear complex with bridging
thiosemicarbazonato sulfur atoms. This species can be
formed from a monomer on dissolution in DMF, in
this case dimethylformamide promoted deprotonation
and aggregation. Alternatively, the same complex can
be synthesized directly from Li2PdCl4 and the thiosemi-
carbazone in methanol–ammonia solution. The stoi-
chiometry of the complexes indicates that palladium(II)
is coordinated by the doubly charged anion Ap4Pr2−
formed on the loss of the two protons from the pheno-
lic oxygen and thioamide nitrogen, N2.
The palladium complex
4 crystallizes with a
Fig. 2. Structural representation of [Pd(Ap3Pr)]3·DMF with the label-
dimethylformamide solvate molecule. A perspective
ing scheme; hydrogen atoms are omitted.

208
P.N. Yada6 et al. / Inorganica Chimica Acta 332 (2002) 204–209
Table 3
and the hydrogen on the N(24) atom, N(24)ꢀH(24).
Further, intramolecular and intermolecular hydrogen
bonds and CꢀH–p interactions [16] stabilize this
structure.
,
Selected bond lengths (A) and angles (°) for [Pd3(Ap3P)3]·DMF
Bond lengths
Pd(1)ꢀO(11)
Pd(1)ꢀN(12)
Pd(1)ꢀS(13)
Pd(1)ꢀS(21)
Pd(2)ꢀO(21)
Pd(2)ꢀN(22)
Pd(2)ꢀS(21)
Pd(2)ꢀS(32)
Pd(3)ꢀO(31)
Pd(3)ꢀN(32)
Pd(3)ꢀS(32)
Pd(3)ꢀS(13)
1.970(4)
2.009(3)
2.2251(18)
2.3282(14)
1.996(3)
3.3. Spectroscopy
The significant IR bands of H2Ap3Pr and the three
complexes of palladium(II) are close in energy to those
found in other compounds with tridentate coordination
[4,17]. The bands at 1595 and 1616 cm−1 are assigned
to w(CꢂN). Coordination of the azomethine nitrogens
causes w(CꢂN) to shift to lower frequencies by 20–40
cm−1 and a band at 453–459 cm−1 is assignable to
w(PdꢀN). Coordination 6ia the thiolato sulphurs is indi-
cated by a decrease in the frequency of the thioamide
IV band found at 821 cm−1 in H2Ap3Pr (80–100 to
720–740 cm−1) and also by the presence of a band
assignable to w(PdꢀS) at 380–429 cm−1. The phenolic
oxygen, on loss of the OH proton, occupies the third
coordination site. A band at 257–292 cm−1 range in
the spectra of the complexes is assignable to w(PdꢀO).
Complex 2 exhibits a strong band at 339 cm−1 at-
tributed to the w(PdꢀCl).
2.010(3)
2.2353(17)
2.3386(15)
1.985(3)
2.015(3)
2.251(2)
2.3154(12)
Bond angles
O(11)ꢀPd(1)ꢀN(12)
O(11)ꢀPd(1)ꢀS(13)
N(12)ꢀPd(1)ꢀS(13)
O(11)ꢀPd(1)ꢀS(21)
N(12)ꢀPd(1)ꢀS(21)
O(21)ꢀPd(2)ꢀN(22)
O(21)ꢀPd(2)ꢀS(21)
N(22)ꢀPd(2)ꢀS(21)
O(21)ꢀPd(2)ꢀS(32)
N(22)ꢀPd(2)ꢀS(32)
O(31)ꢀPd(3)ꢀN(32)
O(31)ꢀPd(3)ꢀS(32)
N(32)ꢀPd(3)ꢀS(32)
O(31)ꢀPd(3)ꢀS(13)
N(32)ꢀPd(3)ꢀS(13)
93.85(15)
177.56(14)
85.91(11)
90.54(12)
174.99(10)
92.55(14)
178.07(10)
86.26(12)
88.77(10)
173.57(10)
93.00(13)
170.05(13)
85.84(10)
85.92(10)
173.51(10)
1
The H NMR spectrum of H2Ap3Pr shows signals
2
for OH and NH at 10.83 and 8.79 ppm [16]. The peak
at 10.83 ppm is consistent with the presence of a
hydrogen bonding isomer (OH···N). The signals for OH
2
and NH are absent from the spectra of 3 and 4, as
involving bridging sulfur atoms are as follows:
Pd(1)ꢀS(21)ꢀPd(2), 96.44(6); Pd(2)ꢀS(32)ꢀPd(3),
130.65(6) and Pd(1)ꢀS(13)ꢀPd(3), 117.02(6)°. The PdꢀN
expected because of their loss on complex formation.
There is considerable shifting of the signals for the ring
protons in the spectra of the complexes compared with
their positions in H2Ap3Pr indicating coordination 6ia
the phenoxy oxygen. The loss of electron density on
,
bond distances range from 2.009(3) to 2.015(3) A, the
,
PdꢀO distances from 1.970(4) to 1.996(3) A and PdꢀS
3
,
distances from 2.2251(18) to 2.3386(15) A and are
complexation is most significant for the carbons CH,
6
4CH and CH; their protons show downfield shifts, and
similar to those found in other palladium complexes
[4,10]. The greater trans influence of the iminic nitro-
gens can be observed in the lengthening of the trans
5
an upfield shift occurs for CH. The small upfield shift
for 5CH, the ring hydrogen expected to be least affected
by coordination of the phenoxy oxygen and azomethine
nitrogen, is probably a result of p-back-bonding. The
,
PdꢀS distances (2.3154(12) to 2.3386(15) A) with re-
spect to the PdꢀS distances trans to the phenoxy oxy-
8
,
gens (2.2251(18)–2.251(2) A). The dihedral angles
large upfield of CH3, which occurs on coordination of
between the planes of the two chelate rings
(PdꢀSꢀCꢀNꢀN, A, and (PdꢀNꢀCꢀCꢀO), B, are
4.00(15), 4.59(15) and 5.46(17)° for Pd(1), Pd(2) and
Pd(3) indicating that there is deviation from planarity
by the ligands. The plane of A of Pd(1) is tilted by
89.99(14) and 59.37(14)° with respect to the plane A of
Pd(2) and Pd(3), respectively.
The negative charge of the dianionic ligand is delo-
calized over the thiosemicarbazonato moiety and the
SꢀC bond distances are consistent with increased single
bond character, while the imine CꢀN distances and
both thioamide CꢀN distances indicate considerable
double bond character. The dimethylformamide
molecule appears to be linked 6ia hydrogen bond. This
hydrogen bond involves O1 on dimethylformaimide
the azomethine nitrogen, may be due to p-back-bond-
ing by the palladium(II) to the p* orbital of the azome-
thine moieties.
The bands of the H2Ap3Pr at approximately 31 000
and 34 000 cm−1 are due to n“p* transitions of the
imine portion of the TSC moiety and the aromatic ring,
respectively [4,18]. The energies of these two bands are
affected by changes in organic solvents due to differ-
ences in the mode of hydrogen bonding. The band at
approximately 33 000 cm−1 is due to the n“p* transi-
tion of the thiosemicarbazone moiety (imine,
thioamide) and charge transfer involving the TSC moi-
ety (L“M). The maximum at 29 000 cm−1 is affected
by the nature of the solvent consistent with its assign-
ment as a charge transfer transition. The broad band at

P.N. Yada6 et al. / Inorganica Chimica Acta 332 (2002) 204–209
209
approximately 24 000–25 000 cm−1 is assignable to a
combination of sulfur“Pd(II), imine nitrogen“Pd(II)
charge transfer (L(p)“MCT) and Pd(II) d–d bands.
The maxima are affected by the nature of the solvent;
i.e. the L(p)“MCT band shifts to higher energy on
increase in the polar character of the solvent, and the
reverse occurs for the M“LCT band [4,17]. Labile and
polar solvents e.g. DMF, DMSO, MeCN, afford the
elimination of hydrogen chloride from 2 and slow
transformation within 24 h to 3, while no polar solvents
(e.g. CHCl3) affords the transformation of the trimer 3
to the monomer 2.
(e) A.C. Skapski, M. Smart, J. Chem. Soc., Chem. Commun.
(1970) 658.
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(b) D. Kovala-Demertzi, A. Domopoulou, M.A. Demertzis, A.
Papageorgiou, D.X. West, Polyhedron 16 (1997) 3625;
(c) D. Kovala-Demertzi, A. Domopoulou, G. Valle, M.A. De-
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4. Supplementary material
[11] (a) B.V. Nonius, CAD4. Express Software, Ver. 5.1/1.2, Enraf
Nonius, Delft, The Netherlands, 1994;
Crystallographic data for C39H52N10O4Pd3S3, CCDC
164884 have been deposited with the Cambridge Crys-
tallographic Data Center as supplementary publication
no. Copies of available material can be obtained, free
of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK, (fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or .www: http://
www.ccdc.cam.ac.uk).
(b) M. Kretschmar, GENHKL. Program for the reduction of CAD
4
Diffractometer data, University of Tuebingen, Germany, 1997;
(c) A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystal-
logr., Sect. A A24 (1968) 351;
(d) G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467;
(e) G.M. Sheldrick, SHELXL-97. Program for the Refinement of
Crystal Structures, University of Go¨ttingen, Germany, 1997;
(f) International Tables for X-ray Crystallography, vol. C,
Kluwer Academic Publishers, Dordrecht, The Netherlands, 1995;
(g) A.L. Spek, PLATON. A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 1998.
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(b) J.C. Miller, J.N. Miller, Statistics for Analytical Chemistry,
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