A model study of alternative approach toward a class of palladium(II) based self-assembly

Article abstract of DOI:10.1016/j.ica.2011.02.009

A different approach developed for the preparation of palladium(II) based complexes [(Pd(bpy))_x(L)_y](NO₃) _2x is modelled by using 4-phenylpyridine as ligand (L = 1). Various solvent systems are inspected to opti

Full text of DOI:10.1016/j.ica.2011.02.009

Inorganica Chimica Acta 372 (2011) 71–78
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A model study of alternative approach toward a class of palladium(II) based
self-assembly
⇑
Niladri Bihari Debata, V. Ramkumar, Dillip Kumar Chand
Department of Chemistry, Indian Institute of Technology Madras, Chennai 600036, Tamil Nadu, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 2 March 2011
A different approach developed for the preparation of palladium(II) based complexes [(Pd(bpy))x(L)y]-
(NO3)2x is modelled by using 4-phenylpyridine as ligand (L = 1). Various solvent systems are inspected to
optimize the reaction condition for the preparation of the model complex [Pd(bpy)(4-phenylpyridine)2]-
(NO3)2. The model complex is obtained quantitatively as a single product from a 1:1:2 mixture of Pd(NO3)2,
2,20-bipyridine and 4-phenylpyridine when stirred at room temperature in CH3CN:H2O (1:1). The same
reaction is performed in CD3CN:D2O (1:1) to monitor the progress of the reaction by recording 1H NMR.
The kinetic products that formed initially got self-healed to give the desired product with in 6 h. However,
in DMSO-d6 spontaneous arrangement leading to the targeted complex was observed and no kinetic prod-
uctcould bedetected. Whenasimilarreactionis performed with ethylenediamine instead of2,20-bipyridine
a mixture of compounds are observed. Theoretical calculation throws some light on the principle behind the
success of this method for the bpy based systems. The assembly, [Pd(bpy)(4-phenylpyridine)2](NO3)2 has
been characterised by NMR, ESI-MS and single-crystal X-ray diffraction methods.
Dedicated to Prof. S.S. Krishnamurthy.
Keywords:
Palladium
Self-assembly
Non-covalent interactions
One pot synthesis
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
Pd(bpy)(NO3)2 with a suitable ligand L is known to result the dis-
crete assembly [{Pd(bpy)}x(L)y](NO3)2x [5].
Synthesis of coordination cage molecules by metal mediated
self-assembly routes has received enormous attention during the
last two decades [1]. The number of metal centres in these resulting
assemblies is mainly attributed to the disposition and number of
binding sites in the ligand as well as preferred coordination geom-
etry of the metal. Among the metal centres being employed, the
diamagnetic palladium(II) deserves a unique place due to its almost
rigid square planar coordination geometry and moderately labile
metal–ligand interactions usually resulting in thermodynamically
controlled discrete products. A variety of molecular architectures
including 3-dimensional cavities are constructed by using either
Pd(II) salts [2] or partially protected Pd(II) components [3] and suit-
able ligands. The number of accepting sites around the metal centre
is lowered by blocking them with protecting units which com-
monly are bidentate and chelating in nature. Partially protected
Pd(II) components such as cis-Pd(XꢀX)(monoanion)2 are usually
complexed with chosen ligands to get the desired assemblies. How-
ever, in some cases mixture of two or more discrete products are
also possible whose ratio can be modulated by optimizing parame-
ters like concentration, solvent or guest molecules [4]. Classical
method for the complexation of a separately prepared sample of
A new method for the synthesis of [{Pd(bpy)}x(L)y](NO3)2x is
reported by us [6] where the cage molecules could be prepared
in a single step in one pot by combining bpy, Pd(NO3)2 and a
bidentate ligand in contrast to the multistep classical synthesis.
The method was validated by using two different bidentate li-
gands where the products formed by classical and one pot meth-
od are identical. In the present work we have tracked the
progress of one pot synthesis of the mononuclear model com-
plex [7] [Pd(bpy)(4-phenylpyridine)2](NO3)2 in order to compre-
hend the rationale behind the success of the one pot synthesis.
2. Results and discussion
2.1. One pot synthesis of the model complex [Pd(bpy)-
(4-phenylpyridine)2](NO3)2, 2: feasible
A mixture of Pd(NO3)2, bpy and ligand 1 at a ratio of 1:1:2 was
taken in CH3CN:H2O (1:1) medium and stirred overnight at room
temperature followed by evaporation of the solvents also at room
temperature using high vacuum. The isolated solid showed the for-
mation of 2 as a single compound (Scheme 1b) whose identity was
confirmed by comparing the 1H NMR and ESI-MS spectra of the
sample prepared by classical method (Scheme 1a) [7]. In compari-
son with one pot synthesis, the classical method of preparation
of 2 is a time consuming and multi-step process. In the classical
⇑
Corresponding author. Fax: +91 44 2257 4202.
E-mail address: dillip@iitm.ac.in (D.K. Chand).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.009

72
N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
Scheme 1. Synthesis of 2 by (a) classical method (Refs. [7] and [8]); (b) one pot synthesis (this work).
method bpy was added to a hot acetonitrile solution of PdCl2 to
prepare Pd(bpy)Cl2 which is also commercially available (Scheme
1a) [8]. The chloride anion of the isolated Pd(bpy)Cl2 was then ex-
changed with nitrate by adding AgNO3 in aq HNO3 at pH 1. Thus
formed Pd(bpy)(NO3)2 upon complexation with ligand 1 gave rise
to 2. The mass spectrum of 2 prepared by either method showed
identical peaks at m/z 286.1 corresponding to [2ꢀ2(NO3)]2+ formed
due to the loss of two nitrate anions. Single crystal of 2 further sup-
ported the formation of the compound. Comparison between clas-
sical and one pot method for the synthesis of 2 is given in Table 1.
Other solvent systems were tried to check the feasibility of the
reaction. In CH3OH reduction of Pd(II) was observed [9] where as in
CH3CN medium, precipitation of 4 (Fig. 1) was observed thus hin-
dering the progress of the reaction. When this reaction was tried in
H2O some amount of brown precipitate was observed. The aqueous
supernatant was found to contain majority of 4 along with 2 and
some other unidentified products. In case of CH3OH:H2O (1:1) as
the medium, reduction of Pd(II) was again observed. This suggests
the superiority of CH3CN:H2O as the best system for one pot
synthesis.
the complex 2 as a single product. ESI-MS for this reaction mixture
was recorded within 15 min of mixing which showed peaks at m/
z = 286.05 [2ꢀ2(NO3)]2+
,
363.12 [3ꢀ2(NO3)]2+ and 209.03
[4ꢀ2(NO3)]2+ corresponding to 2, 3 and 4, respectively for the loss
of two nitrate anions in each cases. To further support this fact for
the formation of 2 from 3 and 4, a reaction was performed between
equimolar ratio of 3 and 4 in CD3CN:D2O mixture (1:1). This mix-
ture gave rise to 2 within 6 h at room temperature which was mon-
itored by 1H NMR (Fig. 3).
1H NMR was recorded for a mixture of Pd(NO3)2, bpy and ligand
1 at a ratio of 1:1:2 in DMSO-d6, which showed spontaneous and
quantitative formation of 2. Thus the formation of targeted product
is found to be most facile in this solvent. However, practical diffi-
culty in isolation of the product from the high boiling solvent being
not attractive, the suggested solvent of choice for the reaction is a
mixture of CH3CN and H2O.
2.2. One pot synthesis of the model complex [Pd(en)(4-
phenylpyridine)2](NO3)2, 5: unfeasible
The complexation reaction was further conducted in
CD3CN:D2O mixture (1:1) so as to monitor the progress of the reac-
tion by recording 1H NMR spectra at different time interval. Ini-
tially 3, 4 and some other complexes were observed as kinetic
products along with the desired complex 2 (Figs. 1 and 2). Forma-
tion of 3 and 4 was confirmed by comparing the 1H NMR spectra of
the pure compounds recorded in CD3CN:D2O mixture (1:1). Within
6 h at room temperature all kinetic products disappeared making
When a similar reaction was tried for ‘‘en’’ instead of ‘‘bpy’’ in
the most favorable system i.e. DMSO-d6 at room temperature a
mixture of product was resulted as 5, 3 and 6 (Figs. 1 and 4). For-
mation of 5, 3 and 6 was confirmed by comparing the 1H NMR
spectra of the pure compounds in DMSO-d6. When ESI-MS for this
reaction mixture was recorded it showed peaks at m/z = 238.00
[5ꢀ2(NO3)]2+
,
363.05 [3ꢀ2(NO3)]2+
,
287.97 [6ꢀ(NO3)]+ and
113.00 [6ꢀ2(NO3)]2+ which informed the presence of all the three
compounds. Thus the one pot synthesis was found to be suitable
for bpy system and not for the en system as observed from the
study of the model complexes.
Table 1
Comparison between classical and one pot method for the synthesis of 2.
Method
Classical
Step
Time
Temperature (°C)
Yield (%)
2.3. Theoretical study to understand the feasibility of bpy system
versus unfeasibility of en system in one pot synthesis
1st
1 h
30 min
1 h
60
60
80
92
83
92a
95
2nd
3rd
one
Optimized structures were obtained at the B3LYP level of theory
and with 6-31G(d) basis set for C, H, N and Lanl2dz for Pd in gas
phase at 298.15 K (Fig. 5). Gibb’s free energy for formation of 2,
One pot
6 h
room temperature
a
Over all yield is 70%.

N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
73
Fig. 1. Complexes 2–6.
Fig. 2. 1H NMR spectra in CD3CN:D2O (1:1) monitored in the process of the preparation of 2 by one pot synthesis at various time (i) t = 6 min; (ii) t = 20 min; (iii) t = 6 h; (py
a
protons for 2 (green) and 3 (red); bpy 4 (pink)). (For interpretation of the references in colour in this figure legend, the reader is referred to the web version of this article.)
a
3, 4, 5 and 6 from Pd(NO3)2 with corresponding ligands are 163.2,
157.51, 182.3, 170.99 and -197.1 kcal molꢀ1, respectively, which
indicate that none of these complexations are spontaneous except
6 which is dedicated to chelation. Enthalpy of formation for 2, 3, 4,
2.4. X-ray crystal structure of the complexes 2–4
The crystal structures of 2 and 3 are reported in this work where
as that of 4 was reported earlier [11]. Single crystals of 2 were
grown by diffusing benzene to an acetonitrile solution of the com-
plex where as for the complex 3 tetrahydrofuran was diffused to an
acetonitrile solution of the complex. The structures were solved by
direct methods (SHELXL-97) and refined by full-matrix least squares
methods on F2 with 951 and 1566 parameters, respectively.
Perspective view of the complexes are given in Figs. 6 and 7 where
as the structural parameters and other details are collected in
Table 2. After solving the crystal structure of 2, a biphenyl kind
of molecule was also found in the lattice. Thus the crystallization
was performed by slow evaporation of water:acetonitrile (1:1)
mixture where the same crystal system was observed . It was fur-
ther supported by recording the 1H NMR of these crystals which
gave a clear idea about the free 4-phenylpyridine. During crystalli-
zation may be some amount of 4-phenylpyridine is dissociated
from the complex to give a clathrate compound. Important bond
distances and angles are given in Table 3 and 4 for crystal 2 and
3, respectively.
5 and 6 are 149.2, 54.73, 177.85, 157.14 and 192.35 kcal molꢀ1
,
respectively, which suggests the endothermic nature of all these
complexation reactions.
The overall free energy and enthalpy for the formation of 2
from 3 and 4 Eq. (1) is ꢀ6.705 kcal molꢀ1 (spontaneous) and
32.91 kcal molꢀ1 (endothermic), respectively where as for forma-
tion of 5 from 3 and 6 Eq. (2) the values are 190.785 kcal molꢀ1
(non-spontaneous) and 33.6 kcalmolꢀ1 (endothermic), respec-
tively. This indicates that the reaction shown in Eq. (1) is favour-
able which may facilitate the one pot synthesis.
3 þ 4 ! 2
3 þ 6 ! 5
ð1Þ
ð2Þ
Also, the log K1 and log K2 for the formation of [Pd(XꢀX)2]2+
complexes are 23.6 and 18.6 for (en) whereas, the values are
19.8 and 8.9 for (bpy) [10] indicating higher stability of 6 as com-
pared to 4.
The structure of 2 contains four cations of [Pd(bpy)(1)2]2+
and one 4-phenylpyridine on a centre of symmetry and two aceto-

74
N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
Fig. 3. 1H NMR spectra for combination of 3 and 4 in CD3CN:D2O (1:1) to generate 2 at verious time interval (i) t = 5 min; (ii) t = 10 min; (iii) t = 15 min; (iv) t = 30 min; (v)
t = 1 h; (vi) t = 2 h; (vii) t = 6 h; (py protons for 2 (green) and 3 (red); bpy 4 (pink)). (For interpretation of the references in colour in this figure legend, the reader is referred
a
a
to the web version of this article.)
Fig. 4. 1H NMR spectrum in DMSO-d6 for the preparation of 5 by one pot synthesis (py protons for 5 (green) and 3 (red); en NH2 for 6 (pink)). (For interpretation of the
a
references in colour in this figure legend, the reader is referred to the web version of this article.)
nitrile as well as two water molecules in the unit cell (Fig. 6). Eight
nitrate anions which corresponds to four Pd(II) are present in a unit
cell. Out of four cations units of Pd(II) each pair exist as crystallo-
graphically different species. Each Pd(II) ion adopts a square planar
geometry with Pd–N bond distances ranges from 2.002 to 2.024 Å.
The bite angle of 2,20-bipyridine with Pd(II) is 80.96° and 80.88° for
N4–Pd1–N3 and N7–Pd2–N6, respectively. Angle between two
pyridine units from 4-phenylpyridine attached to Pd(II) is 81.83°
and each ligand unit remains perpendicular to the square
plane of Pd(II). An acetonitrile molecule is distorted. There exist
There are twelve cation units [Pd(1)4]2+ in a unit cell for the
structure of 3 (Fig. 7). Twenty-four nitrate anions which corre-
sponds to twelve Pd(II) unit and eight water molecules are present
in a unit cell. There are three independent cation units of Pd(II)
which are crystallographically different. Each Pd(II) ion adopts a
square planar geometry with Pd–N bond distances ranges from
1.996 to 2.038 Å. Angle between two pyridine units from
4-phenylpyridine attached to Pd(II) is around 90° and each ligand
unit remains perpendicular to the square plane of Pd(II). The crys-
tal is stabilized by
stacking between 4-phenylpyridine of one cation unit with other
cation unit at a distance of 3.961 Å. There also exist a CHꢁꢁꢁ
interaction between 4-phenylpyridine of one cation unit with
pꢁꢁꢁ
p
and CHꢁꢁꢁ
p
interactions. There exist
pꢁꢁꢁ
p
p p
stacking between 2,20-bipyridine of one cation unit with
ꢁꢁꢁ
4-phenylpyridine of other cation unit of Pd(II) at a distance of
p
3.604 and 3.803 Å.

N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
75
Fig. 5. Optimised structures of the complexes 2–6.
Fig. 6. ORTEP diagram showing the complexed cation [Pd(bpy)(4-phenylpyridine)2]2+ (other fragments are omitted for clarity).
other cation unit at a distance of 3.761 Å. One of the nitrate has
short contact at a distance of 3.126 Å with the fifth coordination
site of Pd(II). Hydrogen bonding exist between oxygen of nitrate
and CH of 4-phenylpyridine. Oxygen of two different nitrates are
connected through hydrogen bonding with one water molecule.
As per the reported data [11] the geometry around Pd(II) in
[Pd(bpy)2](NO3)2, 4 is severely distorted from the square planar
geometry where the dihedral angle between the planes of the
two bpy unit is as large as 33° due to the steric repulsions making
it unfavourable.

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N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
Fig. 7. ORTEP diagram showing the complexed cation [Pd(4-phenylpyridine)4]2+ (other fragments are omitted for clarity).
Table 2
Crystal data and structure refinement parameters for 2 and 3.
Table 3
Compounds
2ꢁ1/4(C11H9N)ꢁ1/2(C2H3N)ꢁ
1/2(H2O)ꢁ3/2(O)
3ꢁ1/3ꢁ(H2OꢁO)
Selected bond lengths (Å) and bond angles (°) for 2ꢁ1/4(C11H9N)ꢁ1/2(C2H3N)ꢁ1/
2(H2O)ꢁ3/2(O).
Empirical formula
Formula weight
Crystal system
space group
a (Å)
C143H123N27O32Pd4
3157.28
C132H110N18O20Pd3
2587.58
monoclinic
P21/c
25.595 (2)
18.480 (2)
25.803 (3)
90
94.796 (4)
90
12162 (2)
4
N1—Pd1
N2—Pd1
N3—Pd1
N4—Pd1
N5—Pd2
N6—Pd2
N7—Pd2
N8—Pd2
2.024
2.018
2.016
2.012
2.016
2.016
2.002
2.022
1.220
1.223
1.227
80.96
176.51
96.09
96.80
175.77
86.03
80.88
176.21
96.40
96.00
171.22
87.07
triclinic
ꢀ
P1
13.2612 (3)
15.7740 (4)
17.4441 (5)
83.674 (1)
82.025 (1)
73.465 (1)
3454.64 (15)
1
b (Å)
c (Å)
a
(°)
b (°)
(°)
N9—O1
N9—O3
N9—O2
c
Volume (Å)3
Z
N4—Pd1—N3
N4—Pd1—N2
N3—Pd1—N2
N4—Pd1—N1
N3—Pd1—N1
N2—Pd1—N1
N7—Pd2—N6
N7—Pd2—N5
N6—Pd2—N5
N7—Pd2—N8
N6—Pd2—N8
N5—Pd2—N8
Wavelength (Å)
Temperature (K)
Calculated density
(g/cm3)
0.71073
173 (2)
1.518
0.71073
173 (2)
1.413
Absorption
coefficient
0.60
0.52
(mmꢀ1
)
F(0 0 0)
1610
0.42 ꢂ 0.38 ꢂ 0.27
5304
0.28 ꢂ 0.25 ꢂ 0.22
Crystal dimensions
(mm)3
h Range for data
collection (°)
2.0–28.4
1.4–28.3
Limiting indices
ꢀ17 6 h 6 12, ꢀ21
6 k 6 20, ꢀ21
6 l 6 23
ꢀ24 6 h 6 34, ꢀ20
6 k 6 24, ꢀ30 6 l 6 34
Reflections collected/
unique
Data/restraints/
parameter
Goodness-of-fit
(GOF) on F
45 848/15 202
81 737/28 342
28 342/0/1566
1.057
3. Conclusion
15 202/8/951
1.053
Synthesis of a class of Pd(II) compounds namely [{Pd(bpy)}x-
(L)y](NO3)2x by an alternative and more efficient one pot technique
is modeled by using 4-phenylpyridine as a ligand. The thermody-
namically favored product [Pd(bpy)(4-phenylpyridine)2](NO3)2 is
formed exclusively by simply combining Pd(NO3)2, bpy and 4-
phenylpyridine at a required ratio under optimized reaction
conditions.
Final R indices
R1 = 0.0529
wR2 = 0.1502
R1 = 0.0841
wR2 = 0.1781
CCDC 795973
R1 = 0.1109
wR2 = 0.3030
R1 = 0.2083
wR2 = 0.3677
CCDC 795974
[I > 2r(I)]
R indices (all data)
CCDC

N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
77
Table 4
reacting Pd(bpy)Cl2 with AgNO3 in aq HNO3 at pH 1 [8]. Thus
formed Pd(bpy)(NO3)2 (0.0193 g, 0.05 mmol) was suspended
in 5 mL of CH3CN and 4-phenylpyridine (0.0155 g, 0.1 mmol)
was added to it. The mixture was refluxed for 1 h with
continuous stirring then it was cooled down to room
temperature. The yellowish solution was evaporated and
dried under vacuum to obtain the complex 2 as a yellow
solid (0.0319 g, 92% yield) [7]. The overall calculated yield
is 70%.
Selected bond lengths (Å) and bond angles (°) for 3ꢁ1/3ꢁ(H2OꢁO).
N1—Pd1
N2—Pd1
N3—Pd1
N4—Pd1
N5—Pd2
N6—Pd2
N7—Pd2
N8—Pd2
N9—Pd3
N10—Pd3
N11—Pd3
N12—Pd3
N1—Pd1—N3
N2—Pd1—N3
N2—Pd1—N1
N4—Pd1—N1
N4—Pd1—N2
N4—Pd1—N3
N5—Pd2—N6
N5—Pd2—N7
N5—Pd2—N8
N6—Pd2—N7
N6—Pd2—N8
N7—Pd2—N8
N9—Pd3—N10
N9—Pd3—N11
N9—Pd3—N12
N10—Pd3—N11
N12—Pd3—N10
N12—Pd3—N11
2.0270
2.0195
2.0270
2.0135
2.0106
2.0111
2.0132
2.0149
1.9965
2.0147
2.0381
2.0009
178.2
88.7
90.6
88.9
179.2
91.8
88.8
179.4
91.0
91.2
179.2
89.0
88.2
177.6
91.4
91.6
179.4
88.8
(b) One pot method: 2,20-bipyridine (0.0078 g, 0.05 mmol) and 4-
phenylpyridine (0.0155 g, 0.1 mmol) was dissolved in 5 mL
of CH3CN:H2O (1:1). To this solution Pd(NO3)2 (0.0138 g,
0.06 mmol) was added and stirred for 6 h at room tempera-
ture. The pale coloured solution was evaporated by N2 flux-
ing and dried under vacuum. The solid was washed with
ether and dried again to afford a pale yellow solid as the
product (0.0332 g, yield 95%).
4.3. Analytical data of the complexes 2–6
4.3.1. [Pd(bpy)(4-phenylpyridine)2](NO3)2, 2
1H NMR (400 MHz, DMSO-d6, external TMS/CDCl3): d 9.84 (d,
J = 6.2 Hz, 4H, a), 9.34 (d, J = 8.0 Hz, 2H, a0), 9.05 (t, J = 8.4 Hz, 2H,
b0), 8.75 (d, J = 6.6 Hz, 4H, b), 8.48 (d, J = 3.6 Hz, 4H, c), 8.28 (t,
J = 6.4 Hz, 2H, c0), 8.10–8.13 (m, 8H, d, e and d0) ppm. 1H NMR
(400 MHz, CD3CN:D2O (1:1), external TMS/CDCl3): d 9.47 (d,
J = 5.9 Hz, 4H, a), 8.89 (d, J = 8.0 Hz, 2H, a0), 8.78 (t, J = 8.0 Hz, 2H,
b0), 8.42 (d, J = 5.8 Hz, 4H, b), 8.24–8.22 (m, 4H, c), 8.02–7.99 (m,
8H, c0, d and e), 7.88 (d, J = 5.6 Hz, 2H, d0) ppm. ESI-MS: m/z
286.1 for [2ꢀ2(NO3)]2+. Anal. Calc. for C32H26N6O6Pd (697.00): C,
55.14; H, 3.76; N, 12.06. Found: C, 55.28; H, 3.90; N, 11.9%.
4. Experimental
4.1. General
4.3.2. [Pd(4-phenylpyridine)4](NO3)2, 3
1H NMR (400 MHz, DMSO-d6, external TMS/CDCl3): d 9.81 (d,
J = 6.1 Hz, 8H, a), 8.64 (d, J = 6 Hz, 8H, b), 8.38–8.36 (m, 8H, c),
8.07–8.06 (m, 12H, d and e) ppm. 1H NMR (400 MHz, CD3CN:D2O
(1:1), external TMS/CDCl3): d 9.33 (d, J = 6.4 Hz, 8H, a), 8.26 (d,
J = 6.4 Hz, 8H, b), 8.15–8.13 (m, 8H, c), 7.95–7.94 (m, 12H, d and
e) ppm. ESI-MS: m/z 363.04 for [3ꢀ2(NO3)]2+. Anal. Calc. for
PdCl2, Pd(NO3)2, 4-phenylpyridine and 2,20-bipyridine were ob-
tained from Aldrich whereas ethylenediamine, AgNO3 and the
usual solvents were obtained from Spectrochem, India. The
deuterated solvents D2O, CD3CN and DMSO-d6 were obtained
from Cambridge Isotope Laboratories. The cis-protected Pd(II)
components i.e. cis-[Pd(bpy)(NO3)2] and cis-[Pd(en)(NO3)2] were
prepared by known methods. The assemblies [Pd(bpy)-
(4-phenylpyridine)2](NO3)2, 2 was prepared by us earlier by
classical method and now by the alternative one pot approach.
The related complexes [Pd(4-phenylpyridine)4](NO3)2, 3; and
[Pd(en)(4-phenylpyridine)2](NO3)2, 5 were prepared by reported
method [12] and [Pd(bpy)2][(NO3)2], 4; [Pd(en)2][(NO3)2], 6 were
prepared according to the literature procedures [7]. 1H NMR spec-
tra were recorded on a Bruker 400 MHz FT NMR instrument using
TMS/CDCl3 as external standard. The 1H NMR spectral data of the
compounds in DMSO-d6 are available in literature. However, for
the purpose of the present study NMR data was obtained in
CD3CN:D2O (1:1) and provided here for the compounds 2, 3 and
4. The NMR data of the complexes 2, 3, 5 and 6 in DMSO-d6 is also
provided for comparison purpose. The mass spectra of the samples
of 2 and 3 were obtained from a Micromass Q-ToF mass spectrom-
eter by electrospray ionisation method. The single crystal X-ray
analysis for 2 and 3 were carried out using a Bruker X8 Kappa
XRD instrument. Elemental analysis was performed on Perkin–
Elmer 2400 series CHNS/O Analyser.
C44H36N6O6Pd (851.21): C, 62.08; H, 4.26; N, 9.87. Found: C,
61.85; H, 4.42; N, 10.11%.
4.3.3. [Pd(bpy)2][(NO3)2], 4
1H NMR (400 MHz, CD3CN:D2O (1:1), external TMS/CDCl3): d
9.10 (d, J = 5.6 Hz, 4H, d0), 8.91–8.84 (m, 8H, a0 and b0), 8.32
(t, J = 6.8 Hz, 4H, c0) ppm.
4.3.4. [Pd(en)(4-phenylpyridine)2](NO3)2, 5
1H NMR (400 MHz, DMSO-d6, external TMS/CDCl3): d 9.37 (d,
J = 6.0 Hz, 4H, a), 8.57 (d, J = 6.2 Hz, 4H, b), 8.43–8.41 (m, 4H, c),
8.07–8.06 (m, 6H, d and e), 6.18 (s, 4H, –NH2), 3.23 (s, 4H, –CH2)
ppm.
4.3.5. [Pd(en)2][(NO3)2], 6
1H NMR (400 MHz, DMSO-d6, external TMS/CDCl3): d 5.42 (s,
4H, NH2) ppm, CH2 peak is merged with DMSO-d6.
Acknowledgments
4.2. Synthesis of [Pd(bpy)(4-phenylpyridine)2](NO3)2, 2
This study was supported by a grant in aid for scientific re-
search from the Department of Science and Technology (DST),
New Delhi, India (No. SR/S1/IC-28/2009). We thank Dr. S. Suvitha
and Dr. N.S. Venkataramanan for helping us in theoretical
calculations.
(a) Classical method: preparation of Pd(bpy)Cl2 which is also
commercially available was carried out by adding bpy to a
hot acetonitrile solution of PdCl2 following literature proce-
dure [8]. The chloride anion was exchanged with nitrate by

78
N.B. Debata et al. / Inorganica Chimica Acta 372 (2011) 71–78
(l) S. Tashiro, M. Tominaga, T. Kusukawa, M. Kawano, S. Sakamoto, K.
Appendix A. Supplementary material
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graphic data for this paper. These data can be obtained free of
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www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
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doi:10.1016/j.ica.2011.02.009.
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