Structural and spectral studies of palladium(II) and platinum(II) complexes derived from N,N,N,N-tetradentate macrocyclic ligands

Article abstract of DOI:10.1016/j.saa.2007.12.051

Palladium(II) and platinum(II) complexes having the general composition [M(L)] X₂ {where M = Pd(II) and Pt(II), L = 3,4,12,13-tetraphenyl-2,5,11,14,19,20-hexaaza tricyclo [13.3.1.1.^6-10] cosa-1(19), 2,4,6,8,10,(20),11,13,15,17-decaen

Full text of DOI:10.1016/j.saa.2007.12.051

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Spectrochimica Acta Part A 71 (2008) 720–724
Structural and spectral studies of palladium(II) and platinum(II)
complexes derived from N,N,N,N-tetradentate macrocyclic ligands
Sulekh Chandraa,∗, Smriti Raizadab, Soni Rania
a Department of Chemistry, Zakir Husain College (University of Delhi), J.L. Nehru Marg, New Delhi 110002, India
b Department of Chemistry, M.M.H. College, Ghaziabad 201001, India
Received 26 April 2007; accepted 8 December 2007
Abstract
Palladium(II) and platinum(II) complexes having the general composition [M(L)] X2 {where M = Pd(II) and Pt(II), L = 3,4,12,13-tetraphenyl-
2,5,11,14,19,20-hexaaza tricyclo [13.3.1.1.6–10] cosa-1(19), 2,4,6,8,10,(20),11,13,15,17-decaene (L1); 3,4,13,14-tetraphenyl-2,5,12,15-tetraaza
tricyclo [11,0,0,6–11] cosa-1(16),2,4,7,9,6(11),12,14,17, 19-decaene (L2); 2,3,8,9-tetraphenyl-1,4,7,10-tetraaza cyclododeca-1,3,7,9-tetraene (L3)
and X = Cl−} have been synthesized. The ligands were characterized on the basis of elemental analyses, IR, 1H NMR and EI mass spectral studies
while that of the complexes were characterized on the basis of elemental analyses, molar conductance measurements, magnetic susceptibility
measurements, IR, and electronic spectral techniques. All the complexes were found to be diamagnetic. The structures consist of monomeric units
in which the Pd(II) and Pt(II) atoms exhibit square planar geometry.
© 2008 Elsevier B.V. All rights reserved.
Keywords: Tetradentate macrocyclic; Metal complexes; Palladium(II) and platinum(II)
1. Introduction
Palladium(II) complexes have been found to cleave proteins
selectively in high yield [15]. It has been well established that
Platinum and Palladium complexes are of biological importance
due to their carcinostatic activity and interest in biological chem-
istry [16]. The carcinostatic action of the drugs is due to their
interaction with nuclear DNA [17]. Charlson et al. [18] have
reported that cesium cis-dichloroserineto palladate(II) induces
filament growth in E. coli. The complexes of palladium(II) with
amino acids like glycine, serine, and glutamine have also been
reported [19,20], to be active against certain tumors. Palla-
dium(II) and platinum(II) complexes of some Schiff base ligands
derived from S-alkyl esters of dithiocarbazic acid have been
found to exhibit marked cytotoxicity against leukaemia [21] and
the human ovarian cancer (Caov-3) cell lines [22].
The intense interest in synthetic macrocycles and their metal
complexes depends on the fact that they mimic naturally occur-
ring macrocyclic molecules in their structure and functional
features and on their rich chemical behaviour [1–4]. In addition,
the study of metal complexes of macrocyclic ligands appears to
be interesting in view of the possibility of obtaining coordinating
compound of unusual structure and stability. The formation of
macrocyclic complexes depends on the size of the macrocycles,
onthenatureofitsdonoratomsandonthecomplexingbehaviour
of the anions involved in coordination [5–7]. Macrocyclic lig-
ands are also of theoretical interest since they are capable of
furnishing an environment of controlled geometry and ligand
field strength [8]. Moreover, macrocyclic Schiff base nitrogen
donor ligands have received special attention because of their
mixed hard–soft donor character [9,10] and versatile coordina-
tion behaviour [11–14].
In view of the above applications, in the present paper we
report the synthesis and characterization of Pd(II) and Pt(II)
complexes with nitrogen donor [N4] macrocyclic ligands L1, L2
and L3 (Fig. 1).
2. Experimental
All the chemicals used were of AnalaR grade and procured
from Sigma–Aldrich and Fluka. Metal salts were obtained
from commercial sources (E. Merck) and used without further
∗
Corresponding author.
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
soni teotia81@yahoo.co.in (S. Rani).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.12.051

S. Chandra et al. / Spectrochimica Acta Part A 71 (2008) 720–724
721
Fig. 1. Structure of ligands.
purification. All solvents used were purified according to
standard procedures.
heated under reflux over 8–11 h at 70–75 ◦C. On cooling up to
4 ◦C a coloured precipitate formed, was collected by filtration.
The resulting solid was finally washed with cold EtOH and dried
in vacuum.
2.1. Synthesis of macrocyclic ligands
To a hot ethanolic (20 mL) solution of benzil (4.2046 g,
0.02 mol), a hot ethanolic (20 mL) solution of correspond-
ing diamines, i.e. 2,6-diaminopyridine (2.1826 g, 0.02 mol),
o-phenylenediamine (2.1628 g, 0.02 mol) and ethylene diamine
(1.2000 g, 0.02 mol) was added dropwise with constant stirring.
This solution was refluxed at 70–75 ◦C for 8 h in presence of few
drops of concentrated hydrochloric acid. On cooling coloured
product was precipitated out. It was filtered, washed several
times with cold EtOH, and dried under vacuum over P4O10.
3. Physical measurements
Elemental analyses of C, H, and N were performed on a
Carbo-Erba EA 1106 analyser, the nitrogen contents of the
complexes were determined using Kjeldahl’s method. Molar
conductancewasmeasuredonanELICO(CM82T)conductivity
bridge. Magnetic susceptibility was measured at room temper-
ature on a Gouy balance using CuSO4·5H2O as a callibrant.
Electron impact mass spectra were recorded on JEOL. JMS, DX-
303 mass spectrometer. The 1H NMR (300 MHz) spectra were
recorded on a Bruker Advance DPX-300 spectrometer using
CDCl3 as solvent. Chemical shifts are given in ppm relative
to tetramethylsilane. IR spectra were recorded as KBr pellets
on a FT-IR spectrum BX-II spectrophotometer. The electronic
spectra were recorded in DMF on Shimazdu UV mini-1240
spectrophotometer.
2.2. Synthesis of complexes
The complexes were prepared by dissolving corresponding
metal salts (0.001 mol) in ethanol and then an ethanolic solution
of respective ligand (0.001 mol) was added to this solution in
1:1 molar ratio. The solution was stirred and the mixture was
Table 1
Elemental analyses data of the ligands and Pd(II) and Pt(II) complexes
Ligands/complexes
M.W. found
Color
M.P. (0 ◦C)
Yield (%)
Elemental analysis found (calculated) %
M
C
H
N
L1 = C38H26N6
567
744
833
563
740
829
470
647
736
Cream
Green
Green
White
Mehendi
Orange
Light yellow
Brown
65
84
85
85
110
98
64
90
95
62
52
60
67
62
68
62
60
50
–
80.19 (80.50)
61.29 (61.33)
54.74 (54.80)
85.40 (85.1)
64.86 (64.74)
57.90 (57.83)
81.82 (82.01)
59.35 (59.93)
52.17 (52.31)
4.66 (4.50)
3.49 (3.50)
3.10 (3.12)
5.16 (4.90)
3.78 (3.77)
3.38 (3.37)
6.03 (5.91)
4.32 (4.34)
3.80 (3.81)
15.12 (14.80)
11.26 (11.29)
10.08 (10.09)
9.82 (9.91)
7.56 (7.55)
6.77 (6.75)
10.35 (11.09)
8.65 (8.68)
7.60 (7.62)
[Pd(L1)]Cl2 PdC38H26N6Cl2
[Pt(L1)]Cl2 PtC38H26N6Cl2
L2 = C40H28N4
[Pd(L2)]Cl2PdC40H28N4Cl2
[Pt(L2)]Cl2 PtC40H28N4Cl2
L3 = C32H28N4
14.24 (14.31)
23.40 (23.43)
–
14.32 (14.30)
23.52 (23.49)
–
[Pd(L3)]Cl2PdC32H28N4Cl2
[Pt(L3)]Cl2PtC32H28N4Cl2
16.38(16.43)
14.40 (14.44)
Brown

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S. Chandra et al. / Spectrochimica Acta Part A 71 (2008) 720–724
Table 2
Molar conductance and Electronic spectral data of the complexes
S. no.
Complexes
Molar conductance
λmax (cm−1
)
(ꢀ−1 cm2 mol−1
)
1
2
3
4
5
6
[Pd(L1)]Cl2
[Pd(L2)]Cl2
[Pd(L3)]Cl2
[Pt(L1)]Cl2
[Pt(L2)]Cl2
[Pt(L3)]Cl2
198
206
208
210
200
195
18622, 27397, 34247
20747, 27933, 36764
30674, 37174
27397, 34364
21413, 29155, 37037
18621, 29412, 36364
4. Result and discussion
The physical properties and analytical data of ligands and
complexes are given in Table 1. The molar conductance mea-
surements in dimethylformamide/nitrobenzene indicate that the
complexes are of 1:2 electrolytic nature [23] (Table 2).
4.1. IR spectra
The IR spectra of ligands do not show any band at 1700 cm−1
(␯C O), 3380 cm−1 (␯asNH2) and 3250 cm−1 (␯sNH2) corre-
sponding to carbonyl group and free primary amine [24], which
suggest the complete condensation of amino group with keto
group. A band corresponding to ␯(C N) (azomethine linkage)
appears at 1650–1660 cm−1 in the ligands (Fig. 2a). On com-
plex formation, the IR band due to azomethine group shifts
to the lower wave number (20–30 cm−1) which indicates that
the nitrogen atom of azomethine groups are coordinated to the
metal atom (Fig. 2b and c). The band in the 360–390 cm−1
region may be assigned to ␯(M–N) vibrations. In ligand L1 the
bands due to pyridine ring deformation, in-plane-ring deforma-
tion and out-of-plane-ring deformation [25] appear at 1593, 642
and 420 cm−1, respectively. These bands are unaffected in com-
plexes suggesting that pyridine nitrogen is not coordinated to the
metal atom. On the basis of above discussion a four coordinated
structure is proposed for all the complexes in which the lig-
ands coordinate via four azomethine nitrogens (N,N,N,N-donor,
tetradentate).
4.2. 1H NMR
The 1H NMR spectra (300 MHz) of the ligands were
recorded in dueterated chloroform at room temperature. The
peak positions of the different protons of the ligands are given
as:
Fig. 2. IR spectra of (a) ligand (L1), (b) [Pd(L1)]Cl2, and (c) [Pt(L1)]Cl2.
• Two signals at ca. δ 8.0 ppm (d,2H,2H) and δ 7.66 ppm (t,H,H)
appear in the spectrum of ligand L1 due to the two types of
pyridine ring protons (Fig. 3a).
• In addition, a multiplet appears in the spectra of ligands at
ca. δ 7.22–7.40 ppm (m,5H,5H,5H,5H) equivalent to the four
phenyl groups protons [26].
• Spectrum of the ligand L2 shows the two doublet of dou-
blet signals at ca. δ 7.77 ppm (dd,2H,2H) and δ 8.18 ppm
(dd,2H,2H) corresponding to the two types of non-equivalent
aromatic protons (Fig. 3b).
4.3. Mass spectra
The electron impact mass spectra confirm the proposed for-
mulae of ligands L1, L2, and L3. The fragmentation patterns of
the ligands are discussed below.
1
• The ligand L3 gives a H NMR singlet at ca. δ 3.70 ppm
(S,4H,4H) due to the ethylinic protons (Fig. 3c).

S. Chandra et al. / Spectrochimica Acta Part A 71 (2008) 720–724
723
Fig. 4. Mass spectrum of ligand (L1).
4.3.3. Ligand (L3)
The mass spectrum shows the peaks at m/z values 470
and 471 due to M+ and M+ + 1 and a most intense peak at
m/z = 77. The various peaks appear at m/z values 14, 51, 89,
178, 206, 248, 262, 290, 314, 319, and 412 due to other frag-
ments.
4.4. Electronic spectra
4.4.1. Palladium(II) complexes
The magnetic moment studies show that all the complexes
of Pd(II) are diamagnetic with spin-paired d8 system, The com-
plexes exhibit three spin allowed d–d transitions from lower
Fig. 3. 1H NMR spectra of ligands (a) L1, (b) L2, and (c) L3.
4.3.1. Ligand (L1)
The molecular ion peak (M+) appears at m/z = 567 which is
at highest m/z value. This peak confirms the molecular formula
of ligand. Moreover a very weak peak at m/z = 568 (M+ + 1)
also appears which corresponds to the 13C isotopic peak. The
mass spectrum shows a most prominent peak at m/z = 77, which
is the base peak and is due to phenyl cation. The other peaks
at m/z = 51, 105, 206, 388, 412, and 475 are due to the different
fragments and the intensities of these peaks indicate the stability
of these ions [27] (Fig. 4).
4.3.2. Ligand (L2)
The peaks at m/z = 563 and 564 corresponds to the M+
(parental ion) and M+ + 1 (13C isotopic). The base peak appears
at m/z = 77 and the other fragment ions give the peaks at m/z = 51,
105, 178, 206, 256, 282, 333, 386, 460, and 487. The peaks area
provide an idea of abundance of these ions.
Fig. 5. Electronic spectra of complexes (a) [Pt(L2)]Cl2 and (b) [Pt(L3)]Cl2.

724
S. Chandra et al. / Spectrochimica Acta Part A 71 (2008) 720–724
lying d-levels to the empty dx2−y2 orbital. Although other two
electronic transitions are also observed but their intensities are
very weak and are neglected. The complexes show the absorp-
tions bands at 18,622–20,747, 27,397–27,933 and 30,674 cm−1
References
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1
1
1
corresponding to 1A2g ← A1g, 1B1g ← A1g and 1Eg ← A1g
d–d transition [28], respectively. Moreover in the complexes,
the high intensity charge transfer absorption bands are also
observed at 34,247 and 36,764–37,174 cm−1 corresponding to
1A2u ← A1g and1Eu ← A1g transitions, respectively(Fig. 5a).
These absorption bands suggest that the complexes possess D4h
symmetry and square planar geometry.
1
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4.4.2. Platinum(II) complexes
The complexes of Pt(II) are diamagnetic with low-spin d8
system having square planar geometry. The spin allowed d–d
transitions are observed at 18,621–21,413 cm−1, 27,397 cm−1
and 29,155–29,412 cm−1 corresponding to A2g ← A1g,
1
1
1
1
1
1B1g ← A1g and Eg ← A1g transitions, respectively, in the
complexes. The complexes show the high-energy absorption
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possess D4h symmetry.
5. Conclusion
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Our proposed structures of macrocyclic ligands on the basis
of the IR, H NMR, EI mass spectra have potential binding
1
sites towards the metal ions and act as tetradentate ligands
by coordinating through four azomethine nitrogens, i.e. in the
N,N,N,N-fashion. The ligands form square planar complexes
with Pd(II) and Pt(II) metal ions. The elemental analysis and
electronic and IR spectral analysis reveal the existence of
monomeric complexes.
[25] O.P. Pandey, Polyhedron 6 (1987) 1021.
Acknowledgements
[26] John R. Dyer, Application of Absorptions Spectroscopy of Organic Com-
pounds, sixth ed., Georgia Institute of Technology, 1987.
[27] D.A. Skoog, F.J. Holler, T.A. Nieman, Principles of Instrumental Analysis,
fifth ed., Thomson, 2003.
[28] A.B.P. Lever, Inorganic Electronic Spectroscopy, first ed., Elsevier, Ams-
terdam, 1968.
The authors thank the instrumentation facilities of Depart-
ment of Chemistry, University of Delhi, Delhi, for recording the
IR, H NMR, EI mass spectra and elemental analysis. We are
1
also thankful to the DRDO, Delhi, for financial assistance.