Synthesis and characterization of tetra-substituted palladium phthalocyanine complexes

Article abstract of DOI:10.1016/j.dyepig.2012.08.018

Tetra-substituted palladium phthalocyanine complexes with different electron withdrawing and electron donating substituents (-H, -NO₂, -NH₂, -Cl, -COOH, aryl thio) have been synthesized with a good yield. The synthesized complexes were characterized using XPS, UV-Vis, IR, Raman, XRD, TGA and electrochemistry. The XPS spectra show that the central metal ion is in the +2 state, while the UV-Vis spectra demonstrate split absorption peaks in the Q-band region 600-700 nm due to the presence of dimeric and oligomeric molecules in addition to the monomeric species. The UV-Vis and Raman spectra demonstrate a shift in the peaks/bands which is a result of the electron withdrawing and electron donating substituents at the periphery of the benzene ring compared to the parent palladium phthalocyanine. The thermogravimetic stability studies show that these complexes undergo two separate decomposition processes. The thermal stability for different complexes are in the order: PdPc < PdTPSPc < PdTClPc < PdTAPc < PdTCAPc = PdTNPc, indicating that the substituents at the periphery have an effect on the thermal stability. The cyclic voltammetric data in DMSO show that the central metal ion Pd does not undergo a redox process and the redox behaviour observed is mainly due to the macrocyclic ring reduction process.

Full text of DOI:10.1016/j.dyepig.2012.08.018

Dyes and Pigments 96 (2013) 269e277
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and characterization of tetra-substituted palladium phthalocyanine
complexes
*
Koodlur Sannegowda Lokesh, Annemie Adriaens
Department of Analytical Chemistry, Ghent University, Krijgslaan 281-S12, 9000 Ghent, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Tetra-substituted palladium phthalocyanine complexes with different electron withdrawing and electron
donating substituents (eH, eNO2, eNH2, eCl, eCOOH, aryl thio) have been synthesized with a good
yield. The synthesized complexes were characterized using XPS, UVeVis, IR, Raman, XRD, TGA and
electrochemistry. The XPS spectra show that the central metal ion is in the þ2 state, while the UVeVis
spectra demonstrate split absorption peaks in the Q-band region 600e700 nm due to the presence of
dimeric and oligomeric molecules in addition to the monomeric species. The UVeVis and Raman spectra
demonstrate a shift in the peaks/bands which is a result of the electron withdrawing and electron
donating substituents at the periphery of the benzene ring compared to the parent palladium phtha-
locyanine. The thermogravimetic stability studies show that these complexes undergo two separate
decomposition processes. The thermal stability for different complexes are in the order:
PdPc < PdTPSPc < PdTClPc < PdTAPc < PdTCAPc ¼ PdTNPc, indicating that the substituents at the
periphery have an effect on the thermal stability. The cyclic voltammetric data in DMSO show that the
central metal ion Pd does not undergo a redox process and the redox behaviour observed is mainly due
to the macrocyclic ring reduction process.
Received 8 May 2012
Received in revised form
25 July 2012
Accepted 15 August 2012
Available online 24 August 2012
Keywords:
Palladium substituted phthalocyanines
Synthesis
UVeVis
Raman
TGA
Electrochemistry
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
stable corresponding to their respective octa and higher-
substituted complexes due to the possible formation of constitu-
Phthalocyanines are a class of N4-macrocycles known for their
very interesting industrial applications due to their high stability,
architectural flexibility, diverse coordination properties, good
spectroscopic characteristics, rich and reversible redox chemistry.
They are extensively used in the field of dyes, semiconductors,
catalysis, linear optics, electrochromics, photovoltaic cells, liquid
crystals, etc [1e3].
tional isomers and the dipole moment results from the unsym-
metrical arrangement of the substituents [4e6].
Phthalocyanines can be tailored such that they consist of certain
properties which are required for different methodologies such as
electrodeposition, electropolymerization, LangmuireBlodgett, self
assembly, stabilizing of nanoparticles which finds numerous
applications in catalysis, sensing and molecular electronics [1e3].
The stability and electron transfer abilities are the main key factors
to determine the functionality of a material. The majority of liter-
ature on phthalocyanines includes studies on the central metal ion
as first-row transition metal and lanthanide ion [1e6]. There is no
systematic study on the synthesis of phthalocyanines with different
electron withdrawing and electron donating substituents and
characterization with third-row transition elements.
Palladium and its complexes are known to be very good cata-
lysts in homogeneous and heterogeneous catalysis [7e10]. It can be
believed that the combined effect of the metal ion palladium and
the phthalocyanine macrocycle, the catalytic and sensing activity of
palladium phthalocyanine complexes will be enhanced to a larger
extent. Information about the synthesis of palladium phthalocya-
nine complexes, however, is very meagre in the literature [11,12].
Research has been focused on the electrochemical characterization
The functions of phthalocyanine derivatives are almost all based
on their electron transfer reactions, because of their
p-electron
conjugated ring system. The physicochemical properties of the
phthalocyanines can be fine-tuned by changing the central metal
ion and also by changing the substituents at the periphery of the
benzene rings. The substitution of functional groups at the
periphery of benzene ring is advantageous because it gives flexi-
bility in solubility and also efficiently tunes the colour of the
material. Substitution of functional groups also changes the elec-
tron density of the macrocycle and finds its use in various fields.
Tetra-substituted phthalocyanines tend to be more soluble and
* Corresponding author. Tel.: þ32 9 2644826; fax: þ32 9 264 4960.
E-mail address: annemie.adriaens@ugent.be (A. Adriaens).
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2012.08.018

270
K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
of some palladium phthalocyanine complexes [13e16], however, to
our best knowledge there is no literature available for the synthesis
of palladium phthalocyanine complexes with different electron
donor and acceptor substituents.
This paper deals with a spectroscopic, thermal and electro-
chemical characterization of newly synthesized palladium phtha-
locyanine complexes, which contain different electron
withdrawing and electron donating substituents, including nitro,
amine, chloro, carboxyl and thio aryl compounds. An effort has
been made to discuss the effect of substituents on the optical,
thermal and electrochemical behaviour of these complexes.
recorded in the wave number region of 100e1800 cmꢂ1 as bulk
powder samples. For each spectrum 15 accumulations of 30 s were
recorded.
XRD spectra were recorded using model ARL X-TRA from Ther-
moFisher Scientific in the range 10e60ꢀ at 25 ꢀC with a scan rate of
1ꢀ/min at a step of 0.020ꢀ and integration time of 1.2 s. XRD spectra
ꢀ
were obtained using Cu K
a
radiation (k ¼ 1.934 A).
Thermogravimetric analyses were carried out using the SDT
2960 of TA instruments. Five to 10 mg of the sample was used for
the analysis at a heating rate of 10 ꢀC/min in dry air atmosphere
with a flow rate of 100 mL/min.
Cyclic voltammetric experiments were used to examine the redox
behaviour of the palladium phthalocyanine complexes. Experiments
were performed using an Autolab potentiostat (PGSTAT 100) with
GPESsoftware, ina threeelectrode cellsystemwithsaturatedcalomel
electrode as reference, a glassy carbon (GC) electrode as working
electrode and carbon as counter electrode. The electrochemical
experiments were performed in 0.01 M tetrabutyl ammonium
perchlorate (TBAP) in dry DMSO at a scan rate of 50 mV/s in an inert
atmosphere by purging with nitrogen gas for 20 min before each
electrochemicalmeasurement. Atotal of2 mM of thecomplexes were
used for the electrochemical characterization in solution.
2. Experimental section
2.1. Materials
Precursors phthalonitrile (C6H4(CN)2) (99%), 4-nitrophthalonitrile
(C6H4(CN)2(NO2)) (99%) and trimellitic anhydride (C9H4O5) (98%)
were purchased from Sigma Aldrich and used as such without any
purification. Palladium chloride (PdCl2), sodium sulphide non-
ahydrate (Na2S$9H2O), sodium nitrite (NaNO2), cuprous chloride
(CuCl), urea (CO(NH2)2), ammonium chloride (NH4Cl), ammonium
molybdate ((NH4)6Mo7O24$4H2O), thiophenol (C6H5SH), potassium
carbonate (K2CO3), nitrobenzene (C6H5NO2), methanol (CH3OH),
ethanol (C2H5OH), tetrahydrofuran (THF), acetone (CH3COCH3),
dimethyl sulphoxide (DMSO, 98%) and hydrochloric acid (HCl) were
also purchased from SigmaeAldrich.
Inlaid glassy carbon disk electrodes with a geometric area
0.071 cm2 (BASi) were used for the electrochemical characteriza-
tion. The electrodes were polished using polishing cloth (Micro-
Cloth, Buehler) using sequentially 1.0 mm and 0.5 mm alumina. The
electrodes were sequentially washed in water and later on in
ethanol while being sonicated for 10 min in an ultrasonic bath.
2.3. Synthesis procedures
2.3.1. Synthesis of palladium(II) phthalocyanine (PdPc)
Palladium(II) phthalocyanine (PdPc) was synthesized by modi-
fying slightly the procedure described for the synthesis of other
metal phthalocyanines [11,18]. A total of 5 g (0.039 mol) phthalo-
nitrile and 1.77 g (0.01 mol) palladium chloride were mixed well
and heated slowly under reflux to 140 ꢀC while stirring over an oil
bath, at which point the phthalonitrile melts and forms a brownish
slurry. The reaction mixture was then heated to 180 ꢀC and main-
tained at 180 ꢀC for 2 h with constant stirring. The crude product
was cooled to room temperature and the solid mass was finely
ground and washed with methanol, hot alcohol and water to
remove the intermediates and unreacted components. The product
was dried in the oven for 1 h to obtain 5.6 g of a bluish green solid.
Anal. for palladium(II) phthalocyanine, C32H16N8Pd: Calc. (%) C,
62.09; H, 2.59; N, 18.11; Pd, 17.21. Found C, 61.73; H, 2.79; N, 18.45,
Pd, 17.03. Electronic absorption, lmax (nm): 328, 436, 617,661. IR
absorption bands (cmꢂ1): 754(w), 871(s), 913(m), 950(w), 1069(w),
1093(m), 1114(s), 1164(s), 1287, 1326(s), 1361(m), 1415(w), 1463(m),
1504(w), 1556(s), 1605(w).
2.2. Methods
Elemental analysis for carbon, hydrogen and nitrogen were done
using Vario EL-III CHNS Element Analyzer (Elementar Analy-
sensysteme GmbH). The metal contents of the metal complexes
were determined by decomposing a known amount of the complex
using a H2SO4eHNO3 mixture, followed by careful evaporation and
calcinations [17].
IR spectra were recorded using a Perkin Elmer spectrum 100 FT-
IR spectrometer attached to Spot light 400-Perkin Elmer FT-IR
imaging system in the ATR mode with germanium crystal.
X-ray photoelectron spectroscopy (XPS) measurements were
carried out using a S-Probe mono-chromatized XPS spectrometer
2.3.2. Synthesis of palladium(II) tetranitrophthalocyanine (PdTNPc)
Palladium(II) tetranitrophthalocyanine (PdTNPc) was prepared
by mixing a total of 6.5 g (0.039 mol) 4-nitrophthalonitrile and
1.77 g (0.01 mol) palladium chloride. The mixture was heated
slowly to 140 ꢀC while stirring to form a slurry [18]. The reaction
mixture was maintained at 160 ꢀC with constant stirring for 3 h
under reflux. The solid crude product was cooled to room
temperature and the crude was purified using the procedure as
explained for PdPc (see above) to afford 6.05 g of a bluish green
product. Anal. for palladium(II) tetranitrophthalocyanine,
C32H12N12O8Pd: Calc. (%) C, 48.1; H, 1.50; N, 21.04; O, 16.03; Pd,
13.33. Found; C, 48.49; H, 1.34; N, 20.79; Pd, 13.56. Electronic
absorption, lmax (nm): 346, 431, 620, 684. IR absorption bands
(cmꢂ1): 755(w), 815(w), 845(s), 909(w), 1048(w), 1104(m), 1143(s),
1256 (s), 1330(s), 1405(m), 1437(w), 1523(s), 1605(m).
from Surface Science Instruments (VG) with an Al K
a X-ray
(1486.6 eV) monochromatic source. The take off angle was 45ꢀ with
the voltage and power of the source 10 kV and 200 W respectively.
A base pressure of 2 ꢁ 10ꢂ9 mbar was obtained in the measuring
chamber and the pass energy spectra was 157.7 eV (resolution
stand 4: 0.15 eV). The analysis surface was 250 ꢁ 1000
m
m2 with
a flood gun (neutralizer) setting of 0.2 eV. The accumulation time
was about 30 min for Pd 3d, N 1s and C1s spectra.
UVeVIS spectra were recorded using a Cary 50 from VARIAN
with DMSO as a blank. A total of 0.5 mM of the complex in DMSO
was used for recording the spectra in the region of 280e800 nm.
Raman spectra were recorded with a confocal Raman spec-
trometer Senterra R200-L (Bruker) using a 785 nm diode laser with
a power of 300 mW at the source. An Olympus microscope, coupled
to the spectrometer was used for the visualization of the sample
and for the microanalysis with an objective lens of 50ꢁ magnifi-
cation. The spectrometer is equipped with a thermo-electrically
cooled CCD detector (1024 ꢁ 256 pixels). Raman spectra were
2.3.3. Synthesis of palladium(II) tetraaminephthalocyanine (PdTAPc)
Palladium(II) tetraaminophthalocyanine was prepared by the
reduction of the nitro derivative using sodiumsulphide[18,19]. A total
of 2.0 g of PdTNPc was placed in 50 mL water. To this slurry 10 g of

K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
271
sodium sulphide nonahydrate was added and stirred at 50 ꢀC for 5 h.
The product was allowed to settle down and washed with 0.5 M
hydrochloric acid and 1 M sodium hydroxide solution, sequentially 3
times. Finally, the compound was washed with water until the filtrate
is neutral to litmus paper. The crude product was dried in the oven at
70 ꢀC for 3 h to obtain 1.4 g of a dark bluish solid. Anal. for palladium
tetraaminephthalocyanine, C32H20N12Pd: Calc. (%) C, 56.59; H, 2.95; N,
24.74;Pd,15.72.Found;C,56.16;H, 3.24;N,24.79;Pd,15.84. Electronic
absorption, lmax (nm):313, 432,648, 724.IRabsorptionbands(cmꢂ1):
754(w), 817(m), 868(s), 909(s), 946(w), 1052(w), 1105(m), 1143(s),
1255(w), 1334(s), 1408(w), 1516(s), 3215(w), 3334(s).
N, 13.79; Pd, 13. 69. Electronic absorption, lmax (nm): 332, 441, 617,
664. IR absorption bands (cmꢂ1): 776(w), 848(s), 942(w), 1105(s),
1152(s), 1247(w), 1319(s), 1380(m), 1512(s), 1667(w), 3182(b).
2.3.6. Synthesis of palladium(II) tetra(thiophenyl)phthalocyanine
(PdTPSPc)
Palladium(II) tetra(thiophenyl)phthalocyanine (PdTPSPc) was
synthesized from phenylthiophthalonitrile. Phenylthiophthalonitrile
[22]wassynthesized from thiophenol and then used for the synthesis
of PdTPSPc.
2.3.6.1. 4-(thiophenyl)phthalonitrile. Thiophenol (2.32 g, 0.021 mol)
and 4-nitrophthalonitrile (3.00 g, 0.018 mmol) were dissolved in
DMSO (20 mL) and stirred at room temperature in a nitrogen
atmosphere for 15 min. Finely ground K2CO3 (7.5 g, 0.058 mol) was
added slowly over a period of 2 h and the reaction mixture was
stirred continuously for 12 h. The mixture was added to water
(100 mL) and stirred for another 30 min. The precipitate was
filtered, washed thoroughly with water and dried. The product was
re-crystallized from hot ethanol. Anal. For 4-(thiophenyl)phthalo-
nitrile, C14H8N2S: Calc. (%) C, 71.16; H, 3.39; N, 11.86; S, 13.59. Found.
C, 71.53; H, 3.24; N, 11.39; S, 13.98.
2.3.4. Synthesis of palladium(II) tetrachlorophthalocyanine
(PdTClPc)
Palladium(II) tetrachlorophthalocyanine, PdTClPc, was synthe-
sized through an intermediate step involving the formation of
a diazonium salt intermediate from PdTAPc [20].
2.3.4.1. Preparation of palladium(II) phthalocyaninetetradiazonium
salt (PdPcTNþ2 Clꢂ). Palladium(II) phthalocyaninetetradiazonium
salt (PdPcTNþ2 Clꢂ) was prepared by adding finely ground palladiu-
m(II) tetraaminophthalocyanine (1.0 g) to 20 mL of a 1.0 N hydro-
chloric acid solution. The mixture was kept in a bath of crushed ice
with constant stirring until the temperature of the solution fell
below 5 ꢀC. To this cold solution, a chilled aqueous solution of
sodium nitrite (0.65 g/5 mL) was added in small portions (0.5 mL at
a time) while constantly stirring. Heat was evolved by the reaction.
The temperature was kept below 10 ꢀC using ice cubes and then this
solution was used in the next step.
2.3.6.2. Palladium(II) tetra(thiophenyl)phthalocyanine. Mixture of
4-(phenylthio)phthalonitrile (0.52 g, 0.002 mol), palladium chlo-
ride (0.12 g, 0.7 mmol) and urea (0.25 g) were stirred at 190 ꢀC for
12 h. The crude product was filtered, and the resulting solid
sequentially washed with methanol and water. Then the product
was purified by column chromatography, using THF as the eluting
solvent. After evaporation of the solvent, the product was further
purified by washing with acetone and then with ethanol in
a Soxhlet apparatus to afford 0.38 g of the title compound as a black
to green solid. Anal. for palladium tetra(thiophenyl)phthalocya-
nine, C56H37N8S4Pd: Calc. (%) C, 63.63; H, 3.50; N, 10.60; S, 12.15; Pd,
10.08. Found. C, 64.23; H, 3.24; N,10.29; S,12.8; Pd,10.63. Electronic
absorption, lmax (nm): 331, 428, 632, 675. IR absorption bands
(cmꢂ1): 776(w), 820(s), 881(w) 928(w), 1037(s), 1064(w), 1112(s),
1152(s), 1247(w), 1306(s), 1342(m), 1389(w), 1437(s), 1510(s).
2.3.4.2. Preparation of palladium(II) tetrachlorophthalocyanine
(PdTClPc). In order to prepare palladium(II) tetrachlorophthalocyanine
(PdTClPc), a clear, chilled (<10 ꢀC) solution of palladium phthalocya-
ninetetradiazoniumchloride was added with constant stirring to
a freshly prepared chilled cuprous chloride solution in concentrated
HCl (5.3 g/8 mL). The mixture was allowed to attain room temperature,
after which it was warmed in a water bath to about 60 ꢀC until the
evolution of nitrogen gas ceased. The green product was filtered and
washed with sodium hydroxide (1.0 N), hydrochloric acid (1.0 N) and
finally with distilled water till the filtrate was neutral. The complex was
dried at 100 ꢀC for 30 min to obtain 0.9 g of a black to green solid. Anal.
for palladium tetrachlorophthalocyanine, C32H12N8Cl4Pd: Calc. (%) C,
50.79; H, 1.59; N, 14.82; Cl, 18.73; Pd, 14.07. Found; C, 50.91; H, 1.24; N,
14.49; Pd,14.40. Electronic absorption, lmax (nm): 349, 443, 624, 673. IR
absorption bands (cmꢂ1): 754(w), 817(s), 840(s), 910(w), 1049(w),
1103(m), 1143(s), 1201(w), 1329(s), 1402(m), 1437(w), 1520(s).
3. Results and discussion
Fig. 1 shows a brief schematic for the synthesis of tetra-
substituted palladium phthalocyanine complexes with the
different functional groups at the periphery of benzene ring. The 4-
substituted precursors lead to the formation of 2,9,16, 23-
tetrasubstituted complexes with four positional isomers (C4h,
C2v, Cs, D2h) [23] and the composition of the isomers depends on
the central metal ion and the structure of the peripheral substituent
[24]. The formation of isomers is due to the symmetry involved in
the condensation reaction used in phthalocyanine synthesis.
Separation of the isomers is extremely difficult, and accordingly
only a few pure tetrasubstituted isomers have been isolated hith-
erto. The use of highly pure precursors and the extreme care taken
during the synthesis and purification leads to formation of
complexes with higher composition of C4h isomer, 2,9,16,23-
symmetrically substituted phthalocyanine. Even then, smaller
amounts of other isomers will be formed which have not been
separated here. Though the elemental analysis data was in agree-
ment with the theoretical calculations, small discrepancies indicate
that the complexes are not 100% pure. In addition it is also difficult
to achieve complete conversion because of the extreme synthetic
conditions employed and the insolubility of phthalocyanines in
most of the aqueous and organic solvents.
2.3.5. Synthesis of palladium(II) phthalocyaninetetracarboxylic acid
(PdTCAPc)
Palladium(II) phthalocyaninetetracarboxylic acid (PdTCAPc) was
prepared by mixing 2.0 g (0.01 mol) trimellitic anhydride, 0.53 g
(0.003 mol) palladium chloride, 4.0 g urea, 0.25 g ammonium
chloride and 0.05 g ammonium molybdate into 10 mL nitroben-
zene. The mixture was gradually heated and maintained at 180 ꢀC
for 4 h with stirring under reflux [21]. The deep bluish black solid
was cooled to room temperature and washed with methanol and
water. Then the crude product was stirred at 90 ꢀC with aqueous
solutions saturated with sodium chloride consecutively with
sodium hydroxide (1.0 M) and then with hydrochloric acid (1.0 N)
till the evaporation of ammonia completely ceased. The product
was finally washed with distilled water till the filtrate was neutral
to the litmus paper. The complex was dried at 100 ꢀC for 30 min to
afford 1.72 g of a black to green product. Anal. for palladium(II)
phthalocyaninetetracarboxylic acid, C36H16N8O8Pd: Calc. (%) C,
54.38; H, 2.01; N, 14.10; O, 16.11; Pd, 13.40. Found; C, 54.63; H, 2.24;
The complexes are dark blue to bluish-green in colour and are
soluble in dimethyl sulfoxide, dimethyl formamide, pyridine,

272
K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
Fig. 1. Brief schematics for the synthesis of palladium phthalocyanine complexes.
chloronaphthalene and concentrated sulphuric acid. The solutions
appear to be stable in these solvents for more than a week. But after
some time, few of the molecules of these complexes become
aggregated and slowly start settling down. The palladium phtha-
locyanine complexes were obtained with a good yield (75e90%).
The ATR-IR spectra for all the complexes (spectra in
supplementary information) showed absorption peaks around 750,
850, 940, 1060, 1110 and 1150 cmꢂ1 which may be assigned to
phthalocyanine skeletal vibrations [25]. Two absorption bands are
observed at 3334 and 3215 cmꢂ1 for the PdTAPc complex which are
the characteristic asymmetric and symmetric stretching vibrations
of the amino group. PdTCAPc showed a broad band at 3100e
3600 cmꢂ1 which can be assigned to the eOH of the carboxylic
acid group. All the spectra showed absorption peaks in the range
around 3060 cmꢂ1 due to the aromatic CeH stretching.
The synthesized complexes were characterized by XPS to study
the presence of different elements in the synthesized complexes
and to study the effect of the substituents on the binding energy.
Fig. 2 shows the XPS spectra of the C1s region for different
complexes and the N1s, Pd3d regions for PdPc. The Pd 3d spectra
Fig. 2. X-ray photoelectron spectra of (a) carbon 1s for different complexes, (b) nitrogen 1s, (c) palladium 3d regions for the PdPc.

K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
273
show two intense peaks at w338.5 and 343.8 eV with a shift of
around 0.1e0.5 eV for different complexes. The peak at lower
binding energy can be attributed to 3d5/2 and the other peak at
higher binding energy to 3d3/2. The Pd3d5/2 peak indicates the
presence of Pd in þ2 state in the phthalocyanine complexes. The
complexes show a main N1s peak at w398 eV. The main peak is
associated with a shoulder and indicates that the phthalocyanine
complexes have nitrogen atoms in two kinds of chemical
environment: four nitrogen atoms only bond with two carbon
atoms and form CeN]C bonds, while the other four nitrogen
atoms not only bond with carbon atoms but also bond with the
copper atom through a coordination bond [26]. The PdPc show
a main C1s peak at 285 eV, whereas the electron donor amine
phthalocyanine shows a peak at 284.5 eV and the electron with-
drawing nitro, chloro and phenylthio groups show peaks at
w288.5 eV. The C1s region of all the complexes show one main
peak with two shoulders which can be assigned to C1s (phenyl
Substitution of the electron donor eNH2 group on the periph-
eral benzene ring of the PdPc structure shows a bathochromic shift
to an extent of 60 nm. The substitution of the electron acceptor e
NO2 and eCl groups also found to affect the bathochromic shift but
to a smaller extent of 20 nm in comparison to the peak observed in
the spectrum for PdPc complex. The presence of the eCOOH
substituent does not have any effect on the spectral shift, whereas
the thiophenyl group also showed a bathochromic shift compared
to the PdPc. The variation in the spectral shift of the peaks is due to
the variation in the electron density of the macrocycle and the
presence of various substituted functional groups. In general, an
edge-to-edge configuration leads to the red shift or bathochromic
effect, while a cofacial arrangement leads to the blue-shift or
hypsochromic effect [14].
Raman analyses were performed to obtain information about the
functional groups and the electron density associated with the
macrocycle. The spectra for the different palladium phthalocyanine
complexes as powder samples are given in Fig. 4. The Raman signals
observed are in good agreement with the data documented in the
literature for different phthalocyanine compounds [31e35]. The
spectra are dominated by strong in-plane stretching and breathing
modes of the phthalocyanine macrocycle. The bands observed are
assigned based on the reported literature [31].
rings), C1s (pyrrole) and C1s (pep*) satellite, respectively [26]. The
C1s spectra of carboxylic phthalocyanine show two peaks which
may be due to the presence of monomeric and oligomeric units.
PdTNPc and PdTCAPc show an O1s peak at w531 eV. The Cl 2p
spectra of PdTClPc show a peak at 196.6 eV whereas a S2p peak was
observed for PdTPSPc at 160.2 eV. The shift in the binding energy
for the different complexes is in accordance with the literature [27].
In general, substituents with more electronegative species tend to
shift core electron binding energies upfield to a higher energy and
vice versa.
UVeVIS experiments were performed in dimethyl sulphoxide
solvent in the range 280e800 nm (the UV cut-off region for DMSO
is 265 nm). The aim was to provide information about the electron
density of the complexes, their aggregation and their spectral shifts.
UVeVisible spectra for the complexes are presented in Fig. 3. The
peaks observed in the Q-band region in the range 615e730 nm are
responsible for the observed green colour of the complexes. These
Table 1 gives an overview of the various bands and their cor-
responding assignments. The most intense band in the spectra of
these complexes is the pyrrole stretching at around 1520 cmꢂ1
,
consistent with the data for other Pc, where the oxidation state of
the central metal is presumed to be þ2 [31e36]. The stretching
vibration of the pyrrole ring on the phthalocyanine macrocycle is
observed around 1340 cmꢂ1. The macrocyclic vibration observed
around 1110 cmꢂ1 can mainly be assigned to
n(C]C) and d(CeH)
vibrations. The peak at 1100 cmꢂ1 shifted towards the higher
wave number for the substituted complexes compared to the
parent palladium phthalocyanine complex. In addition they show
strong peaks in the region 700e1200 cmꢂ1. The spectral pattern in
this region strongly depends on the molecular structure of the
complexes and also on the chemical structure of the central metal.
This can be clearly seen by the substituted phthalocyanines
complexes show a shift in the peaks by 10e20 cmꢂ1 compared to
the parent palladium phthalocyanine. This is due to the electron
with-drawing or electron-donating nature of the functional groups
present on the periphery of the phthalocyanine macrocycle which
alters the electron charge-density in the phthalocyanine macro-
cyclic ligand [1,2]. The pyrrole ring out-of-plane deformation is
transitions may be assigned to the
p / p* transitions [28]. The
peaks obtained in the B-band region are in the range 310e350 nm.
The broad absorption peaks observed in the range 420e450 nm are
probably due to C4V symmetry of the complexes [29]. The UVeVis
spectra of metallic mono-Pcs in solution display a narrow Q-band
[1], but the splitting or two bands observed in these complexes
indicates the presence of both monomeric and dimeric forms of the
complexes in solution. The shoulder or splitting of the peak
observed in the Q-band region may also be due to the vibronic fine
structure in addition to dimeric species in solution [30].
2.0
PdPc
b
1.5
PdTAPc
d
PdTCAPc
1.0
c
a
PdTClPc
PdTNPc
PdTPSPc
e
0.5
f
0.0
300
400
500
600
700
800
1800
1600
1400
1200
1000
800
600
400
200
Raman Shift (cm-1)
Wavelength, nm
Fig. 3. UVeVisible spectra in DMSO for (a) PdPc, (b) PdTNPc, (c) PdTAPc, (d) PdTClPc,
Fig. 4. Raman spectra of the six palladium phthalocyanine complexes as powder
(e) PdTCAPc and (f) PdTPSPc.
samples.

274
K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
Table 1
Files) and found to be in good agreement for the related phthalo-
cyanine complexes [38]. In general, XRD spectra indicate that the
complexes are slightly crystalline in nature.
Raman spectral bands for different palladium phthalocyanine complexes, with the
respective assignments [28e33].
Assignment
of peaks
Raman shift, cmꢂ1
Thermal studies provide information about the thermal stability
and the decomposition behaviour of the complexes at different
temperatures. The TGA curves obtained are shown in Fig. 6. An
overview of the decomposition temperatures of the synthesized
complexes are given in Table 2. The thermogravimetric curve for
PdTCAPc shows a mass loss below 100 ꢀC due to the loss of water
and moisture from the sample with an exothermic decomposition.
The phthalocyanine complexes do not show any sharp melting
point but decompose at elevated temperatures. The onset of the
decomposition is situated around 350 ꢀC, indicating these
complexes are highly stable in air even at high temperatures. The
derivative of the mass signal clearly shows that there are two
separate decomposition processes: the first with a maximum
around 370 ꢀC (ꢃ38 ꢀC) and the second around 425 ꢀC (ꢃ35 ꢀC). The
decomposition temperatures obtained from the derivative of the
mass-signal is given in Table 2. The decomposition temperature for
the different complexes increases in the following order.
PdPc
PdTNPc PdTAPc PdTClPc
PdTCAPc PdTPSPc
n
n
n
n
(Benzene ring)
CaNa
(Isoindole ring) 1448
1610
1522
1438
1606
1521
1449
1399
1346
1605
1520
1444
1605
1524
1452
1422
1342
1592
1521
1444
1416
1345
1313
1257
1208
1182
-pyrrole
1519
C
a
Nb
,
n
CbC
b
1409, 1388
1340
Pyrrole stretch
1336
1306
1257
1206
1190
1141
1343
d
CH
1265
1215
1188
1155
1260
1207
1189
1157
1263
1207
1187
1155
1274
1212
1183
d
d
CH
CH
Pyrrole
ring breathing
CC, CH
(Isoindole)
n
n
d
1108
1116
1117
1058
1114
1048
1118
1025
1115
1006
949.4 961.5
918
802.7
752.6 751.8
725.7
996
962.1
960.7 960.2
943.5
956.1
805.1
751.3
729.5
803.4 804.4
749.7 752.5
727.5
d
CH,
d
CCC
752
726.2
698.1
PdPc < PdTPSPc < PdTClPc < PdTAPc < PdTCAPc ¼ PdTNPc
Macrocycle
breathing
Benzene ring
deformation
676.7 678.1
609.5 624
597.3 599.5
679.7
604.1
522.7
421.3
679.4 683.9
618.3 604.2
597.9
680.2
603.3
This can be indicated in terms of functional groups
eH < eS ꢂ C6H5 < eCl < eNH2 < eCOOH ¼ eNO2
Out-of-plane ring 576.7
deformation
518.8
Pyrrole ring
deformation
480.5
418.3
The latter clearly indicates that the substitution of functional
group at the periphery of the benzene ring leads to the higher
thermal stability of the phthalocyanine macrocycle. The variation in
thermal stability was also observed for phthalocyanine complexes
with different central metal ions [39,40]. The higher stability of the
complexes with carboxylic acid and nitro functional groups can be
attributed to the extra stability achieved by the phthalocyanine
macrocycle due to the extended aromaticity provided by the
carboxylic and nitro groups.
observed at 730 cmꢂ1 and the out-of plane
vibration appears at 750 cmꢂ1 [33].
d(CeH) bending
Powder X-ray diffraction spectra for the different phthalocya-
nine complexes are shown in Fig. 5. The X-ray diffraction pattern of
the complexes, except for PdTCAPc, shows many sharp peaks in the
spectra, indicating the crystalline nature of the samples. The
carboxylic acid substituted complex, PdTCAPc, shows a few peaks
which are broader in nature indicating the formation of dimers and
oligomers in the complex due to the condensation of carboxylic
acid at high temperatures to give the oligomers [37]. PdTCAPc
shows peaks at two-theta values 27.22, 32.96 and 40.17 whereas
other complexes show peaks at 11.42, 13.82, 14.51, 16.92, 22.65,
25.62, 27.22, 32.96 and 40.17ꢀ. The dhkl and 2theta values obtained
were compared with the values reported in literature (ICDD-PDF
If we assume that the mass at 200 ꢀC is that of the dry complex
and the end product formed after decomposition at 500 ꢀC is PdO,
then we can compare the end mass of the experimental sample
with the predicted or theoretical end mass. Table 3 shows the mass
residue at 700 ꢀC. Column 6 and 7 in Table 3 show the experi-
mentally determined PdO residue (compared to the mass at 200 ꢀC)
and the theoretical molecular mass of PdO for the synthesized
samples (% mass difference between experimental and theoretical
e
d
a
b
c
10
20
30
40
50
60
2θ, degree
Fig. 6. Thermogravimetric curves for (a) PdPc, (b) PdTNPc, (c) PdTAPc, (d) PdTClPc, (e)
Fig. 5. XRD spectra of (a) PdPc, (b) PdTNPc, (c) PdTAPc, (d) PdTClPc and (e) PdTCAPc.
PdTCAPc and (f) PdTPSPc.

K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
275
Table 2
Decomposition temperature of the palladium complexes.
Complex
Functional
group
Loss of
water
First
decomposition
step (ꢀC)
Second
decomposition
step (ꢀC)
PdPc
eH
e
e
e
388
401
388
367
389
333
429
430
429
406
456
380
PdTNPc
PdTAPc
PdTClPc
PdTCAPc
PdTPSPc
eNO2
eNH2
eCl
eCOOH
eS-C6H5
Yes
values are given in the bracket). The higher residue obtained in case
of PdTPSPc indicates the formation of PdSO4 instead of PdO in the
temperature region we have studied. Overall thermogravimetric
studies reveal that the complexes are highly stable in air (up to
temperatures of 400 ꢀC) and also reveal that the complexes are pure
as the decomposition products at 700 ꢀC are comparable to the
expected PdO theoretical mass value.
The complexes were also studied for their electrochemical redox
behaviour and the cyclic voltammograms are presented in Fig. 7.
The bare glassy carbon electrode does not show any peaks in the
experimental potential region 1.0 to ꢂ1.5 V. The palladium phtha-
locyanine complexes show three common redox peaks. These
peaks can be attributed to the redox behaviour of the phthalocya-
nine macrocyclic ligand. PdPc complex showed reduction peaks at
around ꢂ0.512 (Ic), ꢂ0.77 (IIc) and ꢂ1.079 (IIIc) V and oxidation
peaks at 0.41 (Ia), ꢂ0.34 (IIa) and ꢂ0.6 (IIIa) V which were less
intense compared to the reduction peaks indicating that the redox
phenomena is quasi-reversible.
Since the Pd metal-ion has no accessible d-orbital levels lying
within the lalu (HOMO) e leg (LUMO) gap of a phthalocyanine
species, its redox chemistry will be similar to redox inactive metal-
lophthalocyanines. In other words the Pd(II) metal centre does not
undergo any redox process and the redox peaks observed are due to
the phthalocyanine macrocyclic ligand [1,12e15]. The reduction
peak at ꢂ0.512 V canbe accounted for(Pc/Pcꢂ1), e0.77to(Pcꢂ1/Pcꢂ2
)
Fig. 7. Cyclic voltammetric curves with GC for (a) blank, 2 mM (b) PdPc, (c) PdTNPc, (d)
and ꢂ1.1 to ꢂ1.2 V can be attributed to the phthalocyanine ring
reduction (Pcꢂ2/Pcꢂ3) [41]. Almost the same peaks and the same
behaviour were observed for PdTNPc, PdTClPc, PdTCAPc, PdTPSPc.
The splitting of the peaks or shoulders observed for some of the
complexes which is well documented in literature that splitting of
a peak arises due to the aggregation of the electroactive species
[1,16]. The shoulder got disappeared at higher scan rates which may
be due tothe disintegrationof the aggregatedmolecules. This type of
behaviour has been observed for palladium phthalocyanine
complexes [15]. PdTAPc showed extra peaks at 0.38 and ꢂ0.05 V
with their oxidation peaks at 0.73 and 0.41 V respectively. The peak
at 0.71 V can be ascribed to the irreversible oxidation of the aromatic
amino group as was observed for aniline in the electrochemical
preparation of polyaniline [42]. The electron transfer abilities of
PdTAPc, (e) PdTClPc, (f) PdTCAPc and (g) PdTPSPc in 10 mM TBAP in DMSO at 50 mV/s.
phthalocyanines depend on the nature and number of substituents
and are due to the interaction between the phthalocyanine ring and
the metal centre which is influenced by conjugated
p-electron
current of the phthalocyanine ring [1,2]. The peak potentials for
these phthalocyanine complexes were observed at considerably low
negative potentials with respect to those of the common phthalo-
cyanines reported in the literature [1,43e46], though the electro-
chemical measurement were carried out in polar solvent, DMSO
which shifts the redox reactions towards more negative potentials. If
the redox inactive metallophthalocyanines showed the redox peak
at ꢂ0.8 V vs SCE, while these complexes showed redox peak
Table 3
Comparison of the mass residues of different complexes.
Complex
(column 1)
Functional
group (column 2)
Molecular mass
(theoretical)
g/mol (column 3)
% of dry mass
Experimental
% of dry mass
theoretical
(Column 7)
Mass at
200 ꢀC (mg)
(column 4)
Mass at 500
ꢀC (mg)
(column 5)
% of dry mass
experimental
(column 6)
PdPc
eH
618.8
798.8
678.8
756.6
794.8
1051.0
6.857
6.320
5.543
6.409
8.817
6.753
1.873
1.395
1.066
1.300
1.908
3.011
23.77
22.07
19.23
13.82
21.64
44.59
19.7(ꢂ4)
15.3(ꢂ6.7)
18(ꢂ1.2)
PdTNPc
PdTAPc
PdTClPc
PdTCAPc
PdTPSPc
eNO2
eNH2
eCl
eCOOH
eS-C6H5
16.2(2.4)
15.4(ꢂ5.2)
11.65(ꢂ32)

276
K.S. Lokesh, A. Adriaens / Dyes and Pigments 96 (2013) 269e277
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Tetra-substituted palladium phthalocyanine complexes of nitro,
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decomposition product except aryl thio substituted complex which
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layers, electrodeposition and electropolymerization as they are very
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The authors are thankful to Prof. D. Depla, Prof. P. Vandenabeele
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2012.08.018.
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