Thermal, UV and FTIR spectral studies in alkali metal cinnamates

Article abstract of DOI:10.1007/s10973-010-0760-6

A single crystal of sodium and potassium cinnamates was grown by slow evaporation of methanol solution at room temperature. The effect of metals sodium and potassium on the electronic structure of cinnamic acid was studied. In this research many analytical methods such as FTIR, UV, second harmonic generation (SHG) and TG-DTA were used: The spectroscopic studies lead to conclusions containing the distribution of the electronic charge in molecule, the delocalisation of π electrons and the reactivity of metal complexes. The SHG efficiency is more pronounced in the presence of sodium and potassium dopant in the growth medium. Incorporation of sodium and potassium increase the thermal stability ensuring the suitability of material for possible non-linear optical (NLO) application up to 180 °C. Akademiai Kiado, Budapest, Hungary 2010.

Full text of DOI:10.1007/s10973-010-0760-6

J Therm Anal Calorim (2010) 100:811–815
DOI 10.1007/s10973-010-0760-6
Thermal, UV and FTIR spectral studies in alkali metal cinnamates
•
•
•
G. Madhurambal B. Ravindran M. Mariappan
S. C. Mojumdar
CTAS2009 Special Chapter
´
´
Ó Akademiai Kiado, Budapest, Hungary 2010
Abstract A single crystal of sodium and potassium cin-
namates was grown by slow evaporation of methanol
solution at room temperature. The effect of metals sodium
and potassium on the electronic structure of cinnamic acid
was studied. In this research many analytical methods such
as FTIR, UV, second harmonic generation (SHG) and TG–
DTA were used: The spectroscopic studies lead to con-
clusions containing the distribution of the electronic charge
in molecule, the delocalisation of p electrons and the
reactivity of metal complexes. The SHG efficiency is more
pronounced in the presence of sodium and potassium
dopant in the growth medium. Incorporation of sodium and
potassium increase the thermal stability ensuring the suit-
ability of material for possible non-linear optical (NLO)
application up to 180 °C.
Introduction
Cinnamic acid (3-phenyl-2-propeonic acid), a derivative of
phenyl alanine, composes a relatively large family of
organic isomers [1–4]. Thermal and spectral analyses are
very useful techniques for materials characterisation.
Therefore, many investigators have used these techniques
for many materials characterisation [2, 5–24]. In nature,
cinnamic acid derivatives are important metabolic building
blocks in the production of lignins for higher plants. Cin-
namic acid possesses antibacterial, antifungal and parasite
fighting abilities. Derivatives of cinnamic acid are impor-
tant pharmaceutics for high blood pressure and stroke
prevention and possess antitumour activity. Cinnamic acid
derivatives and flavonoids in wine create pigments and
tannin agents that give each vintage its characteristic
bouquet and colour. Cinnamic acid extensively studies not
only due to its important biological activity, but also
because of its specific structure. In the spectrum of cin-
namic acid the carboxylic group is separated from the
aromatic ring by a double bond. It causes conjugation
between the C=C and the p electron system. It is very
interesting to compare the electronic structures of cinnamic
acid and the structures of metal cinnamates.
Keywords Solution growth ꢀ Sodium and
potassium cinnamate ꢀ Single crystal ꢀ TG–DTA ꢀ
UV ꢀ FTIR
G. Madhurambal
ADM College for Women, Nagapattinam, Tamil Nadu, India
B. Ravindran
Anjalai Ammal-Mahalingam Engineering College, Kovilvenni,
Tiruvarur District, Tamil Nadu, India
Experimental
M. Mariappan
RVS College of Engineering and Technology, Kalikuppam,
Karaikal 609 609, India
Sample preparation
The metal compounds were prepared by digesting appro-
priate weighed amount of cinnamic acid in methanol of
alkali metal thiocyanides in stechiometric ratio of 1:1.
Then methanol was evaporated in a dryer. The results of
elemental analysis are as follows; for sodium cinnamate
S. C. Mojumdar (&)
Department of Engineering, University of New Brunswick,
Saint John, NB E2L 4L5, Canada
e-mail: scmojumdar@yahoo.com;
subhash.mojumdar@utoronto.ca
123

812
G. Madhurambal et al.
100.0
90
C = 64% and H = 5%; for potassium cinnamate C =
59% and H = 4%.
1891.28
1959.15
3777.97
3920.54
80
70
60
50
40
30
20
Measurements
1073.87
1281.23
938.15
2526.67
The FTIR spectra were recorded with a Bruker IFS spec-
trometer in the range of 400–4000 cm-1. Samples in the
solid state were measured in KBr matrix pellets which were
obtained with hydraulic press under 739 MPa.
767.06
977.47
481.52
1312.36
1216.16
584.35
534.56
682.65
1414.49
1449.73
The UV absorption spectra were recorded using a dou-
ble beam UV spectrometer in the spectral range 100–
400 nm.
3445.72
2359.40
The thermogravimetric and differential thermal analyses
were carried out on a Netzsch STA 409C thermal analyser
in the nitrogen atmosphere. The sample was heated between
30 and 800 °C at a heating rate of 10 °C per minute.
10
1627.42
1667.56
0.0
4000.0
3000
2000
1500
–1
1000
400.0
cm
Fig. 2 FTIR spectrum of sodium cinnamate
Results and discussion
100.0
FTIR spectral studies
1025.55
1491.67
1810.85
90
The FTIR spectra of cinnamic acid, sodium and potassium
cinnamates, recorded in KBr pellet technique and in
organic matrix are presented in Figs. 1, 2 and 3. There is an
intensive band at 3445.72 cm-1 in sodium cinnamate,
3441.31 cm-1 in potassium cinnamate and broad bands in
the range 2359–2528 cm-1 assigned to the –OH stretching
vibrations of acid dimmers [25–27]. In this range there are
also the bands of the –CH stretching vibrations what is seen
in the Figs. 1, 2 and 3.
3917.14
3780.98
1892.16
1073.83
1281.54
80
70
60
50
40
30
20
938.85
2527.76
977.27
766.64
1311.95
1217.20
480.77
584.56
536.46
680.59
2069.66
2360.77
1414.32
1554.34
3441.31
There are splitting bands assigned to the stretching
vibrations of the C=O group (i.e. 1891.28, 1667.56 and
1892.16, 1819.85 cm-1, respectively) in the infrared spec-
tra of sodium and potassium cinnamates. This indicates the
1630.86
10
0.0
4000.0
3000
2000
1500
1000
400
–1
cm
100.0
Fig. 3 FTIR spectrum of potassium cinnamate
3918.81
1026.32
90
1891.31
1957.64
3777.25
80
70
60
50
40
existence of different types of molecular packing and cin-
namic acid with the intermolecular packing and associates
cinnamic acid with intermolecular hydrogen bonds
C=OꢀꢀꢀH–O. Replacement of the carboxylic group hydrogen
with a metal ion causes a break down of the intermolecular
hydrogen bonding and the characteristic changes in the IR
spectra of acid appeared. Namely, the disappearance of
bands which originate from stretching cOH vibration, an
appearance of bands of the unsymmetric and symmetric
vibration of the carboxylate anion cas(COO-) shifted
towards wave numbers along the series (Na ? K) in FTIR
spectra. Moreover, band wave numbers of bS(COO-)
decrease along the metal series (Na ? K). This indicates
the formation of sodium and potassium cinnamates.
1073.49
1493.20
2675.77
3061.92
1282.34
2530.24
2832.79
480.54
584.69
915.21
766.96
30
20
3027.65
536.95
3453.58
977.93
2359.74
1557.06
1313.03
1414.02
697.97
1678.71
10
1216.22
1629.10
0.0
4000.0
3000
2000
1500
–1
1000
400
cm
Fig. 1 FTIR spectrum of cinnamic acid
123

Thermal, UV and FTIR spectral studies in alkali metal cinnamates
UV spectral analysis
813
2.50
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
–0.01
196.77,2.3111
215.22,2.0801
The UV spectra for cinnamic acid and alkali metal cinna-
mates are shown in Figs. 4, 5 and 6. In alkali metal cin-
namates, the p–p* absorption band shifted to lower
wavelength compared to cinnamic acid. This is because of
the formation of co-ordinated bond between metal with
cinnamic acid, thus greater energy required for this tran-
sition and hence the absorption shows the blue end of the
spectrum.
273.67,2.0844
1.70
1.6
1.5
1.4
203.77,1.2864
190.0 300 400 500 600 700 800 900 1000.0
Wavelength/nm
273.57,1.5886
Fig. 6 UV spectrum of potassium cinnamate
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
215.25,1.2453
Second harmonic generation efficiency
An Nd:YAG laser with modulated radiation of 1064 nm
was used as the optical source and directed on the powder
sample through a filter. The doubling frequency was con-
firmed by the green radiation of 532 nm. Input radiation is
5.35 mj/pulse. Interestingly, second harmonic generation
(SHG) gives an indication of NLO efficiency of the
material [28]. Nonlinearity is facilitated in the presence of
dopant. The dopant has catalytic effect on the NLO prop-
erties of cinnamic acid crystals. It is interesting to observe
that the SHG efficiency is more pronounced in the presence
of sodium and potassium dopant in the growth medium. It
appears that the attainment of second-order effects requir-
ing favourable alignment of the molecule within the crystal
structure is well facilitated in the presence of inorganic
dopant sodium and potassium.
–0.01
190.0 300 400 500 600 700 800 900 1000
Wavelength/nm
Fig. 4 UV spectrum of cinnamic acid
1.000
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
203.25,0.54533
Thermal analysis
The single crystal of sodium and potassium doped cin-
namic acid was subjected to simultaneous thermogravi-
metric analysis–differential thermal analysis using a
Netzsch STA 409C thermal analyser in the nitrogen
atmosphere. The samples were heated between 30 and
800 °C at a heating rate of 10 °C per minute to study the
mass loss and thermal stability. The TG–DTA curves of
grown crystals were shown in Figs. 7, 8 and 9. The TG
curves reveal that the major mass loss took place at
253.2 °C in sodium cinnamate and 275 °C in potassium
cinnamate, respectively. Such change was also observed by
DTA. This indicates that incorporation of sodium and
potassium increase the thermal stability ensuring the suit-
ability of material for possible NLO application up to
180 °C.
214.86,0.51459
271.15,0.59652
0.20
0.15
0.10
0.05
–0.010
190.0 300 400 500 600 700 800 900 1000
Wavelength/nm
Fig. 5 UV spectrum of sodium cinnamate
123

814
G. Madhurambal et al.
Conclusions
TG/%
DTG/(%/min)
100
[1]
Optical quality single crystals of sodium and potassium
cinnamates were grown by slow evaporation technique at
room temperature. UV absorption spectra confirm the
transparency of the crystals. The molecular vibration and
functional groups of the grown crystals were studied by
FTIR spectral analysis. Thermal analyses showed that the
crystals retain its texture up to 253.2 °C. The dopants have
catalytic effect on the NLO properties of cinnamic acid
crystals.
0
80
60
40
20
0
–5
–10
Mass change: –100%
–15
–20
Inflection: 273.9 °C
–25
[1]
–30
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