Journal of Minerals and Materials Characterization and Engineering, 2013, 1, 20-23
http://dx.doi.org/10.4236/jmmce.2013.11004 Published Online January 2013 (http://www.scirp.org/journal/jmmce)
Growth and Characterization of Dichloro
Tris(Triphenyl Phosphine Oxide)Cadmium(II)
—Second Harmonic Generation from
a Centrosymmetric Crystal
K. Sreevani1, K. Thangaraj2*, K. Ramamurthi3, S. Selvanayagam4, B. Sridhar5,
V. V. Anierudhe6
1Department of Physics, K. S. R. College of Engineering, Tiruchengode, India
2Department of Physics, Kongu Engineering College, Perundurai, India
3Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli, India
4Department of Physics, Kalasalingam University, Krishnan Koil, India
5Laboratory of X-Ray Crystallography, Indian Institute of Chemical Technology, Hyderabad, India
6Vidyaa Vikas Educational Institutions, Tiruchengode, India
Received August 12, 2012; revised September 27, 2012; accepted October 15, 2012
ABSTRACT
The title compound dichloro tris(triphenyl phosphine oxide)cadmium(II) were grown by slow cooling method from
aqueous solution. The title compound was synthesized and purified by repeated crystallization process. Grown crystals
were characterized by X-ray diffraction and FTIR analysis. The range of optical transmission was determined by re-
cording UV-Vis-NIR spectrum. Thermal properties were investigated by DTA and TGA analyses. Its mechanical hard-
ness was estimated by Vickers microhardness method.
Keywords: Crystal Growth; Single Crystal X-Ray Diffraction; Ultraviolet Spectra; Nonlinear Optical Crystals
1. Introduction
Growth of single crystals of semi organics has been a
subject of perennial concern in order to use the materials
for device application. Due to this, the new semi-organic
crystals have higher mechanical strength and chemical
stability [1]. Metals with d10 configuration like Zinc,
Cadmium, Mercury readily combines with organic mate-
rials resulting in stable compounds with good physic
chemical behaviour. Triphenylphosphine is an interesting
candidate as it binds well to most of the transition metals
of group VII-X [2]. The basic structure of organic NLO
Materials is based on the π bond system, due to the over-
lap of π orbital delocalization of electronic density [3].
On the basis of this, in the present investigation, we re-
port for the first time, the synthesis, growth, crystal
structure and characterization of the title compound di-
chloro tris(triphenyl phosphine oxide)cadmium(II).
2. Experimental Section
2.1. Synthesis of CdCl2 (TPPO)4
The title compound was synthesized by dissolving ana-
lytical reagent grade cadmium chloride (CdCl2) (HIME-
DIA) and triphenyl phosphine oxide (TPPO) (Chanshu
Yangvan Chemical China) in absolute ethanol in stoi-
chiometric ratio. The temperature of the solution was
maintained at about 50˚C and CdCl2 (TPPO)4 was ob-
tained by the evaporation of the solvent. Purity of the
compound was increased by successive recrystallization.


265 265
33
4
CdCl2C HPOCdClC HPO



 

 
2.2. Crystal Growth
CdCl2 (TPPO)4 crystals were grown by slow evaporation
technique. The precipitate was taken as raw material.
Saturated CdCl2 (TPPO)4 solution was prepared at room
temperature with ethanol and Dimethyl sulfoxide
(DMSO) of 1:1 ratio as solvent. DMSO was added to
improve the crystallization. The prepared transparent
solution was filtered. The pH of the solution is 5. The
solution was taken in glass beaker and closed with per-
forated covers and kept in a dust free atmosphere. The
transparent crystals were harvested after 35 days when it
attained a size of 7 × 2 × 2 mm3. The as grown crystal is
shown in Figure 1.
*Corres
p
ondin
g
autho
r
.
C
opyright © 2013 SciRes. JMMCE

K. SREEVANI ET AL. 21
Figure 1. The as grown crystal of dichloro tris(triphenyl-
phosphine oxide)cadmium(II)crystal.
2.3. Characterization of CdCl2 (TPPO)4
The single-crystal XRD data of the grown CdCl2 (TPPO)4
crystal was obtained using accurate unit cell parameters
and orientation matrix were obtained by least-square fit
of several high angle reflection in the range 1.5˚ ≤ θ ≤
25˚ using Mo Kα radiation on BRUKER SMART APEX
CCD area detector using ω scan mode. X-ray powder
pattern of the crystal was recorded on a Rigaku DMaxic
computer controlled X-ray powder diffractometer with
copper (K alpha 1) radiation of wavelength 1.54056 Å.
The scanning rate was maintained at 1.6˚/min over a 2θ
range of 10˚ to 70˚ employing reflection mode of scan-
ning. The elemental analysis of the synthesized
CdCl2(TPPO)4 was carried out by JSM energy dispersive
X-ray microanalyzer equipped with JEOL-6360 SEM.
The functional groups of vibration of CdCl2 (TPPO)4
crystal were identified by FTIR technique using a Perkin
Elmer spectrophotometer using KBr pellet technique in
the range of 400 - 4000 cm−1. The UV-Vis-NIR absorp-
tion spectrum of the CdCl2 (TPPO)4 crystal was exam-
ined in the wavelength range of 450 - 1000 nm using
Lambda 35 (Instrument Model) UV-Vis-NIR spectro-
photometer. Thermogravimetric analysis was carried out
for the as grown crystals of CdCl2 (TPPO)4 using PYRIS
thermal analyzer. The NLO property of CdCl2 (TPPO)4
crystal was confirmed by Kurtzpowder SHG test using
Nd-YAG laser (1064 nm). The pulse width and repetition
rate of the laser pulses were 8 ns with a repetition rate of
10 Hz respectively at 1064 nm radiation. The micro-
hardness studies of single crystal was carried out using a
Vickers microhardness tester fitted with a diamond py-
ramidal indentor.
3. Results and Discussions
3.1. X-Ray Diffraction Analysis
Unit cell parameters of the grown CdCl2 (TPPO)4 crystals
were obtained using the single crystal diffractometer and
are given in Table 1. It is found that CdCl2 (TPPO)4 crys-
tallizes in orthorhombic system with centrosymmetric
space group Pbca and V = 6608.4(7) Å3. The crystallinity
of the grown crystals was checked by taking the X-ray
diffraction pattern of powder samples of CdCl2 (TPPO)4.
The ORTEP plot of the molecule is shown in Figure 2.
3.2. Energy Dispersive X-Ray Analysis
The determination of elemental composition of the single
crystal was done using energy dispersive analysis for
confirming stoichiometry. The energy spectrum of the
crystal is shown in Figure 3. In the present study, the
grown CdCl2 (TPPO)4 single crystal was analyzed by
JSM energy dispersive X-ray micro analyzer equipped
with JEOL-6360 SEM. The energy spectrum confirms
the presence of cadmium chloride and triphenyl phos-
phine oxide.
3.3. Fourier Transform Infrared (FTIR) Analysis
The Fourier Transform Infrared spectrum (FTIR) of
Table 1. Single crystal X-ray data of CdCl2 (TPPO)4.
CCDC Number CCDC 893123
Empirical formula C72H60Cd2Cl4O4P4
Formula weight 1479.68
Crystal system Orthorhombic
Space group Pbca
a = 11.1658(7) Å; α = 90°.
b = 22.0016(14) Å;  = 90°.
Unit cell dimensions
c = 26.8999(16) Å;  = 90°.
Figure 2. ORTEP plot of the molecule drawn at 30% prob-
ability level.

K. SREEVANI ET AL.
22
Figure 3. Energy spectrum of dichloro tris(triphenyl pho-
sphine oxide)cadmium(II)single crystal.
CdCl2 (TPPO)4 crystal was recorded on PerkinElmer
FTIR spectrophotometer using KBr pellet technique in
the range of 400 - 4000 cm−1. The recorded FTIR spec-
trum of CdCl2 (TPPO)4 depicts that stretching vibration
of P=O (~1187 cm−1) shifts to lower frequency (~1160
cm−1) which clearly indicates influence of Cd. Also, fre-
quency 537 cm−1 indicates the influence of metal-oxygen
vibrational modes [4]. The peak at ~3456 cm−1 is assign-
ed for the stretching vibrations of the O-H bond of the
water molecules absorbed by KBr. The vibrational fre-
quencies of CdCl2 (TPPO)4 are compared with that of the
FTIR spectrum of ZnCl2 (TPPO)2 [5] and CdBr2 (TPPO)2
[6] in Table 2.
3.4. UV-Vis-NIR Analysis
The absorption spectrum of CdCl2 (TPPO)4 was recorded
in the wavelengths range of 450 - 1000 nm using Lam-
bda 35 (Instrument Model). UV-Vis-NIR spectrometer.
A crystal with the thickness of about 2 mm was used for
this measurement. From the spectrum, it is evident that
the compound has a very low cut off at ~390 nm, and the
crystal is found to be transparent in the region of 350 -
900 nm, which is an essential requirement for frequency
doubling process.
3.5. Thermal Analysis
Thermogravimetric and differential thermal analysis of
CdCl2 (TPPO)4 were carried out using a PYRIS thermal
analyzer. A ceramic crucible was used for heating the
sample and the analyses was carried out in an atmosphere
of nitrogen at a heating rate of 10 K/min in the tempera-
ture range of 309 - 1136 K. The initial mass of the mate-
rial subjected to analysis was 4.5 mg. A sharp endother-
mic peak at ~463 K depicts a phase transition of the ma-
terial. Thermal studies show that the crystal is stable
without decomposition upto ~573 K and an endothermic
peak observed at ~723 K represents the melting point of
CdCl2 (TPPO)4.
Table 2. Comparison of vibrational frequencies (cm−1) of
CdCl2 (TPPO)4 with reported works.
Assignments ZnCl2 (TPPO)2
[5]
CdBr2 (TPPO)2
[6]
CdCl2 (TPPO)4
(present work)
ν (P=O) 1155 1157 1160
ν (P-C) 1437 1432 1433
ν (C=C) 1588 1589 1586
ν (C-H) 3055 3052 3058
ν (O-H) 3436 3456 3458
(ν) Symmetric stretching
3.6. Microhardness Studies
Vickers microhardness test was carried out on the promi-
nent face of CdCl2 (TPPO)4 crystal using microhardness
tester fitted with a diamond indenter. The indentation
was made using a Vickers Pyramidal indentor for various
loads. The indentation time was kept at 25 s for all the
loads. From the Vicker’s microhardness studies, it is ob-
served that at lower load, there is an increase in the work
hardening of the surface layers. For load above 70 g
crack started developing around the indentation mark,
which may be due to the release of internal stresses [7].
3.7. NLO Activity
The study of SHG conversion efficiency of the grown
crystal was carried out using the modified experimental
setup of Kurtz and Perry [8]. A Q-switched Nd-YAG
laser beam of wavelength 1064 nm, with an input power
of 4.9 mJ, and pulsewidth of 8 ns with a repetition rate of
10 Hz was used. The grown single crystal of was pow-
dered with a uniform particle size and then packed in a
microcapillary of uniform bore and exposed to lase ra-
diations. The output from the sample was monochro-
mated to collect the intensity of 532 nm component. The
generation of the second harmonics was confirmed by
the emission of green light. A sample of potassium dihy-
drogen phosphate (KDP), also powdered to the same par-
ticle size of the experimental sample, was used as the
reference material in the present measurement. Second
harmonic generation efficiency of the powdered CdCl2
(TPPO)4 is ~0.94 times that of potassium dihydrogen
phosphate. The comparison of conversion efficiency of
CdCl2 (TPPO)4 has been compared with other reported
centrosymmetric materials and is given in Table 3.
4. Conclusion
Optical quality single crystals of dichloro tris(triphenyl
phosphine oxide)cadmium(II) (CdCl2 (TPPO)4) have been
grown from aqueous solution by slow cooling method.
The lattice parameters have been calculated by X-ray
diffraction studies. Elemental analysis of the synthesized

K. SREEVANI ET AL.
23
Table 3. Comparitive study of SHG efficiencies of different
centrosymmetric crystals.
Compound Space group
SHG SHG efficiency in
comparison with
KDP(in times)
R,S-serine [9] P21/a 0.02
(p-Nitrophenol,
hexamethyltetramine,
phosphoric acid and water)
super molecular crystal [10]
P21/c 3.1
Glycine picrate [11] P21/a 2.34
CdCl2 (TPPO)4
[present work] Pbca 0.94
material was confirmed by EDAX analysis. The func-
tional groups were identified using FTIR analysis. The
UV-Vis-NIR spectrum reveals the wider transmission
window of CdCl2 (TPPO)4. Thermal analysis indicates
that CdCl2 (TPPO)4 is thermally stable upto ~573 K. The
powder SHG efficiency of this CdCl2 (TPPO)4, a centro-
symmetric crystal is ~0.94 times that of the efficiency of
KDP and can be used in photonics device fabrication.
The mechanical stability of CdCl2 (TPPO)4 has been de-
termined using Vickers microhardness studies.
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