CHAPTER 7
GEL GROWTH AND CHARACTERIZATION OF DIPOTASSIUM
TARTRATE SINGLE CRYSTALS
7.1
Introduction
Crystals of dipotassium tartrate find several practical applications in science
and technology because of their interesting physical properties such as dielectric,
ferroelectric, Piezo-electric and non-linear optical properties.
Materials with
quadratic nonlinear optical (NLO) properties are currently attracting considerable
interest among researchers.
Optoelectronics has stimulated search of highly
nonlinear crystals for efficient signal processing. The NLO materials play an
important role in second harmonic generation, frequency mixing, electro-optic
modulation, optical stability, etc. Nonlinear optics (NLO) is at the forefront of
current research because of its importance for the emerging technologies, in areas
such as telecommunications, signal processing and optical interconnections.
Among various optical non-linear materials dipotassium tartrate (K2C4H4O6) has
significant importance because of its high optical non-linearity (Shen 2003; Ji-Ping
Huang et al. 2007; Frits Zernike et al.2006).
Growth and characterization of various metallic tartrate crystals and mixed
tartrate crystals have been reported by Henisch et al.1965 and Patel et al.1982.
Several authors have reported mixed tartrate crystals, for example, mixed
strontium-calcium tartrate [Firdous et al.2009; Sahaya Shajan et al.2004; Suresh
Kumar et al.2010] and manganese-iron levo tartrate (Quasim et al 2009). Crystal
growth and characterization such as Laser Raman and Infrared spectra of solution
grown dipotassium tartrate has been done already (Srivastava et al.1982). To the
best of the present authors knowledge, there is no report of gel growth and
characterization of dipotassium tartrate. Hence, gel growth of dipotassium tartrate
105 by single diffusion method and characterization such as FTIR, Powder XRD,
magnetic properties and thermal analysis have been made for the first time.
7.1.1
Symmetry classification of Phonon modes
The eight formula unit cell of dipotassium tartrate belongs to C23
(F2≡C2) space group. The dynamics of the dipotassium tartrate crystal containing
140 atoms per unit cell can be described in terms of 420 phonon branches under
the unit cell approximation. The branches arise from different normal modes of
C4H4O6 2- , K+ and H2O and their total number count 336, 48 and 36, respectively.
The chain of carbon atoms is almost planar. The planes of two CO2
groups are inclined at nearly 60˚ to this plane. C2 symmetry is therefore assumed
for the tartrate ion in aqueous solution. The site symmetries of K+, C4H4O6 2- and
H2O have not been established from the x-ray crystallographic data previously
available on this system. On the basis of the study made by Srivastava et al, it is
considered that the C4H4O6
2-
ion and the H2O molecule in this crystal occupy
sites of C1 symmetry. The correlation between different symmetry species of
relevant molecular and crystal point groups leads to the following classification for
420 modes of dipotassium tartrate.
Internal : Γ 294 (C4H4O6 2-) = 147A + 147B
External: Γ 42 (C4H4O6 2-) = 21A +21B
Γ48 K+ = 24A+24B
Internal: Γ12 H2O = 6A+6B
External: Γ24 H2O = 12A+12B
Total
: Γ420 (DKT) = 210A+210B
Although the site symmetry of K+, C4H4O6 2- and H2O are not known, the
possible symmetry species of the phonons in DKT crystal can still be analysed.
This task is much simplified by the fact that only C1 and C2 site symmetries are
possible under C23 space group. The correlation between the molecular and the
106 factor group species through C1 as well as C2 symmetry is given in Table 7.1
which also summarises the symmetry classification of phonons in DKT crystal.
Table 7.1
Symmetry classification of phonon modes in the K2C4H4O6 crystal
Correlations taking C1 site symmetry
Group
Modesa
Molecular
Site
Factor
species
species
group
n x mb
Correlations taking C2 site
symmetry
Site
Factor group
species
species
n x mb
species
C4H4O6 2-
γs
A
A
A+B
4x6
A
A
8x6
(C2)
γs
B
A
A+B
4 x6
B
B
8x6
2 x γns
A
A
A+B
4 x 15
A
A
8 x 15
B
A
A+B
4 x 15
B
B
8 x 15
H2O
γ1, γ2,TZ
A1
A
A+B
2x3
A
A
4x3
(C2γ)
Rz
A2
A
A+B
2x1
A
A
4x1
Tx,Ry
B1
A
A+B
2x2
B
B
4x2
γ3,Ty,Rx
B2
A
A+B
2x3
B
B
4x3
Tb
A
A+B
8x1
A
A
16 x 1
Ta, Tc
A
A+B
8x2
B
B
16 x 2
K+
nxFactor group species= Number of phonons from one particular vibration in a rown x m x Factor group species = Number of
phonons from all vibrations on the rowa
under this column, γs
represents
six skeletal internal
modes, i.e. two γcc (A), γcc (B), δsccc(A), δaccc(B) and CC twist (A),three liberations corresponding to Rb(A),Ra(B) and
Rc(B), three translator lattice modes corresponding to Tb(A),Ta(B) and Tc(B) of C4H4O6 2- ion. γns represents30 nonskeletal internal modes; however, these can be grouped into 15 pairs of identical oscillators from pairs of identical groups such
as CH,OH,etc. In COO.CH (OH)-CH(OH)COO2- ion. Thus, effectively there are 15 types of different modes, each having an
in-phase (A) and an out-of-phase (B) combination of two identical oscillations in identical groups. n x m = {number of
crystallographically distinguishable ions/molecules} x {number of different modes of molecular species as indicated in
column 3}.
107 7.2
Experimental method of crystal growth
Single diffusion gel growth technique was employed to grow the crystals.
The crystallization apparatus were glass tube of 25mm diameter and 140mm
length. The AR grade chemicals were used to grow the crystals. The gel was
prepared by mixing 0.75M levo-tartrate acid solution with sodium meta silicate
(Na2SiO3 9H2O) solution of relative density 1.06g/cm3 in such a manner that pH of
the mixture could be obtained as 4.5. This mixture was transferred into several
glass test tubes to set into gel. The following solutions were poured gently on the
set gels:
Supernatant solutions:
I
1M, 5ml KCl + 1M, 5ml KNO3
II
1.5M, 5ml KCl + 1.5M, 5ml KNO3
III
2M, 5ml KCl + 2M, 5ml KNO3
Fig 7.1 Crystals of dipotassium tartrate grown from gel
108 The following reaction was expected to occur and the crystals were grown in gels:
C4H6O6 + KCl + KNO3 → K2C4H4O6 + HCl + HNO3
The growth was completed within a month and transparent, monoclinic structured
diopotassium tartrate crystals were grown. The grown crystals were shown in
Fig 7.1. The various parameters which affect the formation of crystal are described in
Table 7.2.
Table 7.2
Factors determining the growth process of crystals
S.No.
Gel
density
Gel pH
Gel setting
time
Concentration of the
reactants
Results
1
1.04
4.0
72hrs
U.R: 1M, 5ml KNO3
+ 1M, 5ml KCl
LR: 0.5 M, C4H6O6
Transparent crystals of dimensions
8mm x 5mm x 4mm were obtained
2
1.05
4.5
48hrs
U.R: 1.5M, 5ml KNO3
+ 1.5M, 5ml KCl
LR: 1.0 M, C4H6O6
Transparent crystals of dimensions
12mm x 7mm x 5mm were
obtained
3
1.06
5.0
24hrs
U.R: 2M, 5ml KNO3
+ 2M, 5ml KCl
LR: 1.5 M, C4H6O6
Transparent crystals of dimensions
18mm x 8mm x 6mm were
obtained
U.R: Upper reactant L.R: Lower reactan
7.3.
Results and discussion
7.3.1 Fourier Transform Infrared spectroscopy
The FTIR spectrum of dipotassium tartrate crystals are shown in Fig 7.2.
The observed bands with intensity and their vibrational assignments are given in
Table 7.3. Several authors have reported the vibrational spectra of metal tartrate
crystals (Shiva Shankar et al.2009; Parekh et al. 2009); Joshi 2006 et al.2006).
109 Fig 7.2 FTIR spectrum of dipotassium tartrate crystals
The peak observed at 3318.29 cm-1 is due to OH stretching mode. The band at
2975.85 cm-1 is attributed to CH stretching mode of tartaric acid. The bands at
1784.48 cm-1 and 1572.62cm-1 that are unaffected by deuteration seem to be
associated with γa CO and the band around 1415.93cm-1 is due to γsCO. The
absorption peaks at 1069.99 cm-1 is attributed to γ C(OH). The two sharp peaks at
903.80 cm-1 and 878.64 cm-1 are due to γCC mode of vibrations. The band at
842.61 cm-1 is due to δ COO. The absorption peaks around 789.60 cm-1, 680.21
cm-1 and 616.64 cm-1 are attributed to τ COO mode of vibrations. The absorption
below 500 cm-1 is attributed to Metal-oxygen stretching.
110 Table 7.3
FTIR spectrum assignments for dipotassium tartrate crystals
Absorptions in wavenumber (cm-1)
Assignments
3318.29
OH stretching
2975.85
CH stretching
1784.48
γa CO
1572.62
γa CO
1415.93
γsCO
1069.99
γ C(OH)
903.80
γCC
878.64
γCC
842.61
616.64
δ COO
τ COO
τ COO
τ COO
Below 500
Metal-oxygen stretching
789.60
680.21
7.3.2 Powder X-ray diffraction studies
The X-ray diffraction of the grown dipotassium tartrate crystals was studied
using
X-ray diffractometer at room temperature. The XRD patterns of
dipotassium tartrate are shown in Fig 7.3. The corresponding Indexed XRD data
are presented in Table 7.4. The data observed from Powder X-ray diffraction is
well correlated with the data available in the JCPDS file (file no. 23-0551). Hence,
the grown crystals are having monoclinic structure and the crystal structure data
are found from unit cell software program. The inter-axial angles of dipotassium
tartrate crystals are α = β = 90˚; γ = 106˚ and its unit cell dimensions are
a = 9.8845 Å; b = 7.4420 Å; c = 8.8480 Å.
111 Fig 7.3 Powder XRD spectrum of dipotassium tartrate crystals
Table 7.4
Indexed XRD data for dipotassium tartrate
hkl
2θ (°)
I/Io
102
022
121
310
212
041
303
23.07
24.70
27.89
31.23
34.35
36.65
37.92
32
92
95
40
100
68
42
7.3.3 Magnetic properties
The K2C4H4O6 crystals are finely ground, crushed and the resulting powders
were packed in a Gouy tube of known magnetic susceptibility. The readings of
Gouy balance was recorded when the values became steady. These values are
given in Table 7.5. The magnetic susceptibility of the samples are found out by
112 using the equation mg =
χ H2,where ‘m’ is the mass of the substance; ‘A’ is
the area of cross section of the glass tube; ‘H’ is the magnetic field between the
pole- pieces and ‘χ’ magnetic susceptibility of the substance. A graph is drawn
between ‘m’ and ‘H2’ and the slope gives A χ /2g. Hence the susceptibility
‘ ’
is
calculated. This is shown in Figure 4. The slope is found out at from the graph.
The magnetic moment ‘µ’ of K2C4H4O6 crystals are found out by using the
formula µ = 2.828 (χ x T )1/2 BM, where ‘T’ is the room temperature in terms of
Kelvin. The susceptibility and magnetic moment of the dipotassium tartrate
crystals are found out to be 36.12 x 10-6 e.m.u. and 2.94 BM respectively.
Table 7.5
Change in mass with respect to applied magnetic field for
dipotassium tartrate crystals
Name of the crystal
K2C4H4O6
Magnetic field in
Kilogauss
1
2
3
4
5
Mass in
Kilograms
0.0730
0.0725
0.0721
0.0717
0.0713
Fig 7.4 Graph between ‘m’ and ‘H2’ for dipotassium tartrate crystals
113 7.3.4 Thermal analysis
The TGA curve for dipotassium tartrate is shown in Fig 7.5. There is only
one major stage of decomposition starting from 257˚C and continues upto 304˚C.
The weight loss is about 58.94%.
Comparing the observed and calculated
percentage wight losses suggests chemical formula for the given crystal to be
K2C4H4O6 and there is no evidence for water content in the crystal.
Fig 7.5 TGA curve for dipotassium tartrate crystal
Fig 7.6 DSC trace for dipotassium tartrate crystals
114 DSC is a thermoanalytical technique in which the difference in the amount
of heat required to increase the temperature of a sample and reference is measured
as a function of temperature. Both the sample and reference are maintained at
nearly the same temperature throughout the experiment. The result of a DSC
experiment is a curve of heat flux versus temperature. These curves may be
exothermic or endothermic used to calculate enthalpies of transition. The DSC
analysis was done between 40˚C and 500˚C at a heating rate of 20˚C min-1 in
nitrogen atmosphere. The DSC trace for dipotassium tartrate crystals are shown in
Fig 7.6. The endothermic peak at 285.40˚C confirms decomposition of crystal
under investigation.
Table 7.6
TGA result for dipotassium tartrate crystals
Weight Loss%
Name of the
crystal
Temperature
range (˚C)
Observed
Calculated
Dipotassium
tartrate
257 to 304
58.94
59.69
7.3.5
Reaction
K2C4H4O6
K2O
Anti bacterial sensitivity test
Antimicrobial activities of the synthesized dipotassium tartrate crystals of
different sizes were determined using Gram-negative bacteria (E. coli ) and Grampositive bacteria (S. aureus) following a doped Kirby Bauer disc diffusion method.
In brief, the bacteria were cultured in Müller–Hinton broth at 35°C ± 2°C on an
orbital shaking incubator (Remi, India) at 160 rpm. Nutrient agar plates are
prepared and it’s allowed for solidification. The test organisms ( E.coli, S.aureus)
swabbed over the agar plates. The different concentration of samples is placed in a
agar plates followed by disk diffusion method. The plates are kept for incubation
at 37°C for 24 hours the zone of inhibition was measured. The anti-microbial
115 activity of dipotassium tartrate crystals in terms of E.coli and % Staphyloccoccus
aureus is shown in Fig 7.7.
Fig 7.7 Antimicrobial activity of dipotassium tartrate crystals
7.4
Conclusion
Single crystal of dipotassium tartrate are successfully using gel medium.
FTIR spectroscopy suggests the presence of OH stretching, γ CO asymmetric and
symmetric modes, γ
CC,
δ
COO
and τ
COO
modes of vibration along with metal
oxygen stretching at the end. Powder XRD analysis confirms that the unit cell
volume of dipotassium tartrate crystals to be 657.273 Å3. The magnetic
susceptibility and magnetic moment of the crystals are found out to be
36.12 x 10-6 e.m.u. and 2.94 BM respectively. Thermal analysis of the crystal
showed that there is no water of hydration. The endothermic peak at 285.40˚C
confirms the major stage of decomposition of the sample. The antimicrobial
activities of dipotassium tartrate crystals have been confirmed through the results
obtained from the graph.
116
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