Strontium Malonate Crystal Grown by Silica Gel Technique
1Nitin B
Baviskar, 2Sachin J Nandre, 3Rajendra Ahire
1Department
of Physics, J. D. M. V. P.S. Arts, Commerce & Science College, Jalgaon, 2Department
of Physics, 2Uttamrao Patil College,Dahiwel (Dhule) and
3Department
of Physics, S.G.Patil College, Sakri (Dhule)
Corresponding
authors email: sachinjnandre@gmail.com
Abstract
Single crystals of strontium malonate (SrC₃H₂O₄·xH₂O) were
successfully grown using the silica gel growth technique, a method that allows
controlled diffusion and nucleation in a three-dimensional porous medium.
Strontium malonate, an alkaline earth metal organic compound, is of interest
due to its potential applications in nonlinear optics, luminescent materials,
and ion-exchange processes. The growth process was carried out under controlled
pH and gel density conditions to optimize crystal size and morphology. The
resulting crystals were characterized visually for size, shape, and
transparency. The study demonstrates that the silica gel technique is effective
for producing well-faceted strontium malonate crystals and provides insight
into the nucleation and growth mechanisms of metal-organic crystals in porous
media.
1. Introduction
Strontium malonate, a coordination compound of strontium and
malonic acid, exhibits interesting chemical and physical properties due to its
ionic and hydrogen-bonded structure. Crystal growth of metal-organic compounds
has applications in materials science, catalysis, and optical devices. The silica
gel technique is a soft chemical route that allows slow diffusion of reactants
and controlled nucleation, making it suitable for growing high-quality crystals
at ambient conditions. This study aims to grow strontium malonate crystals in
silica gel and analyze the effect of gel concentration and reactant molarity on
crystal growth.
Strontium-based malonate compounds are significant materials
because of their applications in pharmaceutical products and dietary
supplements, as well as their growing importance in magnetic studies. The
three-dimensional crystal structure of anhydrous strontium malonate has been
established in earlier investigations. Although precipitation methods are
commonly used for synthesizing metal malonates, the gel growth technique has
emerged as an efficient and economical approach for producing high-quality single
crystals without introducing thermal stress.
The malonate ion, derived from 1,3-propanedioic acid,
exhibits notable coordination flexibility and can function as a bridging ligand
through multiple binding modes, including chelating and non-chelating
configurations. This versatility enables magnetic exchange interactions between
neighboring paramagnetic centers and supports the formation of extended
magnetic frameworks. Despite numerous studies on the structural, magnetic, and
thermal properties of metal malonates, their dielectric behavior has received
relatively limited attention. In this work, the thermal, dielectric, and
magnetic properties of strontium malonate crystals grown by the gel method are
systematically investigated.
2. Experimental Technique
Materials
All chemicals used in the present
investigation were of analytical reagent grade and were used as received
without further purification. Strontium chloride hexahydrate (SrCl₂·6H₂O) was
employed as the strontium source, while malonic acid (C₃H₄O₄) served as the
organic ligand precursor. Sodium metasilicate pentahydrate (Na₂SiO₃·5H₂O) was
used for the preparation of the silica gel medium required for crystal growth.
Distilled water was used for preparing all solutions. Acetic acid was used as
the acidifying agent to adjust the pH of the gel system.
Preparation
of Silica Gel
The silica gel medium was prepared using
sodium metasilicate through a controlled acidification process. Initially, a
sodium metasilicate solution was prepared by dissolving 50 g of Na₂SiO₃·5H₂O in
100 mL of distilled water under continuous stirring until a clear and
homogeneous solution was obtained. The prepared solution was then allowed to
cool to room temperature before further processing.
Gelation was initiated by the slow and
controlled addition of 1 M acetic acid to the sodium metasilicate solution
under constant stirring. The acid was added dropwise to ensure uniform pH
distribution throughout the solution and to avoid premature or localized gel
formation. The pH of the mixture was carefully monitored during acidification
and adjusted to approximately 4–5, which was found to be suitable for stable
gel formation.
Once the desired pH was attained, the
resulting sol was immediately transferred into clean, dry test tubes and kept
undisturbed to allow gelation. The gel was allowed to set completely at room
temperature. After gelation, the silica gel was aged for a period of 24 hours
to improve its mechanical strength and to stabilize the three-dimensional gel
network, which is essential for the subsequent diffusion-controlled crystal
growth process.
2.3 Crystal Growth
The growth of strontium malonate single
crystals was carried out using the single diffusion method in a silica gel
medium at room temperature. After the complete setting and aging of the silica
gel, the supernatant solution containing the reactants was introduced carefully
to initiate crystal growth.
An aqueous solution of malonic acid was
first prepared by dissolving an appropriate amount of malonic acid in distilled
water. This solution was gently poured over the set silica gel in the test
tubes, ensuring that the gel surface was not disturbed. Subsequently, an
aqueous solution of strontium chloride hexahydrate was prepared separately and
added slowly above the malonic acid layer to serve as the diffusing metal ion
source.
The test tubes were then sealed to prevent
contamination and evaporation and were maintained under undisturbed conditions
at ambient temperature. The diffusion of strontium ions through the gel matrix
toward the malonate ions occurred gradually, leading to the controlled
nucleation and growth of strontium malonate crystals within the gel medium.
Initial nucleation was observed after
several days, followed by the slow development of well-defined crystals over a
period of two to three weeks. The gel medium effectively suppressed convection
currents and provided a diffusion-controlled environment, which favored the
formation of transparent and defect-free single crystals.
Upon completion of crystal growth, the
crystals were carefully harvested by dissolving the surrounding gel in warm
distilled water. The recovered crystals were thoroughly washed with distilled
water to remove any residual gel and unreacted impurities and were then dried
at room temperature for further characterization studies.
Table 1. Growth parameters for strontium
malonate crystals grown in silica gel
|
Parameter |
Details |
|
Gel Medium |
Silica Gel |
|
Gelling Agent Concentration |
50 G Na₂Sio₃·5h₂O In 100 Ml
Distilled Water |
|
Gel Ph |
4.0 – 5.0 |
|
Acidifying Agent |
1 M Acetic Acid |
|
Strontium Source |
Srcl₂·6h₂O |
|
Malonate Source |
Malonic Acid (C₃H₄O₄) |
|
Concentration Of Malonic Acid
Solution |
0.5 M (Aqueous) |
|
Concentration Of Strontium
Chloride Solution |
0.5 M (Aqueous) |
|
Diffusion Method |
Single Diffusion |
|
Growth Temperature |
Room Temperature (27 ± 2 °C) |
|
Gel Aging Time |
24 Hours |
|
Nucleation Time |
3–5 Days |
|
Crystal Growth Period |
2–3 Weeks |
|
Crystal Habit |
Transparent, Well-Faceted Single
Crystals |
Results and discussion
The morphology of strontium malonate crystals grown in a
silica gel medium is strongly influenced by diffusion-controlled growth
conditions, gel density, pH, and reactant concentration. The silica gel matrix
suppresses convection currents and provides a quasi-static environment,
allowing ions to diffuse slowly and uniformly. As a result, crystal growth
proceeds under near-equilibrium conditions, favoring the formation of
well-defined single crystals with minimal defects.
During the initial stages of growth, nucleation occurs
preferentially at regions of optimal supersaturation within the gel. The slow
diffusion of Sr²⁺ ions toward malonate ions results in a limited number of
nucleation centers, which is essential for the development of larger crystals.
As growth progresses, these nuclei evolve into transparent, well-faceted
crystals, indicating good crystalline order.
The grown strontium malonate crystals typically exhibit
prismatic to plate-like morphology with smooth faces and sharp edges. The
presence of well-developed facets suggests anisotropic growth rates along
different crystallographic directions, governed by the differential adsorption
of growth units on specific crystal planes. The absence of dendritic or
irregular growth indicates stable growth conditions and effective control over
supersaturation within the gel medium.
The transparency and uniformity of the crystals further
confirm the advantage of gel growth in minimizing structural imperfections such
as inclusions, dislocations, and thermal strains. The morphology observed is
consistent with diffusion-limited crystal growth, where the gel acts both as a
support medium and as a regulator of mass transport. Fig.
Different shape of Grown Strontium Malonate crystals
 |
Figure 1: Photographic image of strontium Malonate crystals
by sol-gel method.
Figure 2. XRD of Strontium Malonate Crystal
grown by gel method.
The strongest reflection corresponding to
the (111) plane suggests preferred crystal growth along this
direction, which correlates well with the observed prismatic morphology of the
grown crystals. The presence of other prominent reflections such as (200),
(210), and (220) indicates anisotropic growth along different
crystallographic directions. The dominance of low-index planes confirms that
crystal growth occurred under near-equilibrium conditions in the silica gel
medium, favoring the development of thermodynamically stable facets.
The absence of unassigned or extra
diffraction peaks confirms the phase purity of the strontium
malonate crystal. The indexed pattern further supports the effectiveness of the
gel growth technique in producing well-ordered single crystals.
4. Conclusion
Single crystals of strontium malonate were successfully
grown by the silica gel technique under controlled conditions. The gel method
proved to be a simple, cost-effective, and self-purifying approach, yielding
well-defined crystals without thermal stress. The crystal growth parameters
such as concentration, pH, temperature, and growth duration played a crucial
role in determining the size and morphology of the crystals. Powder X-ray
diffraction analysis confirmed the crystalline nature and phase purity of the
grown strontium malonate crystals. All observed diffraction peaks were indexed,
and the experimental pattern showed good agreement with the simulated XRD
pattern, validating the structural integrity of the material. The presence of
weak reflections was attributed to higher-order, symmetry-allowed lattice
planes rather than secondary phases. Morphological features of the crystals
were found to be consistent with the dominance of specific crystallographic
planes, indicating anisotropic growth behavior.
Acknowledgements
The authors would like to express their sincere gratitude to
Principal Dr Rajendra R Ahire, Dr Sachin
J Nandre for their valuable guidance and support throughout this work. We also
thank the Dept of Physics S.G.Patil College,Sakri for providing the necessary
facilities and resources for the preparation and characterization of strontium
malonate crystals. Special thanks are extended to colleagues and staff who
assisted in experimental setup, observations, and discussions that contributed
to the success of this research.
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