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.PatilCollege,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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