# Synthesis, Growth, Spectral, Thermal and Mechanical Properties of Inorganic – Organic Hybrid NLO Crystal: NH4[Cd(NCS)3] C12H24O6

V Ramesh, K Rajarajan

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V Ramesh, K Rajarajan. Synthesis, Growth, Spectral, Thermal and Mechanical Properties of Inorganic – Organic Hybrid NLO Crystal: NH4[Cd(NCS)3] C12H24O6. Mechanics, Materials Science & Engineering Journal, 2017, 9, 10.2412/mmse.61.54.732. hal-01503678

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# Synthesis, Growth, Spectral, Thermal and Mechanical Properties of Inorganic – Organic Hybrid NLO Crystal: NH₄[Cd(NCS)₃] C₁₂H₂₄O₆

V. Ramesh¹, K. Rajarajan², a

1. Department of Physics, SRM University, Vadapalani, Chennai - 6000026, Tamilnadu, India

2. Department of Physics, Rajeswari Vedachalam Governmen Arts College, Chengalpet - 603001, Tamilnadu, India

a. drkrr2007@gmail.com

<figure><img src="image_2.png" /></figure>

DOI 10.2412/mmse.61.54.732 provided by [Seo4U.link](https://seo4U.link)

**Keywords:** solution growth, optical transmission, SHG, micro-hardness and TG-DSC.

**ABSTRACT.** Ammonium (18-crown-6-ether)cadmium (II) tri-thiocyanate [(NH₄[Cd(NCS)₃].C₁₂H₂₄O₆)] (ACCTC) is the potential inorganic-organic hybrid material, which has many applications in the field of laser displays and optical communications. The crystal growth of ACCTC has been carried out by slow evaporation solvent technique (SEST) at ambient temperature and its dimension was found to be 10×5×5 mm³. The single crystal X-ray diffraction analysis has confirmed the cell parameter of the grown crystal. The FT-IR spectrum is used to identify the functional groups present in ACCTC. The optical transmission is found by UV-Vis-NIR spectrometer. From the optical spectrum, good prominent optical transmission in the entire ultra violet to IR region has been well proved and hence it is an essential requirement for non-linear optical applications. Thermal analysis carried out on ACCTC revealed that it is thermally stable up to 237 °C which is far better than Li[Cd(NCS)₃].C₁₂H₂₄O₆ (CLTC); 170 °C, CdHg(SCN)₄ (CMTC); 199 °C and Hg(N₂H₄CS)₄Zn(SCN)₄ (TMTZ); 185 °C. The Vicker's hardness tester is used to estimate the mechanical hardness of the grown crystal and the results are reported.

**Introduction.** Recently, Nonlinear optical material plays an important role in the photonics and optoelectronics. New nonlinear optical (NLO) frequency conversion materials have a significant impact on laser technology, optical datastorage and telecommunications. The past few decades, a new series of hybrid nonlinear optical crystal based on polymeric cadmium- thiocyanate anions and complex cations [1-3] have received wide attention due to their good optical and interesting physical properties such as thermal, mechanical and second harmonic generation effects. Renewed attention has been received recently for the polymer, inorganic and organic, materials. IPOS series, thiocyanate (SCN) ligand forms a coordination polymeric chain combined with the d¹⁰ transition metal ion and leads a non-centrosymmetric structure. A novel series of coordination solids explained as IPOS with the general formula [H-G] [M-L], where the inorganic anion [M]⁻ is ligand (L) coordination polymer such as [Cd(SCN)₃]⁺ and the organic cation [H-G]⁺ is a host (H)⁻ guest (G) complex such as [(crown ether)-(alkali metl)]. Earlier scientists and researchers [4] reported the growth of a novel hybrid nonlinear optical compound [(18C6)K][Cd(SCN)₃], which is wide optically transparent from 220 to 3,300 nm and exhibits efficient SHG. Based on the design theory, attempts were made to combine 18-crown-6 ether (18C6) and thiocyanate ligands with the transition metal ion Cd²⁺ and the alkali metal ion NH₄⁺. A new nonlinear optical compound [(NH₄)[Cd(NCS)₃].C₁₂H₂₄O₆] [Ammonium (18-crown-6-ether) cadmium (II) tri-thiocyanate, ACCTC] material has been synthesized. Signle crystals of ACCTC with dimension of 10×5×5 mm³ were grown from aqueous solutions via solvent evaporation technique. In this paper, the growth of Ammonium (18-crown-6-ether) cadmium (II) tri-thiocyanate, (ACCTC) single crystal and its characterization by single crystal XRD, FT-IR, UV-Vis, TG-DSC, SHG and microharness are reported.
**Material synthesis.** All the starting materials were of analytical reagent, and deionizer water was used in the preparation of the solutions. the raw material for the growth of ACCTC single crystal was synthesized according to following reaction:

$$C_{12}H_{24}O_{6}+CdCl_{2}+3(NH_{4}SCN) \rightarrow [(NH_{4})Cd(NCS)_{3}].C_{12}H_{24}O_{6}]+2NH_{4}Cl.$$

The calculated amount of salts were dissolved in triple distilled water at room temperature, as a result a small precipitation was formed. The mixed solution was filtered and removed the un-dissolved materials by filter paper. Finally, the clear solution was allowed to slowly evaporate at room temperature. After a period of 10-15 days, the small millimetre seed crystals were grown at surface of the liquid. The repeated recrystallization process provides the high quality synthesized compound (ACCTC), which is shown in Fig.1.

<figure><img src="image_3.png" /><figcaption>Fig.1. Grown crystal of ACCTC.</figcaption></figure>

## Results and discussion

**Single crystal XRD.** Single crystal X – ray diffraction (XRD) analysis was carried out using a Bruker Kappa APEXII CCD diffractometer with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å°). This paper reports the single crystal growth of [(NH₄)[Cd(NCS)₃].C₁₂H₂₄O₆]. This compound crystal lies in an orthorhombic unit cell of space group Cmc21 with cell parameter a = 14.7568 Å, b= 15.4378 Å, c = 10.6383 Å, V = 2423.54 (18) Å³ and Z= 4[5].

**FTIR studies.** The powdered crystal was subjected to FT-IR spectroscopy which, confirm the presence of functional groups and coordination of legends in the wavelength range 400-4000 cm⁻¹ as shown in Fig.2. The prominent absorption of Peaks of ACCTC observed. When it was compared with the spectra of CLTC a few peaks were found to be shifted. The sharp and intense bands observed at 1107.5 and 958.0 cm⁻¹ are shifted from 1100 and 955 cm⁻¹ of CLTC respectively, which is due to C-O-C stretching vibration. In addition, the sharp and intense band observed at 1353.2 is shifted from 1349 cm⁻¹ of CLTC, which is due to –CH₂- stretching vibration. The CN stretching vibration mode of SCN appears as a very strong and highly intense sharp band at 2120.8 cm⁻¹. The comparison of IR vibrational frequencies of ACCTC and CLTC is presented Table.1.
<figure><img src="image_4.png" /><figcaption>Fig.2. FT-IR spectrum of ACCTC crystal.</figcaption></figure>

<table><caption>Table 1. Comparison of FT-IR spectral data of ACCTC single crystal with CLTC.</caption><thead><tr><th colspan="2">Wave number (cm<sup>-1</sup>)</th><th rowspan="2">Assignments</th></tr><tr><th>ACCTC</th><th>CLTC</th></tr></thead><tbody><tr><td>3249.5</td><td>3170</td><td>2δ(NH<sub>2</sub>)</td></tr><tr><td>2860.4</td><td>29047</td><td>vs(NH<sub>2</sub>)</td></tr><tr><td>2746.9</td><td>2742</td><td>v(CN)</td></tr><tr><td>2120.8</td><td>2124,2074</td><td>v(CN)</td></tr><tr><td>1674.3</td><td>1676, 1622</td><td>δ(NH<sub>2</sub>)</td></tr><tr><td>1420.7</td><td>1457, 1415</td><td>v1(SCN<sub>2</sub> H<sub>4</sub>)</td></tr><tr><td>1353.2</td><td>1,349</td><td>v1(SCN<sub>2</sub> H<sub>4</sub>)</td></tr><tr><td>1286.3</td><td>1282</td><td>v1(SCN<sub>2</sub> H<sub>4</sub>)</td></tr><tr><td>1247.1</td><td>1249</td><td>v2(SCN<sub>2</sub> H<sub>4</sub>)</td></tr><tr><td>1107.5</td><td>1100</td><td>v2(SCN<sub>2</sub> H<sub>4</sub>)</td></tr><tr><td>958</td><td>955</td><td>2δ(SCN)</td></tr><tr><td>834.4</td><td>834</td><td>2δ(SCN)</td></tr><tr><td>754.9</td><td>751</td><td>v(CS)</td></tr><tr><td>527.4</td><td>531</td><td>δas(NCN)</td></tr><tr><td>456.3</td><td>453</td><td>δ(NCN)</td></tr></tbody></table>

**Optical studies.** The UV-vis-NIR spectrum of ACCTC single crystal recorded in the wavelength range of 200-1200 nm is shown in Fig.3. In ACCTC, the cut off wavelength lies at 220 nm. The absorption is negligible in the entire visible region of the spectrum. Therefore, ACCTC can be used as a potential material for second harmonic generation (SHG).
<figure><img src="image_5.png" /><figcaption>Fig. 3. Absorption spectrum of ACCTC single crystal.</figcaption></figure>

**NLO Test.** The NLO efficiency of ACCTC crystal was evaluated by the Kurtz and Perry powder technique using a Q-switched mode locked Nd³⁺: YAG laser emitting 1.064 µm, 8ns laser pulses with spot radius of 1mm. The input laser beam was passed through an IR reflector and then directed on the powdered sample. The light emitted by the sample was measured by the photo-diode detector and oscilloscope assembly. A microcrystalline material of KDP was used for comparison with ACCTC for the SHG experiment. For a laser input pulse of 2.48 mJ, the second harmonic signal of 22 and 46 mW were obtained through KDP and ACCTC samples, respectively. Hence, it is observed that the SHG efficiency of ACCTC is 2 times superior to KDP.

<figure><img src="image_6.png" /><figcaption>Fig. 4. TGA-DSC curves of ACCTC single crystal.</figcaption></figure>

**TG-DSC studies.** Thermal stability and physicochemical changes of ACCTC single crystal were studied by thermo gravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) using Universal V4.5A TA Instruments. TGA and DTA analysis of ACCTC sample were carried out from room temperature to 1000 °C in nitrogen atmosphere at a heating rate of 20 °C/min. The TG and DSC curves of ACCTC are shown in Fig.4. The TG curve shows that the decomposition percentage of ACCTC at various temperatures. The TG-DSC thus
observed is shown in Fig.4. There is a first weight loss starting at about 237°C. The DTA curve presents several endothermic peaks due to the decomposition and elimination of volatile pyrolysis products. The TG-DSC thermal analysis revealed that the sample is thermally stable up to 237 °C, which is comparatively far better than the thermal stability of CLTC (170°C).

**Microhardness studies.** The microhardness measurement is made on well polished ACCTC crystal of dimensions 4x3x3 mm³ by REICHERT MD 4000E ultra microhardness tester with a diamond pyramidal indenter. The applied loads were 10, 25, 50 and 100 g. The indentation time was kept as 10s for each load. The Vickers microhardness number (Hv) was calculated using the standard formula.

$$Hv = \frac{1.8544 P}{d^2}$$

Where Hv is the Vickers hardness number in kg/mm², P is the applied load in kg and d is the mean diagonal length of the indenter impression in mm.

Fig. 5 shows the variation of Vickers hardness (Hv) versus applied load (P) ranging from 10 to 100 g. The result shows the micro hardness value increases with increase of load.

<figure><img src="image_7.png" /><figcaption>Fig. 5. Variation of Hv with load for ACCTC crystal.</figcaption></figure>

**Summary.** This paper reports the growth of good quality single crystal of [(NH₄)Cd(NCS)₃].C₁₂H₂₄O₆] through slow evaporation technique. The grown crystal was characterized by single crystal X-ray diffraction. The structural analysis reveals that ACCTC crystallizes in the space group Cmc2₁ with cell parameters a = 14.7568 Å, b= 15.4378 Å, c = 10.6383 Å, V=2423.54(18) Å³ and Z= 4. The presence of function groups and transmittance of ACCTC crystal were analysed by FT-IR and UV-Vis spectral analysis, respectively. The TG-DSC thermal analysis revealed that ACCTC is thermally stable up to 237 °C, which is comparatively far better than the thermal stability of CLTC (170°C). Vickers microhardness measurements show that the Vickers hardness increases with increase in load. The above results reveal that ACCTC is a potential material for NLO applications.
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Cite the paper

V. Ramesh, K. Rajarajan, (2017). Synthesis, Growth, Spectral, Thermal and Mechanical Properties of Inorganic – Organic Hybrid NLO Crystal: NH₄[Cd(NCS)₃] C₁₂H₂₄O₆. Mechanics, Materials Science & Engineering, Vol 9. doi 10.2412/mmse.61.54.732