Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal growth and spectroscopic investigation of novel metal organic crystal: b-Alanine cadmium bromide monohydrate (b-ACBM) R. Renugadevi a, R. Kesavasamy b,⇑ a b
Department of Physics, SriGuru Institute of Technology, Coimbatore 641110, India Department of Physics, Sri Ramakrishna Engineering College, Coimbatore 641020, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The structure is reported for first
time. Spectroscopic characterization and
structure of b-ACBM crystal have been discussed. The title crystal has wide optical transparency window between 344 nm and 1100 nm with optical band gap 3.47 eV. The title complex crystal thermally stable up to 90 °C. This grown crystal belongs to soft magnetic material category.
a r t i c l e
i n f o
Article history: Received 13 December 2013 Received in revised form 7 February 2014 Accepted 7 March 2014 Available online 18 March 2014 Keywords: Molecular structure Crystal structure Crystal growth Chemical synthesis Magnetic materials
a b s t r a c t b-Alanine cadmium bromide monohydrate (b-ACBM), a new metal organic crystal has been grown from aqueous solution by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the crystal structure. The b-ACBM crystallized in monoclinic system with space group P21/c. The presence of protons and carbons in the b-alanine cadmium bromide monohydrate was confirmed by 1H and 13C nuclear magnetic resonance spectral analysis. The mode of vibration of different molecular groups present in b-ACBM was identified by FT-IR spectral analysis. Transparency of crystals in UV–Vis–NIR region has also been studied. The thermal characteristics of as-grown crystals were analyzed using thermo gravimetric and differential thermal analyses. The magnetic property of the grown crystal was investigated using Vibrating Sample Magnetometer (VSM) at ambient temperature. The mechanical stability of b-ACBM was evaluated by Vickers microhardness measurement. Ó 2014 Elsevier B.V. All rights reserved.
Introduction The past few decades have witnessed dramatic progress in the fabrication and self-assembly of metal–organic materials using metal–ligand coordination interactions [1–5]. A category of organometallic and coordination compounds has attracted a considerable ⇑ Corresponding author. Tel.: +91 9842523874. E-mail address: [email protected] (R. Kesavasamy). http://dx.doi.org/10.1016/j.saa.2014.03.005 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
interest in recent years in the search for new materials due to their advantages over traditional inorganic and organic compounds. Organometallic materials are currently under intense investigation, stimulated by potential application in optoelectronics because of the considerable interest in both organic and inorganic materials. In the case of metal–organic coordination complexes, the organic ligand is usually more dominant in the NLO effect. As we discuss metallic part, the focus is mainly on the group of IIB elements like Zn, Cd and Hg, these compounds usually have high transparency
R. Renugadevi, R. Kesavasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628
in the visible and UV spectral region, because of their closed d10 shell. Furthermore, in metal–organic complexes, the metal–ligand bonding is expected to display a large molecular hyper polarizability because of the transfer of electron density between the metal atom and the conjugated ligand system. More importantly, the diversity of central metals, oxidation states and ligands make it possible to optimize the charge-transfer interactions [6]. Amino acids have two or more types of coordination atoms and also it can act as various bridging ligands [7–10]. Taking advantage of the properties of amino acid ligands, an amino acid complex was used as a ligand in order to synthesize a new hetero-nuclear complex. One of the continuing challenges in materials chemistry concerns the elucidation of structure relationships. In L-(a)-alanine, the amino group is attached to the second carbon atoms in the carbon chain, whereas, in b-alanine the amino group is attached to the third carbon atom. L-(a)-alanine is naturally occurring amino acid while b-alanine is purely synthetic amino acid. L-(a)-alanine has two sterioisomeric forms but b-alanine has only one form. b-Alanine, a positional isomer of L-alanine, is not a constituent of proteins or enzymes, but is a component of a very few naturally occurring peptides like carnosine and anserine, and also as pantothenic acid (vitamin B5) [11]. It also forms crystalline complexes with organic and inorganic acids or materials. As the synthesized salt b-ACBM crystallizes in centrosymmetric crystal system with space group P21/c, it does not exhibit second harmonic generation. In this paper, the structure of novel metal–organic single crystal b-alanine cadmium bromide monohydrate have been reported for the first time. The molecular structure, functional groups, transparency and thermal stability of the grown crystals were analyzed with the help of NMR, FT-IR spectroscopy, UV–Vis–NIR spectroscopy, TG and DTA thermal analysis respectively. Magnetic property of the crystal was characterized and Vickers microhardness measurement was carried out on the grown crystal. Experimental procedure Material synthesis b-Alanine (AR grade) and cadmium bromide were used as starting materials to grow b-alanine cadmium bromide monohydrate (b-ACBM) single crystals. The calculate amount of b-alanine and cadmium bromide was taken in the ratio of 1:1 and dissolved separately in deionized water and both were mixed together. The saturated solution was stirred well for about 5 h to get homogeneous solution of the material at room temperature. The saturated solution is filtered using Whatman filter paper. The filtered solution was taken into the 300 ml beaker, tightly covered with perforated sheets. Then the solution was allowed to evaporate at room temperature, which yielded the crystalline salts of b-ACBM. The reaction scheme of the grown crystal is shown in Fig. 1. Solubility and crystal growth Solubility of the compound decides the amount that is available for crystal growth. The volume of 100 ml of deionized water was taken in an air tight 250 ml beaker and known quantity of the syn-
thesized compound was added with constant stirring at 25 °C. Once the saturation attained, the equilibrium concentration of the substance also analyzed gravimetrically. The process was repeated at the interval of 5 °C in the range from 20 to 45 °C and the obtained values were plotted. The b-ACBM crystal have been grown by using constant temperature water bath at 35 °C with accuracy of ±0.02 °C as shown in Fig. 2. The synthesized salt was used for further growth of b-ACBM crystal. Based on solubility data, 300 ml of the saturated solution was prepared. The prepared solution was taken in the beaker and placed in constant temperature water bath maintained at 35 °C and after 25 days the sizes of the grown crystal are 10 12 4 mm3 were obtained. The as-grown crystals are shown in Fig. 3. In order to improve the quality of the crystal further, the repeated recrystallization processes were carried out. Characterization The 1H and 13C NMR spectrum of b-ACBM was recorded using D2O as solvent on a Bruker 300 MHz (Ultra shield) TM instrument at 23 °C (300 MHz for 1H NMR and 75 MHz for 13C NMR) to confirm the molecular structure. The FT-IR spectrum of b-ACBM is recorded using a JASCO FT-IR 410 spectrometer by the KBr pellet method. Optical properties of the crystals were studied using a PerkinElmer Lambda 35 UV–Vis–NIR spectrometer in the region 200–1100 nm. The single crystal XRD data of the grown b-ACBM crystal was obtained using Bruker AXS (Kappa Apex II) diffractometer with Mo Ka (0.71073 Å) radiation at room temperature. The ORTEP plot of the molecule was drawn at 30% probability thermal displacement ellipsoids with the atom numbering scheme [12]. Accurate unit cell parameters were determined from the reflections of 36 frames measured in three different crystallographic zones by the method of difference vectors. Data collection, data reduction and absorption correction were performed by APEX2, SAINT-plus and SADABS program [13]. The TGA/DTA of b-ACBM was recorded using Perkin–Elmer Diamond TGA/DTA instrument. Magnetic properties were measured using a Vibrating Sample Magnetometer (VSM) (lake shore 7410). Vickers micro-hardness measurements were performed on b-ACBM crystal using MATSUZAWA model MMT-X series micro hardness tester fitted with diamond indenter. Results and discussion NMR spectroscopy analysis The NMR spectroscopic techniques are notably 1H NMR and 13C NMR. Hydrogen and carbon are the core elements in organic chemistry and hence 1H NMR and 13C NMR plays an important role in determining the structure of unknown organic molecules. The 1H NMR spectrum of b-ACBM is shown in Fig. 4a. The complex formed between b-alanine and cadmium bromide. Two pairs of methylene protons present in the 1H NMR spectrum. In this compound, one methylene carbon is directly bonded with amino group and the other with the carboxyl group. The amino group gets protonated to give ammonium group (NH+3) of its zwitter ionic form. The downfield signal is due to hydrogen atoms of the methylene
O O HO
NH2
Cd Br2 -
beta-alanine
cadmium bromide
623
O
NH3+
Cd Br2
H2O
beta-alanine cadmium bromide monohydrate
Fig. 1. Reaction scheme for b-ACBM.
624
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Concentration (g/100 ml)
28 26 24 22 20 18 16 14 20
25
30
35
40
45
50
Temperature ( 0C) Fig. 2. Solubility curve of b-ACBM.
Fig. 4b.
13
C NMR spectrum of b-ACBM.
The structure of the title compound is further confirmed from 13 C NMR spectrum. The 13C NMR spectrum of b-ACBM is shown in Fig. 4b. In 13C NMR spectrum, the two signals, one at 36.541 ppm and the other at 33.062 ppm indicates that the presence of two methylene carbon atoms. The signal at 178.633 ppm is due to carbon atom of the carboxyl group. The carboxyl carbon is deshielded in the range 178.633 ppm of the crystal b-ACBM. FT-IR spectral analysis
Fig. 3. As grown single crystals of b-ACBM.
The FT-IR spectrum of b-ACBM crystal is recorded in Fig. 5. The vibrational spectroscopy provides evidence for the charge transfer interaction between the donor and acceptor groups through p-electron movement. The intra molecular hydrogen bonding network formed between amino hydrogen of b-alanine cadmium bromide monohydrate atoms. The amino N of the b-alanine cation forms an NAH O hydrogen bonds with the O atoms of the COO anion. The peak observed at 3462 cm1 due to OH stretching frequency of water. The NH+3 asymmetric stretching vibration appears at 3169 cm1. The characteristic peak observed at 1896 cm1 is assigned for C@O bond stretching frequency. The peak at 1584 cm1 is assigned to the COO asymmetric stretching vibration. The peak at 1533 cm1 is assigned to the deformation vibration of water molecules. The peak at 1441 cm1 is for methylene vibrations. The peak at 1394 cm1 is assigned for CANH2 stretching frequency. The strong band observed at 1257 cm1 and the medium intensity band at 1112 cm1 are for NH+3 rocking vibrations. The bands observed at 1078 cm1 and 1041 cm1 are attributed to CN asymmetric and symmetric stretching respectively. FT-IR spectral data of b-ACBM Crystal is listed in Table 1. UV–Vis–NIR analysis
Fig. 4a. 1H NMR spectrum of b-ACBM.
directly bonded to the NH+3 group. This is explained by the electron attracting power of the ammonium group. There are two triplets at 3.13, 3.12 and 3.11 ppm and 2.53, 2.52 and 2.51 ppm. The peaks for two methylene protons are in fact two sets of triplets, which can be identified due to the splitting of two adjacent methylene protons.
The UV–Vis–NIR transmission spectrum of b-ACBM single crystal was recorded in the range 200–1100 nm to determine the transmission range and hence to know the suitability of the crystal for optical applications. The UV–Vis–NIR transmission spectrum of b-ACBM is shown in Fig. 6a. The grown crystal has 65% transmittance in the entire visible region with lower cutoff wave length of 344 nm. Optical transmission spectra were recorded for the grown crystal with 2 mm thickness. The optical absorption coefficient (a) was calculated using the relation:
a ¼ 2:3026 logð1=TÞ=t
ð1Þ
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R. Renugadevi, R. Kesavasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628
7
100
6
4000
3500
1584
3000
2500
2000
1500
(αh ν)2
4 3 2
835
1112 1078 1041
1533 1441 1317 1257
3169
20 0
1394
40
863 789 685 599
948
1896
5 60
3462
Transmittance (%)
80
1 0
1000
Eg=3.47 eV
500
-1
Wave number (cm-1)
1
2
3
4
5
6
Energy (eV)
Fig. 5. FT-IR spectrum of b-ACBM crystal.
Fig. 6b. Plot of (ahv)2 vs. photon energy of b-ACBM. Table 1 FT-IR spectral data of b-ACBM. Wave number (cm1)
Assignments
3462 3169 1584 1441 1394 1257 1112 1078 1041
OH stretching NH+3 asymmetric stretching COO asymmetric stretching Methylene vibrations CANH2 stretching Strong NH+3 rocking Medium intensity NH3+ rocking CAN asymmetric stretching CAN symmetric stretching
Empirical formula Formula weight Temperature Wavelength Crystal system, space group Unit cell dimensions
Volume Z, calculated density Absorption coefficient F(0 0 0) Crystal size Theta range for data collection Limiting indices Reflections collected/unique Completeness to theta = 27.50 Absorption correction Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
80 70 60
Transmittance (%)
Table 2 Crystal data and structure refinement for b-ACBM.
50 40 30 20 10
C3 H9 Br2 Cd NO3 379.33 293(2) K 0.71073 A Monoclinic, P21/c a = 8.6734(6) A alpha = 90° b = 13.9451(8) A beta = 103.713(2)° c = 7.6801(5) A gamma = 90° 902.44(10) A3 4, 2.792 Mg/m3 11.231 mm1 704 0.25 0.20 0.15 mm 2.42–27.50° 11 6 h 6 11, 18 6 k 6 13, 9 6 l 6 9 9392/2065 [R(int) = 0.0338] 99.90% Semi-empirical from equivalents 0.2836 and 0.1656 Full-matrix least-squares on F2 2065/2/100 1.089 R1 = 0.0252, wR2 = 0.0601 R1 = 0.0291, wR2 = 0.0613 0.0037(3) 1.143 and 0.567 e.A3
0
Single crystal X-ray diffraction analysis 200
400
600
800
1000
1200
Wave length (nm) Fig. 6a. UV–Vis–NIR transmittance spectrum.
where T is the transmittance and t is thickness of the crystal. Optical band gap energy (Eg) was calculated from the transmission spectra and optical absorption coefficient (a) near the absorption edge is given by [14]: 2
ðahmÞ ¼ Aðhm Eg Þ
ð2Þ
where A is a constant, Eg is the optical band gap energy, h is the Planck’s constant and v is the frequency of the incident photons. The band gap energy of b-ACBM crystal was determined by plotting (ahv)2 vs. hv which is shown in Fig. 6b and extrapolating the linear portion near the onset of absorption edge to the energy axis. From the figure, the value of band gap was found to be 3.47 eV.
Single crystal X-ray diffraction analysis reveals that b-alanine cadmium bromide monohydrate belongs to monoclinic crystal system with space group P21/c. The determined lattice parameters are a = 8.6734(6) Å, b = 13.9451(8) Å, c = 7.6801(5) Å, b = 103.713(2)° and volume = 902.44(10) A3. The single crystal X-ray diffraction studies of b-alanine cadmium bromide monohydrate were performed using Bruker AXS Kappa APEX II CCD diffractrometer equipped with graphite monochromated Mo Ka radiation (k = 0.71073 Å) at room temperature. The single crystal of sizes 0.25 0.20 0.15 mm3 was used for the analysis. A total of 9392 reflections were recorded with 2h range of 2.42–27.50° of which 2065 reflections were considered as unique reflections with I > 2r(I). The structure was solved by direct methods procedure using SHELXS-97 program and refined by Full-matrix least squares procedure on F2 using SHELXL-97 program [15]. The final refinement converges to an R-values of R1 = 0.0291 and WR2 = 0.0613. The crystallographic data and the structure refinement parameters of b-ACBM are presented in Table 2.
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to those observed in the crystal structure of CdCl2 with L-alanine and CdCl2 with b-alanine [16]. The packing arrangement of the molecule viewed down in the c-axis is shown in Fig. 8. The hydrogen bond is the most important of all directional intermolecular interactions. The corresponding data for the Hbonds are listed in Table 3. The intermolecular two nitrogen atoms N(1) forms hydrogen bonding with electronegative atom of oxygen and bromine. The symmetrical intermolecular hydrogen bonds were found between N(1)AH(1B) O(3) [x + 2, y, z + 1] N(1)AH(1B) O(1) with short donor–acceptor distances of 2.989(5), 2.820(5) Å respectively. The N(1)AH(1C) Br(1) [x + 1, y, z], N(1)AH(1A) Br(2) [x + 2, y1/2, z + 1/2] hydrogen-bond d(H-A) distances are 2.67 and 2.69 Å respectively. Thermal studies
Fig. 7. ORTEP diagram of b-ACBM.
The molecular structure shows that the carboxylic acid group of b-alanine protonate the amino group to NH+3. The coordination environment around the Cd atom, involving Br atoms and oxygen atoms, may be visualized as distorted tetrahedral environment. The angles around the Cd atom are not exactly tetrahedral as shown in the ORTEP view Fig. 7. The coordination of two bromine atoms with Cd are of different bond length Cd(1)ABr(1) [2.6174(5) Å], Cd(1)ABr (2) [2.6640(5) Å]. These are due to torsion bending of alanine molecule. The carboxylate groups in compound b-ACBM are not planar with the alanine molecule as shown in the torsion angle of O(2)AC(1)AO(1)ACd(1) which are 3.1(4)°. The distorted tetrahedron is shared by the carboxyl group of the b-alanine molecule and fuses directly by sharing BrABr edges to form one dimensional chains in the [0 0 1] direction. It seems to be similar
The TGA/DTA curve of b-alanine cadmium bromide monohydrate is shown in Fig. 9. From the TGA/DTA curves, it is observed that the material starts melting and undergoes an endothermic transition with 7% of weight loss at about 90 °C till the temperature of 124 °C. The first endothermic peak is appeared at 110 °C. In TGA curve, the weight loss is about 7.8% between 90 and 128 °C. This indicates that loss of water hydration (H2O). The strong endothermic peak in DTA around 110 °C with the associated shoulder indicates that the step wise removal of water during this temperature range. There is another endothermic peak in DTA around 218 °C, indicating the complete decomposition of substance. The sharpness of the endothermic peak shows that good degree of crystallinity and purity of the sample. This is associated with the loss of weight of about 20% in TGA curve (between 223 and 341 °C) and this weight loss is due to dissociation of the substance and evaporation of the volatile substances. There is a gradual and significant weight loss as the temperature is increased above the decomposition point. There is no endo or exothermic peak up to 360 °C in DTA curve. Thus, from the thermal analysis, it is seen that b-ACBM crystal is stable up to 90 °C. Magnetic studies Magnetic materials played a prominent role in the development of modern technology. Magnetic materials are the materials which can be made to behave as magnets. When these materials are kept
Fig. 8. Packing diagram of b-ACBM.
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R. Renugadevi, R. Kesavasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628 Table 3 Hydrogen bonds for b-ACBM [A and °]. d(DAH)
d(H A)
d(D A)
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, crystal growth and spectroscopic investigation of novel metal organic crystal: b-Alanine cadmium bromide monohydrate (b-ACBM) R. Renugadevi a, R. Kesavasamy b,⇑ a b
Department of Physics, SriGuru Institute of Technology, Coimbatore 641110, India Department of Physics, Sri Ramakrishna Engineering College, Coimbatore 641020, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
The structure is reported for first
time. Spectroscopic characterization and
structure of b-ACBM crystal have been discussed. The title crystal has wide optical transparency window between 344 nm and 1100 nm with optical band gap 3.47 eV. The title complex crystal thermally stable up to 90 °C. This grown crystal belongs to soft magnetic material category.
a r t i c l e
i n f o
Article history: Received 13 December 2013 Received in revised form 7 February 2014 Accepted 7 March 2014 Available online 18 March 2014 Keywords: Molecular structure Crystal structure Crystal growth Chemical synthesis Magnetic materials
a b s t r a c t b-Alanine cadmium bromide monohydrate (b-ACBM), a new metal organic crystal has been grown from aqueous solution by slow evaporation technique. The grown crystals have been subjected to single crystal X-ray diffraction analysis to determine the crystal structure. The b-ACBM crystallized in monoclinic system with space group P21/c. The presence of protons and carbons in the b-alanine cadmium bromide monohydrate was confirmed by 1H and 13C nuclear magnetic resonance spectral analysis. The mode of vibration of different molecular groups present in b-ACBM was identified by FT-IR spectral analysis. Transparency of crystals in UV–Vis–NIR region has also been studied. The thermal characteristics of as-grown crystals were analyzed using thermo gravimetric and differential thermal analyses. The magnetic property of the grown crystal was investigated using Vibrating Sample Magnetometer (VSM) at ambient temperature. The mechanical stability of b-ACBM was evaluated by Vickers microhardness measurement. Ó 2014 Elsevier B.V. All rights reserved.
Introduction The past few decades have witnessed dramatic progress in the fabrication and self-assembly of metal–organic materials using metal–ligand coordination interactions [1–5]. A category of organometallic and coordination compounds has attracted a considerable ⇑ Corresponding author. Tel.: +91 9842523874. E-mail address: [email protected] (R. Kesavasamy). http://dx.doi.org/10.1016/j.saa.2014.03.005 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
interest in recent years in the search for new materials due to their advantages over traditional inorganic and organic compounds. Organometallic materials are currently under intense investigation, stimulated by potential application in optoelectronics because of the considerable interest in both organic and inorganic materials. In the case of metal–organic coordination complexes, the organic ligand is usually more dominant in the NLO effect. As we discuss metallic part, the focus is mainly on the group of IIB elements like Zn, Cd and Hg, these compounds usually have high transparency
R. Renugadevi, R. Kesavasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628
in the visible and UV spectral region, because of their closed d10 shell. Furthermore, in metal–organic complexes, the metal–ligand bonding is expected to display a large molecular hyper polarizability because of the transfer of electron density between the metal atom and the conjugated ligand system. More importantly, the diversity of central metals, oxidation states and ligands make it possible to optimize the charge-transfer interactions [6]. Amino acids have two or more types of coordination atoms and also it can act as various bridging ligands [7–10]. Taking advantage of the properties of amino acid ligands, an amino acid complex was used as a ligand in order to synthesize a new hetero-nuclear complex. One of the continuing challenges in materials chemistry concerns the elucidation of structure relationships. In L-(a)-alanine, the amino group is attached to the second carbon atoms in the carbon chain, whereas, in b-alanine the amino group is attached to the third carbon atom. L-(a)-alanine is naturally occurring amino acid while b-alanine is purely synthetic amino acid. L-(a)-alanine has two sterioisomeric forms but b-alanine has only one form. b-Alanine, a positional isomer of L-alanine, is not a constituent of proteins or enzymes, but is a component of a very few naturally occurring peptides like carnosine and anserine, and also as pantothenic acid (vitamin B5) [11]. It also forms crystalline complexes with organic and inorganic acids or materials. As the synthesized salt b-ACBM crystallizes in centrosymmetric crystal system with space group P21/c, it does not exhibit second harmonic generation. In this paper, the structure of novel metal–organic single crystal b-alanine cadmium bromide monohydrate have been reported for the first time. The molecular structure, functional groups, transparency and thermal stability of the grown crystals were analyzed with the help of NMR, FT-IR spectroscopy, UV–Vis–NIR spectroscopy, TG and DTA thermal analysis respectively. Magnetic property of the crystal was characterized and Vickers microhardness measurement was carried out on the grown crystal. Experimental procedure Material synthesis b-Alanine (AR grade) and cadmium bromide were used as starting materials to grow b-alanine cadmium bromide monohydrate (b-ACBM) single crystals. The calculate amount of b-alanine and cadmium bromide was taken in the ratio of 1:1 and dissolved separately in deionized water and both were mixed together. The saturated solution was stirred well for about 5 h to get homogeneous solution of the material at room temperature. The saturated solution is filtered using Whatman filter paper. The filtered solution was taken into the 300 ml beaker, tightly covered with perforated sheets. Then the solution was allowed to evaporate at room temperature, which yielded the crystalline salts of b-ACBM. The reaction scheme of the grown crystal is shown in Fig. 1. Solubility and crystal growth Solubility of the compound decides the amount that is available for crystal growth. The volume of 100 ml of deionized water was taken in an air tight 250 ml beaker and known quantity of the syn-
thesized compound was added with constant stirring at 25 °C. Once the saturation attained, the equilibrium concentration of the substance also analyzed gravimetrically. The process was repeated at the interval of 5 °C in the range from 20 to 45 °C and the obtained values were plotted. The b-ACBM crystal have been grown by using constant temperature water bath at 35 °C with accuracy of ±0.02 °C as shown in Fig. 2. The synthesized salt was used for further growth of b-ACBM crystal. Based on solubility data, 300 ml of the saturated solution was prepared. The prepared solution was taken in the beaker and placed in constant temperature water bath maintained at 35 °C and after 25 days the sizes of the grown crystal are 10 12 4 mm3 were obtained. The as-grown crystals are shown in Fig. 3. In order to improve the quality of the crystal further, the repeated recrystallization processes were carried out. Characterization The 1H and 13C NMR spectrum of b-ACBM was recorded using D2O as solvent on a Bruker 300 MHz (Ultra shield) TM instrument at 23 °C (300 MHz for 1H NMR and 75 MHz for 13C NMR) to confirm the molecular structure. The FT-IR spectrum of b-ACBM is recorded using a JASCO FT-IR 410 spectrometer by the KBr pellet method. Optical properties of the crystals were studied using a PerkinElmer Lambda 35 UV–Vis–NIR spectrometer in the region 200–1100 nm. The single crystal XRD data of the grown b-ACBM crystal was obtained using Bruker AXS (Kappa Apex II) diffractometer with Mo Ka (0.71073 Å) radiation at room temperature. The ORTEP plot of the molecule was drawn at 30% probability thermal displacement ellipsoids with the atom numbering scheme [12]. Accurate unit cell parameters were determined from the reflections of 36 frames measured in three different crystallographic zones by the method of difference vectors. Data collection, data reduction and absorption correction were performed by APEX2, SAINT-plus and SADABS program [13]. The TGA/DTA of b-ACBM was recorded using Perkin–Elmer Diamond TGA/DTA instrument. Magnetic properties were measured using a Vibrating Sample Magnetometer (VSM) (lake shore 7410). Vickers micro-hardness measurements were performed on b-ACBM crystal using MATSUZAWA model MMT-X series micro hardness tester fitted with diamond indenter. Results and discussion NMR spectroscopy analysis The NMR spectroscopic techniques are notably 1H NMR and 13C NMR. Hydrogen and carbon are the core elements in organic chemistry and hence 1H NMR and 13C NMR plays an important role in determining the structure of unknown organic molecules. The 1H NMR spectrum of b-ACBM is shown in Fig. 4a. The complex formed between b-alanine and cadmium bromide. Two pairs of methylene protons present in the 1H NMR spectrum. In this compound, one methylene carbon is directly bonded with amino group and the other with the carboxyl group. The amino group gets protonated to give ammonium group (NH+3) of its zwitter ionic form. The downfield signal is due to hydrogen atoms of the methylene
O O HO
NH2
Cd Br2 -
beta-alanine
cadmium bromide
623
O
NH3+
Cd Br2
H2O
beta-alanine cadmium bromide monohydrate
Fig. 1. Reaction scheme for b-ACBM.
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R. Renugadevi, R. Kesavasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 128 (2014) 622–628
Concentration (g/100 ml)
28 26 24 22 20 18 16 14 20
25
30
35
40
45
50
Temperature ( 0C) Fig. 2. Solubility curve of b-ACBM.
Fig. 4b.
13
C NMR spectrum of b-ACBM.
The structure of the title compound is further confirmed from 13 C NMR spectrum. The 13C NMR spectrum of b-ACBM is shown in Fig. 4b. In 13C NMR spectrum, the two signals, one at 36.541 ppm and the other at 33.062 ppm indicates that the presence of two methylene carbon atoms. The signal at 178.633 ppm is due to carbon atom of the carboxyl group. The carboxyl carbon is deshielded in the range 178.633 ppm of the crystal b-ACBM. FT-IR spectral analysis
Fig. 3. As grown single crystals of b-ACBM.
The FT-IR spectrum of b-ACBM crystal is recorded in Fig. 5. The vibrational spectroscopy provides evidence for the charge transfer interaction between the donor and acceptor groups through p-electron movement. The intra molecular hydrogen bonding network formed between amino hydrogen of b-alanine cadmium bromide monohydrate atoms. The amino N of the b-alanine cation forms an NAH O hydrogen bonds with the O atoms of the COO anion. The peak observed at 3462 cm1 due to OH stretching frequency of water. The NH+3 asymmetric stretching vibration appears at 3169 cm1. The characteristic peak observed at 1896 cm1 is assigned for C@O bond stretching frequency. The peak at 1584 cm1 is assigned to the COO asymmetric stretching vibration. The peak at 1533 cm1 is assigned to the deformation vibration of water molecules. The peak at 1441 cm1 is for methylene vibrations. The peak at 1394 cm1 is assigned for CANH2 stretching frequency. The strong band observed at 1257 cm1 and the medium intensity band at 1112 cm1 are for NH+3 rocking vibrations. The bands observed at 1078 cm1 and 1041 cm1 are attributed to CN asymmetric and symmetric stretching respectively. FT-IR spectral data of b-ACBM Crystal is listed in Table 1. UV–Vis–NIR analysis
Fig. 4a. 1H NMR spectrum of b-ACBM.
directly bonded to the NH+3 group. This is explained by the electron attracting power of the ammonium group. There are two triplets at 3.13, 3.12 and 3.11 ppm and 2.53, 2.52 and 2.51 ppm. The peaks for two methylene protons are in fact two sets of triplets, which can be identified due to the splitting of two adjacent methylene protons.
The UV–Vis–NIR transmission spectrum of b-ACBM single crystal was recorded in the range 200–1100 nm to determine the transmission range and hence to know the suitability of the crystal for optical applications. The UV–Vis–NIR transmission spectrum of b-ACBM is shown in Fig. 6a. The grown crystal has 65% transmittance in the entire visible region with lower cutoff wave length of 344 nm. Optical transmission spectra were recorded for the grown crystal with 2 mm thickness. The optical absorption coefficient (a) was calculated using the relation:
a ¼ 2:3026 logð1=TÞ=t
ð1Þ
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7
100
6
4000
3500
1584
3000
2500
2000
1500
(αh ν)2
4 3 2
835
1112 1078 1041
1533 1441 1317 1257
3169
20 0
1394
40
863 789 685 599
948
1896
5 60
3462
Transmittance (%)
80
1 0
1000
Eg=3.47 eV
500
-1
Wave number (cm-1)
1
2
3
4
5
6
Energy (eV)
Fig. 5. FT-IR spectrum of b-ACBM crystal.
Fig. 6b. Plot of (ahv)2 vs. photon energy of b-ACBM. Table 1 FT-IR spectral data of b-ACBM. Wave number (cm1)
Assignments
3462 3169 1584 1441 1394 1257 1112 1078 1041
OH stretching NH+3 asymmetric stretching COO asymmetric stretching Methylene vibrations CANH2 stretching Strong NH+3 rocking Medium intensity NH3+ rocking CAN asymmetric stretching CAN symmetric stretching
Empirical formula Formula weight Temperature Wavelength Crystal system, space group Unit cell dimensions
Volume Z, calculated density Absorption coefficient F(0 0 0) Crystal size Theta range for data collection Limiting indices Reflections collected/unique Completeness to theta = 27.50 Absorption correction Max. and min. transmission Refinement method Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2sigma(I)] R indices (all data) Extinction coefficient Largest diff. peak and hole
80 70 60
Transmittance (%)
Table 2 Crystal data and structure refinement for b-ACBM.
50 40 30 20 10
C3 H9 Br2 Cd NO3 379.33 293(2) K 0.71073 A Monoclinic, P21/c a = 8.6734(6) A alpha = 90° b = 13.9451(8) A beta = 103.713(2)° c = 7.6801(5) A gamma = 90° 902.44(10) A3 4, 2.792 Mg/m3 11.231 mm1 704 0.25 0.20 0.15 mm 2.42–27.50° 11 6 h 6 11, 18 6 k 6 13, 9 6 l 6 9 9392/2065 [R(int) = 0.0338] 99.90% Semi-empirical from equivalents 0.2836 and 0.1656 Full-matrix least-squares on F2 2065/2/100 1.089 R1 = 0.0252, wR2 = 0.0601 R1 = 0.0291, wR2 = 0.0613 0.0037(3) 1.143 and 0.567 e.A3
0
Single crystal X-ray diffraction analysis 200
400
600
800
1000
1200
Wave length (nm) Fig. 6a. UV–Vis–NIR transmittance spectrum.
where T is the transmittance and t is thickness of the crystal. Optical band gap energy (Eg) was calculated from the transmission spectra and optical absorption coefficient (a) near the absorption edge is given by [14]: 2
ðahmÞ ¼ Aðhm Eg Þ
ð2Þ
where A is a constant, Eg is the optical band gap energy, h is the Planck’s constant and v is the frequency of the incident photons. The band gap energy of b-ACBM crystal was determined by plotting (ahv)2 vs. hv which is shown in Fig. 6b and extrapolating the linear portion near the onset of absorption edge to the energy axis. From the figure, the value of band gap was found to be 3.47 eV.
Single crystal X-ray diffraction analysis reveals that b-alanine cadmium bromide monohydrate belongs to monoclinic crystal system with space group P21/c. The determined lattice parameters are a = 8.6734(6) Å, b = 13.9451(8) Å, c = 7.6801(5) Å, b = 103.713(2)° and volume = 902.44(10) A3. The single crystal X-ray diffraction studies of b-alanine cadmium bromide monohydrate were performed using Bruker AXS Kappa APEX II CCD diffractrometer equipped with graphite monochromated Mo Ka radiation (k = 0.71073 Å) at room temperature. The single crystal of sizes 0.25 0.20 0.15 mm3 was used for the analysis. A total of 9392 reflections were recorded with 2h range of 2.42–27.50° of which 2065 reflections were considered as unique reflections with I > 2r(I). The structure was solved by direct methods procedure using SHELXS-97 program and refined by Full-matrix least squares procedure on F2 using SHELXL-97 program [15]. The final refinement converges to an R-values of R1 = 0.0291 and WR2 = 0.0613. The crystallographic data and the structure refinement parameters of b-ACBM are presented in Table 2.
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to those observed in the crystal structure of CdCl2 with L-alanine and CdCl2 with b-alanine [16]. The packing arrangement of the molecule viewed down in the c-axis is shown in Fig. 8. The hydrogen bond is the most important of all directional intermolecular interactions. The corresponding data for the Hbonds are listed in Table 3. The intermolecular two nitrogen atoms N(1) forms hydrogen bonding with electronegative atom of oxygen and bromine. The symmetrical intermolecular hydrogen bonds were found between N(1)AH(1B) O(3) [x + 2, y, z + 1] N(1)AH(1B) O(1) with short donor–acceptor distances of 2.989(5), 2.820(5) Å respectively. The N(1)AH(1C) Br(1) [x + 1, y, z], N(1)AH(1A) Br(2) [x + 2, y1/2, z + 1/2] hydrogen-bond d(H-A) distances are 2.67 and 2.69 Å respectively. Thermal studies
Fig. 7. ORTEP diagram of b-ACBM.
The molecular structure shows that the carboxylic acid group of b-alanine protonate the amino group to NH+3. The coordination environment around the Cd atom, involving Br atoms and oxygen atoms, may be visualized as distorted tetrahedral environment. The angles around the Cd atom are not exactly tetrahedral as shown in the ORTEP view Fig. 7. The coordination of two bromine atoms with Cd are of different bond length Cd(1)ABr(1) [2.6174(5) Å], Cd(1)ABr (2) [2.6640(5) Å]. These are due to torsion bending of alanine molecule. The carboxylate groups in compound b-ACBM are not planar with the alanine molecule as shown in the torsion angle of O(2)AC(1)AO(1)ACd(1) which are 3.1(4)°. The distorted tetrahedron is shared by the carboxyl group of the b-alanine molecule and fuses directly by sharing BrABr edges to form one dimensional chains in the [0 0 1] direction. It seems to be similar
The TGA/DTA curve of b-alanine cadmium bromide monohydrate is shown in Fig. 9. From the TGA/DTA curves, it is observed that the material starts melting and undergoes an endothermic transition with 7% of weight loss at about 90 °C till the temperature of 124 °C. The first endothermic peak is appeared at 110 °C. In TGA curve, the weight loss is about 7.8% between 90 and 128 °C. This indicates that loss of water hydration (H2O). The strong endothermic peak in DTA around 110 °C with the associated shoulder indicates that the step wise removal of water during this temperature range. There is another endothermic peak in DTA around 218 °C, indicating the complete decomposition of substance. The sharpness of the endothermic peak shows that good degree of crystallinity and purity of the sample. This is associated with the loss of weight of about 20% in TGA curve (between 223 and 341 °C) and this weight loss is due to dissociation of the substance and evaporation of the volatile substances. There is a gradual and significant weight loss as the temperature is increased above the decomposition point. There is no endo or exothermic peak up to 360 °C in DTA curve. Thus, from the thermal analysis, it is seen that b-ACBM crystal is stable up to 90 °C. Magnetic studies Magnetic materials played a prominent role in the development of modern technology. Magnetic materials are the materials which can be made to behave as magnets. When these materials are kept
Fig. 8. Packing diagram of b-ACBM.
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d(H A)
d(D A)
