Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13

Contents lists available at ScienceDirect

Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

journal homepage: www.elsevier .com/locate /saa

Synthesis, crystal growth and physical characterizations of organicnonlinear optical crystal: Ammonium hydrogen L-malate

http://dx.doi.org/10.1016/j.saa.2013.12.1151386-1425/� 2014 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 9283105760; fax: +91 44 27475166.E-mail addresses: ramasamyp@ssn.edu.in, proframasamy@hotmail.com

(P. Ramasamy).

K. Boopathi ⇑, P. RamasamyCentre for Crystal Growth, SSN College of Engineering, Kalavakkam, Chennai 603 110, India

h i g h l i g h t s

� Bulk growth of ammonium hydrogenL-malate crystal in monoclinic systemhas been grown.� Chemical structure of compound was

established by FT-IR and NMRtechnique.� The optical transmission spectrum of

AHM crystal reveals 64% transmissionin the entire visible region.� The work hardening coefficient value

of AHM is 4.04.� The second harmonic efficiency of

AHM was found to be 1.2 times thatof KDP.

g r a p h i c a l a b s t r a c t

200 400 600 800 1000 1200

0

10

20

30

40

50

60

70

% o

f tr

ansm

itta

nce

Wave length (nm)

a r t i c l e i n f o

Article history:Received 12 October 2013Received in revised form 24 December 2013Accepted 30 December 2013Available online 10 February 2014

Keywords:Organic crystalOptical materialsCrystal growthChemical synthesisX-ray diffraction

a b s t r a c t

An organic nonlinear optical crystal ammonium hydrogen L-malate (AHM) has been synthesized. Singlecrystals of AHM have successfully been grown by the slow evaporation solution method. Optically clearsingle crystals having dimensions up to 23 � 9 � 4 mm3 have been grown. Single crystal X-ray diffractionstudy confirms that the AHM crystallizes in orthorhombic crystal system with space group P212121. Thepowder X-ray diffraction pattern of the grown crystal has been recorded. FT-IR spectrum was recorded toidentify the various functional groups of AHM. The UV–vis–NIR transmission was analyzed for growncrystal. Thermal analysis was performed to find out thermal stability of the compound. Vickers microh-ardness measurements were carried and also work hardening coefficient has been found. The crystallineperfection of the grown crystal has been analyzed by HRXRD measurements. The second harmonic effi-ciency of AHM was found to be 1.2 times that of KDP.

� 2014 Elsevier B.V. All rights reserved.

Introduction

Nonlinear optical (NLO) materials play a major role in nonlinearoptics and in particular they have a great impact on informationtechnology and industrial applications. In the last decade, thiseffort has also brought its fruits in applied aspects of nonlinear op-tics. This can be essentially traced to the improvement of the

performances of the NLO materials. The understanding of thenonlinear polarization mechanisms and their relation to the struc-tural characteristics of the materials has been considerably im-proved. The new development of techniques for the fabricationand growth of artificial materials has dramatically contributed tothis evolution. The aim is to develop materials presenting largenonlinearities and satisfying at the same time all the technologicalrequirements for applications such as wide transparency range,fast response, and high damage threshold. But in addition to theprocessability, adaptability and interfacing with other materialsimprovements in nonlinear effects in devices, led the way to the

8 K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13

study of new NLO effects and the introduction of new concepts.Optical solutions, optical switching and memory by NLO effects,which depend on light intensity, are expected to result in the real-ization of pivotal optical devices in optical fiber communication(OFC) and optical computing which make the maximum use oflight characteristics such as parallel and spatial processing capabil-ities and high speed.

The current trend of research activities focuses much attentionon materials suitable for displaying excellent second order nonlin-ear optical (SONLO) properties in view of their potential applica-tions in optoelectronics, telecommunications and optical storagedevices. Of particular interest are the materials which can generatehighly efficient second harmonic blue–violet light by using laserdiodes. Materials with large second-order optical nonlinearities,short transparency cutoff wavelengths and stable physico-chemi-cal performances are needed in order to realize many of theseapplications [1–5]. In the recent past, extensive investigations arebeing carried out on organic nonlinear optical materials due totheir high nonlinearity, variety of synthetical methods, and betterlaser damage resistance compared to their inorganic counterparts.

In general, most organic molecules designed for nonlinearapplications are derivatives of an aromatic system substituted withdonor and acceptor substituents. In this system, the conjugatedp-bond enhances the polarizability of the molecule and the donorand acceptor groups contribute their own ‘mesomeric moments’,which give rise to a high nonlinear optical coefficient. On searchfor ultraviolet NLO materials with better mechanical properties,we focused attention on small organic molecules, specifically thecombination of two simple organic molecules, one with a large di-pole moment and the other a chiral molecule with an acentrosym-metric crystal structure. By linking the organic molecules throughhydrogen bonds, we can obtain systems with NLO and strongmechanical property. Malic acid, as a chiral a-hydroxy dicarboxylicacid, plays a key role in metabolic pathways of plants and animalsand is involved in many fundamental biochemical processes, e.g.,the Krebs cycle [6,7] and it is a suitable building block in crystalengineering, being used to create two-dimensional anionic net-works held together by hydrogen bonds [8–10]. The presence ofcomplementary hydrogen-bonding sites implies that this opticallyactive molecule ends to form 2D layers by bonding adjacent ionsinto chains (through head-to-tail OAH� � �O interactions) that arecross-linked via the hydroxyl group [11]. This tendency seems tobe preserved in the presence of a variety of counter ions and be-cause of its specific molecular chirality, its compound crystallizesinto non-centro-symmetric structures described by space groupscontaining only rotation or/and screw axes [12]. Moreover, its chi-rality ensures the absence of a center of symmetry, essential foroptical nonlinear second harmonic generation. Ammonium malate[13], racemic potassium malate [14], zinc malate, 1, 10-phenan-throline [15], cesium hydrogen malate monohydrate [16],strontium bis (hydrogen L-malate) hexahydrate [17], potassiumhydrogen malate monohydrate [18], ammonium malate (racemicmalic acid) [19] are the famous reported malic acid family crystals.The earlier report by Versichel et al. [20] dealt with the crystal

NH3

ammonia

OH

O

HO

O

OH

l-malic acid

Fig. 1. Reaction sch

structure of ammonium hydrogen L-malate. In the present investi-gation, structural, crystal growth, spectral, optical, thermal,mechanical, HRXRD and SHG efficiency of ammonium hydrogenL-malate have been reported.

Experimental procedure

Material synthesis, solubility and crystal growth

The commercially available ammonia and L-malic acid are usedfor the synthesis. AHM was synthesized by taking ammonia andL-malic acid in 1:1 equimolar ratio. Synthesis was carried out atroom temperature using magnetic stirrer. A calculated amount ofL-malic acid was dissolved in deionized water and then ammoniaadded. Its preparative temperature of the solution became 40 �Cdue to exothermic reaction. To make the solution homogeneous,it was continuously stirred for 6 h and filtered. This filtered solu-tion was evaporated to dryness. The dried salt was collected andused for further growth of AHM crystal. The success of growinglarge and high-quality single crystals with low defect density ishighly dependent on the purity of the starting materials. The syn-thesized material was purified by repeated recrystallization pro-cess. Fig. 1 represents the reaction scheme of the title compound.

The solubility of AHM in water was assessed by the function oftemperature in the range 25–50 �C. The experiment was carriedout in a constant temperature bath (CTB) with a cryostat facility.The concentration of the solute was determined gravimetrically.The solubility curve is shown in Fig. 2. Based on solubility data,the saturated solution was prepared by using synthesized salt atroom temperature. The saturated solution is filtered by usingWhatman filter paper. The filtered solution was taken into the300 ml beaker, tightly covered with perforated sheets to controlthe rate of evaporation and kept in dust free environment. In orderto improve the quality of the crystal further, we carried out the re-peated recrystallization process. Optically transparent crystals ofAHM have been grown in the period of 25 days by slow evapora-tion solution technique. The size of the grown crystal was up to20 � 9 � 4 mm3 and it is shown in Fig. 3.

Morphology of the grown crystals was identified by the singlecrystal X-ray diffraction studies (Bruker Kappa APEXII). It showsthat the crystal has 9 developed faces out of which (001), (010)and (011) are prominent faces. The indexed morphology of AHMcrystal is shown in Fig. 4.

Ammonia and L-malic acid used in the present study werebought from M/S. Merck and SPECTROCHEM (GR grade) Indiaand the deionized water got from Millipore water purification unit.The resistivity of used deionized water is 18.2 MO cm.

Characterization studies

Ammonium hydrogen L-malate crystals have been subjected tovarious characterization studies to analyze structural, spectral,optical, thermal, mechanical, HRXRD and SHG efficiency studies.

NH4+

OH

O

HO

O

O-

ammonium hydrogen l-malate

eme of AHM.

25 30 35 40 45 5035

40

45

50

55

60

65

70

Con

cent

rati

on (

g/10

0 m

l)

Temperature (oC)

Fig. 2. Solubility curve of AHM.

Fig. 3. As grown single crystal of AHM.

Fig. 4. Morphology of the crystal.

Table 1Crystal lattice parameters of the AHM crystal.

Lattice meters Single crystal XRD (Present work) Single crystal XRD [20]

a (Å) 7.58 7.62(3)b (Å) 8.08 8.10(4)c (Å) 10.56 10.60(4)a (�) 90.00 90.00b (�) 90.00 90.00m (�) 90.00 90.00Volume (Å3) 646.3 636.9(3)Crystal system Orthorhombic OrthorhombicSpace group P212121 P212121

K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13 9

The Bruker kappa APEXII single crystal X-ray diffractometer withMo Ka (k = 0.71073 A) was used to measure the cell parametersof AHM crystal. X-ray powder diffraction analysis of AHM crystalwas carried out using RICH SEIFERT diffractometer with Cu Ka(k = 1.5405 A) radiation over the range 10–70� at a scanning rate1�/min. The 1H and 13C NMR spectra of AHM were recorded usingD2O as solvent on a Bruker 300 MHz (Ultra shield) TM instrumentat 23 �C (300 MHz for 1H NMR and 75 MHz for 13C NMR) to confirmthe different kinds of proton and carbon. The FT-IR spectra of AHMcrystals were recorded in the range 400–4000 cm�1 employing aJASCO FTIR 410 spectrometer by the KBr pellet method to studythe functional groups in sample. Optical properties of the crystalswere studied using a PerkinElmer Lambda 35 UV–vis–NIRspectrometer in the region 200–1100 nm. The thermal stabilitywas identified by thermogravimetric (TG) and differential thermalanalyses (DTA). Thermogravimetric and differential thermal analy-sis of AHM crystals were carried out between temperature range35 �C and 300 �C in nitrogen atmosphere at heating rate of 10 �C/min using PerkinElmer Diamond TG/DTA instrument. GrownAHM crystals were subjected to indentation along their most planesurface using MATSUZAWA model MMT-X series microhardnesstester fitted with diamond indenter. Load was varied from 1 to100 g with dwell time of 5 s. The Vickers hardness number(VHN) was determined using the average length of the diagonalsby using the relation Hv = 1.854 P/d2 kg/mm2, where d is averagelength of diagonals in mm and P is the indenter load in kg. Crystal-line perfection of the grown crystal was analyzed by highresolution X-ray diffraction measurement (HRXRD). The secondharmonic generation efficiency of AHM has been analyzed by the

Kurtz and Perry powder test using a Q-switched Nd: YAG laserwith KDP as reference sample.

Results and discussion

Single crystal and powder X-ray diffraction studies

The grown crystal AHM belongs to orthorhombic crystal systemwith P212121 space group. The lattice parameters of AHM area = 7.58 ÅA

0

, b = 10.56 ÅA0

c = 8.08 ÅA0

, V = 646.3 ÅA03. From Table 1 one

can observe that the unit cell parameters are in very close agree-ment with the corresponding reported value [20]. X-ray powderdiffraction was used to confirm the homogeneity of the sampleand the crystallinity of the synthesized AHM crystal. The well-defined sharp peaks are indicating the good crystalline nature ofthe compound. The indexed powder XRD pattern of the growncrystal is shown in Fig. 5.

NMR spectral analysis

In the present investigation, the 1H and 13C NMR spectra wererecorded to confirm the molecular structure. The NMR spectral

10 20 30 40 500

200

400

600

800

1000

1200

1400

1600

1800

(10

4)

(13

3) (

050)

(24

0)

(12

3) (

311)

(02

3) (11

3) (

300)

(21

2)

(22

1)

(13

0) (

122)

(21

0) (

200)

(03

1)

(02

1) (

111)

(00

2)

(02

0) (

101) (

011)

Inte

nsit

y (c

ps)

2(θ) degree

(11

0)

Fig. 5. Powder XRD pattern of AHM.

10 K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13

analysis is the important analytical technique used to the study ofthe structure of organic compounds. The spectrum is shown inFig. 6a. An intense singlet peak was observed at d = 4.70 ppm andis due to the presence of D2O. The signals NAH and COOH protonsdo not show up due to fast deuterium exchange taking place inthese two groups, with D2O being used as the solvent. The CH2

(a) protons of malate yielded their signals at 2.5 and 2.7 ppm andthe CH (b) proton of same moiety showed its signal at 4.25 ppm.The 13C chemical shift appearing at d 179.11 and 176.3 ppm con-firms the presence of carboxylate functional group in malic acid(COO�) and the presence of aliphatic carbon chemical shift is at d40.05 ppm (CH2). The conformation of another aliphatic carbon ap-pears at d 68.55 ppm (CH). The 13C spectrum is shown in Fig. 6b.

FT-IR spectral analysis

The room temperature Fourier Transform Infrared (FT-IR) spec-trum of AHM was recorded in the region 400–4000 cm�1 in orderto analyze the synthesized compound qualitatively and the pres-ence of functional groups in the molecule. The recorded FT-IR spec-trum is shown in Fig. 7. In addition, the OAH stretching peakappears at 3459 cm�1. The asymmetric stretch of NAH is assignedto the peak at 3190 cm�1. The acid group carbonyl (C@O) stretch-ing frequency appears at 1719 cm�1. The asymmetric andsymmetric modes of carboxylate anion (COO�) occur at 1563 and

a

b

NH4+

OH

O

HO

O

O-a

b

Fig. 6a. 1H NMR spectrum of AHM.

1410 cm�1 respectively. The CH2 bending appears at 1281 cm�1.The peaks at 1344 and 889 cm�1 are attributed to the stretchingof the OAH deformation. The peak at 972 cm�1 is assigned to theCAC symmetric vibration. The peak at 650 cm�1 is due to theCAH deformation. The observed vibrational frequencies and theirassignments are listed in Table 2.

Optical transmittance spectrum

Transmittance spectrum was taken with 2 mm thickness of thesample. The recorded transmittance spectrum is shown in Fig. 8a.The lower cut off wave length is obtained at 232 nm and there issteady transmittance in the visible region. The transmittance ofthe AHM crystal is found to be 64% in the range between 240 nmand 1100 nm. The optical absorption coefficient (a) was calculatedusing the relation

a ¼ 2:3026ð1=TÞ=t ð1Þ

where T is the transmittance and t is thickness of the crystal.Optical band gap (Eg) was evaluated from the transmission

spectra and optical absorption coefficient (a) near the absorptionedge is given by [21]:

ðhvaÞ1=2 ¼ Aðhv � EgÞ ð2Þ

where A is a constant, Eg the optical band gap, h the Planck constantand v the frequency of the incident photons. The band gap of AHMcrystal was estimated by plotting (ahv)2 versus hv as shown inFig. 8b. As per Tauc’s idea [22], the optical band gap has been calcu-lated from the extrapolation of linear part at absorption edge. Thevalue of band gap was found to be 5.21 eV.

Thermal analysis

The thermal stability of AHM was studied by thermo gravimet-ric (TG) and differential thermal analysis (DTA). The AHM sampleweighing 5.256 mg was analyzed and the thermogram is depictedin Fig. 9. The DTA curve indicates the same changes shown by TGcurve. The TG curve shows single stage weight loss pattern whenthe material is heated from 35 to 280 �C. From the TG curve it isevident that the material is stable up to 130 �C and it is moisturefree. The compound starts to decompose above 150 �C. The com-pound does not lose its weight up to 150 �C. The first major weightloss occurs between the temperatures 150 and 270 �C with theelimination of 57.5% of the material into gaseous products. Theweight loss is due to the loss of CO2 and one molecule of ammonia(NH3).

C4H9NO5 �������!150 to 270�C CO2 " þNH3 " þhydrocarbons

Experimental weight loss : 57:5%

Calculated weight loss : 63%

The weight loss in TGA curve matches with the endotherm inDTA curve. The endotherm at 193 �C suggests that the materialmelts and simultaneously decomposes. The structural and chemi-cal stability of grown crystal can be considered as one of the strongreasons for possible selection of the material for applications.

Microhardness measurements

The structure and molecular composition of crystals greatlyinfluence mechanical properties. In order to study the mechanicalstability, the AHM single crystal was subjected to Vickers microh-ardness test. The indentations were carefully made on as growncrystal surface (010) with a dwell time of 5 s. The plot betweenhardness number (Hv) and load (p) is shown in the Fig. 10a. It is ob-served that hardness number increases as load increases. This can

Fig. 6b. 13CNMR spectrum of AHM.

4000 3500 3000 2500 2000 1500 1000 500

0

20

40

60

80

100

3190

889

616

546

752

650

790

972

1091

1180

1281

1344

1563

1410

1719

3459

Tra

nsm

itta

nce

(%)

Wave number (cm -1)

Fig. 7.. FT-IR spectrum of AHM crystal.

Table 2FT-IR frequency assignments of AHM crystal.

Wave number (cm�1) Assignments

3459 OAH stretching3190 Asymmetric stretching of NAH group1719 C@O stretching frequency1563 Asymmetric modes of carboxylate anion (COO�)1410 Symmetric modes of carboxylate anion (COO�)1281 CH2 bending vibration1344 and 889 Stretching of the OH deformation972 CAC symmetric vibration650 CAH deformation

200 400 600 800 1000 1200

0

10

20

30

40

50

60

70%

of

tran

smit

tanc

e

Wave length (nm)

Fig. 8a. UV–vis–NIR transmittance spectrum.

1 2 3 4 5 60

1x108

2x108

3x108

4x108

5x108

6x108

(αh υ

)2(e

V m

-1)2

Photon energy (eV)

Eg=5.21 eV

Fig. 8b. Plot of (ahv)2 versus photon energy.

K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13 11

be described on the pattern of depth of penetration of the indenter.When load increases, a few surface layers are penetrated initiallyand then inner surface layers are penetrated by the indenter withincrease in load. The measured hardness is a characteristic of theselayers and the increase in hardness number is due to the overall ef-fect on the surface and inner layers of the sample [23]. Beyond100 g, significant cracks occurred around the indentation mark,

which may be due to the release of internal stress generated locallyby indentation. By plotting log P versus log d, the value of the workhardening coefficient ‘n’ was found and it is shown in Fig. 10b.

0 50 100 150 200 250 30040

50

60

70

80

90

100

TGA

DTA

Temperature (oC)

TG

A (

%)

Endo

-60

-50

-40

-30

-20

-10

0

10

DT

A (

μV/m

g)

130oC

193 oC

Fig. 9. TG/DTA curve of AHM.

0 20 40 60 80 100

10

20

30

40

50

Har

dnes

s nu

mbe

r (H

v)

Load (p)

Fig. 10a. Variation of microhardness number with load of AHM.

0 1 2 3 4 5

3.2

3.4

3.6

3.8

4.0

4.2

4.4

4.6

4.8

5.0

Log

(d)

Log (p)

Fig. 10b. Log (p) versus Log (d) of AHM.

-200 -100 0 100 2000

200

400

600D

iffr

acte

d X

-ray

inte

nsit

y [c

/s]

Glancing angle [arc s]

50" 52"

45"

36" 42"

AHM (SEST)MoKα

1(200)planes

(+, -, -,+)

Fig. 11. Diffraction curve recorded for a typical AHM single crystal for (200)Diffracting planes by employing the PAN analytical MRD diffractometer with CuKa1 radiation.

12 K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13

According to Onitsch, the value of n is below 1.6 for hard materialsand n > 1.6 for soft materials [24]. The work hardening coefficientvalue of AHM is 4.04. Hence, it is concluded that the grown AHMcrystal is belongs to soft material category.

High resolution X-ray diffraction analysis

A multicrystal X-ray diffractometer designed and developed atNational Physical Laboratory [25] has been used to study the crys-talline perfection of the single crystal. The divergence of the X-raybeam emerging from a fine focus X-ray tube (Philips X-ray Gener-ator; 0.4 mm, 8 mm; kWMo) is first reduced by a long collimatorfitted with a pair of fine slit assemblies. This collimated beam isdiffracted twice by Bonsee Hart [26] type of monochromator crys-tals and thus the diffracted beam contains well-resolved Mo Ka1and Mo Ka2 components. The Mo Ka1 beam is isolated with thehelp of fine slit arrangement and allowed to further diffract froma third (111) Si monochromator crystal set in dispersive geometry(+, �, �). Due to dispersive configuration, though the lattice con-stant of the monochromator crystal and the specimen are different,the dispersion broadening in the diffraction curve of the specimendoes not arise. Such an arrangement disperses the divergent part ofthe Mo Ka1 beam from the Bragg diffraction peak and thereby

gives a good collimated and monochromatic beam at the Bragg dif-fraction angle, which is used as incident or exploring beam for thespecimen crystal. The dispersion phenomenon is well described bycomparing the diffraction curves recorded in dispersive (+, �, �)and non-dispersive (+, �, +) configurations.

Fig. 11 shows the high resolution X-ray diffraction curve re-corded for (200) diffraction planes using Mo Ka1 radiation for atypical AHM single crystal specimen. On close observation onecan realize that the curve is not a single peak. On deconvolutionof the diffraction curve, it is clear that the curve contains two addi-tional peaks. The solid line (convoluted curve) is well fitted withthe experimental points represented by the filled circles, whichare 50 and 52 arc s away from the central peak on both the sides.These three peaks correspond to three internal structural low angleboundaries [27] (tilt angle > 1 arc min but < 1 deg.) whose tilt an-gles (Tilt angle may be defined as the misorientation angle be-tween the two crystalline regions on both sides of the structuralgrain boundary) are 50 and 52 arc s from their adjoining regions.The FWHM (full width at half maximum) of the low angle bound-aries are 36, 45 and 42 arc s. The relatively low values of FWHM ofthe grains in comparison with that of the real life crystals [28]

Table 3Comparison of malic acid based organic NLO crystal.

Crystal name SHG efficiency(KDP)

Reference

Cesium hydrogen L-malate 2.5 times [16]Strontium bis (hydrogen L-malate)

hexahydrate3.4 times [17]

Potassium hydrogen malate monohydrate 1.2 times [18]Ammonium malate (racemic malic acid) 2 times [19]Ammonium hydrogen L-malate 1.2 times Present

work

K. Boopathi, P. Ramasamy / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 7–13 13

depicts that the crystalline perfection is fairly good. It may be men-tioned here that such low angle boundaries could be detected inthe diffraction curve only because of the high-resolution of the dif-fractometer used in the present investigations. Such defects maynot influence much on the NLO properties. However, a quantitativeanalysis of such unavoidable defects is of great importance, partic-ularly in case of phase matching applications as described in ourrecent article [29].

NLO property

The Kurtz–Perry powder technique remains an extremely valu-able tool for initial screening of materials for second harmonic gen-eration [30]. A laser beam of fundamental wavelength 1064 nm,8 ns pulse width, with 10 Hz pulse rate was made to fall normallyon the sample. The power of the incident beam was measuredusing a power meter. The green light was detected by a photomul-tiplier tube (Hamamatsu). KDP crystal was powdered to theidentical size and was used as reference material in the SHG mea-surement. The SHG relative efficiency of AHM crystal was found tobe 1.2 times that of KDP. The SHG values of some malic acid basedorganic NLO crystals are given in the Table 3.

Conclusion

Single crystals of ammonium hydrogen L-malate were grownfrom slow evaporation solution technique. Single crystal X-ray dif-fraction analysis revealed that the compound crystallizes in anorthorhombic system with non-centro symmetric space groupP212121. The powder X-ray diffraction pattern of the grown crystalhas been indexed. The modes of vibration of different functionalgroups present in the sample were identified by the FT-IR spectralanalysis. The presence of carbons and protons was confirmed by 1Hand 13C NMR analyses. The grown crystals are transparent in theentire visible region. From the TGA curve, it is seen that the

material is stable up to 160 �C. Microhardness study revealed thatthe material belongs to soft material category. HRXRD analysis re-veals that the grown crystal has reasonably good crystalline perfec-tion. The relative second harmonic generation efficiency of AHMwas 1.2 times that of KDP crystal.

Acknowledgements

The authors are thankful to Dr. G. Bhagavannarayana, MaterialCharacterization Division, NPL, New Delhi, India for providingHRXRD studies, Dr. R. Gopalakrishnan, Anna University, Chennaifor providing microhardness studies, SAIF, IIT Madras for the char-acterization studies.

Reference

[1] N.J. Long, Angew. Chem. Int. Ed. Engl. 34 (1995) 21.[2] M.H. Jiang, Q. Fang, Adv. Mater. 11 (1999) 1147.[3] P.A. Angeli Mary, S. Dhanuskodi, Cryst. Res. Technol. 36 (2001) 1231.[4] P. Becker, Adv. Mater. 10 (1998) 979.[5] S. Dhanuskodi, P.A. Angeli Mary, J. Cryst. Growth 253 (2003) 424.[6] H.A. Krebs, W.A. Johnson, Enzymologia 4 (1937) 148.[7] D.C. Crans, in: H. Sigel, A.E. Sigel (Eds.), Metal Ions in Biological Systems:

Vanadium and its Role in Life, Marcel Dekker, New York, 1995, p. 209 (Chapter5).

[8] D. Xue, S. Zhang, Chem. Phys. Lett. 301 (1999) 452.[9] C.B. Aakeroy, M. Nieuwenhuyzen, J. Am. Chem. Soc. 116 (1994) 1091.

[10] C.B. Aakeroy, M. Nieuwenhuyzen, J. Mol. Struct. 374 (1996) 239.[11] C.B. Aakeroy, M. Nieuwenhuyzen, Chem. Mater. 8 (1996) 1229.[12] M. Fleck, E. Tillmanns, L. Bohaty, P. Held, Z. Kristallogr. 219 (2004) 101.[13] K. Betzler, H. Hesse, P. Loose, Opt. Commun. 22 (1977) 70.[14] L. Schuler, K. Betzler, H. Hesse, S. Kapphan, Opt. Commun. 43 (1982) 160.[15] X. He, C.Z. Lu, Y. Yan, Inorg. Chem. Commun. 7 (2004) 853.[16] J.N. Babu Reddy, S. Vanishri, Ganesh Kamath, Suja Elizabeth, H.L. Bhat, D.

Isakov, M. Belsley, E. de Matos Gomes, T.L. Aroso, J. Cryst. Growth 311 (2009)4049.

[17] A. Senthil, P. Ramasamy, J. Cryst. Growth 312 (2010) 281.[18] G. Anandha Babu, G. Bhagavannarayana, P. Ramasamy, J. Cryst. Growth 310

(2008) 1238.[19] G. Anandha Babu, G. Bhagavannarayana, P. Ramasamy, J. Cryst. Growth 310

(2008) 2826.[20] W. Versichel, W. Van de Mieroop, A.T.H. Lenstra, Acta Cryst. B34 (1978) 2645.[21] A. Ashour, N. El-Kadry, S.A. Mahmoud, Thin Solid Films 269 (1995) 117.[22] J. Tauc, R. Grigorovici, A. Vancu, Phys. Status Solidi 15 (1966) 627.[23] M.K. Gupta, N. Sinha, S. Binay Kumar, Physics B 406 (2011) 67.[24] E.M. Onitsch, Mikroscopia 2 (1947) 131.[25] K. Lal, G. Bhagavannarayana, J. Appl. Crystall. 22 (1989) 209.[26] U. Bonse, M. Hart, Appl. Phys. Lett. 7 (1965) 240.[27] G. Bhagavannarayana, R.V. Ananthamurthy, G.C. Budakoti, B. Kumar, K.S.

Bartwal, J. Appl. Cryst. 38 (2005) 771.[28] K. Senthilkumar, S. Moorthy Babu, G. Bhagavannarayana, J. Appl. Cryst. 44

(2011) 318.[29] G. Bhagavannarayana, B. Riscob, Mohd Shakir, Mater. Chem. Phys. 126 (2011)

23.[30] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3813.