chapter-2 synthesis, structure, crystal growth, and...

51

CHAPTER-2

SYNTHESIS, STRUCTURE, CRYSTAL GROWTH, ANDMORPHOLOGY STUDIES ON THE 2-{3-[2-(4-HYDROXYPHENYL) VINYL]-5, 5-DIMETHYLCYCLO-HEX-2-EN-1-

YLIDENE} MALONONITRILE CRYSTAL AND ITSDERIVATIVES

2.1. INTRODUCTION

Organic materials are attractive due to their electronic, optical properties and easy

to modify the molecular structure for suitable applications. Organic materials with

large third-order nonlinear optical (NLO) properties will be the key elements for

future photonic technologies (Dsilva et al; 2012). The use of third order optical

nonlinearity for all optical signal processing has been a goal for many years. There are

no criteria for the design of appropriate materials with large third order nonlinearity.

Therefore, it is still challenging to make high throughput all optical switching devices

responding on picoseconds time scales (Bosshard et al;1996). In several areas of

optoelectronics have been a huge interest for organic materials because the

possibilities of optimization of this nonlinearity through manipulation of their

composition (Prassad et al;1991).

Organic compounds are optically more nonlinear than inorganic materials because

of their hydrogen bonds and weak Vander Waal’s and it possess a high degree of

delocalization (Santhakumari et al;2011). The crystalline organic materials are

difficult to grow in large size with good optical quality. The nonlinear organic

materials have a low threshold are much important as they could be used for the

protection of the human eye from the enfeebling laser effects (Narayanan Rao et al;

2003). Many research articles have reported about third order nonlinear susceptibility

of organic material followed by the report on poly [2,4-hexadiyne-1,6-diol-bis-p-

toluene-sulfonate] in 1976 (Sauteret et al; 1976).The organic materials like

phthalocyanines and its derivatives in 1989 (Mathews et al;2007), organic metallic

compounds (Sun et al;1970), large nonlinear refractive index change in 4- N,N-

dimethylamino-3-acetamidonitrobenzene(DAN) (Kim et al;1993), fullerencies

(Venugopal Rao;1998) has undergone wide investigation with respect to

spectroscopic and structural properties. The key components of next generation

broadband devices are ultrafast optical switching devices. The materials with low

linear and nonlinear losses are required to implement the optical switching devices.

52

Here, the nonlinear optical chromophores based on configurationally locked and

nonlocked polyene are synthesized. The molecule consists of a -conjugated bridge

between dicyanomethylidene acceptor and donor or acceptor aldehydes. At high

intensity, the polarisation response of π-conjugated polyene- type molecule is large to

achieve third order generation. The conjugated bond of molecules contains π-bond

and σ-bond. Compared to σ-bond, π-bond is more active to applied field because it is

less tightly bounded.

The potential use in optical information processing device has been the driving

force behind most of research into characterization of nonlinear optical properties of

materials. For this purpose, considerable attention has been given to the three photon

absorption of -conjugated organic compounds. In the chapter, systematic studies on

the, synthesis, growth, morphology, structural, NMR, and FTIR studies of OH1

organic crystal derivatives are discussed.

2.2. SYNTHESIS SCHEME

Figure.2.1. Synthesis scheme of malononitrile derivative

The starting compound, (C12H14N2) 3,5,5-trimethyl(cyclohex-2-enylidene)-

malonodinitrile, was prepared by means of Knoevenagel condensation is shown in

Fig.2.1. Malonodinitrile and isophorone were dissolved in 50ml of N,N-

dimethylformamide with equal molar ratio and the presence of piperidine as catalyst.

The solution was stirred for eight hours at room temperature (30°C). A yellow

precipitate was obtained from the resulting dark-yellow solution after evaporation of

half of the solvent. In order to achieve purity, the product was filtered and

53

recrystallized several times from ethanol. The malononitrile derivative compound was

prepared according to a published procedure (Tsonko kolev et al;2001). In second

step, 3,5,5-trimethyl(cyclohex-2-enylidene)malonodinitrile and benzaldehyde were

dissolved in a 150 ml trichloromethane solution with continuous stirring for two days

at room temperature. The yellow precipitate was recrystallized from glacial acetic

acid. Crystals were grown by slow evaporation from methanol, ethyl acetate and 2-

butanol etc.

2.2.1 MECHANISM OF CHEMICAL REACTION

Figure.2.2. Mechanism of malononitrile derivatives

In step-1, malononitrile and isophorone were allowed to react in N-N-dimethyl

formamide solvent, in the presence of piperidine as catalyst. The role of piperidine in

reaction, it takes hydrogen or two electrons from malononitrile compound. The

anionic nature of malononitrile attacks isophrone. Due to the electronegativity or

54

patially cationic of carbon in isophorone, malononitrile is attracted and an

intermediate is formed as shown in Fig.2.2. In intermediate compound, hydrogen

forms a double bond and OH reacts with free hydrogen, it removed as water(-H2O).

Finally (C12H14N2) 3,5,5-trimethyl(cyclohex-2-enylidene)-malonodinitrile was

formed.

In second step, similarly piperidine takes two electron or hydrogen from 3,5,5-

trimethyl(cyclohex-2-enylidene)-malonodinitrile. Carbon in benzaldehyde react with

5,5-trimethyl(cyclohex-2-enylidene)-malonodinitrile and forms a conjugate bond

between aldehyde and dicyanomethylidene acceptor. Hydrogen in benzaldehye forms

a double bond and OH reacts with free hydrogen, it removed as water (-H2O)

2.3. INTRODUCTION TO OH1 MOLECULE

An organic novel NLO crystal 2-{3-[2-(4-Hydroxyphenyl) vinyl]-5, 5-

dimethylcyclo-hex-2-en-1-ylidene}malononitrile (OH1) is a non-ionic phenolic

polyene molecular crystals having superior properties compared to those of

stilbazolium salts 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) and 4’-

N,N-dimethylamino-4’-N’-methyl-stilbazolium 2,4,6-trimethylbenzene sulfonate

(DSTMS). It shows an electro-optic figure of merit n33r333= 970±100pm/V and

2070±80pm/v at λ=785nm and 632.8nm respectively, which is among the highest in

organic crystals (Kwon.S.J et al;2010)]. It is well known that Π- donor- acceptor

compounds can exhibit large second- order optical nonlinearity (Marder et al;1989).

The positively charged hydroxyl/phenolic donor and negatively charged cyano

acceptor are linked by hydrogen bond interaction in OH1 molecule (Kwon.O.P et al;

2006). The crystallographic axes coincide with dielectric axes in the high symmetry

OH1 crystals, which is agreeable to crystal preparation for optical applications (Kwon

S.J.et al;2010). The angle between the polar c-axis of the crystals and the charge

transfer axis of the chromophores is 28˚, which results in a large second order

nonlinear optical susceptibility of χ2333=240±20pm/V for second harmonic generation

at a wavelength of 1900nm. The high birefringent of OH1 crystal is due to a highly

anisotropic linear polarizability of the chromophores and their acentric packing Δn >

0.55 in the wavelength range between 0.6 and 2.2 μm (Hunziker et al;2008). The OH1

molecule shows a large dipole moment of μg = 3.44 × 10−29 Cm, which leads to a

large hyperpolarizability of βz = 765 × 10−40m4V−1 (Kwon,O.P et al;2011). It exhibits

a wide transparency range from 800 nm to 1400 nm with an absorption coefficient α<

55

1 cm−1, where low loss optoelectronic devices can be fabricated (Hunziker et al;

2008).

2.3.1. SYNTHESIS PROCEDURE OF 2-{3-[2-(4-HYDROXYPHENYL)VINYL]-5, 5- DIMETHYLCYCLO-HEX-2-EN- 1-YLIDENE}MALONONITRILE (OH1)

The proportional molecular weight of isophorone (660mg) and

malononitrile (1.328g) are dissolved in N-N-dimethylformamide (50ml) in the

presence of piperidine as catalyst. The final product 3, 5, 5-trimethyl (cyclohex-2-

enylidene) malononitrile was recrystallised several times in ethanol solvent. In the

second step, OH1 molecule was synthesized by the knoevenagel condensation of (3,

5, 5-trimethyl cyclohex-2-enylidene) malononitrile (1.86g) and 4-hydroxy

benzaldehyde (1.22g) were dissolved in chloroform (150ml) in the presence of

piperidine as catalyst. The final product was crystallized in ethyl acetate, The

chemical structure of OH1 compound is shown in Fig [2.3].

Figure.2.3. Chemical structure of OH1 compound

2.3.2. FOURIER INFRARED SPECTROSCOPY (FTIR)

FTIR spectral study was carried out to identify the presence of functional groups

in OH1 compound, and it is shown in Fig.2.4. The absorption of O-H bonds occurs at

higher energy region in the range of 3600cm-1 to 2700cm-1. The position of the

absorption band is depending on the strength of O-H bond. OH absorption band has

observed at 3367cm-1 with high intensity stretching vibration.

The weak absorption of O-H bond is observed at 3774.69cm-1 and 3735.12cm-1,

due to the antisymmetry O-H-bending. The stretching and bending vibrations of

aromatic aldehydes are expected in the region of 3080-3000cm-1. The stretching and

bending vibrations of the aromatic ring -C-H-bonds are observed at 2881.65, 2719.91,

2657.59, 1367.53, 1325.10, 1274.95 cm-1, and 1211.30 cm-1. The absorption bands

56

Figure.2.4. FTIR spectrum of OH1 crystal

Table.2.1.Observed FTIR bands of OH1 compound and their assignments.ObservedWavenumber(cm-1)

Assignments

3774.69(w) Anti symmetry -O-H- bending3735.12(w) Anti symmetry-O-H- bending3367.71(s) -O-H stretching, intermolecular bonded OH3066.82(w) -O-H bending, CH-bending in aromatic ring2953.02(s) O-H-streching and CH- asymmetry

stretching2881.65(w) C-H-bending-asymmetric2719.63(w) C-H-bending-asymmetric2657.91(w) C-H-bending2422.59(w) C-H-bending2222.00(s) -C≡N- stretching1602.86(s) -C=C- stretching1562.34(s) -C=C- stretching in aromatic ring1554.63(s) -C=C- stretching in aromatic ring1546.91(s) -C=C- stretching in aromatic ring1502.55(s) -C-C- stretching in aromatic ring1367.53(s) -C-H-streching in aromatic ring1325.10 (s) -C-H-streching in aromatic ring1274.95(s) -C-H-streching1211.30(s) -C-H-streching1197.79(s) -CH3- wagging1168.86 (s) -CH3-wagging1157. 29(s) -CH3-twisting1130. 29(w) -C-C-bending1107.14(w) CH-in plane bending958.62(s) -C-H- deformation, out of plane bending844.82(s) Ring -C-H- deformation, out of plane

bending642.30(s) -C-H- stretching549.71(s) -C-C- streching503.42(m) -C-C-Ring out of plane bending

s-strong, m-medium,w-weak

500100015002000300040001/cm

0

25

50

75

100

%T

3774

.6937

36.12

3545

.1634

58.37

3367

.71

3066

.8229

53.02

2881

.6527

19.63 2657

.91

2422

.59

2222

.00

1602

.8515

62.34

1554

.6315

46.91

1502

.55 1367

.5313

25.10 12

74.95

1211

.3011

97.79

1168

.8611

57.29

1130

.29 1107

.1495

8.62

844.8

2

642.3

0

549.7

150

3.42

1

57

observed at 1197, 1168, 1157cm-1 are attributed to CH3 wagging and twisting. -C-H

out of plane bending vibration is occurring in the region 844.82 and 642.30cm-1.C-H-

plane bending deformation is occurring at 958.62cm-1.The triple bond stretches are

occurring in the region of 2300-2000cm-1 (Kalsi;2007). Similarly, -C≡N- stretching

shows strong absorption at 2222.00cm-1. The strong absorption peak of -C=C- peak is

coming around 1562, 1554, 1546 and 1502 cm-1. It is observed that -C-C- ring out of

plane bending at 503.42cm-1 and stretching at 549.71 cm-1. The assignment of FTIR

spectrum is shown in Table.2.1.

2.3.3. SINGLE CRYSTAL XRD

OH1 is confirmed by Single crystal-XRD. The values of a=9.47 Å, b=10.89 Å,

c=15.30 Å and V=1578Å3 are nearly similar to the reported values (Kolev et al;2001).

OH1 crystal having the space group of pna21 in orthorhombic crystal system is

reported by kolev et.al. The molecular structure of OH1 compound is shown in Fig

.2.5.

Figure.2.5. molecular structure of OH1 compound

2.3.4. CRYSTAL GROWTH

OH1 material is highly soluble in various solvents such as methanol, ethyl

methyl ketone, ethanol, and ethyl acetate. Among these solvents methanol is suitable

for OH1 crystal, reported by S.J.kwon et.al. The spontaneous nucleation affects the

growth of OH1single crystal in methanol due to the high metastability as shown in Fig

.2.6a,b. So the additive phosphoric acid in methanol controls the nucleation of OH1

crystal (i.e., weak acid and more polar than methanol) and it does not affect the

chemical structure of OH1 compound (Young Choi et al;2012).

58

OH1 crystals are grown in methanol by slow evaporation method in the presence

and absence of phosphoric acid. OH1 crystal has grown in methanol of size

4x4x0.5mm3 as shown in Fig.2.6c. In crystal growth experiments, 20μL of H3PO4

acid is added to the OH1 solution containing 0.2mmol OH1 and 10 mL methanol. Fig

2.6d shows the growth of OH1 crystal with a size 5x4x1mm3 (with 20μL additive)

after a period of two weeks. In second experiment, 0.2 mmol of the OH1material is

dissolved in 10 mL methanol, and then, 40μL phosphoric acid is added; the obtained

OH1 crystal with a size 6x5x2mm3 as shown in Fig.2.6e. OH1 crystals are grown

along the direction of 11-1 plane at a constant temperature 35˚C. The powder XRD of

OH1 compound exhibits well defined crystalline peaks and hkl reflections are indexed

by using powderX software, it is shown in Fig.2.7.

Figure.2.6 a) Improper growth of OH1 crystal in methanol solvent. b) OH1 crystal grown in

methanol solvent. c) After the several times of recrystallised OH1 crystal in methanol. d) OH1

Crystals grown in methanol with additive 20μL of H3PO4 (PH-3.6). e) OH1 Crystals grown in

methanol with additive 40μL of H3PO4 (PH=3.4).

Figure.2.7.Powder-XRD pattern of OH1 crystal

59

2.3.5 MORPHOLOGY OF OH1 CRYSTAL.

Fig.2.8.Morphology of OH1 crystal

The morphology of OH1 crystal has been generated from WINXMORP

software (Kaminsky; 2007). Crystal morphologies are predicted from single crystal

hkl reflection data (CIF format). CIF data has given as input in the winxmorp

software, to predict the morphology of OH1 crystal. The morphology of OH1 crystal

is growing along negative c-axis. The morphology of the crystal was shown in

Fig.2.8.

2.4. SYNTHESIS PROCEDURE OF 2-{3-[2-(3-METHYL-4-METHOXYPHENYL) VINYL]-5, 5-DIMETHYLCYCLO-HEX-2-EN-1- YLIDENE}MALONONITRILE (MOT2)

An equal molar ratio of isophorone and malononitrile are added with N-N-

dimethylformamide, to catalyst the reaction piperidine acetate was added. The product

was recrystallised several times in ethanol solvent, yellow crystalline powder of

(3,5,5-trimethylcyclohex-2-enylidene)malononitrile was formed. In the second step,

final product of the first step and 3-methyl-4-methoxy benzaldehyde are allowed to

react in chloroform solution in the presence of piperidine acetate (Kwon,O.P, et

al;2011).The final product of 2-{3-[2-(3-methyl-4-methoxyphenyl) vinyl]-5, 5-

dimethylcyclo-hex-2-en-1-ylidene}malononitrile(MOT2) has been synthesized. The

melting point of synthesized compound is 200˚C, measured using the melting point

apparatus. The chemical structure of MOT2 is shown in Fig.2.9.

60

Figure.2.9. Chemical structure of MOT2 compound

2.4.1. FOURIER TRANSFORM INFRARED SPECTROSCOPY AND

VIBRATION ANALYSIS

FTIR spectrum is used to determine the presence of functional group in MOT2

compound and it is shown in Fig.2.10. The C-H stretching mode of aldehyde appears

at 2837.29cm-1 and near to the peak Fermi doublet as weak intensity, no overlap with

other bands. The hydrogen atoms in methyl group having the same mass and strength,

so the vibration will not be independent anti symmetry and symmetry weak peaks are

observed at 2929.87cm-1 and 2872.01cm-1. C-H bending vibration and out of plane

bending is observed at 1438.90, 893.04, 806.25, 748.38cm-1. Aromatic stretching =C-

H- weak vibration at 3016.67cm-1. -C-N- stretching vibrations are at 1525.69cm-1 and

1502.55cm-1. -C-O- strong stretching vibration at 1259.52cm-1,-C-O- bending

vibrations at 1207.44cm-1 and 1134.14cm-1 is bending vibration of -C-O- (Kalsi;

2007). The assignment of FTIR spectrum is shown in Table.2.2

Figure.2.10.FTIR analysis of MOT2 compound.

50010001500200025003000350040001/cm

0

25

50

75

100

%T

3055

.24

3016

.67

2929

.87

2872

.01

2837

.29

2218

.14

1600

.92

1560

.41

1525

.69

1502

.55

1438

.90

1315

.45

1259

.52

1207

.44

1134

.14

1028

.06

983.

7089

3.04 80

6.25

748.

3864

4.22

590.

2247

6.42

OMM

61

Table.2.2.Observed FTIR bands of MOT2 compound and their assignmentsObservedwavelengths cm-1

Assignments

3055.24w -C=C-H bending3016.67w =C-H- aromatic Stretching2929.87w C-H asymmetry bending in methyl group2872.01m C-H symmetry bending in methyl group2837.29m C-H stretching absorption in aldehyde2218.14s -C≡N-1600.92s -C=C- stretching vibrations1560.41s Symmetry stretching vibrations of nitrogen bonds1525.69s -C-N-stretching1502.55s -C-N-stretching1438.90m CH3 bending vibrations1315.45s Symmetry stretching vibrations of nitrogen bonds1259.52s -C-O- stretching1207.44m -C-O-bending vibrations1134.14m -C-O- bending vibration1028.06m =C-H- bending vibrations983.70m -C-H- Stretching893.04m -C-H out of plane bending806.25m -C-H-out of plane bending748.38w -C-H-out of plane bending644.22w -N-H-bending590.22w -C-C- bending476.42w -C-C-Ring out of plane bending

w-weak, s-strong, m-medium

2.4.2. POWDER X-RAY DIFFRACTION

The powder XRD pattern of MOT2 crystal is shown in Fig.2.11, it is drawn

intensity verses 2theta. The crystalline peaks were obtained from powder form of

MOT2 crystal and hkl reflections were indexed by using powderX program. The

position of a diffraction peak is independent of the atomic positions within the cell

and entirely determined by the size and shape of the unit cell of the crystalline phase.

Each peak represents a certain lattice plane and can therefore be characterized by

a Miller index. Crystal structure determination from powder diffraction data is

extremely challenging due to the overlap of reflections in a powder experiment. In

powder diffraction experiment, where peak overlap due to the presence of reflections

with similar d-spacings. Overlapping peaks in PXRD is other crystallites are not

oriented properly to produce diffraction from nearer planes of atoms and some of the

overlaps are dictated by symmetry and others are accidental.

62

Figure.2.11. Powder-XRD pattern of MOT2 crystal.


Figure.2.12. Molecular structure of MOT2 compound

Single crystal XRD analysis of MOT2 crystal has been studied, it belongs to

monoclinic crystal system and space group P2 (1)/n symmetry is reported by

O.P.Kwon et.al (CCDC-278093).The molecular structure of MOT2 crystal is shown

in Fig.2.12. The unit cell parameter of MOT2 crystal has observed that a=9.973(2),

b=7.512(2), c=12.013(2) and V=1802.3 are similar to the reported values. The

packing fraction of MOT2 crystal has shown in Fig.2.13. The molecule consists of a

-conjugated bridge between dicyanomethylidene acceptor and methoxy donor. In the

molecular packing Inter molecule reaction N1-H13, O1-H14, cyano group interact

hydrogen with nearer molecule and methoxy interact with neighbouring molecule

hydrogen.

63

Figure.2.13. Molecular packing diagram for MOT2 crystal


The growth of highly transparent polar material crystals are purely depends on

the selection of solvents. MOT2 compound has good solubility in organic solvents

like ethanol, methanol, acetone, acetonitrile, toluene, ethyl methyl ketone and N,N-

dimethylformamide. It is observed that the growth of crystals in solvents, methanol

and ethanol are in the form of fiber or sponge, acetonitrile and acetone are in needle

shape and crystalline powder deposited found in N-N-dimethylformamide and

toluene. The highly transparent and red coloured MOT2 crystals were grown well in

ethyl methyl ketone along a,b,c axis. The dipole-dipole interactions between the

MOT2 molecule and solvent molecule are responsible for growth of crystal and its

morphology. So the solvent ethyl methyl ketone has chosen to grow MOT2 crystal.

0.001mole of MOT2 compound is dissolved in 20ml of ketone solvent. After a period

of two weeks, MOT2 crystal has grown at 35˚C by slow evaporation method as

shown in Fig.2.14.

Figure.2.14. MOT2 crystals grown in Ethylmethyl ketone solvent

64

2.4.3. MORPHOLOGY

Figure.2.15.Morphology of MOT2 crystal

The morphology of MOT2 crystal has been generated from WINXMORP software

(Kaminsky;2007). Crystal morphologies are predicted from single crystal hkl

reflection data (CIF format). CIF data given as input in the winxmorp software to

predict the morphology of MOT2 crystal. The morphology of MOT2 crystal has

observed that [010] and [-1 1 0] family of planes elongated along the x-axis. The

morphology of the crystal was shown in Fig.2.15.

2.5. SYNTHESIS PROCEDURE OF (E)-2-{3-[2-(4-CHLOROPHENYL)VINYL]-5, 5-DIMETHYLCYCLO-HEX-2-EN-1- YLIDENE}MALONONITRILE (Cl1)

The stoichiometric ratio 1:1 of the reactants malonodinitrile(10mmol) and

isophorone(10mmol) were dissolved in solvent N-N-dimethylformamide in the

presence of piperidine acetate as a catalyst, to synthesize 3,5,-trimethylcyclohex-2-

enylidene)malononitrile. The final product of the first step (3, 5,-trimethylcyclohex-2-

enylidene) malononitrile (C12H14N2) was dissolved in chloroform (150ml) with 4-

chlorobenzaldehyde in equal molar ratio in the presence of piperidine acetate as a

catalyst. The final product was recrystallized three times in glacial acetic acid. The

purity of synthesized compound was improved by successive recrystallization process

and filtration.The orange coloured final product of 2-{3-[2-(4-chlorophenyl) vinyl]-5,

65

5-dimethylcyclo-hex-2-en-1-ylidene}malononitrile (Cl1) (yield 60%) was synthesized.

The structure of Cl1 compound is shown in Fig.2.16. (Bharath et al;2014).

Figure.2.16. Chemical structure of Cl1 compound

2.5.1. FTIR

Fourier transform infrared spectroscopy has been recorded to analysis the

functional group of synthesized Cl1 compound and, it is shown in Fig.2.17. In the

wavelength range of 400 -4000cm-1 was recorded using the instrument IR Affinity-

1(shimadzu) The weak stretching mode of -C-H- aldehyde is at 2929.87, 2825.72 cm-1

and near to overlapping Fermi doublet. The methyl group –C-H- symmetric bending

is observed at 1390.68 and 1371.39 cm-1.

Figure.2.17. FTIR pattern of Cl1 compound.

The strong symmetry stretching of –C-N- is assigned at 2289.50, 2222, 1531.48,

1180.44, 1155.38 cm-1. The aromatic -C=C- medium stretching in the benzene ring

vibrations are at 1588.13 and 1487.12 cm-1 and -C-C- bending at 1199.72 cm-1 .

500100015002000300040001/cm

-25

0

25

50

75

100

%T

3084

.1829

70.38

2929

.8728

25.72

2289

.5022

22.00

2171

.85

1568

.1315

31.48 14

87.12

1467

.8313

90.68

1371

.3913

38.60

1319

.3112

90.38 11

99.72

1180

.4411

55.36

1087

.85 1006

.8496

0.55

941.2

685

0.61

825.5

381

2.03

761.8

870

4.02

542.0

0

mcl

66

Table.2.3.Observed FTIR bands of MOT2 compound and their assignmentsObservedwavelengths cm-1

Assignments

3084.18m -C-H aromatic stretching2970.38m C-H asymmetry bending in methyl group2929.87w C-H stretching in aldehyde2825.72w C-H stretching in aldehyde2289.50m -C≡N- stretching2222.00s -C≡N- stretching1588.13s -C=C- stretching1531.48s -C-N-stretching1487.12s -C=C- stretching of benzene ring1390.68m -C-H- bending in methyl group1371.39m -C-H- bending in methyl group1338.60s Symmetry stretching of nitrogen bonds1319.31s Symmetry stretching of nitrogen bonds1199.72w -C-C-bending1180.44m -C-N- stretching1155.38m -C-N-stretching1087.85s =C-H- stretching1006.84s =C-H- stretching960.56s -C-H- out of plane stretching941.26s -C-H- out of plane stretching850.61s -C-H out of plane stretching825.53m -C-H-bending812.03s Out of plane -C-H- stretching from disubstituted

benzene ring761.88w -C-H- out of plane bending704.02w =C-H- out of plane bending542.00s -C-Cl- Stretching

The delocalized π-π bond of Cl1 molecule shows strong =C-H- stretching at

1087.85 and 1006.84 cm-1. The strong symmetry stretching of nitrogen bonds is at

1338.60 and1319.31 cm-1. -C-H- out of plane stretching vibrations are at 960.56,

941.26, 850.61 cm-1 and –C-H- out of plane bending are at 761.88, 704.02 cm-1. The

strong stretching of Chlorine atom in the molecule is at 542 cm-1 (Kalsi;2007). The

vibration analysis of Cl1 crystallized material is shown in Table.2.3.

2.5.2 POWDER XRD

The powder XRD pattern of Cl1 crystal is shown in Fig.2.18. The well-defined

crystalline peaks at specific 2theta angles were obtained from powder form of Cl1

crystal. The reflections (hkl) were indexed with corresponding crystalline peaks by

using powderX program.

67

Figure.2.18. powder XRD pattern of Cl1 compound.

2.5.3. SINGLE CRYSTAL XRD AND CRYSTAL PACKING STRUCTURE

The crystallographic structure of Cl1 crystal (0.35x0.30x0.25mm3) has been

measured by single crystal XRD Brucker kappa apex-II diffractometer(Enraf Nonius

CAD4-MV31). The Cl1 crystal structure belongs to the monoclinic space group P21/C

(point group, Z=4) is shown in Fig.2.19.

The strong coulomb forces bind the dicyanomethylidene acceptor and

chlorobenzene donor in pi-conjugated hydrogen bond. The unit cell of lattice

parameters is a=10.114(5) Å, b=11.127(5) Å, c=14.929(5) Å and V=1668.9(12) Å3. In

molecular packing as shown in Fig.2.20, intermolecular interaction is between the

hydrogen of the chlorobenzene electron donor group and one of the nitrogen of the

nitrile electron acceptor group N2-H16A and N1-H4. The single crystal data of Cl1

crystal is given in Table.2.4. The polyene type of Cl1 molecule bonding is shown in

Fig.2.21.

Figure.2.19. molecular structure of Cl1 compound

68

Figure.2.20. molecular packing diagram of Cl1 crystal

Table.2.4. Single crystal XRD data for Cl1 crystalSample name Cl1

Identification code ShelxlEmpirical formula C19 H17 Cl N2

Formula weight 308.80Temperature 293(2)KWavelength 0.71073 ACrystal system, Space group Monoclinic, P21/cUnit cell dimensions a= 10.114(5)A, b=11.127(5)A, c=14.929(5)A

α= 90.000(5)°,β= 96.646(5) °,γ=90.000(5) °Volume 1668.8(12) A3

Z, calculated density 4, 1.229 mg/m3

Absorption coefficient 0.227 mm-1

F(000) 648Crystal size 0.35 x 0.30 x 0.25 mm3

Theta range for data collection 2.29 to 30.76 deg.Limiting indices -14<=h<=14, -15<=k<=15, -21<=l<=20Reflections collected / unique 19995 / 5100 [R(int) = 0.0295]Completeness to theta = 30.76 97.7 %Absorption correction Semi-empirical from equivalentsMax. and min. transmission 0.9455 and 0.8848Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 5100 / 0 / 199Goodness-of-fit on F2 1.039Final R indices [I>2sigma(I)] R1 = 0.0461, wR2 = 0.1169R indices (all data) R1 = 0.0781, wR2 = 0.1373Largest diff. peak and hole 0.202 and -0.403 e.A-3

69

Figure.2.21. Polyene like formation of Cl1 molecule.

2.5.4. GROWTH OF Cl1 SINGLE CRYSTAL

Cl1 Single crystals have been grown by slow evaporation method. The most of

the organic crystals are hygroscopic in nature, but the advantage of Cl1 crystal is the

lack of moisture sensitive. Cl1 compound is insoluble in water, and it is highly soluble

in polar solvents such as ethanol, acetonitrile, methanol and ethylmethyl ketone. The

Cl1 material was crystallized in different solvent, but it was found that ethyl methyl

ketone has suitable medium for the growth of Cl1 crystal. The dipole-dipole

interactions between the Cl1 molecule and solvent molecule are responsible for

growth of crystal and its morphology. The solubility of Cl1 compound in ethyl methyl

ketone was not too high compared with other solvents, 0.001mole of the compound

was dissolved of 25ml of ethyl methylketone at room temperature. The saturation

solution was allowed to evaporate slowly in beaker covered with aluminum foil with

limited holes at a constant temperature 35˚C. The maximum size of brown colored

Cl1crystals (12x2x1mm3) was harvested after the period of 10 days as shown in Fig

2.22.

Figure.2.22. Cl1 crystal grown in ethylmethyl ketone

70

2.5.5. MORPHOLOGY

The morphology of Cl1 crystal has been generated from WINXMORP

software (Kaminsky;2007). Crystal morphologies are predicted from single crystal hkl

reflection data (CIF format). CIF data has given as input in the winxmorp software, to

predict the morphology of Cl1 crystal. The morphology of Cl1 crystal is growing along

b-axis. The morphology of the crystal was shown in Fig.2.23.

Figure.2.23.Morphology of grown Cl1 crystal

2.6. SYNTHESIS PROCEDURE OF 2-{3-[2-(4-BROMOPHENYL) VINYL]-5, 5-

DIMETHYLCYCLO- HEX-2-EN-1-YLIDENE} MALONONITRILE (Br1)

3, 5, 5,-trimethyl (cyclohex-2-enylidene) malononitrile compound was

prepared by means of Knoevenagel condensation of malononitrile (10mmol) and

isophorone (10mmol). The reactants were dissolved in N-N-dimethylformamide in the

presence of piperidine acetate as catalyst. The title compound was synthesized from 3,

5, 5,-trimethyl (cyclohex-2-enylidene) malonodinitrile and 4-bromobenzaldehyde in

a chloroform solution. Piperidinium acetate was used as a catalyst. The final product

was synthesized after continuous stirring of the solution for 48hours at a room

temperature (30˚C). The orange precipitate was filtered and recrystallized from glacial

acetic acid. The final product of 2-{3-[2-(4-bromophenyl) vinyl]-5, 5-dimethylcyclo-

hex-2-en-1-ylidene} malononitrile (Br1) was synthesized. The structure of Br1

compound is shown in Fig .2.24.

71

Figure.2.24. chemical structure of Br1 compound


Figure.2.25. molecular structure of Br1 compound

The crystallographic structure of Br1 crystal (0.35x0.30x0.25mm3) has been

measured by single crystal XRD Brucker kappa apex-II diffractometer (Enraf Nonius

CAD4-MV31). The crystal structure belongs to the monoclinic space group P21/C

(point group, Z=4), and it is shown in Fig.2.25. The lattice parameter of the unit cell is

a=10.064(5) Å, b=11.218(5) Å, c=14.862(5) Å and V=1667.2(12) Å3. The strong

coulomb forces bind the dicyanomethylidene acceptor and chlorobenzene donor in π -

conjugated hydrogen bond. The intermolecular interactions occur between the

hydrogen of the bromobenzene (electron donor group) and one of the nitrogen of the

nitrile (electron acceptor group) which forms polymer like a chain in Br1 crystal. The

intermolecular interaction is between N2-H2 as shown in Fig.2.27. The single crystal

data of Br1 crystal is given in Table.2.5. The polyene type of Cl1 molecule bonding is

shown in Fig.2.26. (Bharath et al;2014).

72

Figure.2.26. Polyene like formation of Br1 molecule.

Table.2.5. Single crystal XRD data for Br1 crystalSample name Br1

Identification code ShelxlEmpirical formula C19 H17 Br N2

Formula weight 353.26Temperature 296(2) KWavelength 0.71073 ACrystal system, Space group Monoclinic, P21/cUnit cell dimensions a= 10.064(5)A, b=11.218(5)A, c=14.862(5)A

α= 90.000(5)°,β= 96.646(5) °,γ=90.000(5) °Volume 1667.2(12)A3

Z, calculated density 4, 1.407mg/m3

Absorption coefficient 2.464mm-1

F(000) 720Crystal size 0.35 x 0.30 x 0.25mm3



73

Figure.2.27. molecular packing diagram of Br1 crystal

2.6.2. GROWTH OF Br1 SINGLE CRYSTAL

Br1 single crystals were grown by slow evaporation method using ethyl methyl

ketone as solvent. Br1 compound (0.01mole) was dissolved in 30ml of ethyl methyl

ketone. The saturated solution was filtered and kept at a constant temperature water

bath at 35˚C. The spontaneous nucleation of Br1 crystal was observed after the period

of two days. The successive recrystallization process improves the purity of Br1

compound. A good optical quality Br1 crystal (20x10x3mm3) was grown during the

period of 2 weeks as shown in Fig.2.28.

Figure.2.28.Br1 crystal grown in ethylmethyl ketone

2.6.3. Morphology

WINXMORP software generates the morphology of Br1 crystal (Kaminsky;

2007). Crystal morphology was predicted from single crystal hkl reflection data (CIF

format). CIF data has given as input in the winxmorp software to predict the

74

morphology of Br1 crystal. The morphology of Br1 crystal is growing along c-axis as

shown in Fig.2.29.

Figure.2.29.Morphology of grown Br1 crystal

2.7. SYNTHESIS PROCEDURE OF 2-{3-[2-(4-ETHOXYPHENYL) VINYL]-5,

5-DIMETHYLCYCLO-HEX-2-EN-1-YLIDENE} MALONONITRILE

(OE1)

The proportional molecular weight of isophorone (10mmol) and malononitrile

(10mmol) were dissolved in N-N-dimethylformamide (50ml) in the presence of

piperidine acetate as a catalyst, to synthesize 3,5,-trimethylcyclohex-2-

enylidene)malononitrile. The intermediate product (3, 5,-trimethylcyclohex-2-

enylidene) malononitrile (C12H14N2) (1.86gm) was dissolved in chloroform with 4-

ethoxy benzaldehyde (10mmol) in equal molar ratio in the presence of piperidine

acetate as a catalyst. The product was recrystallized three times in glacial acetic

acid.The final product of 2-{3-[2-(4-ethoxyphenyl) vinyl]-5, 5-dimethylcyclo-hex-2-

en-1-ylidene} malononitrile was synthesized by the knoevenagel condensation

method. The synthesized OE1 compound was purified by successive recrystallization

process. The orange coloured final product OE1 (yield 50%) was synthesized (HPLC-

98.96% purity). The chemical structure of OE1 compound is shown in Fig.2.30.

Figure.2.30. Chemical structure of OE1 compound

75


2-{3-[2-(4-ethoxyphenyl) vinyl]-5, 5-dimethylcyclo-hex-2-en-1-ylidene}

malononitrile (OE1) is nonlinear optical crystal with the molecular formula

C21H22N2O. The crystallographic structure of OE1 crystal (0.35x0.30x0.30mm3) has

been measured by single crystal XRD Brucker kappa apex-II diffractometer (Enraf

Nonius CAD4-MV31). The molecular ortep structure of OE1 crystal is shown in Fig

2.31.

Figure.2.31. Molecular structure of OE1 compound

Figure.2.32.Packing structure of OE1 crystal

76

OE1 crystal belongs to monoclinic crystal system and space group P21/c symmetry

whose unit cell parameters are a = 6.8790, b = 15.4260 and c = 17.2870. The strong

Coulomb force is bind the dicyanomethylidene acceptor and ethoxy acceptor in π-

conjugated hydrogen bond. The packing diagram of OE1 crystal and the

intermolecular interaction is between C14-H13, H13-C14, as shown in Fig.2.32. The

single crystal data of Br1 crystal is given in Table.2.6

Table.2.6. Single crystal XRD data for OE1 crystal

Sample name OE1

Identification code ShelxlEmpirical formula C21 H22 N2 OFormula weight 318.41Temperature 293(2) KWavelength 0.71073 ÅCrystal system, Space group Monoclinic, P21/cUnit cell dimensions a= 6.879(3)Å , b=15.426(4)Å, c=17.287(3)Å

α= 90.000(5)°,β= 97.856(10) °,γ=90.000(5) °Volume 1817.20(10) Å 3


Absorption coefficient 0.072 mm-1



Data / restraints / parameters 2881 / 300 / 435Goodness-of-fit on F2 1.023Final R indices [I>2sigma(I)] R1 = 0.0322, wR2 = 0.0795R indices (all data) R1 = 0.0755, wR2 = 0.0957Largest diff. peak and hole 0.091 and -0.085e.A-3

Extinction coefficient 0.0163(14)

77


Figure.2.33. a.OE1 crystal grown in ethylmethyl ketone

b.Powder-XRD pattern of OE1 crystal

OE1 single crystals have been grown by slow evaporation method using 2-butanone as

solvent. OE1 compound is insoluble in water and the lack of moisture sensitive. The

OE1 material was crystallized in different solvent, but it was found that 2-butanone

has suitable medium for the growth of OE1 crystal. OE1 compound (0.001mole) was

dissolved in 2-butanone (25ml). The saturated solution was filtered and kept at a

constant temperature water bath at 35˚C. The successive recrystallization process

improves the purity of OE1 compound. The maximum size of OE1crystals

(6x4x2mm3) was harvested after the period of 2 weeks as shown in Fig. 2.33a.

powder XRD pattern of OE1 crystal is shown in Fig.2.33b.

2.7.3 MORPHOLOGY

The morphology of the crystal is purely depending on dipole interactions of the

compound and solvent molecules. WINXMORP software generates the morphology

of OE1 crystal (Kaminsky,2007). Crystal morphology was predicted from single

crystal hkl reflection data (CIF format). CIF data has given as input in the winxmorp

software to predict the morphology of OE1 crystal. It is observed from the

morphology studies that the growth along c direction is faster than other directions as

shown in Fig .2.34.

78

Figure.2.34.Morphology of grown OE1 crystal

2.8. SYNTHESIS PROCEDURE OF 2-{3-[2-(3-ETHOXY-4-HYDROXY

PHENYL) VINYL]-5, 5-DIMETHYL CYCLO-HEX-2-EN-1-YLIDENE}

MALONONITRILE (3E4HM),

An equal molecular weight of isophorone(10mmol) and

malonodinitrile(10mmol) has been dissolved in N-N-dimethylformamide (50ml) in

the presence of piperidine acetate as catalyst. The final product 3, 5, 5-

trimethylcyclohex-2-enylidene)malononitrile compound has synthesized by the

knoevenagel condensation method. The product was recrystallized several times in

ethanol solvent, yellow crystalline powder of (3, 5, 5-trimethylcyclohex-2-

enylidene)malononitrile was formed. The intermediate product 3, 5, 5-

trimethylcyclohex-2-enylidene)malononitrile(1.86gm) was dissolved in chloroform

with 3-ethoxy4-hydroxy benzaldehyde (10mmol) in equal molar ratio in the presence

of piperidine acetate as a catalyst. The final product was recrystallized three times in

glacial acetic acid. The purity of synthesized compound was improved by successive

recrystallization process and filtration. The orange coloured final product of 2-{3-[2-

(3-ethoxy4-hydroxyphenyl) vinyl]-5, 5-dimethylcyclo-hex-2-en-1-

ylidene}malononitrile (3E4HM) (yield 50%) was synthesized. The chemical structure

of 3E4HM compound is shown in Fig.2.35.

79

Figure.2.35.Chemical structure of 3E4HM molecule


The crystallographic structure of 3E4HM crystal (0.35x0.35x0.30mm3) has been

measured by single crystal XRD Brucker kappa apex-II diffractometer (Enraf Nonius

CAD4-MV). The crystal structure belongs to the monoclinic space group P21/C (point

group, Z=4) and it is shown in Fig.2.36.

Figure.2.36. Molecular structure of 3E4HM compound

The lattice parameter of unit cell is a=9.8790(3) Å, b=13.516(4) Å, c=14.414(4)

Å and V=1867.53(9) Å3. The strong coulomb forces bind the dicyanomethylidene

acceptor and 3-ethoxy-4-hydroxy-benzene donor in pi-conjugated hydrogen bond.

The intermolecular interactions in 3E4HM crystal occur between the oxygen of the

ethoxybenzene electron donor group and one of the nitrogen of the nitirile electron

acceptor group. The molecular packing of 3E4HM crystal has shown in Fig.2.37, inter

molecular interaction occurs between N1-H2-O2 and C16-C16 with nearer molecule.

The single crystal data of Br1 crystal is given in Table.2.7.

80

Table.2.7. Single crystal XRD data for 3E4HM crystalSample name 3E4HMIdentification code ShelxlEmpirical formula C21 H22 N2 O2

Formula weight 334.41Temperature 293(2)KWavelength 0.71073 ÅCrystal system, Space group Monoclinic, P21/cUnit cell dimensions a= 9.879(53)Å, b=13.5167(4)Å, c=14.4148(4)Å

α= 90.000(5)°,β= 104.015(10) °,γ=90.000(5) °Volume 1867.53(9) Å3


Absorption coefficient 0.077mm-1


Theta range for data collection 2.10 to 25.00deg.Limiting indices -9<=h<=11, -16<=k<=16, -17<=l<=17Reflections collected / unique 16639 / 3287 [R(int) = 0.0268]Completeness to theta = 30.76 100.0 %Absorption correction Semi-empirical from equivalentsMax. and min. transmission 0.9863 and 0.9635Refinement method Full-matrix least-squares on F2


Figure.2.37.Packing structure of 3E4HM crystal

81


3E4HM Single crystals have been grown by slow evaporation method. The

synthesized compound is insoluble in water and it is highly soluble in polar solvents.

3E4HM compound was crystallized in different solvent and it has partially soluble in

organic solvents like ethanol, methanol, acetone, acetonitrile, toluene, ethyl acetate

and N-N-dimethylformamide. The compound was crystallized in different solvent, but

it was found that ethyl methyl ketone has suitable solvent for the growth. The growth

of single crystal was carried out from ethyl methyl ketone solution by slow

evaporation method. 3E4HM compound (0.001mole) was dissolved in 2-butanone

(30ml) at room temperature. The most of the organic crystals are hygroscopic in

nature, but the advantage of 3E4HM crystal is the lack of moisture sensitive. The

purity of the compound was improved by successive recrystallization process. The

morphology of crystals are depends on the dipole-dipole interactions between solvent

and compound molecules. The maximum size of 3E4HM crystal (5x1x1mm3) was

grown during the period of two weeks as shown in Fig.2.38.

Figure.2.38.3E4HM crystal grown in ethylmethyl ketone

2.8.3. MORPHOLOGY

The morphology of 3E4HM crystal has been generated from WINXMORP

software (Kaminsky;2007). Crystal morphologies are predicted from single crystal hkl

reflection data (CIF format). CIF data is given as input in the winxmorp software to

predict the morphology of 3E4HM crystal. The morphology of crystal is growing

along a-axis and it is shown in Fig.2.39. The morphology of the crystal is purely

depending on dipole interactions of the compound and solvent molecules.

82

Figure.2.39.Morphology of grown 3E4HM crystal

2.9. CONCLUSION

Table.2.8-Compartive data of malononitrile derivative crystals

Molecule Space grouppoint group

Molecularbonding

Unit celldimensionÅ

Crystalgrowthsolvent

Crystalsizemm3

Crystalgrownaxis

OH1 Pna21 O1-H1-

N1

a=9.47,b=10.89,c=15.30

Methanol 6x5x2 11-1

MOT2 P21/n N1-H13,

O1-H14

a=9.973(2),b=7.512(2),c=12.013(2)

Ethylmet-

hyl ketone

5x3x2 -110

OE1 P21/c C14-H13,

H13-C14

a = 6.8790,b = 15.4260c = 17.2870

2-butanone 6x4x2 001

3E4HM P21/C N1-H2-

O2,

C16-C16

a=9.8790(3)b=13.516(4)c=14.414(4)

Ethylmet-

hyl ketone

5x1x1 100

Cl1 P21/C N2-H16A

N1-H4

a=10.114(5)b=11.127(5)c=14.929(5)

Ethylmet-

hyl ketone

12x2x1 010

Br1 P21/C N2-H2 a=10.064(5)b=11.218(5)c=14.862(5)

Ethylmet-

hyl ketone

20x10x3 001

Organic compounds of phenolic conventional locked and non-locked polyene type

molecules are synthesized. The different acceptor and donar benzaldehyde such as 3-

methyl-4-methoxy, 3-ethoxy-4-hydroxy, 4-chloro, 4-bromo, 4-ethoxy benzaldehyde

were substituted. The Synthesized molecules structures were confirmed by single

crystal XRD and packing structures are discussed. The synthesized compounds has

been attempted to grow the crystal in various solvent. The morphology of grown

83

crystals was solved using Winxmorph software. The comparative data of

malononitrile molecule and its derivative are given in Table.2.8.

For high performance of all optical switching applications, the molecule must have

a short lifetime, low absorption loss and large third order coefficient. The design of

synthesis of a malononitrile dye molecule halogen substitution. The presence of

chloro and bromo group in aromatic end allows the molecular orbitals to extend like

polyene chain. It is effectively increases the conjugation length and decreases of

optical band gap. It helps to increases the third order coefficient.

chapter-2 synthesis, structure, crystal growth, and...

Documents