Crystallography Reports, Vol. 45, No. 1, 2000, pp. 98–102. From Kristallografiya, Vol. 45, No. 1, 2000, pp. 104–107.Original English Text Copyright © 2000 by Rajnikant, V. Gupta, R. Gupta, Kumar, Bameza

œ

, Sharma, Varghese.

STRUCTURES OF ORGANIC COMPOUNDS

Structure of a Liquid Crystal of 4-Cyano-4'-n-Octyloxybiphenyl1 Rajnikant*,2 V. K. Gupta*, R. Gupta*, A. Kumar*, R. K. Bamezaœ**,

N. K. Sharma**, and B. Varghese**** X-ray Crystallography Laboratory, Department of Physics, University of Jammu, Jammu Tawi, 180006 India

** Chemistry Department, University of Jammu, Jammu Tawi, 180006 India*** Regional Sophisticated Instrumentation Centre, Indian Institute of Technology, Chennai, 600036 India

Received June 8, 1998; in final form, October 15, 1998

Abstract—The structure of a liquid crystal of 4-cyano-4'-n-octyloxybiphenyl (C21H25NO) is determined byX-ray diffraction analysis. The compound crystallizes in the triclinic crystal system with unit cell parametersa = 7.322(1) Å, b = 12.693(3) Å, c = 20.393(2) Å, α = 92.45(1)°, β = 99.96(1)°, γ = 99.35(2)°, and space groupP . The structure is solved by the direct method and refined to R = 0.057. Two independent molecules arelocated in the asymmetric unit. No short intermolecular contacts are observed in the crystal packing. © 2000MAIK “Nauka/Interperiodica”.

1

The biphenyl and its derivatives have been studiedextensively in the past because of the difference foundin the inter-ring torsion angles ψ in the solid state [1–3]and in the gas phase [4, 5]. This has entailed extendedstudies of the molecular geometry, crystal packing, andthermal motion effects [6–9].

Recent papers is have reported the recrystallizationand crystal structure analysis of a series of 2,3,4-substi-tuted biphenyl systems [10–13]. The range of crystalli-zation conditions reported so far indicate that the lin-early chained biphenyl systems (liquid crystallinematerials) would be good objects for a systematic anal-ysis of growth conditions and morphology modifiersfor the preparation of organic crystals from organic sol-vents. In this respect, we have already reported crystal-lization and structure analysis of two liquid crystallinematerials [14, 15]. The present work is a continuationof systematic investigations on the crystallization andpreparation of single crystals suitable for X-ray diffrac-tion analysis. Crystals of 4-cyano-4'-n-octyloxybiphe-nyl have been grown from acetic acid. It is known thatthis material undergoes transformation to the smectic Aphase at 54.5°C, which finally becomes an isotropicliquid at 80.0°C [16].

EXPERIMENTAL

The growth of X-ray diffraction quality crystals ofthe title compound was carried out with a variety ofknown organic solvents. However, success wasachieved with acetic acid by employing the solvent losstechnique. The X-ray diffraction intensity data for awhite needle-shaped crystal were collected from a sin-gle crystal of approximate dimensions 0.40 × 0.25 ×

1 This article was submitted by the authors in English.2 Author for correspondence.

1063-7745/00/4501- $20.00 © 20098

Table 1. Crystal data and other experimental details

Crystal description White transparent needleChemical formula C21H25NOMolecular weight 307.435Cell parameters a = 7.322(1) Å,

b = 12.693(3) Åc = 20.393(2) Å, α = 92.45(1)°β = 99.96(1)°, γ = 99.35(2)°

Unit cell volume 1837.02Å3

Crystal system TriclinicSpace group PDensity (calculated) 1.112 g/cm3

No. of molecules per unit cell 4Wavelength 1.5418 ÅLinear absorption coefficient 5.185 cm–1

F(000) 664Crystal size 0.40 × 0.25 × 0.15 mmθ range for entire data collec-tion

0 ≤ θ ≤ 68°

No. of measured reflections 6757No. of unique reflections 5409No. of observed reflections 3693Software for structure solu-tion

Direct methods (SHELXS86)

Software for Refinement SHELXL93No. of parameters refined 416Final R-factor 0.057wR(F2) 0.1949Final residual electron den-sity

0.17 < ∆ρ < –0.19 eÅ–3

(∆/σ)max in the final cycle for non-hydrogen atoms

–0.343 for C18

1

000 MAIK “Nauka/Interperiodica”

STRUCTURE OF A LIQUID CRYSTAL 99

Table 2. Atomic coordinates and equivalent isotropic temperature factors (Å2) with e.s.d.’s in parentheses, for the non-hy-drogen atoms

AtomMolecule 1

AtomMolecule 2

x y z x y z

C(1) 0.0408(3) 0.8028(2) 0.4480(1) 0.0549(9) C(1') 0.5130(3) 0.5488(2) 0.7435(1) 0.0579(9)C(2) 0.1835(3) 0.8912(2) 0.4500(1) 0.0623(10) C(2') 0.4980(4) 0.6284(2) 0.7903(1) 0.0671(10)C(3) 0.3137(3) 0.8963(2) 0.4077(1) 0.0660(10) C(3') 0.3612(4) 0.6144(2) 0.8288(1) 0.0690(11)C(4) 0.3034(3) 0.8100(2) 0.3619(1) 0.0603(9) C(4') 0.2333(4) 0.5207(2) 0.8226(1) 0.0629(10)C(5) 0.1620(3) 0.7219(2) 0.3588(1) 0.0600(9) C(5') 0.2465(4) 0.4391(2) 0.7770(1) 0.0673(10)C(6) 0.0343(3) 0.7183(2) 0.4013(1) 0.0629(10) C(6') 0.3837(4) 0.4545(2) 0.7378(1) 0.0647(10)C(7) –0.0936(3) 0.7993(2) 0.4943(1) 0.0560(9) C(7') 0.6583(3) 0.5627(2) 0.7010(1) 0.0553(9)C(8) –0.0377(3) 0.8409(2) 0.5597(1) 0.0631(9) C(8') 0.6182(3) 0.5230(2) 0.6349(1) 0.0589(9)C(9) –0.1639(3) 0.8400(2) 0.6026(1) 0.0644(10) C(9') 0.7544(3) 0.5303(2) 0.5956(1) 0.0598(10)C(10) –0.3518(3) 0.7963(2) 0.5802(1) 0.0589(10) C(10') 0.9366(3) 0.5804(2) 0.6224(1) 0.0554(10)C(11) –0.4104(3) 0.7518(2) 0.5158(1) 0.0633(9) C(11') 0.9790(3) 0.6242(2) 0.6875(1) 0.0680(10)C(12) –0.2826(3) 0.7530(2) 0.4734(1) 0.0619(10) C(12') 0.8424(3) 0.6155(2) 0.7268(1) 0.0665(10)O(13) 0.4267(3) 0.8035(1) 0.3192(1) 0.0718(7) O(13') 0.1028(3) 0.5145(2) 0.8628(1) 0.0767(8)C(14) 0.5787(4) 0.8904(2) 0.3211(1) 0.0661(10) C(14') –0.0438(4) 0.4238(2) 0.8538(1) 0.0694(11)C(15) 0.6937(4) 0.8600(2) 0.2711(1) 0.0706(10) C(15') –0.1735(4) 0.4421(2) 0.9010(1) 0.0729(12)C(16) 0.8627(4) 0.9460(2) 0.2690(1) 0.0706(11) C(16') –0.3307(4) 0.3484(2) 0.8996(1) 0.0715(11)C(17) 0.9750(4) 0.9195(2) 0.2168(2) 0.0763(12) C(17') –0.4582(4) 0.3669(2) 0.9491(1) 0.0713(11)C(18) 1.1394(4) 1.0069(2) 0.2125(1) 0.0729(11) C(18') –0.6136(4) 0.2745(3) 0.9505(2) 0.0813(13)C(19) 1.2520(4) 0.9808(2) 0.1598(2) 0.0804(12) C(19') –0.7400(4) 0.2917(3) 1.0000(2) 0.0836(12)C(20) 1.4141(4) 1.0651(3) 0.1544(2) 0.0938(14) C(20') –0.8991(5) 0.2014(3) 0.9999(2) 0.1129(18)C(21) 1.5245(6) 1.0379(3) 0.1018(2) 0.1288(19) C(21') –1.0204(5) 0.2181(4) 1.0510(2) 0.1452(24)C(22) –0.4839(4) 0.8024(2) 0.6251(1) 0.0670(11) C(22') 1.0822(4) 0.5854(2) 0.5827(1) 0.0657(10)N(23) –0.5866(3) 0.8117(2) 0.6604(1) 0.0902(12) N(23') 1.1964(3) 0.5867(2) 0.5510(1) 0.0827(11)

* Ueq = (1/3) aiaj.

Ueq* Ueq

*

Uijai*a j

*j

∑i∑

0.15 mm on an Enraf–Nonius CAD4 diffractometer(CuKα radiation). The accurate unit-cell dimensionsand the orientation matrix were obtained by the leastsquares fit to the setting angles of 25 reflections. Theω/2θ scan was employed. A total number of 6757reflections were measured in the θ range 0°–68° (–8 ≤h ≤ 8, –15 ≤ k ≤ 14, 0 ≤ l ≤ 20), of which only 3693 weretreated as observed with Fo > 4σ(Fo)). Two strongreflections monitored periodically showed that thecrystal was stable to X-rays. The data were correctedfor Lorentz and polarization effects. The crystal struc-ture was solved by the direct method using theSHELXS86 software package [17]. Two molecules inthe asymmetric unit were found. The isotropic refine-ment of the structure by the least squares methods usingthe SHELXL93 software package [18] was followed bythe anisotropic refinement of all the non-hydrogenatoms. The hydrogen atoms were placed at geometri-cally calculated positions and refined in the structure-factor calculations as riding atoms with fixed isotropic

CRYSTALLOGRAPHY REPORTS Vol. 45 No. 1 2000

temperature factors. The final refinement cycle yieldedthe residual indices R = 0.057 and wR(F2) = 0.1949.The residual electron density in the final differenceFourier map ranges from 0.17 to –0.19 e Å–3. The max-imum ratio (shift / e.s.d) is –0.343 for the C(18) atom.Atomic scattering factors were taken from the Interna-tional Tables for Crystallography (1992, Vol. C, Tables4.2.6.8, 6.1.1.4). Some calculations, for example, thecalculation of the least-squares planes, were performedwith the PC version of the PARST program [19].

RESULTS AND DISCUSSION

Crystal data is presented in Table 1. The atomiccoordinates and equivalent isotropic temperature fac-tors for two independent molecules are given inTable 2. Some selected torsion angles are listed inTable 5. A general view of the molecule with the atomicnumbering scheme is shown in Fig. 1 (ZORTEP) [20].

100

RAJNIKANT

et al

.

Molecule 1

Molecule 2

N(23)

C(22)

C(10)C(9)

C(8)

C(2)

C(1)

C(6)

C(7)C(12)

C(11)C(4)

C(5)

C(14)

C(15)

C(16) C(18)O(13)

C(17) C(19)

C(20)

C(21)

C(19')

C(21')C(20')

C(17')

C(18')C(15') C(14')

C(16')C(4')

C(5') C(6')C(1') C(8') C(9') C(10')

C(22') N(23')

C(11')C(12')

C(7')C(2')

C(3)

C(3')O(13')

Fig. 1. A general view of the molecules and the atomic numbering scheme.

The crystal structure of 4-cyano-4'-n-octyloxybi-phenyl contains two crystallographically independentmolecules (termed as molecule 1 and 2) in the asym-metric unit. The average bond distances for the phenyl

Table 3. Bond distances (Å) with e.s.d.'s in parentheses

Molecule 1 Molecule 2

C1–C2 1.397(3) C1'–C2' 1.391(3)

C1–C6 1.393(3) C1'–C6' 1.397(3)

C1–C7 1.474(3) C1'–C7' 1.478(3)

C2–C3 1.388(3) C2'–C3' 1.370(4)

C3–C4 1.393(3) C3'–C4' 1.375(3)

C4–C5 1.386(3) C4'–C5' 1.389(3)

C4–O13 1.367(3) C4'–O13' 1.358(4)

C5–C6 1.377(3) C5'–C6' 1.383(4)

C7–C8 1.381(3) C7'–C8' 1.383(3)

C7–C12 1.397(3) C7'–C12' 1.405(3)

C8–C9 1.377(3) C8'–C9' 1.376(3)

C9–C10 1.386(3) C9'–C10' 1.387(3)

C10–C11 1.375(3) C10'–C11' 1.381(3)

C10–C22 1.451(5) C10'–C22' 1.441(4)

C11–C12 1.378(3) C11'–C12' 1.380(3)

O13–C14 1.428(3) O13'–C14' 1.422(3)

C14–C15 1.506(4) C14'–C15' 1.500(4)

C15–C16 1.519(4) C15'–C16' 1.510(4)

C16–C17 1.511(5) C16'–C17' 1.526(4)

C17–C18 1.516(4) C17'–C18' 1.501(4)

C18–C19 1.520(5) C18'–C19' 1.514(5)

C19–C20 1.486(4) C19'–C20' 1.494(5)

C20–C21 1.509(6) C20'–C21' 1.510(6)

C22–N23 1.143(4) C22'–N23' 1.140(4)

C

rings in both molecules are in good agreement withthose of linear-chained biphenyls such as 4,4'-bis(n-propylamino)biphenyl [14], 4-cyano-4'-n-dodecylbi-phenyl [15], 4-cyano-4'-n-undecylbiphenyl [21], and 4-

Table 4. Bond angles (°) with e.s.d.'s in parentheses

Molecule 1 Molecule 2

C6–C1–C7 122.0(2) C6'–C1'–C7' 120.7(2)C2–C1–C7 121.0(2) C2'–C1'–C7' 122.3(2)C2–C1–C6 116.9(2) C2'–C1'–C6' 116.9(2)C1–C2–C3 122.4(2) C1'–C2'–C3' 121.5(2)C2–C3–C4 119.0(2) C2'–C3'–C4' 121.1(2)C3–C4–O13 124.8(2) C3'–C4'–O13' 116.8(2)C3–C4–C5 119.4(2) C3'–C4'–C5' 118.7(2)C5–C4–O13 115.8(2) C5'–C4'–O13' 124.5(2)C4–C5–C6 120.6(2) C4'–C5'–C6' 119.7(2)C1–C6–C5 121.6(2) C1'–C6'–C5' 122.0(2)C1–C7–C12 120.9(2) C1'–C7'–C12' 120.9(2)C1–C7–C8 121.4(2) C1'–C7'–C8' 121.1(2)C8–C7–C12 117.6(2) C8'–C7'–C12' 117.9(2)C7–C8–C9 121.5(2) C7'–C8'–C9' 121.8(2)C8–C9–C10 119.8(2) C8'–C9'–C10' 119.5(2)C9–C10–C22 118.6(2) C9'–C10'–C22' 120.2(2)C9–C10–C11 119.9(2) C9'–C10'–C11' 119.9(2)C11–C10–C22 121.4(2) C11'–C10'–C22' 120.0(2)C10–C11–C12 119.8(2) C10'–C11'–C12' 120.3(2)C7–C12–C11 121.3(2) C7'–C12'–C11' 120.5(2)C4–O13–C14 118.6(2) C4'–O13'–C14' 118.9(2)O13–C14–C15 107.0(2) O13'–C14'–C15' 107.3(2)C14–C15–C16 112.2(2) C14'–C15'–C16' 113.0(2)C15–C16–C17 113.1(2) C15'–C16'–C17' 112.4(2)C16–C17–C18 113.4(2) C16'–C17'–C18' 114.0(2)C17–C18–C19 113.6(2) C17'–C18'–C19' 114.4(3)C18–C19–C20 114.8(3) C18'–C19'–C20' 114.8(3)C19–C20–C21 114.1(3) C19'–C20'–C21' 114.2(3)

RYSTALLOGRAPHY REPORTS Vol. 45 No. 1 2000

CRYSTAL

STRUCTURE OF A LIQUID CRYSTAL 101

a

b

c

Fig. 2. Molecular packing viewed along the a-axis.

cyano-4'-n-decylbiphenyl [22]. The four internal ringbond angles in molecule 1 at the atoms C(1)[116.9(2)°], C(4) [119.4(2)°], C(7) [117.6(2)°], andC(10) [118.9(3)°] and in molecule 2 at the atoms C(1')[116.9(2)°], C(4') [118.7(2)°], C(7') [117.9(2)°], and

LOGRAPHY REPORTS Vol. 45 No. 1 2000

C(10') [119.9(2)°] are slightly smaller than the idealangles of 120°. However, more or less, these values arein good agreement with those found in some analogousstructures [14, 15, 21, 22]. The length of the bond join-ing two phenyl rings in both molecules [C(1)–C(7),

Table 5. Torsion angles τ (deg) with the e.s.d.’s in parentheses

Molecule 1 Molecule 2

atoms τ atoms τ

C(6)–C(1)–C(7)–C(8) 141.5(2) C(6')–C(1')–C(7')–C(8') 38.0(3)

C(2)–C(1)–C(7)–C(8) –37.3(3) C(2')–C(1')–C(7')–C(8') –141.6(2)

C(6)–C(1)–C(7)–C(12) –38.2(3) C(6')–C(1')–C(7')–C(12') –141.1(2)

C(2)–C(1)–C(7)–C(12) 142.9(2) C(2')–C(1')–C(7')–C(12') 39.2(3)

C(9)–C(10)–C(22)–N(23) 65.2(6) C(9')–C(10')–C(22')–N(23') –54.6(9)

1.474(3) Å and C(1')–C(7'), 1.478(3) Å] is quite closeto the standard length of a single bond between the trig-onally linked carbon atoms [23]. A respective compar-ison of bond distances and angles for both asymmetricmolecules reveals a high degree of similarity (Tables 3,4). The dihedral angles between the phenyl rings inmolecules 1 and 2 are 37.79(7)° and 38.67(8)°, respec-tively. This shows that the two molecules in the asym-metric unit have identical conformations.

The packing of the molecules in the crystal is shownin Fig. 2 [24]. The molecule is slightly bent at the O(13)atom. This phenomenon generally takes place in thecase of liquid crystalline materials having carbon oroxygen at the position joining the biphenyl moiety. Themolecular pairs of the asymmetric unit are packed inlayers, which is a requirement for the material to be asmectogen. The molecules appear to be extendingalong the bc plane (in the approximate direction [401]).

The cohesion of the structure is due to the van derWaals interactions.

ACKNOWLEDGMENTS

One of the authors (Rajnikant) acknowledges thesupport of the Scientific & Industrial ResearchCouncil of the Government of India, projectno. 3(796)/96/EMR-II.

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