J. MATER. CHEM., 1991, 1(4), 667-672 Crystal Structures of Chiral Smectogenic 4'-Octylbiphenyl-4-yI p[(S)-I-Methylheptyloxy]benzoate and poctylphenyl 4'-[(S)-I -Methylheptyloxy]biphenyl-4-carboxylate Kayako Hori" and Yuji Ohash?' a Department of Chemistry, Ochanomizu University, Otsuka, Bunkyo-ku, Tokyo 1 12, Japan Department of Chemistry, Tokyo Institute of Technology, Gokayama, Meguro-ku, Tokyo 152, Japan Single-crystal X-ray analyses have been carried out for 4'-octylbiphenyl-4-yI p[(S)-1-methylheptyloxy]benzoate (l),which has a phase sequence of cryst.-sb-chol.-iso., and poctylphenyl 4'-[(S)-l-methylheptyloxy]biphenyl-4-carboxylate (2), which has a phase sequence of cryst.-s&+-chol.-iso. Each crystal has a smectic-like layer structure, in which the molecular tilt angle is large (65') in 1, whereas it is small (10') in 2.These features, which are interpreted to result from the molecular geometry, i.e. the length of the moiety sandwiched by polar groups, are closely related to the structures of the liquid-crystalline phases. Keywords: Crystal structure; Smectic C phase; Liquid crystal; Intermolecular interaction; X-ray diffraction Good correlations have been found between the crystal struc- tures and liquid-crystalline behaviours for three series of chiral smectogenic biphenyl esters with a 2-methylbutyl group.'-4 In order to confirm the relationship between crystal struc- ture and liquid-crystalline phase sequence we extended the crystal-structure determination to biphenyl esters with a 1 -methylheptyloxy group, which show various liquid-crys- talline phase sequences according to the isomeric change of the molecular structure^.^ This paper describes the crystal structures of two isomers, 4'-octylbiphenyl-4-y1 p-[(S)-l- methylheptyloxy] benzoate, 1 and p-octylphenyl 4'-[(S)-1-methylheptyloxy]biphenyl-4-car-boxylate. C6H13cH(cH3)0~2~c8H17 2 The former has a phase sequence of cryst.50.0 "C sE 62.5 "C chol. 87.2 "C isotropic liquid, whereas the latter has the phase sequence of cryst. 55.0 "C sz 71.5 "C sA 83.6 "C chol. 92.3 "C isotropic liquid with a metastable sB (39.5 "C sz). Experimental The compounds were supplied by Drs. T. Inukai and K. Furukawa. Single crystals appropriate to the structure deter- mination were grown from an ether-ethanol solution for 1 and were found in the specimen as supplied for 2.Powder diffraction patterns for smectics were measured on a Rigaku Geigerflex RAD-RA diffractometer. No procedures for sample alignments were applied. Temperature control was within fO.l K. Crystal Data. 4-Octylbiphenyl-4-yl p-[(S)-1-methylheptyloxy] benzoate (l),C3&&, M, =514.72, monoclinic, a =44.09( 1) A, b =5.494(3) A, c =39.52(2) A, /?=139.02( l)', U=6278(4)A3 (by least-squares fit for 15 reflections within the range 32 <28/' <59, i=1.54184 A), space group C2, Z =8, pc= 1.090 g crnp3. Transparent long plate-like crystal. Crystal dimensions 0.4 mm x 0.3 mm x 0.05 mm, p(Cu-Ka) = 4.44 cm-'. p-Octylphenyl 4'-[(S)-l-methylheptyloxy]bi-phenyl-4-carboxylate (2), C35H4603,M, =5 14.72, monoclinic, a=33.818(3) A, b=8.2140(9) A, c=5.7128(5) A, /?=98.733(9)', U= 1568.5(3)A3 (by least-squares fit for 16 reflections within the range 33 <28/' <56, A = 1.54184A), space group P2', Z= 2, pc=1.090 g crnp3.Transparent plate-like crystal. Crystal dimensions 0.45 mm x 0.35 mm x 0.05 mm, p(Cu-Ka) = 4.54 cm-'. Data Collection and Processing. Rigaku AFC-4 diffractometer, 01-28 scan mode with 01 scan width =(1.O +0.1 Stan@', scan speed 4'(28) for 1 and 8'(28) for 2, graphite-monochromated Cu-Ka radiation; 5377 (for 1) and 2708 (for 2) independent reflections measured (3 <28/' <125, & h, +k, +I), giving 2252 with lFol >40( IFo[)(for 1) and 1956 with IFo[>34 IFo[)(for 2).A higher criterion was applied to 1, because intensities of 1 were relatively small owing to the low melting point. There was no significant intensity variation. Lorentz polarization but no absorption correction. Structure Analysis and Refinement. A direct method using the programs SHELX8@ for 1 and MULTAN787 for 2 was employed. Full-matrix least-squares (in two blocks) using SHELX76.* For 1, geometries were loosely constrained to avoid divergence due to the pseudosymmetry. In the course of the refinement of 1, a terminal atom of an alkyl chain, C(38B), was disordered because of its considerably large temperature factors. All the non-hydrogen atoms except for the disordered atom were refined anisotropically. Hydrogen atoms found in the difference maps and derived geometrically (C-H, 1.0 A) were refined isotropically for 2, while only eight hydrogen atoms found in the difference map (D-map) were included in the refinement for 1 owing to the limited number of reflections. The quantity minimized was Xw(IFol-IFc1)2, where w =[C(F~)~+0.004(Fo12]-'. Atomic scattering factors were taken from the International Tables for X-ray Crystallography.' Max.A/a and max. Ap in the final D-map were 0.48 and 0.26 e A-3 for 1 and 0.47 and 0.22 e A-3 for 2. Final R (and R,) is 0.109 (0.1 17) for 1 and 0.089 (0.103) for 2. The large R value of 1 was probably due to the low crystallinity. Computations were carried out on a HITAC M-680H computer at the Computer Center of the University of Tokyo and an IBM 4381-R24 computer at the J.MATER. CHEM., 1991, VOL. 1 Information Processing Center of Ochanomizu University. Normal alkyl chains and long chains of the chiral groups Final atomic coordinates are shown in Tables 1 and 2.t have relatively close contacts between layers, as shown in Fig. 3. Results and Discussion Crystal Structure of 1 Crystal Structure of 2 There are two crystallographically independent molecules, A The ORTEP drawing of 2 is shown in Fig. 1. All the geometri- and B, in an asymmetric unit. ORTEP drawings" of the two cal parameters are compatible with those of other mesogens. molecules with the numbering scheme are shown in Fig. 1. The biphenyl moiety is twisted (21.4'). The normal alkyl chain All the bond lengths and angles are compatible with those has an all-trans conformation, whereas the chain of the chiral found in other me~ogens.'-~ All the phenyl rings are planar group is twisted in the middle, as shown in Table 3.within experimental error. Both molecules have nearly planar Fig.4 shows the crystal structure viewed along the b and biphenyl moieties: dihedral angles are 4.2 and 2.1' for the c axes. Molecules are related by a two-fold screw axis in a molecules A and B, respectively. Alkyl chains have approxi- smectic-like layer structure. The twisted chain of the chiral mately extended conformations, as shown in Table 3. group participates in the lateral overlap of the molecules, Fig. 2 shows the crystal structure. Molecular long axes are leading to a large overlap and hence a small tilt of the largely tilted (65 ') in a smectic-like layer structure.The molecular long axis. The tilt angle is estimated to be ca. lo', although it is difficult to designate a molecular long axis independent molecules, A and B' or A' and B, where A and B' are symmetry-related molecules of A and B, are related by rigorously owing to the bent shape of the molecule. The ester an approximate two-fold screw axis. The ester and ether and ether groups in neighbouring molecules lie in close groups are closely arranged at two positions between the proximity. The arrangement provides a large lateral overlap of molecules, since the moiety sandwiched by the polar groups neighbouring molecules, A and B' or A' and B.is long. t Supplementary data available from the Cambridge Crystallo- On the other hand, the normal chains are found between graphic Data Centre: see Information for Authors, J. Muter. Chem., layers with an all-trans conformation. However, the two zigzag 1991, Issue 1. chains facing each other are out of phase, resulting in a rather Table 1 Final atomic coordinates with their estimated standard deviations (x lo4) for 4-octylbiphenyl-4-yl p-[(S)-1-methylheptyloxy]benzoate (1) atom X Y 2 atom X Y 7 Beq/A20 0 (14 0 PA) 0 (3'4) c (14 c (24 c (34 c (44 c (54 c (64 c (74 c (84 c (9A)C( 1 OA) C(11A) C( 12A) C( 13A) C( 14A) C( 15A) C( 16A) C( 17A) C( 18A) C( 19A) C(21A) C(22A) C(23A) C(24A) C(25A) C(26A) C(27A) C(28A) C(3IA) C(32A) C(33A) C(34A) C( 3 5A) C(36A) C(37A)C(38A) 0 (1B) 2968 (4) 2561 (4) 3529 (3) 1656 (5) 1940 (5) 2113 (5) 1964 (5) 1681 (5) 1515 (6) 2115 (5) 2411 (5) 2560 (5) 2403 (5) 2066 (5) 1936 (5) 2861 (5) 3059 (5) 2906 (4) 3081 (5) 3366 (4) 3319 (4) 3877 (3) 3852 (5) 4171 (5) 4196 (4) 4478 (6) 4445 (9)4687( 12) 4340 (5) 1445 (6) 1317 (6) 1075 (5) 996 (6) 787 (6) 656 (7) 511 (7) 383 (7) 2967 (4) 3493 (4) -2093 (21) 1316 (19) 1213 (20) 1459 (29) 3289 (26) 3112 (26) 1314 (27) -500 (29) -412 (29) 1226 3043 (26) 2970 (24) 1077 (31) -545 (32) -584 (26) -405 (25) 28 (26) 2037 (22) 2473 (25) 690 (24) -1424 (25) -1781 (31) -166 (28) -803 (36) -1024 (58) -105 (69) 575 (38) 499 (38) 2249 (70) 268 (42) 1354 (28) 3909 (33) 3683 (32) 6186 (32) 6005 (35) 8480 (33) 8211 (35) 10647 (36) -1636 (22) 7069 (4) 6787 (4) 9013 (3) 3974 (4) 4346 (5) 4818 (4) 4915 (5) 4545 (5) 4074 (5) 5417 (4) 5777 (5) 6241 (4) 6314 (5) 5922 (5) 5476 (5) 7157 (6) 7666 (5) 7722 (4) 8193 (4) 8569 (4) 8511 (5) 8039 (4) 9482 (4) 9832 (5) 10333 (5) 10702 (4) 11179 (6) 11516(10) 11792(13) 9692 (6) 3443 (5) 3208 (5) 2654 (5) 2429 (5) 1896 (5) 1629 (6) 1128 (6) 877 (6) 2012 (4) 8.4 8.0 6.9 7.8 8.I 9.1 7.1 8.3 9.2 6.2 7.9 8.3 7.8 8.4 8.3 6.3 6.4 5.2 6.3 6.2 6.5 7.8 5.8 9.7 9.3 9.0 18.4 16.9 23.3 10.0 7.7 9.7 8.5 8.3 9.8 10.0 10.5 10.7 8.6 0 (2B)0 (3B) c (1B) c (2B) c (3B) c (4B) c (5B) c (6B) c (7B) c (8B) c (9B)C(1OB) C(l1B) C( I2B) C( 13B) C( 14B) C( 15B) C( 16B) C( 17B) C( 18B) C( 19B) C(21B) C(22B) C(23B) C(24B) C(25B) C(26B) C(27B) C(28B) C(31B) C(32B) C(33B) C(34B) C(35B) C(36B) C(37B) C(38B) C(38B) 2584 (3) 3526 (4) 1638 (6) 1931 (6) 1949 (4) 1687 (6) 1512 (6) 2107 (4) 2433 (4) 2555 (5) 2454 (5) 2144 (6) 1981 (5) 2880 (5) 3027 (4) 2917 (5) 3077 (4) 3370 (4) 3317 (5) 3871 (6) 3876 (5) 4219 (6) 4204 (7) 4530 (7) 4513 (7) 4768 (6) 4346 (5) 1446 (7) 1228 (6) 1085 (8) 908(I 1) 758( 12) 728(10) 533(13) 459(22) 222(23) 2100 (4) 3479 (5) 1702 (22) 895 (22) 2603 (33) 4402 (33) 4263 (26) 2401 (25) 504 (26) 662 (32) 2139 (19) 3758 (26) 3799 (26) 1746 (23) 29 (33) 284 (25) 130 (25) 2212 (24) 2290 (26) 594 (21) -30 (23) -1388 (22) -1658 (24) -723 (36) -52 (32) -1587 (33) -857 (48) -2556 (51) -1615 (49) -3402 (52) -260 (56) 2586 (42) 5022 (44) 4736 (50) 7196 (60) 6669 (61) 8652 (66) 8198 (79) 10190 (93) 101OO( 130) 1786 (4) 4009 (4) -200 (5) -1043 (5) -669 (6) -115 (3) -467 (5) -941 (5) 388 (4) 788 (4) 1233 (5) 1334 (4) 964 (5) 499 (5) 2135 (7) 2608 (5) 2696 (5) 3162 (5) 3556 (5) 3446 (5) 2982 (5) 4436 (6) 4818 (5) 5315 (5) 5680 (8) 6174 (7) 6518 (7) 6952 (7) 4675 (5) -1579 (6) -1842 (5) -2329 (6) -258q10) -3066( 12) -3345411) -3868( 12) -4193(23) -4201(26) 7.6 9.1 9.6 9.7 9.1 7.4 10.1 10.7 4.5 6.4 7.2 5.8 9.3 7.0 7.2 5.5 6.5 7.0 6.0 7.6 6.7 12.1 8.1 9.2 12.7 12.0 12.5 13.1 12.3 11.9 12.4 12.3 19.7 19.1 17.1 22.1 15.5(18)b 19.0(2qb a Be,=(4/3) CBij(ai*uj).'Isotropic temperature factor; occupation factors were fixed to be 0.5 for C(38B) and C(38B').ij J. MATER. CHEM., 1991, VOL. 1 669 Table 2 Final atomic coordinates with their estimated standard devi- ations (x lo4) for p-octylphenyl 4-[(S)-l-methylheptyloxy]biphenyl-4-carboxylate (2) Table 3 Torsion angles(/") of alkyl chains 1 mol.A mol. B 2 6873(2) 6902(2)3781(2) 4 186( 2) 4422(2) 4825(2) 50 12(2) 4762(2)4358(2) 5451(2) 5705(2) 6 1 05(2) 6284(2) 6035(2)5629(3) 67 12(2) 7308(2)7474(3)7858(3) 81 1q3) 795 1( 3) 7554(2) 3 564(2) 3131(3) 2872(3) 2428(3)2284( 3) 1826(3) 1684(5)3646(3) 8555( 3) 8778(3) 92 1 O( 3) 9455(3)9873(3)101 15(4) 10533(5) 10782( 4) a As for Table 1. 621 l(10) 7648 (7) 6158 (7) 6300( 10) 7465(10) 7494 (9) 6393 (9) 5257 (9) 5232(10) 6437( 10) 7 174( 10) 7241( 10) 6628 (9) 5860( 10) 5766(10) 6749 799q 10) 8816(14) 924q 1 5) 8835( 13) 8043( 13) 7587( 13) 7168(10) 7024( 15) 8193( 19) 7980( 19) 8486(15) 8496(18)9 1 3 7( 34) 6724( 12) 9388(20) 8834(16) 9445( 18) 9028(21)9565(27) 8999( 24) 9562(32)8933(36) 38 d 36 38' 3 27 75 12( 1 1) 4220 (8)333 (8)987( 1 1) 85(1 1) 850(11)2547( 10) 3443(10)2687( 1 1) 3287(10) 1910(10) 2621(11) 4803(1 1) 62 16( 10)5463(1 1) 5707( 13) 4764( 12) 6761(14) 7 124( 16) 5567( 16) 3498( 15) 3169(13) -13 14( 12) -1002(15) -2425( 18) -2279(22)-11(18) -266(23)1 9 52( 27) -3863( 13) 6OOO( 16) 8322(15)8597(20) 10943(20)I1255(20) 13511(20) 13955(27)16 177(29) 9.6 7.0 6.6 5.2 6.2 5.8 5.0 5.6 5.7 5.1 5.5 6.2 5.4 6.I 6.3 6.5 6.0 8.2 8.8 8.2 8.3 7.6 6.4 8.8 10.8 12.9 10.7 12.7 19.3 7.9 11.6 9.8 11.5 12.3 14.7 14.2 18.1 21.6 o(3)- C(2 1)-C(22)- C( 23) -176 -179 -172 C(21)-C(22)-c(23)-C( 24) -167 179 -175 C(22)-c(23)- C( 24)- C( 25) -175 -176 -73 C( 23) -C( 24)- C( 25)- C( 26) 169 -177 170 C(24)-C(25)-C(26)-C( 27) 71 -173 175 c* -C(3 1)-C( 32)-C( 33) 176 -178 180 C( 3 1)-C( 32) -C( 3 3) -C( 34) 173 175 -177 C( 32)- C( 33) -C( 34) -C(35) 176 178 -179 C( 3 3)-C( 34) -C( 3 5)-C( 36) -174 I56 175 C(34)-C( 3 5)-C( 36) -C( 37) -172 174 178 C( 35)- C( 36) -C( 37)- C( 38) 180 -175, -134 177 C* denotes C( 1) for 1 and C( 17) for 2.long interchain distance (~4.4 A), as shown in Fig. 5. There-fore, it is concluded that the intermolecular interaction within a layer is more dominant in 2 than in 1.Relationship between Crystal Structure and Liquid-crystalline Phase Sequence It has been generally observed that the tilt angle is almost constant (ca.45 ") in sc followed by nematic, whereas it decreases with increasing temperature from ca. 25' at the lower transition temperature to zero or near zero at T, (sc-sA transition) in sc followed by sA.l1-I3 It was observed by means of an optical method5 that the tilt angle of 1 is 42" at T- T,= -30 "C (in the supercooled range of s;), whereas that of 2 changes from 30' at T -T,= -30 "C (in the superco- oled range of s/) to 19' at T-T,= 5 "C, and tends to zero at T =T, (s?-sA transition). These values are consistent with the general aspect of the tilt angle in sc mentioned above.In order to obtain further structural information in the 7 0 28 19 18 Fig. 1 ORTEP drawing with 50% probability thermal ellipsoids of the molecules A (upper), B (middle) of 1 and the molecules of 2 (lower). Disordered atoms are denoted by spheres with an arbitrary diameter. The molecule B is numbered in the same way as A J. MATER. CHEM., 1991, VOL. 1 Fig. 2 The crystal structure of 1 viewed along the b axis. Layer plane, parallel to (100) plane, is denoted by a broken line. Closed circles denote oxygen atoms. Disordered atoms are denoted by shadowed circles. Short 0-0 distances (/A) are as follows: O(2A) (x, y, 2)-O(1A) (x, y+l, Z) 3.82; O(2B) (x, y, z)-O(lB) (x, y+l, Z) 3.84; O(2A) (x, y, z)-O(3B) (1/2-~,1/2+y,l-z) 4.05,O(2A) (x,y,z)--0(3B) (1/2-~, -1/2+y, 1-2) 4.36; O(3A) (x, y, ~)-0(2B) (1/2-~,1/2+y,l-z) 4.44; O(3A) (x, y, ~)-0(2B) (1/2-~,-1/2+~,1 -z) 4.10 A A II I II I 4.23; (4.25 ,'4.30 I I / I I I I1-26 B 22 24 I' I B B Fig.3 Interchain distances (~4.4A) in 1. The values in parentheses denote those between adjacent cells and the values with a prime denote those of C(38B'). a=3.98, (3.62), (4.36) A;b=4.17', (4.15), (3.91') 8, smectics, interlayer distances (d)were measured in the whole temperature range of the smectics by means of powder X-ray diffraction. Fig. 6 shows the temperature dependence of d values in sz of 1 and in sA, sz, and metastable sB of 2. The d value of sz is constant throughout the temperature range of the stable and metastable regions for 1, whereas it increases with increase in temperature for 2.A similar temperature dependence of the latter was observed for 4'-octyloxybiphenyl- 4-carboxylic acid.I4 These facts confirm a constant tilt angle in 1 and a temperature-dependent tilt angle in 2. Thus, the tilt angles observed in the crystals (65' for 1 and 10' for 2) correspond to those (42' for 1 and 29-0' for 2) in sz. The tilt, angles in the crystals are determined by the overlap of molecules within a layer. In both crystals, the ester and ether groups are closely arranged in neighouring molecules. Similar modes, however, lead to a small overlap in 1 and a large one in 2, depending on the length of the moiety sandwiched by two polar groups.The small overlap of molecules in 1indicates a less stable smectic-like layer structure, leading to the tran- sition from the s: phase to the cholesteric, whereas the larger overlap within a layer in 2 would cause the transition from sz to sA. Interlayer interaction due to the close contact of J. MATER. CHEM., 1991, VOL. 1 a sinp 0 Fig.4 The crystal structure of 2 viewed along the b (upper) and c (lower) axes. In the lower, the c axis is taken downward from the sheet of paper. The layer plane is parallel to the (100) plane. Dotted lines denote close arrangements of 0 atoms (denoted by closed circles) with distances in 8, Fig. 5 Interchain distances (4.6 A) in 2 36 SB pU-8 32 =a 28 I I I I I 40 60 80 T/"C Fig.6 Temperature dependence of interlayer distances in smectics. Closed and open circles denote the values for 1 and 2, respectively. x denotes an effective molecular length of 2 67 1 alkyl chains is more significant in 1 than in 2. It is interpreted that the interlayer interaction, which would remain in s& is responsible for the constant tilt angle in sE of 1. Similar correlations between tilt angle in sz and crystal structure were found for two series of biphenyl esters with a 2-methylbutyl group.'9' However, the following differences are also found in the arrangement of the polar groups. The crystal structure 1 shows close contact between the ester and ether groups at two positions, whereas (n=$7) with the same phase sequence as 17 has an antiparallel arrangement of the ester groups.In the case of the crystals that transform to sz adjacent to sA, the ester and ether groups of the molecule are a short distance apart, with two neighbour- ing molecules on opposite sides in 2, as shown in Fig. 4, whereas they make pairwise association with the same mol- ecule in (n=7,8). In spite of these differences, the length of the moiety sandwiched by two polar groups essentially determines the degree of molecular overlap and hence the tilt angle of molecules, which is closely related to the structure of sz. Nearest phenyl rings between adjacent molecules make angles of 60°, on average, for 1 and 79' for 2. These values are similar to those found in the preceding except for the triclinic form of 4'-hexyloxy-4-biphenylyl p-[(S)-2-methylbutyl] benzoate, in which some of the mutual arrange- ments of the phenyl rings are nearly parallel (ca.20°), being related to the highly ordered sJ*.~Therefore, it is interpreted that rotation around the molecular long axis would be readily induced at the crystal-mesophase transition, i.e. the present crystals transform to a smectic phase with higher disorder, s; . For 2, the d value in sA, an orthogonal smectic, is shorter than that (34.2A) of sB, another orthogonal one. This value coincides with the molecular length in the crystal (34.6&, a sum of the distance between the terminal atoms, C(27) and C(38), and twice the van der Waals radius of a methyl group (2.0 A).A reduction of the d-value in sA was observed also for 4'-octyloxybiphenyl-4-carboxylicacid.I4 The value of d/ cod gives the effective molecular length. Those values for 2 show a slight decrease continuously with an increase in temperature throughout sz and sA, as shown in Fig. 6. This indicates a continuous change in the degree of disorder in the two phases. On the other hand, the value for 1, 35.0 8, (at T-T,= -30 "C), is larger than that for 2. This fact probably suggests more extended conformations of 1 than those of 2, not only in the crystal (estimated to be 35.7 and 36.8 A for the molecules A and B of 1, respectively) but also in sz. It is concluded that the liquid-crystalline phase sequences are well interpreted by intermolecular interactions revealed in the crystal structures, which are controlled by the lengths of the moieties sandwiched by polar groups for the compounds with a 1-methylheptyloxy group as was observed for those with a 2-methylbutyl group.I5 We thank Drs.T. Inukai and K. Furukawa of Chisso Coopor- ation for supplying the samples. This work was supported by ~~~~~~~ ~ For n =5 s: appears only monotropically. 672 J. MATER. CHEM., 1991, VOL. 1 a Grant-in-Aid for Scientific Research No. 02640333 from the Ministry of Education, Science and Culture, Japan. 8 Programs for the Automatic Solution of X-ray Diffraction Data, Universities of York, England and Louvain, Belgium, 1978. G. M. Sheldrick, SHELX76, A Program for Crystal Structure 9 Determination, Univ.of Cambridge, 1976. International Tables for X-ray Crystallography, Kynoch Press, Birmingham, 1974, vol. IV. References 1 K. Hori and Y. Ohashi, Bull. Chem. SOC. Jpn., 1988, 61, 3859. 2 K. Hori, M. Takamatsu and Y. Ohashi, Bull. Chem. SOC. Jpn., 1989, 62, 1751. 3 K. Hori and Y. Ohashi, Bull. Chem. SOC. Jpn., 1989, 62, 3216. 4 K. Hori and Y. Ohashi, Liq. Cryst., 1991, 9, 383. 5 T. Inukai, S. Saitoh, H. Inoue, K. Miyazawa, K. Terashima and K. Furukawa, Mol. Cryst. Liq. Cryst., 1986, 141, 251. 6 G. M. Sheldrick, SHELX86, A Program for Crystal Structure Determination, University of Gottingen, 1986. 7 P. Main, S. E. Hull, L. Lessinger, G. Germain, J-P. Declercq, and M. M. Woolfson, MULTAN78, A System of Computer 10 11 12 13 14 15 C. Johnson, ORTEP, Report ORNL-3794, Oak Ridge National Laboratory, Tennessee, 1965. T. R. Taylor, J. L. Fergason and S. L. Arora, Phys. Rev. Lett., 1970, 24, 359. T. R. Taylor, S. L. Arora and J. L. Fergason, Phys. Reu. Lett., 1970, 25, 722. G. W. Gray and J. W. Goodby, Smectic Liquid Crystals, Leonard Hill, Glasgow, 1984, p. 54. G. W. Gray and J. W. Goodby, Mol. Cryst. Liq. Cryst., 1976, 37, 157. K. Hori and Y. Ohashi, Mol. Cryst. Liq. Cryst., in the press. Paper 1/01308D; Received 19th March, 1991