DALTON J. Chem. Soc., Dalton Trans., 1996, Pages 17–19 17 Discotic bimetallomesogens: highly disordered mesophases of columnar hexagonal arrangements in bis(tetraketonate) vanadyl and copper complexes † Chung K. Lai * and Fun-Jane Lin Department of Chemistry, National Central University, Chung-Li, Taiwan, Republic of China A series of bis(tetraketonate) complexes of dicopper and divanadyl has been prepared and their mesomorphic properties investigated by polarized optical microscopy and powder X-ray diffraction.Molecular design and synthesis of new metal complexes with novel mesophases and/or physical properties represent an active research area in metallomesogenic materials.1 The incorporation of a metal or metal centres can not only lead to new structures and geometries capable of generating new mesogenic materials,1,2 but also results in interesting electrical, optical and magnetic properties. In bimetallic liquid crystals the interaction between metal centres in molecular structures, whether in close proximity or remote from each other, may influence the formation of liquid-crystalline mesophases, and consequently determines the physical properties of these complexes.However, this approach to an understanding of bimetallic liquid crystals still remain limited, and only a few bimetallic complexes have been prepared 3 and studied. We report herein our results on the development of the first discotic 4 divanadyl and dicopper liquid-crystalline complexes. We have prepared and characterized a number of bimetallic complexes.The typical synthetic procedures are summarized in Scheme 1. The tetraketones 1,3-bis[3-(3,4,5-trialkoxyphenyl)- 3-oxopropanoyl]benzene‡ and 1,3-bis[3-(3,4-dialkoxyphenyl)-3- oxopropanoyl]benzene, were synthesized by condensation of the isophthalic acid dimethyl esters, the appropriate acetophenone derivatives and sodium hydride in refluxing thf or 1,2- dimethoxyethane. Reactions of the tetraketones with copper acetate and vanadyl sulfate in refluxing CHCl3–MeOH gave the bimetallic tetraketonate complexes 5 in high yields.Satisfactory elemental analysis for these metal complexes were obtained after several recrystallizations (SUP 57200). The mesomorphic properties of these bimetallic complexes are summarized in Table 1. Copper complexes 1a (n = 12 or 18) showed only crystal phases with isotropic temperatures at ca. 250–300 8C. However, when the number of carbon atoms in the sidechains is greater than ten for complexes 2a and six for complexes 3a, the copper complexes exhibited columnar discotic † Supplementary data available, (No.SUP 57200, 6 pp.): tables of enthalpies of phase changes and elemental analyses for all compounds reported. See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. ‡ 1,3-bis[3-(3,4,5-tridocenoxyphenyl)-3-oxopropanoyl]benzene: yield, 86%, light yellow solids. 1H NMR (CDCl3): d 0.87 (t, CH3, 18 H), 1.29– 1.51 (m, CH2, 108 H), 1.76–1.90 (m, CH2, 12 H), 4.06 (t, OCH2, 12 H), 6.83 (s, CH]] C, 2 H), 7.19 (s, C6H2, 4 H), 7.63 (t, C6H4, 1 H), 8.12 (d, C6H4, 2 H), 8.58 (s, C6H4, 1 H), 17.02 (s, COH, 2 H). 13C NMR (CDCl3): d 12.02, 14.71, 19.35, 23.31, 26.74, 30.03, 30.31, 30.99, 32.21, 32.56, 35.29, 36.70, 70.14, 74.26, 93.81, 106.9, 110.7, 126.3, 129.6, 130.9, 131.1, 136.8, 143.5, 153 .8, 183.9, 187.5.liquid phases (SUP 57200). Differential scanning colorimetry (DSC) analysis of complexes 2a and 3a showed typical discotic phase transitions of crystal-to-discotic-to-isotropic (K æÆ D æÆ I).These copper complexes showed a large enthalpy (88.0–305.0 kJ mol–1) for the crystal-to-liquid crystal transitions at lower temperatures (124–132 and 91–120 8C for Scheme 1 (a) RBr (3.0 equivalents), K2CO3 (7.0 equivalents), KI (catalyst) refluxing in MeCOMe, 72 h, 73–94%. (b) KOH (2.0 equivalent), refluxing in tetrahydrofuran (thf)–water (5 : 1), 12 h, 92–98%.(c) LiMe (2.0 equivalents) stirred in dried thf at room temperature, 12 h, 82–87%. (d) Isophthalic acid dimethyl ester (0.5 equivalents), NaH (3.0 equivalents), refluxing in thf, 4 d, 72–85%. (e) Cu(O2CMe)2 or VOSO4 (1.1 equivalents) refluxing in CHCl3–MeOH, 12 h, 73–83% OR RO RO O O O O OR OR OR RO RO OR O O O O OR OR OR M M OR RO RO OH O OH O OR OR OR OH OH OH EtO O OR OR OR EtO O OR OR OR HO O OR OR OR O (a ) (b ) (c ) (d ) (e ) DC6/06770K/A118 J.Chem. Soc., Dalton Trans., 1997, Pages 17–19 complexes 2a and 3a) and a low enthalpy (1.13–5.77 kJ mol–1) for the liquid crystal-to-isotropic transition at higher temperatures (220–258 and 169–236 8C for complexes 2a and 3a), indicating that the mesophases are in highly disordered states. The temperature range of the mesophases is fairly wide and slightly side-chain dependent at about 79–126 8C. Under a polarized microscope these complexes gave pseudo-focal-conic or fan textures with linear birefringent defects and large areas of uniform homeotropic domains.The vanadyl complexes 3b showed similar discotic behaviour. Transitions of crystal-to-isotropic phases were only observed for vanadyl complexes 1b (n = 12) and 2b (n = 10, 12 or 16). The results revealed that the stronger intermolecular co-ordination between the vanadyl centres inhibited the formation of the liquid-crystal phases. However, increasing the total number of side-chains to 12 (when n > 6) in complexes 3b facilitated the Table 1 Phase behaviour of bimetallic complexes * Complex M n 2a Cu 12 14 16 K K K 132.3 (104) 115.6 (29.5) 126.7 (87.4) 114.1 (24.2) 123.5 (115) 116.0 (34.1) Dhd Dhd Dhd 254.4 (1.46) 249.6 (0.75) 232.7 (1.13) 229.5 (4.97) 219.2 (1.76) 215.0 (0.42) I I I 3a Cu 6 10 12 14 K1 K K K 119.2 (2.73) 99.5 (5.10) 107.8 (268) 54.6 (279) 99.7 (307) 48.2 (321) 90.8 (280) 40.8 (245) K2 Dhd Dhd Dhd 248.5 (3.72) 243.7 (4.01) 235.7 (5.14) 232.3 (5.60) 193.2 (5.56) 189.5 (5.77) 169.0 (4.39) 165.5 (3.59) I I I I 2b VO 10 K 183.8 (6.14) 175.1 (6.06) I 3b VO 6 10 12 14 K K K K 289.9 (38.7) 267.3 (38.0) 78.5 (51.4) 48.7 (55.2) 60.5 (36.4) 34.2 (38.2) 48.7 (31.8) 18.2 (29.9) I Dhd Dhd Dhd 223.6 (5.14) 220.6 (4.26) 187.6 (3.51) 185.5 (4.85) 159.5 (0.38) 156.1 (1.05) I I I * K1, K2 = crystal phase; Dhd = discotic hexagonal disordered; I = isotropic; the transition temperature (8C) and enthalpies (in parentheses, kJ mol–1) were determined by DSC at a scan rate of 10 8C min–1.formation of columnar discotic hexagonal phases as for the copper complexes. The identification of columnar hexagonal discotic phases was confirmed by variable-temperature X-ray powder diffraction (XRD), as shown in Table 2. Complex 3b (n = 12) displays a diffraction pattern of a two-dimensional hexagonal lattice with a strong peak and two weak peaks at 33.15, 19.13 and 16.57 Å. However, complexes 2a (n = 16) exhibited similar diffraction patterns at 34.88, 20.14 and 17.07 Å.These are typically characteristic of a Dhd phase with a dspacing ratio2a,3a,c of 1, ÷��� and ��� , respectively. However, liquid-like correlations between the rigid cores occur at wide angle regions of 5.30–4.64 Å. Temperature dependence of the lattice parameters is also observed in these metal complexes. We find that the lowangle reflections of complexes 3a (n = 16) generally shift to a larger d spacing with decreasing temperatures, thereby indicating a lattice expansion.Absence of distinct peaks at wide angles is consistent with DSC analysis of low enthalpies of discotic-toisotropic transitions, indicative of a highly disordered mesophase. The geometry of the divanadyl centres in complexes 1b–3b either syn or anti, is uncertain based on IR data. The growth of single crystals for X-ray structural determination is in progress. In summary, we have discussed our results on the dicopper and divanadyl complexes of tetraketones. Future research will be focused on the study of related physical properties of these bimetallic complexes, particularly in understanding the effects of two remote metal centres on liquid crystallinity.X RO Y O O O O X OR Y Y RO X O O O 1 X = Y = H 2 X = OR, Y = H 3 X = Y = OR M = Cu (a) or VO (b) R = (CH2)n –1CH3 DC6/06770K/A2 Table 2 Variable-temperature XRD diffraction data for the discotic hexagonal disordered bimetallic complexes 2 and 3 * Complex M n T/8C Lattice constant (a)/Å d Spacing obs.(calc.)/Å Miller indices 2a Cu 16 170 40.28 34.88 (34.88) 20.14 (20.14) 17.07 (17.44) 5.30 (br) (100) (110) (200) halo 110 46.60 40.35 (40.35) 23.29 (23.30) 20.16 (20.17) 13.31 5.30 (br) (100) (110) (200) halo 3a Cu 12 100 29.66 29.67 (29.67) 14.86 (14.83) 5.04 (br) (100) (200) halo 3b VO 12 100 38.28 33.15 (33.15) 19.13 (19.14) 16.57 (16.58) 4.64 (br) (100) (110) (200) halo * The measurements were conducted on an INEL MPD-diffractometer with a 2.0 kW Cu-Ka X-ray source equipped with an INEL CPS-120 position sensitive detector and a variable-temperature capillary furnace with an accuracy of ±0.10 8C in the vicinity of the capillary tube.J. 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