A systematic study of the liquid-crystalline properties of 30 metal bis (/3-diketonate) complexes (M = Cu, VO, Pd) that exhibit discotic mesophases is reported. This study has determined that the ability of the metal center to influence the mesophase stability depends upon the density of side chains. In the 10-side-chain complexes series 3, all of the materials were found to be liquid crystalline. In this series the M = VO analogues were found to have lower melting and clearing points than those with M = Cu and M = Pd. For the 12side-chain series 4 the opposite is true, and the M = VO materials have substantially higher clearing points. The differences between series 3 and 4 arise from the enhanced core-core interactions that accompany the increased side-chain density. The side-chain-induced organization assists the expression of the metal center's character in determining the stability and nature of the mesophase. The fact that the transition temperatures of the M = Cu and M = Pd compounds differ more in series 4 than in series 3 is also a manifestation of this greater organization. The influence of the metal centers is discussed in the context of intermolecular dative associations and for some phases of the M = VO materials these interactions produce polymeric (-V=0-V=0-)" structures.

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A series of copper(bis-β-diketonate) complexes are reported which display columnar liquid-crystal phases with a hexagonal disordered structure (D hd). The complexes do not have the disc-shape characteristic of most D hd materials, but produce a disc shape by forming dimers with 90o rotations between nearest neighbors. In the liquid-crystalline state this dimerized nature produces short-range rotational correlations. Three side-chain copper bis-β-diketonates with a single phenyl substituent, 2, are not liquid crystalline, and it was found that an extension of the mesogenic core is necessary to introduce liquid crystallinity. The simple phenyl analogues, 3a, are monotropic, and the addition of electron-withdrawing substituents to the phenyl moiety, 3b − d, results in a stabilization of the mesophase. These substituents produce favorable dipolar interactions which stabilize the mesophase. Consistent with this explanation, electron-donating substituents are not effective at stabilizing the mesophase. Substitution of the complex with thiophene groups rather than phenyls, 4, produces stable mesophases with greatly lowered melting and clearing points. This latter result indicates that thiophene substitution provides dispersive forces which destabilize the crystal phase. Thiophene substitution may provide a general method for reducing transition temperatures in metallomesogens.

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The dependence of mesomorphism of 1,3-diketonate vanadium-oxo (vanadyl) complexes on the number of side chains was investigated. These complexes have a large dipole normal to the disc plane and are under investigation in an effort to generate discotic phases with polar order. Relatively complex phase behaviour is observed when the vanadyl 1,3-diketonate complexes are appended with four phenyl groups with two octyloxy or decyloxy side chains each for a total ofeight side chains. These complexities are most likely related to the order/disorder associated with the polar vanadyl group. Vanadyl 1,3-diketonate complexes with four side chains were prepared by replacement of two of the phenyl groups with methyl or trifluoromethyl groups, and these complexes displayed only crystal phases. Complexes with two trialkyloxy phenyls and two dialkyloxy phenyls were synthesized and found to display a very stable D,, phase. The presence of additional alkyloxy groups was found also to promote a linear chain structure,in the crystal phase. IntroductionNew liquid crystals with polar mesogens are of interest as a means of generating materials which can interact strongly with electric fields. Polar mesogens may also be used to produce new materials with ferroelectric behaviour, given that bulk dipolar order can be established. In the quest for new achiral ferroelectric liquid crystals, columnar phases of pyramid shaped macrocyclic organic mesogens have been investigated [l]. The pyramid shape of the mesogen in these systems promotes a headto-tail organization and hence can create polar order within a given column. There have been a number of elegant studies on these organic pyramidal liquid crystals [l], but ferroelectric behaviour has not been demonstrated. This fact is probably due to small dipoles and large activation energies for redirecting the dipoles, since recent theoretical studies indicate that ferroelectric phases should exist [2].As a result of these difficulties associated with prospective ferroelectric organic discotic systems, we have been focusing on inorganic vanadium-oxo (vanadyl) complexes. The vanadyl group is attractive since it often exhibits a square pyrimidal structure and has a large directional dipole associated with the V=O bond [3]. In addition, work in this laboratory has recently shown that liquid crystalline vanadyl complexes can arrange in a linear chain structure (i.e. --V=O--V=O--), thereby creating local polar order between mesogens [4]. We report herein our results on a series of discotic 1,3-diketonate vanadyl complexes for which we explore the effects of the number of side chains on the mesomorphic behaviour.