Group 8, mesomorphic complexes

A most interesting group of complexes are the mesomorphic 7] -butadienetricarbonyliron(0) materials, 13, reported by Malthete and co-workers. 

Depending on the R group, this reaction could lead to the formation of gold(I) isocyanide complexes that behave as liquid crystals. Thus, complexes [Au(C6F5) (C = N(QH4)OCioH2i-p)] and [Au(QF5)(C = N(QH4)OCnH2n + rP)] [64] where n = 4, 6, 8, 10 and 12 show this behavior. All of these complexes are mesomorphic and behave as liquid crystals showing a nematic (N) phase when the isocyanide has a... 

Derivatives of aliphatic alkynes (14 and 15) are more thermally unstable than 12, but they show SmA and N phases at low temperatures (below 130 °C). The type of phase and the mesophase stability depend on the length of both the terminal and the lateral chains. When both chains are elongated, the mesomorphism becomes metastable and compounds 14 display monotropic N and SmA transitions. Complexes IS, which contains an ester group with an opposite direction to that of complexes 14, display less stable nematic mesophases. 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

When the lateral substituents were changed from ether to gallic ester groups, a columnar hexagonal phase was observed for 112, while complexation with KI destroyed the mesomorphic behavior [121] (Scheme 58). The presence of ion pairs in the complex presumably leads to unfavorable interactions between neighboring molecules leading to non-mesogenity. 

Supramolecular chemistry can be used to create the bent cores that give rise to the symmetry breaking in this family of liquid crystals [139]. The formation of a complex between a calamitic benzoic acid derivative and a bent core terminated with a pyridyl group—neither of which display mesomorphic behaviour—gave rise to a material which displayed SmCP mesophases. The achiral bent cores can also give rise to symmetry breaking when they are attached to flexible polymeric chains, such as poly(siloxane) [140]. 

C. Mesomorphic Stilbazole Complexes of Groups 10 and 11 Metals Hydrogen-Bonded Stilbazole Mesogens... 

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