Non-mesomorphic ligands

Neve has studied a series of complexes based on non-mesomorphic ligands (Figure 41) obtained by acylation of [18]ane N2S4 [83]. A single-crystal X-ray study of one of the silver(I) complexes revealed a tetrahedral geometry for the silver(I) ion and a parallel arrangement for the pendant arms leading to an almost perfect... 

Complexes with the simplest alkoxyphenylisocyanide and several halides are prepared by metathetical reactions of [AuCl(CNR)] with KX salts (Figure 7.19) [17]. The chloro-derivatives (n > 4) andthebromo-complexes (n > 6) display SmA phases. However, the ligands and the iodo-complexes are not liquid crystals. The transition temperatures decrease in the order Cl > Br > I, according to the decrease in polarity of the Au—X bond. It is important to note that the coordination of a very simple non-mesomorphic isocyanide (only one alkoxy chain and one aromatic ring) to Au—Cl allows the formation of a quite ordered and stable smectic mesophase. 

The corresponding pyrazole mononuclear derivatives [AuCl(pzH)] have been prepared with the same ligands (Figure 7.41) [38]. Only the monosubstituted non-mesomorphic pyrazole leads to a liquid crystal, not the disubstituted mesomorphic ligand. The complex displays a SmA mesophase on cooling to 69.2 °C, although this is mixed with some crystallization. Moreover, this derivative is luminescent at 77 in the solid state. In addition, the corresponding trinuclear and mononuclear derivatives, namely [ Au(pz) 3] and [Au(Hpz)2]+, which could be expected to be liquid crystals are non-mesomorphic. 

The effect of the ligand X (Figure 50) has been studied and shows the expected reduction in clearing temperature with increase in the size of X, to the extent that the triflato derivatives are non-mesomorphic. In the light of our findings with orthome-tallated imine complexes, it is perhaps surprising that complexation produces higher... 

Shimizu has studied a series of mesomorphic 5,10,15,20-tetrakis(4 -alkyphenyl)-porphyrins (Figure 75) finding that the ligands were non-mesomorphic until the... 

Swager has described a series of dioxomolybdenum complexes based upon non-mesomorphic substituted pyridinediyl-2,6-dimethanolato ligands [181]. For decy-loxy chains and above, the complexes display disordered hexagonal columnar phases as identified by X-ray diffraction studies. Variable-temperature infrared studies looking at the oxomolybdenum symmetric and asymmetric frequencies show that there are weak interactions within the mesophase compared to the isotropic state and that the strongest interactions are seen in the solid state. These interactions are proposed to help stabilize the columnar mesophase observed (Figure 97). 

Related heteropolynuclear complexes 27, based on a non-mesomorphic Fc enaminoketone ligand, were also prepared (27 M = Cu, pj) displayed only monotropic phases Cr 144 (N 122) I for the copper complex... 

Other ortV o-metallated pyridazine complexes (134, where R = -Me, -CH2CI2) were reported by Guang et For n = m= Q, the free ligand showed a SmA phase (Cr 79 SmA 102 I), as did the /i-Cl precursor complex (Cr 163 SmA 212 I) and the chloro- and bromoacetates (Cr 160 SmA 185 I and Cr 160 SmA 174 I, respectively) the simple /i-acetato complex was non-mesomorphic at all chain lengths reported. The lower symmetry complexes ( = 6, m= 10) were mesomorphic for the chloro- but not the bromoacetate, and a more extensive series where n was fixed as 10 and m was varied from 6 to 12 showed enantiotropic SmA phases for all except that with m = i>. 

Lattermann and co-worker have reported a series of mesomorphic metal tricarbonyl complexes, 77, formed by complexation of the metal fragments M(C0)3 (77 M = Cr(0), Mo(0) and W(0)) by the non-mesomorphic tridentate azamacrocyclic ligand, i.e. l,4,7-tri-(3, 4 -didecyloxy)benzyl-l,4,7-triazacyclononane [139]. 

Tetracatenar mesogens formed from ligand c were found to be non-mesomorphic, while for ligand b, an unidentified mesophase was reported for =14. However, the tetracatenar (2mp)- -(2mp) complexes (108) derived from ligand a were much more interesting and were... 

Related chloro(isocyanato)copper(I) complexes (150) have also been studied, and again, mesomorphic complexes were found even though the ligand was non-mesomorphic. Two series were prepared, and most of the di-3,4- ((150) R = H, n = 4, 6, 8, 10,12), and tri-3,4,5-alkoxyphenyliso-cyanatocopper(I) complexes ((150) R = OC H2 +i, n = 4, 6, 8, 10,12) exhibited Colt phase, some of... 

More recently, 4-alkoxy-2- and 4-alkoxy-3-stilbazoles have been reported (Figure 85) and their silver complexes with AgDOS and AgOTf have been synthesized. While the ligands themselves are non-mesomorphic, the eomplexes show only SmA phases, although complexes of the 2-stilbazoles do not form readily. While the new complexes are Uquid crystalline, the use of the isomeric stilbazoles suppresses the polymorphism of the 4-stilbazole isomers. 

Similarly, smectic mesophases were obtained in heteronuclear or/ o-palladated imine complexes based on various non-mesomorphic enaminoketone ligands ((263) to (265), Figure 104). The precursor chloro-bridged complex was also mesomorphic, showing an SmA phase between 238 and 248°C. ... 

Both Bruce (1485) and Hoshino-Miyajima (1486) and co-workers prepared bis(dithiocarbamate) complexes with long-chain substituents as potential liquid crystals. Most are derived from four-substituted piperazines with flexible alkoxy tails (345), and are mesomorphic, showing smectic phases Sc and crystal B mesophases (1485). Palladium, copper, and zinc bis(dithiocarbamate) complexes of the same ligands showed similar behavior, but nickel piperazine complexes with 4-phenyl, alkyl, and 3-alkoxy tails are non-mesomorphic (1485). 

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