Platinum complexes metallomesogens

Liquid-crystalline complexes (metallomesogens) containing platinum(II) are new types of materials that have been the subject of several studies. These have largely included complexes of the type trans-[PtX2L2] (X = C1, L = cyanobiphenyls 229 X = C1, carboxylate, L = 4-alkoxy-4 stilbazoles 230 X = C1, L = 2,4-, 3,4-, or 3,5-dialkoxystilbazoles, 2,3,4-, 2,4,5-, or 3,4,5-trialkoxystilbazoles).231,232 Their liquid-crystalline properties have also been reported. 

The first systematic study of d-block metallomesogens were carried out by Giroud and Mueller-Westerhoff [11] and marked, in 1977, the beginning of interest in metal-containing systems. They were dithiolene complexes of nickel, palladium and platinum with two p-alkyl phenyl substituents (see structure 3). Nickel and platinum complexes showed nematic and smectic phases, depending on the chain length. Palladium analogs do not possess any mesomorphic properties [81]. 

Gold(III) usually displays a square planar geometry, typically observed in d8 metallic complexes such as palladium(II), platinum(II), rhodium(I) and iridium (I), for which an enormous number of liquid crystals have been described [3-5], mainly as orthometallated compounds. However, only a gold(III) metallomesogen has been published. Since the first gold mesogen was reported in 1986, many other compounds have been described. 

Heterometallic metallomesogens, liquid crystals, 12, 223—224 Heterometallic polynuclear platinum carbonyl complexes heterodinuclear clusters, 8, 415 triangular clusters, 8, 417... 

We have pursued the study of polycatenar metallomesogens using poly(alkoxy) stilbazoles [177], and have recently imdertaken a systematic study of the complexes of series of these ligands with palladium(ll), platinum(II) and silveifl) ions. 

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

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