| Title
| - Columnar Metallomesogens Derived from 1,3,4-Oxadiazoles andX-ray Crystal Structure ofDichlorobis[2,5-bis(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole]palladium(II)
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| Abstract
| - Three series of palladium(II) complexes 1−3 derived from 1,3,4-oxadiazoles exhibiting mesogenicproperties are prepared and characterized. It was found that the formation of mesophases was sensitiveto the numbers of alkoxy side chains. The compounds 3 appended with twelve side chains exhibitedcolumnar (Col) phases, however, all other compounds 1−3 appended with four or eight side chainsformed crystalline phases. Some derivatives (n = 8, 10, 12) of the series 3 were in fact mesogenic atroom temperature. Powder XRD data indicated that the formation of columnar mesophase varied fromrectangular (Colr) to hexagonal arrangements (Colh) was observed as carbon chains length increases.The crystal and molecular structure of palladium(II) complex of 2,5-bis(3,4,5-trimethoxy phenyl)-1,3,4-oxadiazole (3; n = 1) was determined by means of X-ray structural analysis. It crystallizes in the monoclinicspace group p21/n, with a = 8.7736 (3) Å, b = 19.1568 (6) Å, c = 15.7834 (5) Å, β = 100.106 (1)°, andZ = 2. The geometry at palladium center is perfectly square planar, and two trans-chlorine atoms arealmost perpendicularly located to the molecular plane determined by four 1,3,4-oxadiazole rings. Thefluorescent properties of these compounds were also examined. All λmax peaks of the absorption andphotoluminescence spectra of compounds 4 and 6 occurred at ca. 303−312 nm and 358−391 nm,respectively; whereas the quantum yields of some compounds were relatively low.
- A series of palladium(II) complexes derived from 1,3,4-oxadiazoles exhibiting columnar mesophases are prepared and characterized, and X-ray data indicate that the two trans-chloro atoms located perpendicular to the molecular plane might be attributed to a lower melting temperature in this system.
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