Three series of palladium(II) complexes 1-3 derived from 1,3,4-oxadiazoles exhibiting mesogenic properties are prepared and characterized. It was found that the formation of mesophases was sensitive to the numbers of alkoxy side chains. The compounds 3 appended with twelve side chains exhibited columnar (Col) phases, however, all other compounds 1-3 appended with four or eight side chains formed crystalline phases. Some derivatives (n ) 8, 10, 12) of the series 3 were in fact mesogenic at room temperature. Powder XRD data indicated that the formation of columnar mesophase varied from rectangular (Col r ) to hexagonal arrangements (Col h ) 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)-1,3,4oxadiazole (3; n ) 1) was determined by means of X-ray structural analysis. It crystallizes in the monoclinic space group p2 1 /n, with a ) 8.7736 (3) Å, b ) 19.1568 (6) Å, c ) 15.7834 (5) Å, β ) 100.106 (1)°, and Z ) 2. The geometry at palladium center is perfectly square planar, and two trans-chlorine atoms are almost perpendicularly located to the molecular plane determined by four 1,3,4-oxadiazole rings. The fluorescent properties of these compounds were also examined. All λ max peaks of the absorption and photoluminescence 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.

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