Communications ADVANCED MATERIALSsured reflections in the range 2 I 0 I 26'. 962 symmetry-independent reflections with I > 3 0 (I) used, without absorption correction ( p = 4.6 cm-I), in the structure solution (direct methods: SHELX-86) and least-squares refinement (SHELX-76) of 109 parameters. S and C atoms relined anisotropicdlly; H atoms, located in AFmaps, refined isotropically through some least squares cycles, and then held fixed. R = 0.029

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The synthesis and physical characterization (thermotropic and ferroelectric behavior) of eight ortho-palladated dimers [Pd2(ji-C1)2L*2] is reported. They are derived from chiral imines HL* (HL* = />-R1OC6H,(CH=NQH4-OR* 12-p, with R1, R2, or both equal to (R)or (5)-l-methylheptyl). The chiral imines, which contain one or two stereogenic centers, are not liquid crystals themselves. However, the dimeric complexes, which contain two or four stereogenic centers in their structure, exhibit both SmA and SmC* mesophases and enable the first comparative structure-activity study on metal-containing ferroelectric liquid crystals to be made. The ferroelectric properties obtained are better when there are chiral chains on the ortho-metalated aromatic rings, because the fixed conformation of these rings diminishes the chiral tail freedom, thus allowing a better coupling of molecular dipoles. The complexes with two chiral tails show important Psmax values in the range 44-131 nC*cm-2. The complex with four chiral chains (R1 = R2 = (R)-methylheptyl) is the first such compound ever reported containing four stereogenic centers; furthermore, it shows a remarkably high Psmax value of 206 nC-cnr2, the highest value reported so far for a metal-containing liquid crystal.

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