TRANSITION-METALS COMPLEXED TO ORDERED MESOPHASES - SYNTHESIS, CHARACTERIZATION, AND MESOMORPHIC PROPERTIES OF NEW POTENTIALLY FERROELECTRIC LIQUID-CRYSTALS - CHIRAL P,P'-DIALKOXYAZOBENZENES AND THEIR CYCLOPALLADATED DINUCLEAR COMPLEXES

To prepare chiral metallo-mesogens with ferroelectric properties, new azobenzene compounds, HL(N)(n), bearing a chiral substituent have been synthesized. These ligands consist of two aliphatic chains of variable length, one of which contains a stereogenic center located in the para and para' positions of an azobenzene core. The chiral groups (R*O) are as follows: N = 1, (R)-(-)-menthol; N = 2, (S)-(-)-beta-citronellol, and N = 3, (R)-(-)-2-octanol; the aliphatic chains are linear n-alkoxy groups C(n)H2n+1O (n = 7, 10, 12, 14). Only the HL2(n) species display liquid-crystalline properties giving cholesteric or smectic A mesophases. The HL(N)(n) ligands react with [Pd(PhCN)2Cl2], to give the corresponding chloro-bridged dinuclear cyclopalladated products {Pd[L(N)(n)](mu-Cl)}2 as 1:1 mixtures of isomers arising from the nonselective attack of the palladium on the benzene ring bearing the chiral alkoxy group or on the benzene with the aliphatic alkoxy chain. The {Pd[L2(n)](mu-Cl)}2 compounds and the {Pd[L3(n)](mu-Cl)}2 (n = 10, 12,14) exhibit smectic mesophases (Sc* in {Pd[L2(7)](mu-Cl)}2, {Pd[L2(10)](mu-Cl)}2, {Pd[L3(10)](mu-Cl)}2, and {Pd[L3(14)](mu-Cl)}2, S(A) in {Pd[L2(12)](mu-Cl)}2, {Pd[L2(14)](mu-Cl)}2, {Pd[L3(12)]mu-Cl)}2). The Pd[LN(n)](mu-Cl)}2 compounds have been converted into the corresponding iodo analogues {Pd[LN(n)](mu-I)}2. The chloro complexes display a richer mesomorphism than the respective iodo compounds.