Katleen Lodewyckx

Rare-earth complexes of mesomorphic Schiff's base ligands

Rare-earth complexes of mesomorphic Schiff s bases, 4-[(alkylimino)methyl]-3-hydroxyphenyl 4-alkyloxybenzoates, were synthesized. Whereas the ligands LH display a nematic and/or a smectic C phase, the metal complexes show a viscous smectic A phase and decompose at the clearing point. The mesophase was investigated by hot-stage polarizing optical microscopy, by differential scanning calorimetry and by high temperature X-ray diffraction. Two types of complex were found, [Ln(LH)3 (NO3)3] and [Ln(LH)2L(NO3)2], depending on the ligand or the central metal ion. The first coordination sphere of the rare-earth ion in these metallomesogens is comparable to that in the structure of complexes with 4-alkoxy-N-alkyl2-hydroxybenzaldimine ligands.

Trimetallic Nickel - Lanthanum and Nickel - Gadolinium Metallomesogens

Adducts were formed between a mesomorphic Ni(salen) complex [salen=2,2′-N,N′-bis(salicylidene)ethylenediamine] with six terminal alkoxy chains and a lanthanide nitrate (Ln=La, Gd). Different alkoxy chain lengths were used: OC12H25, OC14H29, OC16H33 and OC18H37. Trinuclear nickel–lanthanum and nickel–gadolinium complexes [Ln(NO3)3{Ni(salen)}2] were obtained. The compounds exhibit a wide-temperature-range hexagonal columnar mesophase (ColH) with rather low melting points. The mesophase stability ranges of both the parent nickel complexes and the nickel–lanthanide complexes decrease with increasing chain length. A decrease in the mesophase stability range over the lanthanide series was also observed. The results are compared with those of similar copper–lanthanide complexes. A marked difference is the higher thermal stability of the nickel–lanthanide complexes in comparison with the copper–lanthanide complexes.

Lanthanide complexes of Schiff base ligands containing three aromatic rings: synthesis and thermal behaviour

The synthesis and thermal behaviour of liquid-crystalline lanthanide complexes with Schiff base ligands are described. The w Ž. Ž .x Ž. Ž . Ž . Ž . Ž . Ž . Ž . stoichiometry of the rare-earth complexes is Ln LH L NO , where Lns La III , Nd III , Pr III , Eu III , Gd III , Ho III , Er III , and 23 Ž� w Ž. x 4. Ž . LH is the Schiff base 4- 3-Hydroxy-4- octadecylimino methyl phenoxy carbonyl phenyl 4- hexyloxy benzoate. The ligand displays a Ž. Ž .