XVI. Tage der Seltenen Erden location:Berlin (Germany) date:4-6 December 2003
Lanthanide complexes with a disklike shape (discotic complexes) can form liquid-crystalline phases upon heating. In these liquid-crystalline phases or mesophases the molecular order is between that of an ordered solid and a disordered liquid. The mesophase is an anisotropic fluid. In columnar mesophases, the molecules are stacked into columns. Depending on the type of 2D lattice formed by the columns, one can make a distinction between a hexagonal columnar phase (Colh), a tetragonal columnar phase (Colt) or a rectangular columnar phase (Colr). To stabilize the mesophase and to reduce the transition temperatures, long alkyl chain are attached to the disklike core of these complexes. At the melting point, the alkyl chains obtain a disordered liquid-like conformation, but the columns remain intact. At the clearing point (second melting point), the columnar supramolecular organization is lost. A powerful experimental tool to study these complexes is high-temperature X-ray diffraction, but also hot-stage polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) can provide valuable information.
In this presentation, an overview is given of the different types of discotic liquid-crystalline lanthanide complexes described in the literature . Special attention will be paid to the substituted bis(phthalocyaninato)lanthanide(III) complexes in which the lanthanide ion is sandwiched between two phthalocyanine rings. The lutetium compounds can be considered as one-dimensional molecular semiconductors, and most of these complexes show electrochromism. Another type of interesting compounds are metal-containing liquid crystals (metallomesogens) which contain both a lanthanide ion and a transition metal ion. Different types of liquid-crystalline f-d complexes will be discussed.
 K. Binnemans, C. Görller-Walrand, Chem. Rev. 2002, 102, 3374.