MESOMORPHIC CYCLOMETALATED (CYCLOPENTADIENYL)PALLADIUM AND (CYCLOPENTADIENYL)PLATINUM COMPLEXES

The mesogenic 4,4'-bis[4-(n-octyloxy)benzoyloxy]azobenzene (HL) ligand reacts with [(PhCN)(2)PdCl2] to give the dinuclear cyclometalated com plex [(mu-Cl)(L)Pd](2) (1), from which the mononuclear half-sandwich [ (eta(5)-C5H5)(L)Pd] (2) species has been obtained by reaction with Tl( C5H5). The Pt-II analogue of 2, [(eta(2)-C5H5)(L)Pt] (4), has been pre pared in a similar manner starting from [(mu-Cl)(L)Pt](2) (3). Both di nuclear complexes 1 and 3 display a smectic C phase (S-c) stable over 80 degrees C. Whereas 4 is the first example of an 18-electron Pt-II m esogen, both mononuclear 2 and 4 are mesomorphic materials that exhibi t a nematic phase spanning a wide temperature range.