Combination of molecular rods and half-discs: transition from lamellar to columnar order in multichain mononuclear ortho-palladated metallomesogens

Novel ortho-palladated phenylpyrimidine-1,3-diketonatoorganyls with success ively increasing numbers of alkyl chains were synthesized and investigated by polarizing optical microscopy and X-ray diffraction. A discontinuous tra nsition from a lamellar to a columnar organization is observed, dependent o n the number of chains: molecules with four or five chains from smectic pha ses (SmA, SmC), the related compound with six chains in the molecule is non mesomorphic, whereas molecules with seven or eight chains form hexagonal co lumnar mesophases.