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 successively increasing numbers of alkyl chains were synthesized and investigated by polarizing optical microscopy and X-ray diffraction. A discontinuous transition from a lamellar to a columnar organization is observed, dependent on the number of chains: molecules with four or five chains from smectic phases (SmA, SmC), the related compound with six chains in the molecule is nonmesomorphic, whereas molecules with seven or eight chains form hexagonal columnar mesophases.