Transition metals complexed to ordered mesophases. VI. Synthesis, mesomorphic behaviour and X-ray molecular structure of the cyclopalladated dimer [(L)PdCl]₂ (HL = N-(4-methoxybenzylidene)-4′-butylaniline)

Abstract

The reaction between [Pd(PhCN)₂Cl₂] and the liquid crystalline ligand N-(4-methoxybenzylidene)-4′-butylaniline, (MBBA indicated here as HL) affords the new metallo-mesogen [(L)PdCl]₂, (1). The main feature of the molecular structure (single crystale X-ray analysis) of the dinuclear cyclopalladated complex (1) is the Cl—Cl hinged dihedral angle, 141·3(1)°, which the Pd₂Cl₂ core forms. The Pd—Pd separation is 3·36(2) Å. Complex (1) in the solid state forms a columnar array and upon heating shows a solid-to-solid transition at 160°C, a smectic A mesophase, at 218°C, a nematic mesophase at 245°C (with minor decomposition) and the clearing point at 251°C (with large decomposition). By comparison with similar palladium mesogens, the increase in the transition temperatures by (1) with respect to MBBA, has been tentatively ascribed to the fully anisotropic ellipsoidal molecular shape resulting from palladium complexation.