The effect of polyether terminal chains in the liquid crystalline behavior of ortho-palladated complexes

Abstract

A series of benzylideneanilines bearing terminal polyether chains, HL (HL = R-C 6H 4–CH N–C 6H 4-R′: R = OC 8H 17, R′ = O(CH 2CH 2O) 2C 2H 5; R = O(CH 2CH 2O) 2C 2H 5, R′ = OC 8H 17; R = R′ = O(CH 2CH 2O) 2C 2H 5; R = OC 12H 25, R′ = O(CH 2CH 2O) 3C 2H 5; R = O(CH 2CH 2O) 3C 2H 5, R′ = OC 12H 25; R = R′ = O(CH 2CH 2O) 3C 2H 5) have been prepared. Their dinuclear, [Pd(μ-X)L] 2 (X = OAc, Cl, Br, SC 8), [Pd 2(μ-SCn)(μ-X)L 2] (X = OAc, Cl; n = 8, 2) and mononuclear orthopalladated derivatives, Pd(acac)L, Pd(Ala)L, are reported and their mesogenic properties are compared with those of the analogous compounds with alkoxy chains. In general a great lowering in the melting points is produced for all the products. The free ligands and the alanine complexes are not liquid crystals. The chloro-bridged complexes bearing alkoxy and short polyether chains (O(CH 2CH 2O) 2C 2H 5) show the larger improvement of mesogenic properties. Longer polyether chains (O(CH 2CH 2O) 3C 2H 5) result usually in a destabilization of the mesophases. If only polyether chains are present, the destabilization is important regardless of the chain length. The ability of these molecules as ionic extractants and transporters was qualitatively evaluated for the more propitious cis-dinuclear complexes, which in fact showed some extracting ability, modest but improved compared to the free ligands.