Monomeric and dimeric ortho-metallated palladium(II)-imine systems as liquid crystals

Several types of ortho-palladated complexes derived from the imines HLn=p-CnH2n+1O-C6H4-CH=N-C6H4-OCnH2n+1-p (n=2, 4, 6, 8 and 10) have been prepared and their mesogenic properties studied. The types include the dinuclear complexes [Pd(mu-X)Ln](2) with X=Cl, OAc, (R)-2-Cl-propionato or (S)-2-Br-propionato, and the mononuclear complexes [Pd(acac)Ln] and [Pd(NHacac)Ln](NHacac=4-amino-3-penten-2-onate). Most of the complexes (except the acetato derivatives and some others with very short alkoxy chains) show liquid-crystal behavior. Nematic, smectic A and smectic C phases are found. Most of the derivatives with chiral carboxylates display double melting behavior.