Functional isocyanide metal complexes as building blocks for supramolecular materials: hydrogen-bonded liquid crystals

Abstract

Gold, palladium and platinum complexes with an unusual isocyanide ligand containing a carboxylic acid function, [AuCl(CNC₆H₄COOH)], cis-[MI₂(CNC₆H₄COOH)₂] and trans-[MI₂(CNC₆H₄COOH)₂] (M = Pd, Pt) have been isolated. The carboxylic acid group of the coordinated isocyanide acts as a hydrogen donor for hydrogen-bonding and three series of stable hydrogen-bonded liquid crystalline metal complexes have been prepared with decyloxystilbazole. Although all the metal acid derivatives used are not mesomorphic, and decyloxystilbazole only shows an ordered Smectic E phase, four out of the five hydrogen-bonded decyloxystilbazole complexes studied display enantiotropic smectic A or nematic mesophases. The single crystal X-ray diffraction structure of trans-[PdI₂(CNC₆H₄COOH)₂]·C₄H₈O₂ has been determined and confirms the formation of a supramolecular array in the solid state supported by hydrogen-bonding.