(Pyrazolato)gold Complexes Showing Room-Temperature Columnar Mesophases. Synthesis, Properties, and Structural Characterization

Abstract

Mesogenic (pyrazolato)gold complexes of formula [Au(pz)]3 (pz = 3,5-bis(3‘,4‘-di-n-decyloxyphenyl)pyrazole (1), 3-(3‘,4‘,5‘-tri-n-decyloxyphenyl)-5-(3‘‘,4‘‘-di-n-decyloxyphenyl)pyrazole (2), 3-(2‘,3‘,4‘-tri-n-decyloxyphenyl)-5-(3‘‘,4‘‘,5‘‘-tri-n-decyloxyphenyl)pyrazole (3), 3,5-bis(3‘,4‘,5‘-tri-n-decyloxyphenyl)pyrazole (4)) have been prepared by reaction of the potassium salts of the nonmesogenic pyrazolate ligands with [AuCl(tht)] (tht = tetrahydrothiophene) in a 1:1 molar ratio. All these compounds show columnar mesophases that remain stable, at room temperature, for long periods of time. The formation of isomers for the nonsymmetrical derivativesdetected by spectroscopic studiesare suggested to be responsible for the subtle changes observed in the transition temperatures. Powder X-ray diffraction measurements show clearly that the supramolecular columnar arrangement appears in the crystalline solids as well as in the mesomorphic phase. An analogue of the mesogenic trinuclear complexes 1−4, having a methoxy group at the phenyl substituents of the pyrazolate ligands, [Au{3,5-(MeOPh)2Pz}]3 (5), has been synthesized and characterized by an X-ray single-crystal diffraction experiment. The molecular structure of 5 is based on a nine-membered metallacycle core. The whole molecule exhibits a rough planarity that favors a crystalline structure formed from columnar arrangements of trinuclear complexes. A simple and clear relationship could be established between the solid-state crystal structure of 5 and the X-ray-deduced structure of the mesophases.