(PYRAZOLATO)GOLD COMPLEXES SHOWING ROOM-TEMPERATURE COLUMNAR MESOPHASES - SYNTHESIS, PROPERTIES, AND STRUCTURAL CHARACTERIZATION

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-decyloxy phenyl)-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 prepar ed by reaction of the potassium salts of the nonmesogenic pyrazolate l igands with [AuCl(tht)] (tht = tetrahydrothiophene) in a 1:1 molar rat io. All these compounds show columnar mesophases that remain stable, a t room temperature, for long periods of time. The formation of isomers for the nonsymmetrical derivatives-detected by spectroscopic studies- are suggested to be responsible for the subtle changes observed in the transition temperatures. Powder X-ray diffraction measurements show c learly that the supramolecular columnar arrangement appears in the cry stalline solids as well as in the mesomorphic phase. An analogue of th e mesogenic trinuclear complexes 1-4, having a methoxy group at the ph enyl substituents of the pyrazolate ligands, [Au{3,5-(MeOPh)(2)Pz}](3) (5), has been synthesized and characterized by an X-ray single-crysta l diffraction experiment. The molecular structure of 5 is based on a n ine-membered metallacycle core. The whole molecule exhibits a rough pl anarity that favors a crystalline structure formed from columnar arran gements 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.