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.