(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 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 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.

Silver Pyrazolates as Coordination‐Polymer Luminescent Metallomesogens

“…Indeed, gold(I) complexes of these ligands are trinuclear metallacycles [AuA C H T U N G T R E N N U N G (m-pz)] 3 that show thermodynamically stable columnar mesophases. [18,19] More recently, we have shown that the polycatenar pyrazolates are compatible with different coordination geometries and room-temperature mesophases have been described for coordination compounds with square-planar rhodium(I) or tetrahedral zinc(II); thus, these ligands are very useful for promoting columnar mesomorphism. [20,21] We describe herein a number of silver metallomesogens that exhibit columnar liquid-crystal phases and also report on the different and unexpected behavior compared to the analogous gold complexes.…”

“…A decrease in the clearing points was found on increasing the number of chains (Table 2), a finding consistent with the behavior observed in columnar liquid crystals that contain polycatenar pyrazolates, such as the analogous gold complexes. [19] However, the liquid-crystalline phases of the silver analogues are considerably more stable than those of the gold CTCs. ] n shows a co-A C H T U N G T R E N N U N G lumnar mesophase between room temperature and 143 8C.…”

Pyrazolato Ligands towards Gold(I) Derivatives with Aurophilic Interactions: X-Ray Structure of Bis[3,5-(dibutoxyphenyl)-1H-pyrazolato-κN1]bis(triphenylphosphine)digold(Au⋅⋅⋅Au)([Au(pzR2)(PPh3)]2; RC4H9OC6H4)

“…By considering the flat core of the anionic pyrazolato ligands, the approach of two Au I centers of molecules of the type [Au(pz R 2 )(PPh 3 )] (I) should be possible without considerable steric hindrance. Looking for molecular aggregations through Au ¥¥¥ Au contacts, we determined the crystal structure of a single crystal of [Au(pz R 2 )(PPh 3 )] 2 (R C 4 H 9 ÀOÀC 6 H 4 ; 1).…”

Self‐Assembly in Helical Columnar Mesophases and Luminescence of Chiral 1H‐Pyrazoles

“…[7][8][9][10][11][12] 1H-Pyrazoles are structural building blocks that have the potential to self-organize into a rich variety of superstructures through hydrogen bonding. [13] As part of our research program, we have studied polycatenar 3,5-diaryl-1H-pyrazoles as promesogenic ligands in coordination compounds with boron, [14,15] gold, [16,17] zinc, [18] and rhodium [19] in order to obtain columnar mesophases. All of the complexes reported were liquid crystalline, despite the variety of shapes and geometries, with the mesophases obtained at room temperature in most cases.…”