Synthesis and Characterization of Silver(I) and Gold(I) Complexes Bearing a Pyrido-annelated N-Heterocyclic Carbene: A Rare Example of a Cocrystal Containing Two Different Gold(I) Complexes

Abstract

The cyclohexyl-substituted imidazo[1,5-a]pyridin-2-ium hexafluorophosphate, 2a, has been prepared as precursor for the respective pyrido-annelated N-heterocyclic carbene. [(NHC)2Ag]PF6, 3, has been synthesized by the reaction of 2a with AgCl=KOH in dichloromethane (DCM). Unexpectedly, the reaction of 3 with (tht)AuBr yielded both (NHC)AuBr and [(NHC)Au(tht)]PF6 which formed a 1 : 1 cocrystal (4a,b). The complexes are aggregated to infinite chains, which are governed by both π-π stacking and weak aurophilic interactions. Subsequent oxidation of the co-crystalline material with CsBr3 gave (NHC)AuBr3, 5. All compounds were characterized by NMR spectroscopy, mass spectrometry and elemental analysis. Additionally, compounds 2a and 5 were investigated by electronic spectroscopy: 2a behaves like a typical aromatic compound exhibiting absorption and fluorescence bands attributable to π-π* transitions. The Au(III) complex 5 exhibits ligand-centered fluorescence at room temperature and both ligand-centered fluorescence and a weak phosphorescence at 77 K.

Photophysical Investigation of Silver/Gold Dicyanometallates and Tetramethylammonium Networks: An Experimental and Theoretical Investigation

“…Lifetime measurements at 78 K of K 3 [Me 4 N] 2 [Au(CN) 2 ] 5 indicate the low energy emission band is phosphorescent in nature while the high energy band is fluorescence. This dual emission behavior, as illustrated in Figure , has been previously reported in other Au(I) based coordination polymers and networks , . While the 298 K emission appears to be dominated by fluorescence emission or mixed fluorescence/phosphorescence emission, cooling of the crystal clearly causes a shift where emission by phosphorescence becomes the dominant pathway.…”

Aggregation of Au(i)-complexes on amorphous substrates governed by aurophilicity

“…Such dual emission composed of fluorescence and phosphorescence is typical for gold-tagged aromatic systems. [44][45][46][47][48] Also bromine substituted naphthalene derivatives show comparable dual luminescence behaviour in nitrogen purged solutions with phosphorescence caused by intersystem crossing processes facilitated by the presence of heavy atoms. 49 Accordingly, the iodido species features a more intense phosphorescence band in relation to the fluorescence band than the bromido complex due to the enhanced heavy atom effect.…”