Abstract
A systematic investigation into the relationship between the solid-state luminescence and the intermolecular Au⋅⋅⋅Au interactions in a series of pyrazolate-based gold(I) trimers; tris(μ2-pyrazolato-N,N′)-tri-gold(I) (1), tris(μ2-3,4,5- trimethylpyrazolato-N,N′)-tri-gold(I) (2), tris(μ2-3-methyl-5-phenylpyrazolato-N,N′)-tri-gold(I) (3) and tris(μ2-3,5-diphenylpyrazolato-N,N′)-tri-gold(I) (4) has been carried out using variable temperature and high pressure X-ray crystallography, solid-state emission spectroscopy, Raman spectroscopy and computational techniques. Single-crystal X-ray studies show that there is a significant reduction in the intertrimer Au⋅⋅⋅Au distances both with decreasing temperature and increasing pressure. In the four complexes, the reduction in temperature from 293 to 100 K is accompanied by a reduction in the shortest intermolecular Au⋅⋅⋅Au contacts of between 0.04 and 0.08 Å. The solid-state luminescent emission spectra of 1 and 2 display a red shift with decreasing temperature or increasing pressure. Compound 3 does not emit under ambient conditions but displays increasingly red-shifted luminescence upon cooling or compression. Compound 4 remains emissionless, consistent with the absence of intermolecular Au⋅⋅⋅Au interactions. The largest pressure induced shift in emission is observed in 2 with a red shift of approximately 630 cm−1 per GPa between ambient and 3.80 GPa. The shifts in all the complexes can be correlated with changes in Au⋅⋅⋅Au distance observed by diffraction.
Highlights
Homoleptic gold(I) trimers are an intriguing class of photoemissive materials
We report the first systematic solid-state study of temperature and pressure effects, and the correlation with luminescence, on a series of gold(I) trimeric complexes
Compound 2 behaves more typically, displaying a red shift from approximately 15 200 cmÀ1 to about 13 870 cmÀ1 by about 400 cmÀ1 per GPa (Figure 4 b), in agreement with the prediction that reducing the aurophilic interaction length by 0.258(2) from ambient to 3.91 GPa results in a red shift that may be attributed to a reduction in the HOMO–LUMO gap in the complex.[11]
Summary
Homoleptic gold(I) trimers are an intriguing class of photoemissive materials. They frequently possess bright phosphorescence and “hexamer” style molecular geometries that are commonly associated with the presence of Au···Au “aurophilic interactions” that dominate the solid-state chemistry of gold(I).[1]. Similar behaviour is observed in the other three compounds (see the Supporting Information).[14] The contraction coincides with the direction of intermolecular aurophilic interactions in 1–3 and reduces the distances between the gold centres by approximately 0.05 between 293–100 K (Table 2).
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