Tunable trimers: using temperature and pressure to control luminescent emission in gold(i) pyrazolate-based trimers

A systematic investigation into the relationship between the solid-state luminescence and the intermolecular AuAu 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 AuAu 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 AuAu contacts of between 0.04 and 0.08 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 AuAu 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 AuAu distance observed by diffraction.