Remarkable Variations in the Luminescence of Frozen Solutions of [Au{C(NHMe)₂}₂](PF₆)·0.5(Acetone). Structural and Spectroscopic Studies of the Effects of Anions and Solvents on Gold(I) Carbene Complexes

The unusual luminescence behavior of the two-coordinate gold(I) carbene complex, [Au{C(NHMe)2}2](PF6)·0.5(acetone), is reported. Upon freezing in a liquid N2 bath, the colorless, nonluminescent solutions of [Au{C(NHMe)2}2](PF6)·0.5(acetone) become intensely luminescent. Strikingly, the colors of the emission differ in different solvents and appear only after the solvent has frozen. Solid [Au{C(NHMe)2}2](PF6)·0.5(acetone) is also luminescent, and the luminescence is attributed to the formation of extended chains of gold(I) centers that are connected through aurophilic attractions. Crystallographic studies of [Au{C(NHMe)2}2](PF6)·0.5(acetone) and [Au{C(NHMe)2}2](BF4), which is also luminescent, reveal that both involve extended chains of cations and that the anions are hydrogen bonded to the cations through cation N−H groups. However, these chains differ in the Au···Au separations in each and in the carbene ligand orientations. In contrast, [Au{C(NMe2)(NHMe)}2](PF6) forms a colorless, nonluminescent solid, and in that solid there are no Au···Au interactions, a factor which supports the contention that aggregated species are responsible for the luminescence of [Au{C(NHMe)2}2](PF6)·0.5(acetone) in the solid state and in frozen solutions.