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

Abstract

The unusual luminescence behavior of the two-coordinate gold(I) carbene complex, [Au[C(NHMe)(2)](2)](PF(6)) x 0.5(acetone), is reported. Upon freezing in a liquid N(2) bath, the colorless, nonluminescent solutions of [Au[C(NHMe)(2)](2)](PF(6)) x 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)](PF(6)) x 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)](PF(6)) x 0.5(acetone) and [Au[C(NHMe)(2)](2)](BF(4)), 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(NMe(2))(NHMe)](2)](PF(6)) 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)](PF(6)) x 0.5(acetone) in the solid state and in frozen solutions.

Spectroscopic Studies of “Exciplex Tuning” for Dicyanoaurate(I) Ions Doped in Potassium Chloride Crystals

“…29 More recently, Balch and co-workers have described an example in which the emission energy for frozen solutions of the complex [Au{C(NHMe) 2 } 2 ] + has been tuned to different visible colors by variation of the solvent and counterion. 46 The tuning we achieve for the dicyanoaurate(I) and dicyanoargentate(I) ions, as described above, competes favorably with all these examples and spans a wider emission energy range. …”

Remarkable Luminescence Behaviors and Structural Variations of Two-Coordinate Gold(I) Complexes

“…The structures and luminescence from these crystalline cationic or anionic gold(I) complexes can be altered by changing the counter anion or cation present. The luminescence of the two-coordinate gold(I) carbene cation, [Au I {C(NHMe) 2 } 2 ] + , whose structure is shown below in Scheme 4, offers a good example [48]. To date, four salts of this cation have been reported.…”

Polymorphism and luminescent behavior of linear, two-coordinate gold(i) complexes

“…In crystals of {Au I 3(MeN=COMe)3}, the trinuclear complexes are stacked into two types of columns, one with a prismatic stacking of the molecules, the other a disordered stack in which neighboring molecules in similar stacks are shifted by 60°. In the solid state, emission from the colorless gold carbene cation [Au I {C(NHMe)2}2] + is effected by the chemical nature of anionic counterions that are present (7,8). Solutions of this cation become intensely luminescent when they are frozen and that emission can be used to monitor the freezing point of the solution.…”