Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(CHNC)Au] ions in crystals.

Non-luminescent, isostructural crystals of [(CHNC)Au](EF)·CH (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(CHNC)Au], self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(CHNC)Au] ions are isolated from one another. In [(CHNC)Au](BArF) ((BArF) is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(CHNC)Au](EF) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(CHNC)Au](EF)·CH. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(CHNC)Au](SbF)·CH that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(CHNC)Au](SbF) is formed. In the process, the distances between the gold(i) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(CHNC)Au](AsF)·CH stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(CHNC)Au](AsF) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(CHNC)Au](AsF) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph.