Role of Anions and Mixtures of Anions on the Thermochromism, Vapochromism, and Polymorph Formation of Luminescent Crystals of a Single Cation, [(CHNC)Au].

Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(CHNC)Au]. Thus whereas the yellow polymorphs of [(CHNC)Au](PF) and [(CHNC)Au](AsF) contain single chains of cations and are vapochromic, yellow [(CHNC)Au](SbF) does not form the same polymorph and is not vapochromic but contains two distinct chains of cations connected through aurophilic interactions. Mixed crystals such as [(CHNC)Au](PF)(AsF) have been prepared by adding diethyl ether to a dichloromethane solution containing equimolar amounts of [(CHNC)Au](PF) and [(CHNC)Au](AsF). The initial (kinetic) product for the three combinations of anions ((PF)/(AsF), (PF)/(SbF), and (AsF)/(SbF)) was a precipitate of fine yellow needles with a green emission, which were gradually transformed at rates that depended on the anions present into colorless crystals with a blue emission. Whereas neither polymorph of [(CHNC)Au](PF) nor [(CHNC)Au](SbF) is thermochromic, the colorless mixed crystal [(CHNC)Au](PF)(SbF) is thermochromic and converts from blue-emitting to green-emitting at 87-95 °C. The temperature required to transform a crystal of the type [(CHNC)Au](PF)(AsF) from colorless (blue-emitting) to yellow (green-emitting) increases as the fraction of hexafluorophosphate ion in the crystal increases. The yellow crystals of [(CHNC)Au](PF)(AsF), [(CHNC)Au](PF)(AsF), and [(CHNC)Au](PF)(AsF) are vapochromic, whereas the yellow crystals of [(CHNC)Au](PF)(SbF) and [(CHNC)Au](AsF)(SbF) are not.