Cation and hydrogen bonding effects on the self-association and luminescence of the dicyanoaurate ion, [Au(CN)2]−

Abstract

The colorless salts [C₅H₁₀NH₂][Au^I(CN)₂], [C₄H₈NH₂][Au^I(CN)₂], [Ph₂NNH₃][Au^I(CN)₂]·H₂O and [(n-C₃H₇)₄N][Au^I(CN)₂]·H₂O have been prepared by evaporation of aqueous solutions of potassium dicyanoaurate and the chloride salt of the appropriate cation. Hydrogen bonding between the cations and the cyano groups of the anions facilitates the formation of structures with strong aurophilic interactions between the anions. Thus, the [Au(CN)₂]⁻ ions self-associate in the three salts [C₅H₁₀NH₂][Au^I(CN)₂] (Au⋯Au 3.0969(3) Å), [C₄H₈NH₂][Au^I(CN)₂] (Au1⋯Au2 3.0795(4) Å), [Ph₂NNH₃][Au^I(CN)₂]·H₂O (Au⋯Au 3.0866(4) Å), while in [(n-C₃H₇)₄N][Au^I(CN)₂]·H₂O, which lacks N–H units, the gold ions are widely dispersed. The crystals of [C₅H₁₀NH₂][Au^I(CN)₂], [C₄H₈NH₂][Au^I(CN)₂] and [Ph₂NNH₃][Au^I(CN)₂]·H₂O each show strong blue luminescence at room temperature, while [(n-C₃H₇)₄N][Au^I(CN)₂]·H₂O is non-luminescent.