Assisted self-association of dicyanoaurate, [Au(CN)2]−, and dicyanoargentate, [Ag(CN)2]−, through hydrogen bonding to metal ammonia complexes

The salts – yellow [Cr(NH3)6][Ag(CN)2]3 · 2H2O, red [Co(NH3)6][Ag(CN)2]3 · 2H2O, red [Co(NH3)6][Au(CN)2]3 · 2H2O, pale yellow [Ru(NH3)6][Ag(CN)2]3 · 2H2O, yellow K[Cr(NH3)6]2[Au(CN)2]7 · 4H2O, and colorless [(μ2-NH2)2Pt2(NH3)10][Au(CN)2]6 · 5.5{OS(CH3)2} · 0.5H2O – have been prepared by evaporation of aqueous solutions of potassium dicyanoargenate or potassium dicyanoaurate and salts of the appropriate cations. Hydrogen bonding between the cations and the cyano groups of the anions facilitates the formation of structures with strong metallophilic interactions between the anions. Thus, the [Au(CN)2]− or [Ag(CN)2]− ions self-associate into linear trimers in the isostructural set of crystals, [Cr(NH3)6][Ag(CN)2]3 · 2H2O (Ag⋯Ag distance; 3.1610(4) Å), [Co(NH3)6][Ag(CN)2]3 · 2H2O (Ag⋯Ag distance; 3.1557(2) Å), [Co(NH3)6][Au(CN)2]3 · 2H2O (Au⋯Au distance; 3.0939(4) Å), and [Ru(NH3)6][Ag(CN)2]3 · 2H2O (Ag⋯Ag distance; 3.1584(5) Å). Crystalline [(μ2-NH2)2Pt2(NH3)10][Au(CN)2]6 · 5.5{OS(CH3)2} · 0.5H2O also contains nearly linear trimers of the dicyanoaurate ion. Yellow crystals of K[Cr(NH3)6]2[Au(CN)2]7 · 4H2O contain a centrosymmetric, bent chain of seven dicyanoaurate ions with Au⋯Au separations of 3.1806(3), 3.2584(4), and 3.1294(4) Å.

Graphical abstractAggregation of [Ag(CN)2]− and Au(CN)2]− in salts with metal amine cations (e.g. [Co(NH3)6][Ag(CN)2]3 · 2H2O) has been examined crystallographically.Figure optionsDownload full-size imageDownload as PowerPoint slide