Sodium Tetraazidoaurate(III)—From Na[AuCl ₄ ]·2H ₂ O to Na[Au(N ₃ ) ₄ ] and Beyond One Step at a Time

The novel sodium tetrachlorido-/azidoaurate(III) dihydrates Na[AuCl₄₋ x(N₃)x]·2H₂O (x = 0, 1, 2, 3, 4) provide the first example of a complete series of gradual substitution on square planar complex anions to be described. Transparent yellow to dark orange single crystals of these phases were synthesized by reaction of NaN₃ and AuCl₃ or HAuCl₄ in different molar ratios from aqueous solution. Controlled dehydration of Na[Au(N₃)₄]·2H₂O led to Na[Au(N₃)₄]·H₂O and Na[Au(N₃)₄] in form of orange microcrystalline powders, the latter being a highly explosive material. Predominant structural features of all phases are discrete anions [AuCl₄₋ x(N₃)x]⁻ with gold in an ordered square planar coordination of azide/chloride anions. Vibrational spectra show good agreement with other known azidoaurates(III).