Synthesis, properties, and structure of LiAuI4 and KAuI4 with a discussion of the crystal chemical relationship between the halogenoaurates RbAuCl4, AgAuCl4, RbAuBr4 and LiAuI4

Article abstract of DOI:10.1002/zaac.19976231122

The alkalimetal iodo aurates(III) MAuI₄ (M = Li, K) are obtained in form of single crystals from MI, Au and I₂ in a sealed glass ampoule by heating to 550°C and slow cooling to 300°C. KAuI₄ crystallizes in the monoclinic space group P2₁/c with a = 968.6(4); b = 704.5(2), c = 1393.2(7) pm; β = 100.95(2)° and Z = 4. The crystal structure is built up from square planar AuI₄^- anions and K⁺ cations. The cations are coordinated by eight I atoms of neighbouring AuI₄^- anions with distances K-I between 350.0 and 369.6 pm. At 100°C KAuI₄ is reduced to form K₃Au₃I₈, which at 180°C decomposes to KI, Au and I₂. LiAuI₄ forms black, moisture sensitive needles, decomposing in the absence of iodine at 20°C to LiI, Au and I₂. It crystallizes in a variant of the RbAuBr₄ type structure with the space group P2₁/a and a = 1511.7(4); b = 433.9(4); c = 710.0(2) pm; β = 121.50(2)°; Z = 2. The crystal chemical relationship between the structures of RbAuCl₄, RbAuBr₄, AgAuCl₄ and LiAuI₄ is discussed.