Crystal Growth from Anhydrous HF Solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]−, Not Only Simple M(AuF6)2 Salts

Crystal growth from anhydrous HF solutions of M 2+ (M = Ca, Sr, Ba) and [AuF 6 ] - (molar ratio 1:2) gave [Ca(HF) 2 ](AuF 6 ) 2 , [Sr(HF)](AuF 6 ) 2 , and Ba[Ba(HF)] 6 (AuF 6 ) 14 . [Ca(HF) 2 ](AuF 6 ) 2 exhibits a layered structure in which [Ca(HF) 2 ] 2+ cations are connected by AuF 6 units, while the crystal structure of Ba[Ba(HF)] 6 (AuF 6 ) 14 exhibits a complex three-dimensional (3-D) network consisting of Ba 2+ and [Ba(HF) 2 ] 2+ cations bridged by AuF 6 groups. These results indicate that the previously reported M(AuF 6 ) 2 (M = Ca, Sr, Ba) compounds, prepared in the anhydrous HF, do not in fact correspond to this chemical formula. When the initial M 2+ /[AuF 6 ] - ratio was 1:1, single crystals of [M(HF)](H 3 F 4 )(AuF 6 ) were grown for M = Sr. The crystal structure consists of a 3-D framework formed by [Sr(HF)] 2+ cations associated with [AuF 6 ] - and [H 3 F 4 ] - anions. The latter exhibits a Z-shaped conformation, which has not been observed before. Single crystals of M(BF 4 )(AuF 6 ) (M = Sr, Ba) were grown when a small amount of BF 3 was present during crystallization. Sr(BF 4 )(AuF 6 ) crystallizes in two modifications. A high-temperature α-phase (293 K) crystallized in an orthorhombic unit cell, and a low-temperature β-phase (150 K) crystallized in a monoclinic unit cell. For Ba(BF 4 )(AuF 6 ), only an orthorhombic modification was observed in the range 80-230 K. An attempt to grow crystals of Ca(BF 4 )(AuF 6 ) failed. Instead, crystals of [Ca(HF)](BF 4 ) 2 were grown and the crystal structure was determined. During prolonged crystallization of [AuF] 6 - salts, moisture can penetrate through the walls of the crystallization vessel. This can lead to partial reduction of Au(V) to A(III) and the formation of [AuF 4 ] - byproducts, as shown by the single-crystal growth of [Ba(HF)] 4 (AuF 4 )(AuF 6 ) 7 . Its crystal structure consists of [Ba(HF)] 2+ cations connected by AuF 6 octahedra and square-planar AuF 4 units. The crystal structure of the minor product [O 2 ] 2 [Sr(HF)] 5 [AuF 6 ] 12 ·HF was also determined.