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 M2+ (M = Ca, Sr, Ba) and [AuF6]- (molar ratio 1:2) gave [Ca(HF)(2)](AuF6)(2), [Sr(HF)]-(AuF6)(2), and Ba[Ba(HF)](6)(AuF6)(14). [Ca(HF)(2)](AuF6)(2) exhibits a layered structure in which [Ca(HF)(2)](2+) cations are connected by AuF6 units, while the crystal structure of Ba[Ba(HF)](6)(AuF6)(14) exhibits a complex three-dimensional (3-D) network consisting of Ba2+ and [Ba(HF)(2)](2+) cations bridged by AuF6 groups. These results indicate that the previously reported M(AuF6)(2) (M = Ca, Sr, Ba) compounds, prepared in the anhydrous HF, do not in fact correspond to this chemical formula. When the initial M2+/ [AuF6](-) ratio was 1:1, single crystals of [M(HF)](H3F4)(AuF6) were grown for M = Sr. The crystal structure consists of a 3-D framework formed by [Sr(HF)](2+) cations associated with [AuF6]- and [H3F4](-) anions. The latter exhibits a Z-shaped conformation, which has not been observed before. Single crystals of M(BF4)(AuF6) (M = Sr, Ba) were grown when a small amount of BF3 was present during crystallization. Sr(BF4)(AuF6) crystallizes in two modifications. A high-temperature alpha-phase (293 K) crystallized in an orthorhombic unit cell, and a low-temperature beta-phase (150 K) crystallized in a monoclinic unit cell. For Ba(BF4)(AuF6), only an orthorhombic modification was observed in the range 80-230 K. An attempt to grow crystals of Ca(BF4)(AuF6) failed. Instead, crystals of [Ca(HF)](BF4)(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 [AuF4](-) byproducts, as shown by the single-crystal growth of [Ba(HF)](4)(AuF4)(AuF6)(7). Its crystal structure consists of [Ba(HF)](2+) cations connected by AuF6 octahedra and square-planar AuF4 units. The crystal structure of the minor product [O-2](2)[Sr(HF)]5[AuF6](12).HF was also determined.

Automated summary

Crystal growth from anhydrous HF solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]- (molar ratio 1:2) produced various compounds with different crystal structures. The crystal structures exhibit diversity, including layered structure and three-dimensional networks. It is found that the previously reported compounds M(AuF6)(2) do not correspond to the reported chemical formula. Additionally, crystal structures of some byproducts were observed.