Crystal Growth from Anhydrous HF Solutions of M2+ (M = Ca, Sr, Ba) and [AuF6]-, Not Only Simple M(AuF6)2 Salts.
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ABSTRACT: 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 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(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 [O2]2[Sr(HF)]5[AuF6]12·HF was also determined.
SUBMITTER: Mazej Z
PROVIDER: S-EPMC9377525 | biostudies-literature | 2022 Jul
REPOSITORIES: biostudies-literature
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