Mazej Z, Goreshnik E. Crystal Growth from Anhydrous HF Solutions of M
2+ (M = Ca, Sr, Ba) and [AuF
6]
-, Not Only Simple M(AuF
6)
2 Salts.
Inorg Chem 2022;
61:10587-10597. [PMID:
35770501 PMCID:
PMC9377525 DOI:
10.1021/acs.inorgchem.2c01675]
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Abstract
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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.
Crystal
growth from anhydrous HF solutions of M2+ (M = Ca, Sr,
Ba) and [AuF6]− (molar
ratio 1:2) gave [Ca(HF)2](AuF6)2 and
Ba[Ba(HF)]6(AuF6)14. These results
indicate that the previously reported M(AuF6)2 (M = Ca, Sr, Ba) compounds do not correspond to this chemical formula.
When the initial Sr2+/[AuF6]− ratio was 1:1, crystals of [Sr(HF)](H3F4)(AuF6) were grown. Single crystals of M(BF4)(AuF6) (M = Sr, Ba) were obtained when a small amount of BF3 was present during crystallization. The crystal structures
of [Ba(HF)]4(AuF4)(AuF6)7, [O2]2[Sr(HF)]5[AuF6]12·HF, and Ca(BF4)(AuF6) byproducts
were also determined.
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