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
...