Perchloratoborate
is an
anion
of the form [B(ClO
4
)
4
]
?
. It can form partly stable solid
salts
with heavy
alkali metals
. They are more stable than
nitratoborate
salts.
[1]
K[B(ClO
4
)
4
] decomposes at 35 °C, Rb[B(ClO
4
)
4
] is stable to 50 °C, and Cs[B(ClO
4
)
4
] can exist up to 80 °C.
[2]
Perchloratoborates are analogous to
perchloratoaluminates
([Al(ClO
4
)
4
]
?
).
Another related anion is the chloroperchloratoborate, Cl
3
B(ClO
4
).
[3]
Boron
perchlorate
itself is unstable above ?5 °C.
[4]
Decomposition
[
edit
]
On
thermal decomposition
the alkali perchloratoborate salts form an alkali perchlorate, and
boron trioxide
as a solid residue, and gas containing
dichlorine heptoxide
,
chlorine dioxide
,
chlorine
, and oxygen.
- 2 M[B(ClO
4
)
4
] → 2 MClO
4
+ B
2
O
3
+ (3 Cl
2
O
7
or 6 ClO
2
+
4
+
1
/
2
O
2
or 6 Cl
2
+
10
+
1
/
2
O
2
)
[2]
When the alkali perchloratoborates first start to decompose at the lower temperatures, the reaction is endothermic, and dichlorine heptoxide is formed. However, if caesium perchloratoborate is heated the decomposition becomes exothermic above 90 °C, and at 100 °C it explodes exothermically forming chlorine and oxygen.
[2]
Reactions
[
edit
]
When rubidium perchloratoborate is reacted with extra
perchloric acid
, it forms RbBO(ClO
4
)
2
.
[5]
In water, alkali perchloratoborates decompose exothermically to form
boric acid
, perchloric acid, and the perchlorate.
[5]
Formation
[
edit
]
Nitronium perchloratoborate (NO
2
B(ClO
4
)
4
)can be formed by reacting
nitronium perchlorate
with
boron trichloride
in solution. Similarly
ammonium perchlorate
reacts with BCl
3
forming ammonium perchloratoborate.
[5]
The metal perchloratoborates can also be formed from the metal perchlorate dissolved in anhydrous
perchloric acid
reacting with boron trichloride. Another way is to react a metal
chloridoborate
(MBCl
4
) with perchloric acid. Chloridoborates can be made from the metal chloride and boron trichloride dissolved in
nitrosyl chloride
.
[5]
Extra Cl
2
O
7
drives the reaction forward.
[5]
- BCl
3
+ 3HClO
4
→ B(ClO
4
)
3
Also formed is BCl
2
ClO
4
and BCl(ClO
4
)
2
which
disproportionates
above ?78 °C to the boron perchlorate and dichloroboron perchlorate.
[6]
- B(ClO
4
)
3
+
ClO
?
4
→
B(ClO
4
)
?
4
Properties
[
edit
]
Caesium perchloratoborate is hygroscopic.
[4]
It has a density of 2.5 g/cm
3
.
[4]
It has no colour.
[4]
Infrared absorption bands are observed in caesium perchloratoborate at 640 and 1,087 cm
?1
.
[4]
Potassium perchloratoborate has density 2.18 g/cm
3
, and rubidium perchloratoborate has density 2.32 g/cm
3
.
[5]
The three alkali perchloratoborates fume in moist air, are all crystalline and colourless.
[5]
References
[
edit
]
- ^
Titova, K. V.; V. Ya. Rosolovskii (1975). "Reaction of nitrates of monovalent cations with BCl
3
".
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science
.
24
(10): 2246?2248.
doi
:
10.1007/BF00929774
.
ISSN
0568-5230
.
- ^
a
b
c
Babaeva, V. P.; V. Ya. Rosolovskii (1974). "Thermal decomposition of perchloratoborates of the alkali metals".
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science
.
23
(3): 477?481.
doi
:
10.1007/BF00921126
.
ISSN
0568-5230
.
- ^
Titova, K. V.; V. Ya. Rosolovskii (1974). "Tetraalkylammonium chloroperchloratoborates".
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science
.
23
(10): 2092?2095.
doi
:
10.1007/BF00921261
.
ISSN
0568-5230
.
- ^
a
b
c
d
e
Rosolovskii, V. Ya.; V. P. Babaeva (1971). "Some properties of cesium perchloratoborate".
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science
.
20
(4): 792?794.
doi
:
10.1007/BF00853930
.
ISSN
0568-5230
.
- ^
a
b
c
d
e
f
g
Babaeva, V. P.; V. Ya. Rosolovskii (1973). "Alkali metal perchloratoborates".
Bulletin of the Academy of Sciences of the USSR Division of Chemical Science
.
22
(3): 476?479.
doi
:
10.1007/BF00854006
.
ISSN
0568-5230
.
- ^
Pascal, Jean-Louis; Frederic Favier (1998). "Inorganic perchlorato complexes".
Coordination Chemistry Reviews
. 178?180: 865?902.
doi
:
10.1016/S0010-8545(98)00102-7
.
ISSN
0010-8545
.