borane (B 2 H 6 ): see formula. Other boranes include B 4 H 10 , B 5 H 9 , B 5 H 11 ,
B 6 H 10 , and B 10 H 4 . The larger borane
molecules have open or closed polyhedra of boron atoms. In addition,
there is a wide range of borane derivatives containing atoms of other elements, such as carbon and
phosphorus. Borohydride ions of the
type B 6 H 6
2– also exist. Boranes and
borohydride ions are classiÜed according to their structure. Those
with a complete polyhedron are said
to have a closo-structure. Those in
which the polyhedron is incomplete
by loss of one vertex have a nidostructure (from the Greek for ‘nest’).
Those with open structures by removal of two or more vertices have
an arachno structure (from the Greek
for ‘spider’). See also wade’s rules.
borate Any of a wide range of ionic
compounds that have negative ions
containing boron and oxygen (see
formulae). Lithium borate, for example, contains the simple anion
B(OH) 4
–
. Most borates, however, are
inorganic polymers with rings,
chains, or other networks based on
the planar BO 3 group or the tetrahedral BO 3 (OH) group. ‘Hydrated’ borates are ones containing –OH
groups; many examples occur naturally. Anhydrous borates, which contain BO 3 groups, can be made by
melting together boric acid and
metal oxides.
borax (disodium tetraborate-10water) A colourless monoclinic solid,
Na 2 B 4 O 7 .10H 2 O, soluble in water and
very slightly soluble in ethanol; monoclinic; r.d. 1.73; loses 8H 2 O at 75°C;
loses 10H 2 O at 320°C. The formula
gives a misleading impression of the
structure. The compound contains
the ion [B 4 O 5 (OH) 4 ]
2– (see borate).
Attempts to recrystallize this compound above 60.8°C yield the pentahydrate. The main sources are the
borate minerals kernite (Na 2 B 4 O 7 .
4H 2 O) and tincal (Na 2 B 4 O 7 .10H 2 O).
The ores are puriÜed by carefully
controlled dissolution and recrystallization. On treatment with mineral
acids borax gives boric acid.
Borax is a very important substance in the glass and ceramics industries as a raw material for making
borosilicates. It is also important as a
metallurgical Ûux because of the abilborate
78
b
O –
O
O –
B
B
O
O
B
O –
B 3 O 3 –
6
as in Na 3 B 3 O 6
B
O –
O
B
O –
O
B
O –
(BO 2 )
n–
n as in CaB 2 O 4
HO
B
O
O
B –
OH
O
B
OH
B –
O
OH
O
[B 4 O 5 (OH) 4 ] 2–
as in borax Na 2 B 4 O 7 . 10H 2 O
Borate
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B 6 H 10 , and B 10 H 4 . The larger borane
molecules have open or closed polyhedra of boron atoms. In addition,
there is a wide range of borane derivatives containing atoms of other elements, such as carbon and
phosphorus. Borohydride ions of the
type B 6 H 6
2– also exist. Boranes and
borohydride ions are classiÜed according to their structure. Those
with a complete polyhedron are said
to have a closo-structure. Those in
which the polyhedron is incomplete
by loss of one vertex have a nidostructure (from the Greek for ‘nest’).
Those with open structures by removal of two or more vertices have
an arachno structure (from the Greek
for ‘spider’). See also wade’s rules.
borate Any of a wide range of ionic
compounds that have negative ions
containing boron and oxygen (see
formulae). Lithium borate, for example, contains the simple anion
B(OH) 4
–
. Most borates, however, are
inorganic polymers with rings,
chains, or other networks based on
the planar BO 3 group or the tetrahedral BO 3 (OH) group. ‘Hydrated’ borates are ones containing –OH
groups; many examples occur naturally. Anhydrous borates, which contain BO 3 groups, can be made by
melting together boric acid and
metal oxides.
borax (disodium tetraborate-10water) A colourless monoclinic solid,
Na 2 B 4 O 7 .10H 2 O, soluble in water and
very slightly soluble in ethanol; monoclinic; r.d. 1.73; loses 8H 2 O at 75°C;
loses 10H 2 O at 320°C. The formula
gives a misleading impression of the
structure. The compound contains
the ion [B 4 O 5 (OH) 4 ]
2– (see borate).
Attempts to recrystallize this compound above 60.8°C yield the pentahydrate. The main sources are the
borate minerals kernite (Na 2 B 4 O 7 .
4H 2 O) and tincal (Na 2 B 4 O 7 .10H 2 O).
The ores are puriÜed by carefully
controlled dissolution and recrystallization. On treatment with mineral
acids borax gives boric acid.
Borax is a very important substance in the glass and ceramics industries as a raw material for making
borosilicates. It is also important as a
metallurgical Ûux because of the abilborate
78
b
O –
O
O –
B
B
O
O
B
O –
B 3 O 3 –
6
as in Na 3 B 3 O 6
B
O –
O
B
O –
O
B
O –
(BO 2 )
n–
n as in CaB 2 O 4
HO
B
O
O
B –
OH
O
B
OH
B –
O
OH
O
[B 4 O 5 (OH) 4 ] 2–
as in borax Na 2 B 4 O 7 . 10H 2 O
Borate
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