[B 4 O 6 (OH) 2 ]
2− in which the trigonal hydroxyl of a [B 4 O 5 (OH) 4 ]
2− ion has condensed with a tetrahedral hydroxyl of another to eliminate water [23]. The anhydrous sodium diborate (1:2:0) consists of single and spiro-fused double
6-membered rings [24]. The single rings are linked to double rings, which are
linked together with oxide bridges.
Ezcurrite (2:5:7) consists of chains of [B 5 O 6 (OH) 4 ]
− ions which have condensed
to give two tetrahedral and three trigonal boron atoms [25]. Nasinite (2:5:5) consists
of sheets of [B 5 O 6 (OH) 4 ]
− ions which have condensed to give two tetrahedral and
three trigonal boron atoms [26]. The structure was refined further [27] and a very
similar structure identified [28]. Biringuccite (2:5:3) consists of sheets of condensed
spiro-B 5 O 6 units containing three trigonal and two tetrahedral boron atoms [29].
Ameghinite (1:3:4) consists of monomeric [B 3 O 3 (OH) 4 ]
− ions [30]. Anhydrous
α-sodium triborate (1:3:0) contains both a spiro-fused double 6-membered ring and
a tetraborate core, which link to each other by oxo groups [31]. The β-modification
consists of the spiro-fused double 6-membered ring, a simple 6-membered ring, and
a standalone BO 4 tetrahedra [32]. Anhydrous sodium tetraborate (1:4:0) consists of
layers of single and spiro-fused double 6-membered rings [33]. The single rings are
linked to the double rings, which are linked together with oxide bridges. Both
sborgite, NaB 5 O 8 ⋅ 5H 2 O (1:5:10) [34], and its dehydrated form of sodium
pentaborate (1:5:4) [35], consist of discrete [B 5 O 6 (OH) 4 ]
− ions containing one
tetrahedral and four trigonal boron atoms.
To summarize these results, the following discrete polyborate ions (as a sodium
salt) are known in the solid phase. The trinuclear [B 3 O 3 (O)(OH) 4 ]
3−
,
[B 3 O 3 (O) 2 (OH) 2 ]
3−
, [B 3 O 3 (O) 3 ]
3−
, and [B 3 O 3 (OH) 4 ]
− all contain the B 3 O 3 core.
The tetranuclear [B 4 O 5 (OH) 4 ]
2− contains the B 4 O 5 core. The pentanuclear
[B 5 O 6 (OH) 4 ]
− contains the B 5 O 6 core (two B 3 O 3 cores spiro fused at a boron). The
dodecanuclear [B 12 O 20 (OH) 4 ]
8− containing the B 12 O 18 core (six B 3 O 3 cores spiro
fused into a macrocycle). Upon dehydration, typically chains or sheets of condensed units form (sometimes more than one unit is present). Some plausible
species not observed to date in sodium salts are: BO(OH) 2
− , any dinuclear species;
[B 3 O 3 (OH) 6 ]
3− , or [B 3 O 3 (OH) 5 ]
2− ; [B 4 O 5 (OH) 6 ]
3−
, or [B 4 O 5 (OH) 5 ]
2−
;
[B 5 O 6 (OH) 6 ]
3− , or [B 5 O 6 (OH) 5 ]
2−
.
The crystal structures of numerous potassium borates are given in Table 2. The
previously described discrete ions [B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2− , [B 3 O 3 (OH) 4 ]
−
, and
[B 5 O 6 (OH) 4 ]
− , are all represented. The only new borate anion appearing is
[B 12 O 16 (OH) 8 ]
4- . For lithium borates (Table 3), only the previously-mentioned
discrete ion [B(OH) 4 ]
− is found, but two new ions, B 2 O 5
4− and B 4 O 9
6−
, appear. For
rubidium borates (Table 4), the previously mentioned discrete ions [B 3 O 4 (OH) 4 ]
3−
,
[B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2−
, and [B 5 O 6 (OH) 4 ]
− are represented, and the new ion
[B 7 O 9 (OH) 5 ]
2− ion appears. For cesium borates (Table 5), the previously discussed
[B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2− and [B 5 O 6 (OH) 4 ]
− ions are represented, but no new ions
have been found. Condensation of the triborate, tetraborate, and pentaborate into
chains and sheets is quite common as the water content of the borates decrease.
Conversely, hydration/dissolution of the water-poor solids might be expected
112
C. C. Pye
2− in which the trigonal hydroxyl of a [B 4 O 5 (OH) 4 ]
2− ion has condensed with a tetrahedral hydroxyl of another to eliminate water [23]. The anhydrous sodium diborate (1:2:0) consists of single and spiro-fused double
6-membered rings [24]. The single rings are linked to double rings, which are
linked together with oxide bridges.
Ezcurrite (2:5:7) consists of chains of [B 5 O 6 (OH) 4 ]
− ions which have condensed
to give two tetrahedral and three trigonal boron atoms [25]. Nasinite (2:5:5) consists
of sheets of [B 5 O 6 (OH) 4 ]
− ions which have condensed to give two tetrahedral and
three trigonal boron atoms [26]. The structure was refined further [27] and a very
similar structure identified [28]. Biringuccite (2:5:3) consists of sheets of condensed
spiro-B 5 O 6 units containing three trigonal and two tetrahedral boron atoms [29].
Ameghinite (1:3:4) consists of monomeric [B 3 O 3 (OH) 4 ]
− ions [30]. Anhydrous
α-sodium triborate (1:3:0) contains both a spiro-fused double 6-membered ring and
a tetraborate core, which link to each other by oxo groups [31]. The β-modification
consists of the spiro-fused double 6-membered ring, a simple 6-membered ring, and
a standalone BO 4 tetrahedra [32]. Anhydrous sodium tetraborate (1:4:0) consists of
layers of single and spiro-fused double 6-membered rings [33]. The single rings are
linked to the double rings, which are linked together with oxide bridges. Both
sborgite, NaB 5 O 8 ⋅ 5H 2 O (1:5:10) [34], and its dehydrated form of sodium
pentaborate (1:5:4) [35], consist of discrete [B 5 O 6 (OH) 4 ]
− ions containing one
tetrahedral and four trigonal boron atoms.
To summarize these results, the following discrete polyborate ions (as a sodium
salt) are known in the solid phase. The trinuclear [B 3 O 3 (O)(OH) 4 ]
3−
,
[B 3 O 3 (O) 2 (OH) 2 ]
3−
, [B 3 O 3 (O) 3 ]
3−
, and [B 3 O 3 (OH) 4 ]
− all contain the B 3 O 3 core.
The tetranuclear [B 4 O 5 (OH) 4 ]
2− contains the B 4 O 5 core. The pentanuclear
[B 5 O 6 (OH) 4 ]
− contains the B 5 O 6 core (two B 3 O 3 cores spiro fused at a boron). The
dodecanuclear [B 12 O 20 (OH) 4 ]
8− containing the B 12 O 18 core (six B 3 O 3 cores spiro
fused into a macrocycle). Upon dehydration, typically chains or sheets of condensed units form (sometimes more than one unit is present). Some plausible
species not observed to date in sodium salts are: BO(OH) 2
− , any dinuclear species;
[B 3 O 3 (OH) 6 ]
3− , or [B 3 O 3 (OH) 5 ]
2− ; [B 4 O 5 (OH) 6 ]
3−
, or [B 4 O 5 (OH) 5 ]
2−
;
[B 5 O 6 (OH) 6 ]
3− , or [B 5 O 6 (OH) 5 ]
2−
.
The crystal structures of numerous potassium borates are given in Table 2. The
previously described discrete ions [B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2− , [B 3 O 3 (OH) 4 ]
−
, and
[B 5 O 6 (OH) 4 ]
− , are all represented. The only new borate anion appearing is
[B 12 O 16 (OH) 8 ]
4- . For lithium borates (Table 3), only the previously-mentioned
discrete ion [B(OH) 4 ]
− is found, but two new ions, B 2 O 5
4− and B 4 O 9
6−
, appear. For
rubidium borates (Table 4), the previously mentioned discrete ions [B 3 O 4 (OH) 4 ]
3−
,
[B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2−
, and [B 5 O 6 (OH) 4 ]
− are represented, and the new ion
[B 7 O 9 (OH) 5 ]
2− ion appears. For cesium borates (Table 5), the previously discussed
[B 3 O 6 ]
3−
, [B 4 O 5 (OH) 4 ]
2− and [B 5 O 6 (OH) 4 ]
− ions are represented, but no new ions
have been found. Condensation of the triborate, tetraborate, and pentaborate into
chains and sheets is quite common as the water content of the borates decrease.
Conversely, hydration/dissolution of the water-poor solids might be expected
112
C. C. Pye