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Sodium metaborate
Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula NaBO2. However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is Na3B3O6 or (Na+)3[B3O6]3−. The formula can be written also as Na2O·B2O3 to highlight the relation to the main oxides of sodium and boron. The name is also applied to several hydrates whose formulas can be written NaBO2·nH2O for various values of n.
The anhydrous and hydrates are colorless crystalline solids. The anhydrous form is hygroscopic.
The following hydrates crystallize from solutions of the proper composition in various temperature ranges:
Early reports of a monohydrate NaBO2·H2O have not been confirmed.
Solid anhydrous sodium metaborate has the hexagonal crystal system with space group . It actually contains a six-membered rings with the formula [B3O6]3−, consisting of alternating boron and oxygen atoms with one negatively charged extra oxygen atom attached to each boron atom. All nine atoms lie on a plane. The six oxygen atoms are evenly divided into two distinct structural sites, with different B–O bond lengths: B–O(external) 128.0 pm and B–O(bridge) 143.3 pm. The density is 2.348 ± 0.005 g/cm3. The approximate dimensions of the hexagonal cell are a = 1275 pm, c = 733 pm. However, the true unit cell is rhombohedral and has dimensions: ar= 776 pm, α = 110.6°, Z = 6 (5.98) molecules KB0
The dihydrate NaBO2·2H2O crystallizes in the triclinic crystal system, but is nearly monoclinic, with both α and γ very close to 90°. The cell parameters are a = 678 pm , b = 1058A pm, c = 588 pm, α = 91.5°, β = 22.5°, γ = 89°, Z = 4, density 1.905 g/cm3. The refractive indices at 25°C and wavelength 589.3 nm are α = 1.439, β = 1.473, γ = 1.484. The dispersion is strong, greater at red than at violet.
The transition temperature between the dihydrate and the hemihydrate is 54 °C. However, the crystalline dihydrate will remain metastable until 106 °C to 110 °C, and change slowly above that temperature.
Infrared spectroscopy of the vapor from anhydrous sodium metaborate, heated to between 900 °C and 1400 °C, shows mostly isolated clusters with formula NaBO2, and some dimers thereof. Electron diffraction studies by Akishin and Spiridonov showed a structure O=B−O−Na with linear anion O=B−O− and angle B−O−Na of 90-110°. The atomic distances are O=B: 120 pm, B−O: 136 pm,O−Na: 214 pm
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Sodium metaborate
Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula NaBO2. However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is Na3B3O6 or (Na+)3[B3O6]3−. The formula can be written also as Na2O·B2O3 to highlight the relation to the main oxides of sodium and boron. The name is also applied to several hydrates whose formulas can be written NaBO2·nH2O for various values of n.
The anhydrous and hydrates are colorless crystalline solids. The anhydrous form is hygroscopic.
The following hydrates crystallize from solutions of the proper composition in various temperature ranges:
Early reports of a monohydrate NaBO2·H2O have not been confirmed.
Solid anhydrous sodium metaborate has the hexagonal crystal system with space group . It actually contains a six-membered rings with the formula [B3O6]3−, consisting of alternating boron and oxygen atoms with one negatively charged extra oxygen atom attached to each boron atom. All nine atoms lie on a plane. The six oxygen atoms are evenly divided into two distinct structural sites, with different B–O bond lengths: B–O(external) 128.0 pm and B–O(bridge) 143.3 pm. The density is 2.348 ± 0.005 g/cm3. The approximate dimensions of the hexagonal cell are a = 1275 pm, c = 733 pm. However, the true unit cell is rhombohedral and has dimensions: ar= 776 pm, α = 110.6°, Z = 6 (5.98) molecules KB0
The dihydrate NaBO2·2H2O crystallizes in the triclinic crystal system, but is nearly monoclinic, with both α and γ very close to 90°. The cell parameters are a = 678 pm , b = 1058A pm, c = 588 pm, α = 91.5°, β = 22.5°, γ = 89°, Z = 4, density 1.905 g/cm3. The refractive indices at 25°C and wavelength 589.3 nm are α = 1.439, β = 1.473, γ = 1.484. The dispersion is strong, greater at red than at violet.
The transition temperature between the dihydrate and the hemihydrate is 54 °C. However, the crystalline dihydrate will remain metastable until 106 °C to 110 °C, and change slowly above that temperature.
Infrared spectroscopy of the vapor from anhydrous sodium metaborate, heated to between 900 °C and 1400 °C, shows mostly isolated clusters with formula NaBO2, and some dimers thereof. Electron diffraction studies by Akishin and Spiridonov showed a structure O=B−O−Na with linear anion O=B−O− and angle B−O−Na of 90-110°. The atomic distances are O=B: 120 pm, B−O: 136 pm,O−Na: 214 pm