Lithium metaborate

Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula LiBO₂. It is often encountered as a hydrate, LiBO₂·nH₂O, where n is usually 2 or 4. However, these formulas do not describe the actual structure of the solids.

Lithium metaborate^[1]

Names
Other names boric acid, lithium salt
Identifiers
CAS Number	13453-69-5 Y
3D model (JSmol)	Interactive image
ChemSpider	109911 Y
ECHA InfoCard	100.033.287
EC Number	236-631-5
PubChem CID	123308
CompTox Dashboard (EPA)	DTXSID50894850
InChI InChI=1S/BO2.Li/c2-1-3;/q-1;+1 Y Key: HZRMTWQRDMYLNW-UHFFFAOYSA-N Y InChI=1/BO2.Li/c2-1-3;/q-1;+1 Key: HZRMTWQRDMYLNW-UHFFFAOYAF
SMILES [Li+].[O-]B=O
Properties
Chemical formula	LiBO2
Molar mass	49.751 g/mol
Appearance	white hygroscopic monoclinic crystals
Density	2.223 g/cm3
Melting point	849 °C (1,560 °F; 1,122 K)
Solubility in water	0.89 g/100 mL (0 °C) 2.57 g/100 mL (20 °C) 11.8 g/100 mL (80 °C)
Solubility	soluble in ethanol
Thermochemistry
Heat capacity (C)	59.8 J/mol K
Std molar entropy (S⦵298)	51.3 J/mol K
Std enthalpy of formation (ΔfH⦵298)	−1022 kJ/mol
Std enthalpy of combustion (ΔcH⦵298)	33.9 kJ/mol
Hazards
NFPA 704 (fire diamond)	2 0 0
Safety data sheet (SDS)	External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Lithium metaborate is one of the borates, a large family of salts (ionic compounds) with anions consisting of boron, oxygen, and hydrogen.

Structure

Lithium metaborate has several crystal forms.

The α form consists of infinite chains of trigonal planar metaborate anions [BO₂O⁻]n.

The γ form is stable at 15 kbar and 950 °C. It has a polymeric cation consisting of a tridimensional regular array of [B(O−)₄]⁻ tetrahedra sharing oxygen vertices, alernating with lithium cations, each also surrounded by four oxygen atoms. The B-O distances are 148.3 pm, the Li-O distances are 196 pm.^[2]

Lithium metaborate forms glass relatively easily, and consists of approximately 40% tetrahedral borate anions, and 60% trigonal planar boron. The ratio of tetrahedral to trigonal boron has been shown to be strongly temperature dependent in the liquid and supercooled liquid state.^[3][4]

Applications

Laboratory

Fusion flux consisting of lithium metaborate and lithium teraborate, with a small amount of lithium bromide.

Molten lithium metaborate, often mixed with lithium tetraborate Li₂B₄O₇, is used to dissolve oxide samples for analysis by XRF, AAS, ICP-OES, ICP-AES, and ICP-MS,^[5] modern versions of classical bead test. The process may be used also to facilitate the dissolution of oxides in acids for wet analysis.^[6] Small amounts of lithium bromide LiBr or lithium iodide LiI may be added as mold and crucible release agents.^[6]

Lithium metaborate dissolves acidic oxides Me_xO_y with x < y, such as SiO₂, Al₂O₃, SO₃, P₂O₅, TiO₂, Sb₂O₃, V₂O₅, WO₃, and Fe₂O₃. Lithium tetraborate, on the other hand, dissolves basic oxides with x > y, such as CaO, MgO and other oxides of the alkali metals and alkaline earth metals. Most oxides are best dissolved in a mixture of the two lithium borate salts, for spectrochemical analysis.^[6]