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 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\s)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.

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.

Laboratory


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, modern versions of classical bead test. The process may be used also to facilitate the dissolution of oxides in acids for wet analysis. Small amounts of lithium bromide] LiBr or lithium iodide LiI may be added as mold and crucible release agents.

Lithium metaborate dissolves acidic oxides Me_{x}O_{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.