Lithium metaborate
{{chembox
| Watchedfields = changed
| verifiedrevid = 442344823
| Name = Lithium metaborate
| ImageFile =
| ImageSize =
| ImageName =
| OtherNames = boric acid, lithium salt
|Section1={{Chembox Identifiers
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 109911
| InChI = 1/BO2.Li/c2-1-3;/q-1;+1
| InChIKey = HZRMTWQRDMYLNW-UHFFFAOYAF
| SMILES = [Li+].[O-]B=O
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 1S/BO2.Li/c2-1-3;/q-1;+1
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = HZRMTWQRDMYLNW-UHFFFAOYSA-N
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 13453-69-5
| PubChem = 123308
| EINECS = 236-631-5
}}
|Section2={{Chembox Properties
| Formula = LiBO2
| MolarMass = 49.751 g/mol
| Appearance = white hygroscopic monoclinic crystals
| Density = 2.223 g/cm3
| Solubility = 0.89 g/100 mL (0 °C)
2.57 g/100 mL (20 °C)
11.8 g/100 mL (80 °C)
| SolubleOther = soluble in ethanol
| MeltingPtC = 849
| BoilingPt =
}}
|Section4={{Chembox Thermochemistry
| DeltaHf = −1022 kJ/mol
| DeltaHc = 33.9 kJ/mol
| DeltaGf =
| Entropy = 51.3 J/mol K
| HeatCapacity = 59.8 J/mol K
}}
|Section7={{Chembox Hazards
| ExternalSDS = [http://hazard.com/msds/mf/baker/baker/files/l6600.htm External MSDS]
| NFPA-H = 2
| NFPA-R = 0
| NFPA-F = 0
}}
}}
Lithium metaborate is a chemical compound of lithium, boron, and oxygen with elemental formula {{chem2|LiBO2}}. It is often encountered as a hydrate, {{chem2|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 {{chem2|[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 {{chem2|[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.{{cite journal |last1=Alderman |first1=Oliver |last2=Benmore |first2=Chris |last3=Weber |first3=Rick |title=Consequences of sp2–sp3 boron isomerization in supercooled liquid borates |journal=Applied Physics Letters |date=2020 |volume=117 |issue=13 |page=131901 |doi=10.1063/5.0024457 |url=https://pubs.aip.org/aip/apl/article/117/13/131901/567154/Consequences-of-sp2-sp3-boron-isomerization-in|doi-access=free }}{{cite journal |last1=Alderman |first1=Oliver |last2=Benmore |first2=Chris |last3=Reynolds |first3=Bryce |last4=Royle |first4=Brock |last5=Feller |first5=Steve |last6=Weber |first6=Rick |title=Liquid fragility maximum in lithium borate glass-forming melts related to the local structure |journal=International Journal of Applied Glass Science |date=2023 |volume=14 |pages=52–68 |doi=10.1111/ijag.16611 |doi-access=free }}
Applications
=Laboratory=
Molten lithium metaborate, often mixed with lithium tetraborate {{chem2|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 {{chem2|LiBr}} or lithium iodide {{chem2|LiI}} may be added as mold and crucible release agents.
Lithium metaborate dissolves acidic oxides {{chem2|Me_{x}O_{y}|}} with x < y, such as SiO2, alumina, sulfur trioxide, phosphorus pentoxide, titanium dioxide, antimony oxide, vanadium(V) oxide, tungsten trioxide, 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.
References
{{Lithium compounds}}
{{inorganic-compound-stub}}