Lithium selenate
| Names | |
|---|---|
| Other names
Dilithium selenate | |
| Identifiers | |
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| ECHA InfoCard | 100.036.046 |
| EC Number |
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CompTox Dashboard (EPA) |
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| Properties | |
| Li2SeO4 | |
| Molar mass | 156.84 g/mol |
| Appearance | Colorless crystals |
| Density | 2.99 g/cm3 |
| Soluble in water | |
| Structure | |
| Trigonal | |
| R3, No. 148 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Lithium selenate is an inorganic compound of lithium and the selenate ion, with the chemical formula Li2SeO4. It is a colorless, water-soluble crystalline salt. It forms a well-characterized monohydrate, Li2SeO4·H2O, which is a polar and pyroelectric crystal.[1][2]
Preparation
[edit]Lithium selenate can be prepared by neutralizing selenic acid with lithium carbonate:
- Li2CO3 + H2SeO4 → Li2SeO4 + CO2↑ + H2O
Crystallization from aqueous solution generally gives the hydrated salt. Large single crystals of the monohydrate have been grown from aqueous solution at about 343 K.[2]
Properties
[edit]Structure
[edit]Anhydrous Li2SeO4 crystallizes in the trigonal crystal system, in space group R3 (No. 148). Its crystal structure was refined by Pertlik and Fuith in 1989.[3]
The structure consists of isolated SeO42− tetrahedra connected through lithium–oxygen coordination polyhedra.[3]
Monohydrate
[edit]Lithium selenate monohydrate, Li2SeO4·H2O, crystallizes in the monoclinic space group P21 (No. 4). At room temperature its lattice parameters are approximately a = 5.580 Å, b = 5.028 Å, c = 8.452 Å and β = 107.63°, with two formula units per unit cell.[1]
It is isostructural with lithium sulfate monohydrate. The crystal structure contains LiO4 and LiO3(H2O) tetrahedra together with SeO4 tetrahedra. These share oxygen vertices to form a three-dimensional framework.[1]
Because space group P21 is polar, the monohydrate is pyroelectric. Its pyroelectric coefficient and thermal expansion have been measured between approximately 183 and 343 K.[2]
The crystal is also optically anisotropic. Refractive indices have been measured over wavelengths from 365 to 1530 nm, and calculations indicate that Li2SeO4·H2O permits both type-I and type-II phase matching for second-harmonic generation from wavelengths of roughly 650 nm into the near-infrared.[2]
Thermal behaviour
[edit]Hydrated lithium selenate loses water on heating. Thermogravimetric studies of hydrated samples found dehydration mainly between about 120 and 250 °C.[4]
At still higher temperature, molten Li2SeO4 is progressively reduced to lithium selenite, Li2SeO3, between approximately 650 and 850 °C.[4]
- Li2SeO4 → Li2SeO3 + 1⁄2 O2
Above about 900 °C, further mass loss occurs through decomposition and volatilization of the selenite; lithium oxide remains among the final solid products.[4]
References
[edit]- 1 2 3 Johnston, Magnus G.; Harrison, William T. A. (2003). "Dilithium selenate hydrate, Li2SeO4·H2O". Acta Crystallographica Section E. 59: i25–i27. doi:10.1107/S1600536803002526.
- 1 2 3 4 Becker, Petra; Ahrweiler, S.; Held, Peter; Schneeberger, Helmut; Bohatý, Ladislav (2003). "Thermal expansion, pyroelectricity and linear optical properties of Li2SeO4·H2O and Li2SO4·H2O". Crystal Research and Technology. 38 (10): 881–889. doi:10.1002/crat.200310107.
- 1 2 Pertlik, F.; Fuith, A. H. (1989). "Structure of dilithium selenate(VI)". Acta Crystallographica Section C. 45: 158–159. doi:10.1107/S0108270188009795.
- 1 2 3 Ionashiro, M.; Giolito, I. (1980). "Thermal decomposition of the alkali metal selenates". Thermochimica Acta. 40: 143–148. doi:10.1016/0040-6031(80)85042-8.