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Tetranitratoborate
Anion composed of boron with 4 nitrate groups From Wikipedia, the free encyclopedia
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Tetranitratoborate is an anion composed of boron with four nitrate groups. It has formula [B(NO3)4]−.[1] It can form salts with large cations such as tetramethylammonium nitratoborate,[2] or tetraethylammonium tetranitratoborate.[3] The ion was first discovered by C. R. Guibert and M. D. Marshall in 1966 after failed attempts to make neutral (non-ionic) boron nitrate, B(NO3)3,[2] which has resisted attempts to make it; if it exists, it is unstable above −78 °C.[3]
Other related ions are the slightly more stable tetraperchloratoborates, with perchlorate groups instead of nitrate, and tetranitratoaluminate[4] with the next atom down the periodic table, aluminium instead of boron ([Al(NO3)4]−).
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Formation
Tetramethylammonium chloride reacts with BCl3 to make [N(CH3)4]+[BCl4]−. Then the tetrachloroborate is reacted with N2O4 at around −20 °C to form tetramethylammonium nitratoborate, and other gases such as NO2Cl and Cl2.[3]
Another mechanism to make tetranitratoborate salts is to shake a metal nitrate with BCl3 in chloroform at 20 °C for several days. Trichloronitratoborate [BCl3(NO3)]− is an unstable intermediate.
- M+NO−3 + BCl3 → M+[BCl3(NO3)]−
- 4 M+[BCl3(NO3)]− → 3 M+[BCl4]− + M+[B(NO3)4]−[5]
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Properties
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The infrared spectrum of tetramethylammonium nitratoborate includes a prominent line at 1,612 cm−1 with shoulders at 1582 and 1,626 cm−1 attributed to v4. Also prominent is 1,297 and 1,311 cm−1 attributed to v1, with these vibrations due to the nitrate bonded via one oxygen.[2]
The density of tetramethylammonium nitratoborate is 1.555 g·cm−3. It is colourless and crystalline. As tetramethylammonium nitratoborate is heated it has some sort of transition between 51 and 62 °C. It decomposes above 75 °C producing gas. Above 112 °C it is exothermic, and a solid is left if it is heated to 160 °C.[3]
Tetramethylammonium nitratoborate is insoluble in cold water but slightly soluble in hot water. It does not react with water. It also dissolves in liquid ammonia, acetonitrile, methanol, and dimethylformamide.[2] It reacts with liquid sulfur dioxide.[2][6]
At room temperature tetramethylammonium nitratoborate is stable for months. It does not explode with impact.[2]
Alkali metal tetranitratoborates are unstable at room temperature and decompose.[5]
1-Ethyl-3-methyl-imidazolimium tetranitratoborate was discovered in 2002. It is an ionic liquid that turns solid at −25 °C.[7]
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References
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