Tetranitratoborate is an anion composed of boron with four nitrate groups. It has formula . It can form salts with large cations such as tetramethylammonium nitratoborate,[1] or tetraethylammonium tetranitratoborate. 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,, which has resisted attempts to make it; if it exists, it is unstable above −78 °C.
Other related ions are the slightly more stable tetraperchloratoborates, with perchlorate groups instead of nitrate, and tetranitratoaluminate[2] with the next atom down the periodic table, aluminium instead of boron .
Tetramethylammonium chloride reacts with to make . Then the tetrachloroborate is reacted with at around −20 °C to form tetramethylammonium nitratoborate, and other gases such as and .
Another mechanism to make tetranitratoborate salts is to shake a metal nitrate with in chloroform at 20 °C for several days. Trichloronitratoborate is an unstable intermediate.
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.[1]
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.[4]
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.[1] It reacts with liquid sulfur dioxide.[1] [5]
At room temperature tetramethylammonium nitratoborate is stable for months. It does not explode with impact.[1]
Alkali metal tetranitratoborates are unstable at room temperature and decompose.[3]
1-Ethyl-3-methyl-imidazolimium tetranitratoborate was discovered in 2002. It is an ionic liquid that turns solid at −25 °C.[6]