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Tetranitratoborate is an anion composed of boron with four nitrate groups. It has formula [B(NO₃)₄]⁻. It can form salts with large cations such as tetramethylammonium nitratoborate,^[1] or tetraethylammonium tetranitratoborate.^[2] 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,^[1] which has resisted attempts to make it; if it exists, it is unstable above −78 °C.^[2]

Other related ions are the slightly more stable tetraperchloratoborates, with perchlorate groups instead of nitrate, and tetranitratoaluminate^[3] with the next atom down the periodic table, aluminium instead of boron ([Al(NO₃)₄]⁻).

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.^[2]

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]⁻^[4]

Properties

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.^[2]

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.^[4]

1-Ethyl-3-methyl-imidazolimium tetranitratoborate was discovered in 2002. It is an ionic liquid that turns solid at −25 °C.^[6]

References

^ ^a ^b ^c ^d ^e ^f Guibert, C. R.; M. D. Marshall (1966). "Synthesis of the Tetranitratoborate Anion". Journal of the American Chemical Society. 88 (1): 189–190. doi:10.1021/ja00953a051. ISSN 0002-7863.
^ ^a ^b ^c ^d Titova, K. V.; V. Ya. Rosolovskii (1970). "Tetraalkylammonium nitratoborates". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 19 (12): 2515–2519. doi:10.1007/BF00854900. ISSN 0568-5230.
^ Jones, CJ Bigler (2007). Transition and Main Group Metals Applied to Oxidative Functionalization of Methane and Use as High Oxygen Carriers for Rocket Propellants. p. 139. ISBN 9780549231066. Retrieved 3 February 2014.
^ ^a ^b Titova, K. V.; V. Ya. Rosolovskii (1975). "Reaction of nitrates of monovalent cations with BCl₃". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 24 (10): 2246–2248. doi:10.1007/BF00929774. ISSN 0568-5230.
^ C.C. Addison; D. Sutton. Progress in Inorganic Chemistry. Vol. 8. p. 216.
^ Jones, C. Bigler; Ralf Haiges; Thorsten Schroer; Karl O. Christe (2006). "Oxygen-Balanced Energetic Ionic Liquid". Angewandte Chemie International Edition. 45 (30): 4981–4984. doi:10.1002/anie.200600735. ISSN 1433-7851. PMID 16819744.