Tetranitratoborate

"Boron nitrate" redirects here. For the coating material used in casting, see Boron nitride.

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]

Tetranitratoborate

Names
IUPAC name Tetranitratoborate
Identifiers
3D model (JSmol)	Interactive image
InChI InChI=1S/BN4O12/c6-2(7)14-1(15-3(8)9,16-4(10)11)17-5(12)13/q-1 Key: DWOWQYMUXLKXAA-UHFFFAOYSA-N
SMILES [O-][N+](=O)O[B-](O[N+](=O)[O-])(O[N+](=O)[O-])O[N+](=O)[O-]
Properties
Chemical formula	[B(NO3)4]−
Molar mass	258.83 g·mol−1
Related compounds
Other anions	Tetraperchloratoborate
Other cations	Tetranitratoaluminate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

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]⁻).

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]

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.^[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]