Perchloratoborate is an anion of the form [B(ClO4)4]−. It can form partly stable solid salts with heavy alkali metals. They are more stable than nitratoborate salts.[1] K[B(ClO4)4] decomposes at 35 °C, Rb[B(ClO4)4] is stable to 50 °C, and Cs[B(ClO4)4] can exist up to 80 °C.[2]
2 M[B(ClO4)4] → 2 MClO4 + B2O3 + (3 Cl2O7 or 6 ClO2 + 4+1/2O2 or 6 Cl2 + 10+1/2O2)[2]
When the alkali perchloratoborates first start to decompose at the lower temperatures, the reaction is endothermic, and dichlorine heptoxide is formed. However, if caesium perchloratoborate is heated the decomposition becomes exothermic above 90 °C, and at 100 °C it explodes exothermically forming chlorine and oxygen.[2]
The metal perchloratoborates can also be formed from the metal perchlorate dissolved in anhydrous perchloric acid reacting with boron trichloride. Another way is to react a metal chloridoborate (MBCl4) with perchloric acid. Chloridoborates can be made from the metal chloride and boron trichloride dissolved in nitrosyl chloride.[5]
Extra Cl2O7 drives the reaction forward.[5]
BCl3 + 3HClO4 → B(ClO4)3
Also formed is BCl2ClO4 and BCl(ClO4)2 which disproportionates above −78 °C to the boron perchlorate and dichloroboron perchlorate.[6]
^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. ISSN0568-5230.
^ abcBabaeva, V. P.; V. Ya. Rosolovskii (1974). "Thermal decomposition of perchloratoborates of the alkali metals". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 23 (3): 477–481. doi:10.1007/BF00921126. ISSN0568-5230.
^Titova, K. V.; V. Ya. Rosolovskii (1974). "Tetraalkylammonium chloroperchloratoborates". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 23 (10): 2092–2095. doi:10.1007/BF00921261. ISSN0568-5230.
^ abcdeRosolovskii, V. Ya.; V. P. Babaeva (1971). "Some properties of cesium perchloratoborate". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 20 (4): 792–794. doi:10.1007/BF00853930. ISSN0568-5230.
^ abcdefgBabaeva, V. P.; V. Ya. Rosolovskii (1973). "Alkali metal perchloratoborates". Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 22 (3): 476–479. doi:10.1007/BF00854006. ISSN0568-5230.
