FORMATION AND DECOMPOSITION MECHANISM OF NF4+ SALTS

The thermal decompositions of NF4BF4 and NF4AsF6 were studied in a sapphire reactor at different temperatures by total-pressure measurements. It was found that the rates, previously reported by Solomon and co-workers for NF4AsF6, significantly differ from those of the present investigation, although both studies result in a 3/2 reaction order. From the temperature dependence of the observed decomposition rates, the following values were obtained for the global activation energies: ENF = 36.6 ± 0.8 kcal mol-1 and ENF = 44.7 ± 4.2 kcal mol-1. The suppression of the decomposition rates by NF3, F2, and BF3 or AsF5 was measured. A critical evaluation of all experimental data available on the NF4+ salt formation and decomposition suggests the following reversible reaction mechanism: F2 ⇄ 2F; F + NF3 ⇄ NF4; NF4+ AsF5 ⇄ NF3+AsF6: NF3+AsF + F ⇄ NF4+AsF61. A Born-Haber cycle calculated for NF4BF4 shows that the global decomposition activation energy and the heat of the formation reaction are identical within experimental errors and that the second step of the above mechanism is approximately thermochemically neutral. The rate of the thermal formation of NF4SbF6 at 250 °C was also studied. © 1979, American Chemical Society. All rights reserved.