Dinitrogen Difluoride Chemistry. Improved Synthesis of cis- and trans-N2F2, Synthesis and Characterization of N2F+Sn2F9 High-Level Electronic Structure Calculations of cis-N2F2, trans-N2F2, F2N=N, and N2F+, and Mechanism of the trans-cis Isomerization of N2F2 (Preprint)
Journal article (preprint)
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE
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N2F salts are important precursors in the synthesis of N5 compounds, and better methods are reported for their larger scale production. A new, marginally stable N2F salt, N2FSn2F9-, was prepared and characterized. An ordered crystal structure was obtained for N2FSb2F11-, resulting in the first observation of individual NN and N and N-F bond distances for N2F in the solid phase. The observed NN and N-F bond distances of 1.0899 and 1.2578A respectively, are among the shortest experimentally observed N-N and N-F bonds. High-level electronic structure calculations at the CCSDT level with correlation-consistent basis sets extrapolated to the complete basis limit show that cis-N2F2 is more stable than trans-N2F2 by 1.4 kcalmol at 298 K. The calculations also demonstrate that the lowest uncatalyzed pathway for the trans-cis isomerization of N2F2 has a barrier of 60 kcalmol and involves rotation about the NN double bond. This barrier is substantially higher than the energy required for the dissociation of N2F2 to N2 and 2 F. Therefore, some of the N2F2 dissociates before undergoing an uncatalyzed isomerization, with some of the dissociation products probably catalyzing the isomerization. Furthermore, it is shown that the trans-cis isomerization of N2F2 is catalyzed by strong Lewis acids, involves a planar transition state of symmetry Cs, and yields a 91 equilibrium mixture of cis-N2F2 and trans-N2F2. Explanations are given for the increased reactivity of cis-N2F2 with Lewis acids and the exclusive formation of cis-N2F2 in the reaction of N2F with F-. The geometry and vibrational frequencies of the F2NN isomer have also been calculated and imply strong contributions from ionic N2F F- resonance structures, similar to those in F3NO and FNO.
- Inorganic Chemistry
- Polymer Chemistry