13812-43-6Relevant articles and documents
The N2F+ cation. An unusual ion containing the shortest presently known nitrogen-fluorine bond
Christe, Karl O.,Wilson, Richard D.,Wilson, William W.,Bau, Robert,Sukumar, Sunanda,Dixon, David A.
, p. 3795 - 3800 (1991)
The N2F+AsF6- salt was prepared in high yield from trans-N2F2 by thermal trans-cis isomerization in the presence of AsF5 at 70°C. A displacement reaction between N2F+AsF6- and FNO yields exclusively cis-N2F2. The Lewis acids BF3 and PF5 do not form a stable adduct with cis-N2F2 at temperatures as low as -78°C and do not catalyze the N2F2 trans-cis isomerization. A semiempirical molecular orbital model is used to explain the puzzling differences in the reaction chemistry of cis- and trans-N2F2. The crystal structure of N2F+AsF6- (monoclinic, C2/m, a = 9.184 (5) A?, b = 5.882 (2) A?, c = 5.160 (2) A?, β = 90.47 (4)°, Z = 2) was determined. Alternate space groups (Cm and C2) can be rejected on the basis of the observed vibrational spectra. Since in C2/m the N2F+ cations are disordered, only the sum of the N-F and N-N bond distances could be determined from the X-ray data. Local density functional calculations were carried out for N2F+ and the well-known isoelectronic FCN molecule. The results from these calculations allowed the sum of the N2F+ bond lengths to be partitioned into the individual bond distances. The resulting N-F bond length of 1.217 A? is by far the shortest presently known N-F bond, while the N-N bond length of 1.099 A? is comparable to the shortest presently known N-N bond length of 1.0976 (2) A? in N2. The surprising shortness of both bonds is attributed to the high s-character (sp hybrid) of the σ-bond orbitals on nitrogen and the formal positive charge on the cation. Thus, the shortening of the N-F bond on going from sp3-hybridized NF4+ (1.30 A?) to sp-hybridized N2F+ (1.22 A?) parallels those found for the C-H and C-F bonds in the CH4, CH2=CH2, CH≡CH and CF4, CF2=CF2, FC≡N series, respectively. The oxidative power of N2F+ has also been studied. The N2F+ cation oxidized Xe and ClF to XeF+ and ClF2+, respectively, but did not oxidize ClF5, BrF5, IF5, XeF4, NF3, or O2.
Dinitrogen difluoride chemistry. Improved syntheses of cis- and trans-N2F2, Synthesis and characterization of N 2F+Sn2F9-, ordered crystal structure of N2F+Sb2F11 -, High-level electronic structure calculations of cis-N 2F2
Christe, Karl O.,Dixon, David A.,Grant, Daniel J.,Haiges, Ralf,Tham, Fook S.,Vij, Ashwani,Vij, Vandana,Wang, Tsang-Hsiu,Wilson, William W.
, p. 6823 - 6833 (2010/09/06)
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, N2F+Sn2F9 -, was prepared and characterized. An ordered crystal structure was obtained for N2F+Sb2F11-, resulting in the first observation of individual N - N and N-F bond distances for N2F+ in the solid phase. The observed N - N and N-F bond distances of 1.089(9) and 1.257(8) A, respectively, are among the shortest experimentally observed N-N and N-F bonds. High-level electronic structure calculations at the CCSD(T) level with correlation-consistent basis sets extrapolated to the complete basis limit show that cis-N2F 2 is more stable than trans-N2F2 by 1.4 kcal/mol at 298 K. The calculations also demonstrate that the lowest uncatalyzed pathway for the trans-cis isomerization of N2F2 has a barrier of 60 kcal/mol and involves rotation about the N - N 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 9:1 equilibrium mixture of cis-N2F2 and trans-N2F2. Explanations are given for the increased reactivity of cis-N2F 2 with Lewis acids and the exclusive formation of cis-N 2F2 in the reaction of N2F+ with F-. The geometry and vibrational frequencies of the F2N - N isomer have also been calculated and imply strong contributions from ionic N2F+ F- resonance structures, similar to those in F3NO and FNO.
