Matrix Isolation and EPR Spectroscopy of Septet 3,5-Difluoropyridyl-2,4,6-trinitrene

Abstract

Septet 3,5-difluoropyridyl-2,4,6-trinitrene along with quintet 2-azido-3,5-difluoropyridyl-4,6-dinitrene, quintet 4-azido-3,5-difluoropyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-difluoropyridyl-4-nitrene, and triplet 2,4-diazido-3,5-difluoropyridyl-6-nitrene have been obtained by photolysis of 2,4,6-triazido-3,5-difluoropyridine in solid argon at 4 K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from computer spectral simulations. All signals in the EPR spectra of the nitrenes randomly oriented in the solid phase were unambiguously assigned on the basis of eigenfield calculations of the Zeeman energy levels and angular dependencies of resonance fields from the direction of the applied magnetic field.

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

“…By analogy with previous studies of dinitrenes 5a – c [29–31], the quintet molecule with D Q = 0.215 cm −1 and E Q = 0.0545 cm −1 can safely be assigned to dinitrene 15 with Θ = 115.7°. Thus, for instance, quintet dinitrene 5a showed D Q = 0.202 cm −1 and E Q = 0.0554 cm −1 [30], and its difluoro-derivative 5b displayed D Q = 0.213 cm −1 and E Q = 0.0556 cm −1 [29].…”

“…Surprisingly, the ZFS parameters of quintet and septet nitrenes formed in the reaction were very close to the magnetic parameters of previously studied quintet dinitrenes 4c ( D Q = 0.210 cm −1 , E Q = 0.039 cm −1 ) and 5c ( D Q = 0.209 cm −1 , E Q = 0.0542 cm −1 ) and septet trinitrene 6c ( D S = −0.1011 cm −1 , E S = −0.0043 cm −1 ) [31]. The EPR spectra of such nitrenes, including the complete assignment of all transitions, have been reported previously [29–31]. Quintet and septet nitrenes formed during the photolysis of triazide 11 display very similar EPR spectra.…”

“…Thus, for instance, quintet dinitrene 5a showed D Q = 0.202 cm −1 and E Q = 0.0554 cm −1 [30], and its difluoro-derivative 5b displayed D Q = 0.213 cm −1 and E Q = 0.0556 cm −1 [29]. The most accurate theoretical estimations of the magnetic parameters in dinitrene 5a – c were obtained by using the PBE/DZ calculations [32].…”

“…This accuracy of calculations is sufficient for reliable identification of isomeric dinitrenes 4a – c and 5a – c formed during the photolysis of triazides 1a – c (Scheme 1). Although these dinitrenes show nearly the same D Q values (≈0.21 cm −1 ), the E Q values of 4a – c and 5a – c differ significantly ( E Q 4 ≈ 0.055 cm −1 , E Q 5 ≈ 0.040 cm −1 ), thus allowing one to unambiguously discriminate such isomers [29–31]. …”

Synthesis and structure of 2,6-diazidotrichloropyridine N-oxide

“…Di-and triazidopyridines attract strong interest as energetic materials and starting compounds for the generation of high-spin nitrenes [1][2][3][4][5][6][7][8][9]. The main procedure for the synthesis of such azides is based on reaction of perhalogenated pyridines with sodium azide in aqueous acetone.…”