Cryogenic matrix photolysis of 3,5-dichloro-2,4,6-triazidopyridine, 3-chloro-5-cyano-2,4,6-triazidopyridine, 3,5-dicyano-2,4,6-triazidopyridine, and 3,5-difluoro-2,4,6-triazidopyridine (1-4) gives rise to ESR spectral peaks of various triplet mononitrene, quintet dinitrene, and septet trinitrene species. The quintet 2,4dinitrenes derived from 1-2 and 4 have zero-field splittings (zfs) of |D/hc| ∼ 0.22-0.24 cm -1 , similar to values observed elsewhere for m-phenylene dinitrenes. 3,5-Dicyano-2,4,6-triazidopyridine (3) photolysis gives only a weak ESR signal corresponding to a mononitrene with a zfs of |D/hc| ∼ 1.22 cm -1 . The spectrum from 1 also shows a 2,6-dinitrene with |D/hc| ) 0.283 cm -1 , |E/hc| ) 0.036 cm -1 , which illustrates the effects of heteroatom perturbation upon the zfs of a geometrically rigid m-arylene dinitrene. Spectral peaks for unusual septet 2,4,6-trinitrenopyridines derived from complete deazetation of 1-2 were also identified by simulation of the septet spectra. The zfs parameters for the trinitrenes were estimated to be |D/hc| ∼ 0.1 cm -1 , with small E-values in both cases. Experimental and computational results support high spin ground states for the dinitrene and trinitrene species.

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.

Septet 3,5‐dicyanopyridyl‐2,4,6‐trinitrene was synthesized together with quintet 2‐azido‐3,5‐dicyanopyridyl‐4,6‐dinitrene, quintet 4‐azido‐3,5‐dicyanopyridyl‐2,6‐dinitrene, triplet 2,6‐diazido‐3,5‐dicyanopyridyl‐4‐nitrene, and triplet 2,4‐diazido‐3,5‐dicyanopyridyl‐6‐nitrene by photolysis of 2,4,6‐triazido‐3,5‐dicyanopyridine 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 spectral simulations. All signals in the EPR spectra of the nitrenes, randomly oriented in the solid phase, were unambiguously assigned based on eigenfield calculations of the Zeeman energy levels and angular dependences of resonance fields. Copyright © 2009 John Wiley & Sons, Ltd.