The powder X-band electron paramagnetic resonance spectroscopy of septet pyridyl-2,4,6-trinitrene

The first X-band EPR spectrum containing only non-overlapping signals of septet pyridyl-2,4,6-trinitrene and triplet pyridylnitrenes is reported. This spectrum was recorded after photolysis of 2,4,6-triazidopyridine in solid argon at 5 K. The zero-field splitting (ZFS) parameters of this trinitrene as well as of intermediate triplet mononitrenes and quintet dinitrenes formed at early stages of the photolysis were determined using the combination of modern computer line-shape spectral simulations and density functional theory (DFT) calculations. It was found that septet pyridyl-2,4,6-trinitrene has the record negative parameter D_S  = -0.1031 cm^-1 among all known to date septet pyridyl-2,4,6-trinitrenes and may be of interest as a model multi-qubit spin system for investigations of quantum computation processing.

EPR spectroscopy of multicomponent, multispin molecular system obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon

Complex multicomponent, multispin molecular system, consisting of a septet trinitrene, two quintet dinitrenes, and three triplet mononitrenes, was obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon. To identify these paramagnetic products, electron paramagnetic resonance spectroscopy in combination with line-shape spectral simulations and density functional theory calculations was used. The products of the photolysis was found to be triplet 2,4-diazido-3-cyano-5-fluoropyridyl-6-nitrene (D_T  = 1.000 cm^-1 , E_T  = 0), triplet 2,4-diazido-3-cyano-5-fluoropyridyl-2-nitrene (D_T  = 1.043 cm^-1 , E_T  = 0), triplet 2,6-diazido-3-cyano-5-fluoropyridyl-4-nitrene (D_T  = 1.128 cm^-1 , E_T  = 0 cm^-1 ), quintet 4-azido-3-cyano-5-fluoropyridyl-2,6-dinitrene (D_Q  = 0.211 cm^-1 , E_Q  = 0.0532 cm^-1 ), quintet 2-azido-3-cyano-5-fluoropyridyl-4,6-dinitrene (D_Q  = 0.208 cm^-1 , E_Q  = 0.0386 cm^-1 ), and septet 3-cyano-5-fluoropyridyl-2,4,6-trinitrene (D_S  = -0.1017 cm^-1 , E_S  = -0.0042 cm^-1 ) in a 38:4:7:22:14:4 ratio, respectively.

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

In contrast to theoretical expectations, the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine in argon at 5 K gives rise to EPR peaks of just two triplet mononitrenes, two quintet dinitrenes, and a septet trinitrene. EPR spectral simulations in combination with DFT calculations show that observable nitrenes can be assigned to triplet 2,4-diazido-3-chloro-5-fluoropyridyl-6-nitrene (D T = 1.026 cm(-1), E T = 0), triplet 2,6-diazido-3-chloro-5-fluoropyridyl-4-nitrene (D T = 1.122 cm(-1), E T = 0.0018 cm(-1)), quintet 4-azido-3-chloro-5-fluoropyridyl-2,6-dinitrene (D Q = 0.215 cm(-1), E Q = 0.0545 cm(-1)), quintet 2-azido-3-chloro-5-fluoropyridyl-4,6-dinitrene (D Q = 0.209 cm(-1), E Q = 0.039 cm(-1)) and septet 3-chloro-5-fluoropyridyl-2,4,6-trinitrene (D S = -0.1021 cm(-1), E S = -0.0034 cm(-1)). Preferential photodissociation of the azido groups located in ortho-positions to the fluorine atom of pyridines is associated with strong π-conjugation of these groups with the pyridine ring. On photoexcitation, such azido groups are more efficiently involved in reorganization of the molecular electronic system and more easily adopt geometries of the locally excited predissociation states.