Radiolysis and photolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine: Generation of Quintet dinitrenes

Low-temperature radiolysis and photolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine (TAP) were studied by means of the ESR technique. It was found that the long-term irradiation of TAP at 77 K leads to the appearance of characteristic signals of quintet 2,6-dinitreno-4-azido-3,5-dichloropyridine and 2,4-dinitreno-6-azido-3,5-dichloropyridine; their radiation-chemical yield was 0.035 and 0.012 molecule/100 eV, respectively. The photolysis of crystalline 2,4,6-triazido-3,5-dichloropyridine proceeded less effectively, producing only quintet 2,6 dinitrene with a quantum yield of ～4.5 × 10^?4. The study showed that the generation of high-spin nitrenes via radiolysis of crystalline azides is much superior to the photochemical technique in efficiency and may be of practical importance for the preparation of magnetically active organic materials.     

Synthesis of pyrido[3,4-<Emphasis Type="Italic">d</Emphasis>]pyrimidines by condensation of ethyl 1-benzyl-3-oxopiperidine-4-carboxylate with morpholine-4-carboxamidine

A method has been developed for the synthesis of 4-amino-substituted 7-benzyl-2-morpholin-4-yl-5,6,7,8-tetrahydropyrido[3,4-d]pyrimidines by condensation of ethyl 1-benzyl-3-oxopiperidine-4-carboxylate with morpholine-4-carboxamidine and subsequent reaction of the 7-benzyl-2-morpholin-4-yl-5,6,7,8-tetrahydro-3H-pyrido[3,4-d]pyrimidin-4-one with trifluoromethanesulfonic anhydride and secondary amines. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 762–768, May, 2007.     

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.     

Synthesis,structure, and the energetic properties of tetraazidopyridine-4-carbonitrile

Chemistry of Heterocyclic Compounds - Nucleophilic substitution of fluorine atoms in 2,3,5,6-tetrafluoropyridine-4-carbonitrile with sodium azide was used to obtain...     

Investigation of the molecular and crystalline structure of 2,4,6-triazido-3-chloro-5-trifluoromethylpyridine and rotation barrier of the γ-azidogroup around a C-N bond

The molecular and crystalline structure of 2,4,6-triazido-3-chloro-5-trifluoromethylpyridine has been investigated by X-ray diffraction at temperatures of 200 and 293 K. The triazide molecule is nonplanar, and the γ-azidogroup significantly deviates from the aromatic ring plane. Nonempirical quantum-chemical calculations of the internal rotation barrier of the γ-azidogroup around the C-N bond have been performed in the B3LYP/6-311G** approximation. It is shown that the minimum of the total energy of this system corresponds to the dihedral angle between the γ-azidogroup and pyridine cycle planes (～34.5°), whereas the structures with the γ-azidogroup, oriented in the pyridine cycle plane or perpendicularly to it, are characterized by very low barriers: ～0.26 and 1.74 kcal mol^?1, respectively.     

Strain effects in electron spin resonance spectroscopy of quintet 2,6-bis(4'-nitrenophenyl)-4-phenylpyridine

Photolysis of 2,6-bis(4'-azidophenyl)-4-phenylpyridine in 2-methyltetrahydrofuran (2MTHF) glass at 7 K leads to quintet 2,6-bis(4'-nitrenophenyl)-4-phenylpyridine as a mixture of rotational isomers. The electron spin resonance (ESR) spectrum of this mixture of rotamers shows a considerable broadening of many transitions in the range of 0-5000 G and cannot be reproduced by computer simulations solely based on the tuning of the spin Hamiltonian parameters g, D(Q), and E(Q) alone or on predictions of DFT calculations. The best modeling of the experimental ESR spectrum is obtained only when the large line-broadening parameter of Γ(E(Q)) = 1200 MHz along with the spin Hamiltonian g = 2.003, D(Q) = 0.154 cm(-1), and E(Q) = 0.050 cm(-1) is used in the spectral simulations. The most accurate theoretical estimations of the magnetic parameters of the dinitrene in a 2MTHF glass are obtained from the B3LYP/6-311+G(d,p)+PBE/DZ/COSMO calculations of the spin-spin coupling parameters D(SS) and E(SS). Such calculations overestimate the E(Q) and D(Q) values of the dinitrene just by 1% and 10%, respectively, demonstrating that contributions of the spin-orbit coupling parameters D(SOC) and E(SOC) to the total D(Q) and E(Q) values are negligibly small. The research shows that ESR studies of polynuclear high-spin nitrenes, obtained by photolysis of rotational isomers of the starting azides, can only be successful if large E(Q) strain effects are taken into account in the spectral simulations.     

Persistent Organic High‐Spin Trinitrenes

The septet ground state trinitrenes 1,3,5‐trichloro‐2,4,6‐trinitrenobenzene and 1,3,5‐tribromo‐2,4,6‐trinitrenobenzene were isolated in inert (Ar, Ne, and Xe) as well as reactive matrices (H₂, O₂, and H₂O) at cryogenic temperatures. These trinitrenes were obtained in high yields by UV photolysis of the corresponding triazides and characterized by IR and UV/Vis spectroscopy. The trinitrenes, despite bearing six unpaired electrons, are remarkably unreactive towards molecular oxygen and hydrogen and are persistent in water ice up to 160 K where the water matrix starts to sublime off.     

Single crystal X-ray diffraction study of 2,4,6-triazidopyridine and its 3,5-dibromosubstituted derivative

By the single crystal X-ray diffraction analysis in combination with quantum chemical calculations the molecular and crystal structures of high-energy 2,4,6-triazidopyridine and 2,4,6-triazido-3,5- dibromopyridine are studied; the dependence of structural parameters of their azido groups on the size of substituents in β-positions of the pyridine ring is analyzed. The effect of the intramolecular contact involving the central nitrogen atom of γ-azido groups in substituted triazides on their structure and properties is revealed.