title: Strain effects in electron spin resonance spectroscopy of quintet 2,6-bis(4'-nitrenophenyl)-4-phenylpyridine.
abstract: 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.
authors.affiliation: Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia. chap@icp.ac.ru
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Chapyshev
authors.forename: Denis V
authors.initials: DV
authors.lastname: Korchagin
authors.forename: Mikhail F
authors.initials: MF
authors.lastname: Budyka
authors.forename: Tatiana N
authors.initials: TN
authors.lastname: Gavrishova
authors.forename: Patrik
authors.initials: P
authors.lastname: Neuhaus
authors.forename: Wolfram
authors.initials: W
authors.lastname: Sander
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D015394:Molecular Structure; D010782:Photolysis; D011725:Pyridines / Q000737:chemistry*; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: C568119:2,6-bis(4'-nitrenophenyl)-4-phenylpyridine; D011725:Pyridines