Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia.
J Phys Chem A. 2011 Aug 4;115(30):8419-25. doi: 10.1021/jp203038k. Epub 2011 Jul 8.
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.
在 7 K 下，2-甲基四氢呋喃（2MTHF）玻璃中 2,6-双（4'-叠氮苯基）-4-苯基吡啶的光解导致五重态 2,6-双（4'-氮烯苯基）-4-苯基吡啶作为旋转异构体的混合物。该混合物的电子自旋共振（ESR）谱在 0-5000 G 的范围内显示出许多跃迁的相当大的展宽，并且不能仅通过基于自旋哈密顿参数 g、D(Q)和 E(Q)的调谐或通过 DFT 计算的预测来通过计算机模拟再现。仅当使用大的线展宽参数 Γ(E(Q))=1200 MHz 以及自旋哈密顿量 g=2.003、D(Q)=0.154 cm(-1) 和 E(Q)=0.050 cm(-1) 时，才能获得实验 ESR 谱的最佳建模。只有当使用大的线展宽参数 Γ(E(Q))=1200 MHz 以及自旋哈密顿量 g=2.003、D(Q)=0.154 cm(-1) 和 E(Q)=0.050 cm(-1) 时，才能获得实验 ESR 谱的最佳建模。只有当使用大的线展宽参数 Γ(E(Q))=1200 MHz 以及自旋哈密顿量 g=2.003、D(Q)=0.154 cm(-1) 和 E(Q)=0.050 cm(-1) 时，才能获得实验 ESR 谱的最佳建模。只有当使用大的线展宽参数 Γ(E(Q))=1200 MHz 以及自旋哈密顿量 g=2.003、D(Q)=0.154 cm(-1) 和 E(Q)=0.050 cm(-1) 时，才能获得实验 ESR 谱的最佳建模。在光谱模拟中考虑大的 E(Q)应变效应时，通过光解起始叠氮化物的旋转异构体获得的多核高自旋氮烯的 ESR 研究才能取得成功。
