Akimov Alexander, Masitov Artem, Korchagin Denis, Chapyshev Sergei, Misochko Eugenii, Savitsky Anton
Institute of Problems of Chemical Physics RAS, Chernogolovka, Russia.
Max-Planck Institute for Chemical Energy Conversion, Mulheim/Ruhr, Germany.
J Chem Phys. 2015 Aug 28;143(8):084313. doi: 10.1063/1.4929589.
First W-band 94 GHz EPR spectra of randomly oriented triplet, quintet, and septet nitrenes formed during the photolysis of 1,3,5-triazido-2,4,6-tribromobenzene in cryogenic matrices are reported. In comparison with conventional X-band 9 GHz electron paramagnetic resonance (EPR) spectroscopy, W-band EPR spectroscopy allows the detection and complete spectroscopic characterization of all paramagnetic species formed at different stages of the photolysis of aromatic polyazides. This type of spectroscopy is of paramount importance for experimental determination of the sign of the zero-field splitting (ZFS) parameters of high-spin molecules with large spin-orbit contribution to the ZFS, caused by the effect of heavy atoms. The study shows that triplet 1,3-diazido-2,4,6-tribromo-5-nitrenobenzene (T1) has DT = 1.369 cm(-1), ET = 0.093 cm(-1), and g = 2.0033, quintet 1-azido-2,4,6-tribromo-3,5-dinitrenobenzene (Q1) shows DQ = - 0.306 cm(-1), EQ = 0.0137 cm(-1), and g = 2.0070, and septet 2,4,6-tribromo-1,3,5-trinitrenobenzene (S1) has DS = - 0.203 cm(-1), ES = 0, and g = 2.0073. The experimental ZFS parameters agree well with the results of density functional theory calculations at the PBE/Ahlrichs-DZ level of theory, showing that such calculations adequately describe the magnetic properties of bromine-containing high-spin nitrenes. Both experimental and theoretical data indicate that, in contrast to all known to date quintet dinitrenes, dinitrene Q1 has the negative sign of magnetic anisotropy due to the "heavy atom effect." This dinitrene along with septet trinitrene S1 possess the largest negative value of D among all known quintet and septet organic polyradicals.
报道了在低温基质中1,3,5-三叠氮基-2,4,6-三溴苯光解过程中形成的随机取向的三重态、五重态和七重态氮烯的首个W波段94 GHz电子顺磁共振（EPR）光谱。与传统的X波段9 GHz电子顺磁共振（EPR）光谱相比，W波段EPR光谱能够检测并对芳族多叠氮化物光解不同阶段形成的所有顺磁物种进行完整的光谱表征。这种光谱对于实验测定高自旋分子的零场分裂（ZFS）参数的符号至关重要，这些高自旋分子由于重原子的作用，其自旋轨道对ZFS有很大贡献。研究表明，三重态1,3-二叠氮基-2,4,6-三溴-5-氮烯苯（T1）的DT = 1.369 cm⁻¹，ET = 0.093 cm⁻¹，g = 2.0033；五重态1-叠氮基-2,4,6-三溴-3,5-二氮烯苯（Q1）的DQ = -0.306 cm⁻¹，EQ = 0.0137 cm⁻¹，g = 2.0070；七重态2,4,6-三溴-1,3,5-三氮烯苯（S1）的DS = -0.203 cm⁻¹，ES = 0，g = 2.0073。实验得到的ZFS参数与密度泛函理论在PBE/Ahlrichs-DZ理论水平下的计算结果吻合良好，表明此类计算能够充分描述含溴高自旋氮烯的磁性性质。实验和理论数据均表明，与迄今为止所有已知的五重态二氮烯不同，由于“重原子效应”，二氮烯Q1具有负的磁各向异性符号。在所有已知的五重态和七重态有机多自由基中，这种二氮烯与七重态三氮烯S1的D值具有最大的负值。
