Institute of Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia.
J Chem Phys. 2012 Aug 14;137(6):064308. doi: 10.1063/1.4742342.
High-spin organic molecules with dominant spin-orbit contribution to magnetic anisotropy are reported. Quintet 4-azido-3,5-dibromopyridyl-2,6-dinitrene (Q-1), quintet 2-azido-3,5-dibromopyridyl-4,6-dinitrene (Q-2), and septet 3,5-dibromopyridyl-2,4,6-trinitrene (S-1) were generated in solid argon matrices by ultraviolet irradiation of 2,4,6-triazido-3,5-dibromopyridine. The zero-field splitting (ZFS) parameters, derived from electron spin resonance spectra, show unprecedentedly large magnitudes of the parameters D: ∣D(Q1)∣ = 0.289, ∣D(Q2)∣ = 0.373, and ∣D(S1)∣ = 0.297 cm(-1). The experimental ZFS parameters were successfully reproduced by density functional theory calculations, confirming that magnetic anisotropy of high-spin organic molecules can considerably be enhanced by the "heavy atom effect." In bromine-containing high-spin nitrenes, the spin-orbit term is dominant and governs both the magnitude and the sign of magnetic anisotropy. The largest negative value of D among septet trinitrenes is predicted for 1,3,5-trinitrenobenzene bearing three heavy atoms (Br) in positions 2, 4, and 6 of the benzene ring.
报道了具有主导自旋轨道贡献的高自旋有机分子的各向异性磁矩。通过对 2,4,6-三叠氮-3,5-二溴吡啶进行紫外线辐照，在固体氩基质中生成了五重态 4-叠氮-3,5-二溴吡啶基-2,6-二叠氮（Q-1）、五重态 2-叠氮-3,5-二溴吡啶基-4,6-二叠氮（Q-2）和七重态 3,5-二溴吡啶基-2,4,6-三叠氮（S-1）。零场分裂（ZFS）参数来源于电子自旋共振谱，表现出前所未有的大参数 D 值：∣D(Q1)∣=0.289、∣D(Q2)∣=0.373 和 ∣D(S1)∣=0.297 cm(-1)。实验 ZFS 参数通过密度泛函理论计算成功再现，证实了高自旋有机分子的磁各向异性可以通过“重原子效应”得到极大增强。在含溴的高自旋氮烯中，自旋轨道项占主导地位，控制着磁各向异性的大小和符号。预测在苯环的 2、4 和 6 位带有三个重原子（Br）的 1,3,5-三叠氮苯中，七重态三叠氮的 D 值将具有最大的负值。
