Two spin-containing fragments connected by a two-electron one-center heteroatom π spacer. A new open-shell organic molecule witha singlet ground state
作者:Ll. Viadel、J. Carilla、E. Brillas、A. Labarta、L. Juliá
DOI:10.1039/a707993a
日期:——
The synthesis of 4,4-iminobis(2,2â²,2â³,4â²,4â³,6,6â²,6â³-octachlorotriphenylmethyl) diradical3, a stable organic magnetic molecule consisting of two spin-containing fragments linked by a nitrogen atom, is reported. Electron paramagnetic resonance (EPR) analysis in methyltetrahydrofuran solution (â¼10â3 m) at low temperatures showed a typical fine structure (gxx=2.0042;gyy=2.0048;gzz=2.0027) of Îms=±1transition( | D/hc |=0.0071 cmâ1; | E/hc |=0.0006 cmâ1) as well as a broad (ÎHpp=7.5 G) and weak signal of Îms=±2 transition (g=4.124), due to an asymmetric and excited triplet state corresponding to an intramolecular spinâspin interaction which diminishes with decreasing temperature. It also showed a pair of small peaks, that might be associated with a weaker dipoleâdipole interaction which diminishes with increasing temperature, emerging at both sides of a central and single peak due to a doublet state resonance corresponding to 2,2â²,2â³,4â²,4â³,6,6â²,6â³-octachloro-4-3,5-dichloro-4-[bis(2,4,6-trichlorophenyl)methylene]cyclohexa-2,5-dienylideneamino}triphenylmethyl radical 4, obtained by smooth oxidation of 3. From magnetic susceptibility measurements of the sample in the solid, a linear four-spin model was applied to establish that the singlet is the ground state of the molecule and that two triplets (Jintra=â286±30 K, Jâ²inter=â160±50 K) were the low-lying excited states. Organic solutions of 3 in air slowly oxidize to give 4, a much more persistent monoradical which is also obtained by a smooth oxidation of 3 with AgNO3 in CHCl3 . Cyclic voltammograms for the reduction of 3 and 4 in dimethylformamide (DMF) with tetra-n-butylammonium perchlorate exhibited three consecutive redox couples with standard potentials of â0.23, â0.58 and â0.74 V vs. SCE, indicating a reasonable stability of anions 3âand32â in DMF solution.
报道了4,4-亚氨基双(2,2′,2′′,4′,4′′,6,6′,6′′-八氯三苯甲基)二自由基3的合成,这是一种稳定的有机磁分子,由两个包含自旋的片段通过氮原子连接而成。在低温下,甲基四氢呋喃溶液(约10–3 m)的电子顺磁共振(EPR)分析显示了典型的精细结构(gxx=2.0042; gyy=2.0048; gzz=2.0027),对应于Δms=±1跃迁(|D/hc|=0.0071 cm–1; |E/hc|=0.0006 cm–1),以及一条宽且弱的Δms=±2跃迁信号(g=4.124),这归因于与分子内自旋-自旋相互作用相关的非对称激发三重态,且该相互作用随着温度降低而减小。它还显示了一对小峰,可能与较弱的偶极-偶极相互作用相关,随着温度升高而减小,这些峰出现在由于双重态共振而导致的中心单峰的两侧,该双重态共振与4-(3,5-二氯-4-[双(2,4,6-三氯苯基)亚甲基]环己烯-2,5-二烯基氨基)三苯甲基自由基相关,后者是通过对3的温和氧化获得的。从固态样本的磁敏感性测量中,应用线性四自旋模型确定单重态是分子的基态,而两个三重态(Jintra=–286±30 K,J′inter=–160±50 K)是低能激发态。3的有机溶液在空气中缓慢氧化生成4,这是一种更持久的单自由基,也可以通过在CHCl3中用AgNO3对3进行温和氧化获得。3和4在二甲基甲酰胺(DMF)中与四正丁基铵过氯酸盐的还原的循环伏安图显示出三个连续的氧化还原对,其标准电位分别为–0.23, –0.58和–0.74 V相对于标准氯电极(SCE),表明阴离子3–和32–在DMF溶液中具有合理的稳定性。