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首页> 外文期刊>Chemistry: A European journal >The Cyano Nitronyl Nitroxide Radical: Experimental and Theoretical Evidence for the Fourth Case of the McConnell-I Mechanism
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The Cyano Nitronyl Nitroxide Radical: Experimental and Theoretical Evidence for the Fourth Case of the McConnell-I Mechanism

机译：氰基亚硝基氧自由基：McConnell-I机理第四例的实验和理论证据

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摘要

The nitronyl nitroxide-2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42_1m space group with a = 7.4050 (7), c = 8.649(1) A. In the crystal the molecules form layers parallel to the ab plane in which they are orthogonal to each other. In the layers there are close contacts, 2.953 (2) A, between the NO groups and the bridging carbon atoms of the O-N-C-N-O fragment of neighbouring radicals. The calculated spin density shows a positive population mainly and equally localised on the NO groups and small but significant negative spin densities on the bridging carbon atom and the cyano nitrogen. Absorption spectra show temeprature-dependent transitions related to the magnetic behaviour. The temperature dependence of the magnetic susceptibility in the range 2-300 K reveals that couplings between the radicals are antiferromagnetic, and is interpreted by conhsidering a two-dimensional square array of spin S = 1/2 antiferromagnetically coupled (J = -10 cm~(-1) and g = 2.01). This is interpreted as an exchange coupling through close contact between positive and negative spin densities in orthogonal orbitals on oxygen and carbon atoms, respectively.
机译：硝酰基硝基氧-2-氰基-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物（1）在四边形P42_1m空间群中结晶，a = 7.4050（7），c = 8.649（1）A在晶体中，分子形成平行于ab平面的层，在b平面中它们彼此正交。在这些层中，NO基团与相邻基团的O-N-C-N-O片段的桥连碳原子之间有紧密的接触2.953（2）A。计算出的自旋密度显示出一个主要且均等地分布在NO基团上的正种群，而在桥连的碳原子和氰基氮上却有一个很小但很明显的负自旋密度。吸收光谱显示与磁性行为有关的依赖于温度的转变。磁化率在2-300 K范围内的温度相关性表明，自由基之间的偶联是反铁磁性的，并且可以通过考虑自旋S = 1/2的二维正方形阵列来反磁耦合（J = -10 cm〜 （-1）和g = 2.01）。这被解释为通过分别在氧和碳原子上的正交轨道上的正和负自旋密度之间的紧密接触进行的交换耦合。

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