Hirel Catherine, Luneau Dominique, Pécaut Jacques, Ohrström Lars, Bussière Guillaume, Reber Christian
Service de Chimie Inorganique et Biologique, UMR 5046, DRFMC, CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble cedex 09, France.
Chemistry. 2002 Jul 15;8(14):3157-61. doi: 10.1002/1521-3765(20020715)8:14<3157::AID-CHEM3157>3.0.CO;2-F.
The nitronyl nitroxide 2-cyano-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (1) crystallises in the tetragonal P42(1)m 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 temperature-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 considering 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.
硝酰氮氧化物2-氰基-4,4,5,5-四甲基咪唑啉-1-氧基-3-氧化物（1）以四方晶系P42(1)m空间群结晶，a = 7.4050(7)，c = 8.649(1) Å。在晶体中，分子形成平行于ab平面的层，层内分子相互正交。在这些层中，相邻自由基的O-N-C-N-O片段的NO基团与桥连碳原子之间存在紧密接触，距离为2.953(2) Å。计算得到的自旋密度显示，主要且均匀地定域在NO基团上的自旋密度为正，而在桥连碳原子和氰基氮上存在小但显著的负自旋密度。吸收光谱显示出与磁行为相关的温度依赖性跃迁。在2 - 300 K范围内，磁化率的温度依赖性表明自由基之间的耦合是反铁磁性的，通过考虑自旋S = 1/2的二维方形反铁磁耦合阵列（J = -10 cm⁻¹，g = 2.01）来解释。这被解释为分别通过氧原子和碳原子正交轨道上正、负自旋密度之间的紧密接触进行的交换耦合。
