Two stable nitronyl nitroxide free radicals {R¹ = 4′-methoxy-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide (NNPhOMe) and R² = 2-(2′-thienyl)-4,4,5,5-tetramethylimidazoline 3-oxide 1-oxyl (NNT)} are successfully synthesized using Ullmann condensation. The reactions of these two radicals with 3d transition metal ions, in the form of M(hfac)₂ (where M = Co or Mn, hfac: hexafluoroacetylacetone), result in four metal–organic complexes Co(hfac)₂(NNPhOMe)₂, 1; Co(hfac)₂(NNT)₂·(H₂O), 2; Mn(hfac)₂(NNPhOMe)·x(C₇H₁₆), 3; and Mn(hfac)₂(NNT)₂, 4. The crystal structure and magnetic properties of these complexes are investigated by single-crystal X-ray diffraction, dc magnetization, infrared, and electron paramagnetic resonance spectroscopies. The compounds 1 and 4 crystallize in the triclinic, P1̅, space group, whereas complex 3 crystallizes in the monoclinic structure with the C2/c space group and forms chain-like structure along the c direction. The complex 2 crystallizes in the monoclinic symmetry with the P2₁/c space group in which the N–O unit of the radical coordinates with the Co ion through hydrogen bonding of a water molecule. All compounds exhibit antiferromagnetic interactions between the transition metal ions and nitronyl nitroxide radicals. The magnetic exchange interactions (J/K_B) are derived using isotropic spin Hamiltonian H = −2J∑(S_metalS_radical) for the model fitting to the magnetic susceptibility data for 1, 2, 3, and 4. The exchange interaction strengths are found to be −328, −1.25, −248, and −256 K, for the 1, 2, 3, and 4 metal–organic complexes, respectively. Quantum chemical density functional theory (DFT) computations are carried out on several models of the metal–radical complexes to elucidate the magnetic interactions at the molecular level. The calculations show that a small part of the inorganic spins are delocalized over the oxygens from hfac {∼0.03 for Co(II) and ∼0.015 for Mn(II)}, whereas a more significant fraction {∼0.24 for Mn(II) and ∼0.13 for Co(II)} of delocalized spins from the metal ion is transferred to the coordinated oxygen atom(s) of nitronyl nitroxide.

中文翻译：

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3d金属配合物基于一氧化氮氮自由基的单晶中的磁交换相互作用：组合的实验和理论研究

两个稳定的硝酰基硝基氧自由基{ R ¹ = 4'-甲氧基-苯基-4,4,5,5，-四甲基咪唑啉-1-氧基-3-氧化物（NNPhOMe），R ² = 2-（2'-噻吩基）使用乌尔曼缩合法成功合成了-4,4,5,5-四甲基咪唑啉3-氧化物1-氧基（NNT）}。这两个自由基与3d过渡金属离子的反应形式为M（hfac）₂（其中M = Co或Mn，hfac：六氟乙酰丙酮），生成四个金属有机配合物Co（hfac）₂（NNPhOMe）₂，1 ; Co（hfac）₂（NNT）₂ ·（H ₂ O），2；Mn（hfac）₂（NNPhOMe）· x（C ₇ H ₁₆），3；和Mn（HFAC）₂（NNT）₂，4。通过单晶X射线衍射，直流磁化，红外和电子顺磁共振波谱研究了这些配合物的晶体结构和磁性。化合物1和4中的三斜晶系，结晶P 1，空间群，而复杂的3个在单斜晶结构结晶与Ç 2 / ç空间群和形式链状沿着结构Ç方向。复杂2以P 2 ₁ / c空间群单斜对称结晶，其中自由基的N–O单元通过水分子的氢键与Co离子配位。所有化合物都在过渡金属离子和硝酰基硝基氧自由基之间表现出反铁磁相互作用。磁交换相互作用（Ĵ / ķ_乙）使用各向同性自旋哈密顿衍生ħ = -2 Ĵ Σ（小号_金属š_自由基）的模型拟合到磁化率数据为1，2，3，和4。交换作用强度被发现是-328，-1.25，-248，-256和K，为1，2，3，和4的金属-有机络合物，分别。在多种金属-自由基配合物模型上进行了量子化学密度泛函理论（DFT）计算，以阐明分子水平上的磁性相互作用。计算结果表明，一小部分无机自旋在hfac的氧上离域化（对于Co（II）约为0.03，对于Mn（II）约为0.015}，而对于更显着的分数{对于Mn（II）约为0.24}来自金属离子的离域自旋的Co（II）的〜0.13被转移到硝酰基硝基氧的配位氧原子上。