A biradical consisting of two nitronyl nitroxide (NN) radicals bridged by diphenyl-hexaethylene glycol chain [phenyl-O-(CH₂CH₂O)₆-phenyl (GBN1)] was synthesized and investigated using electron paramagnetic resonance (EPR) spectroscopy in solution at different temperature ranges. The reversible temperature dependence behavior of spin coupling exchange is comprehensively reflected by the different lifetime of conformations due to a tumbling motion of the flexible hexaethylene glycol chain. The influences of different solvent on the exchange interactions between the radical entities are described by a two-conformational model, which was, for the first time, applied for di-NN molecule and revealed the thermodynamic parameters enthalpy and entropy (ΔH and ΔS) of the conformational changes. The positive value of enthalpy indicates lower energy of the stretched form (as calculated) compared to the bent form. The transition enthalpy in polar MeCN is larger than in toluene and the positive entropy sign indicates more chain conformation options in the bent state. The magnetic properties of this molecule were investigated in solid state by magnetization studies and EPR spectroscopy.

中文翻译：

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溶液中柔性桥连的一氧化氮氮自由基的温度依赖性分子内自旋偶联相互作用

由两个由二苯基-六甘醇链[苯基-O-（CH ₂ CH ₂ O）_6-苯基（GBN1）]的合成和研究，使用电子顺磁共振（EPR）光谱在不同温度范围内的溶液中进行。由于柔性六甘醇链的翻滚运动，构象的不同寿命全面反映了自旋偶合交换的可逆温度依赖性行为。两种构象模型描述了不同溶剂对自由基实体之间的交换相互作用的影响，该模型首次应用于di-NN分子，并揭示了焓和熵的热力学参数（ΔH和ΔS）的构象变化。焓的正值表示与弯曲形式相比，拉伸形式（计算得出）的能量较低。极性MeCN中的过渡焓大于甲苯中的过渡焓，正熵符号表示在弯曲状态下有更多的链构象选择。通过磁化研究和EPR光谱在固态下研究了该分子的磁性。