Molecular aggregation of bis(salicylaldiminato) Zn^II Schiff base, ZnL, complexes is a topic of current interest. In this paper, we report a novel complex derived from the enantiopure trans-1,2-cyclopentanediamine, (R)-1, in order to probe the effect of the defined stereochemistry on its coordination geometry and aggregation properties, through detailed ¹H NMR, DOSY NMR, UV/vis, and circular dichroism spectroscopic studies and accurate DFT calculations. This complex shows several peculiarities in solution, behaving very differently from ZnL complexes and more importantly from the related trans-1,2-diaminocyclohexane derivative. Unexpectedly, experimental data suggest the existence in DMSO of two species in equilibrium, the classical monomeric adduct and a dimer, indicating that the DMSO is not sufficiently strong Lewis basic to completely deaggregate the complex. Also, in chloroform an unusual behavior is observed with the existence of a single defined dimeric species characterized as a dinuclear double helicate Zn₂L₂ structure which does not deaggregate even with the addition of pyridine in large stoichiometric excess. The formation of mononuclear adducts occurs only when dissolving the complex in the stronger Lewis base pyridine. All these data indicate the helicate (R)-1-h complex has a higher thermodynamic stability than that of the cyclohexane analogue, leading to its unique aggregation properties.

中文翻译：

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定义的立体化学支架的聚集体：对映纯反式-1,2-环戊烷二胺衍生的锌（II）Schiff碱配合物溶液的研究

双（水杨基醛二氨基）Zn ^II Schiff碱ZnL配合物的分子聚集是当前关注的主题。在本文中，我们报告了一种从对映体纯的反式-1,2-环戊二胺（R）-1衍生的新型配合物，以通过详细的¹ H NMR探究定义的立体化学对其配位几何形状和聚集性质的影响，DOSY NMR，UV / vis和圆二色性光谱研究以及准确的DFT计算。该络合物在溶液中显示出一些特殊性，与ZnL络合物有很大的不同，更重要的是与相关的反式-1,2-二氨基环己烷衍生物。出乎意料的是，实验数据表明DMSO中存在两种处于平衡状态的物质，即经典的单体加合物和二聚体，表明DMSO的路易斯碱性不足，无法完全分解该复合物。同样，在氯仿中，观察到不寻常的行为，即存在一个单一的定义为二聚体的物种，其特征是双核双螺旋Zn ₂ L ₂结构，即使添加大量化学计量过量的吡啶也不会解聚。仅当将络合物溶解在较强的路易斯碱吡啶中时，才发生单核加合物的形成。所有这些数据表明螺旋线（R）-1 - h 该配合物比环己烷类似物具有更高的热力学稳定性，从而具有独特的聚集特性。