The analysis of crystal structures deposited in the Cambridge Structural Database showed that indenyl ligands of transition metal complexes prefer to form stacking interactions with one of the three geometries: two of them (types 1 and 2) at small horizontal displacements and one (type 3) at large horizontal displacements. Density functional theory calculations on several model molecules showed that types 1 and 2 are minima at potential energy surfaces, with substantial interaction energies that surpass −8.0 kcal/mol. Type 3 has a small energy contribution (around −2.0 kcal/mol) to the stability of supramolecular structures; however, it is combined with simultaneous stronger stacking or aromatic C–H/π interactions. Stacking of indenyl ligands is significantly stronger than the stacking of corresponding cyclopentadienyl ligands (−3.0 kcal/mol), due to the larger size of the indenyl ligand. The strength of stacking interactions depends on the electrostatic potential surface of indenyl ligands, depending on the nature and number of the other ligands of the transition metal.

中文翻译：

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过渡金属配合物的茚基配体之间的堆积相互作用：晶体学和密度泛函研究

对剑桥结构数据库中沉积的晶体结构的分析表明，过渡金属配合物的茚基配体更倾向于与三种几何结构之一形成堆积相互作用：其中两种（1型和2型）在水平方向上的位移较小，而一种（3型）在大的水平位移。在几个模型分子上的密度泛函理论计算表明，类型1和2在势能表面处是最小值，相互作用能超过-8.0 kcal / mol。3型对超分子结构的稳定性贡献很小（约-2.0 kcal / mol）。但是，它同时具有更强的堆积性或芳族CH–H /π相互作用。茚基配体的堆积明显强于相应的环戊二烯基配体的堆积（-3.0 kcal / mol），由于茚基配体的尺寸较大。堆积相互作用的强度取决于茚基配体的静电势表面，取决于过渡金属的其他配体的性质和数量。