Modulation of Zn–C Bond Lengths Induced by Ligand Architecture in Zinc Carbatrane Compounds

Bond lengths between pairs of atoms in covalent molecules are generally predicted well by the sum of their respective covalent radii, such that there are usually only small variations in related compounds. It is, therefore, significant that we have demonstrated that the incorporation of appropriately sized linkers between carbon and a metal center provides a means to modulate the length and nature of a metal–carbon interaction. Specifically, X-ray diffraction studies on a series of tris­(1-methyl­imidazol-2-ylthio)­methyl zinc complexes, [TitmMe]­ZnX, demonstrate how the Zn–C bond lengths are highly variable (2.17–2.68 Å) and are up to 0.67 Å longer than the average value listed in the Cambridge Structural Database (2.01 Å). Furthermore, density functional theory calculations on [TitmMe]­ZnCl demonstrate that the interaction is very flexible, such that either increasing or decreasing the Zn–C length from that in the equilibrium structure is associated with little energy change in comparison to that for other compounds with Zn–C bonds.共价分子中原子间的键长通常可通过各自共价半径之和精准预测，因此同类化合物的键长差异通常极小。值得关注的是，我们的研究证实：在碳与金属中心之间引入尺寸适配的连接基团，可实现对金属-碳相互作用的键长与性质的调控。具体而言，对一系列三(1-甲基咪唑-2-硫基)甲基锌配合物[TitmMe]ZnX开展的X射线衍射（X-ray diffraction）研究显示，Zn-C键长具有高度可变性（2.17~2.68 Å），较剑桥结构数据库（Cambridge Structural Database）收录的平均键长（2.01 Å）最长可超出0.67 Å。此外，对[TitmMe]ZnCl进行的密度泛函理论（density functional theory）计算表明，该相互作用具有极强的柔性：相较于其他含Zn-C键的化合物，从平衡结构处增减Zn-C键长，仅会伴随极小的能量变化。