Adeniyi Emmanuel, Odubo Favour E, Zeller Matthias, Torubaev Yury V, Rosokha Sergiy V
Department of Chemistry, Ball State University, Muncie, Indiana 47306, United States.
Department of Chemistry, Purdue University, West Lafayette, Indiana 47907, United States.
Inorg Chem. 2023 Nov 6;62(44):18239-18247. doi: 10.1021/acs.inorgchem.3c02843. Epub 2023 Oct 23.
X-ray structural measurements and computational analysis demonstrated the similarity of the geometries and electronic structures of the X-I···N (X = Cl, Br, I, and N) bonding in strong halogen-bonded (HaB) complexes and in the anionic or cationic halonium ions. In particular, I···N bond lengths in the solid-state associations formed by strong HaB donors (, I, IBr, ICl, and -iodosuccinimide) and acceptors (, quinuclidine or pyridines) were in the same range of 2.3 ± 0.1 Å as those in the halonium ions [, the bis(quinuclidine)iodonium cation or the 1,1'-iodanylbis(pyrrolidine-2,5-dione) anion]. In all cases, bond lengths were much closer to those of the N-I covalent bond than to the van der Waals separations of these atoms. The strong N···I bonding in the HaB complexes led to a substantial charge transfer, lengthening and weakening of the I···X bonds, and polarization of the HaB donors. As a result, the central iodine atoms in the strong HaB complexes bear partial positive charges akin to those in the halonium ions. The energies and Mayer bond orders for both N···I and I···X bonds in such associations are also comparable to those in the halonium ions. The similarity of the bonding in such complexes and in halonium ions was further supported by the analysis of electron densities and energies at bond critical (3, -1) points in the framework of the quantum theory of atoms in molecules and by the density overlap region indicator. Overall, all these data point out the analogy of the symmetric N···I···N bonding in the halonium ions and the asymmetric X···I···N bonding in the strong HaB complexes, as well as the weakly covalent character of these 3c-4e interactions.
X射线结构测量和计算分析表明，在强卤键（HaB）配合物以及阴离子或阳离子卤鎓离子中，X-I···N（X = Cl、Br、I和N）键合的几何结构和电子结构具有相似性。特别是，由强HaB供体（、I、IBr、ICl和-碘代琥珀酰亚胺）和受体（、奎宁环或吡啶）形成的固态缔合物中的I···N键长与卤鎓离子[、双（奎宁环）碘鎓阳离子或1,1'-亚碘基双（吡咯烷-2,5-二酮）阴离子]中的I···N键长处于相同范围，为2.3±0.1 Å。在所有情况下，键长更接近N-I共价键的键长，而不是这些原子的范德华间距。HaB配合物中强的N···I键合导致了大量的电荷转移、I···X键的延长和减弱以及HaB供体的极化。结果，强HaB配合物中的中心碘原子带有类似于卤鎓离子中的部分正电荷。此类缔合物中N···I和I···X键的能量和迈耶键级也与卤鎓离子中的相当。分子中原子量子理论框架下键临界点（3，-1）处的电子密度和能量分析以及密度重叠区域指标进一步支持了此类配合物和卤鎓离子中键合的相似性。总体而言，所有这些数据都指出了卤鎓离子中对称的N···I···N键合与强HaB配合物中不对称的X···I···N键合的相似性，以及这些3c - 4e相互作用的弱共价性质。
