Bhakhoa Hanusha, Rhyman Lydia, Lee Edmond P, Mok Daniel K W, Ramasami Ponnadurai, Dyke John M
Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit 80837, Mauritius.
Dalton Trans. 2017 Nov 14;46(44):15301-15310. doi: 10.1039/c7dt03002a.
Metal-cyclen complexes have a number of important applications. However, the coordination chemistry between metal ions and cyclen-based macrocycles is much less well studied compared to their metal ion-crown ether analogues. This work, which makes a contribution to address this imbalance by studying complex ions of the type [M(Mecyclen)(L)], was initiated by results of an experimental study which prepared some Group 1 metal cyclen complexes, namely [Li(Mecyclen)(HO)][BAr] and [Na(Mecyclen)(THF)][BAr] and obtained their X-ray crystal structures [J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]. The lowest [M(Mecyclen)(L)] minimum energy structures (M = Li, Na, K, and L = HO, THF, DEE, MeOH, DCM) are studied using density functional theory (DFT) calculations. The geometry of each [M(Mecyclen)(L)] structure and, in particular, the conformation of L are found to be mainly governed by steric hindrance which decreases as the size of the ionic radius increases from Li → Na → K. Good agreement of computed geometrical parameters of [Li(Mecyclen)(HO)] and [Na(Mecyclen)(THF)] with the corresponding geometrical parameters derived from the crystal structures [Li(Mecyclen)(HO)][BAr] and [Na(Mecyclen)(THF)][BAr] is obtained. Bonding analysis indicates that the stability of the [M(Mecyclen)(L)] structures originates mainly from ionic interaction between the Mecyclen/L ligands and the M centres. The experimental observation that [M(Mecyclen)(L)][BAr] complexes could be prepared in crystalline form for M = Li and Na, but that experiments aimed at synthesising the corresponding K, Rb, and Cs complexes failed resulting in formation of [MecyclenH][BAr] is investigated using DFT and explicitly correlated calculations, and explained by considering production of [MecyclenH] by a hydrolysis reaction, involving traces of water, which competes with [M(Mecyclen)(L)] formation. [MecyclenH] formation dominates for M = K, Rb, and Cs whereas formation of [M(Mecyclen)(L)] is energetically favoured for M = Li and Na. The results indicate that the number and type of ligands, play a key role in stabilising the [M(Mecyclen)] complexes and it is hoped that this work will encourage experimentalists to prepare and characterise other [M(Mecyclen)(L)] complexes.
金属环配合物有许多重要应用。然而，与金属离子 - 冠醚类似物相比，金属离子与基于环烯的大环之间的配位化学研究得要少得多。这项工作通过研究[M(Mecyclen)(L)]型络合离子，为解决这种不平衡做出了贡献，它是由一项实验研究的结果引发的，该实验制备了一些第1族金属环烯配合物，即[Li(Mecyclen)(HO)][BAr]和[Na(Mecyclen)(THF)][BAr]，并获得了它们的X射线晶体结构[J. M. Dyke, W. Levason, M. E. Light, D. Pugh, G. Reid, H. Bhakhoa, P. Ramasami, and L. Rhyman, Dalton Trans., 2015, 44, 13853]。使用密度泛函理论（DFT）计算研究了最低的[M(Mecyclen)(L)]最低能量结构（M = Li、Na、K，L = HO、THF、DEE、MeOH、DCM）。发现每个[M(Mecyclen)(L)]结构的几何形状，特别是L的构象，主要受空间位阻控制，随着离子半径从Li→Na→K增大，空间位阻减小。[Li(Mecyclen)(HO)]和[Na(Mecyclen)(THF)]的计算几何参数与从晶体结构[Li(Mecyclen)(HO)][BAr]和[Na(Mecyclen)(THF)][BAr]得出的相应几何参数取得了良好的一致性。键合分析表明，[M(Mecyclen)(L)]结构的稳定性主要源于Mecyclen/L配体与M中心之间的离子相互作用。利用DFT和显式相关计算研究了实验观察结果，即对于M = Li和Na，可以制备结晶形式的[M(Mecyclen)(L)][BAr]配合物，但旨在合成相应的K、Rb和Cs配合物的实验失败，导致形成[MecyclenH][BAr]，并通过考虑由涉及痕量水的水解反应产生[MecyclenH]来解释，该反应与[M(Mecyclen)(L)]的形成相互竞争。对于M = K、Rb和Cs，[MecyclenH]的形成占主导，而对于M = Li和Na，[M(Mecyclen)(L)]的形成在能量上更有利。结果表明，配体的数量和类型在稳定[M(Mecyclen)]配合物中起关键作用，希望这项工作将鼓励实验人员制备和表征其他[M(Mecyclen)(L)]配合物。
