Austin C A, Rodgers M T
Department of Chemistry, Wayne State University , Detroit, Michigan 48202, United States.
J Phys Chem A. 2014 Jul 24;118(29):5488-500. doi: 10.1021/jp502275q. Epub 2014 Jul 11.
Threshold collision-induced dissociation (CID) of alkali metal cation-hexacyclen (ha18C6) complexes, M(+)(ha18C6), with xenon is studied using guided ion beam tandem mass spectrometry techniques. The alkali metal cations examined here include: Na(+), K(+), Rb(+), and Cs(+). In all cases, M(+) is the only product observed, corresponding to endothermic loss of the intact ha18C6 ligand. The cross-section thresholds are analyzed to extract zero and 298 K M(+)-ha18C6 bond dissociation energies (BDEs) after properly accounting for the effects of multiple M(+)(ha18C6)-Xe collisions, the kinetic and internal energy distributions of the M(+)(ha18C6) and Xe reactants, and the lifetimes for dissociation of the activated M(+)(ha18C6) complexes. Ab initio and density functional theory calculations are used to determine the structures of ha18C6 and the M(+)(ha18C6) complexes, provide molecular constants necessary for the thermodynamic analysis of the energy-resolved CID data, and theoretical estimates for the M(+)-ha18C6 BDEs. Calculations using a polarizable continuum model are also performed to examine solvent effects on the binding. In the absence of solvent, the M(+)-ha18C6 BDEs decrease as the size of the alkali metal cation increases, consistent with the noncovalent nature of the binding in these complexes. However, in the presence of solvent, the ha18C6 ligand exhibits selectivity for K(+) over the other alkali metal cations. The M(+)(ha18C6) structures and BDEs are compared to those previously reported for the analogous M(+)(18-crown-6) and M(+)(cyclen) complexes to examine the effects of the nature of the donor atom (N versus O) and the number donor atoms (six vs four) on the nature and strength of binding.
利用导向离子束串联质谱技术研究了碱金属阳离子 - 六氮杂环十二烷（ha18C6）配合物M(+)(ha18C6)与氙的阈碰撞诱导解离（CID）。此处研究的碱金属阳离子包括：Na(+)、K(+)、Rb(+)和Cs(+)。在所有情况下，观察到的唯一产物是M(+)，这对应于完整的ha18C6配体的吸热损失。在适当考虑多个M(+)(ha18C6) - Xe碰撞的影响、M(+)(ha18C6)和Xe反应物的动能和内能分布以及活化的M(+)(ha18C6)配合物的解离寿命后，分析横截面阈值以提取零温度和298 K时的M(+) - ha18C6键解离能（BDE）。使用从头算和密度泛函理论计算来确定ha18C6和M(+)(ha18C6)配合物的结构，提供能量分辨CID数据热力学分析所需的分子常数，以及M(+) - ha18C6 BDE的理论估计值。还使用极化连续介质模型进行计算，以研究溶剂对结合的影响。在没有溶剂的情况下，M(+) - ha18C6 BDE随着碱金属阳离子尺寸的增加而降低，这与这些配合物中结合的非共价性质一致。然而，在有溶剂的情况下，ha18C6配体对K(+)表现出比对其他碱金属阳离子更高的选择性。将M(+)(ha18C6)结构和BDE与先前报道的类似M(+)(18 - 冠 - 6)和M(+)(环烯)配合物的结构和BDE进行比较，以研究供体原子性质（N对O）和供体原子数量（六个对四个）对结合性质和强度的影响。
