Charkin O P, Klimenko N M, Moran D, Mebel A M, Charkin D O, Schleyer P R
Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei 10764, Taiwan, ROC.
Inorg Chem. 2001 Dec 31;40(27):6913-22. doi: 10.1021/ic010573s.
Geometries, energies, vibrational frequencies, and magnetic properties have been computed at the B3LYP level with the 6-31G and 6-311+G basis sets for a family of endohedral closo-boranes, -alanes, and -gallanes Ng@A(12)H(12)(2-) with noble gas atoms (Ng) located in the centers of icosahedral [B(12)], [Al(12)], and [Ga(12)] clusters. The endohedral structures of most of the systems are minima lying above separated Ng + A(12)H(12)(2-) by 166 (He@B(12)H(12)(2-)) and 403 (Ne@B(12)H(12)(2-)) kcal/mol for boranes; 29 (He@Al(12)H(12)(2-)), 63 (Ne@Al(12)H(12)(2-)), 154 (Ar@Al(12)H(12)(2-)), and 189 (Kr@Al(12)H(12)(2-)) kcal/mol for alanes; and 39 (He@Ga(12)H(12)(2-)), 71 (Ne@Ga(12)H(12)(2-)), and 213 (Ar@Ga(12)H(12)(2-)) kcal/mol for gallanes. Three types of transition states are found for the exit of Ng from a cage: via an edge (TS-1), through a face (TS-2), and via a more extensive deformation through a pentagonal cage "neck" (TS-3). The most favorable exit path depends on the rigidity of the cage, the exothermicity of the dissociation, and the relationship between the size of the internal cavity of the cage and the Ng atomic radius. Ng exit via TS-3 is preferred for He@Al(12)H(12)(2-), Ne@Al(12)H(12)(2-), He@Ga(12)H(12)(2-), Ne@Ga(12)H(12)(2-), Ar@Al(12)H(12)(2), and Kr@Al(12)H(12)(2-). Helium exits via a cage edge (TS-1) for He@B(12)H(12)(2-), while for Ne@B(12)H(12)(2-) the neon exits via a triangular face (TS-2). Exit barriers (H(exit)(double dagger)) are high enough (30-60 kcal/mol) for all helium clusters and for Ne@Al(12)H(12)(2-) and Ne@Ga(12)H(12)(2-) to ensure the kinetic stability of these systems. The barriers for Ar@Al(12)H(12)(2-) and Kr@Al(12)H(12)(2-) decrease to 10-15 kcal/mol, while Ne@B(12)H(12)(2-) has a very low exit barrier and is not expected to be stable kinetically. There is a linear dependence of Ng@A(12)H(12)(2-) cage size on the Ng atomic radii; that is, the heavier Ng atoms "bulge" the cages. Nucleus independent chemical shifts (NICS) indicate that all three A(12)H(12)(2-) anions are aromatic but the alanes are the least so. A face- or edge-coordinated external Li(+) cation has a moderate effect on the structure and vibrational and magnetic properties of the helium-containing clusters, i.e., LiHe@A(12)H(12). In contrast, for systems with very large exothermicities of Ng exit, Li(+) complexation promotes their dissociation. Thus, the internal atom Ne exits from the cage of LiNe@B(12)H(12) and the salt dissociates into Ne + LiB(12)H(12)(-) without barrier. Systems with two Li(+) ions located initially above opposite cage faces (Li(2)[Ng@A(12)H(12)]) undergo complex intramolecular rearrangements leading to destruction of the icosahedral closo structures.
对于一系列内包式闭式硼烷、铝烷和镓烷Ng@A(12)H(12)(2-)，其中稀有气体原子（Ng）位于二十面体[B(12)]、[Al(12)]和[Ga(12)]簇的中心，已在B3LYP水平上使用6 - 31G和6 - 311 + G基组计算了其几何结构、能量、振动频率和磁性。大多数体系的内包结构是极小值，对于硼烷，其能量比分离的Ng + A(12)H(12)(2-)高166（He@B(12)H(12)(2-)）和403（Ne@B(12)H(12)(2-)）kcal/mol；对于铝烷，分别为29（He@Al(12)H(12)(2-)）、63（Ne@Al(12)H(12)(2-)）、154（Ar@Al(12)H(12)(2-)）和189（Kr@Al(12)H(12)(2-)）kcal/mol；对于镓烷，分别为39（He@Ga(12)H(12)(2-)）、71（Ne@Ga(12)H(12)(2-)）和213（Ar@Ga(12)H(12)(2-)）kcal/mol。发现了Ng从笼中逸出的三种过渡态：通过棱边（TS - 1）、通过面（TS - 2）以及通过五角形笼“颈部”的更广泛变形（TS - 3）。最有利的逸出路径取决于笼的刚性、解离的放热性以及笼内腔尺寸与Ng原子半径之间的关系。对于He@Al(12)H(12)(2-)、Ne@Al(12)H(12)(2-)、He@Ga(12)H(12)(2-)、Ne@Ga(12)H(12)(2-)、Ar@Al(12)H(12)(2)和Kr@Al(12)H(12)(2-)，通过TS - 3逸出Ng是首选。对于He@B(12)H(12)(2-)，氦通过笼边（TS - 1）逸出，而对于Ne@B(12)H(12)(2-)，氖通过三角形面（TS - 2）逸出。对于所有含氦簇以及Ne@Al(12)H(12)(2-)和Ne@Ga(12)H(12)(2-)，逸出势垒（H(exit)(双 dagger)）足够高（30 - 60 kcal/mol），以确保这些体系的动力学稳定性。Ar@Al(12)H(12)(2-)和Kr@Al(12)H(12)(2-)的势垒降至10 - 15 kcal/mol，而Ne@B(12)H(12)(2-)具有非常低的逸出势垒，预计其动力学不稳定。Ng@A(12)H(12)(2-)笼尺寸与Ng原子半径呈线性关系；即，较重的Ng原子使笼“膨胀”。核独立化学位移（NICS）表明，所有三种A(12)H(12)(2-)阴离子都是芳香性的，但铝烷的芳香性最弱。面配位或棱边配位的外部Li(+)阳离子对含氦簇LiHe@A(12)H(12)的结构、振动和磁性有适度影响。相比之下，对于Ng逸出具有非常大放热性的体系，Li(+)络合促进其解离。因此，内原子Ne从LiNe@B(12)H(12)的笼中逸出，盐无障碍地解离为Ne + LiB(12)H(12)(-)。最初位于相对笼面上方的两个Li(+)离子的体系（Li(2)[Ng@A(12)H(12)]）会发生复杂的分子内重排，导致二十面体闭式结构的破坏。
