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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Tetracarbaboranes: nido structures without bridging hydrogens
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Tetracarbaboranes: nido structures without bridging hydrogens

机译：四碳硼烷：不桥接氢的Nido结构

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The structures and energetics of the tetracarbaboranes C4Bn-4Hn (n = 6 to 13) have been investigated by density functional theory and coupled cluster calculations. In general, the lowest energy structures of the tetracarbaboranes C(4)B(n-)4Hn minimize the number of C-C polyhedral edges as well as the degrees of the carbon vertices. For the C4B2H6 and C4B3H7 systems the lowest energy structures are pyramidal structures having all four carbon atoms located on the base of the pyramid. The lowest energy structure for the 9-vertex C4B5H9 system is a capped square antiprism. The frameworks of the lowest energy C4B4H8 and C4B6H10 structures resemble those of the isoelectronic experimentally known B8H12 and B10H14 structures. However, an experimentally known S-4 adamantane-like 10-vertex structure found in Me4C4B6Et6 based on a tetracapped octahedron lies only similar to 7 kcal mol(-1) in energy above the lowest energy structure. The lowest energy structures for the 11- to 13-vertex C4Bn-4Hn (n = 11, 12, 13) systems can be derived from an (n + 1)-vertex closo deltahedron by removing a high-degree vertex. At least three of the four carbon atoms are located on edges of the resulting pentagonal or hexagonal open face in the low-energy structures. However, the structures of the experimentally known R4C4B8H8 (R = Me, Et) obtained from the dimerization of R2C2B4H42 differ from these low-energy structures. The Me4C4B8H8 polyhedron has a C-4 chain and two tetragonal faces whereas the Et4C4B8H8 polyhedron has a hexagonal face with two C-2 units. These structures lie within 2 kcal mol(-1) of each other thereby accounting for the fluxional properties of these systems observed by NMR spectroscopy.
机译：已经通过密度泛函理论和耦合簇计算研究了四碳硼烷C4Bn-4Hn（n = 6至13）的结构和能量。通常，四碳硼烷C（4）B（n-）4Hn的最低能级结构使C-C多面体边缘的数量以及碳顶点的程度最小化。对于C4B2H6和C4B3H7系统，最低能级结构是具有所有四个碳原子都位于金字塔基部上的金字塔结构。 9顶点C4B5H9系统的最低能量结构是带帽方形反棱镜。最低能量的C4B4H8和C4B6H10结构的框架类似于等电子学实验已知的B8H12和B10H14结构的框架。但是，基于四封八面体的Me4C4B6Et6中发现的实验已知的S-4金刚烷样10顶点结构在最低能量结构上方的能量仅类似于7 kcal mol（-1）。 11至13顶点C4Bn-4Hn（n = 11，12，13）系统的最低能量结构可以通过移除高阶顶点从（n +1）顶点closo deltaahedron派生而来。四个碳原子中的至少三个位于低能结构中所得五边形或六边形开口面的边缘上。但是，从R2C2B4H42二聚得到的实验已知R4C4B8H8（R = Me，Et）的结构与这些低能结构不同。 Me4C4B8H8多面体具有C-4链和两个四边形面，而Et4C4B8H8多面体具有具有两个C-2单元的六边形面。这些结构彼此之间在2 kcal mol（-1）之内，从而说明了通过NMR光谱法观察到的这些系统的通量特性。

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