Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, Cluj-Napoca, Romania.
Phys Chem Chem Phys. 2019 Oct 9;21(39):22022-22030. doi: 10.1039/c9cp04263f.
Density functional theory studies on the experimentally known Cp3Rh3B12H12Rh(B4H9RhCp) as well as the model compounds Cp4Rh4B12H12 and Cp3Rh3B12H12Rh(η3-C3H5) indicate low energy structures with central Rh4B12 tetracapped tetratruncated tetrahedra (TTT) for these 32 Wadean skeletal electron systems. This skeletal electron count corresponds to 2k2 (k = 4) skeletal electrons suggesting a spherical aromatic system with filled 1s + 1p + 1d + 1f molecular orbitals as well as an isocloso 2n (= 32 for n = 16) skeletal electron count. Similar TTT structures are found for the valence isoelectronic 32 skeletal electron systems [Cp4M''4B12H12]4+ (M'' = Ni, Pd, Pt) and [Cp4M'4B12H12]4- (M' = Fe, Ru, Os). The preferred structures of the 34 skeletal electron systems [Cp4M4B12H12]2- (M = Co, Rh, Ir), [Cp4M''4B12H12]2+ (M'' = Ni, Pd, Pt) are not the most spherical TTT despite their 2n + 2 skeletal electron count (= 34 for n = 16) for a closo structure by the Wade-Mingos rules. Instead they are prolate (elongated) polyhedra with two degree 6 and two degree 5 metal vertices with a central M4 macrobutterfly having one long MM distance of ∼5.0 Å between the wingtips. The preferred structures for the still electron richer 36 skeletal electron systems Cp4M''4B12H12 (M'' = Pd, Pt) are derived from triple square antiprisms with two open M''2B2 square faces. A distorted version of this polyhedron is the deltahedral structure with four degree 5 metal vertices and four degree 6 boron vertices found in the valence isoelectronic 36 skeletal electron first row transition metal derivatives Cp4Ni4B12H12 and [Cp4Co4B12H12]4-. However, this polyhedron is not found in the 36 skeletal electron [Cp4M4B12H12]4- (M = Rh, Ir), that instead have symmetrical central M4B12 TTTs. For some 16-vertex [Cp4M4B12H12]z systems deviating from the favored 32 skeletal electron count, low-energy structures are found in which hydrogen atoms migrate to bridge B-B edges or bend over to bridge M-B edges. In addition, the hypoelectronic hexacations [Cp4M4B12H12]6+ (M = Co, Rh, Ir; Ni, Pd, Pt) are found to have low-energy structures in which three of the four Cp rings are hydrogenated to give tetrahapto cyclopentadiene η4-C5H6 rings.
密度泛函理论研究表明，实验已知的 Cp3Rh3B12H12Rh(B4H9RhCp) 以及模型化合物 Cp4Rh4B12H12 和 Cp3Rh3B12H12Rh(η3-C3H5) 具有低能量结构，其中中心 Rh4B12 四帽四截断四面体 (TTT) 用于这些 32 个 Wadean 骨架电子系统。这个骨架电子计数对应于 2k2（k = 4）骨架电子，表明具有充满 1s + 1p + 1d + 1f 分子轨道的球形芳香体系以及等角 2n（n = 16 时为 32）骨架电子计数。对于价电子等电子的 32 个骨架电子系统 [Cp4M''4B12H12]4+（M'' = Ni、Pd、Pt）和 [Cp4M'4B12H12]4-（M' = Fe、Ru、Os），也发现了类似的 TTT 结构。34 个骨架电子系统 [Cp4M4B12H12]2-（M = Co、Rh、Ir）和 [Cp4M''4B12H12]2+（M'' = Ni、Pd、Pt）的优选结构不是最球形的 TTT，尽管它们的 2n + 2 个骨架电子计数（n = 16 时为 34）符合 Wade-Mingos 规则的闭壳结构。相反，它们是拉长的多面体，具有两个度 6 和两个度 5 金属顶点，中心 M4 macrobutterfly 具有一个长 MM 距离，在翼尖之间约为 5.0 Å。对于仍然富含电子的 36 个骨架电子系统 Cp4M''4B12H12（M'' = Pd、Pt），首选结构来自于具有两个开放的 M''2B2 正方形面的三重正方形反棱柱体。这个多面体的扭曲版本是具有四个度 5 金属顶点和四个度 6 硼顶点的三角面体结构，在价电子等电子的 36 个骨架电子第一过渡金属衍生物 Cp4Ni4B12H12 和 [Cp4Co4B12H12]4-中发现。然而，在 36 个骨架电子 [Cp4M4B12H12]4-（M = Rh、Ir）中没有发现这种多面体，而是具有对称的中心 M4B12 TTT。对于一些偏离理想 32 个骨架电子计数的 16 个顶点 [Cp4M4B12H12]z 系统，发现低能量结构中氢原子迁移到桥接 B-B 边缘或弯曲到桥接 M-B 边缘。此外，低电子六阳离子 [Cp4M4B12H12]6+（M = Co、Rh、Ir；Ni、Pd、Pt）被发现具有低能量结构，其中四个 Cp 环中的三个被氢化以生成四配位环戊二烯 η4-C5H6 环。
