Influence of Antipodally Coupled Iodine and Carbon Atoms on the Cage Structure of 9,12-I₂-closo-1,2-C₂B₁₀H₁₀: An Electron Diffraction and Computational Study

Abstract

Because of the comparable electron scattering abilities of carbon and boron, the electron diffraction structure of the C2v-symmetric molecule closo-1,2-C2B10H12 (1), one of the building blocks of boron cluster chemistry, is not as accurate as it could be. On that basis, we have prepared the known diiodo derivative of 1, 9,12-I2-closo-1,2-C2B10H10 (2), which has the same point-group symmetry as 1 but in which the presence of iodine atoms, with their much stronger ability to scatter electrons, ensures much better structural characterization of the C2B10 icosahedral core. Furthermore, the influence on the C2B10 geometry in 2 of the antipodally positioned iodine substituents with respect to both carbon atoms has been examined using the concerted application of gas electron diffraction and quantum chemical calculations at the MP2 and density functional theory (DFT) levels. The experimental and computed molecular geometries are in good overall agreement. Molecular dynamics simulations used to obtain vibrational parameters, which are needed for analyzing the electron diffraction data, have been performed for the first time for this class of compound. According to DFT calculations at the ZORA-SO/BP86 level, the (11)B chemical shifts of the boron atoms to which the iodine substituents are bonded are dominated by spin-orbit coupling. Magnetically induced currents within 2 have been calculated and compared to those for [B12H12](2-), the latter adopting a regular icosahedral structure with Ih point-group symmetry. Similar total current strengths are found but with a certain anisotropy, suggesting that spherical aromaticity is present; electron delocalization in the plane of the hetero atoms in 2 is slightly hindered compared to that for [B12H12](2-), presumably because of the departure from ideal icosahedral symmetry.

Icosahedral Carbaboranes with Peripheral Hydrogen–Chalcogenide Groups: Structures from Gas Electron Diffraction and Chemical Shielding in Solution

“…Gas‐phase structures of 1 and 2 (Figure ) were refined with the program UNEX . Previously, we successfully refined the molecular structure of 9,12‐I 2 ‐ closo ‐1,2‐C 2 B 10 H 10 in Cartesian coordinates with the aid of regularization . The same method was applied in this work.…”

“…Similarly to sulfur, selenium has a much greater scattering ability for electrons than hydrogen and, consequently, the carbaborane core can be characterized in the gas phase more accurately than in the parent ortho ‐carbaborane . Iodine substitution has also served this purpose …”

Application of classical simulations for the computation of vibrational properties of free molecules

“…Vishnevskiy et al 23 Experimental data for BNZ at 300 K were obtained in this work. The description of the experiment is given in the next paragraph.…”

“…23 All of them were investigated using GED. Different theoretical thermally-averaged structures for these molecules including those obtained on the basis of classical MD and MC simulations were compared with the experimental data.…”

“…55 Equilibrium geometries of BNZ and CMTC at CCSD(T)/cc-pVTZ level of theory and ICBb at MP2/SDB-cc-pVTZ and B3LYP/SDB-cc-pVTZ levels were taken from the results of the earlier studies. 22,23,59 CCSDT, CCSD(T), 60 73 were taken from EMSL BSE Library.…”