Molecular Structures of arachno-Decaborane Derivatives 6,9-X₂B₈H₁₀ (X = CH₂, NH, Se) Including a Gas-Phase Electron-Diffraction Study of 6,9-C₂B₈H₁₄

Abstract

The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the (11)B chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta((11)B) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation.

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

“…This means that no large spin–orbit (SO) corrections are expected for calculations of the 11 B magnetic shieldings in the ZORA approach, since such effects are usually transmitted by a Fermi‐contact‐type relay mechanism. This is very efficient when bonds with high s character are involved, as was also found for arachno ‐Se 2 B 8 H 10 and closo ‐1‐SeB 11 H 11 , in which chalcogen atoms are much closer with respect to the boron arrangement. The explicit ZORA‐BP86(SO) approach unambiguously confirmed this expectation, since scalar ZORA values estimated from those listed in Table simply by subtracting SO contributions were almost the same as the ZORA‐BP86(SO) values reported in this table.…”

“…The 641(d) and 962(d) basis sets for Se are the Binning–Curtiss [6s4p1d] contraction of the Dunning (14s11p5d) primitive set . These basis‐set combinations have performed very well for similar types of molecules …”

The gas-phase structure of 1-selena-closo-dodecaborane(11), 1-SeB11H11, determined by the concerted use of electron diffraction and computational methods

“…All MP2 calculations were spin-restricted and frozen-core, using one of the following all-electron (AE) basis-set combinations: 641(d) on Se and 6-31G(d) on B and H (denoted AE1), 641(d) on Se and 6-311+G(d) 18 20 These basis-set combinations have performed very well for similar types of molecules. 21 Additional calculations were performed using the quasirelativistic Stuttgart-Dresden effective core potential (ECP) 22 for Se with the polarised double-zeta valence basis set augmented with a diffuse sp set 23 and a d polarisation function, 24 together with 6-31G(d) basis on B and H (denoted ECP1). Values for salient bond lengths and angles calculated at the MP2 level are given in Table 1.…”

“…32 The two-component relativistic zeroth-order regular approximation Absolute shieldings obtained at each level are given in ref. 21. NMR chemical shifts are given in Table 2.…”

Stereochemistry of free boranes and heteroboranes from electron scattering and model chemistries

“…It has also been possible to get gasphase diffraction data, analysed using the SARACEN method, for some ten-vertex arachno species. These include arachno-6,9-C 2 B 8 H 14 , 21d 69 and arachno-6,9-CSB 8 H 12 21e. 70 Computational studies have also been made both for some analogues of 21d, arachno-6,9-N 2 B 8 H 12 , 21f, and arachno-6,9-Se 2 B 8 H 10 , 21g.…”