Expanding the structural chemistry of the weakly coordinating closo-carborane CB₁₁H₁₂⁻: its monoiodo derivatives with and without C_5v symmetry

Two iodo derivatives of closo-CB11H12 (-), i.e., 12-I-1-CB11H11 (-) (C (5v) symmetry) and 7-I-1-CB11H11 (-) (C (s) symmetry), were prepared (the latter for the first time) and the influence of differently positioned iodine substituents on the geometry of the CB11 icosahedral core was structurally examined both by X-ray diffraction and quantum-chemical computation at the MP2 level. Observed and computed molecular geometries are in overall agreement. Supramolecular architectures of these two anionic substituted monocarboranes are shown. According to DFT computations at the ZORA-SO/BP86 level, the B-11 chemical shifts of the boron atoms to which iodine substituents are bonded are dominated by spin-orbit coupling. Different positions of iodine atoms in these two isomers may result in different acidities of the (C)-H atoms in the icosahedral bodies, as suggested by visually analyzing the corresponding lowest unoccupied molecular orbitals.