Icosahedral Carborane Superacids and their Conjugate Bases Comprising H, F, Cl, and CN Substituents: A Theoretical Investigation of Monomeric and Dimeric Cages.

Theoretical investigation of the H(CHB ₁₁ X ₁₁ ) (X=H, F, Cl, CN), H(CHB ₁₁ X _n Y _11-n ) (X,Y=F, Cl; n=1,5), and dimeric (H(CHB ₁₁ X ₁₁ )) ₂ (X=F, Cl) carborane superacids performed at the B3LYP/6-311++G(d,p) theory level revealed the similarity of their equilibrium structures and the possibility of nearly barrierless hydrogen atom migration among the substituents attached to one side of the icosahedral CB ₁₁ cage. The vertical electron detachment energies predicted at the OVGF/6-311++G(3df,2pd) theory level for the conjugate bases (CHB ₁₁ X ₁₁ ) ^- were found to span the 5.82-9.00 ev range. The acid strengths (manifested by the Gibbs free deprotonation energies spanning the 213-266 kcal/mol range) predicted for the icosahedral H(CHB ₁₁ X ₁₁ ) carborane systems confirm their superacidic properties which might be increased even further by the attachment of the second carborane H(CHB ₁₁ X ₁₁ ) unit that leads to a dimeric structure mimicking a part of an experimentally observed H-bridged polymeric chain. The Gibbs free deprotonation energy of the dimeric (H(CHB ₁₁ Cl ₁₁ )) ₂ acid was predicted to be smaller by 17 kcal/mol than that of the corresponding monomeric H(CHB ₁₁ Cl ₁₁ ) acid.
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