LAUSR

Abstract Conjugate superacids consist of Bronsted/Lewis acid components, which can be designed by the protonation of superhalogen anions, the anions with larger vertical detachment energy (VDE) than halogens. The most stable superhalogen anions are composed of central electropositive atoms with halogen ligands such as BF 4 − , AlF 4 − . Using DFT computation at ωB97xD/6-311++G(d,p) level, we design complex superhalogen anions B(BF 4 ) 4 − , B(AlF 4 ) 4 − , Al(BF 4 ) 4 − and Al(AlF 4 ) 4 − by replacing all F by BF 4 and AlF 4 moieties in BF 4 − and AlF 4 − , whose VDEs exceed to 10 eV. We propose new superacids by protonation of these complex superhalogen anions such that the acidic strengths of HB(BF 4 ) 4 and HAl(AlF 4 ) 4 are comparable to that of HSbF 6 , the strongest superacid reported so far. Moreover, the acidic strength of HAl(BF 4 ) 4 is larger than that of HSbF 6 . All the proposed superacids are expected to be thermodynamically more stable than HBF 4 , an experimentally observed superacid.