The Combination of Superhalogens and Brønsted Acids HX (X = F, Cl, Br): An Effective Strategy for Designing Strong Superacids.

A series of 27 composite structures, consisting of superhalogen and Brønsted acid, is designed and systematically studied based on combined ab initio and DFT calculations focusing on their potentials as novel superacids. As indicated by high-level CCSD(T) results, all the composites here fulfill the theoretical criterion for superacid and the acidities of two of them are close to the strongest superacid ever reported. The influences of various factors on the superacid properties of these composites were analyzed in detail. Our results demonstrate that the acidity of these superacids is mainly determined by the superhalogen components while the effect of Brønsted acids, irrespective of their number or type, is relatively mild. Therefore, it is probable to design novel composite superacid with enhanced property through the regulation of the superhalogen component. It is encouraging that MP2 and DFT could also provide reliable results when compared with the high-level CCSD(T) method. The reliability of these low-cost methods implies the capability of theoretical calculations for future composite superacid of enlarged size, and thus it is highly probable that an effective guide to the related experimental research could be provided by the theory.