Predicting the structure and NMR coupling constant1J(129Xe-19F) of XeF6using quantum mechanics methods

The XeF6molecule exists as a monomer in the gas phase and as the (XeF6)4tetramer in solution. Herein we used distinct quantum mechanics methods to study the conformational equilibrium for the XeF6monomer, which is represented mainly byOhandC3vsymmetric geometries, and for the (XeF6)4structure found in condensate phases. The NMR1J(129Xe-19F) coupling constant is predicted using our own NMR-DKH basis set, designed for NMR properties. TheC3vconformer of XeF6was stable only with HF, CCSD, and hybrid DFT functionals with at least 28% exact HF exchange. Increasing the % of HF exchange improves the description of the geometry and theOh→C3vequilibrium. The BMK, BHandHLYP and LC-ωPBE functionals produce results in excellent agreement with experiments and high-level calculations for the XeF6molecule. When it comes to the1J(129Xe-19F) coupling constant, the (XeF6)4structure must be considered. For that compound, BHandHLYP leads to the best structure, and BMK leads to the best coupling constant; therefore, the generalized protocol BMK/NMR-DKH//BHandHLYP/def2-SVP is recommended to study the XeF6molecule in the gas phase and solution.