A Noncovalent Binding Strategy to Capture Noble Gases, Hydrogen and Nitrogen

A molecular design strategy to develop receptor systems for the entrapment of noble gases, H₂ and N₂ is described using M06L-D3/6-311++G(d,p)//M06L/6-311++G(d,p) DFT method. These receptors made with two-, three-, four- and five-fluorinated benzene cores, linked with methelene units viz. R_I , R_II , R_III and R_IV as well as the corresponding non-fluorinated hydrocarbons viz. R_IH , R_IIH , R_IIIH and R_IVH show a steady and significant increase in binding energy (E_int ) with increase in the number of aromatic rings in the receptor. A stabilizing "cage effect" is observed in the cyclophane type receptors R_IV and R_IVH which is 26-48% of total E_int for all except the larger sized Kr, Xe and N₂ complexes. E_int of R_IV …He, R_IV …Ne, R_IV …Ar, R_IV …Kr, R_IV …H₂ and R_IV …N₂ is 4.89, 7.03, 6.49, 6.19, 8.57 and 8.17 kcal/mol, respectively which is 5- to9-fold higher than that of hexafluorobenzene. Similarly, compared to benzene, multiple fold increase in E_int is observed for R_IVH receptors with noble gases, H₂ and N₂ . Fluorination of the aromatic core has no significant impact on E_int (∼ ±0.5 kcal/mol) for most of the systems with a notable exception of the cage receptor R_IV for N₂ where fluorination improves E_int by 1.61 kcal/mol. The E_int of the cage receptors may be projected as one of the highest interaction energy ranges reported for noble gases, H₂ and N₂ for a neutral carbon framework. Synthesis of such systems is promising in the study of molecules in confined environment. © 2018 Wiley Periodicals, Inc.