Host-Guest Interactions of Sodiumsulfonatomethyleneresorcinarene and Quaternary Ammonium Halides: An Experimental-Computational Analysis of the Guest Inclusion Properties

The molecular recognition of nine quaternary alkyl- and aryl-ammonium halides (Bn) by two different receptors, Calkyl-tetrasodiumsulfonatomethyleneresorcinarene (An), were studied in solution using 1H NMR spectroscopy. Substitution of methylenesulfonate groups at 2-positions of resorcinol units resulted in an increase of cavity depth by ∼2.80 A and a narrow cavity aperture compared to Calkyl-2-H-resorcinarenes. The effect of alkyl chain lengths on the endo-complexation, that is the ability to incorporate other than N-methyl chains inside the cavities, were investigated using ammonium cations of the type ⁺NH2(R1)(R2), (R1 = Me, Et, Bu, R2 = Bu, Ph, Bz ). The C−H⋯ interactions between guests and hosts are the key driving forces for 14 out of 16 observed endo-complexes. In case of N-butyl-N-benzylammonium cation, the hydrogen bonding between -NH2 and sulfonate oxygens and the larger size hamper the N-butyl and N-benzyl groups from entering the host cavity. Association constants derived from isothermal calori...