Host-Guest Interactions of Sodiumsulfonatomethyleneresorcinarene and Quaternary Ammonium Halides: An Experimental-Computational Analysis of the Guest Inclusion Properties
Research output: Contribution to journal › Article › Scientific › peer-review
|Number of pages||10|
|Journal||Crystal Growth and Design|
|Publication status||Published - 1 Apr 2020|
|Publication type||A1 Journal article-refereed|
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 Å and a narrow cavity portal 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, was investigated using ammonium cations of the type +NH2(R1)(R2), (R1 = Me, Et, Bu, R2 = Bu, Ph, Bz). The C-H···πinteractions between guests and hosts are the key driving forces for 14 out of 16 observed endo-complexes. In the case of the 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 calorimetry titrations confirm 1:1 host-guest complexes highlighting guest affinity, based on size and orientation. X-ray crystallographic analysis revealed two types of complexes viz. sodium-containing cocrystals, [(An)4 -·m(Bn)+·qNa+], and sodium-free, [(An)4 -·4(Bn)+]. Both types accommodate (Bn+) guests in their cavities. The N-methylated heterocycle guests and host form capsule-like structures in which the two halves were joined by O-Na coordination bonds and self-assembly into two-dimensional polymeric sheets. From the crystal structures, different conformations of methylenesulfonate groups with respect to cavity arising due to tetrahedral geometry of methylene linker were observed. Density functional theory (DFT) computations were used to analyze the effects of endo-guests on host conformations and to estimate the relative strengths of host-guest interactions.