Highly constrained guests in complexes of p-tert-butylcalix[6]arene dianion: pentane-1,5-diammonium and choline

Abstract

The structures of the complexes of choline and pentane-1,5-diammonium with p-t-bu-calix[6]arene dianion were determined. Both salts display the calixarene moiety at 1,2,3-alternate conformation, with two concave surfaces formed by three aromatic rings, and the phenolate units are at distal positions, interacting with two phenol units by hydrogen bonds. The salt of pentane-1,5-diammonium shows the diammonium connecting both calixarene dianion units, and one NH3 + is located endo-calix position and the other occupies an exo-calix position. The t-butyl groups and the calix cavity constrains the pentane-1,5-diammonium chain to near syn-eclipsed and gauche conformations. The other semi-calix accomodates a THF solvent molecule. The salt of choline shows the trimethylammonium groups of choline units immersed in these concave surfaces, with several interactions N+-C-H-p interactions with the aromatic semi-cavities.