Host–Guest\nComplexes of <i>p</i>‑Sulfonato-calix[4]arene\nand Benzamidine: A Matter of Counterion and Aging in the Mother Liquor

<i>p</i>-Sulfonato-calix[4]arene is commercially\navailable\neither as a sodium salt or as a sulfonic acid. We aimed to clarify\nthe complexation and crystallization pathways of <i>p</i>-sulfonato-calix[4]arene with benzamidine ligand employing these\ntwo commercial forms of macrocyclic host. The additional aspect that\nwe considered is what happens when initially formed crystals are kept\nin the mother solution simply over passing of time, allowing slow\nevaporation. This seems to be not as innocent as it intuitively appears.\nThe “aging” of multicomponent crystals exposed to concentration\nchanges of the dissolved components during crystal growth and partial\nevaporation of the mother solution can embrace different scenarios,\nincluding dissolution–recrystallization transformations. Our\nfindings highlight the need of taking into account <i>p</i>-sulfonato-calix[4]arene counterion and crystal aging in the mother\nliquor as important variables for supramolecular and crystal design\nof host–guest complexes.