Acid/base- and base/acid-switchable complexation between anionic-/cationic-pillar[6]arenes and a viologen ditosylate salt.

Two new host-guest complexes between water-soluble anionic pillar[6]arene (WP6) or cationic pillar[6]arene (CP6) and a viologen ditosylate salt G·2TsO were constructed, among which one formed from WP6 and G2+ ions can be controlled by the sequential addition of an acid and a base (HCl and NaOH, respectively), whereas the other fabricated from CP6 and TsO- ions can be switched through the sequential addition of basic and acidic reagents (NaOH and HCl, respectively).