Closed and open clamlike structures formed by hydrogen-bonded pairs of cyclotricatechylene anions that contain cationic "meat".

Clamming up: The hexaphenolic compound cyclotricatechylene, which has a bowl-shaped cavity, forms clamlike pairs that encapsulate cations (see picture). Variable hydrogen bonding allows two linked cyclotricatechylene clamshells to be in a closed arrangement when smaller cations such Rb(+) or Cs(+) provide the clam meat, whereas larger cations such as NMe(4) (+) and NEt(4) (+) cause the clam to be partially opened.