Allosteric Binding of Halide Anions by a New Dimeric Interpenetrated Coordination Cage

Packed in like sardines: Three BF4− ions are packed into the three cavities of an interpenetrated dimer of a coordination cage (see scheme). While the inner BF4− ion is tightly bound inside the central position, the loosely bound outer anions can be replaced with halide anions by an allosteric binding mechanism and a concerted structural change. In particular, Cl− is bound with great affinity.