A new heteroditopic receptor and sensor highly selective for bromide in the presence of a bound cation

The heteroditopic receptor 2 containing a crown ether and amidoferrocence groups was synthesized and the binding abilities with various anions are reported in the presence and absence of metal cations. In the presence of Na+, 2 showed positive co-operative binding towards Br− with the binding affinity Kass = 16,096 M−1. Therefore, receptor 2 showed a switched-on binding for Br− in the presence of Na+ and a switched-off binding in the absence of Na+. Compound 2 was also found to sense Cl− and Br− electrochemically.