Redox Active Macrocyclic Receptors for Neutral Guests

A novel series of triazine-appended macrocyclic complexes has been investigated as potential hydrogen bonding
receptors for complementarily disposed heterocycles. Cocrystallization of a melamine-appended azacyclam complex
of CuII has been achieved with barbitone, the barbiturate anion and thymine. In each case, a complementary
DAD/ADA hydrogen bonding motif between the melamine group and the heterocycle has been identified by X-ray
crystallography. Electrochemical studies of the copper macrocycles in both nonaqueous and aqueous solution
show anodic shifts of the CuII/I redox couple of more than 60 mV upon addition of guest molecules with matching
H-bonding motifs. The ZnII analogues have been synthesized via transmetalation of the CuII complex, and their
guest binding properties investigated by NMR spectroscopy. 1H NMR shifts of up to 0.8 ppm were observed upon
addition of guest, and stability constants are similar to those obtained electrochemically.