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 Cu(II) 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 Cu(II/)(I) redox couple of more than 60 mV upon addition of guest molecules with matching H-bonding motifs. The Zn(II) analogues have been synthesized via transmetalation of the Cu(II) complex, and their guest binding properties investigated by NMR spectroscopy. (1)H NMR shifts of up to 0.8 ppm were observed upon addition of guest, and stability constants are similar to those obtained electrochemically.