Noncovalent interactions between acidic heterocycles and amidine bases

Noncovalent-binding interactions of tetrazoles with an imidazoline and an N,N′-diethylsubstituted amidine have been studied. The acid–base complexes were obtained by crystallization. Association constants were found to be high in chloroform, whereas binding was negligible in more competitive, protic solvents. The tetrazolate anion proved susceptible to changes in binding mode as evidenced by X-ray crystallography and solution 1H NMR studies.