Tautomerism in polyguanide

Tautomerism in polyguanide is theoretically discussed. For biguanide, triguanide (melamine), and linear polyguanides, stability of the most stable tautomer is investigated by semi-empirical and DFT calculations. Amino tautomers are more stable than the corresponding imino tautomers, and the energy gaps are ca. 6–7 kcal/mol per guanide unit. In polyguanides, amino tautomers with cis-type NCNC chains are preferred, and flat bands appear near the non-bonding level. Based on the cis-amino tautomers, applications to metal-complexing agents and magnetic materials are proposed.