A QUANTUM-CHEMICAL INVESTIGATION ON 5,5'-BI(1H-1.2,4-TRIAZOLE))

The conformational analysis of flexible 5,5'-bi(1H-1,2,4-triazole) mol ecule containing various reaction centers has been performed by the se miempirical methods MNDO,AM1 and PM3, and the internal rotation barrie r calculated. The most stable conformation of the molecule has been de termined to be the planar trans conformation. According to the three m ethods, 5,5'-bi(1H-1,2,4-triazole) molecule (C) has been found to be r elatively more stable than its tautomer 3,3'-bi(1H-1,2,4-triazole) (B) and to be less stable than its other tautomer 3,3'-bi(4H-1,2,4-triazo le) (A), Moreover, the electronic properties of 5,5'-bi(1H-1,2,4-triaz ole) molecule and the effect of conformational changing on electronic and geometric properties have also been investigated. To determine the protonation sites of the 5,5'-bitriazole system, the molecular electr ostatic poential (MESP) of the molecule has been calculated. The elect ronic properties and conformations of the monoprotonated species forme d from the protonation of the molecule have also been studied using AM 1 and PM3 routes. The proton affinity of the 5,5'-bitriazole molecule has been calculated for the different nitrogens using AM1 and PM3 meth ods and the possible protonation centers have been determined. The ele ctronic properties and the geometry of Fe2+ complex of the bitriazole system have been investigated by ZINDO/1 method and its formation proc ess has been searched theoretically According to proton affinity value s, the complex formation ability of A, B and C tautomers of bi(1,2,4-t riazole) system have been evaluated and the stabilities of their Fe2complexes have been determined by ZINDO/1 route. It has been found tha t tautomer B has a higher complex formation ability and forms more sta ble metal complexes relative to the other tautomers.