Theoretical study of [ XN5]- (X = O, S, Se, Te) systems.

A series of [XN5]- (X = O, S, Se, Te) compounds has been examined with ab initio and Density Functional Theory (DFT) methods. The five-membered nitrogen ring series of structures are global minima and may exist or be characterized due to their significant dissociation barriers (29.7-32.7 kcal mol(-1)). Nucleus-independent chemical shifts (NICS) criteria and the presence of (4n+2) pi-electrons confirmed that the five-membered nitrogen ring in their structures exhibits characteristics of aromaticity. Thus, the strong stability of the five-membered nitrogen ring structures may be attributed partially to their aromaticity.