A series of [XN6](2-) (X = O, S, Se, Te) compounds have been examined with ab initio and density functional theory (DFT) methods. The five-membered nitrogen ring series of structures are global minima for all singlet [XN6]2- systems. Kinetic analysis shows that the five-membered nitrogen ring [XN6]2- (X = S, Se, Te) species may exist or be characterized due to their significant dissociation barriers (22.2-30.4 kcal/mol). Nucleus-independent chemical shifts (NICS) criteria and the presence of (4n + 2) number of pi-electrons confirmed that some five-, six- and seven-membered rings in their structures exhibit characteristics of aromaticity. (c) 2005 Elsevier B.V. All rights reserved.