Nitrenium ion ↔ nitreone resonance in fused cyclic five-membered triazolium ions (fCFTIs): a quantum chemical study

Density functional analysis, employing the CBS-QB3 level of theory, has been carried out to explore the possible resonance between a few fCFTIs (fused cyclic five-membered triazolium ions). The modelled fCFTIs represent a unique set of CFTIs that provide an opportunity to consider two different architectures-(i) the nitrenium ions with regular N-N covalent bonds and (ii) nitreones with the N → N coordination bonds within a cyclic framework. Compounds F9-F16 can preferably be considered as a cyclic nitrenium ion with a single lone pair at the positively charged nitrogen center. Compounds F17-F24 exhibit a nitreone character with two lone pairs at the central nitrogen atom. A small bond length alteration (within 0.1 Å) in these compounds can lead to the exchange of electronic characteristics, thus providing an opportunity to bridge the gap between two sets of compounds, which were traditionally considered as independent sets.