a NICS(0) and NICS(1) represent NICS values at
the center of and 1 Å above the four-membered rings.b NICS(0)zz and NICS(1)zzrepresent the out-of-plane component of shielding tensor at the center
of and 1 Å above the four-membered rings.
We have further analyzed the strength of the π bonding ofS2N2 ring using the EDA–NOCV
analysis. Frenking and co-workers have used the energy decomposition
analysis (EDA) as a powerful tool for investigating the conjugation and
aromaticity in carbocyclic and heterocyclic
systems.[62,63] The EDA–NOCV analysis ofS2N2 is carried out using the
fragmentation pattern shown the scheme S1, where the S–N bond was
fragmented homolytically in two quartet SN fragments in the frozen
geometry of the molecule S2N2for this purpose (Scheme S1). Since S–N single-bond has \(\sigma\)symmetry, the \(\pi\) contributions to the total orbital interactions
(ΔEπ) can be considered as a measure for the\(\pi\)-electron delocalization as compared to the respective
fragments.[18] The negative interaction energies
ΔEint indicates stabilizing interaction between the
fragments for the formation ofS2N2 (Table 3). The major
contribution to the total interaction, ΔEint, comes from
the orbital term ΔEorb (62.8%), indicating a strong
covalent bonding. The breakdown of ΔEorb into pairwise
orbital interactions shows that the bonding interaction between the
fragments comes mainly from the σ-interaction (ΔEσ,
87.5%) between the respective quartet fragments. However, the
contribution for the π-interaction is significant (-73.2 kcal/mol) and
contributes 10.6% to the total ΔEorb. The EDA results
indicate the nature of π-interaction in π electron-rich cyclic
sulfur-nitrogen systems S2N2 and
S3N3 are
similar.[18]