Specific
2Ch–2N square interactions between pairs of heterocyclic
rings have been the target of many recent crystallographic and computational
studies. According to our search of the Cambridge Structural Database
(CSD), a number of crystal structures of the derivatives of 1,2,3,5-dichalcogenadiazolyl
(DChDA) radicals, which consist of 2Ch–2N square motifs in
the dimer units, were extracted. On the basis of the CSD survey results,
a set of dimeric complexes of DChDA-based radicals with diverse aryl
substituents at the 4-position were selected to model such squares.
Similar to that in conventional chalcogen bonds, 2Ch–2N square
interactions become stronger as the atomic size of chalcogens increases.
Both the orbital term and electrostatics contribute significantly
to the attraction of these interactions, while the dispersion contribution
is small but unneglectable. Some five-membered aryl substituents,
such as imidazole, thiazole, and oxazole, produce markedly enhanced
square interactions, leading to a pronounced influence on the distribution
of spin populations on DChDA rings.
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