| Abstract
| - The electronic structures and molecular properties of S2N2 as well as the currently unknown chalcogen nitridesSe2N2 and SeSN2 have been studied using various ab initio and density functional methods. All moleculesshare a qualitatively similar electronic structure and can be primarily described as 2π-electron aromaticshaving minor singlet diradical character of 6−8% that can be attributed solely to the nitrogen atoms. Thisdiradical character is manifested in the prediction of their molecular properties, in which coupled cluster andmulticonfigurational approaches, as well as density functional methods, show the best performance. Theconventional ab initio methods RHF and MP2 completely fail to describe these systems. Predictions for thevibrational frequencies, IR intensities, Raman activities, and 14N, 15N, and 77Se chemical shifts, as well assinglet excitation energies of Se2N2 and SeSN2, have been made. The computed high-level spectroscopic datawill be of considerable value in future efforts aimed at the preparation of the conducting polymers (SeN)xand (SeNSN)x.
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