Electronic Structures and Molecular Properties of Chalcogen Nitrates Se2N2 and SeSN2

The electronic structures and molecular properties of S2N2 as well as the currently unknown chalogen nitrides Se2N2 have been studied using various ab initio and density functional methods. All molecules share a qualitatively similar electronic structure and can be primarily descripeed as 2 pi electron aromatics having minor singlet diradical character 6-8 % that can be attributed solely to the nitrogen atoms. This diradical character is manifested in the prediction of their molecular properties, in which coulped cluster and multionfigurational approaches, as well as density fynctional methods, show the best performance. The conventional ab initio methods RHF and MP2 completely fail to descripe these systems. Predictions for the vibrational frequencies, IR intensities, Raman activities, and N-14, N-15 and Se-77 chemical shifts, as well as singlet excitation energies of Se2N2 and SeSN2 have been made. The computed high-level spectroscopic data will be of considerable value in future efforts aimed at the preparation of the conducting polymers (SeN)chi and (SeNSN)chi.