Electronic Structures and Molecular Properties of Chalcogen Nitrides Se₂N₂ and SeSN₂

Abstract

The electronic structures and molecular properties of S2N2 as well as the currently unknown chalcogen nitrides Se2N2 and SeSN2 have been studied using various ab initio and density functional methods. All molecules share a qualitatively similar electronic structure and can be primarily described as 2π-electron aromatics having minor singlet diradical character of 68% that can be attributed solely to the nitrogen atoms. This

Magnetic Shielding, Aromaticity, Antiaromaticity and Bonding in the Low‐Lying Electronic States of S2N2

“…The σ iso ( r ) calculations for the low‐lying electronic states of S 2 N 2 were carried out using state‐optimized CASSCF‐GIAO wave functions. The selected “22 in 16” active space is analogous to that adopted by Tuononen et al . and includes, as an initial guess, the 11 highest occupied and 5 lowest virtual RHF orbitals.…”

“…. In a subsequent paper, Tuononen et al. argued that whereas the non‐singlet instability of a RHF wave function is an indication of its inadequate quality, which can be linked to singlet diradical character, the analogous stability analysis of a spin‐restricted DFT solution tests only the ability of a certain exchange‐correlation potential to describe the electron density of a singlet system using a closed‐shell Slater determinant of Kohn–Sham orbitals.…”

“…Electronic excited states of S 2 N 2 have been calculated at several levels of theory, including configuration interaction (CI), multi‐reference CI (MRCI), time‐dependent DFT (TDDFT), equations‐of‐motion coupled‐cluster with single and double excitations (EOM‐CCSD), state‐averaged CASSCF(22,16) and CASPT2(22,16) (second‐order perturbation theory with a state‐averaged CASSCF reference) . Tuononen et al . also carried out time‐dependent HF (TDHF) and second‐order polarization propagator approximation (SOPPA) excited‐state energy calculations but did not report the results because they were found to be unsatisfactory.…”

“…The only electric dipole allowed transitions from the 1 1 A 1g ground state are to singlet excited states of B 1u , B 2u and B 3u symmetries. Calculated oscillator strengths show that the intensity of the transition to the 1 1 B 2u state is much higher than that to the 1 1 B 3u state, whereas the intensity of the transition to the 1 1 B 1u state is negligibly low. The most thorough excited‐state calculations on S 2 N 2 available to date, including time‐dependent DFT (TDPBEPBE and TDPBE0), EOM‐CCSD, and state‐averaged CASSCF(22,16) and CASPT2(22,16) in the cc‐pVTZ and aug‐cc‐pVTZ basis sets, predict that the 1 1 B 2u state is lower in energy than the 1 1 B 3u state, although the reverse ordering of these states that is observed in some TDDFT results would fit better with the shape of the broad band in the experimental absorption spectrum.…”

Isomers of Disulfur Dinitride, S2N2

“…UV irradiation into the p-p* electronic band of S 2 N 2 [12] using two different light sources of l max = 255 and 248 nm strongly depleted its IR bands. 5 mg) was transferred in vacuo into a small U-trap and placed in front of the matrix support.…”