Magnetic shielding, aromaticity, antiaromaticity and bonding in the low-lying electronic states of S₂N₂

Karadakov, PB, Al-Yassiri, MAH and Cooper, DL ORCID: 0000-0003-0639-0794
(2018) Magnetic shielding, aromaticity, antiaromaticity and bonding in the low-lying electronic states of S₂N₂. Chemistry: A European Journal, 24 (63). pp. 16791-16803.

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Aromaticity, antiaromaticity and chemical bonding in the ground (S₀), first singlet excited (S₁) and lowest triplet (T₁) electronic states of disulfur dinitride, S₂N₂, are investigated by analysing isotropic magnetic shielding, σiso(r), in the space surrounding the molecule for each electronic state. The σiso(r) values are calculated using state-optimized CASSCF/cc-pVTZ wavefunctions with 22 electrons in 16 orbitals constructed from gauge-including atomic orbitals (GIAOs). The S₁ and T₁ electronic states are confirmed as 1¹Au and 1³B₃u, respectively, through linear response CC3/aug-cc-pVTZ calculations of the vertical excitation energies for eight singlet (S₁–S₈) and eight triplet (T₁–T₈) electronic states. The aromaticities of S₀, S₁ and T₁ are also assessed using additional magnetic criteria including nucleus-independent chemical shifts (NICS) and magnetic susceptibilities calculated at several levels of theory, the highest of which are CCSDT-GIAO/cc-pVTZ for S₀ and CASSCF(22,16)-GIAO/aug-cc-pVQZ for S₁ and T₁. The results strongly suggest that the S₀ electronic ground state of S₂N₂ is aromatic, but less so than is the electronic ground state of benzene, S₁ is profoundly antiaromatic, to an extent that removes any bonding interactions that would keep the atoms together, and T₁ is also antiaromatic, but its antiaromaticity is more moderate and similar to that observed in the electronic ground state of square cyclobutadiene. S₂N₂ is the first example of an inorganic ring for which theory predicts substantial changes in aromaticity upon vertical transition from the ground state to the first singlet excited or lowest triplet electronic states.

Item Type: Article
Uncontrolled Keywords: disulfur dinitride, bonding in S₂N₂, aromaticity of S₂N₂, excited-state aromaticity, ³³S isotropic magnetic shielding, ¹⁵N isotropic magnetic shielding, nucleus-independent chemical shifts, magnetic susceptibilities
Depositing User: Symplectic Admin
Date Deposited: 19 Oct 2018 10:32
Last Modified: 19 Jan 2023 01:15
DOI: 10.1002/chem.201804292
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