Is the S₂N₂ ring a singlet diradical? Critical analysis of alternative valence bond descriptions

Penotti, Fabio E, Cooper, David L ORCID: 0000-0003-0639-0794 and Karadakov, Peter B (2019) Is the S₂N₂ ring a singlet diradical? Critical analysis of alternative valence bond descriptions. INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, 119 (7). e25845-e25845.

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Abstract

<jats:title>Abstract</jats:title><jats:p>Rival valence bond (VB) descriptions are investigated for the <jats:italic>π</jats:italic>‐electron systems of the sulfur‐nitrogen rings S<jats:sub>2</jats:sub>N<jats:sub>2</jats:sub> and S<jats:sub>4</jats:sub>N<jats:sub>4</jats:sub><jats:sup>2+</jats:sup> near equilibrium geometry. The lowest‐energy compact spin‐coupled generalized VB (SCGVB) descriptions are provided by variational optimization of two configurations that are found to be symmetry related to one another. Optimization instead of symmetry‐pure single‐configuration SCGVB wave functions introduces three‐center SNS or NSN orbitals, which seem to be an unnecessary complication. For neither system is much achieved by mixing competing solutions. Breathing orbital VB (BOVB) calculations for S<jats:sub>2</jats:sub>N<jats:sub>2</jats:sub> confirm NN singlet diradical character to be more important than SS singlet diradical character, but the largest contribution (<jats:italic>ca</jats:italic>. 60%) comes from the symmetry‐determined linear combination of four symmetry‐equivalent structures that lack any obvious diradical character. Much the same pattern was consistently found using a simple but robust projection of various SCGVB descriptions for S<jats:sub>2</jats:sub>N<jats:sub>2</jats:sub> onto the basis of BOVB structures (plus an orthogonal complement).</jats:p>

Item Type:	Article
Uncontrolled Keywords:	breathing orbital valence bond, pi-electron rings, generalized multiconfiguration spin-coupled, S2N2 and S4N42+, spin-coupled generalized valence bond (SCGVB)
Depositing User:	Symplectic Admin
Date Deposited:	23 Oct 2020 09:08
Last Modified:	14 Oct 2023 08:36
DOI:	10.1002/qua.25845
Related URLs:	Author Publisher
URI:	https://livrepository.liverpool.ac.uk/id/eprint/3104687

Available Versions of this Item

• Is the S2N2 ring a singlet diradical? Critical analysis of alternative valence bond descriptions. (deposited 02 Nov 2018 10:08)
  • Is the S₂N₂ ring a singlet diradical? Critical analysis of alternative valence bond descriptions. (deposited 23 Oct 2020 09:08) [Currently Displayed]