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

Fabio E. Penotti; David L. Cooper; Peter B. Karadakov

doi:10.1002/qua.25845

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

Fabio E. Penotti, David L. Cooper^*, Peter B. Karadakov

^*Corresponding author for this work

Chemistry

Research output: Contribution to journal › Article › peer-review

Abstract

Rival valence bond (VB) descriptions are investigated for the π-electron systems of the sulfur-nitrogen rings S₂N₂ and S₄N₄ ²⁺ 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 S₂N₂ confirm NN singlet diradical character to be more important than SS singlet diradical character, but the largest contribution (ca. 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 S₂N₂ onto the basis of BOVB structures (plus an orthogonal complement).

Original language	English
Article number	e25845
Number of pages	10
Journal	INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY
Volume	119
Issue number	7
Early online date	7 Dec 2018
DOIs	https://doi.org/10.1002/qua.25845
Publication status	Published - 5 Apr 2019

Bibliographical note

© 2018 Wiley Periodicals, Inc. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

Keywords

breathing orbital valence bond
generalized multiconfiguration spin-coupled
SN and SN
spin-coupled generalized valence bond (SCGVB)
π-electron rings

Access to Document

10.1002/qua.25845

Spin-Coupled Generalized Valence Bond (SCGVB) Descriptions of π-Electron Systems in S2N2 and S4N42+ Rings
© 2018 Wiley Periodicals, Inc. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.
Accepted author manuscript, 428 KBLicence: Other

Cite this

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abstract = "Rival valence bond (VB) descriptions are investigated for the π-electron systems of the sulfur-nitrogen rings S2N2 and S4N4 2+ 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 S2N2 confirm NN singlet diradical character to be more important than SS singlet diradical character, but the largest contribution (ca. 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 S2N2 onto the basis of BOVB structures (plus an orthogonal complement).",

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N2 - Rival valence bond (VB) descriptions are investigated for the π-electron systems of the sulfur-nitrogen rings S2N2 and S4N4 2+ 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 S2N2 confirm NN singlet diradical character to be more important than SS singlet diradical character, but the largest contribution (ca. 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 S2N2 onto the basis of BOVB structures (plus an orthogonal complement).

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