Deciphering the ground state of a C3-symmetrical Blatter-type triradical by CW and pulse EPR spectroscopy

Athanassios K Boudalis; Christos P Constantinides; Nicolas Chrysochos; Raanan Carmieli; Gregory Leitus; Andreas Kourtellaris; Daniel B Lawson; Panayiotis A Koutentis

doi:10.1016/j.jmr.2023.107406

Deciphering the ground state of a C₃-symmetrical Blatter-type triradical by CW and pulse EPR spectroscopy

J Magn Reson. 2023 Apr:349:107406. doi: 10.1016/j.jmr.2023.107406. Epub 2023 Feb 17.

Authors

Athanassios K Boudalis¹, Christos P Constantinides², Nicolas Chrysochos³, Raanan Carmieli⁴, Gregory Leitus⁴, Andreas Kourtellaris³, Daniel B Lawson⁵, Panayiotis A Koutentis³

Affiliations

¹ Institut de Chimie de Strasbourg (UMR 7177, CNRS-Unistra), Université de Strasbourg, 4 rue Blaise Pascal, CS 90032, F-67081 Strasbourg, France. Electronic address: bountalis@unistra.fr.
² Department of Natural Sciences, University of Michigan - Dearborn, 4901 Evergreen Rd, Dearborn, MI 48128, United States. Electronic address: cconst@umich.edu.
³ Department of Chemistry, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
⁴ Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel.
⁵ Department of Natural Sciences, University of Michigan - Dearborn, 4901 Evergreen Rd, Dearborn, MI 48128, United States.

PMID: 36841142
DOI: 10.1016/j.jmr.2023.107406

Abstract

3,3',3''-(Benzene-1,3,5-triyl)tris(1-phenyl-1H-benzo[e][1,2,4]triazin-4-yl) (1) is a C₃-symmetrical triradical comprised of three Blatter radical units connected at the 1, 3, 5 positions of a central trimethylenebenzene core. This triradical has an excellent air, moisture, and thermal stability. Single-crystal XRD indicates that triradical 1 adopts a propeller-like geometry with the benzotriazinyl moieties twisted by 174.1(2)° and packs in 1D chains along the c axis to form an extensive network of weak intermolecular interactions. Frozen solution continuous wave (CW) EPR spectra and variable-temperature field-sweep echo-detected (FSED) spectra revealed an intramolecular ferromagnetic exchange within the spin system, supporting a quartet S = 3/2 ground state. DFT calculations further supported these experimental findings.

Keywords: Benzotriazinyls; Blatter; Ferromagnetic coupling; Organic radicals; Quartet; Triradicals.