The Ground State of Multispin Systems Based on Verdazyl and Nitrene Radicals: An EPR and Quantum-Chemical Study

In this study, low-temperature EPR spectroscopy and quantum-chemical techniques were employed to investigate multispin systems-1,5-diphenyl-3-(3-nitrenophenyl)-6-oxoverdazyl and 1,5-diphenyl-3-(4-nitrenophenyl)-6-oxoverdazyl-that contain a nitrene center at either a meta- or para-position, respectively. Ground states and magnetic zero-field splitting (ZFS) parameters of these multispin systems were determined by experimental and computational methods. The results indicated that the high-spin quartet state is a ground state, and the quartet-doublet energy gap is close to 10 kcal/mol for the para-position of the nitrene group, with ZFS parameters D = 0.292 cm-1 and E/D = 0.002 cm-1. In contrast, for the meta-position, the low-spin doublet state is favored with an energy gap of 1 kcal/mol. The observed difference in the ground states could be qualitatively explained by an analysis of the spin density distribution and by delocalization of the unpaired pi-electron of the nitrene center. Overall, this study provides valuable insights into the electronic structures and magnetic parameters of such multispin systems.