title: 2,3,5,6-Tetrafluorophenylnitren-4-yl: electron paramagnetic resonance spectroscopic characterization of a quartet-ground-state nitreno radical.
abstract: 2,3,5,6-Tetrafluorophenylnitren-4-yl (5) was synthesized in argon at 4 K via the photolysis of 2,3,5,6-tetrafluoro-4-iodo-phenyl azide (6). Electron paramagnetic resonance (EPR) spectroscopy allows us to observe triradical 5 in its quartet state with the zero-field splitting (ZFS) parameters |D/hc| = 0.285 and |E/hc| = 0.043 cm-1. The quartet ground state of 5 is in accordance with our previous infrared (IR) spectroscopic investigation, in which the high-spin quartet state, but no low-spin doublet state, of 5 was observed in solid argon at 4 K [Wenk, H. H.; Sander, W. Angew. Chem., Int. Ed. 2002, 41, 2742-2745]. Because annealing of the matrix at temperatures of >10 K results in the rapid recombination of the highly reactive species 5 with I atoms produced during the photolysis of 6, the Curie-Weiss behavior could not be investigated. However, the absence of low-spin states in the IR investigations, as well as the results of ab initio and density functional theory (DFT) calculations, strongly suggest that 5 has a robust quartet ground state that is best-described as an unprecedented sigma,sigma,pi-triradical. The ZFS of 5 has been successfully reproduced by DFT calculations, which furthermore provide qualitative insight into the origin of the observed EPR parameters.
authors.affiliation: Lehrstuhl für Organische Chemie II, Ruhr-Universität Bochum, D-44780 Bochum, Germany. wolfram.sander@rub.de
authors.forename: Wolfram
authors.initials: W
authors.lastname: Sander
authors.forename: Dirk
authors.initials: D
authors.lastname: Grote
authors.forename: Simone
authors.initials: S
authors.lastname: Kossmann
authors.forename: Frank
authors.initials: F
authors.lastname: Neese
mesh_terms: D001386:Azides / Q000737:chemistry / Q000528:radiation effects; D003198:Computer Simulation; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005609:Free Radicals / Q000737:chemistry / Q000528:radiation effects; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D011789:Quantum Theory; D014466:Ultraviolet Rays
chemical_list: C528317:2,3,5,6-tetrafluorophenylnitren-4-yl; D001386:Azides; D005609:Free Radicals; D006845:Hydrocarbons, Fluorinated