Ferromagnetic interactions in a 1D Heisenberg linear chain of 1-phenyl-3,7-bis(trifluoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yls

Abstract

1-Phenyl-3,7-bis(trifluoromethyl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (2), an exceptionally stable radical, was characterized by single crystal X-ray diffractometry and variable temperature SQUID magnetometry to investigate its structure-magnetism correlation. Radical 2 forms a 1D column of slipped π-stacked molecules along the crystallographic a-axis. Within the columns, radicals are equidistantly separated by 3.57 Å. Magnetic susceptibility studies indicated that radical 2 obeys the Curie–Weiss law (C = 0.370 emu K mol⁻¹) with local ferromagnetic interactions between radicals inside the 1D column (θ = 6.7 K). Fitting of the magnetic data revealed that the temperature dependence of χT (5–300 K) was best described using the 1D regular linear ferromagnetic chain model with J/k = 9 K (6.3 cm⁻¹), g_solid = 2.0047. DFT calculations supported the assignment of the macroscopic 1D ferromagnetism to local interactions between slipped π-stacked radicals along the a-axis of the 1D column.