Thermally induced dimensionality changes in derivatives of a "super stable" Blatter radical

Two derivatives of a "super stable" Blatter radical (1,3-diphenyl-7-trifluoromethyl-1,4-dihydrobenzo[e][1,2,4]triazin-4-yl) with N(1)-Ar = 2-CF₃C₆H₄ and 2-MeOC₆H₄ were obtained and investigated using XRD and SQUID magnetometry methods. The investigation revealed strong antiferromagnetic interactions in both radicals, which are described using the Hatfield model. For the latter radical, an abrupt and reversible change in the χ(T) plot was observed at 29 K. It was ascribed to a structural transition, consistent with a two-dimensional to one-dimensional thermally activated crossover, as supported by specific heat measurements (C_vHvs. T). It is suggested that the transition is related to an order-disorder transition of the CF₃ group, which is corroborated using XRD structural analysis.