title: Seeking hidden magnetic phenomena by theoretical means in a thiooxoverdazyl adduct.
abstract: The oxidation of 1,5-dimethyl-3-(2'-pyridyl)-6-thiooxotetrazane (SvdH(3) py) by benzoquinone leads to a 1:1 adduct of 1,5-dimethyl-3-(2'-pyridyl)-6-thiooxoverdazyl radical (Svdpy) with hydroquinone (hq). The single-crystal X-ray diffraction of this adduct at room temperature (RT) shows that the radicals exhibit a slight curvature that leads to the formation of alternating head-to-tail (antiparallel) stacked 1D chains. Moreover, temperature-dependent X-ray measurements at 100, 200, and 303 K reveal that the lateral slippages between the radicals of the stacks |δ(1) | and |δ(2) | vary from 0.64 to 0.78 Å and 0.54 to 0.40 Å between 100 and 303 K. Despite the alternation of the inter-radical distances and lateral slippages, the magnetic susceptibility data can be fitted with excellent agreement using a regular one-dimensional antiferromagnetic chain model with J=-5.9 cm(-1). Wavefunction-based calculations indicate an alternation of the magnetic interaction parameters correlated with the structural analysis at RT. Moreover, they demonstrate that the thermal slippage of the radicals induces a switching of the physical behavior, since the exchange interaction changes from antiferromagnetic (-0.9 cm(-1)) at 100 K to ferromagnetic (1.4 cm(-1)) at 303 K. The theoretical approach thus reveals a much richer magnetic behavior than the analysis of the magnetic susceptibility data and ultimately questions the relevance of a spin-coupled picture based on temperature-independent parameters.
authors.affiliation: Laboratoire de Chimie, École Normale Supérieure de Lyon, CNRS, 46 allée d'Italie, F-69364 Lyon, France.
authors.forename: Martin
authors.initials: M
authors.lastname: Vérot
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bréfuel
authors.forename: Jacques
authors.initials: J
authors.lastname: Pécaut
authors.forename: Cyrille
authors.initials: C
authors.lastname: Train
authors.forename: Vincent
authors.initials: V
authors.lastname: Robert