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.

Black-box determination of temperature-dependent susceptibilities for crystalline organic radicals with complex magnetic topologies

“…Another literature example, 29 where our results agree with the experimental data, is discussed in the ESI. †…”

“…At the same time we provide detailed microscopic information based on quantum chemical calculations to back up the results which were obtained by fitting only in the original publication. As an additional literature example, we show results obtained with our approach for a thiooxo-verdazyl adduct 29 in the ESI. † Additionally, we analyze in detail the magnetic structures of molecules 2 to 5 which were synthesized and characterized in our collaborative research center.…”

Electronic Structure and Magnetic Interactions in the Radical Salt [BEDT-TTF]2[CuCl4]

“…In order to analyze the potential effect of the dynamic thermal agitation on the electronic structure of the system, we have carried out a computational experiment, similar to that performed by Robert et al 35,36 in verdazyl-based compounds. We have modified the relative slippage between the two BEDT-TTF units by an horizontal movement that increases (decreases) the relative slippage of the AB (BA) dimer, maintaining fixed the intermolecular distance (Table S7).…”

Magnetic Coupling Constants of Self‐Assembled CuII [3×3] Grids: Alternative Spin Model from Theoretical Calculations

“…This is not an isolate case, but also found in [4+2] Cu II cubanes, [27,[48][49][50] a parent Cu II [2 2] grid [41] and also in a pure organic radical-based one, a 1:1 adduct of thiooxoverdazyl radical with hydroquinone. [51] This is a new example where theoretical calculations put in evidence the difficulties to assign a spin interaction model in these complex systems solely based on the quality of the fittings.…”