The origin of the bistability in the thiazyl radical 1,3,5-trithia-2,4,6-triazapentalenyl (TTTA): A first principles bottom-up investigation of the magnetic properties of its high temperature polymorph

Origin of the Magnetic Bistability in Molecule-Based Magnets: A First-Principles Bottom-Up Study of the TTTA Crystal

“…Notice that the values are grouped according to where they are found in the crystal structure for an easier comparison between monoclinic and triclinic structures (A, B, C, etc.). Among these pairs, there are 8 significant J M AB couplings in the monoclinic HT structure, as described in our preliminary report, 31 and 16 significant J T AB couplings in the triclinic LT structure, whose |J AB | is larger than 1.0 cm -1 . Monoclinic and triclinic crystals thus show very different sets of J AB parameters due to the higher symmetry of the monoclinic space group.…”

“…As already mentioned, six crystal structures have been published for the TTTA radical (Table gives unit cell parameters). − ,, These six structures can be grouped into two families of structures according to the polymorph type (namely, monoclinic HT and triclinic LT) that share the same packing and show small changes in the intermolecular distances due to thermal expansion. These thermal effects are the cause of the contraction of the a , b , and c cell parameters when the temperature decreases.…”

Radical–Radical Recognition: Switchable Magnetic Properties and Re-entrant Behavior

“…It is important to highlight that the rupturing of [pyDTDA] 2 dimers has never been observed before in the solid state. However, a small number of related 1,3,2-dithiazole radicals are known to exhibit structural phase transitions from diamagnetic π-dimers to undimerized paramagnetic monomers with large hysteresis. − These phase transitions are either the result of significant “plate slippage” of molecular/crystallographic planes or of “tilting” of molecular planes in a “domino cascade”. − Thus, although there is precedent for solid-state monomer–dimer phase transitions in related thiazyl species, the actual structural changes are only marginally comparable.…”

Evaluating the high-pressure structural response and crystal lattice interactions of the magnetically-bistable organic radical TTTA

“…The large hysteresis loop exhibited between the two magnetic phases has previously been attributed to the strength of the inter-column interactions in both polymorphs, 16 throughout the crystal lattices of both polymorphs, and shown that the coupling constants for the intra-column π-stacking interactions ( -436 ± 40 cm -1 for the P2 1 /c phase and -2018 ± 35 cm -1 for the eclipsed dimer in the P1 � phase) significantly outweighed the inter-column interactions. 18,22,23 Moreover, the magnetic behaviour of TTTA has been evaluated at various temperatures under the application of pressure. 24 In these experiments, the transition temperatures T ↑ and T ↓ shift to higher temperatures with pressure, reaching close to room temperature values (of 275 K and 330 K, respectively) by 1.5 GPa.…”